WorldWideScience

Sample records for polarization-doped light-emitting diodes

  1. Polymer light emitting diodes

    International Nuclear Information System (INIS)

    Gautier-Thianche, Emmmanuelle

    1998-01-01

    We study sandwich type semiconducting polymer light emitting diodes; anode/polymer/cathode. ITO is selected as anode, this polymer is a blend of a commercially available polymer with a high hole transport ability: polyvinyl-carbazole and a laser dye: coumarin-515. Magnesium covered with silver is chosen for the anode. We study the influence of polymer thickness and coumarin doping ratio on electroluminescence spectrum, electric characteristics and quantum efficiency. An important drawback is that diodes lifetime remains low. In the second part of our study we determine degradations causes with X-Ray reflectivity experiments. It may be due to ITO very high roughness. We realize a new type of planar electroluminescent device: a channel type electroluminescent device in which polymer layer is inserted into an aluminium channel. Such a device is by far more stable than using classical sandwich structures with the same polymer composition: indeed, charges are generated by internal-field ionization and there is no injection from the electrode to the polymer. This avoids electrochemical reactions at electrodes, thus reducing degradations routes. (author) [fr

  2. Light Emitting Diode (LED)

    Science.gov (United States)

    1997-01-01

    A special lighting technology was developed for space-based commercial plant growth research on NASA's Space Shuttle. Surgeons have used this technology to treat brain cancer on Earth, in two successful operations. The treatment technique called photodynamic therapy, requires the surgeon to use tiny pinhead-size Light Emitting Diodes (LEDs) (a source releasing long wavelengths of light) to activate light-sensitive, tumor-treating drugs. Laser light has been used for this type of surgery in the past, but the LED light illuminates through all nearby tissues, reaching parts of a tumor that shorter wavelengths of laser light carnot. The new probe is safer because the longer wavelengths of light are cooler than the shorter wavelengths of laser light, making the LED less likely to injure normal brain tissue near the tumor. It can also be used for hours at a time while still remaining cool to the touch. The LED probe consists of 144 tiny pinhead-size diodes, is 9-inches long, and about one-half-inch in diameter. The small balloon aids in even distribution of the light source. The LED light source is compact, about the size of a briefcase, and can be purchased for a fraction of the cost of a laser. The probe was developed for photodynamic cancer therapy by the Marshall Space Flight Center under a NASA Small Business Innovative Research program grant.

  3. Light Emitting Diodes (LEDs)

    Science.gov (United States)

    1997-01-01

    A special lighting technology was developed for space-based commercial plant growth research on NASA's Space Shuttle. Surgeons have used this technology to treat brain cancer on Earth, in two successful operations. The treatment technique, called Photodynamic Therapy, requires the surgeon to use tiny, pinhead-size Light Emitting Diodes (LEDs) (a source that releases long wavelengths of light ) to activate light-sensitive, tumor-treating drugs. 'A young woman operated on in May 1999 has fully recovered with no complications and no evidence of the tumor coming back,' said Dr. Harry Whelan, a pediatric neurologist at the Medical Hospital of Wisconsin in Milwaukee. Laser light has been used for this type of surgery in the past, but the LED light illuminates through all nearby tissues, reaching parts of a tumor that shorter wavelengths of laser light carnot. The new probe is safer because the longer wavelengths of light are cooler than the shorter wavelengths of laser light, making the LED less likely to injure normal brain tissue near the tumor. It can be used for hours at a time while still remaining cool to the touch. The LED light source is compact, about the size of a briefcase, and can be purchased for a fraction of the cost of a laser. The LEDs, developed and managed by NASA's Marshall Space Flight Center, have been used on seven Space Shuttle flights inside the Microgravity Astroculture Facility. This technology has also been successfully used to further commercial research in crop growth.

  4. Phototherapy with Light Emitting Diodes

    Science.gov (United States)

    2018-01-01

    Within the field of dermatology, advances in the use of light emitting diodes (LEDs) have led to their clinical application for a variety of medical and cosmetic uses. Of note, one phototherapy device has demonstrated beneficial effects over a range of clinical applications (Omnilux™; GlobalMed Technologies, Glen Ellen, California). The study included a literature review of published studies. Using LEDs with frequencies of 415nm (blue), 633nm (red), and 830nm (infrared), this device has demonstrated significant results for the treatment of medical conditions, including mild-to-moderate acne vulgaris, wound healing, psoriasis, squamous cell carcinoma in situ (Bowen’s disease), basal cell carcinoma, actinic keratosis, and cosmetic applications. Although photodynamic therapy with the photosensitizer 5-aminolevulinic acid might cause stinging and burning, phototherapy is free of adverse events. We determined that phototherapy using LEDs is beneficial for a range of medical and aesthetic conditions encountered in the dermatology practice. This treatment displays an excellent safety profile.

  5. Light-Emitting Diodes: A Hidden Treasure

    Science.gov (United States)

    Planinšic, Gorazd; Etkina, Eugenia

    2014-01-01

    LEDs, or light-emitting diodes, are cheap, easy to purchase, and thus commonly used in physics instruction as indicators of electric current or as sources of light (Fig. 1). In our opinion LEDs represent a unique piece of equipment that can be used to collect experimental evidence, and construct and test new ideas in almost every unit of a general…

  6. Light-Emitting Diodes: Learning New Physics

    Science.gov (United States)

    Planinšic, Gorazd; Etkina, Eugenia

    2015-01-01

    This is the third paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide the readers with the description of experiments and pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper, published…

  7. Fluorescence lifetime imaging using light emitting diodes

    International Nuclear Information System (INIS)

    Kennedy, Gordon T; Munro, Ian; Poher, Vincent; French, Paul M W; Neil, Mark A A; Elson, Daniel S; Hares, Jonathan D

    2008-01-01

    We demonstrate flexible use of low cost, high-power light emitting diodes as illumination sources for fluorescence lifetime imaging (FLIM). Both time-domain and frequency-domain techniques have been implemented at wavelengths spanning the range 450-640 nm. Additionally, we demonstrate optically sectioned fluorescence lifetime imaging by combining structured illumination with frequency-domain FLIM

  8. Phosphorescent Nanocluster Light-Emitting Diodes.

    Science.gov (United States)

    Kuttipillai, Padmanaban S; Zhao, Yimu; Traverse, Christopher J; Staples, Richard J; Levine, Benjamin G; Lunt, Richard R

    2016-01-13

    Devices utilizing an entirely new class of earth abundant, inexpensive phosphorescent emitters based on metal-halide nanoclusters are reported. Light-emitting diodes with tunable performance are demonstrated by varying cation substitution to these nanoclusters. Theoretical calculations provide insight about the nature of the phosphorescent emitting states, which involves a strong pseudo-Jahn-Teller distortion. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Efficient organic light emitting-diodes (OLEDs)

    CERN Document Server

    Chang, Yi-Lu

    2015-01-01

    Following two decades of intense research globally, the organic light-emitting diode (OLED) has steadily emerged as the ultimate display technology of choice for the coming decades. Portable active matrix OLED displays have already become prevalent, and even large-sized ultra-high definition 4K TVs are being mass-produced. More exotic applications such as wearable displays have been commercialized recently. With the burgeoning success in displays, researchers are actively bringing the technology forward into the exciting solid-state lighting market. This book presents the knowledge needed for

  10. Wheat Under LED's (Light Emitting Diodes)

    Science.gov (United States)

    2004-01-01

    Astroculture is a suite of technologies used to produce and maintain a closed controlled environment for plant growth. The two most recent missions supported growth of potato, dwarf wheat, and mustard plants, and provided scientists with the first opportunity to conduct true plant research in space. Light emitting diodes have particular usefulness for plant growth lighting because they emit a much smaller amount of radiant heat than do conventional lighting sources and because they have potential of directing a higher percentage of the emitted light onto plants surfaces. Furthermore, the high output LED's have emissions in the 600-700 nm waveband, which is of highest efficiency for photosynthesis by plants.

  11. Light-emitting diodes for analytical chemistry.

    Science.gov (United States)

    Macka, Mirek; Piasecki, Tomasz; Dasgupta, Purnendu K

    2014-01-01

    Light-emitting diodes (LEDs) are playing increasingly important roles in analytical chemistry, from the final analysis stage to photoreactors for analyte conversion to actual fabrication of and incorporation in microdevices for analytical use. The extremely fast turn-on/off rates of LEDs have made possible simple approaches to fluorescence lifetime measurement. Although they are increasingly being used as detectors, their wavelength selectivity as detectors has rarely been exploited. From their first proposed use for absorbance measurement in 1970, LEDs have been used in analytical chemistry in too many ways to make a comprehensive review possible. Hence, we critically review here the more recent literature on their use in optical detection and measurement systems. Cloudy as our crystal ball may be, we express our views on the future applications of LEDs in analytical chemistry: The horizon will certainly become wider as LEDs in the deep UV with sufficient intensity become available.

  12. Light-Emitting Diodes: Phosphorescent Nanocluster Light-Emitting Diodes (Adv. Mater. 2/2016).

    Science.gov (United States)

    Kuttipillai, Padmanaban S; Zhao, Yimu; Traverse, Christopher J; Staples, Richard J; Levine, Benjamin G; Lunt, Richard R

    2016-01-13

    On page 320, R. R. Lunt and co-workers demonstrate electroluminescence from earth-abundant phosphorescent metal halide nanoclusters. These inorganic emitters, which exhibit rich photophysics combined with a high phosphorescence quantum yield, are employed in red and near-infrared light-emitting diodes, providing a new platform of phosphorescent emitters for low-cost and high-performance light-emission applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Laterally injected light-emitting diode and laser diode

    Science.gov (United States)

    Miller, Mary A.; Crawford, Mary H.; Allerman, Andrew A.

    2015-06-16

    A p-type superlattice is used to laterally inject holes into an III-nitride multiple quantum well active layer, enabling efficient light extraction from the active area. Laterally-injected light-emitting diodes and laser diodes can enable brighter, more efficient devices that impact a wide range of wavelengths and applications. For UV wavelengths, applications include fluorescence-based biological sensing, epoxy curing, and water purification. For visible devices, applications include solid state lighting and projection systems.

  14. Power saving regulated light emitting diode circuit

    International Nuclear Information System (INIS)

    Haville, G. D.

    1985-01-01

    A power saving regulated light source circuit, comprising a light emitting diode (LED), a direct current source and a switching transistor connected in series with the LED, a control voltage producing resistor connected in series with the LED to produce a control voltage corresponding to the current through the LED, a storage capacitor connected in parallel with the series combination of the LED and the resistor, a comparator having its output connected to the input of the transistor, the comparator having a reference input and a control input, a stabilized biasing source for supplying a stabilized reference voltage to the reference input, the control input of the comparator being connected to the control voltage producing resistor, the comparator having a high output state when the reference voltage exceeds the control voltage while having a low output state when the control voltage exceeds the reference voltage, the transistor being conductive in response to the high state while being nonconductive in response to the low state, the transistor when conductive being effective to charge the capacitor and to increase the control voltage, whereby the comparator is cycled between the high and low output states while the transistor is cycled between conductive and nonconductive states

  15. Light-Emitting Diodes: Solving Complex Problems

    Science.gov (United States)

    Planinšič, Gorazd; Etkina, Eugenia

    2015-05-01

    This is the fourth paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide readers with the description of experiments and the pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper1 provided an overview of possible uses of LEDs in physics courses. The second paper2 discussed how one could help students learn the foundational aspects of LED physics through a scaf-folded inquiry approach, specifically the ISLE cycle. The third paper3 showed how the physics inherent in the functioning of LEDs could help students deepen their understanding of sources of electric power and the temperature dependence of resistivity, and explore the phenomenon of fluorescence also using the ISLE cycle.4 The goal of this fourth paper is to use LEDs as black boxes that allow students to study certain properties of a system of interest, specifically mechanical, electric, electromagnetic, and light properties. The term "black box" means that we use a device without knowing the mechanism behind its operation.

  16. Improved performance of organic light-emitting diode with vanadium ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 88; Issue 6. Improved performance of organic light-emitting ... Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED).With 12nm optimal thickness of V 2 O 5 ...

  17. Organic light emitting diode with surface modification layer

    Science.gov (United States)

    Basil, John D.; Bhandari, Abhinav; Buhay, Harry; Arbab, Mehran; Marietti, Gary J.

    2017-09-12

    An organic light emitting diode (10) includes a substrate (12) having a first surface (14) and a second surface (16), a first electrode (32), and a second electrode (38). An emissive layer (36) is located between the first electrode (32) and the second electrode (38). The organic light emitting diode (10) further includes a surface modification layer (18). The surface modification layer (18) includes a non-planar surface (30, 52).

  18. Organic light emitting diode with light extracting electrode

    Science.gov (United States)

    Bhandari, Abhinav; Buhay, Harry

    2017-04-18

    An organic light emitting diode (10) includes a substrate (20), a first electrode (12), an emissive active stack (14), and a second electrode (18). At least one of the first and second electrodes (12, 18) is a light extracting electrode (26) having a metallic layer (28). The metallic layer (28) includes light scattering features (29) on and/or in the metallic layer (28). The light extracting features (29) increase light extraction from the organic light emitting diode (10).

  19. Types of organic light-emitting diode (OLED)

    OpenAIRE

    Askari Mohammad Bagher

    2016-01-01

    An organic light-emitting diode (OLED) consists of several semiconducting organic layers sandwiched between two electrodes, at least one of them being transparent. OLEDs can provide brighter, crisper displays on electronic devices and use less power than conventional light-emitting diodes (LEDs) or liquid crystal displays (LCDs) used today. OLEDs are made by placing thin films of organic materials between two conductors. When electrical current is applied, a bright light is emitted. The OLED ...

  20. Operation of AC Adapters Visualized Using Light-Emitting Diodes

    Science.gov (United States)

    Regester, Jeffrey

    2016-01-01

    A bridge rectifier is a diamond-shaped configuration of diodes that serves to convert alternating current(AC) into direct current (DC). In our world of AC outlets and DC electronics, they are ubiquitous. Of course, most bridge rectifiers are built with regular diodes, not the light-emitting variety, because LEDs have a number of disadvantages. For…

  1. Electrically driven surface plasmon light-emitting diodes

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke

    We investigate device performance of GaN light-emitting diodes (LEDs) with a 30-nm p-GaN layer. The metallization used to separate the p-contact from plasmonic metals, reveals limitations on current spreading which reduces surface plasmonic enhancement.......We investigate device performance of GaN light-emitting diodes (LEDs) with a 30-nm p-GaN layer. The metallization used to separate the p-contact from plasmonic metals, reveals limitations on current spreading which reduces surface plasmonic enhancement....

  2. The Light-Emitting Diode as a Light Detector

    Science.gov (United States)

    Baird, William H.; Hack, W. Nathan; Tran, Kiet; Vira, Zeeshan; Pickett, Matthew

    2011-01-01

    A light-emitting diode (LED) and operational amplifier can be used as an affordable method to provide a digital output indicating detection of an intense light source such as a laser beam or high-output LED. When coupled with a microcontroller, the combination can be used as a multiple photogate and timer for under $50. A similar circuit is used…

  3. Improvement in light-extraction efficiency of light emitting diode ...

    Indian Academy of Sciences (India)

    The effect of various microlens parameters such as diameter and area fraction on light-extraction efficiency was systematically studied. Improvement of 4% in extraction efficiency was obtained by employing it on white light emitting diode. The area fraction of microlenses was increased up to 0.34 by reducing the spin speed.

  4. Improved performance of organic light-emitting diode with vanadium ...

    Indian Academy of Sciences (India)

    Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED).With 12nm optimal thickness of V 2 O 5 , the luminance efficiency is increased by 1.66 times compared to the single FTO-based OLED. The improvement of ...

  5. Pulsed Ultraviolet Light Emitting Diodes for Advanced Oxidation of Tartrazine

    Science.gov (United States)

    2015-03-26

    using ozone alone in the degradation of pesticide in the water (Paillard et al, 1988). The third method is the combination of ozone and a catalyst to...2-1.pdf 13) Sari H. Vilhunen, Mika E.T. Sillanpaa. (2008). Ultraviolet light emitting diodes and hydrogen peroxide in the photodegradation of

  6. Gallium-Nitride-Based Light-Emitting Diodes

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 20; Issue 7. Gallium-Nitride-Based Light-Emitting Diodes: 2014 Nobel Prize in Physics. Kota V R M Murali Vinayak Bharat Naik Deepanjan Datta. General Article Volume 20 Issue 7 July 2015 pp 605-616 ...

  7. Using high-power light emitting diodes for photoacoustic imaging

    DEFF Research Database (Denmark)

    Hansen, R. S.

    2011-01-01

    The preliminary result of using a high-power light emitting diode, LED, for photoacoustic imaging is presented. The pulsed light source is created by a 1Watt red Luxeon LED. The LED delivers light pulses with 25W peak power when supplied by 40A peak, 60ns wide current pulses. The phantom used for...

  8. Gallium-Nitride-Based Light-Emitting Diodes

    Indian Academy of Sciences (India)

    IAS Admin

    The advent of the semiconductor light-emitting diode (LED) emerged as a key component in our modern lighting technologies. While LEDs of various colors have been invented since 1950s, the blue LED was elusive till the 1990s. Blue light, with blue being one of the primary colors, is essential for white light emission.

  9. Device Physics of White Polymer Light-Emitting Diodes

    NARCIS (Netherlands)

    Nicolai, Herman T.; Hof, Andre; Blom, Paul W. M.

    2012-01-01

    The charge transport and recombination in white-emitting polymer light- emitting diodes (PLEDs) are studied. The PLED investigated has a single emissive layer consisting of a copolymer in which a green and red dye are incorporated in a blue backbone. From single-carrier devices the effect of the

  10. Tuning the colour of white polymer light emitting diodes

    NARCIS (Netherlands)

    Kok, M.M. de; Sarfert, W.; Paetzold, R.

    2010-01-01

    Colour tuning of white polymer light emitting diode (LED) light sources can be attained by various methods at various stages in the production process of the lamps and/or by the design of the active material incorporated in the LEDs. In this contribution we will describe the methods and discuss the

  11. Determination of illuminants representing typical white light emitting diodes sources

    DEFF Research Database (Denmark)

    Jost, S.; Ngo, M.; Ferrero, A.

    2017-01-01

    Solid-state lighting (SSL) products are already in use by consumers and are rapidly gaining the lighting market. Especially, white Light Emitting Diode (LED) sources are replacing banned incandescent lamps and other lighting technologies in most general lighting applications. The aim of this work...

  12. Improvement in light-extraction efficiency of light emitting diode ...

    Indian Academy of Sciences (India)

    2018-02-02

    Feb 2, 2018 ... parameters such as diameter and area fraction on light-extraction efficiency was systematically studied. Improvement of. 4% in extraction efficiency was obtained by employing it on white light emitting diode. The area fraction .... on feature size due to (i) weak van der Waals destabilizing forces and (ii) high ...

  13. Fabrication of organic light emitting diode using Molybdenum ...

    Indian Academy of Sciences (India)

    65

    Abstract: In this study high-performance of organic light-emitting diodes (OLEDs) with a buffer layer of MoO3 are demonstrated. With an optimal thickness of MoO3 (12 nm), the luminance efficiency is found to be increased compared to the single layer anode OLED. To study the performance of OLED by the buffer layer we ...

  14. Light Converting Inorganic Phosphors for White Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Chiao-Wen Yeh

    2010-03-01

    Full Text Available White light-emitting diodes (WLEDs have matched the emission efficiency of florescent lights and will rapidly spread as light source for homes and offices in the next 5 to 10 years. WLEDs provide a light element having a semiconductor light emitting layer (blue or near-ultraviolet (nUV LEDs and photoluminescence phosphors. These solid-state LED lamps, rather than organic light emitting diode (OLED or polymer light-emitting diode (PLED, have a number of advantages over conventional incandescent bulbs and halogen lamps, such as high efficiency to convert electrical energy into light, reliability and long operating lifetime. To meet with the further requirement of high color rendering index, warm light with low color temperature, high thermal stability and higher energy efficiency for WLEDs, new phosphors that can absorb excitation energy from blue or nUV LEDs and generate visible emissions efficiently are desired. The criteria of choosing the best phosphors, for blue (450-480 nm and nUV (380-400 nm LEDs, strongly depends on the absorption and emission of the phosphors. Moreover, the balance of light between the emission from blue-nUV LEDs and the emissions from phosphors (such as yellow from Y3Al5O12:Ce3+ is important to obtain white light with proper color rendering index and color temperature. Here, we will review the status of phosphors for LEDs and prospect the future development.

  15. Hybrid Light-Emitting Diode Enhanced With Emissive Nanocrystals

    DEFF Research Database (Denmark)

    Kopylov, Oleksii

    of the hybrid diode fabrication including process techniques for GaN LED and incorporation of the nanocrystals are presented with the emphasis on the differences with standard LED processing. Results and analysis of optical and electrical characterization including photoluminescence (PL), micro-PL, time......This thesis investigates a new type of white light emitting hybrid diode, composed of a light emitting GaN/InGaN LED and a layer of semiconductor nanocrystals for color conversion. Unlike standard white LEDs, the device is configured to achieve high color conversion efficiency via non......-radiative energy transfer from the primary LED to the nanocrystals. LED structures with sub-10 nm separation the between quantum well and the surface and patterned standard bright LEDs are considered for the hybrid devices, which require close proximity of the nanocrystals to the quantum well. The development...

  16. Organic light-emitting diodes from homoleptic square planar complexes

    Science.gov (United States)

    Omary, Mohammad A

    2013-11-12

    Homoleptic square planar complexes [M(N.LAMBDA.N).sub.2], wherein two identical N.LAMBDA.N bidentate anionic ligands are coordinated to the M(II) metal center, including bidentate square planar complexes of triazolates, possess optical and electrical properties that make them useful for a wide variety of optical and electrical devices and applications. In particular, the complexes are useful for obtaining white or monochromatic organic light-emitting diodes ("OLEDs"). Improved white organic light emitting diode ("WOLED") designs have improved efficacy and/or color stability at high brightness in single- or two-emitter white or monochrome OLEDs that utilize homoleptic square planar complexes, including bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) ("Pt(ptp).sub.2").

  17. Vacuum Nanohole Array Embedded Phosphorescent Organic Light Emitting Diodes

    Science.gov (United States)

    Jeon, Sohee; Lee, Jeong-Hwan; Jeong, Jun-Ho; Song, Young Seok; Moon, Chang-Ki; Kim, Jang-Joo; Youn, Jae Ryoun

    2015-01-01

    Light extraction from organic light-emitting diodes that utilize phosphorescent materials has an internal efficiency of 100% but is limited by an external quantum efficiency (EQE) of 30%. In this study, extremely high-efficiency organic light emitting diodes (OLEDs) with an EQE of greater than 50% and low roll-off were produced by inserting a vacuum nanohole array (VNHA) into phosphorescent OLEDs (PhOLEDs). The resultant extraction enhancement was quantified in terms of EQE by comparing experimentally measured results with those produced from optical modeling analysis, which assumes the near-perfect electric characteristics of the device. A comparison of the experimental data and optical modeling results indicated that the VNHA extracts the entire waveguide loss into the air. The EQE obtained in this study is the highest value obtained to date for bottom-emitting OLEDs. PMID:25732061

  18. Light-emitting diodes in dermatology: stimulation of wound healing

    Directory of Open Access Journals (Sweden)

    Justyna Fryc

    2016-05-01

    Full Text Available Low-level light therapy (LLLT, which is sometimes included in phototherapy, is an effective therapeutic strategy to improve wound healing and reduce pain, inflammation and swelling. Nowadays, new sources of light, such as light-emitting diodes (LEDs with a broad range of wavelengths, are widely available. The biological effects promoted by LEDs are dependent on irradiation parameters, mainly wavelength and dose. This review article focuses on recent clinical trials using light-emitting diode low-level light therapy (LED-LLLT for enhancing wound healing. In this article, we also cover the mechanisms of action of LLLT on cells and tissues and highlight the importance of defining optimum LLLT parameters for stimulation of wound healing.

  19. High extraction efficiency ultraviolet light-emitting diode

    Science.gov (United States)

    Wierer, Jonathan; Montano, Ines; Allerman, Andrew A.

    2015-11-24

    Ultraviolet light-emitting diodes with tailored AlGaN quantum wells can achieve high extraction efficiency. For efficient bottom light extraction, parallel polarized light is preferred, because it propagates predominately perpendicular to the QW plane and into the typical and more efficient light escape cones. This is favored over perpendicular polarized light that propagates along the QW plane which requires multiple, lossy bounces before extraction. The thickness and carrier density of AlGaN QW layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. At Al>0.3, thinner QW layers (light preferentially polarized parallel to the QW plane. Also, active regions consisting of six or more QWs, to reduce carrier density, and with thin barriers, to efficiently inject carriers in all the QWs, are preferred.

  20. Versatile multispectral microscope based on light emitting diodes.

    Science.gov (United States)

    Brydegaard, Mikkel; Merdasa, Aboma; Jayaweera, Hiran; Ålebring, Jens; Svanberg, Sune

    2011-12-01

    We describe the development of a novel multispectral microscope, based on light-emitting diodes, capable of acquiring megapixel images in thirteen spectral bands from the ultraviolet to the near infrared. The system captures images and spectra in transmittance, reflectance, and scattering modes. We present as examples of applications ground truth measurements for remote sensing and parasitology diagnostics. The system is a general purpose scientific instrument that could be used to develop dedicated simplified instruments with optimal bands and mode selection.

  1. All-Quantum-Dot Infrared Light-Emitting Diodes

    KAUST Repository

    Yang, Zhenyu

    2015-12-22

    © 2015 American Chemical Society. Colloidal quantum dots (CQDs) are promising candidates for infrared electroluminescent devices. To date, CQD-based light-emitting diodes (LEDs) have employed a CQD emission layer sandwiched between carrier transport layers built using organic materials and inorganic oxides. Herein, we report the infrared LEDs that use quantum-tuned materials for each of the hole-transporting, the electron-transporting, and the light-emitting layers. We successfully tailor the bandgap and band position of each CQD-based component to produce electroluminescent devices that exhibit emission that we tune from 1220 to 1622 nm. Devices emitting at 1350 nm achieve peak external quantum efficiency up to 1.6% with a low turn-on voltage of 1.2 V, surpassing previously reported all-inorganic CQD LEDs.

  2. Light emitting diodes as a plant lighting source

    Energy Technology Data Exchange (ETDEWEB)

    Bula, R.J.; Tennessen, D.J.; Morrow, R.C. [Wisconsin Center for Space Automation and Robotics, Madison, WI (United States); Tibbitts, T.W. [Univ. of Wisconsin, Madison, WI (United States)

    1994-12-31

    Electroluminescence in solid materials is defined as the generation of light by the passage of an electric current through a body of solid material under an applied electric field. A specific type of electroluminescence, first noted by Lossew in 1923, involves the generation of photons when electrons are passed through a p-n junction of certain solid materials (junction of a n-type semiconductor, an electron donor, and a p-type semiconductor, an electron acceptor). Development efforts to translate these observations into visible light emitting devices, however, was not undertaken until the 1950s. The term, light emitting diode (LEDs), was first used in a report by Wolfe, et al., in 1955. The development of this light emitting semiconductor technology dates back less than 30 years. During this period of time, the LED has evolved from a rare and expensive light generating device to one of the most widely used electronic components. The most popular applications of the LED are as indicators or as optoelectronic switches. However, several recent advances in LED technology have made possible the utilization of LEDs for applications that require a high photon flux, such as for plant lighting in controlled environments. The new generation of LEDs based on a gallium aluminum arsenide (GaAlAS) semiconductor material fabricated as a double heterostructure on a transparent substrate has opened up many new applications for these LEDs.

  3. Light-emitting diodes - Their potential in biomedical applications

    Energy Technology Data Exchange (ETDEWEB)

    Yeh, Naichia Gary; Wu, Chia-Hao [College of Applied Sciences, MingDao University, 369 Wen-Hua Road, Peetou, Changhua 52345 (China); Cheng, Ta Chih [Department of Tropical Agriculture and International Cooperation, National Pingtung University of Science and Technology, 1 Hseuh-Fu Rd., Nei-Pu Hsiang, Pingtung 91201 (China)

    2010-10-15

    The rapid development of high brightness light-emitting diodes (LEDs) makes feasible the use of LEDs, among other light sources (such as laser, intense pulse light and other incoherent light systems), for medical treatment and light therapy. This paper provides a general review on red, green, blue, ultraviolet LED applications in photo rejuvenation and medical treatments of a variety of physical abnormalities, as well as the relief of stress, circadian rhythm disorders, and seasonal affective disorder. The review, concentrated in the papers published after 1990, intends to show that LEDs are well qualified to succeed its more energy demanding counterparts in the named areas and beyond. (author)

  4. Broadband mid-infrared superlattice light-emitting diodes

    Science.gov (United States)

    Ricker, R. J.; Provence, S. R.; Norton, D. T.; Boggess, T. F.; Prineas, J. P.

    2017-05-01

    InAs/GaSb type-II superlattice light-emitting diodes were fabricated to form a device that provides emission over the entire 3-5 μm mid-infrared transmission window. Variable bandgap emission regions were coupled together using tunnel junctions to emit at peak wavelengths of 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.4 μm, 4.7 μm, and 5.0 μm. Cascading the structure recycles the electrons in each emission region to emit several wavelengths simultaneously. At high current densities, the light-emitting diode spectra broadened into a continuous, broadband spectrum that covered the entire mid-infrared band. When cooled to 77 K, radiances of over 1 W/cm2 sr were achieved, demonstrating apparent temperatures above 1000 K over the 3-5 μm band. InAs/GaSb type-II superlattices are capable of emitting from 3 μm to 30 μm, and the device design can be expanded to include longer emission wavelengths.

  5. New Optoelectronic Technology Simplified for Organic Light Emitting Diode (OLED

    Directory of Open Access Journals (Sweden)

    Andre F. S. Guedes

    2014-06-01

    Full Text Available The development of Organic Light Emitting Diode (OLED, using an optically transparent substrate material and organic semiconductor materials, has been widely utilized by the electronic industry when producing new technological products. The OLED are the base Poly (3,4-ethylenedioxythiophene, PEDOT, and Polyaniline, PANI, were deposited in Indium Tin Oxide, ITO, and characterized by UV-Visible Spectroscopy (UV-Vis, Optical Parameters (OP and Scanning Electron Microscopy (SEM. In addition, the thin film obtained by the deposition of PANI, prepared in perchloric acid solution, was identified through PANI-X1. The result obtained by UV-Vis has demonstrated that the Quartz/ITO/PEDOT/PANI-X1 layer does not have displacement of absorption for wavelengths greaters after spin-coating and electrodeposition. Thus, the spectral irradiance of the OLED informed the irradiance of 100 W/m2, and this result, compared with the standard Light Emitting Diode (LED, has indicated that the OLED has higher irradiance. After 1000 hours of electrical OLED tests, the appearance of nanoparticles visible for images by SEM, to the migration process of organic semiconductor materials, was present, then. Still, similar to the phenomenon of electromigration observed in connections and interconnections of microelectronic devices, the results have revealed a new mechanism of migration, which raises the passage of electric current in OLED.

  6. Combinational light emitting diode-high frequency focused ultrasound treatment for HeLa cell.

    Science.gov (United States)

    Choe, Se-Woon; Park, Kitae; Park, Chulwoo; Ryu, Jaemyung; Choi, Hojong

    2017-12-01

    Light sources such as laser and light emitting diode or ultrasound devices have been widely used for cancer therapy and regenerative medicines, since they are more cost-effective and less harmful than radiation therapy, chemotherapy or magnetic treatment. Compared to laser and low intensity ultrasound techniques, light emitting diode and high frequency focused ultrasound shows enhanced therapeutic effects, especially for small tumors. We propose combinational light emitting diode-high frequency focused ultrasound treatment for human cervical cancer HeLa cells. Individual red, green, and blue light emitting diode light only, high frequency focused ultrasound only, or light emitting diode light combined with high frequency focused ultrasound treatments were applied in order to characterize the responses of HeLa cells. Cell density exposed by blue light emitting diode light combined with high frequency focused ultrasound (2.19 ± 0.58%) was much lower than that of cells exposed by red and green light emitting diode lights (81.71 ± 9.92% and 61.81 ± 4.09%), blue light emitting diode light (11.19 ± 2.51%) or high frequency focused ultrasound only (9.72 ± 1.04%). We believe that the proposed combinational blue light emitting diode-high frequency focused ultrasound treatment could have therapeutic benefits to alleviate cancer cell proliferation.

  7. Current path in light emitting diodes based on nanowire ensembles

    International Nuclear Information System (INIS)

    Limbach, F; Hauswald, C; Lähnemann, J; Wölz, M; Brandt, O; Trampert, A; Hanke, M; Jahn, U; Calarco, R; Geelhaar, L; Riechert, H

    2012-01-01

    Light emitting diodes (LEDs) have been fabricated using ensembles of free-standing (In, Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth mode by molecular beam epitaxy. Electron-beam-induced current analysis, cathodoluminescence as well as biased μ-photoluminescence spectroscopy, transmission electron microscopy, and electrical measurements indicate that the electroluminescence of such LEDs is governed by the differences in the individual current densities of the single-NW LEDs operated in parallel, i.e. by the inhomogeneity of the current path in the ensemble LED. In addition, the optoelectronic characterization leads to the conclusion that these NWs exhibit N-polarity and that the (In, Ga)N quantum well states in the NWs are subject to a non-vanishing quantum confined Stark effect. (paper)

  8. III-nitride based light emitting diodes and applications

    CERN Document Server

    Han, Jung; Amano, Hiroshi; Morkoç, Hadis

    2013-01-01

    Light emitting diodes (LEDs) are already used in traffic signals, signage lighting, and automotive applications. However, its ultimate goal is to replace traditional illumination through LED lamps since LED lighting significantly reduces energy consumption and cuts down on carbon-dioxide emission. Despite dramatic advances in LED technologies (e.g., growth, doping and processing technologies), however, there remain critical issues for further improvements yet to be achieved for the realization of solid-state lighting. This book aims to provide the readers with some contemporary LED issues, which have not been comprehensively discussed in the published books and, on which the performance of LEDs is seriously dependent. For example, most importantly, there must be a breakthrough in the growth of high-quality nitride semiconductor epitaxial layers with a low density of dislocations, in particular, in the growth of Al-rich and and In-rich GaN-based semiconductors. The materials quality is directly dependent on th...

  9. III-nitride based light emitting diodes and applications

    CERN Document Server

    Han, Jung; Amano, Hiroshi; Morkoç, Hadis

    2017-01-01

    The revised edition of this important book presents updated and expanded coverage of light emitting diodes (LEDs) based on heteroepitaxial GaN on Si substrates, and includes new chapters on tunnel junction LEDs, green/yellow LEDs, and ultraviolet LEDs. Over the last two decades, significant progress has been made in the growth, doping and processing technologies of III-nitride based semiconductors, leading to considerable expectations for nitride semiconductors across a wide range of applications. LEDs are already used in traffic signals, signage lighting, and automotive applications, with the ultimate goal of the global replacement of traditional incandescent and fluorescent lamps, thus reducing energy consumption and cutting down on carbon-dioxide emission. However, some critical issues must be addressed to allow the further improvements required for the large-scale realization of solid-state lighting, and this book aims to provide the readers with details of some contemporary issues on which the performanc...

  10. Quantum key distribution with an entangled light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Shields, A. J. [Toshiba Research Europe Limited, 208 Science Park, Milton Road, Cambridge CB4 0GZ (United Kingdom); Farrer, I.; Ritchie, D. A. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

    2015-12-28

    Measurements performed on entangled photon pairs shared between two parties can allow unique quantum cryptographic keys to be formed, creating secure links between users. An advantage of using such entangled photon links is that they can be adapted to propagate entanglement to end users of quantum networks with only untrusted nodes. However, demonstrations of quantum key distribution with entangled photons have so far relied on sources optically excited with lasers. Here, we realize a quantum cryptography system based on an electrically driven entangled-light-emitting diode. Measurement bases are passively chosen and we show formation of an error-free quantum key. Our measurements also simultaneously reveal Bell's parameter for the detected light, which exceeds the threshold for quantum entanglement.

  11. Cooling analysis of a light emitting diode automotive fog lamp

    Directory of Open Access Journals (Sweden)

    Zadravec Matej

    2017-01-01

    Full Text Available Efficiency of cooling fins inside of a light emitting diode fog lamp is studied using computational fluid dynamics. Diffusion in heat sink, natural convection and radiation are the main principles of the simulated heat transfer. The Navier-Stokes equations were solved by the computational fluid dynamics code, including Monte Carlo radiation model and no additional turbulence model was needed. The numerical simulation is tested using the existing lamp geometry and temperature measurements. The agreement is excellent inside of few degrees at all measured points. The main objective of the article is to determine the cooling effect of various heat sink parts. Based on performed simulations, some heat sink parts are found to be very ineffective. The geometry and heat sink modifications are proposed. While radiation influence is significant, compressible effects are found to be minor.

  12. Luminescence and squeezing of a superconducting light-emitting diode

    Science.gov (United States)

    Hlobil, Patrik; Orth, Peter P.

    2015-05-01

    We investigate a semiconductor p -n junction in contact with superconducting leads that is operated under forward bias as a light-emitting diode. The presence of superconductivity results in a significant increase of the electroluminescence in a sharp frequency window. We demonstrate that the tunneling of Cooper pairs induces an additional luminescence peak on resonance. There is a transfer of superconducting to photonic coherence that results in the emission of entangled photon pairs and squeezing of the fluctuations in the quadrature amplitudes of the emitted light. We show that the squeezing angle can be electrically manipulated by changing the relative phase of the order parameters in the superconductors. We finally derive the conditions for lasing in the system and show that the laser threshold is reduced due to superconductivity. This reveals how the macroscopic coherence of a superconductor can be used to control the properties of light.

  13. Characterization, Modeling, and Optimization of Light-Emitting Diode Systems

    DEFF Research Database (Denmark)

    Thorseth, Anders

    This thesis explores, characterization, modeling, and optimization of light-emitting diodes (LED) for general illumination. An automated setup has been developed for spectral radiometric characterization of LED components with precise control of the settings of forward current and operating...... temperature. The automated setup has been used to characterize commercial LED components with respect to multiple settings. It is shown that the droop in quantum efficiency can be approximated by a simple parabolic function. The investigated models of the spectral power distributions (SPD) from LEDs...... comparing the chromaticity of the measured SPD with tted models, the deviation is found to be larger than the lower limit of human color perception. A method has been developed to optimize multicolored cluster LED systems with respect to light quality, using multi objective optimization. The results...

  14. Semiconductor-nanocrystals-based white light-emitting diodes.

    Science.gov (United States)

    Dai, Quanqin; Duty, Chad E; Hu, Michael Z

    2010-08-02

    In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid-state lighting, such as white light-emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat-panel displays and solid-state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever-increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor-nanocrystals-based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid-state lighting technology are discussed.

  15. Randomized controlled trial of light-emitting diode phototherapy.

    Science.gov (United States)

    Maisels, M J; Kring, E A; DeRidder, J

    2007-09-01

    We wished to compare the efficacy of light-emitting diode (LED) phototherapy with special blue fluorescent (BB) tube phototherapy in the treatment of neonatal hyperbilirubinemia. We randomly assigned 66 infants >or=35 weeks of gestation to receive phototherapy using an LED device or BB. In addition to phototherapy from above, all infants also received phototherapy from below using four BB tubes or a fiberoptic pad. After 15+/-5 h of phototherapy, the rate of decline in the total serum bilirubin (TSB) was 0.35+/-0.25 mg/dl/h in the LED group vs 0.27+/-0.25 mg/dl/h in the BB group (P=0.20). LED phototherapy is as effective as BB phototherapy in lowering serum bilirubin levels in term and near-term newborns.

  16. Empirical Measurements of Filtered Light Emitting Diode (FLED) Replacements

    Science.gov (United States)

    Craine, Eric R.

    2016-05-01

    Low pressure sodium (LPS) public lighting, long favored by astronomers and dark sky advocates, is in decline due to a variety of economic issues. Light emitting diode (LED) technology is a rapidly ascendant mode of lighting in everything from residential to commercial applications. The resulting transition from LPS to LED has been accompanied by great angst in the environmental community, but very little has been done in the way of empirical measurement of LEDs in the field and their actual impacts on communities. The community of Waikoloa Village, Hawaii is located on the western slopes of Mauna Kea, within direct line of sight view of the major astronomical observatories on the mountain summit. Waikoloa has been rigorously illuminated almost exclusively by LPS for many years in acknowledgement of the importance of the Mauna Kea Observatories to the Big Island of Hawaii. As LPS ceases to be a viable alternative for local government support, a decision has been made to experimentally retrofit all of the Waikoloa street lighting with filtered light emitting diode (FLED) fixtures. This action has rendered Waikoloa Village a unique laboratory for evaluating the effects of such a change. STEM Laboratory has been awarded a research grant to make a variety of measurements of the light at night environment of Waikoloa Village both before and after the street light retrofit program. Measurements were conducted using a combination of techniques: Satellite Data Surveys (SDS), Ground Static Surveys (GSS photometry), Ground Mobile Surveys (GMS photometry), Airborne Surveys (ABS photography), and Spectroscopic Surveys (SpecS). The impact of the changes in lighting sources was profound, and the preliminary results of this extensive program are discussed in this presentation.

  17. Spin-polarized light-emitting diodes based on organic bipolar spin valves

    Energy Technology Data Exchange (ETDEWEB)

    Vardeny, Zeev Valentine; Nguyen, Tho Duc; Ehrenfreund, Eitan Avraham

    2017-10-25

    Spin-polarized organic light-emitting diodes are provided. Such spin-polarized organic light-emitting diodes incorporate ferromagnetic electrodes and show considerable spin-valve magneto-electroluminescence and magneto-conductivity responses, with voltage and temperature dependencies that originate from the bipolar spin-polarized space charge limited current.

  18. Luminescence of the InGaN/GaN Blue Light-Emitting Diodes

    Science.gov (United States)

    2000-07-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADPO 11314 TITLE: Luminescence of the InGaN/GaN Blue Light -Emitting Diodes...ADP011332 UNCLASSIFIED Luminescence of the InGaN/GaN blue light -emitting diodes J. K. Sheu a), T. W. Yeh and G. C. Chi Optical Sciences Center, National

  19. Heat transfer and structure stress analysis of micro packaging component of high power light emitting diode

    Directory of Open Access Journals (Sweden)

    Hsu Chih-Neng

    2013-01-01

    Full Text Available This paper focuses on the heat transfer and structural stress analysis of the micro- scale packaging structure of a high-power light emitting diode. The thermal-effect and thermal-stress of light emitting diode are determined numerically. Light emitting diode is attached to the silicon substrate through the wire bonding process by using epoxy as die bond material. The silicon substrate is etched with holes at the bottom and filled with high conductivity copper material. The chip temperature and structure stress increase with input power consumption. The micro light emitting diode is mounted on the heat sink to increase the heat dissipation performance, to decrease chip temperature, to enhance the material structure reliability and safety, and to avoid structure failure as well. This paper has successfully used the finite element method to the micro-scale light emitting diode heat transfer and stress concentration at the edges through etched holes.

  20. Device model investigation of bilayer organic light emitting diodes

    International Nuclear Information System (INIS)

    Crone, B. K.; Davids, P. S.; Campbell, I. H.; Smith, D. L.

    2000-01-01

    Organic materials that have desirable luminescence properties, such as a favorable emission spectrum and high luminescence efficiency, are not necessarily suitable for single layer organic light-emitting diodes (LEDs) because the material may have unequal carrier mobilities or contact limited injection properties. As a result, single layer LEDs made from such organic materials are inefficient. In this article, we present device model calculations of single layer and bilayer organic LED characteristics that demonstrate the improvements in device performance that can occur in bilayer devices. We first consider an organic material where the mobilities of the electrons and holes are significantly different. The role of the bilayer structure in this case is to move the recombination away from the electrode that injects the low mobility carrier. We then consider an organic material with equal electron and hole mobilities but where it is not possible to make a good contact for one carrier type, say electrons. The role of a bilayer structure in this case is to prevent the holes from traversing the device without recombining. In both cases, single layer device limitations can be overcome by employing a two organic layer structure. The results are discussed using the calculated spatial variation of the carrier densities, electric field, and recombination rate density in the structures. (c) 2000 American Institute of Physics

  1. White Light Emitting Diode Development for General Illumination Applications

    Energy Technology Data Exchange (ETDEWEB)

    James Ibbetson

    2006-05-01

    This report contains a summary of technical achievements during a 3-year project aimed at developing the chip and packaging technology necessary to demonstrate efficient, high flux light-emitting diode (LED) arrays using Cree's gallium nitride/silicon carbide (GaN/SiC) LED technology as the starting point. Novel chip designs and fabrication processes are described that led to high power blue LEDs that achieved 310 mW of light output at 350 mA drive current, corresponding to quantum and wall plug efficiencies of 32.5% and 26.5%, respectively. When combined with phosphor, high power white LEDs with luminous output of 67 lumens and efficacy of 57 lumens per watt were also demonstrated. Advances in packaging technology are described that enabled compact, multi-chip white LED lamp modules with 800-1000 lumens output at efficacies of up to 55 lumens per watt. Lamp modules with junction-to-ambient thermal resistance as low as 1.7 C/watt have also been demonstrated.

  2. Emerging Transparent Conducting Electrodes for Organic Light Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Tze-Bin Song

    2014-03-01

    Full Text Available Organic light emitting diodes (OLEDs have attracted much attention in recent years as next generation lighting and displays, due to their many advantages, including superb performance, mechanical flexibility, ease of fabrication, chemical versatility, etc. In order to fully realize the highly flexible features, reduce the cost and further improve the performance of OLED devices, replacing the conventional indium tin oxide with better alternative transparent conducting electrodes (TCEs is a crucial step. In this review, we focus on the emerging alternative TCE materials for OLED applications, including carbon nanotubes (CNTs, metallic nanowires, conductive polymers and graphene. These materials are selected, because they have been applied as transparent electrodes for OLED devices and achieved reasonably good performance or even higher device performance than that of indium tin oxide (ITO glass. Various electrode modification techniques and their effects on the device performance are presented. The effects of new TCEs on light extraction, device performance and reliability are discussed. Highly flexible, stretchable and efficient OLED devices are achieved based on these alternative TCEs. These results are summarized for each material. The advantages and current challenges of these TCE materials are also identified.

  3. Simulated evolution of fluorophores for light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Shu, Yinan; Levine, Benjamin G., E-mail: levine@chemistry.msu.edu [Department of Chemistry, Michigan State University, East Lansing, Michigan 48824 (United States)

    2015-03-14

    Organic light emitting diodes based on fluorophores with a propensity for thermally activated delayed fluorescence (TADF) are able to circumvent limitations imposed on device efficiency by spin statistics. Molecules with a propensity for TADF necessarily have two properties: a small gap between the lowest lying singlet and triplet excited states and a large transition dipole moment for fluorescence. In this work, we demonstrate the use of a genetic algorithm to search a region of chemical space for molecules with these properties. This algorithm is based on a flexible and intuitive representation of the molecule as a tree data structure, in which the nodes correspond to molecular fragments. Our implementation takes advantage of hybrid parallel graphics processing unit accelerated computer clusters to allow efficient sampling while retaining a reasonably accurate description of the electronic structure (in this case, CAM-B3LYP/6-31G{sup ∗∗}). In total, we have identified 3792 promising candidate fluorophores from a chemical space containing 1.26 × 10{sup 6} molecules. This required performing electronic structure calculations on only 7518 molecules, a small fraction of the full space. Several novel classes of molecules which show promise as fluorophores are presented.

  4. Carrier Modulation Layer-Enhanced Organic Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Jwo-Huei Jou

    2015-07-01

    Full Text Available Organic light-emitting diode (OLED-based display products have already emerged in the market and their efficiencies and lifetimes are sound at the comparatively low required luminance. To realize OLED for lighting application sooner, higher light quality and better power efficiency at elevated luminance are still demanded. This review reveals the advantages of incorporating a nano-scale carrier modulation layer (CML, also known as a spacer, carrier-regulating layer, or interlayer, among other terms, to tune the chromaticity and color temperature as well as to markedly improve the device efficiency and color rendering index (CRI for numerous OLED devices. The functions of the CML can be enhanced as multiple layers and blend structures are employed. At proper thickness, the employment of CML enables the device to balance the distribution of carriers in the two emissive zones and achieve high device efficiencies and long operational lifetime while maintaining very high CRI. Moreover, we have also reviewed the effect of using CML on the most significant characteristics of OLEDs, namely: efficiency, luminance, life-time, CRI, SRI, chromaticity, and the color temperature, and see how the thickness tuning and selection of proper CML are crucial to effectively control the OLED device performance.

  5. Infrared Organic Light-Emitting Diodes with Carbon Nanotube Emitters.

    Science.gov (United States)

    Graf, Arko; Murawski, Caroline; Zakharko, Yuriy; Zaumseil, Jana; Gather, Malte C

    2018-01-30

    While organic light-emitting diodes (OLEDs) covering all colors of the visible spectrum are widespread, suitable organic emitter materials in the near-infrared (nIR) beyond 800 nm are still lacking. Here, the first OLED based on single-walled carbon nanotubes (SWCNTs) as the emitter is demonstrated. By using a multilayer stacked architecture with matching charge blocking and charge-transport layers, narrow-band electroluminescence at wavelengths between 1000 and 1200 nm is achieved, with spectral features characteristic of excitonic and trionic emission of the employed (6,5) SWCNTs. Here, the OLED performance is investigated in detail and it is found that local conduction hot-spots lead to pronounced trion emission. Analysis of the emissive dipole orientation shows a strong horizontal alignment of the SWCNTs with an average inclination angle of 12.9° with respect to the plane, leading to an exceptionally high outcoupling efficiency of 49%. The SWCNT-based OLEDs represent a highly attractive platform for emission across the entire nIR. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Printable candlelight-style organic light-emitting diode

    Science.gov (United States)

    Jou, J. H.; Singh, M.; Song, W. C.; Liu, S. H.

    2017-06-01

    Candles or oil lamps are currently the most friendly lighting source to human eyes, physiology, ecosystems, artifacts, environment, and night skies due to their blue light-less emission. Candle light also exhibits high light-quality that provides visual comfort. However, they are relatively low in power efficacy (0.3 lm/W), making them energy-wasting, besides having problems like scorching hot, burning, catching fire, flickering, carbon blacking, oxygen consuming, and release of green house gas etc. In contrast, candlelight organic light-emitting diode (OLED) can be made blue-hazard free and energy-efficient. The remaining challenges are to maximize its light-quality and enable printing feasibility, the latter of which would pave a way to cost-effective manufacturing. We hence demonstrate herein the design and fabrication of a candlelight OLED via wet-process. From retina protection perspective, its emission is 13, 12 and 8 times better than those of the blue-enriched white CFL, LED and OLED. If used at night, it is 9, 6 and 4 times better from melatonin generation perspective.

  7. Thin film Encapsulations of Flexible Organic Light Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Tsai Fa-Ta

    2016-01-01

    Full Text Available Various encapsulated films for flexible organic light emitting diodes (OLEDs were studied in this work, where gas barrier layers including inorganic Al2O3 thin films prepared by atomic layer deposition, organic Parylene C thin films prepared by chemical vapor deposition, and their combination were considered. The transmittance and water vapor transmission rate of the various organic and inorgabic encapsulated films were tested. The effects of the encapsulated films on the luminance and current density of the OLEDs were discussed, and the life time experiments of the OLEDs with these encapsulated films were also conducted. The results showed that the transmittance are acceptable even the PET substrate were coated two Al2O3 and Parylene C layers. The results also indicated the WVTR of the PET substrate improved by coating the barrier layers. In the encapsulation performance, it indicates the OLED with Al2O3 /PET, 1 pair/PET, and 2 pairs/PET presents similarly higher luminance than the other two cases. Although the 1 pair/PET encapsulation behaves a litter better luminance than the 2 pairs/PET encapsulation, the 2 pairs/PET encapsulation has much better life time. The OLED with 2 pairs/PET encapsulation behaves near double life time to the 1 pair encapsulation, and four times to none encapsulation.

  8. Microtube Light-Emitting Diode Arrays with Metal Cores.

    Science.gov (United States)

    Tchoe, Youngbin; Lee, Chul-Ho; Park, Jun Beom; Baek, Hyeonjun; Chung, Kunook; Jo, Janghyun; Kim, Miyoung; Yi, Gyu-Chul

    2016-03-22

    We report the fabrication and characteristics of vertical microtube light-emitting diode (LED) arrays with a metal core inside the devices. To make the LEDs, gallium nitride (GaN)/indium gallium nitride (In(x)Ga(1-x)N)/zinc oxide (ZnO) coaxial microtube LED arrays were grown on an n-GaN/c-aluminum oxide (Al2O3) substrate. The microtube LED arrays were then lifted-off the substrate by wet chemical etching of the sacrificial ZnO microtubes and the silicon dioxide (SiO2) layer. The chemically lifted-off LED layer was then transferred upside-down on other supporting substrates. To create the metal cores, titanium/gold and indium tin oxide were deposited on the inner shells of the microtubes, forming n-type electrodes inside the metal-cored LEDs. The characteristics of the resulting devices were determined by measuring electroluminescence and current-voltage characteristic curves. To gain insights into the current-spreading characteristics of the devices and understand how to make them more efficient, we modeled them computationally.

  9. Effect of encapsulation technology on organic light emitting diode lifetime

    Science.gov (United States)

    Zhong, Jian; Gao, Zhuo; Gao, Juan; Dai, Ke; Chen, Jiule

    2012-03-01

    A kind of green organic light-emitting diodes (OLED) was prepared via vacuum thermal evaporation, of which the multilayer structure was indium-tin oxide (ITO)/copper-phthalocyanine (CuPc) (200 Å)/ N,N'-bis(1-naphthyl)- N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine ( α-NPD) (600 Å)/ N'-diphenyl- N,N'-tris(8-hydroxyquinoline) aluminium (Alq3) (400 Å):10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1 H,5 H,11 H-(l)benzopyropyrano(6,7,8- i, j)quinolizin-11-one (C545T) (2%)/Alq3 (200 Å)/LiF (10 Å)/Al (1000 Å). And we used both traditional glass encapsulation and thin film encapsulation (TFE) technologies to protect the device, reducing impact of vapor and oxygen. Organic film offered an excellent surface morphology, while inorganic film was nearly a perfect barrier to vapor and oxygen. Both of them constituted the encapsulation unit of TFE. According to the results of acceleration life test, the operation lifetime of device using TFE was 22% less than that of device using traditional glass cap encapsulation. So, the technology of TFE should be optimized further, and the quality of TFE needs a great improvement. There is a long way to go and a lot of hard work before realizing flexible display with OLED, but the dream will be true one day.

  10. Multilayer polymer light-emitting diodes by blade coating method

    Science.gov (United States)

    Tseng, Shin-Rong; Meng, Hsin-Fei; Lee, Kuan-Chen; Horng, Sheng-Fu

    2008-10-01

    Multilayer polymer light-emitting diodes fabricated by blade coating are presented. Multilayer of polymers can be easily deposited by blade coating on a hot plate. The multilayer structure is confirmed by the total thickness and the cross section view in the scanning electron microscope. The film thickness variation is only 3.3% in 10cm scale and the film roughness is about 0.3nm in the micron scale. The efficiency of single layer poly(para-phenylene vinylene) copolymer Super Yellow and poly(9,9-dioctylfluorene) (PFO, deep blue) devices are 9 and 1.7cd/A, respectively, by blade coating. The efficiency of the PFO device is raised to 2.9cd/A with a 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) hole-blocking layer and to 2.3cd/A with a poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)] elec-tron-blocking layer added by blade coating.

  11. Device physics of single layer organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Crone, B.K.; Campbell, I.H.; Davids, P.S.; Smith, D.L. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Neef, C.J.; Ferraris, J.P. [The University of Texas at Dallas, Richardson, Texas 75080 (United States)

    1999-11-01

    We present experimental and device model results for electron only, hole only, and bipolar organic light-emitting diodes fabricated using a soluble poly ({ital p}-phenylene vinylene) based polymer. Current{endash}voltage (I{endash}V) characteristics were measured for a series of electron only devices in which the polymer thickness was varied. The I{endash}V curves were described using a device model from which the electron mobility parameters were extracted. Similarly, the hole mobility parameters were extracted using a device model description of I{endash}V characteristics for a series of hole only devices where the barrier to hole injection was varied by appropriate choices of hole injecting electrode. The electron and hole mobilities extracted from the single carrier devices are then used, without additional adjustable parameters, to describe the measured current{endash}voltage characteristics of a series of bipolar devices where both the device thickness and contacts were varied. The model successfully describes the I{endash}V characteristics of single carrier and bipolar devices as a function of polymer thickness and for structures that are contact limited, space charge limited, and for cases in between. We find qualitative agreement between the device model and measured external luminance for a thickness series of devices. We investigate the sensitivity of the device model calculations to the magnitude of the bimolecular recombination rate prefactor. {copyright} {ital 1999 American Institute of Physics.}

  12. Enhanced Phycocyanin Production from Spirulina platensis using Light Emitting Diode

    Science.gov (United States)

    Bachchhav, Manisha Bhanudas; Kulkarni, Mohan Vinayak; Ingale, Arun G.

    2017-06-01

    This work investigates the performance of different cultivation conditions using Light Emitting Diode (LED) as a light source for the production of phycocyanin from Spirulina platensis. With LEDs under autotrophic conditions, red LED produced maximum amount of biomass (8.95 g/l). As compared to autotrophic cultivation with fluorescent lamp (control), cultivations using LEDs under autotrophic and mixotrophic mode significantly enhanced the phycocyanin content. For autotrophic conditions (with LED) phycocyanin content was in the range of 103-242 mg/g of dry biomass, whereas for mixotrophic conditions (0.1% glucose and LED) it was in the range of 254-380 mg/g of dry biomass. Spirulina cultivated with yellow LED under mixotrophic conditions had 5.4-fold more phycocyanin (380 mg/g of dry biomass) than control (70 mg/g of dry biomass). The present study demonstrates that the LEDs under mixotrophic conditions gave sixfold (2497 mg/l) higher yields of phycocyanin as compared to autotrophic condition under white light (415 mg/l).

  13. The antifungal effect of light emitting diode on Malassezia yeasts.

    Science.gov (United States)

    Wi, Hyun Seung; Na, Eui Young; Yun, Sook Jung; Lee, Jee-Bum

    2012-07-01

    Malassezia (M.) species are members of the normal part of the skin flora, but they might induce or be involved with various cutaneous diseases. Although the role of Malassezia in the pathogenesis of cutaneous diseases is not fully understood, recent studies have shown that decreased density of Malassezia led to improvement of these diseases. To identify the antifungal effect of light emitting diode (LED) against Malassezia, its antifungal mechanisms and the impact on the keratinocytes. LED with various wavelengths (370-630nm) on Malassezia furfur, Malassezia sympodialis and Malassezia globosa was irradiated according to dose and then the antifungal effects were thereafter assessed. After irradiating LED with 392.5±1nm of wavelength according to dose on Malassezia species, reactive oxygen species (ROS) and lipid hydroperoxide production assay were measured. In addition, cell viability and inflammatory cytokines (IL-1α, IL-1β, TNF-α, TGF-β, TLR-2 and COX-2) expressions in normal human epidermal keratinocytes (NHEKs) by LED irradiation were evaluated. The growth of Malassezia species was dose-dependently suppressed by both LED with 380±2 and 392.5±1nm wavelengths. The increases of intracellular and extracellular ROS by LED irradiation with 392.5±1nm wavelengths were significantly observed compared to control group. The cell viability and cytokines in NHEKs were not significantly affected by LED irradiation under 5J/cm(2)in vitro. LED irradiation with 380±2 and 392.5±1nm wavelengths proved to have antifungal effect against Malassezia species and no impact on NHEKs under 5J/cm(2). The findings suggest that LED might be an adjunctive therapeutic light tool against Malassezia yeasts related cutaneous diseases. Copyright © 2012 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.

  14. 3D printed quantum dot light-emitting diodes.

    Science.gov (United States)

    Kong, Yong Lin; Tamargo, Ian A; Kim, Hyoungsoo; Johnson, Blake N; Gupta, Maneesh K; Koh, Tae-Wook; Chin, Huai-An; Steingart, Daniel A; Rand, Barry P; McAlpine, Michael C

    2014-12-10

    Developing the ability to 3D print various classes of materials possessing distinct properties could enable the freeform generation of active electronics in unique functional, interwoven architectures. Achieving seamless integration of diverse materials with 3D printing is a significant challenge that requires overcoming discrepancies in material properties in addition to ensuring that all the materials are compatible with the 3D printing process. To date, 3D printing has been limited to specific plastics, passive conductors, and a few biological materials. Here, we show that diverse classes of materials can be 3D printed and fully integrated into device components with active properties. Specifically, we demonstrate the seamless interweaving of five different materials, including (1) emissive semiconducting inorganic nanoparticles, (2) an elastomeric matrix, (3) organic polymers as charge transport layers, (4) solid and liquid metal leads, and (5) a UV-adhesive transparent substrate layer. As a proof of concept for demonstrating the integrated functionality of these materials, we 3D printed quantum dot-based light-emitting diodes (QD-LEDs) that exhibit pure and tunable color emission properties. By further incorporating the 3D scanning of surface topologies, we demonstrate the ability to conformally print devices onto curvilinear surfaces, such as contact lenses. Finally, we show that novel architectures that are not easily accessed using standard microfabrication techniques can be constructed, by 3D printing a 2 × 2 × 2 cube of encapsulated LEDs, in which every component of the cube and electronics are 3D printed. Overall, these results suggest that 3D printing is more versatile than has been demonstrated to date and is capable of integrating many distinct classes of materials.

  15. Electrical pulse burnout testing of light-emitting diodes

    International Nuclear Information System (INIS)

    Kalma, A.H.; Fischer, C.J.

    1975-01-01

    Electrical pulse burnout thresholds were measured in GaAs, GaAsP, and GaP light-emitting diodes (LEDs) by studying the degradation in light output and the change in I-V characteristics both during the pulse and in the steady state. Pulse widths ranging from a few hundred nsec to 100 μsec were used. Light output degradation was the most sensitive parameter and was used to determine the thresholds. Just above threshold, damage is caused by an increase in generation-recombination current in the space-charge retion. This current is non-radiative and the light output drops, but the damage is not catastrophic. At higher power, the junction burns through and shunt resistance paths are formed which more drastically degrade the light output. The experimental data match reasonably with the theoretical Wunsch--Bell/Tasca model if a burnout area of 1 / 10 the junction area is assumed. Both the adiabatic term (At -1 ) and the heat flow term (Bt - /sup 1 / 2 /) contribute in all devices, and the equilibrium term (C) contributes in some GaAsP devices. The scatter in the data for GaAs devices is greater than that for GaAsP devices, apparently because the former types have a significant fraction of mavericks with lower-than-normal thresholds. The use of LEDs to examine electrical pulse burnout is advantageous because the light output is quite sensitive to damage and the combined measurement of optical and electrical properties provides additional information about the mechanisms involved

  16. Benzoporphyrin derivative and light-emitting diode for use in photodynamic therapy: Applications of space light-emitting diode technology

    Science.gov (United States)

    Whelan, Harry T.; Houle, John M.; Bajic, Dawn M.; Schmidt, Meic H.; Reichert, Kenneth W.; Meyer, Glenn A.

    1998-01-01

    Photodynamic therapy (PDT) is a cancer treatment modality that recently has been applied as adjuvant therapy for brain tumors. PDT consists of intravenously injecting a photosensitizer, which preferentially accumulates in tumor cells, into a patient and then activating the photosensitizer with a light source. This results in free radical generation followed by cell death. The development of more effective light sources for PDT of brain tumors has been facilitated by applications of space light-emitting diode array technology; thus permitting deeper tumor penetration of light and use of better photosensitizers. Currently, the most commonly used photosensitizer for brain tumor PDT is Photofrin®. Photofrin® is a heterogeneous mixture of compounds derived from hematoporphyrin. Photofrin® is activated with a 630 nm laser light and does destroy tumor cells in animal models and humans. However, treatment failure does occur using this method. Most investigators attribute this failure to the limited penetration of brain tissue by a 630 nm laser light and to the fact that Photofrin® has only a minor absorption peak at 630 nm, meaning that only a small fraction of the chemical is activated. Benzoporphyrin Derivative Monoacid Ring A (BPD) is a new, second generation photosensitizer that can potentially improve PDT for brain tumors. BPD has a major absorption peak at 690 nm, which gives it two distinct advantages over Photofrin®. First, longer wavelengths of light penetrate brain tissue more easily so that larger tumors could be treated, and second, the major absorption peak means that a larger fraction of the drug is activated upon exposure to light. In the first part of this project we have studied the tumoricidal effects of BPD in vitro using 2A9 canine glioma and U373 human glioblastoma cell cultures. Using light emitting diodes (LED) with a peak emission of 688 nm as a light source, cell kill of up to 86 percent was measured in these cell lines by tumor DNA synthesis

  17. Benzoporphyrin derivative and light-emitting diode for use in photodynamic therapy: Applications of space light-emitting diode technology

    International Nuclear Information System (INIS)

    Whelan, Harry T.; Houle, John M.; Bajic, Dawn M.; Schmidt, Meic H.; Reichert, Kenneth W. II; Meyer, Glenn A.

    1998-01-01

    Photodynamic therapy (PDT) is a cancer treatment modality that recently has been applied as adjuvant therapy for brain tumors. PDT consists of intravenously injecting a photosensitizer, which preferentially accumulates in tumor cells, into a patient and then activating the photosensitizer with a light source. This results in free radical generation followed by cell death. The development of more effective light sources for PDT of brain tumors has been facilitated by applications of space light-emitting diode array technology; thus permitting deeper tumor penetration of light and use of better photosensitizers. Currently, the most commonly used photosensitizer for brain tumor PDT is Photofrin registered . Photofrin registered is a heterogeneous mixture of compounds derived from hematoporphyrin. Photofrin registered is activated with a 630 nm laser light and does destroy tumor cells in animal models and humans. However, treatment failure does occur using this method. Most investigators attribute this failure to the limited penetration of brain tissue by a 630 nm laser light and to the fact that Photofrin registered has only a minor absorption peak at 630 nm, meaning that only a small fraction of the chemical is activated. Benzoporphyrin Derivative Monoacid Ring A (BPD) is a new, second generation photosensitizer that can potentially improve PDT for brain tumors. BPD has a major absorption peak at 690 nm, which gives it two distinct advantages over Photofrin registered . First, longer wavelengths of light penetrate brain tissue more easily so that larger tumors could be treated, and second, the major absorption peak means that a larger fraction of the drug is activated upon exposure to light. In the first part of this project we have studied the tumoricidal effects of BPD in vitro using 2A9 canine glioma and U373 human glioblastoma cell cultures. Using light emitting diodes (LED) with a peak emission of 688 nm as a light source, cell kill of up to 86 percent was

  18. Evaluation of light-emitting diode beacon light fixtures : final report.

    Science.gov (United States)

    2009-12-01

    Rotating beacons containing filament light sources have long been used on highway maintenance trucks : to indicate the presence of the truck to other drivers. Because of advances in light-emitting diode (LED) : technologies, flashing lights containin...

  19. On the photosynthetic responses of crops to intracanopy lighting with light emitting diodes

    NARCIS (Netherlands)

    Trouwborst, G.

    2011-01-01

    Key words: Cucumis sativus, intracanopy lighting, light-emitting diodes (LEDs), light distribution, light interception, light quality, photosynthesis, photosynthetic acclimation

    Assimilation lighting is a production factor of increasing importance in Dutch greenhouse horticulture.

  20. Best practices : bus signage for persons with visual impairments : light-emitting diode (LED) signs

    Science.gov (United States)

    2004-01-01

    This best-practices report provides key information regarding the use of Light-Emitting Diode (LED) sign technologies to present destination and route information on transit vehicles. It will assist managers and engineers in the acquisition and use o...

  1. Investigation of Light-Emitting Diode (LED) Point Light Source Color Visibility against Complex Multicolored Backgrounds

    Science.gov (United States)

    2017-11-01

    ARL-TR-8214 ● NOV 2017 US Army Research Laboratory Investigation of Light-Emitting Diode (LED) Point Light Source Color...ARL-TR-8214 ● NOV 2017 US Army Research Laboratory Investigation of Light-Emitting Diode (LED) Point Light Source Color Visibility against...instructions, searching existing data sources , gathering and maintaining the data needed, and completing and reviewing the collection information. Send

  2. Fabrication of InGaN/GaN nanopillar light-emitting diode arrays

    DEFF Research Database (Denmark)

    Ou, Yiyu; Fadil, Ahmed; Ou, Haiyan

    Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction.......Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction....

  3. Surface Plasmon Enhanced Phosphorescent Organic Light Emitting Diodes

    International Nuclear Information System (INIS)

    Bazan, Guillermo; Mikhailovsky, Alexander

    2008-01-01

    The objective of the proposed work was to develop the fundamental understanding and practical techniques for enhancement of Phosphorescent Organic Light Emitting Diodes (PhOLEDs) performance by utilizing radiative decay control technology. Briefly, the main technical goal is the acceleration of radiative recombination rate in organometallic triplet emitters by using the interaction with surface plasmon resonances in noble metal nanostructures. Increased photonic output will enable one to eliminate constraints imposed on PhOLED efficiency by triplet-triplet annihilation, triplet-polaron annihilation, and saturation of chromophores with long radiative decay times. Surface plasmon enhanced (SPE) PhOLEDs will operate more efficiently at high injection current densities and will be less prone to degradation mechanisms. Additionally, introduction of metal nanostructures into PhOLEDs may improve their performance due to the improvement of the charge transport through organic layers via multiple possible mechanisms ('electrical bridging' effects, doping-like phenomena, etc.). SPE PhOLED technology is particularly beneficial for solution-fabricated electrophosphorescent devices. Small transition moment of triplet emitters allows achieving a significant enhancement of the emission rate while keeping undesirable quenching processes introduced by the metal nanostructures at a reasonably low level. Plasmonic structures can be introduced easily into solution-fabricated PhOLEDs by blending and spin coating techniques and can be used for enhancement of performance in existing device architectures. This constitutes a significant benefit for a large scale fabrication of PhOLEDs, e.g. by roll-to-roll fabrication techniques. Besides multieexciton annihilation, the power efficacy of PhOLEDs is often limited by high operational bias voltages required for overcoming built-in potential barriers to injection and transport of electrical charges through a device. This problem is especially

  4. Surface Plasmon Enhanced Phosphorescent Organic Light Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Guillermo Bazan; Alexander Mikhailovsky

    2008-08-01

    The objective of the proposed work was to develop the fundamental understanding and practical techniques for enhancement of Phosphorescent Organic Light Emitting Diodes (PhOLEDs) performance by utilizing radiative decay control technology. Briefly, the main technical goal is the acceleration of radiative recombination rate in organometallic triplet emitters by using the interaction with surface plasmon resonances in noble metal nanostructures. Increased photonic output will enable one to eliminate constraints imposed on PhOLED efficiency by triplet-triplet annihilation, triplet-polaron annihilation, and saturation of chromophores with long radiative decay times. Surface plasmon enhanced (SPE) PhOLEDs will operate more efficiently at high injection current densities and will be less prone to degradation mechanisms. Additionally, introduction of metal nanostructures into PhOLEDs may improve their performance due to the improvement of the charge transport through organic layers via multiple possible mechanisms ('electrical bridging' effects, doping-like phenomena, etc.). SPE PhOLED technology is particularly beneficial for solution-fabricated electrophosphorescent devices. Small transition moment of triplet emitters allows achieving a significant enhancement of the emission rate while keeping undesirable quenching processes introduced by the metal nanostructures at a reasonably low level. Plasmonic structures can be introduced easily into solution-fabricated PhOLEDs by blending and spin coating techniques and can be used for enhancement of performance in existing device architectures. This constitutes a significant benefit for a large scale fabrication of PhOLEDs, e.g. by roll-to-roll fabrication techniques. Besides multieexciton annihilation, the power efficacy of PhOLEDs is often limited by high operational bias voltages required for overcoming built-in potential barriers to injection and transport of electrical charges through a device. This problem is

  5. Magnetic field effect in organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Niedermeier, Ulrich

    2009-12-14

    The discovery of a magnetic field dependent resistance change of organic light emitting diodes (OLEDs) in the year 2003 has attracted considerable scientific and industrial research interest. However, despite previous progress in the field of organic spin-electronics, the phenomenon of the ''organic magnetoresistance (OMR) effect'' is not yet completely understood. In order to improve the understanding of the microscopic mechanisms which ultimately cause the OMR effect, experimental investigations as well as theoretical considerations concerning the OMR are addressed in this thesis. In polymer-based OLED devices the functional dependencies of the OMR effect on relevant parameters like magnetic field, operating voltage, operating current and temperature are investigated. Based on these results, previously published models for potential OMR mechanisms are critically analyzed and evaluated. Finally, a concept for the OMR effect is favored which suggests magnetic field dependent changes of the spin state of electron-hole pairs as being responsible for changes in current flow and light emission in OLEDs. In the framework of this concept it is possible to explain all results from own measurements as well as results from literature. Another important finding made in this thesis is the fact that the value of the OMR signal in the investigated OLED devices can be enhanced by appropriate electrical and optical conditioning processes. In particular, electrical conditioning causes a significant enhancement of the OMR values, while at the same time it has a negative effect on charge carrier transport and optical device characteristics. These results can be explained by additional results from charge carrier extraction measurements which suggest that electrical conditioning leads to an increase in the number of electronic trap states inside the emission layer of the investigated OLED devices. The positive influence of trap states on the OMR effect is

  6. Light-emitting diode phototherapy for unconjugated hyperbilirubinaemia in neonates.

    Science.gov (United States)

    Kumar, Praveen; Chawla, Deepak; Deorari, Ashok

    2011-12-07

    Phototherapy is the mainstay of treatment of neonatal hyperbilirubinaemia. The commonly used light sources for providing phototherapy are special blue fluorescent tubes, compact fluorescent tubes and halogen spotlights. However, light emitting diodes (LEDs) as light sources with high luminous intensity, narrow wavelength band and higher delivered irradiance could make phototherapy more efficacious than the conventional phototherapy units. To evaluate the effect of LED phototherapy as compared to conventional phototherapy in decreasing serum total bilirubin levels and duration of treatment in neonates with unconjugated hyperbilirubinaemia. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2010, Issue 1), MEDLINE (1966 to April 30, 2010) and EMBASE (1988 to July 8, 2009). Handsearches of the proceedings of annual meetings of The European Society for Paediatric Research and The Society for Pediatric Research were conducted through 2010. Randomised or quasi-randomised controlled trials were eligible for inclusion if they enrolled neonates (term and preterm) with unconjugated hyperbilirubinaemia and compared LED phototherapy with other light sources (fluorescent  tubes, compact fluorescent tubes, halogen spotlight; method of administration: conventional or fibreoptic). We used the standard methods of The Cochrane Collaboration and its Neonatal Review Group for data collection and analysis. Six randomised controlled trials met the inclusion criteria for this review. Four studies compared LED and halogen light sources. Two studies compared LED and compact fluorescent light sources. The duration of phototherapy (six studies, 630 neonates) was comparable in LED and non-LED phototherapy groups (mean difference (hours) -0.43, 95% CI -1.91 to 1.05). The rate of decline of serum total bilirubin (STB) (four studies, 511 neonates) was also similar in the two groups (mean difference (mg/dL/hour) 0.01, 95% CI -0.02 to 0.04). Treatment

  7. Investigating Bandgap Energies, Materials, and Design of Light-Emitting Diodes

    Science.gov (United States)

    Wagner, Eugene P., II

    2016-01-01

    A student laboratory experiment to investigate the intrinsic and extrinsic bandgaps, dopant materials, and diode design in light-emitting diodes (LEDs) is presented. The LED intrinsic bandgap is determined by passing a small constant current through the diode and recording the junction voltage variation with temperature. A second visible…

  8. Phosphorescent organic light emitting diodes with high efficiency and brightness

    Energy Technology Data Exchange (ETDEWEB)

    Forrest, Stephen R; Zhang, Yifan

    2015-11-12

    An organic light emitting device including a) an anode; b) a cathode; and c) an emissive layer disposed between the anode and the cathode, the emissive layer comprising an organic host compound and a phosphorescent compound exhibiting a Stokes Shift overlap greater than 0.3 eV. The organic light emitting device may further include a hole transport layer disposed between the emissive layer and the anode; and an electron transport layer disposed between the emissive layer and the cathode. In some embodiments, the phosphorescent compound exhibits a phosphorescent lifetime of less than 10 .mu.s. In some embodiments, the concentration of the phosphorescent compound ranges from 0.5 wt. % to 10 wt. %.

  9. Tradeoff between laser diodes and light-emitting diodes (LEDs) for the common weapon control system

    Science.gov (United States)

    Greenwell, R. A.

    1982-07-01

    The use of laser diodes or light emitting diodes (LEDs) for the ground-launched cruise missile (GLCM) is comparatively evaluated. Source characteristics of interest, including radiated power output, spectral width and peak emission, modulation bandwidth, size coupling efficiency, lifetime, rise time, and price, are presented for noncoherent LED and the coherent laser diode. The advantages and disadvantages of laser diodes and LEDs are briefly discussed, and nuclear explosion effects on these instruments, including catastrophic damage, transient ionization effects, and permanent degradation, are summarized. A link analysis of the cable parameters required for the GLCM fiber optic data link is given, arriving at power levels consistent with a LED-PIN link. Two LEDs which meet these requirements are briefly discussed.

  10. White polymer light-emitting diode based on polymer blending

    International Nuclear Information System (INIS)

    Lee, Yong Kyun; Kwon, Soon Kab; Kim, Jun Young; Park, Tae Jin; Song, Dae Ho; Kwon, Jang Hyuk; Choo, Dong Jun; Jang, Jin; Jin, Jae Kyu; You, Hong

    2006-01-01

    A series of white polymer light emitting devices have been fabricated by using a polymer blending system of polyfluorene-based blue and MEH-PPV red polymers. A device structure of ITO/PEDOT:PSS/polymer/LiF/Al was employed. The white polymer device exhibited a current efficiency of 4.33 cd/A (4,816 cd/m 2 , Q.E. = 1.9 %) and a maximum luminance of 21,430 cd/m 2 at 9.2 V. The CIE coordinates were (0.35, 0.37) at 5 V and (0.29, 0.30) at 9 V.

  11. Light extraction from organic light-emitting diodes enhanced by spontaneously formed buckles

    Science.gov (United States)

    Koo, Won Hoe; Jeong, Soon Moon; Araoka, Fumito; Ishikawa, Ken; Nishimura, Suzushi; Toyooka, Takehiro; Takezoe, Hideo

    2010-04-01

    Most of the light in conventional organic light-emitting diodes is confined to high-refractive-index layers (such as an organic medium, indium tin oxide and glass substrate) resulting in a low light extraction efficiency of ~20% (refs 1,2). Many studies have used wavelength-scale periodic gratings to increase the external efficiency of organic light-emitting diodes. However, the efficiency is only enhanced at particular wavelengths satisfying the Bragg condition. Here, we demonstrate that a quasi-periodic buckling structure with broad distribution and directional randomness can enhance the light extraction efficiency without introducing spectral changes and directionality. Organic light-emitting diodes corrugated by buckles showed improved current and power efficiencies and an electroluminescence spectrum enhanced by at least a factor of two across the entire visible wavelength regime. These buckling patterns are formed spontaneously on elastic materials with a thin metallic film. The buckled organic light-emitting diode devices are practical and attractive for use in fabricating full colour and white organic light-emitting diodes.

  12. Aluminum-nanodisc-induced collective lattice resonances: Controlling the light extraction in organic light emitting diodes

    Science.gov (United States)

    Auer-Berger, Manuel; Tretnak, Veronika; Wenzl, Franz-Peter; Krenn, Joachim R.; List-Kratochvil, Emil J. W.

    2017-10-01

    We examine aluminum-nanodisc-induced collective lattice resonances as a means to enhance the efficiency of organic light emitting diodes. Thus, nanodisc arrays were embedded in the hole transporting layer of a solution-processed phosphorescent organic blue-light emitting diode. Through extinction spectroscopy, we confirm the emergence of array-induced collective lattice resonances within the organic light emitting diode. Through finite-difference time domain simulations, we show that the collective lattice resonances yield an enhancement of the electric field intensity within the emissive layer. The effectiveness for improving the light generation and light outcoupling is demonstrated by electro-optical characterization, realizing a gain in a current efficiency of 35%.

  13. Red phosphorescent organic light-emitting diodes using pyridine based electron transport type triplet host materials

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Soon Ok [Department of Polymer Science and Engineering, Dankook University, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-701 (Korea, Republic of); Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr [Department of Polymer Science and Engineering, Dankook University, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-701 (Korea, Republic of)

    2011-05-16

    Research highlights: {yields} Pyridine based host material for red phosphorescent organic light emitting diode. {yields} Device optimization at low doping concentration of 2%. {yields} Simplified red phosphorescent organic light emitting diodes. - Abstract: Pyridine based electron transport type host materials were developed and their device performances were investigated according to doping concentration. The pyridine substituent was combined with a spirofluorenebenzofluorene core unit and a high quantum efficiency of 13.3% was achieved in red phosphorescent organic light-emitting diodes at a low doping concentration of 2%. A simple red device without any electron transport layer could be fabricated and a simple device without any electron transport layer showed better power efficiency than the standard device with an electron transport layer.

  14. Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

    Science.gov (United States)

    Zhang, Liuqi; Yang, Xiaolei; Jiang, Qi; Wang, Pengyang; Yin, Zhigang; Zhang, Xingwang; Tan, Hairen; Yang, Yang (Michael); Wei, Mingyang; Sutherland, Brandon R.; Sargent, Edward H.; You, Jingbi

    2017-06-01

    Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m-2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

  15. Blue fluorescent organic light emitting diodes with multilayered graphene anode

    International Nuclear Information System (INIS)

    Hwang, Joohyun; Choi, Hong Kyw; Moon, Jaehyun; Shin, Jin-Wook; Joo, Chul Woong; Han, Jun-Han; Cho, Doo-Hee; Huh, Jin Woo; Choi, Sung-Yool; Lee, Jeong-Ik; Chu, Hye Yong

    2012-01-01

    As an innovative anode for organic light emitting devices (OLEDs), we have investigated graphene films. Graphene has importance due to its huge potential in flexible OLED applications. In this work, graphene films have been catalytically grown and transferred to the glass substrate for OLED fabrications. We have successfully fabricated 2 mm × 2 mm device area blue fluorescent OLEDs with graphene anodes which showed 2.1% of external quantum efficiency at 1000 cd/m 2 . This is the highest value reported among fluorescent OLEDs using graphene anodes. Oxygen plasma treatment on graphene has been found to improve hole injections in low voltage regime, which has been interpreted as oxygen plasma induced work function modification. However, plasma treatment also increases the sheet resistance of graphene, limiting the maximum luminance. In summary, our works demonstrate the practical possibility of graphene as an anode material for OLEDs and suggest a processing route which can be applied to various graphene related devices.

  16. [White organic light-emitting diodes applied for lighting technology].

    Science.gov (United States)

    Huang, Qing-Yu; Zhao, Su-Ling; Xu, Zheng; Fan, Xing; Wang, Jian; Yang, Qian-Qian

    2014-01-01

    Lighting accounts for approximately 22 percent of the electricity consumed in buildings in the United States, with 40 percent of that amount consumed by inefficient incandescent lamps. This has generated increased interest in the use of white electroluminescent organic light-emitting devices (WOLEDS) as the next generation solid-state lighting source, owing to their potential for significantly improved efficiency over incandescent sources, combined with low-cost, high-throughput manufacturability. The research and application of the devices have witnessed great progress. WOLEDS have incomparable advantages for its special characteristics. This progress report sketched the principle of WOLEDS and provided some common structures, and further investigation of the mechanism of different structures was made. Meanwhile, the key technologies of WOLEDS were summarized. Finally, the latest research progress of WOLEDS was reviewed.

  17. Printed assemblies of ultrathin, microscale inorganic light emitting diodes for deformable and semitransparent displays

    Science.gov (United States)

    Rogers, John A.; Nuzzo, Ralph; Kim, Hoon-sik; Brueckner, Eric; Park, Sang Il; Kim, Rak Hwan

    2017-05-09

    Described herein are printable structures and methods for making, assembling and arranging electronic devices. A number of the methods described herein are useful for assembling electronic devices where one or more device components are embedded in a polymer which is patterned during the embedding process with trenches for electrical interconnects between device components. Some methods described herein are useful for assembling electronic devices by printing methods, such as by dry transfer contact printing methods. Also described herein are GaN light emitting diodes and methods for making and arranging GaN light emitting diodes, for example for display or lighting systems.

  18. Investigations of thin p-GaN light-emitting diodes with surface plasmon compatible metallization

    DEFF Research Database (Denmark)

    Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke

    2016-01-01

    We investigate device performance of InGaN light-emitting diodes with a 30-nm p-GaN layer. The metallization used to separate the p-contact from plasmonic metals, reveals limitations on current spreading which reduces surface plasmonic enhancement.......We investigate device performance of InGaN light-emitting diodes with a 30-nm p-GaN layer. The metallization used to separate the p-contact from plasmonic metals, reveals limitations on current spreading which reduces surface plasmonic enhancement....

  19. High efficiency blue phosphorescent organic light-emitting diodes without electron transport layer

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Soon Ok [Department of Polymer Science and Engineering, Dankook University, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-701 (Korea, Republic of); Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr [Department of Polymer Science and Engineering, Dankook University, Jukjeon-dong, Suji-gu, Yongin-si, Gyeonggi-do 448-701 (Korea, Republic of)

    2011-08-15

    High efficiency blue phosphorescent organic light-emitting diodes were fabricated without an electron transport layer using a spirobifluorene based blue triplet host material. The simple blue PHOLEDs without the electron transport layer showed a high external quantum efficiency and current efficiency of 16.1% and 30.2 cd/A, respectively. The high device performances of the electron transport layer free blue PHOLEDs were comparable to those of blue PHOLEDs with the electron transport layer. - Highlights: > Simple device structure without electron transport layer. > High efficiency blue phosphorescent organic light-emitting diode. > Spirobifluorene based high triplet energy host material.

  20. Low-cost photoacoustic imaging systems based on laser diode and light-emitting diode excitation

    Directory of Open Access Journals (Sweden)

    Qingkai Yao

    2017-07-01

    Full Text Available Photoacoustic imaging, an emerging biomedical imaging modality, holds great promise for preclinical and clinical researches. It combines the high optical contrast and high ultrasound resolution by converting laser excitation into ultrasonic emission. In order to generate photoacoustic signal efficiently, bulky Q-switched solid-state laser systems are most commonly used as excitation sources and hence limit its commercialization. As an alternative, the miniaturized semiconductor laser system has the advantages of being inexpensive, compact, and robust, which makes a significant effect on production-forming design. It is also desirable to obtain a wavelength in a wide range from visible to near-infrared spectrum for multispectral applications. Focussing on practical aspect, this paper reviews the state-of-the-art developments of low-cost photoacoustic system with laser diode and light-emitting diode excitation source and highlights a few representative installations in the past decade.

  1. The Development of Ultraviolet Light Emitting Diodes on p-SiC Substrates

    Science.gov (United States)

    Brummer, Gordon

    Ultraviolet (UV) light emitting diodes (LEDs) are promising light sources for purification, phototherapy, and resin curing applications. Currently, commercial UV LEDs are composed of AlGaN-based n-i-p junctions grown on sapphire substrates. These devices suffer from defects in the active region, inefficient p-type doping, and poor light extraction efficiency. This dissertation addresses the development of a novel UV LED device structure, grown on p-SiC substrates. In this device structure, the AlGaN-based intrinsic (i) and n-layers are grown directly on the p-type substrate, forming a p-i-n junction. The intrinsic layer (active region) is composed of an AlN buffer layer followed by three AlN/Al0.30Ga0.70N quantum wells. After the intrinsic layer, the n-layer is formed from n-type AlGaN. This device architecture addresses the deficiencies of UV LEDs on sapphire substrates while providing a vertical device geometry, reduced fabrication complexity, and improved thermal management. The device layers were grown by molecular beam epitaxy (MBE). The material properties were optimized by considering varying growth conditions and by considering the role of the layer within the device. AlN grown at 825 C and with a Ga surfactant yielded material with screw dislocation density of 1x10 7 cm-2 based on X-ray diffraction (XRD) analysis. AlGaN alloys grown in this work contained compositional inhomogeneity, as verified by high-resolution XRD, photoluminescence, and absorption measurements. Based on Stokes shift measurements, the degree of compositional inhomogeneity was correlated with the amount of excess Ga employed during growth. Compositional inhomogeneity yields carrier localizing potential fluctuations, which are advantages in light emitting device layers. Therefore, excess Ga growth conditions were used to grow AlN/Al0.30Ga0.70N quantum wells (designed using a wurtzite k.p model) with 35% internal quantum efficiency. Potential fluctuations limit the mobility of carriers

  2. Hand-Drawn Resistors and a Simple Tester Using a Light-Emitting Diode

    Science.gov (United States)

    Kamata, Masahiro; Abe, Mayumi

    2012-01-01

    A thick line drawn on a sheet of paper with a 6B pencil is electrically conductive and its resistance can be roughly estimated using a simple tester made of a light-emitting diode (LED) and a lithium coin-type cell. Using this hand-drawn resistor and the LED tester, we developed teaching materials that help students to understand how electrical…

  3. Two-phase cooling of light emitting diode for higher light output and increased efficiency

    NARCIS (Netherlands)

    Ye, H.; Mihailovic, M.; Wong, C.K.Y.; Zeijl, H.W. van; Gielen, A.W.J.; Zhang, G.Q.; Sarro, P.M.

    2013-01-01

    High Power Light Emitting Diode (HP LED) is one of the promising candidates for future lighting systems with efficient energy consumption. However, around 70% of the input power will be still transferred to heat. Recently, to obtain more light output, the increased electrical currents consequently

  4. Photodynamic effect of light-emitting diode light on cell growth ...

    Indian Academy of Sciences (India)

    The aim of this study was to propose the use of red light-emitting diode (LED) as an alternative light source for methylene blue (MB) photosensitizing effect in photodynamic therapy (PDT). Its effectiveness was tested against Staphylococcus aureus (ATCC 26923), Escherichia coli (ATCC 26922), Candida albicans (ATCC ...

  5. LIGHT-EMITTING DIODE BULBS IN PAEDIATRIC AIRWAY- A CASE SERIES

    Directory of Open Access Journals (Sweden)

    Abhik Sikdar

    2017-11-01

    Full Text Available PRESENTATION OF CASE On extensive internet search of published English literature, we found only 3 cases of Light-Emitting Diode (LED bulb in airway. 1,2,3 We present 2 cases of LED bulb aspiration presenting to us in the last 6 months.

  6. Peculiarities of electrooptical characteristics of gallium phosphide light-emitting diodes in high injection level conditions

    Directory of Open Access Journals (Sweden)

    O. M. Hontaruk

    2015-04-01

    Full Text Available Electroluminescence of green N-doped gallium phosphide light-emitting diodes was studied. The negative differential resistance region in the current-voltage characteristics was found at low temperature (Т ≤ 90 К. Possible reason of this phenomenon is the redistribution of recombinational flows between annihilation channels on isolated nitrogen atoms and annihilation channel on the NN1 pairs.

  7. Light emitting diodes as an alternative ambient illumination source in photolithography environment

    DEFF Research Database (Denmark)

    Corell, Dennis Dan; Ou, Haiyan; Dam-Hansen, Carsten

    2009-01-01

    We explored an alternative light emitting diode (LED) - based solution to replace the existing yellow fluorescent light tubes (YFT) used in photolithography rooms. A no-blue LED lamp was designed and a prototype was fabricated. For both solutions, the spectral power distribution (SPD) was measure...

  8. Entangled-Photon Pair Emission from a Light-Emitting Diode

    International Nuclear Information System (INIS)

    Salter, Cameron L; Stevenson, R Mark; Shields, Andrew J; Farrer, Ian; Nicoll, Christine A; Ritchie, David A

    2011-01-01

    Electrically-driven entangled-photon generation is demonstrated for the first time using a single InAs/GaAs quantum dot embedded in a light emitting diode structure. Under alternating-current injection, we found that the entanglement fidelity was of sufficient quality for quantum information applications such as quantum key distribution.

  9. Joint structure in high brightness light emitting diode (HB LED) packages

    International Nuclear Information System (INIS)

    Park, Jin-Woo; Yoon, Young-Bok; Shin, Sang-Hyun; Choi, Sang-Hyun

    2006-01-01

    We present the transmission electron microscopy (TEM) analysis of 1.5 μm-thick Au-20Sn solder joint between a high brightness light emitting diode (HB LED) and a Si heat sink. Due to intermetallic compound formation, global Sn depletion occurred in the thin solder, which raised the melting point of the solder and caused local incompleteness of bonding

  10. Optical Experiments Using Mini-Torches with Red, Green and Blue Light Emitting Diodes

    Science.gov (United States)

    Kamata, Masahiro; Matsunaga, Ai

    2007-01-01

    We have developed two kinds of optical experiments: color mixture and fluorescence, using mini-torches with light emitting diodes (LEDs) that emit three primary colors. Since the tools used in the experiments are simple and inexpensive, students can easily retry and develop the experiments by themselves. As well as giving an introduction to basic…

  11. Photodynamic effect of light-emitting diode light on cell growth ...

    Indian Academy of Sciences (India)

    Madhu urs

    Photodynamic effect of LED light on cell growth inhibition induced by methylene blue. 231. J. Biosci. 33(2) ... The aim of this study was to propose the use of red light-emitting diode (LED) as an alternative light source for methylene blue (MB) .... identical groups, with one group being illuminated (1 h) and the other group ...

  12. All-solution processed polymer light-emitting diodes with air stable metal-oxide electrodes

    NARCIS (Netherlands)

    Bruyn, P. de; Moet, D.J.D.; Blom, P.W.M.

    2012-01-01

    We present an all-solution processed polymer light-emitting diode (PLED) using spincoated zinc oxide (ZnO) and vanadium pentoxide (V2O5) as electron and hole injecting contact, respectively. We compare the performance of these devices to the standard PLED design using PEDOT:PSS as anode and Ba/Al as

  13. Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control

    KAUST Repository

    Sun, Liangfeng

    2012-05-06

    Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr \\'1 m \\'2) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH 2 groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.© 2012 Macmillan Publishers Limited.

  14. Optimum Structure Adjustment for Flexible Fluorescent and Phosphorescent Organic Light Emitting Diodes

    OpenAIRE

    Juang, Fuh-Shyang; Tsai, Yu-Sheng; Wang, Shun-Hsi; Su, Shin-Yuan; Chen, Shin-Liang; Chen, Shen-Yaur

    2010-01-01

    This research successfully improved the luminance efficiency and lifetime of flexible fluorescent and phosphorescent organic light emitting diodes by optimizing organic layer thicknesses or inserting a spin-coated buffer layer. From the results, the best phosphorescent device structure (ITO/ NPB (50nm)/ Ir(ppy)3:CBP (40nm)/ TPBi (10nm)/ Alq3 (50nm)/ LiF

  15. Electrical-thermal-luminous-chromatic model of phosphor-converted white light-emitting diodes

    NARCIS (Netherlands)

    Ye, H.; Koh, S.W.; Yuan, C.; Zeijl, H. van; Gielen, A.W.J.; Lee, S.W.R.; Zhang, G.

    2014-01-01

    The drive of increased electrical currents to achieve high luminous output for phosphor-converted white light-emitting diodes (PW-LED) has led to a series of thermal problems. The light performance of PW-LED is affected by the heat generated by the two major sources in a package/module: chip(s) and

  16. Medical Applications of Space Light-Emitting Diode Technology--Space Station and Beyond

    Energy Technology Data Exchange (ETDEWEB)

    Whelan, H.T.; Houle, J.M.; Donohoe, D.L.; Bajic, D.M.; Schmidt, M.H.; Reichert, K.W.; Weyenberg, G.T.; Larson, D.L.; Meyer, G.A.; Caviness, J.A.

    1999-06-01

    Space light-emitting diode (LED) technology has provided medicine with a new tool capable of delivering light deep into tissues of the body, at wavelengths which are biologically optimal for cancer treatment and wound healing. This LED technology has already flown on Space Shuttle missions, and shows promise for wound healing applications of benefit to Space Station astronauts.

  17. Passivation of organic light emitting diode anode grid lines by pulsed Joule heating

    NARCIS (Netherlands)

    Janka, M.; Gierth, R.; Rubingh, J.E.; Abendroth, M.; Eggert, M.; Moet, D.J.D.; Lupo, D.

    2015-01-01

    We report the self-aligned passivation of a current distribution grid for an organic light emitting diode (OLED) anode using a pulsed Joule heating method to align the passivation layer accurately on the metal grid. This method involves passing an electric current through the grid to cure a polymer

  18. Molecular-scale simulation of electroluminescence in a multilayer white organic light-emitting diode

    DEFF Research Database (Denmark)

    Mesta, Murat; Carvelli, Marco; de Vries, Rein J

    2013-01-01

    we show that it is feasible to carry out Monte Carlo simulations including all of these molecular-scale processes for a hybrid multilayer organic light-emitting diode combining red and green phosphorescent layers with a blue fluorescent layer. The simulated current density and emission profile...

  19. Furopyridine derivatives as host materials for solution processed blue phosphorescent organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Yook, Kyoung Soo; Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr

    2014-07-01

    Soluble blue phosphorescent organic light-emitting diodes were developed using a pyridofuropyridine derivative, 3-(3-(carbazole-9-yl)phenyl) pyrido[3′,2′:4,5]furo[2,3-b]pyridine (CzPFP), and a benzofuropyridine derivative, 6-(3-(carbazole-9-yl)phenyl)benzofuro[2,3-b]pyridine (PCz-6BFP) as host materials. The CzPFP and PCz-6BFP hosts formed a smooth film morphology with a surface roughness less than 0.5 nm after spin coating. The PCz-6BFP host showed better quantum efficiency than the CzPFP host and a high quantum efficiency of 19.5% was achieved in solution processed blue phosphorescent organic light-emitting diodes using the PCz-6BFP host. - Highlights: • High quantum efficiency of 19.5% in blue phosphorescent organic light-emitting diodes • Stable film morphology using benzofuropyridine and pyridofuropyridine derivatives • High efficiency solution processed blue phosphorescent organic light-emitting diodes.

  20. All-solution processed polymer light-emitting diodes with air stable metal-oxide electrodes

    NARCIS (Netherlands)

    de Bruyn, P.; Moet, D. J. D.; Blom, P. W. M.

    We present an all-solution processed polymer light-emitting diode (PLED) using spincoated zinc oxide (ZnO) and vanadium pentoxide (V2O5) as electron and hole injecting contact, respectively. We compare the performance of these devices to the standard PLED design using PEDOT:PSS as anode and Ba/Al as

  1. Exciton quenching at PEDOT:PSS anode in polymer blue-light-emitting diodes

    NARCIS (Netherlands)

    Abbaszadeh, D.; Wetzelaer, G.A.H.; Nicolai, H.T.; Blom, P.W.M.

    2014-01-01

    The quenching of excitons at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) PEDOT:PSS) anode in blue polyalkoxyspirobifluorene-arylamine polymer light-emitting diodes is investigated. Due to the combination of a higher electron mobility and the presence of electron traps, the

  2. Exciton quenching at PEDOT : PSS anode in polymer blue-light-emitting diodes

    NARCIS (Netherlands)

    Abbaszadeh, D.; Wetzelaer, G. A. H.; Nicolai, H. T.; Blom, P. W. M.

    2014-01-01

    The quenching of excitons at the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) anode in blue polyalkoxyspirobifluorene-arylamine polymer light-emitting diodes is investigated. Due to the combination of a higher electron mobility and the presence of electron traps, the

  3. Highly Efficient p-i-n Type Organic Light-emitting Diodes Using ...

    African Journals Online (AJOL)

    set of three quantum states of a system, each with total spin S=1. The process of charge injection and recombination in OLEDs (Tang and Van Slyke,. 1987) results in the generation of singlets and triplets. Furthermore, high efficiency electro-phosphorescent organic light-emitting diodes using phosphorescent dyes have ...

  4. Graphene as anode electrode for colloidal quantum dots based light emitting diodes

    Science.gov (United States)

    Klekachev, Alexander V.; Kuznetsov, Sergey N.; Asselberghs, Inge; Cantoro, Mirco; Hun Mun, Jeong; Jin Cho, Byung; Stesmans, André L.; Heyns, Marc M.; De Gendt, Stefan

    2013-07-01

    Graphene films demonstrating low sheet resistance and high transparency in the visible light range are promising to be used as electrodes for light-emitting applications. In this work, we report the implementation of single layer graphene as hole injecting electrode for CdSe/ZnS quantum dot-light emitting diodes (QD-LED). We compare graphene vs. indium-tin-oxide (ITO)-based anode junctions by electroluminescence intensity performance of QD-LEDs. Our results demonstrate better hole injection efficiency for the graphene-based electrode at technologically relevant current densities J graphene as a valuable alternative to replace ITO in QD-LED technology.

  5. Phosphorescent Neutral Iridium (III) Complexes for Organic Light-Emitting Diodes.

    Science.gov (United States)

    Bin Mohd Yusoff, Abd Rashid; Huckaba, Aron J; Nazeeruddin, Mohammad Khaja

    2017-04-01

    The development of transition metal complexes for application in light-emitting devices is currently attracting significant research interest. Among phosphorescent emitters, those involving iridium (III) complexes have proven to be exceedingly useful due to their relatively short triplet lifetime and high phosphorescence quantum yields. The emission wavelength of iridium (III) complexes significantly depends on the ligands, and changing the electronic nature and the position of the ligand substituents can control the properties of the ligands. In this chapter, we discuss recent developments of phosphorescent transition metal complexes for organic light-emitting diode applications focusing solely on the development of iridium metal complexes.

  6. Preliminary evaluation of discomfort glare from organic light-emitting diode and edge-lit light-emitting diode lighting panels

    Science.gov (United States)

    Mou, Xi; Freyssinier, Jean Paul; Narendran, Nadarajah; Bullough, John D.

    2017-05-01

    The organic light-emitting diode (OLED) is an area light source, and its primary competing technology is the edge-lit light-emitting diode (LED) panel. Both technologies are similar in shape and appearance, but there is little understanding of how people perceive discomfort glare (DG) from area sources. The objective of this study was to evaluate the DG of these two technologies under similar operating conditions. Additionally, two existing DG models were compared to evaluate the correlation between predicted values and observed values. In an earlier study, we found no statistically significant difference in human response in terms of DG between OLED and edge-lit LED panels when the two sources produced the same luminous stimulus. The range of testing stimulus was expanded to test different panel luminances at three background illuminations. The results showed no difference in perceived glare between the panels, and, as the background illumination increased, the perceived glare decreased. In other words, both appeared equally glary beyond a certain luminance and background illumination. We then compared two existing glare models with the observed values and found that one model showed a good estimation of how humans perceive DG. That model was further modified to increase its power.

  7. Organic Light-Emitting Diodes on Solution-Processed Graphene Transparent Electrodes

    KAUST Repository

    Wu, Junbo

    2010-01-26

    Theoretical estimates indicate that graphene thin films can be used as transparent electrodes for thin-film devices such as solar cells and organic light-emitting diodes, with an unmatched combination of sheet resistance and transparency. We demonstrate organic light-emitting diodes with solution-processed graphene thin film transparent conductive anodes. The graphene electrodes were deposited on quartz substrates by spincoating of an aqueous dispersion of functionalized graphene, followed by a vacuum anneal step to reduce the sheet resistance. Small molecular weight organic materials and a metal cathode were directly deposited on the graphene anodes, resulting in devices with a performance comparable to control devices on indium-tin-oxide transparent anodes. The outcoupling efficiency of devices on graphene and indium-tin-oxide is nearly identical, in agreement with model predictions. © 2010 American Chemical Society.

  8. Morphology control of perovskite light-emitting diodes by using amino acid self-assembled monolayers

    Science.gov (United States)

    Wang, Nana; Cheng, Lu; Si, Junjie; Liang, Xiaoyong; Jin, Yizheng; Wang, Jianpu; Huang, Wei

    2016-04-01

    Amino acid self-assembled monolayers are used in the fabrication of light-emitting diodes based on organic-inorganic halide perovskites. The monolayers of amino acids provide modified interfaces by anchoring to the surfaces of ZnO charge-transporting layers using carboxyl groups, leaving the amino groups to facilitate the nucleation of MAPbBr3 perovskite films. This surface-modification strategy, together with chlorobenzene-assisted fast crystallization method, results in good surface coverage and reduced defect density of the perovskite films. These efforts lead to green perovskite light emitting diodes with a low turn-on voltage of 2 V and an external quantum efficiency of 0.43% at a brightness of ˜5000 cd m-2.

  9. Morphology control of perovskite light-emitting diodes by using amino acid self-assembled monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Nana; Cheng, Lu; Wang, Jianpu, E-mail: iamjpwang@njtech.edu.cn [Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials - SICAM, Nanjing Tech University - NanjingTech, 30 South Puzhu Road, Nanjing 211816 (China); Si, Junjie; Liang, Xiaoyong [State Key Laboratory of Silicon Materials, Center for Chemistry of High-Performance and Novel Materials, and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Jin, Yizheng [Center for Chemistry of High-Performance and Novel Materials, State Key Laboratory of Silicon Materials, and Department of Chemistry, Zhejiang University, Hangzhou 310027 (China); Huang, Wei [Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials - SICAM, Nanjing Tech University - NanjingTech, 30 South Puzhu Road, Nanjing 211816 (China); Key Laboratory for Organic Electronics and Information Displays and Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023 (China)

    2016-04-04

    Amino acid self-assembled monolayers are used in the fabrication of light-emitting diodes based on organic-inorganic halide perovskites. The monolayers of amino acids provide modified interfaces by anchoring to the surfaces of ZnO charge-transporting layers using carboxyl groups, leaving the amino groups to facilitate the nucleation of MAPbBr{sub 3} perovskite films. This surface-modification strategy, together with chlorobenzene-assisted fast crystallization method, results in good surface coverage and reduced defect density of the perovskite films. These efforts lead to green perovskite light emitting diodes with a low turn-on voltage of 2 V and an external quantum efficiency of 0.43% at a brightness of ∼5000 cd m{sup −2}.

  10. Output Properties of Transparent Submount Packaged FlipChip Light-Emitting Diode Modules

    Directory of Open Access Journals (Sweden)

    Preetpal Singh

    2016-06-01

    Full Text Available Flip chip technology has been widely adopted in modern power light-emitting diode (LED fabrications and its output efficiency is closely related to the submount material properties. Here, we present the electrical, optical and thermal properties of flip chip light-emitting diodes mounted on transparent sapphire and borosilicate glass which have shown a higher output luminous flux when compared to the traditional non-transparent mounted LEDs. Exhibiting both better thermal conductivity and good optical transparency, flip chip LEDs with a sapphire submount showed superior performance when compared to the non-transparent silicon submount ones, and also showed better optical performance than the flip chip LEDs mounted on transparent but poor-thermal-conducting glass substrates. The correspondent analysis was carried out using ANSYS 14 to compare the experimental thermal imaging with the simulation results. TracePro software was also used to check the output luminous flux dependency on different LED mounting designs.

  11. Influence of Pre-trimethylindium flow treatment on blue light emitting diode

    International Nuclear Information System (INIS)

    Xu, Bing; Zhao, Jun Liang; Dai, Hai Tao; Wang, Shu Guo; Lin, Ray-Ming; Chu, Fu-Chuan; Huang, Chou-Hsiung; Yu, Sheng-Fu; Sun, Xiao Wei

    2014-01-01

    The effects of Pre-trimethylindium (TMIn) flow treatment prior to quantum well growth on blue light emitting diode properties were investigated. High-resolution X-ray diffraction indicated that Pre-TMIn flow treatment did not change the composition of indium in quantum wells, but influenced electrical and optical properties of blue light emitting diode. Electroluminescence exhibited redshift with increasing TMIn treatment time. Though, the forward voltage became a little larger with longer Pre-TMIn treatment time due to the slight phase separation and indium aggregation, the efficiency droop of the device was improved effectively. - Highlights: • Pre-trimethylindium treatment can lead to longer wavelength. • External quantum efficiency can be improved effectively. • Electrical properties are not decreased using Pre-trimethylindium treatment

  12. Influence of Pre-trimethylindium flow treatment on blue light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Bing; Zhao, Jun Liang [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Dai, Hai Tao, E-mail: htdai@tju.edu.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Wang, Shu Guo [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Lin, Ray-Ming, E-mail: rmlin@mail.cgu.edu.tw [Graduate Institute of Electronic Engineering and Green Technology Research Center, Chang Gung University, Taoyuan 333, Taiwan (China); Chu, Fu-Chuan; Huang, Chou-Hsiung [Graduate Institute of Electronic Engineering and Green Technology Research Center, Chang Gung University, Taoyuan 333, Taiwan (China); Yu, Sheng-Fu [Institute of Microelectronics and Department of Electrical Engineering, Center for Micro/Nano Science and Technology, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Sun, Xiao Wei, E-mail: xwsun@sustc.edu.cn [South University of Science and Technology of China, Shenzhen, Guangdong (China)

    2014-01-31

    The effects of Pre-trimethylindium (TMIn) flow treatment prior to quantum well growth on blue light emitting diode properties were investigated. High-resolution X-ray diffraction indicated that Pre-TMIn flow treatment did not change the composition of indium in quantum wells, but influenced electrical and optical properties of blue light emitting diode. Electroluminescence exhibited redshift with increasing TMIn treatment time. Though, the forward voltage became a little larger with longer Pre-TMIn treatment time due to the slight phase separation and indium aggregation, the efficiency droop of the device was improved effectively. - Highlights: • Pre-trimethylindium treatment can lead to longer wavelength. • External quantum efficiency can be improved effectively. • Electrical properties are not decreased using Pre-trimethylindium treatment.

  13. The influence of melt purification and structure defects on mid-infrared light emitting diodes

    CERN Document Server

    Krier, A

    2003-01-01

    Mid-infrared light emitting diodes which exhibit more than 7 mW (pulsed) and 0.35 mW dc output power at 3.3 mu m and at room temperature have been fabricated by liquid phase epitaxy using Pb as a neutral solvent. Using Pb solution an increase in pulsed output power of between two and three times was obtained compared with InAs light emitting diodes (LEDs) made using rare-earth gettering. The performance improvements were attributed to a reduction in residual carrier concentration arising from the removal of un-intentional donors and structure defects in the InAs active region material. These LEDs are well matched to the CH sub 4 absorption spectrum and potentially could form the basis of a practical infrared CH sub 4 gas sensor.

  14. Enhanced light extraction of organic light-emitting diodes using recessed anodes

    International Nuclear Information System (INIS)

    Hsu, C.M.; Zeng, Y.X.; Lin, B.T.; Lin, W.M.; Wu, W.T.

    2014-01-01

    Recessed indium tin oxide films were prepared to serve as anodes for enhancing light extraction efficiency of organic light-emitting diodes (OLEDs). The power efficiency of OLEDs with the proposed films was enhanced by up to 28%. This improvement can be attributed to enhanced light extraction due to the wall effect and the bottom scattering effect of the recesses. The power efficiency increased with recess depth but was limited by the accompanying high electrical resistivity and large optical loss.

  15. Bactericidal effects of deep ultraviolet light-emitting diode for solutions during intravenous infusion

    OpenAIRE

    Omotani, Sachiko; Tani, Katsuji; Aoe, Mai; Esaki, Seiji; Nagai, Katsuhito; Hatsuda, Yasutoshi; Mukai, Junji; Teramachi, Hitomi; Myotoku, Michiaki

    2018-01-01

    Background: Ultraviolet irradiation is effectively used as a disinfection method for inactivating microorganisms. Methods: We investigated the bactericidal effects by irradiation with a deep-ultraviolet light-emitting diode (DUV-LED) on the causative microorganisms of catheter related blood stream infection contaminating the solution for intravenous infusion. For irradiation, prototype modules for water disinfection with a DUV-LED were used. Experiments were conducted on five kinds of microor...

  16. Topology optimisation of passive coolers for light-emitting diode lamps

    DEFF Research Database (Denmark)

    Alexandersen, Joe

    2015-01-01

    This work applies topology optimisation to the design of passive coolers for light-emitting diode (LED) lamps. The heat sinks are cooled by the natural convection currents arising from the temperature difference between the LED lamp and the surrounding air. A large scale parallel computational....... The optimisation results show interesting features that are currently being incorporated into industrial designs for enhanced passive cooling abilities....

  17. Evaluation of light-emitting diodes as attractant for sandflies (Diptera: Psychodidae: Phlebotominae) in northeastern Brazil

    OpenAIRE

    Silva, Francinaldo Soares; Brito, Jefferson Mesquita; Costa, Benedita Maria; Lobo, Shelre Emile Pereira Duarte

    2015-01-01

    Hoover Pugedo light traps were modified for use with green and blue-light-emitting diodes to trap phlebotomine sandflies in northeastern Brazil. A total of 2,267 specimens belonging to eight genera and 15 species were sampled. The predominant species were Nyssomyia whitmani(34.41%) and Micropygomyia echinatopharynx(17.25%).The green LED trap prevailed over the blue and control lights; however, no statistically significant difference could be detected among the three light sources. Even withou...

  18. Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering

    KAUST Repository

    Pan, Jun

    2016-08-16

    A two-step ligand-exchange strategy is developed, in which the long-carbon-chain ligands on all-inorganic perovskite (CsPbX3, X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-paircapped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.

  19. Light emitting diode (LED) use in artificial lighting for broiler chicken production

    OpenAIRE

    Santana,Mayara R. de; Garcia,Rodrigo G.; Naas,Irenilza de A.; Paz,Ibiara C. de L. A.; Caldara,Fabiana R.; Barreto,Bruna

    2014-01-01

    Light emitting diode (LED) has been used in commercial poultry industry by presenting superior energy savings and providing feasibility on production process. The objective of this research was to evaluate performance and carcass yield of broiler chickens exposed to different LED colors compared with fluorescent lamps. For that, two experiments (E1 and E2) were performed and 2,646 Cobb® chickens were used. In experiment E1, male birds were exposed to 20 lux artificial lighting with red, yello...

  20. Light emitting diodes (LED): applications in forest and native plant nurseries

    Science.gov (United States)

    Thomas D. Landis; Jeremiah R. Pinto; R. Kasten Dumroese

    2013-01-01

    It was quotes like this that made us want to learn more about light emitting diodes (LED). Other than knowing that LEDs were the latest innovation in artificial lighting, we knew that we had a lot to learn. So we started by reviewing some of the basics. The following review is a brief synopsis of how light affects plants and some discussion about LED lighting. If you...

  1. Finger-shaped red light emitting diode to ascertain the depth of periungual wart

    Directory of Open Access Journals (Sweden)

    Balakrishnan Nirmal

    2016-01-01

    Full Text Available Management of periungual wart is a great challenge, especially when there is subungual extension. The major cause of recurrence of wart is improper clinical assessment of its extent and not directing therapy against the entire wart. This difficulty of ascertaining its extent could be overcome with this finger-shaped red light emitting diode device. Red light in the device penetrates the thick palmar skin and dark constitutive skin colour due to its longer wavelength.

  2. Amber light-emitting diode comprising a group III-nitride nanowire active region

    Science.gov (United States)

    Wang, George T.; Li, Qiming; Wierer, Jr., Jonathan J.; Koleske, Daniel

    2014-07-22

    A temperature stable (color and efficiency) III-nitride based amber (585 nm) light-emitting diode is based on a novel hybrid nanowire-planar structure. The arrays of GaN nanowires enable radial InGaN/GaN quantum well LED structures with high indium content and high material quality. The high efficiency and temperature stable direct yellow and red phosphor-free emitters enable high efficiency white LEDs based on the RGYB color-mixing approach.

  3. Advanced Oxidation of Tartrazine and Brilliant Blue with Pulsed Ultraviolet Light Emitting Diodes

    OpenAIRE

    Scott, Robert; Mudimbi, Patrick; Miller, Michael E.; Magnuson, Matthew; Willison, Stuart; Phillips, Rebecca; Harper, Willie F.

    2017-01-01

    This study investigated the effect of ultraviolet light-emitting diodes (UVLEDs) coupled with hydrogen peroxide as an advanced oxidation process (AOP) for the degradation of two test chemicals. Brilliant Blue FCF consistently exhibited greater degradation than tartrazine, with 83% degradation after 300 minutes at the 100% duty cycle compared with only 17% degradation of tartrazine under the same conditions. These differences are attributable to the structural properties of the compounds. Duty...

  4. Design of passive coolers for light-emitting diode lamps using topology optimisation

    DEFF Research Database (Denmark)

    Alexandersen, Joe; Sigmund, Ole; Meyer, Knud Erik

    2018-01-01

    Topology optimised designs for passive cooling of light-emitting diode (LED) lamps are investigated through extensive numerical parameter studies. The designs are optimised for either horizontal or vertical orientations and are compared to a lattice-fin design as well as a simple parameter......, while maintaining low sensitivity to orientation. Furthermore, they exhibit several defining features and provide insight and general guidelines for the design of passive coolers for LED lamps....

  5. Invariable optical properties of phosphor-free white light-emitting diode under electrical stress

    International Nuclear Information System (INIS)

    Hao, Long; Hao, Fang; Sheng-Li, Qi; Li-Wen, Sang; Wen-Yu, Cao; Jian, Yan; Jun-Jing, Deng; Zhi-Jian, Yang; Guo-Yi, Zhang

    2010-01-01

    This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours' current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  6. Surface plasmon enhanced organic light emitting diodes by gold nanoparticles with different sizes

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Chia-Yuan; Chen, Ying-Chung [Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan (China); Chen, Kan-Lin [Department of Electronic Engineering, Fortune Institute of Technology, Kaohsiung, Taiwan (China); Huang, Chien-Jung, E-mail: chien@nuk.edu.tw [Department of Applied Physics, National University of Kaohsiung, Kaohsiung, Taiwan (China)

    2015-11-30

    Highlights: • Different varieties, sizes, and shapes for nanoparticles will generate different surface plasmon resonance effects in the devices. • The red-shift phenomenon for absorption peaks is because of an increasing contribution of higher-order plasmon modes for the larger gold nanoparticles. • The mobility of electrons in the electron-transport layer of organic light-emitting diodes is a few orders of magnitude lower than that of holes in the hole-transport layer of organic light-emitting diodes. - Abstract: The influence of gold nanoparticles (GNPs) with different sizes doped into (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)) (PEDOT:PSS) on the performance of organic light-emitting diodes is investigated in this study. The current efficiency of the device, at a current density of 145 mA/cm, with PEDOT:PSS doped with GNPs of 8 nm is about 1.57 times higher than that of the device with prime PEDOT:PSS because the absorption peak of GNPs is closest to the photoluminescence peak of the emission layer, resulting in maximum surface plasmon resonance effect in the device. In addition, the surface-enhanced Raman scattering spectroscopy also reveals the maximum surface plasmon resonance effect in the device when the mean particle size of GNPs is 8 nm.

  7. Pixel arrangement optimization of two-dimensional light-emitting diode panel for low-crosstalk autostereoscopic light-emitting diode displays

    Science.gov (United States)

    Zeng, Xiang-Yao; Yang, Lan; Zhou, Xiong-Tu; Zhang, Yong-Ai; Chen, En-Guo; Guo, Tai-Liang

    2017-06-01

    We propose an effective and efficient method that reduces the crosstalk level in autostereoscopic light-emitting diode (LED) displays by optimizing the pixel arrangement of the associated two-dimensional (2-D) LED panel. In the proposed method, first a series of parallax barrier patterns, based on predesignated LED packaging units, are designed and simulated by sequentially regulating the width of black stripes on the 2-D LED panel. This design principle removes the black stripes from conventional autostereoscopic LED display pixels for optimal parallax barrier calculation. Furthermore, the mathematical relationship between average crosstalk level and visual flux density is obtained from the simulation. A mathematical fitting method that includes a cubic fitting function is finally applied to achieve proper pixel arrangement in the 2-D LED panel. The simulation results obtained for a dual viewpoint autostereoscopic LED display system indicate that the most suitable value for the width of the black stripes is within the range of 3.17604 to 3.34277 mm, with a light-emitting pixel width of 2 mm. This method can effectively guide the 2-D LED panel's design and result in high performance autostereoscopic three-dimensional LED displays, which will have broad application prospects in the near future.

  8. Color stable white phosphorescent organic light emitting diodes with red emissive electron transport layer

    Energy Technology Data Exchange (ETDEWEB)

    Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin [Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan 336-795 (Korea, Republic of); Eun Lee, Song; Kwan Kim, Young [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of); Hwa Yu, Hyeong; Turak, Ayse [Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4L7 (Canada); Young Kim, Woo, E-mail: wykim@hoseo.edu [Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan 336-795 (Korea, Republic of); Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4L7 (Canada)

    2015-06-28

    We analyzed the performance of multi-emissive white phosphorescent organic light-emitting diodes (PHOLEDs) in relation to various red emitting sites of hole and electron transport layers (HTL and ETL). The shift of the recombination zone producing stable white emission in PHOLEDs was utilized as luminance was increased with red emission in its electron transport layer. Multi-emissive white PHOLEDs including the red light emitting electron transport layer yielded maximum external quantum efficiency of 17.4% with CIE color coordinates (−0.030, +0.001) shifting only from 1000 to 10 000 cd/m{sup 2}. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq){sub 3} as phosphorescent red dopant in electron transport layer.

  9. Colour-tunable light-emitting diodes based on InP/GaP nanostructures

    International Nuclear Information System (INIS)

    Hatami, Fariba; Masselink, W Ted; Harris, James S

    2006-01-01

    We describe a novel colour-tunable light-emitting diode whose operation is based on direct band-gap emission from coupled configurations of InP quantum dots and quantum wells embedded in GaP. The control of the emission colour stems from a marked difference in the current dependence of intensities of two different emission processes. At lower currents, the emission is dominated by the 720 nm luminescence from the quantum dots and appears red; at higher currents, the emission is dominated by the 550 nm quantum-well luminescence and the perceived colour is green. Thus, we are able to tune the colour of such diodes from red to green by means of drive current. A multi-colour pixel can be realized by a single diode, with rapid switching between colour states to provide a range of colour mix

  10. Single cavity Fabry-Perot modulator enhancements and integrated vertically coupled cavity light-emitting diode

    Science.gov (United States)

    Liu, Daxin

    Fabry-Perot modulators with Multi-Quantum Wells (MQWs) cavities have been studied with great interest during recent years. Usually operating as intensity modulators, these devices have very high modulation contrast ratios, can be operated at very high speed, can be easily made into two dimensional arrays and can be integrated with silicon ICs. They are thus very promising for optical interconnects, optical switching and image processing applications. But before these modulators are to be used in real applications, there are several issues that need to be solved, including the parasitic phase modulation, the bandwidth of such modulators and the alignment of modulator operation wavelength with the wavelength of lasers or light emitting diodes. In this work, the phase properties of Fabry-Perot reflection modulators will be discussed first and an experimental method using a modified Michelson interferometer to characterize the exact phase change will be demonstrated. It is demonstrated that the phase of the reflection light beam from a Fabry-Perot modulator is determined not only by the refractive index change inside the cavity but also by the absorption change inside the cavity. With the purpose of expanding the limited bandwidth of such modulator, devices with short passive cavities are designed and fabricated, the results are described and trade-offs between modulation depth and bandwidth will be discussed. In order to solve the problem of alignment and expand the functionality of Fabry-Perot modulators further, vertically coupled cavity devices with each cavity being electrically controlled independently have been developed. Both a coupled cavity modulator and an integrated light emitting diode with a transmission Fabry-Perot modulator are demonstrated; the first device enhances the modulation bandwidth while the second device has the potential of combining the advantage of high speed operation of MQWs modulators with the long lifetime and low cost of light

  11. Optimization of light quality from color mixing light-emitting diode systems for general lighting

    DEFF Research Database (Denmark)

    Thorseth, Anders

    2012-01-01

    are simulated using radiometrically measured single LED spectra. The method uses electrical input powers as input parameters and optimizes the resulting spectral power distribution with regard to color rendering index, correlated color temperature and chromaticity distance. The results indicate Pareto optimal......To address the problem of spectral light quality from color mixing light-emitting diode systems, a method for optimizing the spectral output of multicolor LED system with regards to standardized quality parameters has been developed. The composite spectral power distribution from the LEDs...

  12. Effects of gamma radiation on superluminescent light emitting diodes (SLEDs) for fibre optic gyroscope applications

    Science.gov (United States)

    Occhi, L.; Rezzonico, R.; Vélez, C.; van Uffelen, M.; Berghmans, F.

    2017-11-01

    In this work we present a study on teh Super Luminescent LIght Emitting Diodes (SLEDs) performance under high doses of gamma radiation. We investigate GaAs SLEDs with emission wavelengths around 830 nm. The devices were exposed to ionising radiation at a dose rate of about 4.7 Gy/s, up to a cumulated dose of 10.1 MGy in the CMF facility of the Belgian nuclear research centre SCK•CEN. We measured the device characteristics before adn after irradiation. We show that the SLED performance is only marginally affected.

  13. Charge injection and transport properties of an organic light-emitting diode

    Directory of Open Access Journals (Sweden)

    Peter Juhasz

    2016-01-01

    Full Text Available The charge behavior of organic light emitting diode (OLED is investigated by steady-state current–voltage technique and impedance spectroscopy at various temperatures to obtain activation energies of charge injection and transport processes. Good agreement of activation energies obtained by steady-state and frequency-domain was used to analyze their contributions to the charge injection and transport. We concluded that charge is injected into the OLED device mostly through the interfacial states at low voltage region, whereas the thermionic injection dominates in the high voltage region. This comparison of experimental techniques demonstrates their capabilities of identification of major bottleneck of charge injection and transport.

  14. Optical sectioning microscopes with no moving parts using a micro-stripe array light emitting diode.

    Science.gov (United States)

    Poher, V; Zhang, H X; Kennedy, G T; Griffin, C; Oddos, S; Gu, E; Elson, D S; Girkin, M; French, P M W; Dawson, M D; Neil, M A

    2007-09-03

    We describe an optical sectioning microscopy system with no moving parts based on a micro-structured stripe-array light emitting diode (LED). By projecting arbitrary line or grid patterns onto the object, we are able to implement a variety of optical sectioning microscopy techniques such as grid-projection structured illumination and line scanning confocal microscopy, switching from one imaging technique to another without modifying the microscope setup. The micro-structured LED and driver are detailed and depth discrimination capabilities are measured and calculated.

  15. Improved color purity and efficiency in polyfluorene-based light-emitting diodes

    International Nuclear Information System (INIS)

    Chen Zhenyu; Ma Dongge

    2007-01-01

    Polyfluorene (PF) is a class of typical blue electroluminescent (EL) material, but it exhibits undesired feature in the green spectral region under operation condition. We investigated the spectral properties of different device structures of poly(9,9-dioctylfluorene) (PFO)-based light-emitting diodes, and found that the interaction between cathode and PFO is the main origination of green emission in EL devices. The general method of inserting a buffer layer between the PFO and cathode can decrease the low energy band emission to purify the color and improve the EL performance of devices

  16. High-efficiency white organic light-emitting diodes using thermally activated delayed fluorescence

    International Nuclear Information System (INIS)

    Nishide, Jun-ichi; Hiraga, Yasuhide; Nakanotani, Hajime; Adachi, Chihaya

    2014-01-01

    White organic light-emitting diodes (WOLEDs) have attracted much attention recently, aimed for next-generation lighting sources because of their high potential to realize high electroluminescence efficiency, flexibility, and low-cost manufacture. Here, we demonstrate high-efficiency WOLED using red, green, and blue thermally activated delayed fluorescence materials as emissive dopants to generate white electroluminescence. The WOLED has a maximum external quantum efficiency of over 17% with Commission Internationale de l'Eclairage coordinates of (0.30, 0.38).

  17. Device Fabrication of 60 μm Resonant Cavity Light-Emitting Diode

    Directory of Open Access Journals (Sweden)

    J. J. C. Reyes

    2004-12-01

    Full Text Available An array of 60-mm-diameter resonant cavity light-emitting diodes suited for coupling with fiber opticwere fabricated using standard device fabrication technique. I-V characterization was used to determinethe viability of the device fabricating process. Under forward bias, the turn-on voltage of the devices is1.95–2.45 V with a series resistance of 17–14 kW. Under reverse bias, the devices showed a breakdownvoltage of 35 V.

  18. Single layer graphene electrodes for quantum dot-light emitting diodes

    Science.gov (United States)

    Yan, Long; Zhang, Yu; Zhang, Xiaoyu; Zhao, Jia; Wang, Yu; Zhang, Tieqiang; Jiang, Yongheng; Gao, Wenzhu; Yin, Jingzhi; Zhao, Jun; Yu, William W.

    2015-03-01

    Single layer graphene was employed as the electrode in quantum dot-light emitting diodes (QD-LEDs) to replace indium tin oxide (ITO). The graphene layer demonstrated low surface roughness, good hole injection ability, and proper work function matching with the poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) layer. Together with the hole transport layer and electron transport layer, the fabricated QD-LED showed good current efficiency and power efficiency, which were even higher than an ITO-based similar device under low current density. The result indicates that graphene can be used as anodes to replace ITO in QD-LEDs.

  19. High light extraction efficiency in bulk-GaN based volumetric violet light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    David, Aurelien, E-mail: adavid@soraa.com; Hurni, Christophe A.; Aldaz, Rafael I.; Cich, Michael J.; Ellis, Bryan; Huang, Kevin; Steranka, Frank M.; Krames, Michael R. [Soraa Inc., 6500 Kaiser Dr., Fremont, California 94555 (United States)

    2014-12-08

    We report on the light extraction efficiency of III-Nitride violet light-emitting diodes with a volumetric flip-chip architecture. We introduce an accurate optical model to account for light extraction. We fabricate a series of devices with varying optical configurations and fit their measured performance with our model. We show the importance of second-order optical effects like photon recycling and residual surface roughness to account for data. We conclude that our devices reach an extraction efficiency of 89%.

  20. Evaluation of light-emitting diodes as attractant for sandflies (Diptera: Psychodidae: Phlebotominae) in northeastern Brazil.

    Science.gov (United States)

    Silva, Francinaldo Soares; Brito, Jefferson Mesquita; Costa Neta, Benedita Maria; Lobo, Shelre Emile Pereira Duarte

    2015-09-01

    Hoover Pugedo light traps were modified for use with green and blue-light-emitting diodes to trap phlebotomine sandflies in northeastern Brazil. A total of 2,267 specimens belonging to eight genera and 15 species were sampled. The predominant species were Nyssomyia whitmani(34.41%) and Micropygomyia echinatopharynx(17.25%).The green LED trap prevailed over the blue and control lights; however, no statistically significant difference could be detected among the three light sources. Even without statistical significance, we suggest using LEDs as an attractant for the capture of sandflies because of several advantages over the conventional method with incandescent lamps.

  1. Evaluation of light-emitting diodes as attractant for sandflies (Diptera: Psychodidae: Phlebotominae in northeastern Brazil

    Directory of Open Access Journals (Sweden)

    Francinaldo Soares Silva

    2015-09-01

    Full Text Available Hoover Pugedo light traps were modified for use with green and blue-light-emitting diodes to trap phlebotomine sandflies in northeastern Brazil. A total of 2,267 specimens belonging to eight genera and 15 species were sampled. The predominant species were Nyssomyia whitmani(34.41% and Micropygomyia echinatopharynx(17.25%.The green LED trap prevailed over the blue and control lights; however, no statistically significant difference could be detected among the three light sources. Even without statistical significance, we suggest using LEDs as an attractant for the capture of sandflies because of several advantages over the conventional method with incandescent lamps.

  2. Importance of 'blue' photon levels for lettuce seedlings grown under red-light-emitting diodes

    Science.gov (United States)

    Hoenecke, M. E.; Bula, R. J.; Tibbitts, T. W.

    1992-01-01

    Light-emitting diodes (LEDs) with high-intensity output are being studied as a photosynthetic light source for plants. High-output LEDs have peak emission at approximately 660 nm concentrated in a waveband of +/- 30 nm. Lettuce (Lactuca sativa Grand Rapids') seedlings developed extended hypocotyls and elongated cotyledons when grown under these LEDs as a sole source of irradiance. This extension and elongation was prevented when the red LED radiation was supplemented with more than 15 micromoles m-2 s-1 of 400- to 500-nm photons from blue fluorescent lamps. Blue radiation effects were independent of the photon level of the red radiation.

  3. Enhanced Light Extraction From Triangular GaN-Based Light-Emitting Diodes

    OpenAIRE

    J. Y. Kim; M. K. Kwon; J. P. Kim; S. J. Park

    2007-01-01

    This study investigated the characteristics of a triangular light-emitting diode (LED) and compared it to a standard quadrangular LED. The total radiant flux from the packaged triangular LED increased by 48% and 24% at input currents of 20 and 100 mA, respectively, compared to that of a quadrangular LED which was grown on patterned sapphire substrate. In light far-field beam distribution, the light extraction in the horizontal direction of the LED was much higher than that of the quadrangular...

  4. [Development of a portable high-power light-emitting diode phototherapy system for neonatal jaundice].

    Science.gov (United States)

    Hu, Jiang; Li, Xiaoyuan

    2012-02-01

    Our group have introduced a portable light emitting diode (LED) phototherapy system for treating neonatal jaundice. The device selects blue narrow-band LED as the light source, driven by MAX5035. The light intensity is linearly adjusted as the alteration of the pulse-width modulation signal, controlled by ATmega16L, and the value can be displayed in LCD12864. The device breaks the bonds of traditional phototherapy, it features small size and can provide an intense irradiance-controlled treatment as it's needed.

  5. Light-emitting diode versus laser irradiation phototherapy with lutetium texaphyrin (PCI-0123)

    Science.gov (United States)

    Woodburn, Kathryn W.; Young, Stuart W.; Qing, Fan; Miles, Dale R.; Thiemann, Patricia A.

    1997-05-01

    Lutetium texaphyrin (PCI-0123) is presently in clinical trials for the treatment of neoplasms. An argon-pumped dye laser has mostly been used to generate light for PCI-0123 photoactivation. However, lasers are expensive and produce a limited area of illumination, so the efficacy of light emitting diodes (LEDs) was investigated. An LED array was developed so that the spectral emission matched the far red absorption spectrum of PCI-0123. A preclinical PDT efficacy study comparing the laser and the LED was undertaken using EMT6-bearing animals. The LED and laser light sources were statistically comparable in eradicating the murine mammary sarcomas using PCI-0123 as the photosensitizer.

  6. Irradiance Decay in Fluorescent and Light-emitting Diode-based Phototherapy Devices: A Pilot Study.

    OpenAIRE

    Olusanya, Bolajoko

    2016-01-01

    We set out to determine the rate of decline of irradiance for fluorescent tube (FT) and light-emitting diode (LED) phototherapy devices in resource-limited settings where routine irradiance monitoring is uncommon. Irradiance levels (μW/cm 2 /nm) were measured weekly using BiliBlanket ® II Meter on three FT-based and two LED-based phototherapy devices over a 19 week period. The two LED devices showed stable irradiance levels and did not require any lamp changes. The three FT-based devices show...

  7. Sharply directed emission in microcavity organic light-emitting diodes with a cholesteric liquid crystal film

    Science.gov (United States)

    Jeong, Soon Moon; Takanishi, Yoichi; Ishikawa, Ken; Nishimura, Suzushi; Suzaki, Goroh; Takezoe, Hideo

    2007-05-01

    A flexible microcavity organic light-emitting diode (OLED) was fabricated and the emitting characteristics were examined. A pair of right- and left-handed cholesteric liquid crystal (CLC) films were attached to the microcavity OLED between aluminum (Al) and silver (Ag). Sharply directed spontaneous emission was observed from microcavity OLEDs, in which a typical luminescent material, 8-hydroxyquinoline aluminum (Alq 3), with a broad emission spectrum was used for emitting layer. The introduction of the CLC film improved both the emission bandwidth and directionality, preserving the turn-on voltage and maximum brightness.

  8. Electric-field-induced spin accumulation in polymer light-emitting diodes.

    Science.gov (United States)

    Li, Sheng; George, Thomas F; Sun, Xin; Chen, Liang-Shan

    2007-06-07

    An electric-field-induced spin accumulation phenomenon is presented for electroluminescent conjugated polymers as light-emitting diodes (LEDs). When an electric field is applied along a polymer chain and exceeds a critical value, it quenches the luminescence and dissociates the singlet exciton into two carriers with opposite spin signs. Simultaneously, the field drives these two opposite spin carriers to move in opposite directions, leading to spin accumulation at the two ends of the organic material LED, which can be detected through Kerr rotation microscopy.

  9. Bactericidal effects of 310?nm ultraviolet light-emitting diode irradiation on oral bacteria

    OpenAIRE

    Takada, Ayuko; Matsushita, Kenji; Horioka, Satoru; Furuichi, Yasushi; Sumi, Yasunori

    2017-01-01

    Background Ultraviolet (UV) light is used for phototherapy in dermatology, and UVB light (around 310?nm) is effective for treatment of psoriasis and atopic dermatitis. In addition, it is known that UVC light (around 265?nm) has a bactericidal effect, but little is known about the bactericidal effect of UVB light. In this study, we examined the bactericidal effects of UVB-light emitting diode (LED) irradiation on oral bacteria to explore the possibility of using a 310?nm UVB-LED irradiation de...

  10. Deep Ultraviolet Light Emitting Diode (LED)-Based Sensing of Sulfur Dioxide.

    Science.gov (United States)

    Michel, Anna P M; Kapit, Jason

    2017-05-01

    With the recent development of deep ultraviolet (DUV) light emitting diodes (LEDs) comes the possibility of targeting absorption bands of several gases, including sulfur dioxide (SO 2 ). SO 2 has strong absorption bands in the 300 nm spectral region. The low cost and small size of DUV LEDs, coupled with their spectral coverage, makes them viable sources for new gas sensors. Here, we demonstrate the capability to use absorption spectroscopy with a balanced detection scheme using a 300 nm DUV LED source for SO 2 detection at concentrations ranging from less than 1 ppm to 50 ppm.

  11. Plasma-free nitrogen doping and homojunction light-emitting diodes based on ZnO

    International Nuclear Information System (INIS)

    Zeng, Y J; Ye, Z Z; Lu, Y F; Xu, W Z; Zhu, L P; Huang, J Y; He, H P; Zhao, B H

    2008-01-01

    The authors develop a plasma-free metalorganic chemical vapour deposition method to grow N-doped p-type ZnO films. The incorporation of the N acceptor and the corresponding change in the Fermi level are well confirmed by x-ray photoelectron spectroscopy. Temperature-dependent photoluminescence reveals the acceptor-related emissions, namely, neutral acceptor-bound exciton and probably donor-acceptor pair transition. In addition, typical rectifying I-V characteristics and room-temperature electroluminescence from ZnO homojunction light-emitting diodes are demonstrated

  12. Solution processed phosphorescent white organic light emitting diodes using a small molecule host material

    Energy Technology Data Exchange (ETDEWEB)

    Yook, Kyoung Soo; Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr

    2013-11-15

    Highly efficient phosphorescent white organic light-emitting diodes (PHWOLEDs) were developed using a solution processed 9-(3-(dibenzo[b,d]furan-2-yl)phenyl)-9H-carbazole (CzDBF) host material. Blue and orange phosphorescent emitters were doped into the CzDBF host and balanced blue and orange emission was obtained. High quantum efficiency of 13.2% was achieved in the solution processed PHWOLEDs using the CzDBF host material. Highlights: • Balanced hole and electron densities at optimized composition. • Large change of hole current density according to mixed host composition. • Little change of electron current density according to mixed host composition.

  13. White organic light-emitting diodes with 9, 10-bis (2-naphthyl) anthracene

    International Nuclear Information System (INIS)

    Guan Yunxia; Niu Lianbin

    2009-01-01

    White organic light-emitting diodes were fabricated by 9, 10-bis (2-naphthyl) anthracene (ADN) doped with Rubrene with a structure of ITO/copper phthalocyanine (CuPc) / NPB /ADN: Rubrene /Alq 3 /CsF/Mg:Ag/Ag. Multilayer organic devices using AND and Rubrene as an emitting layer produced white emissions with good chromaticity and luminous efficiency as high as 5.93 cd/A. This performance can be explained by Foerster energy transfer from the blue-emitting host to the orange-emitting dopant.

  14. Irreversible Thermodynamic Bound for the Efficiency of Light-Emitting Diodes

    Science.gov (United States)

    Xue, Jin; Li, Zheng; Ram, Rajeev J.

    2017-07-01

    A thermodynamic model for light-emitting diodes (LEDs) is developed by considering energy and entropy flows in the system. Thermodynamic constraints have previously been considered separately for the reversible process of electroluminescence in LEDs and for light extraction and collimation in other optical systems. By considering both processes in the LED model, an irreversible upper bound for the conversion of electrical energy to optical energy is derived and shown to be higher than unity, but tighter and more realistic than the reversible case. We also model a LED as an endoreversible heat engine where the carrier-transport processes can be directly connected to the elements of a thermodynamic cycle.

  15. Mixed-mode oscillations via canard explosions in light-emitting diodes with optoelectronic feedback

    Science.gov (United States)

    Marino, F.; Ciszak, M.; Abdalah, S. F.; Al-Naimee, K.; Meucci, R.; Arecchi, F. T.

    2011-10-01

    Chaotically spiking attractors in semiconductor lasers with optoelectronic feedback have been recently observed to be the result of canard phenomena in three-dimensional phase space (incomplete homoclinic scenarios). Since light-emitting diodes display the same dynamics and are much more easily controllable, we use one of these systems to complete the attractor analysis demonstrating experimentally and theoretically the occurrence of complex sequences of periodic mixed-mode oscillations. In particular, we investigate the transition between periodic and chaotic mixed-mode states and analyze the effects of the unavoidable experimental noise on these transitions.

  16. Towards developing a tandem of organic solar cell and light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Jai [School of Engineering and IT, B-purple-12, Faculty of EHS, Charles Darwin University, Darwin, NT 0909 (Australia)

    2011-01-15

    It is proposed here to design a tandem of organic solar cell (OSC) and white organic light emitting diode (WOLED) which can generate power in the day time from the sun and provide lighting at night. With the advancement of chemical technology, such device is expected to be very-cost effective and reasonably efficient. A device thus fabricated has the potential of meeting the world's sustainable domestic and commercial power and lighting needs (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes

    OpenAIRE

    Kai Ding; Vitaliy Avrutin; Ümit Özgür; Hadis Morkoç

    2017-01-01

    We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV) light-emitting diodes (LEDs), with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances i...

  18. ZnO-nanowires/PANI inorganic/organic heterostructure light-emitting diode.

    Science.gov (United States)

    He, Ying; Wang, Jun-an; Zhang, Wenfei; Song, Jizhong; Pei, Changlong; Chen, Xiaoban

    2010-11-01

    In this paper, we report a flexible inorganic/organic heterostructure light-emitting diode, in which inorganic ZnO nanowires are the optically active components and organic polyaniline (PANI) is the hole-transporting layer. The fabrication of the hybrid LED is as follows, the ordered single-crystalline ZnO nanowires were uniformly distributed on flexible polyethylene terephthalate (PET)-based indium-tin-oxide-coated substrates by our polymer-assisted growth method, and proper materials were chosen as electrode and carrier. In this construction, an array of ZnO nanowires grown on PET substrate is successfully embedded in a polyaniline thin film. The performance of the hybrid device of organic-inorganic hetero-junction of ITO/(ZnO nanowires-PANI) for LED application in the blue and UV ranges are investigated, and tunable electroluminescence has been demonstrated by contacting the upper tips of ZnO nanowires and the PET substrate. The effect of surface capping with polyvinyl alcohol (PANI) on the photocarrier relaxation of the aqueous chemically grown ZnO nanowires has been investigated. The photoluminescence spectrum shows an enhanced ultraviolet emission and reduced defect-related emission in the capped ZnO NWs compared to bare ZnO. The results of our study may offer a fundamental understanding in the field of inorganic/organic heterostructure light-emitting diode, which may be useful for potential applications of hybrid ZnO nanowires with conductive polymers.

  19. Vertical excitation profile in diffusion injected multi-quantum well light emitting diode structure

    Science.gov (United States)

    Riuttanen, L.; Kivisaari, P.; Svensk, O.; Vasara, T.; Myllys, P.; Oksanen, J.; Suihkonen, S.

    2015-03-01

    Due to their potential to improve the performance of light-emitting diodes (LEDs), novel device structures based on nanowires, surface plasmons, and large-area high-power devices have received increasing amount of interest. These structures are almost exclusively based on the double hetero junction (DHJ) structure, that has remained essentially unchanged for decades. In this work we study a III-nitride diffusion injected light-emitting diode (DILED), in which the active region is located outside the pn-junction and the excitation of the active region is based on bipolar diffusion of charge carriers. This unorthodox approach removes the need of placing the active region in the conventional current path and thus enabling carrier injection in device structures, which would be challenging to realize with the conventional DHJ design. The structure studied in this work is has 3 indium gallium nitride / gallium nitride (InGaN/GaN) quantum wells (QWs) under a GaN pn-junction. The QWs are grown at diferent growth temperatures for obtaining distinctive luminescence peaks. This allows to obtain knowledge on the carrier diffusion in the structure. When the device is biased, all QWs emit light indicating a significant diffusion current into the QW stack.

  20. Emissive ZnO-graphene quantum dots for white-light-emitting diodes

    Science.gov (United States)

    Son, Dong Ick; Kwon, Byoung Wook; Park, Dong Hee; Seo, Won-Seon; Yi, Yeonjin; Angadi, Basavaraj; Lee, Chang-Lyoul; Choi, Won Kook

    2012-07-01

    Hybrid nanostructures combining inorganic materials and graphene are being developed for applications such as fuel cells, batteries, photovoltaics and sensors. However, the absence of a bandgap in graphene has restricted the electrical and optical characteristics of these hybrids, particularly their emissive properties. Here, we use a simple solution method to prepare emissive hybrid quantum dots consisting of a ZnO core wrapped in a shell of single-layer graphene. We then use these quantum dots to make a white-light-emitting diode with a brightness of 798 cd m-2. The strain introduced by curvature opens an electronic bandgap of 250 meV in the graphene, and two additional blue emission peaks are observed in the luminescent spectrum of the quantum dot. Density functional theory calculations reveal that these additional peaks result from a splitting of the lowest unoccupied orbitals of the graphene into three orbitals with distinct energy levels. White emission is achieved by combining the quantum dots with other emissive materials in a multilayer light-emitting diode.

  1. Developing daisy chain receivers for light-emitting diode illumination adopting the digital multiplex-512 protocol.

    Science.gov (United States)

    Um, Keehong; Yoo, Sooyeup

    2013-10-01

    Protocol for digital multiplex with 512 pieces of information is increasingly adopted in the design of illumination systems. In conventional light-emitting diode systems, the receivers are connected in parallel and each of the receiving units receives all the data from the master dimmer console, but each receiving unit operates by recognizing as its own data that which corresponds to the assigned number of the receiver. Because the serial numbers of illumination devices are transmitted in binary code, synchronization is too complicated to be used properly. In order to improve the protocol of illumination control systems, we propose an algorithm of protocol reception to install and manage the system in a simpler and more convenient way. We propose the systems for controlling the light-emitting diode illumination of simplified receiver slaves adopting the digital multiplex-512 protocol where master console and multiple receiver slaves are connected in a daisy chain fashion. The digital multiplex-512 data packet is received according to the sequence order of their locations from the console, without assigning the sequence number of each channel at the receiving device. The purpose of this paper is to design a simple and small-sized controller for the control systems of lamps and lighting adopting the digital multiplex-512 network.

  2. Degradation mechanism of green phosphorescent dye doped polymer light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyong-Jun, E-mail: hkim@kongju.ac.kr [Department of Chemical Engineering, Kongju National University, Cheonan 330-717 (Korea, Republic of); An, Cheng-Guo [School of Materials Science and Engineering, and OLED Center, Seoul National University, Seoul 151-744 (Korea, Republic of); Kim, Jang-Joo, E-mail: jjkim@snu.ac.kr [School of Materials Science and Engineering, and OLED Center, Seoul National University, Seoul 151-744 (Korea, Republic of)

    2013-03-01

    Poly (N-vinylcarbazole) (PVK) based polymer light-emitting diode doped with green phosphorescent dye fac-tris (2-phenylpyridinato)iridium(III) [Ir(ppy){sub 3}] showed two orders of magnitude shorter lifetime than 4,4′-bis (N-carbazolyl)-2,2′-biphenyl : Ir(ppy){sub 3} based device with the same device structure. Rapid degradation of the polymer based device was primarily originated from the instability of the doubly reduced Ir(ppy){sub 3}{sup 2−} in PVK, which was found from the reduction of photoluminescence intensity under electrical stress in hole only and electron–hole flowing devices, and the cyclic voltammetry experiments. Large difference of the lowest unoccupied molecular orbital energy level between PVK and Ir(ppy){sub 3} (∼ 0.5 eV) and low electron mobility of PVK allow electrons transport only through Ir(ppy){sub 3}, so that there is large probability for Ir(ppy){sub 3} to be doubly reduced upon electron injection. - Highlights: ► We explore a degradation mechanism of phosphorescent organic light emitting diode. ► Polyvinylcabazole is unstable and anionic iridium complex degraded upon reduction. ► Assisted electron injection into the emitting layer improves device lifetime.

  3. Efficient charge balance in blue phosphorescent organic light emitting diodes by two types of mixed layer

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hyung Jin; Lee, Ho Won; Lee, Song Eun; Sun, Yong; Hwang, Kyo Min; Yoo, Han Kyu; Lee, Sung Kyu [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of); Kim, Woo Young, E-mail: wykim@hoseo.edu [Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan 336-795 (Korea, Republic of); Kim, Young Kwan, E-mail: kimyk@hongik.ac.kr [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of)

    2015-07-31

    The authors have demonstrated a highly efficient and long-lifetime blue phosphorescent organic light emitting diode (PHOLED) that uses two types of mixed layers. The mixed layers play the role of carrier injection control and exciton generation zone extension. One of the layers is applied for mixing the hole transport layer (HTL) and host material at the HTL side for carrier injection control. The other works as a mixed electron transporting layer (ETL) and host material at the ETL side. The optimized blue PHOLED has been shown to achieve high performance owing to the mixed layer effects. It gave a maximum luminous efficiency of 25.55 cd/A, maximum external quantum efficiency of 13.05%, and lifetime of 7.24 h under 500 cd/m{sup 2}. These results indicate that applying mixed layers is a simple and efficient method that does not require significant structural change. - Highlights: • Highly efficient blue phosphorescent organic light-emitting diode (PHOLEDs) • Hole transporting layer consists with mixed layer for delayed hole injection • The blue PHOLEDs with long lifetime due to suppression of quenching process.

  4. Light emitting diode package element with internal meniscus for bubble free lens placement

    Science.gov (United States)

    Tarsa, Eric; Yuan, Thomas C.; Becerra, Maryanne; Yadev, Praveen

    2010-09-28

    A method for fabricating a light emitting diode (LED) package comprising providing an LED chip and covering at least part of the LED chip with a liquid encapsulant having a radius of curvature. An optical element is provided having a bottom surface with at least a portion having a radius of curvature larger than the liquid encapsulant. The larger radius of curvature portion of the optical element is brought into contact with the liquid encapsulant. The optical element is then moved closer to the LED chip, growing the contact area between said optical element and said liquid encapsulant. The liquid encapsulant is then cured. A light emitting diode comprising a substrate with an LED chip mounted to it. A meniscus ring is on the substrate around the LED chip with the meniscus ring having a meniscus holding feature. An inner encapsulant is provided over the LED chip with the inner encapsulant having a contacting surface on the substrate, with the meniscus holding feature which defines the edge of the contacting surface. An optical element is included having a bottom surface with at least a portion that is concave. The optical element is arranged on the substrate with the concave portion over the LED chip. A contacting encapsulant is included between the inner encapsulant and optical element.

  5. GaN/ZnO nanorod light emitting diodes with different emission spectra.

    Science.gov (United States)

    Ng, A M C; Xi, Y Y; Hsu, Y F; Djurisić, A B; Chan, W K; Gwo, S; Tam, H L; Cheah, K W; Fong, P W K; Lui, H F; Surya, C

    2009-11-04

    Light emitting diodes (LEDs) consisting of p-GaN epitaxial films and n-ZnO nanorods have been fabricated and characterized. The rectifying behavior and emission spectra were strongly dependent on the electronic properties of both GaN film and ZnO nanorods. Light emission under both forward and reverse bias was obtained in all cases, and emission spectra could be changed by annealing the ZnO nanorods. The emission spectra could be further tuned by using a GaN LED epiwafer as a substrate. Both forward and backward diode behavior has been observed and the emission spectra were significantly affected by both the properties of the GaN substrate and the annealing conditions for the ZnO nanorods.

  6. White-light-emitting diode based on a single-layer polymer

    Science.gov (United States)

    Wang, B. Z.; Zhang, X. P.; Liu, H. M.

    2013-05-01

    A broad-band light-emitting diode was achieved in a single-layer device based on pure poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFB). Electromer emission was observed in the red with a center wavelength of about 620 nm in electroluminescence (EL) spectrum. This kind of emission exhibits strong dependence on the thickness of the PFB layer, so that the shape of the EL spectrum may be adjusted through changing the thickness of the active polymer layer to balance between the intrinsic PFB emission in the blue and the electromer emission in the red. Thus, white light emission may be achieved from such a single-layer single-material diode.

  7. Disinfection of Pseudomonas aeruginosa biofilm contaminated tube lumens with ultraviolet C light emitting diodes

    DEFF Research Database (Denmark)

    Bak, Jimmy; Ladefoged, Søren D; Tvede, Michael

    2010-01-01

    Bacterial biofilms on long-term catheters are a major source of infection. Exposure to ultraviolet C (UVC - 265 nm) light was shown in an earlier study to reduce the number of bacteria substantially on ex vivo treated urinary patient catheters. Very large doses (long treatment times) should......, however, be applied to obtain 99.9% disinfection rates. The major reason was that besides cells the mature biofilm contained absorbing and scattering particulates, which made the biofilm opaque. The potential of UVC light emitting diodes (LED) for disinfection purposes in catheter-like tubes contaminated...... with biofilm was investigated. It was shown that UVC light propagation was possible through both Teflon and catheter tubes (silicone). The disinfection efficiency of the diodes was demonstrated on tubes contaminated artificially with a Pseudomonas aeruginosa biofilm. The tubes were connected to a flow system...

  8. Field effect transistor based on light-emitting polymers and its integration with light-emitting diode

    Science.gov (United States)

    Meng, Hsin-Fei; Horng, Sheng-Fu

    2003-03-01

    Field-effect transistors based on poly(2-methoxy-5(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and other light-emitting conjugated polymers are fabricated on glass for easy integration with polymer LED. In the integrated device the polymer LED (pixel) and its driving transistor share the same polymer layer as their active semiconductor, with much simplified structures. Despite of the amorphous nature of the polymer film, the transistors can supply up to one micro Ampere of electric current and can be operated under gate modulation of 1 kHz. The hole mobility along the source/drain channel parallel to the glass substrate is found to be 100-1000 times larger than the perpendicular mobility for transport in the sandwich structures, presumably due to the extended chain conformation in spin-coated films. The molecular weight of the polymers is identified as an important factor for the carrier mobility and characteristics of the transistors.

  9. Thermal transient effect and improved junction temperature measurement method in high-voltage light-emitting diodes

    NARCIS (Netherlands)

    Ye, H.; Chen, X.; Zeijl, H. van; Gielen, A.W.J.; Zhang, G.

    2013-01-01

    The diode forward voltage method with pulsed currents was widely used for monitoring junction temperature (Tj of light-emitting diodes (LEDs). However, a thermal transient effect (TTE) was observed by the pulsed currents and consequent errors were introduced. Thermoelectric physics was conducted to

  10. A theoretical and experimental investigation of light extraction from polymer light-emitting diodes

    Science.gov (United States)

    Ziebarth, Jonathan M.

    Low operating voltages, a wide range of emission wavelengths, and solution processing make polymer light-emitting diodes attractive for high-growth markets including flexible displays, large-area displays, and solid-state lighting. However, the external efficiencies of these devices must be improved in order to compete with existing technologies. Currently, the majority of the light generated inside polymer LEDs remains trapped within the device by total internal reflection. Extracting this trapped light can significantly increase the external efficiency. In this thesis, I use both theoretical tools and experimental results to study light extraction from polymer LEDs. First, I examine the optical properties of the light-emitting polymer. The properties of this layer have important implications for light extraction and need to be measured carefully. I have developed a method to accurately measure the optical properties of a light-emitting polymer by using grating outcoupling. The results show that the polymer layers are anisotropic and dispersive. Using numerical modeling techniques, I predict the emission into air, substrate, polymer/indium tin oxide (ITO) and surface plasmon modes of a polymer light-emitting diode. The results give good insight into the possible efficiency increases that can be expected for various light extraction techniques. In addition, the effects of various optical properties and layer thicknesses on the optical performance of the device are reported. I show how modification of the substrate can be used to focus light into mode types that can be easily extracted. I then report my experimental results for two very different light extraction techniques. First, I demonstrate how Bragg gratings can be used to extract light from waveguide modes in the polymer/indium tin oxide (ITO) layers. With an optimized Bragg grating, I have increased the external power efficiency by 25% at high brightness levels. In addition, I have used substrate

  11. ZnO PN Junctions for Highly-Efficient, Low-Cost Light Emitting Diodes

    International Nuclear Information System (INIS)

    David P. Norton; Stephen Pearton; Fan Ren

    2007-01-01

    By 2015, the US Department of Energy has set as a goal the development of advanced solid state lighting technologies that are more energy efficient, longer lasting, and more cost-effective than current technology. One approach that is most attractive is to utilize light-emitting diode technologies. Although III-V compound semiconductors have been the primary focus in pursuing this objective, ZnO-based materials present some distinct advantages that could yield success in meeting this objective. As with the nitrides, ZnO is a direct bandgap semiconductor whose gap energy (3.2 eV) can be tuned from 3.0 to 4 eV with substitution of Mg for higher bandgap, Cd for lower bandgap. ZnO has an exciton binding energy of 60 meV, which is larger than that for the nitrides, indicating that it should be a superior light emitting semiconductor. Furthermore, ZnO thin films can be deposited at temperatures on the order of 400-600 C, which is significantly lower than that for the nitrides and should lead to lower manufacturing costs. It has also been demonstrated that functional ZnO electronic devices can be fabricated on inexpensive substrates, such as glass. Therefore, for the large-area photonic application of solid state lighting, ZnO holds unique potential. A significant impediment to exploiting ZnO in light-emitting applications has been the absence of effective p-type carrier doping. However, the recent realization of acceptor-doped ZnO material overcomes this impediment, opening the door to ZnO light emitting diode development In this project, the synthesis and properties of ZnO-based pn junctions for light emitting diodes was investigated. The focus was on three issues most pertinent to realizing a ZnO-based solid state lighting technology, namely (1) achieving high p-type carrier concentrations in epitaxial and polycrystalline films, (2) realizing band edge emission from pn homojunctions, and (3) investigating pn heterojunction constructs that should yield efficient light

  12. PEDOT:PSS/Graphene Nanocomposite Hole-Injection Layer in Polymer Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Chun-Hsuan Lin

    2012-01-01

    Full Text Available We report on effects of doping graphene in poly(3,4-ethylenedioxythiophene: poly(styrene sulfonate, PEDOT:PSS, as a PEDOT:PSS/graphene nanocomposite hole injection layer on the performance enhancement of polymer light-emitting diodes (PLEDs. Graphene oxides were first synthesized and then mixed in the PEDOT:PSS solution with specifically various amounts. Graphenes were reduced in the PEDOT:PSS matrix through thermal reduction. PLED devices with hole-injection nanocomposite layer containing particular doping concentration were fabricated, and the influence of doping concentration on device performance was examined by systematically characterizations of various device properties. Through the graphene doping, the resistance in the hole-injection layer and the turn-on voltage could be effectively reduced that benefited the injection and transport of holes and resulted in a higher overall efficiency. The conductivity of the hole-injection layer was monotonically increased with the increase of doping concentration, performance indices from various aspects, however, did not show the same dependence because faster injected holes might alter not only the balance of holes and electrons but also their combination locations in the light-emitting layer. Results show that optimal doping concentration was the case with 0.03 wt% of graphene oxide.

  13. Design of micro, flexible light-emitting diode arrays and fabrication of flexible electrodes

    International Nuclear Information System (INIS)

    Gao, Dan; Wang, Weibiao; Liang, Zhongzhu; Liang, Jingqiu; Qin, Yuxin; Lv, Jinguang

    2016-01-01

    In this study, we design micro, flexible light-emitting diode (LED) array devices. Using theoretical calculations and finite element simulations, we analyze the deformation of the conventional single electrode bar. Through structure optimization, we obtain a three-dimensional (3D), chain-shaped electrode structure, which has a greater bending degree. The optimized electrodes not only have a bigger bend but can also be made to spin. When the supporting body is made of polydimethylsiloxane (PDMS), the maximum bending degree of the micro, flexible LED arrays (4  ×  1 arrays) was approximately 230 µ m; this was obtained using the finite element method. The device (4  ×  1 arrays) can stretch to 15%. This paper describes the fabrication of micro, flexible LED arrays using microelectromechancial (MEMS) technology combined with electroplating technology. Specifically, the isolated grooves are made by dry etching which can isolate and protect the light-emitting units. A combination of MEMS technology and wet etching is used to fabricate the large size spacing. (paper)

  14. Organic Light-Emitting Diodes with a Perylene Interlayer Between the Electrode-Organic Interface

    Science.gov (United States)

    Saikia, Dhrubajyoti; Sarma, Ranjit

    2018-01-01

    The performance of an organic light-emitting diode (OLED) with a vacuum-deposited perylene layer over a fluorine-doped tin oxide (FTO) surface is reported. To investigate the effect of the perylene layer on OLED performance, different thicknesses of perylene are deposited on the FTO surface and their current density-voltages (J-V), luminance-voltages (L-V) and device efficiency characteristics at their respective thickness are studied. Further analysis is carried out with an UV-visible light double-beam spectrophotometer unit, a four-probe resistivity unit and a field emission scanning electron microscope set up to study the optical transmittance, sheet resistance and surface morphology of the bilayer anode film. We used N,N'-bis(3-methyl phenyl)- N,N'(phenyl)-benzidine (TPD) as the hole transport layer, Tris(8-hydroxyquinolinato)aluminum (Alq3) as a light-emitting layer and lithium fluoride as an electron injection layer. The luminance efficiency of an OLED structure with a 9-nm-thick perylene interlayer is increased by 2.08 times that of the single-layer FTO anode OLED. The maximum value of current efficiency is found to be 5.25 cd/A.

  15. A Closed-Loop Smart Control System Driving RGB Light Emitting Diodes

    KAUST Repository

    Al-Saggaf, Abeer

    2015-05-01

    The demand for control systems that are highly capable of driving solid-state optoelectronic devices has significantly increased with the advancement of their efficiency and elevation of their current consumption. This work presents a closed-loop control system that is based on a microcontroller embedded system capable of driving high power optoelectronic devices. In this version of the system, the device in the center of control is a high-power red, green, and blue light emitting diode package. The system features a graphical user interface, namely an Android mobile phone application, in which the user can easily use to vary the light color and intensity of the light-emitting device wirelessly via Bluetooth. Included in the system is a feedback mechanism constituted by a red, green, and blue color sensor through which the user can use to observe feedback color information about the emitted light. The system has many commercial application including in-door lighting and research application including plant agriculture research fields.

  16. Fast Postmoisture Treatment of Luminescent Perovskite Films for Efficient Light-Emitting Diodes.

    Science.gov (United States)

    Wang, Haoran; Li, Xiaomin; Yuan, Mingjian; Yang, Xuyong

    2018-02-23

    Despite the recent advances in the performance of perovskite light-emitting diodes (PeLEDs), the effects of water on the perovskite emissive layer and its electroluminescence are still unclear, even though it has been previously demonstrated that moisture has a significant impact on the quality of perovskite films in the fabrication process of perovskite solar cells and is a prerequisite for obtaining high-performance PeLEDs. Here, the effects of postmoisture on the luminescent CH 3 NH 3 PbBr 3 (MAPbBr 3 ) perovskite films are systematically investigated. It is found that postmoisture treatment can efficiently control the morphology and growth of perovskite films and only a fast moisture exposure at a 60% high relative humidity results in significantly improved crystallinity, carrier lifetime, and photoluminescence quantum yield of perovskite films. With the optimized moisture-treated perovskite films, a high-performance PeLED is fabricated, exhibiting a maximum current efficiency of 20.4 cd A -1 , which is an almost 20-fold enhancement when compared with perovskite films without moisture treatment. The results provide valuable insights into the moisture-assisted growth of luminescent perovskite films and will aid in the development of high-performance perovskite light-emitting devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Highly stable cesium lead iodide perovskite quantum dot light-emitting diodes

    Science.gov (United States)

    Zou, Chen; Huang, Chun-Ying; Sanehira, Erin M.; Luther, Joseph M.; Lin, Lih Y.

    2017-11-01

    Recently, all-inorganic perovskites such as CsPbBr3 and CsPbI3, have emerged as promising materials for light-emitting applications. While encouraging performance has been demonstrated, the stability issue of the red-emitting CsPbI3 is still a major concern due to its small tolerance factor. Here we report a highly stable CsPbI3 quantum dot (QD) light-emitting diode (LED) with red emission fabricated using an improved purification approach. The device achieved decent external quantum efficiency (EQE) of 0.21% at a bias of 6 V and outstanding operational stability, with a L 70 lifetime (EL intensity decreases to 70% of starting value) of 16 h and 1.5 h under a constant driving voltage of 5 V and 6 V (maximum EQE operation) respectively. Furthermore, the device can work under a higher voltage of 7 V (maximum luminance operation) and retain 50% of its initial EL intensity after 500 s. These findings demonstrate the promise of CsPbI3 QDs for stable red LEDs, and suggest the feasibility for electrically pumped perovskite lasers with further device optimizations.

  18. Luminescence and the light emitting diode the basics and technology of leds and the luminescence properties of the materials

    CERN Document Server

    Williams, E W; Pamplin, BR

    2013-01-01

    Luminescence and the Light Emitting Diode: The Basics and Technology of LEDS and the Luminescence Properties of the Materials focuses on the basic physics and technology of light emitting diodes (LEDS) and pn junction lasers as well as their luminescence properties. Optical processes in semiconductors and the useful devices which can be made are discussed. Comprised of 10 chapters, this book begins with an introduction to the crystal structure and growth, as well as the optical and electrical properties of LED materials. The detailed fabrication of the LED is then considered, along with the lu

  19. Highly efficient greenish-blue platinum-based phosphorescent organic light-emitting diodes on a high triplet energy platform

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Y. L., E-mail: yilu.chang@mail.utoronto.ca; Gong, S., E-mail: sgong@chem.utoronto.ca; White, R.; Lu, Z. H., E-mail: zhenghong.lu@utoronto.ca [Department of Materials Science and Engineering, University of Toronto, 184 College St., Toronto, Ontario M5S 3E4 (Canada); Wang, X.; Wang, S., E-mail: wangs@chem.queensu.ca [Department of Chemistry, Queen' s University, 90 Bader Lane, Kingston, Ontario K7L 3N6 (Canada); Yang, C. [Department of Chemistry, Wuhan University, Wuhan 430072 (China)

    2014-04-28

    We have demonstrated high-efficiency greenish-blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a dimesitylboryl-functionalized C^N chelate Pt(II) phosphor, Pt(m-Bptrz)(t-Bu-pytrz-Me). Using a high triplet energy platform and optimized double emissive zone device architecture results in greenish-blue PHOLEDs that exhibit an external quantum efficiency of 24.0% and a power efficiency of 55.8 lm/W. This record high performance is comparable with that of the state-of-the-art Ir-based sky-blue organic light-emitting diodes.

  20. Enhancement of mosquito trapping efficiency by using pulse width modulated light emitting diodes

    Science.gov (United States)

    Liu, Yu-Nan; Liu, Yu-Jen; Chen, Yi-Chian; Ma, Hsin-Yi; Lee, Hsiao-Yi

    2017-01-01

    In this study, a light-driving bug zapper is presented for well controlling the diseases brought by insects, such as mosquitoes. In order to have the device efficient to trap the insect pests in off-grid areas, pulse width modulated light emitting diodes (PWM-LED) combined with a solar power module are proposed and implemented. With specific PWM electric signals to drive the LED, it is found that no matter what the ability of catching insects or the consumed power efficiency can be enhanced thus. It is demonstrated that 40% of the UV LED consumed power and 25.9% of the total load power consumption can be saved, and the trapped mosquitoes are about 250% increased when the PWM method is applied in the bug zapper experiments.

  1. Tunneling Injection and Exciton Diffusion of White Organic Light-Emitting Diodes with Composed Buffer Layers

    Science.gov (United States)

    Yang, Su-Hua; Wu, Jian-Ping; Huang, Tao-Liang; Chung, Bin-Fong

    2018-02-01

    Four configurations of buffer layers were inserted into the structure of a white organic light emitting diode, and their impacts on the hole tunneling-injection and exciton diffusion processes were investigated. The insertion of a single buffer layer of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) resulted in a balanced carrier concentration and excellent color stability with insignificant chromaticity coordinate variations of Δ x diffusion of excitons were confirmed by the preparation of a dual buffer layer of CBP:tris-(phenylpyridine)-iridine (Ir(ppy)3)/BCP. A maximum current efficiency of 12.61 cd/A with a luminance of 13,850 cd/m2 was obtained at 8 V when a device with a dual-buffer layer of CBP:6 wt.% Ir(ppy)3/BCP was prepared.

  2. On the Hole Injection for III-Nitride Based Deep Ultraviolet Light-Emitting Diodes.

    Science.gov (United States)

    Li, Luping; Zhang, Yonghui; Xu, Shu; Bi, Wengang; Zhang, Zi-Hui; Kuo, Hao-Chung

    2017-10-24

    The hole injection is one of the bottlenecks that strongly hinder the quantum efficiency and the optical power for deep ultraviolet light-emitting diodes (DUV LEDs) with the emission wavelength smaller than 360 nm. The hole injection efficiency for DUV LEDs is co-affected by the p-type ohmic contact, the p-type hole injection layer, the p-type electron blocking layer and the multiple quantum wells. In this report, we review a large diversity of advances that are currently adopted to increase the hole injection efficiency for DUV LEDs. Moreover, by disclosing the underlying device physics, the design strategies that we can follow have also been suggested to improve the hole injection for DUV LEDs.

  3. The effects of light-emitting diode lighting on greenhouse plant growth and quality

    Directory of Open Access Journals (Sweden)

    Margit Olle

    2013-06-01

    Full Text Available The aim of this study is to present the light emitting diode (LED technology for greenhouse plant lighting and to give an overview about LED light effects on photosynthetic indices, growth, yield and nutritional value in green vegetables and tomato, cucumber, sweet pepper transplants. The sole LED lighting, applied in closed growth chambers, as well as combinations of LED wavelengths with conventional light sources, fluorescent and high pressure sodium lamp light, and natural illumination in greenhouses are overviewed. Red and blue light are basal in the lighting spectra for green vegetables and tomato, cucumber, and pepper transplants; far red light, important for photomorphogenetic processes in plants also results in growth promotion. However, theoretically unprofitable spectral parts as green or yellow also have significant physiological effects on investigated plants. Presented results disclose the variability of light spectral effects on different plant species and different physiological indices.

  4. Using Pre-TMIn Treatment to Improve the Optical Properties of Green Light Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Bing Xu

    2014-01-01

    Full Text Available We investigated the effects of pre-TMIn treatment on the optical properties of green light emitting diodes (LEDs. Although pre-TMIn treatment did not affect the epitaxial structure of quantum wells, it significantly improved the quality of the surface morphology relative to that of the untreated sample. Indium cluster can be seen by high-resolution transmission electron microscopy (HR-TEM, which is the explanation for the red-shift of photoluminescence (PL. Time-resolved photoluminescence measurements indicated that the sample prepared with pre-TMIn treatment had a shorter radiative decay time. As a result, the light output power of the treated green LED was higher than that of the conventional untreated one. Thus, pre-TMIn treatment appears to be a simple and efficient means of improving the performance of green LEDs.

  5. Indwelling Stent Embedded with Light-Emitting Diodes for Photodynamic Therapy of Malignant Biliary Obstruction

    Energy Technology Data Exchange (ETDEWEB)

    Baran, Timothy M., E-mail: timothy.baran@rochester.edu [University of Rochester Medical Center, Department of Imaging Sciences (United States); Mironov, Oleg, E-mail: oleg.mironov@uhn.ca [University Health Network, The Joint Department of Medical Imaging (Canada); Sharma, Ashwani K., E-mail: Ashwani-Sharma@URMC.Rochester.edu; Foster, Thomas H., E-mail: thomas.foster@rochester.edu [University of Rochester Medical Center, Department of Imaging Sciences (United States)

    2016-06-15

    PurposeWe describe the design and preliminary characterization of a stent incorporating light-emitting diodes (LEDs) for photodynamic therapy (PDT) of malignant biliary obstruction.MethodsA prototype was constructed with red (640 nm) LEDs embedded in a 14.5 French polyurethane tube. The device was evaluated for optical power and subjected to physical and electrical tests. PDT-induced reactive oxygen species were imaged in a gel phantom.ResultsThe stent functioned at a 2.5-cm bend radius and illuminated for 6 months in saline. No stray currents were detected, and it was cool after 30 minutes of operation. Optical power of 5–15 mW is applicable to PDT. Imaging of a reactive oxygen indicator showed LED-stent activation of photosensitizer.ConclusionsThe results motivate biological testing and design optimization.

  6. Numerical Investigation on Micro-Cavity Effect of Top-Emitting Organic Light Emitting Diode.

    Science.gov (United States)

    Lee, Hyeongi; Hwang, Youngwook; Won, Taeyoung

    2015-02-01

    In this paper, we report our numerical investigation on the top-emitting OLED (Organic Light Emitting Diodes) with micro-cavity. Our numerical model includes an ensemble of radiating dipole antennas for light emission as well as Poisson Equation for carrier injection and transportation. We formulated a set of differential equations by the Finite Element Method. Our simulation revealed that the recombination rate is affected by the thickness of each layer comprising the OLED structure and the amount of emission is determined by the total thickness of the OLED structure due to micro-cavity effect which is observed in between the total reflection layer and the half reflection layer. Our numerical solver enables us to optimize the OLED structure and thereby improve the external quantum efficiency.

  7. Transparent conductive graphene electrode in GaN-based ultra-violet light emitting diodes.

    Science.gov (United States)

    Kim, Byung-Jae; Mastro, Michael A; Hite, Jennifer; Eddy, Charles R; Kim, Jihyun

    2010-10-25

    We report a graphene-based transparent conductive electrode for use in ultraviolet (UV) GaN light emitting diodes (LEDs). A few-layer graphene (FLG) layer was mechanically deposited. UV light at a peak wavelength of 368 nm was successfully emitted by the FLG layer as transparent contact to p-GaN. The emission of UV light through the thin graphene layer was brighter than through the thick graphene layer. The thickness of the graphene layer was characterized by micro-Raman spectroscopy. Our results indicate that this novel graphene-based transparent conductive electrode holds great promise for use in UV optoelectronics for which conventional ITO is less transparent than graphene.

  8. Superluminescent light emitting diodes on naturally survived InGaN/GaN lateral nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Banerjee, D.; Sankaranarayanan, S.; Khachariya, D.; Nadar, M. B.; Ganguly, S.; Saha, D., E-mail: dipankarsaha@iitb.ac.in [Applied Quantum Mechanics Laboratory, Centre of Excellence in Nanoelectronics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India)

    2016-07-18

    We demonstrate a method for nanowire formation by natural selection during wet anisotropic chemical etching in boiling phosphoric acid. Nanowires of sub-10 nm lateral dimensions and lengths of 700 nm or more are naturally formed during the wet etching due to the convergence of the nearby crystallographic hexagonal etch pits. These nanowires are site controlled when formed in augmentation with dry etching. Temperature and power dependent photoluminescence characterizations confirm excitonic transitions up to room temperature. The exciton confinement is enhanced by using two-dimensional confinement whereby enforcing greater overlap of the electron-hole wave-functions. The surviving nanowires have less defects and a small temperature variation of the output electroluminescent light. We have observed superluminescent behaviour of the light emitting diodes formed on these nanowires. There is no observable efficiency roll off for current densities up to 400 A/cm{sup 2}.

  9. Polymer Light-Emitting Diode Prepared by Floating-Off Film-Transfer Technique

    KAUST Repository

    Park, Jihoon

    2015-12-22

    © 2015 Copyright Taylor & Francis Group, LLC. Floating-off film-transfer technique was used for the formation of semiconducting polymer multi-layers and the effect on the performance of polymer light-emitting diode (PLED) was studied. This method made it possible to avoid the solvent compatibility problem that was typically encountered in successive coating of polymeric multilayer by solution processing. F8BT and MEH-PPV were used for electron transporting layer (ETL) and for emissive layer, respectively. Current-voltage-luminance characteristics and luminescence efficiency results showed that the insertion of ETL by floating-off film-transfer technique followed by proper heat treatment resulted in a significant improvement in PLED operation due to its electron-transporting and hole-blocking abilities.

  10. White organic light-emitting diodes with 4 nm metal electrode

    International Nuclear Information System (INIS)

    Lenk, Simone; Schwab, Tobias; Schubert, Sylvio; Müller-Meskamp, Lars; Leo, Karl; Reineke, Sebastian; Gather, Malte C.

    2015-01-01

    We investigate metal layers with a thickness of only a few nanometers as anode replacement for indium tin oxide (ITO) in white organic light-emitting diodes (OLEDs). The ultrathin metal electrodes prove to be an excellent alternative that can, with regard to the angular dependence and efficiency of the OLED devices, outperform the ITO reference. Furthermore, unlike ITO, the thin composite metal electrodes are readily compatible with demanding architectures (e.g., top-emission or transparent OLEDs, device unit stacking, etc.) and flexible substrates. Here, we compare the sheet resistance of both types of electrodes on polyethylene terephthalate for different bending radii. The electrical performance of ITO breaks down at a radius of 10 mm, while the metal electrode remains intact even at radii smaller than 1 mm

  11. Organic light-emitting diodes using novel embedded al gird transparent electrodes

    Science.gov (United States)

    Peng, Cuiyun; Chen, Changbo; Guo, Kunping; Tian, Zhenghao; Zhu, Wenqing; Xu, Tao; Wei, Bin

    2017-03-01

    This work demonstrates a novel transparent electrode using embedded Al grids fabricated by a simple and cost-effective approach using photolithography and wet etching. The optical and electrical properties of Al grids versus grid geometry have been systematically investigated, it was found that Al grids exhibited a low sheet resistance of 70 Ω □-1 and a light transmission of 69% at 550 nm with advantages in terms of processing conditions and material cost as well as potential to large scale fabrication. Indium Tin Oxide-free green organic light-emitting diodes (OLED) based on Al grids transparent electrodes was demonstrated, yielding a power efficiency >15 lm W-1 and current efficiency >39 cd A-1 at a brightness of 2396 cd m-2. Furthermore, a reduced efficiency roll-off and higher brightness have been achieved compared with ITO-base device.

  12. Study on thermal and structural stability of high power light-emitting diode lighting system.

    Science.gov (United States)

    Kwag, Dong-Soon; So, Soo-Hyun; Baek, Seung-Myeong

    2014-05-01

    In this paper, we have been analyzed the thermal-fluid flow and structural stress of high power Light-emitting diode (LED) lighting system for outdoor lighting. Thermal and Structural performances of LED lighting systems were designed using computer aided engineering (CAE) and after securing their structural and thermal safety, simulated in order to develop 400 W high-efficiency LED floodlight. The temperature of LED was shown to rise up to 136 degrees C. This means that the cooling system should be improved. Maximum strain was detected in the glass, yet they appeared largely safe. It is important for the design to focus on the cooling fin. Regarding the lifespan of LED, it is necessary to have a plan for minimizing errors when testing designs for optimizing air-cooling structures. Which measured the lifetime of the lighting equipment has passed.

  13. Sound intensity probe for ultrasonic field in water using light-emitting diodes and piezoelectric elements

    Science.gov (United States)

    Zeng, Xi; Mizuno, Yosuke; Nakamura, Kentaro

    2017-12-01

    The sound intensity vector provides useful information on the state of an ultrasonic field in water, since sound intensity is a vector quantity expressing the direction and magnitude of the sound field. In the previous studies on sound intensity measurement in water, conventional piezoelectric sensors and metal cables were used, and the transmission distance was limited. A new configuration of a sound intensity probe suitable for ultrasonic measurement in water is proposed and constructed for trial in this study. The probe consists of light-emitting diodes and piezoelectric elements, and the output signals are transmitted through fiber optic cables as intensity-modulated light. Sound intensity measurements of a 26 kHz ultrasonic field in water are demonstrated. The difference in the intensity vector state between the water tank with and without sound-absorbing material on its walls was successfully observed.

  14. Emergence of White Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence

    Directory of Open Access Journals (Sweden)

    Peng Xiao

    2018-02-01

    Full Text Available Recently, thermally activated delayed fluorescence (TADF organic light-emitting diodes (OLEDs have attracted both academic and industrial interest due to their extraordinary characteristics, such as high efficiency, low driving voltage, bright luminance, lower power consumption and potentially long lifetime. In this invited review, the fundamental concepts of TADF have been firstly introduced. Then, main approaches to realize WOLEDs based on TADF have been summarized. More specifically, the recent development of WOLEDs based on all TADF emitters, WOLEDs based on TADF and conventional fluorescence emitters, hybrid WOLEDs based on blue TADF and phosphorescence emitters and WOLEDs based on TADF exciplex host and phosphorescence dopants is highlighted. In particular, design strategies, device structures, working mechanisms and electroluminescent processes of the representative WOLEDs based on TADF are reviewed. Finally, challenges and opportunities for further enhancement of the performance of WOLEDs based on TADF are presented.

  15. Enhancement and Quenching of Fluorescence by Silver Nanoparticles in Organic Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Ying-Chung Chen

    2013-01-01

    Full Text Available The influence of silver nanoparticles (SNPs on the performance of organic light-emitting diodes (OLEDs is investigated in this study. The SNPs are introduced between the electron-transport layers by means of thermal evaporation. SNPs are found to have the surface plasmon resonance at wavelength 525 nm when the mean particle size of SNPs is 34 nm. The optimized OLED, in terms of the spacing between the emitting layer and SNPs, is found to have the maximum luminance 2.4 times higher than that in the OLED without SNPs. The energy transfer between exciton and surface plasmons with the different spacing distances has been studied.

  16. White organic light-emitting diodes with 4 nm metal electrode

    Energy Technology Data Exchange (ETDEWEB)

    Lenk, Simone; Schwab, Tobias; Schubert, Sylvio; Müller-Meskamp, Lars; Leo, Karl; Reineke, Sebastian [Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Straße 1, 01069 Dresden (Germany); Gather, Malte C. [Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Straße 1, 01069 Dresden (Germany); Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom)

    2015-10-19

    We investigate metal layers with a thickness of only a few nanometers as anode replacement for indium tin oxide (ITO) in white organic light-emitting diodes (OLEDs). The ultrathin metal electrodes prove to be an excellent alternative that can, with regard to the angular dependence and efficiency of the OLED devices, outperform the ITO reference. Furthermore, unlike ITO, the thin composite metal electrodes are readily compatible with demanding architectures (e.g., top-emission or transparent OLEDs, device unit stacking, etc.) and flexible substrates. Here, we compare the sheet resistance of both types of electrodes on polyethylene terephthalate for different bending radii. The electrical performance of ITO breaks down at a radius of 10 mm, while the metal electrode remains intact even at radii smaller than 1 mm.

  17. Cold welding of organic light emitting diode: Interfacial and contact models

    Directory of Open Access Journals (Sweden)

    J. Asare

    2016-06-01

    Full Text Available This paper presents the results of an analytical and computational study of the contacts and interfacial fracture associated with the cold welding of Organic Light Emitting diodes (OLEDs. The effects of impurities (within the possible interfaces are explored for contacts and interfacial fracture between layers that are relevant to model OLEDs. The models are used to study the effects of adhesion, pressure, thin film layer thickness and dust particle modulus (between the contacting surfaces on contact profiles around impurities between cold-welded thin films. The lift-off stage of thin films (during cold welding is then modeled as an interfacial fracture process. A combination of adhesion and interfacial fracture theories is used to provide new insights for the design of improved contact and interfacial separation during cold welding. The implications of the results are discussed for the design and fabrication of cold welded OLED structures.

  18. Organic semiconductor heterojunctions and its application in organic light-emitting diodes

    CERN Document Server

    Ma, Dongge

    2017-01-01

    This book systematically introduces the most important aspects of organic semiconductor heterojunctions, including the basic concepts and electrical properties. It comprehensively discusses the application of organic semiconductor heterojunctions as charge injectors and charge generation layers in organic light-emitting diodes (OLEDs). Semiconductor heterojunctions are the basis for constructing high-performance optoelectronic devices. In recent decades, organic semiconductors have been increasingly used to fabricate heterojunction devices, especially in OLEDs, and the subject has attracted a great deal of attention and evoked many new phenomena and interpretations in the field. This important application is based on the low dielectric constant of organic semiconductors and the weak non-covalent electronic interactions between them, which means that they easily form accumulation heterojunctions. As we know, the accumulation-type space charge region is highly conductive, which is an important property for high...

  19. Compact quantum random number generator based on superluminescent light-emitting diodes

    Science.gov (United States)

    Wei, Shihai; Yang, Jie; Fan, Fan; Huang, Wei; Li, Dashuang; Xu, Bingjie

    2017-12-01

    By measuring the amplified spontaneous emission (ASE) noise of the superluminescent light emitting diodes, we propose and realize a quantum random number generator (QRNG) featured with practicability. In the QRNG, after the detection and amplification of the ASE noise, the data acquisition and randomness extraction which is integrated in a field programmable gate array (FPGA) are both implemented in real-time, and the final random bit sequences are delivered to a host computer with a real-time generation rate of 1.2 Gbps. Further, to achieve compactness, all the components of the QRNG are integrated on three independent printed circuit boards with a compact design, and the QRNG is packed in a small enclosure sized 140 mm × 120 mm × 25 mm. The final random bit sequences can pass all the NIST-STS and DIEHARD tests.

  20. Fabrication and characterization of 395 nm ultraviolet GaN light-emitting diodes

    Science.gov (United States)

    Lin, Min-Pang; Chen, Chien-Ju; Shan, Li-Wei; Wu, Meng-Chyi

    2017-09-01

    In this article, we demonstrated the fabrication and characterization of 395 nm GaN ultraviolet light-emitting diodes grown on patterned sapphire substrates. The current confining aperture is designed as 45, 55, 65, 75 and 85 μm. The indium tin oxide (ITO) was used as a current spreading layer. Use the metals of nickel and gold to form ohmic contact with P-AlGaN layer prior to dry etching. The 45-μm-diameter LED exhibits a 3-dB modulation bandwidth of 134 MHz at 50 mA and a light output power density of 1.2 mW (78 W/cm2) at 30 mA. In addition, the 3-dB frequency bandwidth is proportional to the square root of the injected current density.

  1. Charge generation layers for solution processed tandem organic light emitting diodes with regular device architecture.

    Science.gov (United States)

    Höfle, Stefan; Bernhard, Christoph; Bruns, Michael; Kübel, Christian; Scherer, Torsten; Lemmer, Uli; Colsmann, Alexander

    2015-04-22

    Tandem organic light emitting diodes (OLEDs) utilizing fluorescent polymers in both sub-OLEDs and a regular device architecture were fabricated from solution, and their structure and performance characterized. The charge carrier generation layer comprised a zinc oxide layer, modified by a polyethylenimine interface dipole, for electron injection and either MoO3, WO3, or VOx for hole injection into the adjacent sub-OLEDs. ToF-SIMS investigations and STEM-EDX mapping verified the distinct functional layers throughout the layer stack. At a given device current density, the current efficiencies of both sub-OLEDs add up to a maximum of 25 cd/A, indicating a properly working tandem OLED.

  2. Disentangling degradation and auto-recovery of luminescence in Alq3 based organic light emitting diodes

    International Nuclear Information System (INIS)

    Rao, K. Sudheendra; Mohapatra, Y.N.

    2014-01-01

    Organic semiconductor devices and materials have matured sufficiently to be limited by intrinsic degradation processes which are as yet not understood well. We use high quality Alq 3 based organic light emitting diodes to study the rate processes involved in degradation due to electrical stressing and its auto-recovery. The method involves interspersing degradation due to electrical pulsing with variable relaxation windows to monitor time evolution of loss and recovery of luminescence. The corresponding rate processes for permanent and auto-recoverable degradation is discussed on the basis of charging and discharging of traps, and a phenomenological model based on metastability in configuration-coordinate diagram is proposed. -- Highlights: • Luminescence degradation of high quality Alq 3 based OLED device. • Auto-recovery of luminance as function of relaxation time is exponential. • Individual rates of permanent, recoverable and relaxation process measured. • A Phenomenological model based on metastable state in configuration-coordinate

  3. Charge carrier tunneling in the light-emitting diodes of poly (p-phenylene) thin films

    CERN Document Server

    Jeon, J W; Lee, C H; Song, W J; Seoul, C

    2000-01-01

    We have studied the temperature dependence of the current-voltage (I-V) and the electroluminescence-voltage (EL-V) characteristics in the blue light-emitting diodes of vacuum-deposited poly (p-phenylene) (PPP) thin films in the temperature range between 14 and 290 K. The onset of the EL occurs at an electric field of about 7x10 sup 7 V/m, independent of the thickness of the PPP layer. The I-V and EL-V dependences show very weak temperature dependences and fit very well with the Fowler-Nordheim tunneling formula. The results suggest that charge carrier injection is a tunneling process through an energy barrier of about 0.6 approx 0.8 eV in indium tin oxide (ITO)/PPP/Al devices.

  4. Transient electroluminescence in the light-emitting diodes of poly (p-phenylene) thin films

    CERN Document Server

    Kang, G W; Song, W J; Seoul, C

    2000-01-01

    We have studied the temporal response of the electroluminescence (EL) emission in the light-emitting diodes fabricated with a vacuum-deposited poly (p-phenylene) (PPP) thin film as an emissive layer sandwiched between indium-tin-oxide (ITO) and Al electrodes. Upon application of a rectangular driving voltage with a forward bias, we observed a time delay between the onset of the bias voltage pulse and the EL emission. The EL time delay results from the charge carrier transport towards the recombination zone. Since the hole mobility is much larger than the electron mobility in PPP, the EL delay time is the transit time for holes in PPP thin films. The hole mobility is estimated to be approx 1x10 sup - sup 5 cm sup 2 /Vs in vacuum-deposited PPP films.

  5. Transient electroluminescence in the light-emitting diodes of poly (p-phenylene) thin films

    International Nuclear Information System (INIS)

    Kang, G. W.; Lee, C. H.; Song, W. J.; Seoul, C.

    2000-01-01

    We have studied the temporal response of the electroluminescence (EL) emission in the light-emitting diodes fabricated with a vacuum-deposited poly (p-phenylene) (PPP) thin film as an emissive layer sandwiched between indium-tin-oxide (ITO) and Al electrodes. Upon application of a rectangular driving voltage with a forward bias, we observed a time delay between the onset of the bias voltage pulse and the EL emission. The EL time delay results from the charge carrier transport towards the recombination zone. Since the hole mobility is much larger than the electron mobility in PPP, the EL delay time is the transit time for holes in PPP thin films. The hole mobility is estimated to be ∼1x10 -5 cm 2 /Vs in vacuum-deposited PPP films

  6. Charge carrier tunneling in the light-emitting diodes of poly (p-phenylene) thin films

    International Nuclear Information System (INIS)

    Jeon, J. W.; Kang, G. W.; Lee, C. H.; Song, W. J.; Seoul, C.

    2000-01-01

    We have studied the temperature dependence of the current-voltage (I-V) and the electroluminescence-voltage (EL-V) characteristics in the blue light-emitting diodes of vacuum-deposited poly (p-phenylene) (PPP) thin films in the temperature range between 14 and 290 K. The onset of the EL occurs at an electric field of about 7x10 7 V/m, independent of the thickness of the PPP layer. The I-V and EL-V dependences show very weak temperature dependences and fit very well with the Fowler-Nordheim tunneling formula. The results suggest that charge carrier injection is a tunneling process through an energy barrier of about 0.6∼0.8 eV in indium tin oxide (ITO)/PPP/Al devices

  7. High-power light-emitting diode based facility for plant cultivation

    Energy Technology Data Exchange (ETDEWEB)

    Tamulaitis, G [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9-III, LT-10222 Vilnius (Lithuania); Duchovskis, P [Lithuanian Institute of Horticulture, Babtai, LT-54333 Kaunas District (Lithuania); Bliznikas, Z [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9-III, LT-10222 Vilnius (Lithuania); Breive, K [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9-III, LT-10222 Vilnius (Lithuania); Ulinskaite, R [Lithuanian Institute of Horticulture, Babtai, LT-54333 Kaunas District (Lithuania); Brazaityte, A [Lithuanian Institute of Horticulture, Babtai, LT-54333 Kaunas District (Lithuania); Novickovas, A [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9-III, LT-10222 Vilnius (Lithuania); Zukauskas, A [Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9-III, LT-10222 Vilnius (Lithuania)

    2005-09-07

    Based on perspectives of the development of semiconductor materials systems for high-power light-emitting diodes (LEDs), an illumination facility for greenhouse plant cultivation was designed with the dominating 640 nm photosynthetically active component delivered by AlGaInP LEDs and supplementary components from AlGaN (photothropic action, 455 nm) and AlGaAs (photosynthetic 660 nm and photomorphogenetic 735 nm) LEDs. Photosynthesis intensity, photosynthetic productivity and growth morphology as well as chlorophyll and phytohormone concentrations were investigated in radish and lettuce grown in phytotron chambers under the LED-based illuminators and under high-pressure sodium (HPS) lamps with an equivalent photon flux density. Advantages of the high-power LED-based illuminators over conventional HPS lamps, applicability of AlGaInP LEDs for photosynthesis and control of plant growth by circadian manipulation of a relatively weak far-red component were demonstrated.

  8. Monolithic integration of nitride light emitting diodes and photodetectors for bi-directional optical communication.

    Science.gov (United States)

    Jiang, Zhenyu; Atalla, Mahmoud R M; You, Guanjun; Wang, Li; Li, Xiaoyun; Liu, Jie; Elahi, Asim M; Wei, Lai; Xu, Jian

    2014-10-01

    Design and fabrication of monolithically integrated III-nitride visible light-emitting-diodes (LEDs) and ultraviolet Schottky barrier-photodetectors (SB-PDs) have been proposed and demonstrated. Responsivity up to 0.2  AW(-1) at 365 nm for GaN SB-PDs has been achieved. It is shown that those UV SB-PDs were capable of sensitive UV light detection down to 7.16×10(-4)  W/cm2 at 365 nm, whereas simultaneous operation of on-chip blue LEDs has produced negligible crosstalk at practical illumination brightness. Monolithically integrated LEDs and SB-PDs can function as transmitters to emit visible light signals, and as receivers to analyze incoming UV signals, respectively; this offers the potential of using such devices for bi-directional optical wireless communication applications.

  9. Gravure printed PEDOT:PSS as anode for flexible ITO-free organic light emitting diodes

    Directory of Open Access Journals (Sweden)

    M. Montanino

    2017-06-01

    Full Text Available Roll-to-roll gravure printing is considered as potential leading manufacturing technology for flexible, low cost and large area optoelectronics. However, solution processed multilayer organic electronics are still challenging to be produced, especially in the case of electrodes. In this work, the gravure printing technique was successfully employed to realize the highly conductive poly(3,4ethylenedioxythiophene:poly(styrene sulfonate (PEDOT:PSS polymeric anode and tested for the first time in flexible ITO-free (Indium Thin Oxide organic light emitting diodes (OLEDs. The device performances were found to be similar to those of a reference device containing a spin-coated polymeric anode. A gravure printed dimethyl sulfoxide (DMSO post-treatment was successfully tried to improve the printed anode characteristics. The obtained results show the way for future development for processing flexible ITO-free devices using the most attractive printing technology for roll-to-roll large area manufacturing.

  10. Electron irradiation of near-UV GaN/InGaN light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Lee, In-Hwan; Cho, Han-Su [Department of Materials Science and Engineering, Korea University, Seoul (Korea, Republic of); Polyakov, Alexander Y.; Smirnov, N.B.; Shchemerov, I.V.; Zinovyev, R.A.; Didenko, S.I.; Lagov, P.B. [National University of Science and Technology MISiS, Moscow (Russian Federation); Shmidt, N.M.; Shabunina, E.I. [Ioffe Physico-Technical Institute, St. Petersburg (Russian Federation); Tal' nishnih, N.A. [Submicron Heterostructures for Microelectronics Research and Engineering Center, St. Petersburg (Russian Federation); Hwang, Sung-Min [Soft-Epi, Inc., Opo-ro 240, Gwangju-si, Gyeonggi-do (Korea, Republic of); Pearton, S.J. [Department of Materials Science and Engineering, University of Florida, Gainesville, FL (United States)

    2017-10-15

    Irradiation with 6 MeV electrons of near-UV (peak wavelength 385-390 nm) multi-quantum-well (MQW) GaN/InGaN light emitting diodes (LEDs) causes an increase in density of deep electron traps near E{sub c} -0.8 and E{sub c} -1 eV, and correlates to a 90% decrease of electroluminescence (EL) efficiency after a fluence of 1.1 x 10{sup 16} cm{sup -2}. The likely origin of the EL efficiency decrease is this increase in concentration of the E{sub c} -0.8 eV and E{sub c} -1 eV traps. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Optical and electrical characteristics of GaN vertical light emitting diode with current block layer

    International Nuclear Information System (INIS)

    Guo Enqing; Liu Zhiqiang; Wang Liancheng; Yi Xiaoyan; Wang Guohong

    2011-01-01

    A GaN vertical light emitting diode (LED) with a current block layer (CBL) was investigated. Vertical LEDs without a CBL, with a non-ohmic contact CBL and with a silicon dioxide CBL were fabricated. Optical and electrical tests were carried out. The results show that the light output power of vertical LEDs with a non-ohmic contact CBL and with a silicon dioxide CBL are 40.6% and 60.7% higher than that of vertical LEDs without a CBL at 350 mA, respectively. The efficiencies of vertical LEDs without a CBL, with a non-ohmic contact CBL and with a silicon dioxide CBL drop to 72%, 78% and 85.5% of their maximum efficiency at 350 mA, respectively. Moreover, vertical LEDs with a non-ohmic contact CBL have relatively superior anti-electrostatic ability. (semiconductor devices)

  12. Light extraction efficiency enhancement for fluorescent SiC based white light-emitting diodes

    DEFF Research Database (Denmark)

    Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

    Fluorescent SiC based white light-emitting diodes(LEDs) light source, as an innovative energy-efficient light source, would even have longer lifetime, better light quality and eliminated blue-tone effect, compared to the current phosphor based white LED light source. In this paper, the yellow....... At a device level, the focus is on improving the light extraction efficiency due to the rather high refractive index of SiC by nanostructuring the surface of SiC. Both periodic nanostructures made by e-beam lithography and nanosphere lithography and random nanostructures made by self-assembled Au nanosphere...... mask and a thin layer of Al film have been investigated and all of them showed much enhanced extraction efficiency. All these good results pave the way to a very promising fluorescent SiC based white LED light source...

  13. Blue light emitting diodes for optical stimulation of quartz in retrospective dosimetry and dating

    DEFF Research Database (Denmark)

    Bøtter-Jensen, L.; Duller, G.A.T.; Murray, A.S.

    1999-01-01

    Recently developed blue light emitting diodes (LEDs) for the optical stimulation of quartz for use in routine optically stimulated luminescence (OSL) dating and retrospective dosimetry have been tested. For similar power densities, it was found that the higher energy light provided by the blue LEDs...... (470 nm) gives order of magnitude greater rate of stimulation in quartz than that from conventional blue-green light filtered from a halogen lamp. A practical blue LED OSL configuration is described. From comparisons of OSL decay curves produced by green and blue light sources, and by examination...... of the dependence of the blue LED OSL on preheat temperature, it is deduced that there is no evidence that the blue LEDs stimulate deep traps in a different manner from broadband filtered light. It is concluded that blue LEDs offer a practical alternative to existing stimulation sources. They have the significant...

  14. Improvement of light-extraction efficiency of organic light-emitting diodes using dielectric nanoparticles

    Science.gov (United States)

    Mann, Vidhi; Hooda, Babita; Rastogi, Vipul

    2017-07-01

    Use of dielectric nanoparticles placed at the anode (indium tin oxide) for the improvement of light-extraction efficiency of an organic light-emitting diode (OLED) has been reported. The nanoparticle layer will act as a scattering medium for the light trapped in the waveguiding modes of the device. Mie theory has been applied to study the scattering efficiency of the isolated dielectric nanoparticle. The effect of dielectric nanoparticles on the light-extraction efficiency of OLED has been analyzed by the finite-difference time-domain method. The light-extraction efficiency of the device depends upon the diameter, interparticle separation, and refractive index of dielectric nanoparticles. At optimal nanoparticle parameters, the enhancement factor of 1.7 times is obtained with the proposed design.

  15. Plasmon enhanced green GaN light-emitting diodes - Invited paper

    DEFF Research Database (Denmark)

    Ou, Haiyan; Fadil, Ahmed; Iida, Daisuke

    High-efficiency garnium nitride (GaN) based blue light-emitting diode (LED) paves the way for solid statelighting to take the place of the conventional incandescent bulbs and fluorescent light tubes.Compared to the traditional light sources, solid state lighting is more efficient, more flexible...... in spectral design, more compact etc. TheIII-nitride (GaN, InNetc.) semiconductors are attracting a lot of research effort because the combination of both could emit light with wavelength range from UV to infrared. Basically one material platform could provide all the solutions to light sources.However huge...... point of view, the efficiency of green LED is being improved by growing the GaInN material on non-polar or semi-polar surface of sapphire substrate. In parallel with the material growth effort, surface plasmons are implemented by taking use of the interactionbetween metals and active areas to increase...

  16. Efficient Light Extraction from Organic Light-Emitting Diodes Using Plasmonic Scattering Layers

    Energy Technology Data Exchange (ETDEWEB)

    Rothberg, Lewis

    2012-11-30

    Our project addressed the DOE MYPP 2020 goal to improve light extraction from organic light-emitting diodes (OLEDs) to 75% (Core task 6.3). As noted in the 2010 MYPP, “the greatest opportunity for improvement is in the extraction of light from [OLED] panels”. There are many approaches to avoiding waveguiding limitations intrinsic to the planar OLED structure including use of textured substrates, microcavity designs and incorporating scattering layers into the device structure. We have chosen to pursue scattering layers since it addresses the largest source of loss which is waveguiding in the OLED itself. Scattering layers also have the potential to be relatively robust to color, polarization and angular distributions. We note that this can be combined with textured or microlens decorated substrates to achieve additional enhancement.

  17. Quantum-Dot and Polychalcone Mixed Nanocomposites for Polymer Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Vanaraj Ramkumar

    2017-01-01

    Full Text Available The present work is aimed at improving the efficiency of light-emitting diodes (LEDs through the amalgamation of polymeric materials and quantum dots (QDs in nanocomposites. Herein, we report on the polytriphenylamine-based chalcone (PTpC or polycarbazole-based chalcone- (PCzC- QDs mixture nanocomposites as emissive layers for polymer LEDs (PLEDs. QDs were evenly dispersed in the polymer matrix and the synthesized PTpC-QDs and PCzC-QDs nanocomposites were able to form smooth thin films. The luminance characteristics of PTpC-QDs and PCzC-QDs nanocomposites were better than those of the pristine QD, PTpC, and PCzC materials, owing to the high charge-carrier transport ability of polymer-QDs nanocomposites. These results indicate that the proposed polymer-QDs nanocomposites could be potential candidates for application in PLEDs.

  18. Small molecule host materials for solution processed phosphorescent organic light-emitting diodes.

    Science.gov (United States)

    Yook, Kyoung Soo; Lee, Jun Yeob

    2014-07-02

    Solution processed phosphorescent organic light-emitting diodes (OLEDs) have been actively developed due to merits of high quantum efficiency of phosphorescent materials and simple fabrication processes of solution processed OLEDs. The device performances of the solution processed phosphorescent OLEDs have been greatly improved in the last 10 years and the progress of the device performances was made by the development of small molecule host materials for solution processes. A hybrid host of polymer and small molecules, a single small molecule host and a mixed host of small molecule hosts have effectively enhanced the quantum efficiency of the solution processed phosphorescent OLEDs. Therefore, this paper reviews recent developments in small molecule host materials for solution processed phosphorescent OLEDs and provides future directions for the development of the small molecule host materials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Nano-honeycomb structured transparent electrode for enhanced light extraction from organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Xiao-Bo; Qian, Min; Wang, Zhao-Kui, E-mail: zkwang@suda.edu.cn, E-mail: lsliao@suda.edu.cn; Liao, Liang-Sheng, E-mail: zkwang@suda.edu.cn, E-mail: lsliao@suda.edu.cn [Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM), and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123 (China)

    2015-06-01

    A universal nano-sphere lithography method has been developed to fabricate nano-structured transparent electrode, such as indium tin oxide (ITO), for light extraction from organic light-emitting diodes (OLEDs). Perforated SiO{sub 2} film made from a monolayer colloidal crystal of polystyrene spheres and tetraethyl orthosilicate sol-gel is used as a template. Ordered nano-honeycomb pits on the ITO electrode surface are obtained by chemical etching. The proposed method can be utilized to form large-area nano-structured ITO electrode. More than two folds' enhancement in both current efficiency and power efficiency has been achieved in a red phosphorescent OLED which was fabricated on the nano-structured ITO substrate.

  20. Strategies to Achieve High-Performance White Organic Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Lirong Zhang

    2017-12-01

    Full Text Available As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin characteristics, and flexibility. In this invited review, the main parameters which are used to characterize the performance of WOLEDs are introduced. Subsequently, the state-of-the-art strategies to achieve high-performance WOLEDs in recent years are summarized. Specifically, the manipulation of charges and excitons distribution in the four types of WOLEDs (fluorescent WOLEDs, phosphorescent WOLEDs, thermally activated delayed fluorescent WOLEDs, and fluorescent/phosphorescent hybrid WOLEDs are comprehensively highlighted. Moreover, doping-free WOLEDs are described. Finally, issues and ways to further enhance the performance of WOLEDs are briefly clarified.

  1. Phosphorescent dye-based supramolecules for high-efficiency organic light-emitting diodes.

    Science.gov (United States)

    Kim, Kwon-Hyeon; Lee, Sunghun; Moon, Chang-Ki; Kim, Sei-Yong; Park, Young-Seo; Lee, Jeong-Hwan; Woo Lee, Jin; Huh, June; You, Youngmin; Kim, Jang-Joo

    2014-09-10

    Organic light-emitting diodes (OLEDs) are among the most promising organic semiconductor devices. The recently reported external quantum efficiencies (EQEs) of 29-30% for green and blue phosphorescent OLEDs are considered to be near the limit for isotropically oriented iridium complexes. The preferred orientation of transition dipole moments has not been thoroughly considered for phosphorescent OLEDs because of the lack of an apparent driving force for a molecular arrangement in all but a few cases, even though horizontally oriented transition dipoles can result in efficiencies of over 30%. Here we use quantum chemical calculations to show that the preferred orientation of the transition dipole moments of heteroleptic iridium complexes (HICs) in OLEDs originates from the preferred direction of the HIC triplet transition dipole moments and the strong supramolecular arrangement within the co-host environment. We also demonstrate an unprecedentedly high EQE of 35.6% when using HICs with phosphorescent transition dipole moments oriented in the horizontal direction.

  2. Enhanced biomass production and lipid accumulation of Picochlorum atomus using light-emitting diodes (LEDs).

    Science.gov (United States)

    Ra, Chae Hun; Kang, Chang-Han; Jung, Jang-Hyun; Jeong, Gwi-Taek; Kim, Sung-Koo

    2016-10-01

    The effects of light-emitting diode (LED) wavelength, light intensity, nitrate concentration, and time of exposure to different LED wavelength stresses in a two-phase culture on lipid production were evaluated in the microalga, Picochlorum atomus. The biomass produced by red LED light was higher than that produced by purple, blue, green, or yellow LED and fluorescent lights from first phase of two-phase culture. The highest lipid production of P. atomus was 50.3% (w/w) with green LED light at 2days of second phase as light stress. Fatty acid analysis of the microalgae showed that palmitic acid (C16:0) and linolenic acid (C18:3) accounted for 84-88% (w/w) of total fatty acids from P. atomus. The two-phase culture of P. atomus is suitable for biofuel production due to higher lipid productivity and favorable fatty acid composition. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Reliability study of opto-coupled semiconductor devices and Light Emitting Diodes (LED)

    Science.gov (United States)

    Maurer, R. C.; Weissflug, V. A.; Sisul, E. V.

    1977-01-01

    Opto-coupler and light emitting diode (LED) failure mechanisms and associated activation energies were determind from the results of environmental and accelerated lift tests of over 2,400 devices. The evaluation program included LED phototransistor opto-couplers from three sources, LED photoamplifier opto-couplers from a single source, and discrete infrared emitting LEDs from two sources. Environmental tests to evaluate device mechanical integrity included power cycling (10,000 cycles), temperature cycling (500 cycles) and a sequence of monitored shock, monitored vibration and constant acceleration. Multiple temperature operating life tests were conducted at ambient temperatures between 25 C and 200 C. Opto-couplers were operated in both the 'on' and 'off' states during life testing.

  4. Developing Quantum Dot Phosphor-Based Light-Emitting Diodes for Aviation Lighting Applications

    International Nuclear Information System (INIS)

    Wu, F.; Dawei, Z.; Shuzhen, S.; Yiming, Z.; Songlin, Z.; Jian, X.

    2012-01-01

    We have investigated the feasibility of employing quantum dot (QD) phosphor-based light-emitting diodes (LEDs) in aviation applications that request Night Vision Imaging Systems (NVIS) compliance. Our studies suggest that the emerging QD phosphor-based LED technology could potentially be superior to conventional aviation lighting technology by virtue of the marriage of tight spectral control and broad wavelength tunability. This largely arises from the fact that the optical properties of semiconductor nano crystal QDs can be tailored by varying the nano crystal size without any compositional changes. It is envisioned that the QD phosphor-based LEDs hold great potentials in cockpit illumination, back light sources of monitor screens, as well as the LED indicator lights of aviation panels.

  5. Emission behavior of dual-side emissive transparent white organic light-emitting diodes.

    Science.gov (United States)

    Choi, Wing Hong; Tam, Hoi Lam; Ma, Dongge; Zhu, Furong

    2015-06-01

    White organic light-emitting diodes (WOLEDs) resemble light more naturally, with emission spectrum that is comfortable to the human eye. The transparent WOLEDs can be almost invisible by day and can emit a pleasant diffused light at night, allowing the surface light source to shine in both directions, an exciting new lighting technology that could bring new device concepts. However, undesirable angular-dependent emission in transparent WOLEDs is often observed, due to the microcavity effect. In this work, the emission behavior of dual-side emissive transparent WOLEDs was studied experimentally and theoretically. It is found that avoidance of the overlap between the peak wavelengths of the emitters and the resonant wavelength of the organic microcavity moderates the angular-dependent electroluminescence emission behavior, thereby improving the color stability of the transparent white WOLEDs over a broad range of the viewing angle.

  6. Developing Quantum Dot Phosphor-Based Light-Emitting Diodes for Aviation Lighting Applications

    Directory of Open Access Journals (Sweden)

    Fengbing Wu

    2012-01-01

    Full Text Available We have investigated the feasibility of employing quantum dot (QD phosphor-based light-emitting diodes (LEDs in aviation applications that request Night Vision Imaging Systems (NVIS compliance. Our studies suggest that the emerging QD phosphor-based LED technology could potentially be superior to conventional aviation lighting technology by virtue of the marriage of tight spectral control and broad wavelength tunability. This largely arises from the fact that the optical properties of semiconductor nanocrystal QDs can be tailored by varying the nanocrystal size without any compositional changes. It is envisioned that the QD phosphor-based LEDs hold great potentials in cockpit illumination, back light sources of monitor screens, as well as the LED indicator lights of aviation panels.

  7. Vertical thinking in blue light emitting diodes: GaN-on-graphene technology

    Science.gov (United States)

    Bayram, C.; Kim, J.; Cheng, C.-W.; Ott, J.; Reuter, K. B.; Bedell, S. W.; Sadana, D. K.; Park, H.; Dimitrakopoulos, C.

    2014-03-01

    In this work, we show that a 2D cleave layer (such as epitaxial graphene on SiC) can be used for precise release of GaNbased light emitting diodes (LEDs) from the LED-substrate interface. We demonstrate the thinnest GaN-based blue LED and report on the initial electrical and optical characteristics. Our LED device employs vertical architecture: promising excellent current spreading, improved heat dissipation, and high light extraction with respect to the lateral one. Compared to conventional LED layer release techniques used for forming vertical LEDs (such as laser-liftoff and chemical lift-off techniques), our process distinguishes itself with being wafer-scalable (large area devices are possible) and substrate reuse opportunity.

  8. Promotion of neural sprouting using low-level green light-emitting diode phototherapy

    Science.gov (United States)

    Alon, Noa; Duadi, Hamootal; Cohen, Ortal; Samet, Tamar; Zilony, Neta; Schori, Hadas; Shefi, Orit; Zalevsky, Zeev

    2015-02-01

    We irradiated neuroblastoma SH-SY5Y cell line with low-level light-emitting diode (LED) illumination at a visible wavelength of 520 nm (green) and intensity of 100 mW/cm2. We captured and analyzed the cell morphology before LED treatment, immediately after, and 12 and 24 h after treatment. Our study demonstrated that LED illumination increases the amount of sprouting dendrites in comparison to the control untreated cells. This treatment also resulted in more elongated cells after treatment in comparison to the control cells and higher levels of expression of a differentiation related gene. This result is a good indication that the proposed method could serve in phototherapy treatment for increasing sprouting and enhancing neural network formation.

  9. Spectral matching technology for light-emitting diode-based jaundice photodynamic therapy device

    Science.gov (United States)

    Gan, Ru-ting; Guo, Zhen-ning; Lin, Jie-ben

    2015-02-01

    The objective of this paper is to obtain the spectrum of light-emitting diode (LED)-based jaundice photodynamic therapy device (JPTD), the bilirubin absorption spectrum in vivo was regarded as target spectrum. According to the spectral constructing theory, a simple genetic algorithm as the spectral matching algorithm was first proposed in this study. The optimal combination ratios of LEDs were obtained, and the required LEDs number was then calculated. Meanwhile, the algorithm was compared with the existing spectral matching algorithms. The results show that this algorithm runs faster with higher efficiency, the switching time consumed is 2.06 s, and the fitting spectrum is very similar to the target spectrum with 98.15% matching degree. Thus, blue LED-based JPTD can replace traditional blue fluorescent tube, the spectral matching technology that has been put forward can be applied to the light source spectral matching for jaundice photodynamic therapy and other medical phototherapy.

  10. The efficiency challenge of nitride light-emitting diodes for lighting

    KAUST Repository

    Weisbuch, Claude

    2015-03-13

    © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. We discuss the challenges of light-emitting diodes in view of their application to solid-state lighting. The requirement is to at least displace the quite efficient fluorescent, sodium, and high intensity discharge lamps used today in the main energy consuming lighting sectors, industrial, commercial and outdoors, with more efficient and better light quality lamps. We show that both from the point of view of cost of ownership and carbon emissions reduction, the relevant metric is efficiency, more than the cost of lumens. Then, progress from present performance requires identification of the loss mechanisms in light emission from LEDs, and solutions competing with mainstream c-plane LEDS grown on sapphire need to be on par with these. Special attention is devoted to a discussion of the efficiency droop mechanisms, and of a recent direct measurement of Auger generated electrons which appear to be responsible for droop.

  11. Optimization design of integrated reflective optics for white light-emitting diodes

    Science.gov (United States)

    Chen, Enguo; Wu, Rengmao

    2014-07-01

    White light-emitting diodes are gradually dominating the illumination markets that new design challenges arise for this emerging source. Based on the white LEDs, an efficient optimization method is presented for integrated reflective optics. During the design process, initial structure of reflective optics is numerically calculated. For further optimization, initial parameters are adjusted by section-modeling method to determine optimal starting point. To complete the design, subsequent spline-modeling method is applied. Design example show that the designed reflective optics for LED illumination could offer both high performance and low space occupancy rate. Comparing to the numerical method, the method offers a 15% uniformity improvement and 6-times rise of processing efficiency. It is believed that the effective optimization method will has practical applications in other integrated optics.

  12. Light-emitting diodes fabricated on an electrical conducting flexible substrate

    Science.gov (United States)

    Choi, Won-Sik; Kim, Wan Jae; Park, Si-Hyun; Cho, Sung Oh; Lee, June Key; Park, Jun Beom; Ha, Jun-Seok; Chung, Tae Hoon; Jeong, Tak

    2017-01-01

    An array of InGaN-based flexible light-emitting diodes (FLEDs) was fabricated on a Ni-embedded electrical conducting flexible fabric with a full-scale 2-in. size. The FLED chip operation under current injection was realized using a single current probe as the negative electrode on the n-GaN surface; the conducting substrate was used as the positive electrode. The stability of the output power in the FLEDs was improved dramatically on the Ni-embedded conducting flexible fabric compared to that on the conventional polyimide flexible substrate. The former showed linear operation up to an input current 950 mA with no wavelength shift, whereas the latter exhibited rolling-over behavior after an input current of 200 mA.

  13. Carbon Nanotube Driver Circuit for 6 × 6 Organic Light Emitting Diode Display

    KAUST Repository

    Zou, Jianping

    2015-06-29

    Single-walled carbon nanotube (SWNT) is expected to be a very promising material for flexible and transparent driver circuits for active matrix organic light emitting diode (AM OLED) displays due to its high field-effect mobility, excellent current carrying capacity, optical transparency and mechanical flexibility. Although there have been several publications about SWNT driver circuits, none of them have shown static and dynamic images with the AM OLED displays. Here we report on the first successful chemical vapor deposition (CVD)-grown SWNT network thin film transistor (TFT) driver circuits for static and dynamic AM OLED displays with 6 × 6 pixels. The high device mobility of ~45 cm2V−1s−1 and the high channel current on/off ratio of ~105 of the SWNT-TFTs fully guarantee the control capability to the OLED pixels. Our results suggest that SWNT-TFTs are promising backplane building blocks for future OLED displays.

  14. NASA sponsored Light Emitting Diode (LED) development helps in cancer treatment

    Science.gov (United States)

    1997-01-01

    What started out as an attempt to develop a light which would allow for the growth of plants in space led to a remarkable discovery: The Light Emitting Diode (LED). This device through extensive study and experimentation has developed into a tool used by surgeons in the fight against brain cancer in children. Pictured is a mock-up of brain surgery being performed. By encapsulating the end of the LED with a balloon, light is diffused over a larger area of the brain allowing the surgeon a better view. This is one of many programs that begin as research for the space program, and through extensive study end up benefitting all of mankind.

  15. High luminance phosphorescent organic light emitting diodes based on Re(I) complex

    Science.gov (United States)

    Su, Bin; Zhao, Jing; Wang, Fujun; Che, Guangbo; Wang, Yang; Wang, Bo; Gao, Lin; Yan, Yongsheng

    2016-10-01

    A novel Re(I) complex with the acenaphtho[1,2-b]pyrazino[2,3-f][1,10]phenanthroline (APPT) ligand Re(APPT)(CO)3Br (abbreviated as Re-APPT) was used to fabricate organic light emitting diodes (OLEDs). From the electroluminescence (EL) spectra of the device at different bias voltages, it could be found that the EL maxima shifted approximately 30 nm. For OLEDs with 5% Re-APPT doped emissive layer, turn-on voltage of 6 V, maximum luminance of 7631 cd/m2 and a current efficiency up to 2.36 cd/A were obtained. We suppose that a direct charge trapping took the dominant position in the EL process. Trapping contributed mostly to this relatively higher luminance.

  16. Graded-host phosphorescent light-emitting diodes with high efficiency and reduced roll-off

    Directory of Open Access Journals (Sweden)

    S. W. Liu

    2012-03-01

    Full Text Available We demonstrated graded-host phosphorescent organic light-emitting diodes with high efficiency and reduced efficiency roll-off. The emissive layer of the graded host device consists of both electron and hole transport type hosts, 1,3,5-tris(N-phenylbenzimidazole-2-ylbenzene (TPBI and 4,4′,4′′-tris(N-carbazolyltriphenylamine, respectively, with graded composition, and the phosphorescent red emitter bis(2-phenylquinoline (acetylacetonate iridium(III, which was uniformly doped into the graded host matrix. The graded host device shows improved quantum efficiency and power efficiency with significantly reduced efficiency roll-off as compared to the unipolar-host and double layer heterojunction host devices.

  17. Lifetime enhanced phosphorescent organic light emitting diode using an electron scavenger layer

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob, E-mail: sy96.lee@samsung.com [Samsung Advanced Institute of Technology, Samsung Electronics Co., Ltd., 130 Samsung-ro, Suwon, Gyeonggi 443-803 (Korea, Republic of)

    2015-07-27

    We demonstrate a method to improve lifetime of a phosphorescent organic light emitting diode (OLED) using an electron scavenger layer (ESL) in a hole transporting layer (HTL) of the device. We use a bis(1-(phenyl)isoquinoline)iridium(III)acetylacetonate [Ir(piq){sub 2}(acac)] doped HTL to stimulate radiative decay, preventing thermal degradation in HTL. The ESL effectively prevented non-radiative decay of leakage electron in HTL by converting non-radiative decay to radiative decay via a phosphorescent red emitter, Ir(piq){sub 2}(acac). The lifetime of device (t{sub 95}: time after 5% decrease of luminance) has been increased from 75 h to 120 h by using the ESL in a phosphorescent green-emitting OLED.

  18. An Exciplex Host for Deep-Blue Phosphorescent Organic Light-Emitting Diodes.

    Science.gov (United States)

    Lim, Hyoungcheol; Shin, Hyun; Kim, Kwon-Hyeon; Yoo, Seung-Jun; Huh, Jin-Suk; Kim, Jang-Joo

    2017-11-01

    The use of exciplex hosts is attractive for high-performance phosphorescent organic light-emitting diodes (PhOLEDs) and thermally activated delayed fluorescence OLEDs, which have high external quantum efficiency, low driving voltage, and low efficiency roll-off. However, exciplex hosts for deep-blue OLEDs have not yet been reported because of the difficulties in identifying suitable molecules. Here, we report a deep-blue-emitting exciplex system with an exciplex energy of 3.0 eV. It is composed of a carbazole-based hole-transporting material (mCP) and a phosphine-oxide-based electron-transporting material (BM-A10). The blue PhOLEDs exhibited maximum external quantum efficiency of 24% with CIE coordinates of (0.15, 0.21) and longer lifetime than the single host devices.

  19. Improving the efficiency of red phosphorescent organic light emitting diodes by exciton management

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Yi-Lu; Wang, Zhibin; Helander, Michael G.; Qiu, Jacky; Lu, Zheng-Hong [Department of Materials Science and Engineering, University of Toronto, 184 College St., M5S 3E4, Toronto (Canada); Puzzo, Danny P. [Department of Chemistry, University of Toronto, 80 St George St., M5S 3H6, Toronto (Canada); Castrucci, Jeffrey [Department of Chemical Engineering and Applied Chemistry, University of Toronto, 200 College Street, M5S 3E5, Toronto (Canada)

    2012-12-15

    Phosphorescent organic light emitting diodes (PHOLEDs) have undergone remarkable development from both academia and industry in the past decade. Nevertheless, devices with higher efficiency remain highly desirable for energy-efficient general lighting as well as low power consumption LED backlight applications. In this respect, several groups have conducted complex device engineering designs such as doping of the transport layers to increase charge carrier mobility, incorporation of blocking layers to confine excitons/charge carriers, or use of multiple emissive layers to widen the emission zone, in order to achieve higher device performances. In this work, we report an alternative and relatively simple approach to improve the efficiency of red PHOLEDs by exciton management to attain a high external quantum efficiency (EQE) of >20%. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Study of natural organic dyes as active material for fabrication of organic light emitting diodes

    Science.gov (United States)

    Sánchez Juárez, A.; Castillo, D.; Guaman, A.; Espinosa, S.; Obregón, D.

    2016-09-01

    The scientific community and some sectors of industry have been working with organic dyes for successful applications in OLED's, OSC's, however, most of the used dyes and pigments are synthetic. In this work is investigated the use of natural dyes for its application in organic light emitting diodes, some of the studied species are chili, blackberry, guayacan flower, cochinilla, tree tomato, capuli, etc. In this study the dyes are deposited by direct deposition and SOL-GEL process doped with the natural organic dye, both methods show good performance and lower fabrication costs for dye extraction, this represents a new alternative for the fabrication of OLED devices with low requirements in technology. Most representative results are presented for Dactylopius Coccus Costa (cochinilla) and raphanus sativus' skin.

  1. Modification of Conductive Polymer for Polymeric Anodes of Flexible Organic Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Wang Guang-Feng

    2009-01-01

    Full Text Available Abstract A conductive polymer, poly(3,4-ethylenedioxythiophene:poly(styrene sulfonate (PEDOT:PSS, was modified with dimethyl sulfoxide (DMSO in solution state, together with sub-sequential thermal treatment of its spin-coated film. The electrical conductivity increased by more than three orders of magnitude improvement was achieved. The mechanism for the conductivity improvement was studied at nanoscale by particle size analysis, field emission scanning electron microscopy (FESEM, and X-ray photoelectron spectroscopy (XPS. Smaller particle size was observed, resulting in larger contact area and better electrical conductive connections. Connection of conductive PEDOT increased on the surface of the PEDOT:PSS particles, which promoted high conductivity. Flexible anodes based on the modified PEDOT:PSS were fabricated. Flexible organic light-emitting diodes (FOLED based the polymeric anodes have a comparable performance to those on indium–tin–oxide (ITO anodes.

  2. Plasmonic Perovskite Light-Emitting Diodes Based on the Ag-CsPbBr3 System.

    Science.gov (United States)

    Zhang, Xiaoli; Xu, Bing; Wang, Weigao; Liu, Sheng; Zheng, Yuanjin; Chen, Shuming; Wang, Kai; Sun, Xiao Wei

    2017-02-08

    The enhanced luminescence through semiconductor-metal interactions suggests the great potential of device performance improvement via properly tailored plasmonic nanostructures. Surface plasmon enhanced electroluminescence in an all-inorganic CsPbBr 3 perovskite light-emitting diode (LED) is fabricated by decorating the hole transport layer with the synthesized Ag nanorods. An increase of 42% and 43.3% in the luminance and efficiency is demonstrated for devices incorporated with Ag nanorods. The device with Ag introduction indicates identical optoelectronic properties to the controlled device without Ag nanostructures. The increased spontaneous emission rate caused by the Ag-induced plasmonic near-field effect is responsible for the performance enhancement. Therefore, the plasmonic Ag-CsPbBr 3 nanostructure studied here provides a novel strategy on the road to the future development of perovskite LEDs.

  3. Tunable photoluminescence of CsPbBr3 perovskite quantum dots for light emitting diodes application

    Science.gov (United States)

    Chen, Weiwei; Xin, Xing; Zang, Zhigang; Tang, Xiaosheng; Li, Cunlong; Hu, Wei; Zhou, Miao; Du, Juan

    2017-11-01

    All-inorganic cesium lead halide (CsPbBr3) perovskite quantum dots (QDs), as one kind of promising materials, have attracted considerable attention in optoelectronic applications. Herein, we synthesized the colloidal CsPbBr3 QDs with tunable photoluminescence (PL) (493-531 nm) by adjusting the reaction temperatures, which revealed narrow emission bandwidths of about 25 nm. The average diameters of the QDs could be adjusted from 7.1 to 12.3 nm as the temperature increased from 100 °C to 180 °C. Moreover, the radiative lifetimes of CsPbBr3 QDs were measured to be 2 ns, and the single QD fluorescence intensity time trace results demonstrated its suppressed blinking emission. Moreover, green light emitting diodes by using CsPbBr3 QDs casted on blue LED chips were further fabricated, which provided potential applications in the field of display and lighting technology.

  4. Advanced Oxidation of Tartrazine and Brilliant Blue with Pulsed Ultraviolet Light Emitting Diodes.

    Science.gov (United States)

    Scott, Robert; Mudimbi, Patrick; Miller, Michael E; Magnuson, Matthew; Willison, Stuart; Phillips, Rebecca; Harper, Willie F

    2017-01-01

      This study investigated the effect of ultraviolet light-emitting diodes (UVLEDs) coupled with hydrogen peroxide as an advanced oxidation process (AOP) for the degradation of two test chemicals. Brilliant Blue FCF consistently exhibited greater degradation than tartrazine, with 83% degradation after 300 minutes at the 100% duty cycle compared with only 17% degradation of tartrazine under the same conditions. These differences are attributable to the structural properties of the compounds. Duty cycle was positively correlated with the first-order rate constants (k) for both chemicals but, interestingly, negatively correlated with the normalized first-order rate constants (k/duty cycle). Synergistic effects of both hydraulic mixing and LED duty cycle were manifested as novel oscillations in the effluent contaminant concentration. Further, LED output and efficiency were dependent upon duty cycle and less efficient over time perhaps due to heating effects on semiconductor performance.

  5. Organic Light-Emitting Diodes Based on Phthalimide Derivatives: Improvement of the Electroluminescence Properties

    Directory of Open Access Journals (Sweden)

    Frédéric Dumur

    2018-03-01

    Full Text Available In this study, a phthalimide-based fluorescent material has been examined as a green emitter for multilayered organic light-emitting diodes (OLEDs. By optimizing the device stacking, a maximum brightness of 28,450 cd/m2 at 11.0 V and a maximum external quantum efficiency of 3.11% could be obtained. Interestingly, OLEDs fabricated with Fluo-2 presented a 20-fold current efficiency improvement compared to the previous results reported in the literature, evidencing the crucial role of the device stacking in the electroluminescence (EL performance of a selected emitter. Device lifetime was also examined and an operational stability comparable to that reported for a standard triplet emitter i.e., bis(4-methyl-2,5-diphenyl-pyridineiridium(III acetylacetonate [(mdppy2Iracac] was evidenced.

  6. Superluminescent light emitting diodes on naturally survived InGaN/GaN lateral nanowires

    Science.gov (United States)

    Banerjee, D.; Sankaranarayanan, S.; Khachariya, D.; Nadar, M. B.; Ganguly, S.; Saha, D.

    2016-07-01

    We demonstrate a method for nanowire formation by natural selection during wet anisotropic chemical etching in boiling phosphoric acid. Nanowires of sub-10 nm lateral dimensions and lengths of 700 nm or more are naturally formed during the wet etching due to the convergence of the nearby crystallographic hexagonal etch pits. These nanowires are site controlled when formed in augmentation with dry etching. Temperature and power dependent photoluminescence characterizations confirm excitonic transitions up to room temperature. The exciton confinement is enhanced by using two-dimensional confinement whereby enforcing greater overlap of the electron-hole wave-functions. The surviving nanowires have less defects and a small temperature variation of the output electroluminescent light. We have observed superluminescent behaviour of the light emitting diodes formed on these nanowires. There is no observable efficiency roll off for current densities up to 400 A/cm2.

  7. Stolephorus sp Behavior in Different LED (Light Emitting Diode) Color and Light Intensities

    Science.gov (United States)

    Fitri Aristi, D. P.; Ramadanita, I. A.; Hapsari, T. D.; Susanto, A.

    2018-02-01

    This research aims to observe anchovy (Stolephorus sp) behavior under different LED light intensities that affect eye physiology (cell cone structure). The materials used were Stolephorus sp taken from the waters off Jepara and 13 and 10 watt light emitting diode (LED). The research method was an experiment conducted from March through August 2015 in the waters off Jepara. Data analysis of visual histology and fish respond was carried out at the fishing gear material laboratory, anatomy and cultivate. Cone cell structure (mosaic cone) of Stolephorus sp forms a connected regular square pattern with every single cone surrounded by four double cones, which indicate that anchovies are sensitive to light. The 13 watt LED (628 lux) has faster response than the 10 watt LED (531 lux) as it has wider and higher emitting intensity, which also attracts fish to gather quicker.

  8. Oxidation of tartrazine with ultraviolet light emitting diodes: pH and duty cycles effects.

    Science.gov (United States)

    Stewart, Brandon M; Miller, Michael E; Kempisty, David M; Stubbs, John; Harper, Willie F

    2018-03-01

    The presence of tartrazine (TAR) in the water cycle poses serious threats to human health. This study investigated the used of light emitting diodes (LEDs) in the advanced oxidation of TAR under different pH and duty cycle (DC) conditions. The first order reaction rate constant for TAR oxidation was positively correlated with DC, negatively correlated with pH, and typically greatest at pH 6. Chemical byproduct analysis indicated that OH addition, H abstraction, and electron transfer without molecule transfer were among the relevant reaction mechanisms for TAR degradation. Six byproducts were identified, four were reported for the first time, and two demonstrated that TAR rings were cleaved. This research is the first to determine the optimal pH for UVLED-driven oxidation of TAR and the first to identify new TAR-related byproducts from UVLED-based water treatment.

  9. Improving the performance of MEH-PPV based light emitting diode by incorporation of graphene nanosheets

    Energy Technology Data Exchange (ETDEWEB)

    Prasad, Neetu, E-mail: neetu23686@gmail.com [Department of Electronic Science, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021 (India); Singh, Inderpreet [Department of Electronic Science, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021 (India); SGTB Khalsa College, Department of Electronics, University of Delhi, Delhi 110007 (India); Kumari, Anita [Department of Electronic Science, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021 (India); Madhwal, Devinder [Amity Institute for advanced research and studies, Amity University, UP (India); Madan, Shikha; Dixit, Shiv Kumar; Bhatnagar, P.K.; Mathur, P.C. [Department of Electronic Science, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021 (India)

    2015-03-15

    The effect of incorporation of graphene nanosheets on the efficiency of poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) based light emitting diodes (LED) has been examined by varying the graphene concentration from 0 to 0.1 wt%. It was observed that graphene doping enhances the photoluminescence (PL) emission from the PPV layer by ∼6 times at the blending concentration of 0.005 wt%. This is attributed to the isolation of individual polymer chains that quenches the inter-chain relaxations and boosts the intra-chain transitions. The improvement in device luminance is also found to be ∼6 times as compared to that with MEH-PPV only LED at 0.005 wt% graphene concentration. This is due to the high charge carrier mobility in graphene nanostructure that assists in balancing the charge carrier concentration in the emissive layer. Also due to its low LUMO level, graphene improves electron injection from the cathode. Both these effects lead to enhancement in the device luminescence. Employment of graphene in this manner also leads to lowering of turn-on voltage of the device. This is attributed to the ability of graphene sheets to establish an interconnected conducting network in the polymer matrix that lowers the device resistance. However, at higher graphene concentration, this property short circuits the device structure, which greatly deteriorates its performance. The graphene concentration, therefore, should be kept below the percolation threshold level to develop high efficiency devices. - Highlights: • Incorporation of graphene greatly improves the efficiency of MEH-PPV based light emitting diode. • It isolates individual polymer chain and suppresses inter-chain interaction leading to improve the luminescence. • Owing to its high carrier mobility, graphene balances the charge carrier concentration in the emissive layer. • Its low LUMO level also improves the electron injection from the cathode. • It also reduces the turn

  10. Comparison of the alendronate and irradiation with a light-emitting diode (LED) on murine osteoclastogenesis.

    Science.gov (United States)

    Sohn, Hong Moon; Ko, Youngjong; Park, Mineon; Kim, Bora; Park, Jung Eun; Kim, Donghwi; Moon, Young Lae; Lim, Wonbong

    2017-01-01

    Photomodulation therapy (PBMT) using light-emitting diode (LED) has been proposed as an alternative to conventional osteoporosis therapies. Our aim was to determine the effect of irradiation with a light-emitting diode on receptor activator of NF-κB ligand (RANKL)-mediated differentiation of mouse bone marrow macrophages into osteoclasts and compare it to alendronate treatment. The cells were irradiated with LED at 635±10 nm, 9-cm spot size, 5 mW/cm 2 , and 18 J for 60 min/day in a CO 2 incubator. The differentiation of irradiated and untreated RANKL-stimulated bone marrow macrophages into osteoclasts was evaluated by tartrate-resistant acid phosphatase (TRAP) staining and by molecular methods. These included assessing messenger RNA (mRNA) expression of osteoclastic markers such as TRAP, c-Fos, Atp6v0d2, DC-STAMP, NFATc1, cathepsin K, MMP9 and OSCAR; phosphorylation of various MAPKs, including extracellular signal-regulated kinase ERK1/2, P38, and JNK; NF-κB translocation; and resorption pit formation. Results were compared to those obtained with sodium alendronate. Production of reactive oxygen species was measured by a 2',7'-dihydrodichlorofluorescein diacetate assay. LED irradiation and alendronate inhibited mRNA expression of osteoclast-related genes, such as TRAP, c-Fos, and NFATc1, and reduced the osteoclast activity of RANKL-stimulated bone marrow macrophages. LED irradiation, but not alendronate, also inhibited the production of reactive oxygen species (ROS); phosphorylation of ERK, P38, and IκB; and NF-κB translocation. These findings suggest that LED irradiation downregulates osteoclastogenesis by ROS production; this effect could lead to reduced bone loss and may offer a new therapeutic tool for managing osteoporosis.

  11. High-intensity light-emitting diode vs fluorescent tubes for intensive phototherapy in neonates.

    Science.gov (United States)

    Sherbiny, Hanan S; Youssef, Doaa M; Sherbini, Ahmad S; El-Behedy, Rabab; Sherief, Laila M

    2016-05-01

    Special blue fluorescent tubes are recommended by the American Academy of Pediatrics (AAP) as the most effective light source for lowering serum bilirubin. A high-intensity light-emitting diode ('super LED') could render intensive phototherapy more effective than the above conventional methods. This study compared the efficacy and safety of a high-intensity light-emitting diode bed vs conventional intensive phototherapy with triple fluorescent tube units as a rescue treatment for severe unconjugated neonatal hyperbilirubinaemia. This was a randomised, prospective trial. Two hundred jaundiced neonates ≥ 35 weeks gestation who met the criteria for intensive phototherapy as per AAP guidelines were randomly assigned to be treated either with triple fluorescent tube units (group 1, n = 100) or a super LED bed (group 2, n = 100). The outcome was the avoidance of exchange transfusion by successful control of hyperbilirubinaemia. Statistically significant higher success rates of intensive phototherapy were achieved among neonates treated with super LED (group 2) than in those treated conventionally (group 1) (87% vs 64%, P = 0.003). Significantly higher 'bilirubin decline' rates were reported in both haemolytic and non-haemolytic subgroups treated with the super LED bed compared with a similar sub-population in the conventionally treated group. Comparable numbers of neonates in both groups developed rebound jaundice (8% vs 10% of groups 1 and 2, respectively). Side-effects were mild in both groups, but higher rates of hyperthermia (12% vs 0%, P = 0.03), dehydration (8% vs 2%, P = 0.26) and skin rash (39% vs 1%, P = 0.002) were reported in the fluorescent tubes-treated group compared with the LED group. Super LED is a safe rescue treatment for severe neonatal hyperbilirubinaemia, and its implementation may reduce the need for exchange transfusion.

  12. Analytical model for current distribution in large-area organic light emitting diodes with parallel metal grid lines

    NARCIS (Netherlands)

    Barink, M.; Harkema, S.

    2012-01-01

    In this study, an analytical solution for the current distribution of a large-area organic light emitting diodes (OLEDs) with parallel equidistant gridlines is derived. In contrast to numerical methods, this analytical solution allows for a very quick scan of the OLED design space, even for very

  13. A Yellow Emitting InGaN/GaN Nanowires-based Light Emitting Diode Grown on Scalable Quartz Substrate

    KAUST Repository

    Prabaswara, Aditya

    2017-05-08

    The first InGaN/GaN nanowires-based yellow (λ = 590 nm) light-emitting diodes on scalable quartz substrates are demonstrated, by utilizing a thin Ti/TiN interlayer to achieve simultaneous substrate conductivity and transparency.

  14. Enhanced Emission Efficiency of Size-Controlled InGaN/GaN Green Nanopillar Light-Emitting Diodes

    DEFF Research Database (Denmark)

    Ou, Yiyu; Iida, Daisuke; Fadil, Ahmed

    2016-01-01

    Nanopillar InGaN/GaN green light-emitting diode (LED) arrays were fabricated by self-assembled Au nanoparticles patterning and dry etching process. Structure size and density of the nanopillar arrays have been modified by varying the Au film thickness in the nanopatterning process. Fabricated...

  15. The Use of Light-Emitting Diodes (LEDs) as Green and Red/Far-Red Light Sources in Plant Physiology.

    Science.gov (United States)

    Jackson, David L.; And Others

    1985-01-01

    The use of green, red, and far-red light-emitting diodes (LEDs) as light sources for plant physiological studies is outlined and evaluated. Indicates that LED lamps have the advantage over conventional light sources in that they are lightweight, low-cost, portable, easily constructed, and do not require color filters. (Author/DH)

  16. Blue Light Emitting Diodes based on a partially conjugated Si-containing PPV-copolymer in a multilayer configuration

    NARCIS (Netherlands)

    Garten, F; Hilberer, A; Cacialli, F.; Esselink, F.J; van Dam, Y.; Schlatmann, A.R.; Friend, R.H.; Klapwijk, T.M; Hadziioannou, G

    1997-01-01

    Efficient blue Light Emitting Diodes (LEDs) based on a novel partially conjugated co-polymer (SiPPV) have been realized by a combination of techniques known to enhance the quantum efficiency of organic devices. The copolymer is homogeneously blended in a PVK-matrix to reduce the number of

  17. A Simple, Small-Scale Lego Colorimeter with a Light-Emitting Diode (LED) Used as Detector

    Science.gov (United States)

    Asheim, Jonas; Kvittingen, Eivind V.; Kvittingen, Lise; Verley, Richard

    2014-01-01

    This article describes how to construct a simple, inexpensive, and robust colorimeter from a few Lego bricks, in which one light-emitting diode (LED) is used as a light source and a second LED as a light detector. The colorimeter is suited to various grades and curricula.

  18. Highly efficient red phosphorescent organic light-emitting diodes based on solution processed emissive layer

    International Nuclear Information System (INIS)

    Liu, Baiquan; Xu, Miao; Tao, Hong; Ying, Lei; Zou, Jianhua; Wu, Hongbin; Peng, Junbiao

    2013-01-01

    Highly efficient red phosphorescent organic polymer light-emitting diodes (PhOLEDs) were fabricated based on a solution-processed small-molecule host 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) by doping an iridium complex, tris(1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine)iridium (III) (Ir(MPCPPZ) 3 ). A hole blocking layer 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBI) with a function of electron transport was thermally deposited onto the top of CBP layer. The diode with the structure of ITO/PEDOT:PSS (50 nm)/CBP:Ir(MPCPPZ) 3 (55 nm)/TPBI (30 nm)/Ba (4 nm)/Al (120 nm) showed an external quantum efficiency (QE ext ) of 19.3% and luminous efficiency (LE) of 18.3 cd/A at a current density of 0.16 mA/cm 2 , and Commission International de I'Eclairage (CIE) coordinates of (0.607, 0.375). It was suggested that the diodes using TPBI layer exhibited nearly 100% internal quantum efficiency and one order magnitude enhanced LE or QE ext efficiencies. -- Highlights: • Efficient red PhOLEDs based on a solution-processed small-molecule host were fabricated. • By altering volume ratio of chloroform/chlorobenzene solvent, we got best film quality of CBP. • EQE of the diode was 19.3%, indicating nearly 100% internal quantum yield was achieved

  19. Highly efficient red phosphorescent organic light-emitting diodes based on solution processed emissive layer

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Baiquan; Xu, Miao; Tao, Hong; Ying, Lei [Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640 (China); State Key Laboratory of Luminescent Materials and Devices, Guangzhou 510640 (China); Zou, Jianhua, E-mail: zou1007@gmail.com [Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640 (China); State Key Laboratory of Luminescent Materials and Devices, Guangzhou 510640 (China); Wu, Hongbin; Peng, Junbiao [Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640 (China); State Key Laboratory of Luminescent Materials and Devices, Guangzhou 510640 (China)

    2013-10-15

    Highly efficient red phosphorescent organic polymer light-emitting diodes (PhOLEDs) were fabricated based on a solution-processed small-molecule host 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) by doping an iridium complex, tris(1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine)iridium (III) (Ir(MPCPPZ){sub 3}). A hole blocking layer 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBI) with a function of electron transport was thermally deposited onto the top of CBP layer. The diode with the structure of ITO/PEDOT:PSS (50 nm)/CBP:Ir(MPCPPZ){sub 3} (55 nm)/TPBI (30 nm)/Ba (4 nm)/Al (120 nm) showed an external quantum efficiency (QE{sub ext}) of 19.3% and luminous efficiency (LE) of 18.3 cd/A at a current density of 0.16 mA/cm{sup 2}, and Commission International de I'Eclairage (CIE) coordinates of (0.607, 0.375). It was suggested that the diodes using TPBI layer exhibited nearly 100% internal quantum efficiency and one order magnitude enhanced LE or QE{sub ext} efficiencies. -- Highlights: • Efficient red PhOLEDs based on a solution-processed small-molecule host were fabricated. • By altering volume ratio of chloroform/chlorobenzene solvent, we got best film quality of CBP. • EQE of the diode was 19.3%, indicating nearly 100% internal quantum yield was achieved.

  20. Highly Efficient Light-Emitting Diodes of Colloidal Metal-Halide Perovskite Nanocrystals beyond Quantum Size.

    Science.gov (United States)

    Kim, Young-Hoon; Wolf, Christoph; Kim, Young-Tae; Cho, Himchan; Kwon, Woosung; Do, Sungan; Sadhanala, Aditya; Park, Chan Gyung; Rhee, Shi-Woo; Im, Sang Hyuk; Friend, Richard H; Lee, Tae-Woo

    2017-07-25

    Colloidal metal-halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter D B (quantum size regime) emerged as promising light emitters due to their spectrally narrow light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nanocrystals (NCs) in a dimension > D B (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than D B show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and perfluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (∼60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic-inorganic metal-halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.

  1. Hybrid tunnel junction contacts to III–nitride light-emitting diodes

    KAUST Repository

    Young, Erin C.

    2016-01-26

    In this work, we demonstrate highly doped GaN p–n tunnel junction (TJ) contacts on III–nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10−4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a ($20\\\\bar{2}\\\\bar{1}$) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

  2. Simple assembling of organic light emitting diodes for teaching purposes in undergraduate labs

    Science.gov (United States)

    Vázquez-Córdova, Sergio; Ramos-Ortiz, Gabriel; Maldonado, José Luis; Meneses-Nava, Marco A.; Barbosa-García, Oracio

    2008-04-01

    Electroluminescent organic molecules and polymers have emerged as advanced materials used to fabricate organic light emitting diodes (OLED's) whose unique technological features could revolutionize the industry of flat panel displays. Although these novel organic materials combine low cost and ease of processing, the OLED's fabrication for educational purposes has been rarely reported. In this work, we report a simple and inexpensive method to fabricate OLED's devices intended for educational purposes in the undergraduate level of physics, chemistry and material sciences. For ease of fabrication the cathode in the diode structure was conformed by either an alloy of Bi-Pb-Cd-Sn or by a Ga-In alloy in liquid phase, or simply by silver paint, whereas we used ITO (Indium tin oxide) deposited on glass substrates as anode. Substrates of flexible plastic were also used. The OLED's were fabricated using the spin-coating technique with solutions of the fluorescent materials Alq3 and MEH:PPV, as well as the phosphorescent complex Ru(bpy)3. We report measurement data on current-voltage curves and luminescence obtained by students fabricating and testing the devices under normal room conditions.

  3. Fluorescence digital photography of acne using a light-emitting diode illuminator.

    Science.gov (United States)

    Ahn, Hyo Hyun; Kim, Soo Nam; Kye, Young Chul

    2006-11-01

    The fluorescence findings of several dermatological diseases, such as erythrasma, tinea versicolor, and acne are helpful for diagnosis and follow-up. However, many experience difficulty taking photographic images of fluorescence. The aim of this study was to develop a 405 nm light-emitting diode (LED) system for fluorescence digital photography of acne and to determine whether such a diode can be used to evaluate acne. Eight healthy acne patients were compared with controls by fluorescence digital photography using a digital camera equipped with a 405 nm LED illuminator. Digital photographs were taken by two different ways of exposure, i.e. appropriate exposure level and longer exposure. One side of the nose, cheek, and glabella was compared. The numbers and extents of fluorescence dots were counted and measured. As normal controls, seven individuals with apparent oiliness and no acne were enrolled. Red fluorescent facial dots were observed and photographed digitally using the 405 nm LED illuminator. These were more numerous and extensive on the glabella and cheeks of acne patients. Fluorescence digital photography of acne was successfully performed using a 405 nm LED illuminator. This illuminator could be used for acne evaluations.

  4. Color tunable hybrid light-emitting diodes based on perovskite quantum dot/conjugated polymer

    Science.gov (United States)

    Germino, José C.; Yassitepe, Emre; Freitas, Jilian N.; Santiago, Glauco M.; Bonato, Luiz Gustavo; de Morais, Andréia; Atvars, Teresa D. Z.; Nogueira, Ana F.

    2017-08-01

    Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX3, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of the optical properties of the PQDs and their interaction with wide bandgap conjugated polymers, associated with the solution processing ability of these materials.

  5. Study of Nanostructured Polymeric Composites Used for Organic Light Emitting Diodes and Organic Solar Cells

    Directory of Open Access Journals (Sweden)

    Nguyen Nang Dinh

    2012-01-01

    Full Text Available Polymeric nanocomposite films from PEDOT and MEH-PPV embedded with surface modified TiO2 nanoparticles for the hole transport layer and emission layer were prepared, respectively, for organic emitting diodes (OLEDs. The composite of MEH-PPV+nc-TiO2 was used for organic solar cells (OSCs. The characterization of these nanocomposites and devices showed that electrical (I-V characteristics and spectroscopic (photoluminescent properties of conjugate polymers were enhanced by the incorporation of nc-TiO2 in the polymers. The organic light emitting diodes made from the nanocomposite films would exhibit a larger photonic efficiency and a longer lasting life. For the organic solar cells made from MEH-PPV+nc-TiO2 composite, a fill factor reached a value of about 0.34. Under illumination by light with a power density of 50 mW/cm2, the photoelectrical conversion efficiency was about 0.15% corresponding to an open circuit voltage Voc = 0.126 V and a shortcut circuit current density Jsc = 1.18 mA/cm2.

  6. Effects of Light-Emitting Diode Therapy on Muscle Hypertrophy, Gene Expression, Performance, Damage, and Delayed-Onset Muscle Soreness

    Science.gov (United States)

    Ferraresi, Cleber; Bertucci, Danilo; Schiavinato, Josiane; Reiff, Rodrigo; Araújo, Amélia; Panepucci, Rodrigo; Matheucci, Euclides; Cunha, Anderson Ferreira; Arakelian, Vivian Maria; Hamblin, Michael R.; Parizotto, Nivaldo; Bagnato, Vanderlei

    2016-01-01

    Ferraresi C, Bertucci D, Schiavinato J, Reiff R, Araújo A, Panepucci R, Matheucci E, Cunha AF, Arakelian VM, Hamblin MR, Parizotto N, Bagnato V: Effects of light-emitting diode therapy on muscle hypertrophy, gene expression, performance, damage, and delayed-onset muscle soreness: case-control study with a pair of identical twins. Objective The aim of this study was to verify how a pair of monozygotic twins would respond to light-emitting diode therapy (LEDT) or placebo combined with a strength-training program during 12 weeks. Design This case-control study enrolled a pair of male monozygotic twins, allocated randomly to LEDT or placebo therapies. Light-emitting diode therapy or placebo was applied from a flexible light-emitting diode array (λ = 850 nm, total energy = 75 J, t = 15 seconds) to both quadriceps femoris muscles of each twin immediately after each strength training session (3 times/wk for 12 weeks) consisting of leg press and leg extension exercises with load of 80% and 50% of the 1-repetition maximum test, respectively. Muscle biopsies, magnetic resonance imaging, maximal load, and fatigue resistance tests were conducted before and after the training program to assess gene expression, muscle hypertrophy and performance, respectively. Creatine kinase levels in blood and visual analog scale assessed muscle damage and delayed-onset muscle soreness, respectively, during the training program. Results Compared with placebo, LEDT increased the maximal load in exercise and reduced fatigue, creatine kinase, and visual analog scale. Gene expression analyses showed decreases in markers of inflammation (interleukin 1β) and muscle atrophy (myostatin) with LEDT. Protein synthesis (mammalian target of rapamycin) and oxidative stress defense (SOD2 [mitochondrial superoxide dismutase]) were up-regulated with LEDT, together with increases in thigh muscle hypertrophy. Conclusions Light-emitting diode therapy can be useful to reduce muscle damage, pain, and atrophy, as

  7. Effectiveness of composite resin polymerization using light-emitting diodes (LEDs) or halogen-based light-curing units

    OpenAIRE

    Micali,Bianca; Basting,Roberta Tarkany

    2004-01-01

    The clinical performance of composite resins is greatly influenced by the quality of the light-curing unit used. The aim of this study was to compare the efficiency of a commercial light-emitting diode (LED) with that of a halogen-based light-curing unit by means of dye penetration of a micro hybrid composite resin. The composite resin evaluated was Filtek Z250 (3M Dental). The composite was filled into acrylic moulds that were randomly polymerized for 40 seconds by each of the light-emitting...

  8. Recent progress in the use of fluorescent and phosphorescent organic compounds for organic light-emitting diode lighting

    Science.gov (United States)

    Jeong, Hyocheol; Shin, Hwangyu; Lee, Jaehyun; Kim, Beomjin; Park, Young-Il; Yook, Kyoung Soo; An, Byeong-Kwan; Park, Jongwook

    2015-01-01

    Organic light-emitting diodes (OLEDs) have attracted considerable attention in both academic and industrial circles. Certain properties of OLEDs make them especially attractive in the lighting market, including area emission characteristics not found in other existing light sources, environmentally friendly efficient use of energy, large area, ultra-light weight, and ultra-thin shape. Fluorescent and phosphorescent materials that are being applied to white OLEDs have been categorized, and the chemical structures and device performances of the important blue, orange, and red light-emitting materials have been summarized. Such a systematic classification and understanding of the materials that have already been reported can aid the development and study of new light-emitting materials through quantitative and qualitative approaches.

  9. Clinical comparison between the bleaching efficacy of light-emitting diode and diode laser with sodium perborate.

    Science.gov (United States)

    Koçak, Sibel; Koçak, Mustafa Murat; Sağlam, Baran Can

    2014-04-01

    The aim of this clinical study was to test the efficacy of a light-emitting diode (LED) light and a diode laser, when bleaching with sodium perborate. Thirty volunteers were selected to participate in the study. The patients were randomly divided into two groups. The initial colour of each tooth to be bleached was quantified with a spectrophotometer. In group A, sodium perborate and distilled water were mixed and placed into the pulp chamber, and the LED light was source applied. In group B, the same mixture was used, and the 810 nm diode laser was applied. The final colour of each tooth was quantified with the same spectrophotometer. Initial and final spectrophotometer values were recorded. Mann-Whitney U-test and Wicoxon tests were used to test differences between both groups. Both devices successfully whitened the teeth. No statistical difference was found between the efficacy of the LED light and the diode laser. © 2013 The Authors. Australian Endodontic Journal © 2013 Australian Society of Endodontology.

  10. Effect of multi-wavelength irradiation on color characterization with light-emitting diodes (LEDs)

    Science.gov (United States)

    Park, Hyeong Ju; Song, Woosub; Lee, Byeong-Il; Kim, Hyejin; Kang, Hyun Wook

    2017-06-01

    In the current study, a multi-wavelength light-emitting diode (LED)-integrated CMOS imaging device was developed to investigate the effect of various wavelengths on multiple color characterization. Various color pigments (black, red, green, and blue) were applied on both white paper and skin phantom surfaces for quantitative analysis. The artificial skin phantoms were made of polydimethylsiloxane (PDMS) mixed with coffee and TiO2 powder to emulate the optical properties of the human dermis. The customized LED-integrated imaging device acquired images of the applied pigments by sequentially irradiating with the LED lights in the order of white, red, green, and blue. Each color pigment induced a lower contrast during illumination by the light with the equivalent color. However, the illumination by light with the complementary (opposite) color increased the signal-to-noise ratio by up to 11-fold due to the formation of a strong contrast ( i.e., red LED = 1.6 ± 0.3 vs. green LED = 19.0 ± 0.6 for red pigment). Detection of color pigments in conjunction with multi-wavelength LEDs can be a simple and reliable technique to estimate variations in the color pigments quantitatively.

  11. Ghost Spectroscopy with Classical Thermal Light Emitted by a Superluminescent Diode

    Science.gov (United States)

    Janassek, Patrick; Blumenstein, Sébastien; Elsäßer, Wolfgang

    2018-02-01

    We propose and realize the first classical ghost-imaging (GI) experiment in the frequency or wavelength domain, thus performing ghost spectroscopy using thermal light exhibiting photon bunching. The required wavelength correlations are provided by light emitted by spectrally broadband near-infrared amplified spontaneous emission of a semiconductor-based superluminescent diode. They are characterized by wavelength-resolved intensity cross-correlation measurements utilizing two-photon-absorption interferometry. Finally, a real-world spectroscopic application of this ghost spectroscopy with a classical light scheme is demonstrated in which an absorption band of trichloromethane (chloroform) at 1214 nm is reconstructed with a spectral resolution of 10 nm as a proof-of-principle experiment. This ghost-spectroscopy work fills the gap of a hitherto missing analogy between the spatial and the spectral domain in classical GI modalities, with the expectation of contributing towards a broader dissemination of correlated photon ghost modalities, hence paving the way towards more applications which exploit the favorable advantages.

  12. Aluminum nitride nanowire light emitting diodes: Breaking the fundamental bottleneck of deep ultraviolet light sources.

    Science.gov (United States)

    Zhao, S; Connie, A T; Dastjerdi, M H T; Kong, X H; Wang, Q; Djavid, M; Sadaf, S; Liu, X D; Shih, I; Guo, H; Mi, Z

    2015-02-16

    Despite broad interest in aluminum gallium nitride (AlGaN) optoelectronic devices for deep ultraviolet (DUV) applications, the performance of conventional Al(Ga)N planar devices drastically decays when approaching the AlN end, including low internal quantum efficiencies (IQEs) and high device operation voltages. Here we show that these challenges can be addressed by utilizing nitrogen (N) polar Al(Ga)N nanowires grown directly on Si substrate. By carefully tuning the synthesis conditions, a record IQE of 80% can be realized with N-polar AlN nanowires, which is nearly ten times higher compared to high quality planar AlN. The first 210 nm emitting AlN nanowire light emitting diodes (LEDs) were achieved, with a turn on voltage of about 6 V, which is significantly lower than the commonly observed 20 - 40 V. This can be ascribed to both efficient Mg doping by controlling the nanowire growth rate and N-polarity induced internal electrical field that favors hole injection. In the end, high performance N-polar AlGaN nanowire LEDs with emission wavelengths covering the UV-B/C bands were also demonstrated.

  13. Nanopatterned aluminum nitride template for high efficiency light-emitting diodes.

    Science.gov (United States)

    Kim, Sang-Mook; Park, Tae-Young; Park, Seong-Ju; Lee, Seung-Jae; Baek, Jong Hyeob; Park, Yun Chang; Jung, Gun Young

    2009-08-17

    Nanopatterned aluminum nitride (NP-AlN) templates were used to enhance the light extraction efficiency of the light-emitting diodes (LEDs). Here, the NP-AlN interlayer between the sapphire substrate and GaN-based LED was used as an effective light outcoupling layer at the direction of bottom side and as a buffer layer for growth of GaN LEDs. The cross-sectional transmission electron microscopy (TEM) analysis showed that the formation of stacking faults and voids could help reduce the threading dislocations. Micro Raman spectra also revealed that the GaN-based epilayer grown on the NP-AlN template had smaller residual stress than that grown on a planar sapphire substrate. The normalized electroluminescence (EL) spectra at the top and bottom sides of device revealed that the enhancement of the bottom side emission of the LED with the NP-AlN interlayer was more notable than a planar sapphire substrate due to the graded-refractive-index (GRIN) effect of the NP-AlN. (c) 2009 Optical Society of America

  14. Bactericidal effects of deep ultraviolet light-emitting diode for solutions during intravenous infusion.

    Science.gov (United States)

    Omotani, Sachiko; Tani, Katsuji; Aoe, Mai; Esaki, Seiji; Nagai, Katsuhito; Hatsuda, Yasutoshi; Mukai, Junji; Teramachi, Hitomi; Myotoku, Michiaki

    2018-01-01

    Background: Ultraviolet irradiation is effectively used as a disinfection method for inactivating microorganisms. Methods: We investigated the bactericidal effects by irradiation with a deep-ultraviolet light-emitting diode (DUV-LED) on the causative microorganisms of catheter related blood stream infection contaminating the solution for intravenous infusion. For irradiation, prototype modules for water disinfection with a DUV-LED were used. Experiments were conducted on five kinds of microorganisms. We examined the dependence of bactericidal action on eleven solutions. Administration sets were carried out three types. Results: When the administration set JY-PB343L containing the infusion tube made of polybutadiene was used, the bactericidal action of the DUV-LED against all tested microorganisms in the physiological saline solutions was considered to be effective. We confirmed that the number of viable bacteria decreased in 5% glucose solution and electrolyte infusions with DUV-LED irradiation. Conclusions: These results indicate that the DUV-LED irradiation has bactericidal effects in glucose infusion and electrolyte infusions by irradiating via a plasticizer-free polybutadiene administration set. We consider DUV-LED irradiation to be clinically applicable.

  15. Frustrated total internal reflection in organic light-emitting diodes employing sphere cavity embedded in polystyrene

    International Nuclear Information System (INIS)

    Zhu, Peifen

    2016-01-01

    The light extraction efficiency of top-emitting organic light-emitting diodes (OLEDs) is numerically investigated employing the finite-difference time-domain method. The periodic nanostructures formed by embedding the sphere arrays in polystyrene (PS) are placed on top of OLED to frustrate the total internal reflection at the interface between OLED and free space. These nanostructures serve as an intermediate medium to extract the light out of OLED devices. Efficiently coupling both evanescent waves and propagation waves into spheres and subsequently extracting these light waves out of the sphere is key to achieving high extraction efficiency. By tuning the thickness of PS layer, both of the in-coupling efficiency and out-coupling efficiency are optimized for achieving high light extraction efficiency. Thicker PS layer results in higher in-coupling efficiency in sphere while the thinner PS layer leads to higher out-coupling efficiency. Thus the maximum light extraction is a trade-off between the in-coupling efficiency and out-coupling efficiency. The study shows that light extraction efficiency of 89% can be achieved by embedding 0.90 μm TiO 2 sphere in 0.30 μm PS layer with optimized in-coupling efficiency, out-coupling efficiency and cavity effect. (paper)

  16. Recycled Thermal Energy from High Power Light Emitting Diode Light Source.

    Science.gov (United States)

    Ji, Jae-Hoon; Jo, GaeHun; Ha, Jae-Geun; Koo, Sang-Mo; Kamiko, Masao; Hong, JunHee; Koh, Jung-Hyuk

    2018-09-01

    In this research, the recycled electrical energy from wasted thermal energy in high power Light Emitting Diode (LED) system will be investigated. The luminous efficiency of lights has been improved in recent years by employing the high power LED system, therefore energy efficiency was improved compared with that of typical lighting sources. To increase energy efficiency of high power LED system further, wasted thermal energy should be re-considered. Therefore, wasted thermal energy was collected and re-used them as electrical energy. The increased electrical efficiency of high power LED devices was accomplished by considering the recycled heat energy, which is wasted thermal energy from the LED. In this work, increased electrical efficiency will be considered and investigated by employing the high power LED system, which has high thermal loss during the operating time. For this research, well designed thermoelement with heat radiation system was employed to enhance the collecting thermal energy from the LED system, and then convert it as recycled electrical energy.

  17. Light-emitting diode and laser fluorescence-based devices in detecting occlusal caries

    Science.gov (United States)

    Rodrigues, Jonas A.; Hug, Isabel; Neuhaus, Klaus W.; Lussi, Adrian

    2011-10-01

    The aim of this study was to assess the performance of two light-emitting diode (LED)- and two laser fluorescence-based devices in detecting occlusal caries in vitro. Ninety-seven permanent molars were assessed twice by two examiners using two LED- (Midwest Caries - MID and VistaProof - VP) and two laser fluorescence-based (DIAGNOdent 2095 - LF and DIAGNOdent pen 2190 - LFpen) devices. After measuring, the teeth were histologically prepared and classified according to lesion extension. At D1 the specificities were 0.76 (LF and LFpen), 0.94 (MID), and 0.70 (VP); the sensitivities were 0.70 (LF), 0.62 (LFpen), 0.31 (MID), and 0.75 (VP). At D3 threshold the specificities were 0.88 (LF), 0.87 (LFpen), 0.90 (MID), and 0.70 (VP); the sensitivities were 0.63 (LF and LFpen), 0.70 (MID), and 0.96 (VP). Spearman's rank correlations with histology were 0.56 (LF), 0.51 (LFpen), 0.55 (MID), and 0.58 (VP). Inter- and intraexaminer ICC values were high and varied from 0.83 to 0.90. Both LF devices seemed to be useful auxiliary tools to the conventional methods, presenting good reproducibility and better accuracy at D3 threshold. MID was not able to differentiate sound surfaces from enamel caries and VP still needs improvement on the cut-off limits for its use.

  18. Candlelight style organic light-emitting diode: a plausibly human-friendly safe night light

    Science.gov (United States)

    Jou, Jwo-Huei; Hsieh, Chun-Yu; Chen, Po-Wei; Kumar, Sudhir; Hong, James H.

    2014-01-01

    Candles emit sensationally warm light with a very low color temperature, comparatively most suitable for use at night. In response to the need for such a human-friendly night light, we demonstrate the employment of a high number of candlelight complementary organic emitters to generate and mimic candlelight based on organic light emitting diode (OLED). One resultant candlelight style OLED shows a very-high color rendering index (CRI), with an efficacy at least 300 times that of a candle or at least two times that of an incandescent bulb. The device can be fabricated, for example, by using four candlelight complementary emitters: red, yellow, green, and sky-blue phosphorescent dyes. These dyes, in the present system, can be vacuum deposited into two emission layers that are separated by a nanolayer of carrier modulation material that is used to maximize very high CRI and energy efficiency. A nano carrier modulation layer also played a significant role in maintaining the low blue emission and high-red emission, the low color temperature of device was obtained. Importantly, a romantic sensation giving and supposedly physiologically friendly candlelight style emission can hence be driven by electricity in lieu of hydrocarbon burning and greenhouse gas-releasing candles that were invented 5000 years ago.

  19. Assessing the therapeutic effect of 625-nm light-emitting diodes

    Science.gov (United States)

    Mao, Zongzhen; Xu, Guodong; Yang, Yi

    2014-09-01

    To evaluate the effects of red Light-Emitting Diodes on elbow extensor and flexor strength and the recovery of exercise induced fatigue, the torque values from the isokinetic dynamometer as well as biochemistry parameters were used as outcome measures. A randomized double-blind placebo-controlled crossover trial was performed with twenty male young tennis athletes. Active LED therapy (LEDT, with wavelength 625nm, 10 minutes total irradiation time, irradiated area amount to 30cm2, and 900J of total energy irradiated) or an identical placebo was delivered under double-blinded conditions to the left elbow just before exercise. The isokinetic muscle strength was measured immediately after irradiation. The blood lactate levels were sampled pre-exercise and post-exercise. The peak torque values of elbow extensor strength were significantly different between two groups. As in elbow flexor strength, the difference of peak torque was not significant. The blood lactate concentration of LEDT group post-exercise was significantly lower than those of placebo group. The results indicate that 625nm LED therapy is effective in preventing muscle fatigue as it can significantly reduce peak torque value of elbow extensors and blood lactate concentration. It has no effect on the strength of left elbow flexor or backhand performance in tennis.

  20. Enhanced efficiency in single-host white organic light-emitting diode by triplet exciton conversion

    International Nuclear Information System (INIS)

    Wu, Qingyang; Zhang, Shiming; Yue, Shouzhen; Zhang, Zhensong; Xie, Guohua; Zhao, Yi; Liu, Shiyong

    2013-01-01

    The authors observe that the external quantum efficiency (EQE) of the Iridium (III) bis(4-phenylthieno [3,2-c]pyridinato-N,C 2′ )acetylacetonate (PO-01) based yellow organic light-emitting diode (OLED) is significantly increased by uniformly co-doping Iridium (III)bis[(4,6-difluorophenyl)-pyridinato-N,C 2− ] (FIrpic) and PO-01 into the same wide band-gap host of N,N ′ -dicarbazolyl-3, 5-benzene (mCP). Detailed investigation indicates that the efficiency enhancement is ascribed to effective triplet exciton gathering by FIrpic, followed by energy transfer to PO-01. Compared to the control device, which has maximum EQE of 10.5%, an improved maximum EQE of 13.2% is obtained in the optimization white device based on FIrpic and PO-01 emission according to this principle. This work makes it easier for a single host white OLED to simultaneously harvest high efficiency in both blue and yellow units. Comprehensive experimental results show that this phenomenon can also be found and utilized in other popular hosts to realize more efficient white devices. -- Highlights: • This work makes easier for a single host white OLED to harvest high efficiency in both blue and yellow units. • Efficiency enhancement is ascribed to effective triplet exciton gathering by FIrpic, followed by energy transfer to PO-01. • This phenomenon can also be found and utilized in other popular hosts to realize more efficient white devices

  1. Multicolor fluorescent light-emitting diodes based on cesium lead halide perovskite quantum dots

    International Nuclear Information System (INIS)

    Wang, Peng; Bai, Xue; Sun, Chun; Zhang, Xiaoyu; Zhang, Yu; Zhang, Tieqiang

    2016-01-01

    High quantum yield, narrow full width at half-maximum and tunable emission color of perovskite quantum dots (QDs) make this kind of material good prospects for light-emitting diodes (LEDs). However, the relatively poor stability under high temperature and air condition limits the device performance. To overcome this issue, the liquid-type packaging structure in combination with blue LED chip was employed to fabricate the fluorescent perovskite quantum dot-based LEDs. A variety of monochromatic LEDs with green, yellow, reddish-orange, and red emission were fabricated by utilizing the inorganic cesium lead halide perovskite quantum dots as the color-conversion layer, which exhibited the narrow full width at half-maximum (<35 nm), the relatively high luminous efficiency (reaching 75.5 lm/W), and the relatively high external quantum efficiency (14.6%), making it the best-performing perovskite LEDs so far. Compared to the solid state LED device, the liquid-type LED devices exhibited excellent color stability against the various working currents. Furthermore, we demonstrated the potential prospects of all-inorganic perovskite QDs for the liquid-type warm white LEDs.

  2. Phosphor-Free InGaN White Light Emitting Diodes Using Flip-Chip Technology

    Directory of Open Access Journals (Sweden)

    Ying-Chang Li

    2017-04-01

    Full Text Available Monolithic phosphor-free two-color gallium nitride (GaN-based white light emitting diodes (LED have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN/GaN quantum dot and reported LED’s color rendering index (CRI are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL and electroluminescence (EL spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications.

  3. Vacuum-free transparent quantum dot light-emitting diodes with silver nanowire cathode.

    Science.gov (United States)

    Jing, Pengtao; Ji, Wenyu; Zeng, Qinghui; Li, Di; Qu, Songnan; Wang, Jia; Zhang, Dandan

    2015-07-22

    Efficient transparent quantum-dot light emitting diodes (QD-LEDs) are demonstrated by using a silver nanowire (AgNW) cathode. The devices are fabricated through a solution technique, not any vacuum processes are involved. Almost identical performance is obtained for both sides of the transparent device, which is primary due to the high transmittance of AgNW cathode. The maximum luminance (efficiency) for ITO and AgNW side is 25,040 cd/m(2) (5.6 cd/A) and 23,440 cd/m(2) (5.2 cd/A), respectively. The average specular transmittance of the device (involving the glass substrate) is over 60% in the visible range. This study indicates that AgNW electrodes can serve as a cost-effective, flexible alternative to ITO, and thereby improve the economic viability and mechanical stability of QD-LEDs. All the results suggest that this is an important progress toward producing transparent QD-LEDs based displays and lighting sources.

  4. Polychromatic light-emitting diodes with a fluorescent nanosphere opal coating

    International Nuclear Information System (INIS)

    Hui, K N; Fu, W Y; Ng, W N; Leung, C H; Lai, P T; Wong, K K Y; Choi, H W

    2008-01-01

    A hexagonally close-packed array consisting of fluorescent nanospheres was coated onto short-wavelength GaN light-emitting diodes to demonstrate polychromatic white light emission. The spherical particles self-assemble into ordered three-dimensional opal structures, performing the role of color conversion to generate a polychromatic spectrum with smooth and uniform emission patterns. Different ratios of green and orange-red fluorescent nanospheres were mixed and coated onto high-extraction-efficiency micro-LEDs. Four devices with different shades of white emission were demonstrated. Device A, with a high content of orange-red nanospheres, offers the highest CRI value of 80, whereas device C with a well-balanced ratio of green and orange-red nanospheres exhibits color characteristics closest to ideal white with CIE coordinate at (0.34, 0.34). At 20 mA driving current, the luminous efficacy of the devices A, B, C, and D are 40.5 lm W -1 , 57.7 lm W -1 , 63.1 lm W -1 , and 67.2 lm W -1 respectively, while the correlated color temperatures (CCTs) of the corresponding devices are 3587, 4778, 5271, and 13 000 K

  5. Degradation effects of the active region in UV-C light-emitting diodes

    Science.gov (United States)

    Glaab, Johannes; Haefke, Joscha; Ruschel, Jan; Brendel, Moritz; Rass, Jens; Kolbe, Tim; Knauer, Arne; Weyers, Markus; Einfeldt, Sven; Guttmann, Martin; Kuhn, Christian; Enslin, Johannes; Wernicke, Tim; Kneissl, Michael

    2018-03-01

    An extensive analysis of the degradation characteristics of AlGaN-based ultraviolet light-emitting diodes emitting around 265 nm is presented. The optical power of LEDs stressed at a constant dc current of 100 mA (current density = 67 A/cm2 and heatsink temperature = 20 °C) decreased to about 58% of its initial value after 250 h of operation. The origin of this degradation effect has been studied using capacitance-voltage and photocurrent spectroscopy measurements conducted before and after aging. The overall device capacitance decreased, which indicates a reduction of the net charges within the space-charge region of the pn-junction during operation. In parallel, the photocurrent at excitation energies between 3.8 eV and 4.5 eV and the photocurrent induced by band-to-band absorption in the quantum barriers at 5.25 eV increased during operation. The latter effect can be explained by a reduction of the donor concentration in the active region of the device. This effect could be attributed to the compensation of donors by the activation or diffusion of acceptors, such as magnesium dopants or group-III vacancies, in the pn-junction space-charge region. The results are consistent with the observed reduction in optical power since deep level acceptors can also act as non-radiative recombination centers.

  6. Ultraviolet Laser SQUID Microscope for GaN Blue Light Emitting Diode Testing

    International Nuclear Information System (INIS)

    Daibo, M; Kamiwano, D; Kurosawa, T; Yoshizawa, M; Tayama, N

    2006-01-01

    We carried out non-contacting measurements of photocurrent distributions in GaN blue light emitting diode (LED) chips using our newly developed ultraviolet (UV) laser SQUID microscope. The UV light generates the photocurrent, and then the photocurrent induces small magnetic fields around the chip. An off-axis arranged HTS-SQUID magnetometer is employed to detect a vector magnetic field whose typical amplitude is several hundred femto-tesla. Generally, it is difficult to obtain Ohmic contacts for p-type GaN because of the low hole concentration in the p-type epitaxial layer and the lack of any available metal with a higher work function compared with the p-type GaN. Therefore, a traditional probecontacted electrical test is difficult to conduct for wide band gap semiconductors without an adequately annealed electrode. Using the UV-laser SQUID microscope, the photocurrent can be measured without any electrical contact. We show the photocurrent vector map which was reconstructed from measured magnetic fields data. We also demonstrate how we found the position of a defect of the electrical short circuits in the LED chip

  7. Efficiency of solution-processed multilayer polymer light-emitting diodes using charge blocking layers

    Science.gov (United States)

    Kasparek, Christian; Rörich, Irina; Blom, Paul W. M.; Wetzelaer, Gert-Jan A. H.

    2018-01-01

    By blending semiconducting polymers with the cross-linkable matrix ethoxylated-(4)-bisphenol-a-dimethacrylate (SR540), an insoluble layer is acquired after UV-illumination. Following this approach, a trilayer polymer light-emitting diode (PLED) consisting of a blend of poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (poly-TPD) and SR540 as an electron-blocking layer, Super Yellow-Poly(p-phenylene vinylene) (SY-PPV) blended with SR540 as an emissive layer, and poly(9,9-di-n-octylfluorenyl-2,7-diyl) as a hole-blocking layer is fabricated from solution. The trilayer PLED shows a 23% increase in efficiency at low voltage as compared to a single layer SY-PPV PLED. However, at higher voltage, the advantage in current efficiency gradually decreases. A combined experimental and modelling study shows that the increased efficiency is not only due to the elimination of exciton quenching at the electrodes but also due to suppressed nonradiative trap-assisted recombination due to carrier confinement. At high voltages, holes can overcome the hole-blocking barrier, which explains the efficiency roll-off.

  8. Enhancing Carrier Injection Using Graded Superlattice Electron Blocking Layer for UVB Light-Emitting Diodes

    KAUST Repository

    Janjua, Bilal

    2014-12-01

    We have studied enhanced carrier injection by having an electron blocking layer (EBL) based on a graded superlattice (SL) design. Here, we examine, using a selfconsistent 6 × 6 k.p method, the energy band alignment diagrams under equilibrium and forward bias conditions while also considering carrier distribution and recombination rates (Shockley-Read-Hall, Auger, and radiative recombination rates). The graded SL is based on AlxGa1-xN (larger bandgap) Al0:5Ga0:5N (smaller bandgap) SL, where x is changed from 0.8 to 0.56 in steps of 0.06. Graded SL was found to be effective in reducing electron leakage and enhancing hole injection into the active region. Due to our band engineering scheme for EBL, four orders-of-magnitude enhancement were observed in the direct recombination rate, as compared with the conventional bulk EBL consisting of Al0:8Ga0:2N. An increase in the spatial overlap of carrier wavefunction was obtained due to polarization-induced band bending in the active region. An efficient single quantum-well ultraviolet-B light-emitting diode was designed, which emits at 280 nm. This is the effective wavelength for water disinfection application, among others.

  9. Flexible organic light emitting diodes fabricated on biocompatible silk fibroin substrate

    International Nuclear Information System (INIS)

    Liu, Yuqiang; Xie, Yuemin; Liu, Yuan; Song, Tao; Liao, Liangsheng; Sun, Baoquan; Zhang, Ke-Qin

    2015-01-01

    Flexible and biodegradable electronics are currently under extensive investigation for biocompatible and environmentally-friendly applications. Synthetic plastic foils are widely used as substrates for flexible electronics. But typical plastic substrates such as polyethylene naphthalate (PEN) could not be degraded in a natural bio-environment. A great demand still exists for a next-generation biocompatible and biodegradable substrate for future application. For example, electronic devices can be potentially integrated into the human body. In this work, we demonstrate that the biocompatible and biodegradable natural silk fibroin (SF) films embedded with silver nanowires (AgNWs) mesh could be employed as conductive transparent substrates to fabricate flexible organic light emitting diodes (OLEDs). Compared with commercial PEN substrates coated with indium tin oxide, the AgNWs/SF composite substrates exhibit a similar sheet resistance of 12 Ω sq −1 , a lower surface roughness, as well as a broader light transmission range. Flexible OLEDs based on AgNWs/SF substrates achieve a current efficiency of 19 cd A −1 , demonstrating the potential of the flexible AgNWs/SF films as conductive and transparent substrates for next-generation biodegradable devices. (paper)

  10. Transparent conductive oxide films embedded with plasmonic nanostructure for light-emitting diode applications.

    Science.gov (United States)

    Chuang, Shih-Hao; Tsung, Cheng-Sheng; Chen, Ching-Ho; Ou, Sin-Liang; Horng, Ray-Hua; Lin, Cheng-Yi; Wuu, Dong-Sing

    2015-02-04

    In this study, a spin coating process in which the grating structure comprises an Ag nanoparticle layer coated on a p-GaN top layer of InGaN/GaN light-emitting diode (LED) was developed. Various sizes of plasmonic nanoparticles embedded in a transparent conductive layer were clearly observed after the deposition of indium tin oxide (ITO). The plasmonic nanostructure enhanced the light extraction efficiency of blue LED. Output power was 1.8 times the magnitude of that of conventional LEDs operating at 350 mA, but retained nearly the same current-voltage characteristic. Unlike in previous research on surface-plasmon-enhanced LEDs, the metallic nanoparticles were consistently deposited over the surface area. However, according to microstructural observation, ITO layer mixed with Ag-based nanoparticles was distributed at a distance of approximately 150 nm from the interface of ITO/p-GaN. Device performance can be improved substantially by using the three-dimensional distribution of Ag-based nanoparticles in the transparent conductive layer, which scatters the propagating light randomly and is coupled between the localized surface plasmon and incident light internally trapped in the LED structure through total internal reflection.

  11. Temperature rise induced by some light emitting diode and quartz-tungsten-halogen curing units.

    Science.gov (United States)

    Asmussen, Erik; Peutzfeldt, Anne

    2005-02-01

    Because of the risk of thermal damage to the pulp, the temperature rise induced by light-curing units should not be too high. LED (light emitting diode) curing units have the main part of their irradiation in the blue range and have been reported to generate less heat than QTH (quartz-tungsten-halogen) curing units. This study had two aims: first, to measure the temperature rise induced by ten LED and three QTH curing units; and, second, to relate the measured temperature rise to the power density of the curing units. The light-induced temperature rise was measured by means of a thermocouple embedded in a small cylinder of resin composite. The power density was measured by using a dental radiometer. For LED units, the temperature rise increased with increasing power density, in a statistically significant manner. Two of the three QTH curing units investigated resulted in a higher temperature rise than LED curing units of the same power density. Previous findings, that LED curing units induce less temperature rise than QTH units, does not hold true in general.

  12. Spectral matching research for light-emitting diode-based neonatal jaundice therapeutic device light source

    Science.gov (United States)

    Gan, Ruting; Guo, Zhenning; Lin, Jieben

    2015-09-01

    To decrease the risk of bilirubin encephalopathy and minimize the need for exchange transfusions, we report a novel design for light source of light-emitting diode (LED)-based neonatal jaundice therapeutic device (NJTD). The bilirubin absorption spectrum in vivo was regarded as target. Based on spectral constructing theory, we used commercially available LEDs with different peak wavelengths and full width at half maximum as matching light sources. Simple genetic algorithm was first proposed as the spectral matching method. The required LEDs number at each peak wavelength was calculated, and then, the commercial light source sample model of the device was fabricated to confirm the spectral matching technology. In addition, the corresponding spectrum was measured and the effect was analyzed finally. The results showed that fitted spectrum was very similar to the target spectrum with 98.86 % matching degree, and the actual device model has a spectrum close to the target with 96.02 % matching degree. With higher fitting degree and efficiency, this matching algorithm is very suitable for light source matching technology of LED-based spectral distribution, and bilirubin absorption spectrum in vivo will be auspicious candidate for the target spectrum of new LED-based NJTD light source.

  13. AZO/Ag/AZO anode for resonant cavity red, blue, and yellow organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Gentle, A. R., E-mail: angus.gentle@uts.edu.au; Smith, G. B. [School of Mathematical and Physical Sciences and Institute of Nanoscale Technology, University of Technology Sydney, P.O. Box 123, Broadway, New South Wales 2007 (Australia); Yambem, S. D.; Burn, P. L.; Meredith, P. [Centre for Organic Photonics and Electronics, School of Chemistry and Molecular Biosciences and School of Mathematics and Physics, The University of Queensland, St Lucia, Queensland 4072 (Australia)

    2016-06-28

    Indium tin oxide (ITO) is the transparent electrode of choice for organic light-emitting diodes (OLEDs). Replacing ITO for cost and performance reasons is a major drive across optoelectronics. In this work, we show that changing the transparent electrode on red, blue, and yellow OLEDs from ITO to a multilayer buffered aluminium zinc oxide/silver/aluminium zinc oxide (AZO/Ag/AZO) substantially enhances total output intensity, with better control of colour, its constancy, and intensity over the full exit hemisphere. The thin Ag containing layer induces a resonant cavity optical response of the complete device. This is tuned to the emission spectra of the emissive material while minimizing internally trapped light. A complete set of spectral intensity data is presented across the full exit hemisphere for each electrode type and each OLED colour. Emission zone modelling of output spectra at a wide range of exit angles to the normal was in excellent agreement with the experimental data and hence could, in principle, be used to check and adjust production settings. These multilayer transparent electrodes show significant potential for both eliminating indium from OLEDs and spectrally shaping the emission.

  14. Improvement in Device Performance and Reliability of Organic Light-Emitting Diodes through Deposition Rate Control

    Directory of Open Access Journals (Sweden)

    Shun-Wei Liu

    2014-01-01

    Full Text Available We demonstrated a fabrication technique to reduce the driving voltage, increase the current efficiency, and extend the operating lifetime of an organic light-emitting diode (OLED by simply controlling the deposition rate of bis(10-hydroxybenzo[h]qinolinato beryllium (Bebq2 used as the emitting layer and the electron-transport layer. In our optimized device, 55 nm of Bebq2 was first deposited at a faster deposition rate of 1.3 nm/s, followed by the deposition of a thin Bebq2 (5 nm layer at a slower rate of 0.03 nm/s. The Bebq2 layer with the faster deposition rate exhibited higher photoluminescence efficiency and was suitable for use in light emission. The thin Bebq2 layer with the slower deposition rate was used to modify the interface between the Bebq2 and cathode and hence improve the injection efficiency and lower the driving voltage. The operating lifetime of such a two-step deposition OLED was 1.92 and 4.6 times longer than that of devices with a single deposition rate, that is, 1.3 and 0.03 nm/s cases, respectively.

  15. Nozzle Printed-PEDOT:PSS for Organic Light Emitting Diodes with Various Dilution Rates of Ethanol

    Directory of Open Access Journals (Sweden)

    Dai Geon Yoon

    2018-01-01

    Full Text Available In this study, we investigated the ink formulation of poly(3,4-ethylenedioxythiophene polystyrene sulfonate (PEDOT:PSS as the hole injection layer (HIL in an organic light emitting diode (OLED structure. Generally, in a PEDOT:PSS solution, water is incorporated in the solution for the solution process. However, the fabrication of thin film which contained the water, main solvent, could not easily form by using printing technology except spin-coating process because of the high surface tension of water. On the other hand, mixing PEDOT:PSS solution and ethanol (EtOH, a dilution solvent, could restrain the non-uniform layer that forms by the high surface tension and low volatility of water. Therefore, we printed a PEDOT:PSS solution with various concentrations of EtOH by using a nozzle printer and obtained a uniform pattern. The line width of PEDOT:PSS diluted with 90% (volume ratio ehtanol was measured as about 4 mm with good uniformity with a 0.1 mm nozzle. Also, imaging software and a scanning electron microscope (SEM were used to measure the uniformity of PEDOT:PSS coated on a substrate. Finally, we fabricated a green phosphorescent OLED device with printed-PEDOT:PSS with specific concentrations of EtOH and we achieved a current efficiency of 27 cd/A with uniform quality of luminance in the case of device containing 90% EtOH.

  16. Solution processed organic light-emitting diodes using the plasma cross-linking technology

    Energy Technology Data Exchange (ETDEWEB)

    He, Kongduo [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Liu, Yang [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433 (China); Gong, Junyi; Zeng, Pan; Kong, Xun; Yang, Xilu; Yang, Cheng; Yu, Yan [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Liang, Rongqing [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433 (China); Ou, Qiongrong, E-mail: qrou@fudan.edu.cn [Department of Light Sources and Illuminating Engineering, Fudan University, Shanghai 200433 (China); Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Shanghai 200433 (China)

    2016-09-30

    Highlights: • Mixed acetylene and Ar plasma treatment makes the organic film surface cross-linked. • The plasma treatment for 30 s does not affect the performance of OLEDs. • Cross-linking surface can resist rinsing and corrosion of organic solvent. • The surface morphology is nearly unchanged after plasma treatment. • The plasma cross-linking method can realize solution processed multilayer OLEDs. - Abstract: Solution processed multilayer organic light-emitting diodes (OLEDs) present challenges, especially regarding dissolution of the first layer during deposition of a second layer. In this work, we first demonstrated a plasma cross-linking technology to produce a solution processed OLED. The surfaces of organic films can be cross-linked after mixed acetylene and Ar plasma treatment for several tens of seconds and resist corrosion of organic solvent. The film thickness and surface morphology of emissive layers (EMLs) with plasma treatment and subsequently spin-rinsed with chlorobenzene are nearly unchanged. The solution processed triple-layer OLED is successfully fabricated and the current efficiency increases 50% than that of the double-layer OLED. Fluorescent characteristics of EMLs are also observed to investigate factors influencing the efficiency of the triple-layer OLED. Plasma cross-linking technology may open up a new pathway towards fabrication of all-solution processed multilayer OLEDs and other soft electronic devices.

  17. Photovoltaic effect on the performance enhancement of organic light-emitting diodes with planar heterojunction architecture

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Dan; Huang, Wei; Guo, Hao [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054 (China); Wang, Hua, E-mail: wanghua001@tyut.edu.cn [Research Center of Advanced Materials Science and Technology, Taiyuan University of Technology (TYUT), Taiyuan 030024 (China); Yu, Junsheng, E-mail: jsyu@uestc.edu.cn [State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, University of Electronic Science and Technology of China (UESTC), Chengdu 610054 (China)

    2017-04-15

    Highlights: • The photovoltaic effect on the performance of OLEDs was studied. • The device performance with different planar heterojunctions was investigated. • The mechanism relies on the overlap of electroluminescence and absorption spectrum. - Abstract: Organic light-emitting diodes (OLEDs) with planar heterojunction (PHJ) architecture consisting of photovoltaic organic materials of fullerene carbon 60 (C{sub 60}) and copper (II) phthalocyanine (CuPc) inserted between emitting unit and cathode were constructed, and the photovoltaic effect on OLEDs performance was studied. The electroluminescent (EL) characteristics and mechanism of device performance variation without and with different PHJs (herein including C{sub 60}/CuPc, CuPc/C{sub 60} and CuPc) were systematically investigated in red, green and blue OLEDs. Of the three combinations, OLEDs with C{sub 60}/CuPc showed the highest efficiency. It is revealed that the photovoltaic C{sub 60}/CuPc PHJ can absorb part of photons, which are radiated from emission zone, then form excitons, and dissociated into free charges. Consequently, the high device efficiency of OLEDs performance improvement was acquired. This research demonstrates that PHJ consisting of two n- and p-type photovoltaic organic materials could be a promising methodology for high performance OLEDs.

  18. Synergetic electrode architecture for efficient graphene-based flexible organic light-emitting diodes.

    Science.gov (United States)

    Lee, Jaeho; Han, Tae-Hee; Park, Min-Ho; Jung, Dae Yool; Seo, Jeongmin; Seo, Hong-Kyu; Cho, Hyunsu; Kim, Eunhye; Chung, Jin; Choi, Sung-Yool; Kim, Taek-Soo; Lee, Tae-Woo; Yoo, Seunghyup

    2016-06-02

    Graphene-based organic light-emitting diodes (OLEDs) have recently emerged as a key element essential in next-generation displays and lighting, mainly due to their promise for highly flexible light sources. However, their efficiency has been, at best, similar to that of conventional, indium tin oxide-based counterparts. We here propose an ideal electrode structure based on a synergetic interplay of high-index TiO2 layers and low-index hole-injection layers sandwiching graphene electrodes, which results in an ideal situation where enhancement by cavity resonance is maximized yet loss to surface plasmon polariton is mitigated. The proposed approach leads to OLEDs exhibiting ultrahigh external quantum efficiency of 40.8 and 62.1% (64.7 and 103% with a half-ball lens) for single- and multi-junction devices, respectively. The OLEDs made on plastics with those electrodes are repeatedly bendable at a radius of 2.3 mm, partly due to the TiO2 layers withstanding flexural strain up to 4% via crack-deflection toughening.

  19. Effect of molecular properties on the performance of polymer light-emitting diodes

    International Nuclear Information System (INIS)

    Ramos, Marta M.D.; Almeida, A.M.; Correia, Helena M.G.; Ribeiro, R. Mendes; Stoneham, A.M.

    2004-01-01

    The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations, we follow the charge evolution in time from some initial state to the steady state. The intra-molecular properties of the polymer molecules obtained from self-consistent quantum molecular dynamics calculations are used in the mesoscopic model. The purpose of the present work is to clarify the effects of intra-molecular charge mobility and energy disorder on recombination efficiency. In particular, we find that charge mobility along the polymer chains has a serious influence on recombination within the polymer layer. Our results also show that energy disorder due to differences in ionization potential and electron affinity of neighbouring molecules affects mainly recombinations that occur near the electrodes at polymer chains parallel to them

  20. Green-light supplementation for enhanced lettuce growth under red- and blue-light-emitting diodes

    Science.gov (United States)

    Kim, Hyeon-Hye; Goins, Gregory D.; Wheeler, Raymond M.; Sager, John C.

    2004-01-01

    Plants will be an important component of future long-term space missions. Lighting systems for growing plants will need to be lightweight, reliable, and durable, and light-emitting diodes (LEDs) have these characteristics. Previous studies demonstrated that the combination of red and blue light was an effective light source for several crops. Yet the appearance of plants under red and blue lighting is purplish gray making visual assessment of any problems difficult. The addition of green light would make the plant leave appear green and normal similar to a natural setting under white light and may also offer a psychological benefit to the crew. Green supplemental lighting could also offer benefits, since green light can better penetrate the plant canopy and potentially increase plant growth by increasing photosynthesis from the leaves in the lower canopy. In this study, four light sources were tested: 1) red and blue LEDs (RB), 2) red and blue LEDs with green fluorescent lamps (RGB), 3) green fluorescent lamps (GF), and 4) cool-white fluorescent lamps (CWF), that provided 0%, 24%, 86%, and 51% of the total PPF in the green region of the spectrum, respectively. The addition of 24% green light (500 to 600 nm) to red and blue LEDs (RGB treatment) enhanced plant growth. The RGB treatment plants produced more biomass than the plants grown under the cool-white fluorescent lamps (CWF treatment), a commonly tested light source used as a broad-spectrum control.

  1. Determination of RNA degradation by capillary electrophoresis with cyan light-emitted diode-induced fluorescence.

    Science.gov (United States)

    Yang, Tzu-Hsueh; Chang, Po-Ling

    2012-05-25

    RNA integrity plays an important role in RNA studies because poor RNA quality may have a great impact on downstream methodologies. This study proposes a cost-effective, rapid, and sensitive method for determining RNA integrity based on capillary electrophoresis that utilizes a cyan light-emitted diode-induced fluorescence as a separation tool. The capillary was initially coated with 0.1% Poly(vinylpyrrolidone) (M(ave) 1,300,000 Da) to reduce electroosmotic flow and avoid RNA adsorption. When the capillary was filled with 0.4% poly(ethylene) oxide (M(ave) 4,000,000) and a nucleic acid-specific fluorescent dye, SYTO 9, the baseline separation of the 18S and 28S ribosomal RNAs (rRNAs) in total RNA was accomplished within 15 min. The lowest detectable concentration for the 18S and 28S rRNAs was estimated to be 50 pg/μL. Some peaks longer than the 28S rRNA that migrated slowly were observed as long as the initial total RNA concentration was optimized. The temperature-induced degradation of the large RNA fragments (longer than the 28S rRNA) was faster than that of 18S rRNA and 28S rRNA. These large RNA fragments may serve as a promising marker for testing RNA integrity compared to the traditional method. Copyright © 2012 Elsevier B.V. All rights reserved.

  2. Current spreading in GaN-based light-emitting diodes

    International Nuclear Information System (INIS)

    Li Qiang; Li Yufeng; Ding Wen; Yun Feng; Zhang Minyan

    2016-01-01

    We have investigated the factors affecting the current spreading length (CSL) in GaN-based light-emitting diodes (LEDs) by deriving theoretical expressions and performing simulations with APSYS. For mesa-structure LEDs, the effects of both indium tin oxide (ITO) and n-GaN are taken into account for the first time, and a new Q factor is introduced to explain the effects of different current flow paths on the CSL. The calculations and simulations show that the CSL can be enhanced by increasing the thickness of the ITO layer and resistivity of the n-GaN layer, or by reducing the resistivity of the ITO layer and thickness of the n-GaN layer. The results provide theoretical support for calculating the CSL clearly and directly. For vertical-structure LEDs, the effects of resistivity and thickness of the CSL on the internal quantum efficiency (IQE) have been analyzed. The theoretical expression relating current density and the parameters (resistivity and thickness) of the CSL is obtained, and the results are then verified by simulation. The IQE under different current injection conditions is discussed. The effects of CSL resistivity play a key role at high current injection, and there is an optimal thickness for the largest IQE only at a low current injection. (paper)

  3. Submicrometre resolved optical characterization of green nanowire-based light emitting diodes

    International Nuclear Information System (INIS)

    Bavencove, A-L; Tourbot, G; Garcia, J; Desieres, Y; Gilet, P; Levy, F; Andre, B; Gayral, B; Daudin, B; Dang, Le Si

    2011-01-01

    The electroluminescent properties of InGaN/GaN nanowire-based light emitting diodes (LEDs) are studied at different resolution scales. Axial one-dimensional heterostructures were grown by plasma-assisted molecular beam epitaxy (PAMBE) directly on a silicon (111) substrate and consist of the following sequentially deposited layers: n-type GaN, three undoped InGaN/GaN quantum wells, p-type AlGaN electron blocking layer and p-type GaN. From the macroscopic point of view, the devices emit light in the green spectral range (around 550 nm) under electrical injection. At 100 mA DC current, a 1 mm 2 chip that integrates around 10 7 nanowires emits an output power on the order of 10 μW. However, the emission of the nanowire-based LED shows a spotty and polychromatic emission. By using a confocal microscope, we have been able to improve the spatial resolution of the optical characterizations down to the submicrometre scale that can be assessed to a single nanowire. Detailed μ-electroluminescent characterization (emission wavelength and output power) over a representative number of single nanowires provides new insights into the vertically integrated nanowire-based LED operation. By combining both μ-electroluminescent and μ-photoluminescent excitation, we have experimentally shown that electrical injection failure is the major source of losses in these nanowire-based LEDs.

  4. Contact light-emitting diodes based on vertical ZnO nanorods

    International Nuclear Information System (INIS)

    Panin, G. N.; Cho, H. D.; Lee, S. W.; Kang, T. W.

    2014-01-01

    We report vertical contact light-emitting diodes (VCLEDs), that are based on heterojunctions formed by using the point contacts of n-ZnO nanorods (NRs) to the p-type semiconductor substrate and that are fabricated using a new approach to the formation of LEDs (Appl. Phys. Lett. 98, 093110 (2011)). A p-type GaN film grown on a sapphire substrate was used to form n-ZnO NRs/pGaN VCLEDs on a large area of about 4 cm 2 . The VCLEDs emitted a pure blue electroluminescence with high efficiency. Electroluminescence at 470 nm, which is visible to the naked eye, started at small current of about 50 μA and is attributed to the good optical properties of the structurally perfect heterojunctions in the point contacts. The VCLED configuration allows the creation of ZnO/p-GaN nano-LEDs of high density and high-quality with a greatly reduced concentration of nonradiative defects in the active regions. The VCLEDs showed the high brightness of light required for active matrix displays and general solid-state lighting.

  5. Inhibitory effect of blue light emitting diode on migration and invasion of cancer cells.

    Science.gov (United States)

    Oh, Phil-Sun; Kim, Hyun-Soo; Kim, Eun-Mi; Hwang, Hyosook; Ryu, Hyang Hwa; Lim, SeokTae; Sohn, Myung-Hee; Jeong, Hwan-Jeong

    2017-12-01

    The aim of this study was to determine the effects and molecular mechanism of blue light emitting diode (LED) in tumor cells. A migration and invasion assay for the metastatic behavior of mouse colon cancer CT-26 and human fibrosarcoma HT-1080 cells was performed. Cancer cell migration-related proteins were identified by obtaining a 2-dimensional gel electrophoresis (2-DE) in total cellular protein profile of blue LED-irradiated cancer cells, followed by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis of proteins. Protein levels were examined by immunoblotting. Irradiation with blue LED inhibited CT-26 and HT-1080 cell migration and invasion. The anti-metastatic effects of blue LED irradiation were associated with inhibition of matrix metalloproteinase (MMP)-2 and MMP-9 expression. P38 MAPK phosphorylation was increased in blue LED-irradiated CT-26 and HT-1080 cells, but was inhibited after pretreatment with SB203580, a specific inhibitor of p38 MAPK. Inhibition of p38 MAPK phosphorylation by SB203580 treatment increased number of migratory cancer cells in CT-26 and HT-1080 cells, indicating that blue LED irradiation inhibited cancer cell migration via phosphorylation of p38 MAPK. Additionally blue LED irradiation of mice injected with CT-26 cells expressing luciferase decreased early stage lung metastasis compared to untreated control mice. These results indicate that blue LED irradiation inhibits cancer cell migration and invasion in vitro and in vivo. © 2017 Wiley Periodicals, Inc.

  6. Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes.

    Science.gov (United States)

    Lee, Ho Won; Jeong, Hyunjin; Kim, Young Kwan; Ha, Yunkyoung

    2015-10-01

    Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds. Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4'-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N'-dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and could be extended to additional research on flexible applications.

  7. Fully transparent quantum dot light-emitting diode integrated with graphene anode and cathode.

    Science.gov (United States)

    Seo, Jung-Tak; Han, Junebeom; Lim, Taekyung; Lee, Ki-Heon; Hwang, Jungseek; Yang, Heesun; Ju, Sanghyun

    2014-12-23

    A fully transparent quantum dot light-emitting diode (QD-LED) was fabricated by incorporating two types (anode and cathode) of graphene-based electrodes, which were controlled in their work functions and sheet resistances. Either gold nanoparticles or silver nanowires were inserted between layers of graphene to control the work function, whereas the sheet resistance was determined by the number of graphene layers. The inserted gold nanoparticles or silver nanowires in graphene films caused a charge transfer and changed the work function to 4.9 and 4.3 eV, respectively, from the original work function (4.5 eV) of pristine graphene. Moreover the sheet resistance values for the anode and cathode electrodes were improved from ∼63,000 to ∼110 Ω/sq and from ∼100,000 to ∼741 Ω/sq as the number of graphene layers increased from 1 to 12 and from 1 to 8, respectively. The main peak wavelength, luminance, current efficiency, and optical transmittance of the fully transparent QD-LED integrated with graphene anode and cathode were 535 nm, ∼358 cd/m2, ∼0.45 cd/A, and 70-80%, respectively. The findings of the study are expected to lay a foundation for the production of high-efficiency, fully transparent, and flexible displays using graphene-based electrodes.

  8. Enhanced performance of photonic crystal GaN light-emitting diodes with graphene transparent electrodes.

    Science.gov (United States)

    Ge, Hai-Liang; Xu, Chen; Xu, Kun; Xun, Meng; Wang, Jun; Liu, Jie

    2015-01-01

    The two-dimensional (2D) triangle lattice air hole photonic crystal (PC) GaN-based light-emitting diodes (LED) with double-layer graphene transparent electrodes (DGTE) have been produced. The current spreading effect of the double-layer graphene (GR) on the surface of the PC structure of the LED has been researched. Specially, we found that the part of the graphene suspending over the air hole of the PC structure was of much higher conductivity, which reduced the average sheet resistance of the graphene transparent conducting electrode and improved the current spreading of the PC LED. Therefore, the work voltage of the DGTE-PC LED was obviously decreased, and the output power was greatly enhanced. The COMSOL software was used to simulate the current density distribution of the samples. The results show that the etching of PC structure results in the degradation of the current spreading and that the graphene transparent conducting electrode can offer an uniform current spreading in the DGTE-PC LED. 85.60.Jb; 68.65.Pq; 42.70.Qs.

  9. Fully Transparent Quantum Dot Light-Emitting Diode with a Laminated Top Graphene Anode.

    Science.gov (United States)

    Yao, Li; Fang, Xin; Gu, Wei; Zhai, Wenhao; Wan, Yi; Xie, Xixi; Xu, Wanjin; Pi, Xiaodong; Ran, Guangzhao; Qin, Guogang

    2017-07-19

    A new method to employ graphene as top electrode was introduced, and based on that, fully transparent quantum dot light-emitting diodes (T-QLEDs) were successfully fabricated through a lamination process. We adopted the widely used wet transfer method to transfer bilayer graphene (BG) on polydimethylsiloxane/polyethylene terephthalate (PDMS/PET) substrate. The sheet resistance of graphene reduced to ∼540 Ω/□ through transferring BG for 3 times on the PDMS/PET. The T-QLED has an inverted device structure of glass/indium tin oxide (ITO)/ZnO nanoparticles/(CdSSe/ZnS quantum dots (QDs))/1,1-bis[(di-4-tolylamino)phenyl] cyclohexane (TAPC)/MoO 3 /graphene/PDMS/PET. The graphene anode on PDMS/PET substrate can be directly laminated on the MoO 3 /TAPC/(CdSSe/ZnS QDs)/ZnO nanoparticles/ITO/glass, which relied on the van der Waals interaction between the graphene/PDMS and the MoO 3 . The transmittance of the T-QLED is 79.4% at its main electroluminescence peak wavelength of 622 nm.

  10. Generating Hydrated Electrons for Chemical Syntheses by Using a Green Light-Emitting Diode (LED).

    Science.gov (United States)

    Naumann, Robert; Lehmann, Florian; Goez, Martin

    2018-01-22

    We present the first working system for accessing and utilizing laboratory-scale concentrations of hydrated electrons by photoredox catalysis with a green light-emitting diode (LED). Decisive are micellar compartmentalization and photon pooling in an intermediate that decays with second-order kinetics. The only consumable is the nontoxic and bioavailable vitamin C. A turnover number of 1380 shows the LED method to be on par with electron generation by high-power pulsed lasers, but at a fraction of the cost. The extreme reducing power of the electron and its long unquenched life as a ground-state species are synergistic. We demonstrate the applicability to the dechlorination, defluorination, and hydrogenation of compounds that are inert towards all other visible-light photoredox catalysts known to date. A comprehensive mechanistic investigation from microseconds to hours yields results of general validity for photoredox catalysis with photon pooling, allowing optimization and upscaling. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Development and evaluation of a light-emitting diode endoscopic light source

    Science.gov (United States)

    Clancy, Neil T.; Li, Rui; Rogers, Kevin; Driscoll, Paul; Excel, Peter; Yandle, Ron; Hanna, George; Copner, Nigel; Elson, Daniel S.

    2012-03-01

    Light-emitting diode (LED) based endoscopic illumination devices have been shown to have several benefits over arclamp systems. LEDs are energy-efficient, small, durable, and inexpensive, however their use in endoscopy has been limited by the difficulty in efficiently coupling enough light into the endoscopic light cable. We have demonstrated a highly homogenised lightpipe LED light source that combines the light from four Luminus LEDs emitting in the red, green, blue and violet using innovative dichroics that maximise light throughput. The light source spectrally combines light from highly divergent incoherent sources that have a Lambertian intensity profile to provide illumination matched to the acceptance numerical aperture of a liquid light guide or fibre bundle. The LED light source was coupled to a standard laparoscope and performance parameters (power, luminance, colour temperature) compared to a xenon lamp. Although the total illuminance from the endoscope was lower, adjustment of the LEDs' relative intensities enabled contrast enhancement in biological tissue imaging. The LED light engine was also evaluated in a minimally invasive surgery (MIS) box trainer and in vivo during a porcine MIS procedure where it was used to generate 'narrowband' images. Future work using the violet LED could enable photodynamic diagnosis of bladder cancer.

  12. Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting

    Energy Technology Data Exchange (ETDEWEB)

    Arto V. Nurmikko; Jung Han

    2007-03-31

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the duration of the contract period include (i) new means of synthesizing AlGaN and InN quantum dots by droplet heteroepitaxy, (ii) synthesis of AlGaInN nanowires as building blocks for GaN-based microcavity devices, (iii) progress towards direct epitaxial alignment of the dense arrays of nanowires, (iv) observation and measurements of stimulated emission in dense InGaN nanopost arrays, (v) design and fabrication of InGaN photonic crystal emitters, and (vi) observation and measurements of enhanced fluorescence from coupled quantum dot and plasmonic nanostructures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  13. Hybrid Perovskite Light-Emitting Diodes Based on Perovskite Nanocrystals with Organic-Inorganic Mixed Cations.

    Science.gov (United States)

    Zhang, Xiaoli; Liu, He; Wang, Weigao; Zhang, Jinbao; Xu, Bing; Karen, Ke Lin; Zheng, Yuanjin; Liu, Sheng; Chen, Shuming; Wang, Kai; Sun, Xiao Wei

    2017-05-01

    Organic-inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed-cation perovskite nanocrystals based on FA (1- x ) Cs x PbBr 3 (FA = CH(NH 2 ) 2 ). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA (1- x ) Cs x PbBr 3 , is significantly dependent on the substitution content of the Cs cations in the perovskite composition. These mixed-cation perovskites are employed as light emitters in light-emitting diodes (LEDs). With an optimized composition of FA 0.8 Cs 0.2 PbBr 3 , the LEDs exhibit encouraging performance with a highest reported luminance of 55 005 cd m -2 and a current efficiency of 10.09 cd A -1 . This work provides important instructions on the future compositional optimization of mixed-cation perovskite for obtaining high-performance LEDs. The authors believe this work is a new milestone in the development of bright and efficient perovskite LEDs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Compact environmental spectroscopy using advanced semiconductor light-emitting diodes and lasers

    Energy Technology Data Exchange (ETDEWEB)

    Fritz, I.J.; Klem, J.F.; Hafich, M.J. [and others

    1997-04-01

    This report summarizes research completed under a Laboratory Directed Research and Development program funded for part of FY94, FY95 and FY96. The main goals were (1) to develop novel, compound-semiconductor based optical sources to enable field-based detection of environmentally important chemical species using miniaturized, low-power, rugged, moderate cost spectroscopic equipment, and (2) to demonstrate the utility of near-infrared spectroscopy to quantitatively measure contaminants. Potential applications would include monitoring process and effluent streams for volatile organic compound detection and sensing head-space gasses in storage vessels for waste management. Sensing is based on absorption in the 1.3-1.9 {mu}m band from overtones of the C-H, N-H and O-H stretch resonances. We describe work in developing novel broadband light-emitting diodes emitting over the entire 1.4-1.9 {mu}m wavelength range, first using InGaAs quantum wells, and second using a novel technique for growing digital-alloy materials in the InAlGaAs material system. Next we demonstrate the utility of near-infrared spectroscopy for quantitatively determining contamination of soil by motor oil. Finally we discuss the separability of different classes of organic compounds using near-infrared spectroscopic techniques.

  15. Surface-Passivated AlGaN Nanowires for Enhanced Luminescence of Ultraviolet Light Emitting Diodes

    KAUST Repository

    Sun, Haiding

    2017-12-19

    Spontaneously-grown, self-aligned AlGaN nanowire ultraviolet light emitting diodes still suffer from low efficiency partially because of the strong surface recombination caused by surface states, i.e., oxidized surface and high density surface states. Several surface passivation methods have been introduced to reduce surface non-radiative recombination by using complex and toxic chemicals. Here, we present an effective method to suppress such undesirable surface recombination of the AlGaN nanowires via diluted potassium hydroxide (KOH) solution; a commonly used chemical process in semiconductor fabrication which is barely used as surface passivation solution in self-assembled nitride-based nanowires. The transmission electron microscopy investigation on the samples reveals almost intact nanowire structures after the passivation process. We demonstrated an approximately 49.7% enhancement in the ultraviolet light output power after 30-s KOH treatment on AlGaN nanowires grown on titanium-coated silicon substrates. We attribute such a remarkable enhancement to the removal of the surface dangling bonds and oxidized nitrides (Ga-O or Al-O bonds) at the surface as we observe the change of the carrier lifetime before and after the passivation. Thus, our results highlight the possibility of employing this process for the realization of high performance nanowire UV emitters.

  16. Improving lumen maintenance by nanopore array dispersed quantum dots for on-chip light emitting diodes

    Science.gov (United States)

    Chen, Quan; Yang, Fan; Wan, Renzhuo; Fang, Dong

    2017-12-01

    The temperature stability of quantum dots (QDs), which is crucial for integrating into high power light-emitting diodes (LEDs) in the on-chip configuration, needs to be further improved. In this letter, we report warm white LEDs, where CdSe/ZnS nanoparticles were incorporated into a porous anodic alumina (PAA) matrix with a chain structure by the self-assembly method. Experiments demonstrate that the QD concentration range in toluene solvent from 1% mg/μl to 1.2% mg/μl in combination with the PAA matrix shows the best luminous property. To verify the reliability of the as-prepared device, a comparison experiment was conducted. It indicates excellent lumen maintenance of the light source and less chromaticity coordinate shift under accelerated life testing conditions. Experiments also prove that optical depreciation was only up to 4.6% of its initial value after the 1500 h aging test at the junction temperature of 76 °C.

  17. Application of light-emitting diodes (LEDs) in cultivation of phototrophic microalgae: current state and perspectives.

    Science.gov (United States)

    Glemser, M; Heining, M; Schmidt, J; Becker, A; Garbe, D; Buchholz, R; Brück, T

    2016-02-01

    The quality and regulation of the incident light is crucial in microalgae cultivation processes. Depending on wavelength, spectrum, and intensity, growth characteristics and biochemical composition of these organisms vary. With mainly fluorescent lamps (FL) used previously for illumination, such variabilities could not be studied adequately due to their broad emission spectrum. In contrast, light-emitting diodes (LEDs) emit a very narrow wavelength band and enable flexible photobioreactor designs due to their small size. This review provides a condensed overview on the application of LEDs in microalgal cultivation processes. It summarizes the current availability and applicability of LED technologies as an illumination source for research-focused photobioreactor systems. A particular focus is the use of narrow-wavelength LEDs to address fundamental as well as applied aspects of light color on algae biomass and value-added compound formation. In this respect, the application of internal and external illumination systems is reviewed together with trends in the industrial use of LED systems to intensify algae process efficiency.

  18. Technology Analysis of Global Smart Light Emitting Diode (LED Development Using Patent Data

    Directory of Open Access Journals (Sweden)

    Sangsung Park

    2017-08-01

    Full Text Available Technological developments related to smart light emitting diode (LED systems have progressed rapidly in recent years. In this paper, patent documents related to smart LED technology are collected and analyzed to understand the technology development of smart LED systems. Most previous studies of the technology were dependent on the knowledge and experience of domain experts, using techniques such as Delphi surveys or technology road-mapping. These approaches may be subjective and lack robustness, because the results can vary according to the selected expert groups. We therefore propose a new technology analysis methodology based on statistical modeling to obtain objective and relatively stable results. The proposed method consists of visualization based on Bayesian networks and a linear count model to analyze patent documents related to smart LED technology. Combining these results, a global hierarchical technology structure is created that can enhance the sustainability in smart LED system technology. In order to show how this methodology could be applied to real-world problems, we carry out a case study on the technology analysis of smart LED systems.

  19. Improved performance of organic light-emitting diode with vanadium pentoxide layer on the FTO surface

    Science.gov (United States)

    Saikia, D.; Sarma, R.

    2017-06-01

    Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED). With 12 nm optimal thickness of V2O5, the luminance efficiency is increased by 1.66 times compared to the single FTO-based OLED. The improvement of current efficiency implies that there is a better charge injection and better controlling of hole current. To investigate the performance of OLED by the buffer layer, V2O5 films of different thicknesses were deposited on the FTO anode and their J- V and L- V characteristics were studied. Further analysis was carried out by measuring sheet resistance, optical transmittance and surface morphology with the FE-SEM images. This result indicates that the V2O5 (12 nm) buffer layer is a good choice for increasing the efficiency of FTO-based OLED devices within the tunnelling region. Here the maximum value of current efficiency is found to be 2.83 cd / A.

  20. Self-sensing of temperature rises on light emitting diode based optrodes

    Science.gov (United States)

    Dehkhoda, Fahimeh; Soltan, Ahmed; Ponon, Nikhil; Jackson, Andrew; O’Neill, Anthony; Degenaar, Patrick

    2018-04-01

    Objective. This work presents a method to determine the surface temperature of microphotonic medical implants like LEDs. Our inventive step is to use the photonic emitter (LED) employed in an implantable device as its own sensor and develop readout circuitry to accurately determine the surface temperature of the device. Approach. There are two primary classes of applications where microphotonics could be used in implantable devices; opto-electrophysiology and fluorescence sensing. In such scenarios, intense light needs to be delivered to the target. As blue wavelengths are scattered strongly in tissue, such delivery needs to be either via optic fibres, two-photon approaches or through local emitters. In the latter case, as light emitters generate heat, there is a potential for probe surfaces to exceed the 2 °C regulatory. However, currently, there are no convenient mechanisms to monitor this in situ. Main results. We present the electronic control circuit and calibration method to monitor the surface temperature change of implantable optrode. The efficacy is demonstrated in air, saline, and brain. Significance. This paper, therefore, presents a method to utilize the light emitting diode as its own temperature sensor.

  1. Analyzing degradation effects of organic light-emitting diodes via transient optical and electrical measurements

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Tobias D., E-mail: Tobias.Schmidt@physik.uni-augsburg.de; Jäger, Lars; Brütting, Wolfgang, E-mail: Wolfgang.Bruetting@physik.uni-augsburg.de [Institute of Physics, University of Augsburg, Augsburg (Germany); Noguchi, Yutaka [Department of Electronics and Bioinformatics, School of Science and Technology, Meiji University, Kawasaki (Japan); Center of Frontier Science, Chiba University, Chiba (Japan); Ishii, Hisao [Center of Frontier Science, Chiba University, Chiba (Japan)

    2015-06-07

    Although the long-term stability of organic light-emitting diodes (OLEDs) under electrical operation made significant progress in recent years, the fundamental underlying mechanisms of the efficiency decrease during operation are not well understood. Hence, we present a comprehensive degradation study of an OLED structure comprising the well-known green phosphorescent emitter Ir(ppy){sub 3}. We use transient methods to analyze both electrical and optical changes during an accelerated aging protocol. Combining the results of displacement current measurements with time-resolved investigation of the excited states lifetimes of the emitter allows for a correlation of electrical (e.g., increase of the driving voltage due to trap formation) and optical (e.g., decrease of light-output) changes induced by degradation. Therewith, it is possible to identify two mechanisms resulting in the drop of the luminance: a decrease of the radiative quantum efficiency of the emitting system due to triplet-polaron-quenching at trapped charge carriers and a modified charge carrier injection and transport, as well as trap-assisted non-radiative recombination resulting in a deterioration of the charge carrier balance of the device.

  2. Quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Price, J. S.; Giebink, N. C., E-mail: ncg2@psu.edu [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

    2015-06-29

    Various exciton annihilation processes are known to impact the efficiency roll-off of organic light emitting diodes (OLEDs); however, isolating and quantifying their contribution in the presence of other factors such as changing charge balance continue to be a challenge for routine device characterization. Here, we analyze OLED electroluminescence resulting from a sinusoidal dither superimposed on the device bias and show that nonlinearity between recombination current and light output arising from annihilation mixes the quantum efficiency measured at different dither harmonics in a manner that depends uniquely on the type and magnitude of the annihilation process. We derive a series of analytical relations involving the DC and first harmonic external quantum efficiency that enable annihilation rates to be quantified through linear regression independent of changing charge balance and evaluate them for prototypical fluorescent and phosphorescent OLEDs based on the emitters 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran and platinum octaethylporphyrin, respectively. We go on to show that, in most cases, it is sufficient to calculate the needed quantum efficiency harmonics directly from derivatives of the DC light versus current curve, thus enabling this analysis to be conducted solely from standard light-current-voltage measurement data.

  3. Phosphorescent cyclometalated complexes for efficient blue organic light-emitting diodes.

    Science.gov (United States)

    Suzuri, Yoshiyuki; Oshiyama, Tomohiro; Ito, Hiroto; Hiyama, Kunihisa; Kita, Hiroshi

    2014-10-01

    Phosphorescent emitters are extremely important for efficient organic light-emitting diodes (OLEDs), which attract significant attention. Phosphorescent emitters, which have a high phosphorescence quantum yield at room temperature, typically contain a heavy metal such as iridium and have been reported to emit blue, green and red light. In particular, the blue cyclometalated complexes with high efficiency and high stability are being developed. In this review, we focus on blue cyclometalated complexes. Recent progress of computational analysis necessary to design a cyclometalated complex is introduced. The prediction of the radiative transition is indispensable to get an emissive cyclometalated complex. We summarize four methods to control phosphorescence peak of the cyclometalated complex: (i) substituent effect on ligands, (ii) effects of ancillary ligands on heteroleptic complexes, (iii) design of the ligand skeleton, and (iv) selection of the central metal. It is considered that novel ligand skeletons would be important to achieve both a high efficiency and long lifetime in the blue OLEDs. Moreover, the combination of an emitter and a host is important as well as the emitter itself. According to the dependences on the combination of an emitter and a host, the control of exciton density of the triplet is necessary to achieve both a high efficiency and a long lifetime, because the annihilations of the triplet state cause exciton quenching and material deterioration.

  4. Highly Efficient Blue Phosphorescent Organic Light-Emitting Diodes Employing a Host Material with Small Bandgap.

    Science.gov (United States)

    Zhang, Lei; Zhang, Ye-Xin; Hu, Yun; Shi, Xiao-Bo; Jiang, Zuo-Quan; Wang, Zhao-Kui; Liao, Liang-Sheng

    2016-06-29

    Blue phosphorescent organic light-emitting diode (PhOLED) with a high maximum external quantum efficiency (EQE) of 26.6% was achieved using a new material, 2,8-bis(9,9-dimethylacridin-10(9H)-yl)dibenzo[b,d]furan (DBF-DMS) with a small bandgap, as the host. The device with DBF-DMS showed improved performance compared with that with 1,3-di-9-carbazolylbenzene, which is ascribed to the enhancement in carrier injection and transporting abilities and material stability of DBF-DMS. A lifetime of more than 100 h (time to 50% of the initial luminance, 1000 cd/m(2) with an EQE of 19.6%) in the other DBF-DMS-based device is obtained by further utilizing better device structure. This is a report indicating that host material with a small bandgap like DBF-DMS can be successfully utilized toward blue PhOLEDs with high performance.

  5. Temperature and current dependent electroluminescence measurements on colour-coded multiple quantum well light emitting diodes

    International Nuclear Information System (INIS)

    Bergbauer, Werner; Laubsch, Ansgar; Peter, Matthias; Mayer, Tobias; Bader, Stefan; Oberschmid, Raimund; Hahn, Berthold; Benstetter, Guenther

    2008-01-01

    As the efficiency and the luminous flux have been increased enormously in the last few years, today Light Emitting Diodes (LEDs) are even pushed to applications like general lighting and Home Cinema Projection. Still, InGaN/GaN heterostructure based LEDs suffer from loss-mechanisms like non-radiative defect and Auger recombination, carrier leakage and piezo-field induced carrier separation. To optimize the high current efficiency we evaluated the benefit of Multiple Quantum Well (MQW) compared to Single Quantum Well (SQW) LEDs. Temperature dependent electroluminescence of colour-coded structures with different Indium content in certain Quantum Wells was measured. The experiments demonstrated a strong temperature and current dependence of the MQW operation. The comparison between different LED structures showed effectively the increased LED performance of those structures which operate with a well adjusted MQW active area. Due to the enhanced carrier distribution in the high current range, these LEDs show a higher light output and additionally a reduced wavelength shift

  6. ESR study of camphorquinone/amine photoinitiator systems using blue light-emitting diodes.

    Science.gov (United States)

    Teshima, Wataru; Nomura, Yuji; Tanaka, Nobuyuki; Urabe, Hidenori; Okazaki, Masayuki; Nahara, Yukinori

    2003-05-01

    New light-activation units equipped with high-illuminant blue light-emitting diodes (LEDs) have recently been proposed as a replacement for the halogen units that are widely used in dentistry to polymerize light-cured resins. The photoinitiators in light-cured dental resins, typified by the camphorquinone (CQ)/amine photoinitiator system, generate primary radicals with light irradiation that attack the double bonds of resin monomers. The physical properties of the cured resins are affected by the generation of primary radicals during the initial stage of polymerization. This study examined two types of photoinitiator systems, CQ/DMPT and CQ/DMAEMA, and three types of curing units, a new LED unit and two conventional halogen units. The primary radicals generated by irradiation were quantified using electron spin resonance (ESR) spectroscopy with a trapping method, using phenyl-tert-butyl nitrone as the trapping agent. The energy efficiencies of the LED and halogen units were compared by quantifying the generated radicals and emitted light energy (J/cm(2)). The energy required to generate a given amount of radicals using the LED unit was smaller than that using the halogen units (p<0.05). These results suggest that the new LED unit performs better than conventional halogen units with respect to light energy.

  7. Real-time optical monitoring of microbial growth using optimal combination of light-emitting diodes

    Science.gov (United States)

    Kobayashi, Ken-ichi; Yamada, Takeshi; Hiraishi, Akira; Nakauchi, Shigeki

    2012-12-01

    We developed a real-time optical monitoring system consisting of a monochrome complementary metal-oxide semiconductor (CMOS) camera and two light-emitting diodes (LEDs) with a constant temperature incubator for the rapid detection of microbial growth on solid media. As a target organism, we used Alicyclobacillus acidocaldarius, which is an acidophilic thermophilic endospore-forming bacterium able to survive in pasteurization processes and grow in acidic drink products such as apple juice. This bacterium was cultured on agar medium with a redox dye applied to improve detection sensitivity. On the basis of spectroscopic properties of the colony, medium, and LEDs, an optimal combination of two LED illuminations was selected to maximize the contrast between the colony and medium areas. We measured A. acidocaldarius and Escherichia coli at two different dilution levels using these two LEDs. From the results of time-course changes in the number of detected pixels in the detection images, a similar growth rate was estimated amongst the same species of microbes, regardless of the dilution level. This system has the ability to detect a colony of approximately 26 μm in diameter in a detection image, and it can be interpreted that the size corresponds to less than 20 μm diameter in visual inspection.

  8. Effects of white light-emitting diode (LED) exposure on retinal pigment epithelium in vivo.

    Science.gov (United States)

    Jaadane, Imene; Villalpando Rodriguez, Gloria Elisa; Boulenguez, Pierre; Chahory, Sabine; Carré, Samuel; Savoldelli, Michèle; Jonet, Laurent; Behar-Cohen, Francine; Martinsons, Christophe; Torriglia, Alicia

    2017-12-01

    Ageing and alteration of the functions of the retinal pigment epithelium (RPE) are at the origin of lost of vision seen in age-related macular degeneration (AMD). The RPE is known to be vulnerable to high-energy blue light. The white light-emitting diodes (LED) commercially available have relatively high content of blue light, a feature that suggest that they could be deleterious for this retinal cell layer. The aim of our study was to investigate the effects of "white LED" exposure on RPE. For this, commercially available white LEDs were used for exposure experiments on Wistar rats. Immunohistochemical stain on RPE flat mount, transmission electron microscopy and Western blot were used to exam the RPE. LED-induced RPE damage was evaluated by studying oxidative stress, stress response pathways and cell death pathways as well as the integrity of the outer blood-retinal barrier (BRB). We show that white LED light caused structural alterations leading to the disruption of the outer blood-retinal barrier. We observed an increase in oxidized molecules, disturbance of basal autophagy and cell death by necrosis. We conclude that white LEDs induced strong damages in rat RPE characterized by the breakdown of the BRB and the induction of necrotic cell death. © 2017 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.

  9. Comparative effectiveness of light emitting diodes (LEDs) and Lasers in near infrared photoimmunotherapy

    Science.gov (United States)

    Sato, Kazuhide; Watanabe, Rira; Hanaoka, Hirofumi; Nakajima, Takahito; Choyke, Peter L.; Kobayashi, Hisataka

    2016-01-01

    Near infrared photoimmunotherapy (NIR-PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by photosensitizers after exposure to near infrared (NIR) light. Herein we compare two NIR-light sources; light emitting diodes (LEDs) and Lasers, for their effectiveness in NIR-PIT. A photosensitizer, IRDye-700DX, conjugated to panitumumab (pan-IR700), was incubated with EGFR-expressing A431 and MDA-MB-468-luc cells. NIR-light was provided by LEDs or Lasers at the same light dose. Laser-light produced more cytotoxicity and greater reductions in IR700-fluorescence intensity than LED-light. Laser-light also produced more cytotoxicity in vivo in both cell lines. Assessment of super-enhanced permeability and retention (SUPR) effects were stronger with Laser than LED. These results suggest that Laser-light produced significantly more cytotoxic effects compared to LEDs. Although LED is less expensive, Laser-light produces superior results in NIR-PIT. PMID:26885688

  10. Image quality of a novel light-emitting diode (LED)-illuminated colonoscope.

    Science.gov (United States)

    Sasaki, Sho; Nishikawa, Jun; Yanai, Hideo; Nakamura, Munetaka; Nishimura, Junichi; Goto, Atsushi; Kiyotoki, Shu; Saito, Mari; Hamabe, Kouichi; Tanabe, Ryo; Nakamura, Yohei; Tokiyama, Hiroshi; Hashimoto, Shinichi; Okamoto, Takeshi; Higaki, Shingo; Kurai, Satoshi; Ogihara, Hiroyuki; Hamamoto, Yoshihiko; Sakaida, Isao

    2016-10-01

    Light-emitting diodes (LEDs) are used widely for their high luminous efficiency and durability. We developed a novel prototype high definition endoscope with white LEDs and evaluated the image quality it produced against a commercial endoscope with conventional light source. The specifications of both colonoscopes were identical, except for the LED light source at the tip of the prototype. We examined 20 patients with rectal or sigmoid colon lesions and the image quality was evaluated in 40 images (one image from the LED colonoscope and one from the conventional colonoscope for each lesion) by three endoscopists. We additionally evaluated the 17 videos recorded with the LED colonoscope that were available. Image quality, mucosal and vascular color, and luminous distribution and intensity were scored on a 5-point scale. The mean score for vascular color given by one evaluator was significantly higher using the LED colonoscope than using the conventional colonoscope. The mean scores for mucosal color and luminous intensity from another evaluator were significantly lower with the LED colonoscope than with the conventional colonoscope. There were no significant differences in the luminous distribution scores for any of the evaluators. The image quality of the videos was evaluated as being similar with both colonoscopes. Image quality from the LED and conventional colonoscopes were similar, although the luminous intensity of the LEDs is inferior to that of the conventional light source at the present time. © Georg Thieme Verlag KG Stuttgart · New York.

  11. Sugarcane micropropagation using light emitting diodes and adjustment in growth-medium sucrose concentration

    Directory of Open Access Journals (Sweden)

    Paulo Sérgio Gomes da Rocha

    2013-07-01

    Full Text Available The aim of this research was to evaluate the use of light emitting diodes (LEDs instead of white fluorescent lamps as light source and adequate growth-medium sucrose concentration for sugarcane micropropagation (Saccharum officinarum L.. Sugarcane (RB 872552 variety bud explants were evaluated during the multiplication and rooting phases under controlled growth-room conditions. Different light sources (blue, red and green LEDs; Growlux and white fluorescent lamps and different medium sucrose concentrations (0; 15; 30 and 45g L-1 were used, maintaining constant light intensity (20µmol m-2 s-1, photoperiod (16h and temperature (25+2°C. The experiment was a completely randomized design, and treatments were arranged in a 5x4 factorial (five light sources and four medium sucrose concentrations with six replications. Sugarcane bud growth was satisfactory under the three LED types studied. The presence of sucrose in growth media was essential for bud multiplication and rooting. Nevertheless, each light source requires the respective medium sucrose concentration adjustment for best results. Red LEDs provided a significantly high multiplication rate (although not the highest with 8.5 buds per sub-culture and 34.9g L-1 of sucrose; also, the highest bud length (33.3mm and the best plantlet acclimatization. Therefore, LED sources can advantageously substitute fluorescent lamps in laboratories of sugarcane micropropagation.

  12. A new integrating sphere design for spectral radiant flux determination of light-emitting diodes

    International Nuclear Information System (INIS)

    Hanselaer, P; Keppens, A; Forment, S; Ryckaert, W R; Deconinck, G

    2009-01-01

    Light-emitting diode (LED) technology is developing very quickly and may be considered an alternative for traditional light sources. However, at this moment, manufacturers and end users of LEDs are facing a rather basic but major problem. The lack of standardization regarding optical and electrical characterization of LEDs appears to compromise a successful implementation. In particular, numbers quoted for the luminous flux, and consequently for the efficacy of LEDs, are very sensitive data because they are used to impress and push the LED market. In this paper, the most was made of the typical hemispherical radiation of high-power LEDs to increase the accuracy of the flux determination using a custom-made integrating sphere. Recently developed measurement techniques such as the use of an external spectral irradiance standard and an optimized spectral irradiance detection head are combined with a very particular port geometry and a minimized baffle area. This results in a uniform spatial response distribution function (SRDF), which guarantees an accurate radiant and luminous flux determination, irrespective of the spatial intensity distribution of the LED package or luminaire. The effect of the directional response of the detector head on the SRDF has been explored. Measurements on LED devices with and without external optics are presented, illustrating the possibilities of the measurement setup

  13. Solution processed organic light-emitting diodes using the plasma cross-linking technology

    International Nuclear Information System (INIS)

    He, Kongduo; Liu, Yang; Gong, Junyi; Zeng, Pan; Kong, Xun; Yang, Xilu; Yang, Cheng; Yu, Yan; Liang, Rongqing; Ou, Qiongrong

    2016-01-01

    Highlights: • Mixed acetylene and Ar plasma treatment makes the organic film surface cross-linked. • The plasma treatment for 30 s does not affect the performance of OLEDs. • Cross-linking surface can resist rinsing and corrosion of organic solvent. • The surface morphology is nearly unchanged after plasma treatment. • The plasma cross-linking method can realize solution processed multilayer OLEDs. - Abstract: Solution processed multilayer organic light-emitting diodes (OLEDs) present challenges, especially regarding dissolution of the first layer during deposition of a second layer. In this work, we first demonstrated a plasma cross-linking technology to produce a solution processed OLED. The surfaces of organic films can be cross-linked after mixed acetylene and Ar plasma treatment for several tens of seconds and resist corrosion of organic solvent. The film thickness and surface morphology of emissive layers (EMLs) with plasma treatment and subsequently spin-rinsed with chlorobenzene are nearly unchanged. The solution processed triple-layer OLED is successfully fabricated and the current efficiency increases 50% than that of the double-layer OLED. Fluorescent characteristics of EMLs are also observed to investigate factors influencing the efficiency of the triple-layer OLED. Plasma cross-linking technology may open up a new pathway towards fabrication of all-solution processed multilayer OLEDs and other soft electronic devices.

  14. Phototherapy rash in newborn infants: does it differ between conventional and light emitting diode phototherapy?

    Science.gov (United States)

    Surmeli-Onay, Ozge; Korkmaz, Ayse; Yigit, Sule; Yurdakok, Murat

    2013-01-01

    Data comparing the cutaneous side effects of light emitting diode (LED) phototherapy (LP) and conventional phototherapy (CP) devices in jaundiced newborn infants are very limited. We investigated the incidence and extent of skin eruptions caused by different phototherapy devices in preterm infants who are more prone to neonatal jaundice. This prospective, randomized controlled trial was conducted in the neonatal intensive care unit (NICU) of Hacettepe University Ihsan Dogramaci Childrens' Hospital in Ankara, Turkey. Preterm infants without skin lesions before and requiring phototherapy in the first week of life were included in the study. The infants were randomly assigned to receive CP or LP and were monitored closely for skin eruptions during phototherapy. Fifty-eight infants were included in the study: 25 (43.1%) received CP while 33 (56.9%) received LP. The duration of phototherapy was similar in the two groups (30.4 ± 9.6 hours and 31.8 ± 15.6 hours, respectively). Baseline and control bilirubin levels were similar for the two groups (p = 0.101 and p = 0.105, respectively). The frequency of skin eruptions was 36% in the CP group and 33% in the LP group (p = 0.83). The skin eruptions were macules in 13 (22.4%), papules in 5 (8.6%), and maculopapular rashes in 2 (3.4%) infants.There were no differences in the incidence and extent of skin eruptions in preterm infants who received CP or LP. © 2013 Wiley Periodicals, Inc.

  15. Efficacy of new microprocessed phototherapy system with five high intensity light emitting diodes (Super LED).

    Science.gov (United States)

    Martins, Bianca M R; de Carvalho, Manoel; Moreira, Maria E L; Lopes, José M A

    2007-01-01

    To evaluate the efficacy of a microprocessed phototherapy (PT) system with five high intensity light emitting diodes (Super LED) for the treatment of neonatal hyperbilirubinemia of premature infants. Randomized clinical trial using Super LED phototherapy in the study group and twin halogen spotlight phototherapy in the control group. A stratified blocked randomization, based on birth weight, was performed. The duration of phototherapy and the rate of decrease of total serum bilirubin (TSB) concentration in the first 24 hours of treatment were the main outcome measures. We studied 88 infants, 44 in the Super LED group and 44 in the halogen spotlight PT group. The demographic characteristics of the patients in both groups were similar. Infants in the Super LED group had a similar mean initial serum bilirubin level (10.1+/-2.4 mg%) to those receiving halogen spotlight treatment (10.9+/-2.0 mg%). After 24 hours of treatment, the decrease in total serum bilirubin levels was significantly greater in the Super LED group (27.9 vs. 10.7%, pphototherapy was significantly shorter in this group (36.8 h vs. 63.8 h, pLED phototherapy had reached serum bilirubin concentrations low enough to allow withdrawal of treatment (23 vs. 10, pLED phototherapy for treating hyperbilirubinemia in premature infants was significantly better than halogen phototherapy.

  16. Effects of 940 nm light-emitting diode (led) on sciatic nerve regeneration in rats.

    Science.gov (United States)

    Serafim, Karla Guivernau Gaudens; Ramos, Solange de Paula; de Lima, Franciele Mendes; Carandina, Marcelo; Ferrari, Osny; Dias, Ivan Frederico Lupiano; Toginho Filho, Dari de Oliveira; Siqueira, Cláudia Patrícia Cardoso Martins

    2012-01-01

    The objective of the present study was to evaluate the effect of 940 nm wavelength light emitting diode (LED) phototherapy on nerve regeneration in rats. Forty male Wistar rats weighing approximately 300 g each were divided into four groups: control (C); control submitted to LED phototherapy (CLed); Sciatic Nerve Lesion without LED phototherapy (L); Sciatic Nerve Lesion with LED phototherapy (LLed). The lesion was caused by crushing the right sciatic nerve. A dose of 4 J/cm(2) was used for ten consecutive days beginning on the first postoperative day. Groups C and L were submitted to the same procedure as the LLed group, but the equipment was turned off. The LED phototherapy with 940 nm wavelength reduced the areas of edema, the number of mononuclear cells present in the inflammatory infiltration, and increased functional recovery scores at 7, 14 and 21 days. The results suggest that the use of phototherapy at 940 nm after nerve damage improves morphofunctional recovery and nerve regeneration.

  17. Irradiance Decay in Fluorescent and Light-emitting Diode-based Phototherapy Devices: A Pilot Study.

    Science.gov (United States)

    Olusanya, Bolajoko O; Osibanjo, Folashade B; Emokpae, Abieyuwa A; Slusher, Tina M

    2016-10-01

    We set out to determine the rate of decline of irradiance for fluorescent tube (FT) and light-emitting diode (LED) phototherapy devices in resource-limited settings where routine irradiance monitoring is uncommon. Irradiance levels (μW/cm(2)/nm) were measured weekly using BiliBlanket(®) II Meter on three FT-based and two LED-based phototherapy devices over a 19 week period. The two LED devices showed stable irradiance levels and did not require any lamp changes. The three FT-based devices showed rapid decline in irradiance, and all required three complete lamp exchanges approximately every 5-6 weeks. FT-based devices are associated with more rapid decline in irradiance to sub-therapeutic levels and require more frequent lamp changes than LED devices. Clinicians should be alert to the maintenance requirements of the phototherapy devices available in their settings to ensure efficacy of treatment. © The Author [2016]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  18. Development of substrate-removal-free vertical ultraviolet light-emitting diode (RefV-LED

    Directory of Open Access Journals (Sweden)

    N. Kurose

    2014-02-01

    Full Text Available A vertical ultraviolet (UV light-emitting diode (LED that does not require substrate removal is developed. Spontaneous via holes are formed in n-AlN layer epitaxially grown on a high conductive n+Si substrate and the injected current flows directly from the p-electrode to high doped n+ Si substrate through p-AlGaN, multi-quantum wells, n-AlGaN and spontaneous via holes in n-AlN. The spontaneous via holes were formed by controlling feeding-sequence of metal-organic gas sources and NH3 and growth temperature in MOCVD. The via holes make insulating n-AlN to be conductive. We measured the current-voltage, current-light intensity and emission characteristics of this device. It exhibited a built-in voltage of 3.8 V and emission was stated at 350 nm from quantum wells with successive emission centered at 400 nm. This UV LED can be produced, including formation of n and p electrodes, without any resist process.

  19. Development of substrate-removal-free vertical ultraviolet light-emitting diode (RefV-LED)

    Energy Technology Data Exchange (ETDEWEB)

    Kurose, N., E-mail: kurose@fc.ritsumei.ac.jp; Aoyagi, Y. [The Research Organization of Science and Technology, Ritsumeikan University, 1-1-1, Noji-higashi, Kusatsu, Shiga 525-8577 (Japan); Shibano, K.; Araki, T. [Department of Science and Technology, Ritsumeikan University, 1-1-1, Noji-higashi, Kusatsu, Shiga 525-8577 (Japan)

    2014-02-15

    A vertical ultraviolet (UV) light-emitting diode (LED) that does not require substrate removal is developed. Spontaneous via holes are formed in n-AlN layer epitaxially grown on a high conductive n+Si substrate and the injected current flows directly from the p-electrode to high doped n{sup +} Si substrate through p-AlGaN, multi-quantum wells, n-AlGaN and spontaneous via holes in n-AlN. The spontaneous via holes were formed by controlling feeding-sequence of metal-organic gas sources and NH{sub 3} and growth temperature in MOCVD. The via holes make insulating n-AlN to be conductive. We measured the current-voltage, current-light intensity and emission characteristics of this device. It exhibited a built-in voltage of 3.8 V and emission was stated at 350 nm from quantum wells with successive emission centered at 400 nm. This UV LED can be produced, including formation of n and p electrodes, without any resist process.

  20. Influence of the hole injection layer on the luminescent performance of organic light-emitting diodes

    Science.gov (United States)

    Chen, Shih-Fang; Wang, Ching-Wu

    2004-08-01

    We investigate the influence of the hole injection layer (HIL) on the performance of vapor-deposited tris-(8-hydroxyquinoline) aluminum-based organic light-emitting diodes. Four different HIL materials were used: 4,4', 4″-tris{N ,(3-methylphenyl)-N-phenylamino}-triphenylamine) (m-MTDATA), 4,4', 4″-tris{N ,-(2-naphthyl)-N-phenylamino}-triphenylamine, copper phthalocyanine, and oxotitanium phthalocyanine. In all cases, Alq3 acts as the emitting layer as well as electron-transporting layers. Evidence showed that m-MTDATA exhibits a dense film structure and fine surface morphology, leading to easier hole migration at the indium tin oxide/m-MTDATA and m-MTDATA/hole-transport layer junctions. It also possesses a shallow bulk trap level, providing more detrapping holes from the bulk trap states to highest occupied molecular orbital states for transporting in m-MTDATA. We suggest that these are the main contributing factors to the superior current density-voltage and luminance-voltage performance of this device.

  1. Tuning the white light spectrum of light emitting diode lamps to reduce attraction of nocturnal arthropods.

    Science.gov (United States)

    Longcore, Travis; Aldern, Hannah L; Eggers, John F; Flores, Steve; Franco, Lesly; Hirshfield-Yamanishi, Eric; Petrinec, Laina N; Yan, Wilson A; Barroso, André M

    2015-05-05

    Artificial lighting allows humans to be active at night, but has many unintended consequences, including interference with ecological processes, disruption of circadian rhythms and increased exposure to insect vectors of diseases. Although ultraviolet and blue light are usually most attractive to arthropods, degree of attraction varies among orders. With a focus on future indoor lighting applications, we manipulated the spectrum of white lamps to investigate the influence of spectral composition on number of arthropods attracted. We compared numbers of arthropods captured at three customizable light-emitting diode (LED) lamps (3510, 2704 and 2728 K), two commercial LED lamps (2700 K), two commercial compact fluorescent lamps (CFLs; 2700 K) and a control. We configured the three custom LEDs to minimize invertebrate attraction based on published attraction curves for honeybees and moths. Lamps were placed with pan traps at an urban and two rural study sites in Los Angeles, California. For all invertebrate orders combined, our custom LED configurations were less attractive than the commercial LED lamps or CFLs of similar colour temperatures. Thus, adjusting spectral composition of white light to minimize attracting nocturnal arthropods is feasible; not all lights with the same colour temperature are equally attractive to arthropods. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  2. Transillumination by light-emitting diode facilitates peripheral venous cannulations in infants and small children.

    Science.gov (United States)

    Hosokawa, K; Kato, H; Kishi, C; Kato, Y; Shime, N

    2010-09-01

    Transillumination facilitates the visualization of peripheral veins in infants and children. The clinical usefulness of light-emitting diode (LED)-powered devices has not been thoroughly studied. We randomly assigned 136 infants and children weighing LED-powered transillumination (TM group, n=67) vs. the usual method (UM group, n=69) of peripheral venous cannulations. Venous puncture was performed following anesthesia induction with sevoflurane and nitrous oxide. The primary and secondary study endpoints were the rate of successful cannulations at initial attempt, and the duration of insertion attempts, respectively. The median score of the estimated cannulation difficulty before attempted puncture was similar in both groups. The success rates at first attempt were 75% and 61% (NS) and mean+/-SD times to successful venous access were 47+/-34 and 68+/-66 s (NS) in the TM and UM groups, respectively. The cannulation procedures were completed significantly earlier in the TM group than in the UM group (hazard ratio, 1.59; 95% confidence interval, 1.03-2.47; P=0.03). In the subgroup of infants and children LED-powered transillumination devices facilitated peripheral venous cannulations in small infants and children.

  3. Diffusion voltage in polymer light emitting diodes measured with electric field induced second harmonic generation

    Energy Technology Data Exchange (ETDEWEB)

    Kristensen, P.K.; Rafaelsen, J.; Pedersen, T.G.; Pedersen, K. [Department of Physics and Nanotechnology, Aalborg University, Pontoppidanstraede 103, 9220 Aalborg East (Denmark)

    2005-12-01

    We apply electric field induced second harmonic (EFISH) to polymer light emitting diodes (PLEDs) and demonstrate the ability to determine the diffusion voltage in PLED devices. The EFISH signal is proportional to the square of the effective field, which is the sum of the diffusion voltage and the applied voltage. By minimizing the EFISH-signal as a function of the applied voltage, the diffusion voltage is determined by measuring the applied voltage that cancels out the diffusion voltage. The PLEDs are fabricated with indium tin oxide (ITO) as the hole injecting contact and two different electron injecting contacts, namely aluminum and calcium. The diffusion voltage originates from the rearranged charges caused by the difference in Fermi levels in the materials in the PLEDs. Different contacts will thus cause different diffusion voltages. We demonstrate here that the EFISH signal is proportional to the square of the effective field in both reverse and forward bias, and discuss the dependence on contact materials. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Influence of heterojunction interface on exciplex emission from organic light-emitting diodes under electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Shengyi; Zhang, Xiulong; Lou, Zhidong; Hou, Yanbing [Beijing Jiaotong University, Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing (China)

    2008-03-15

    In this paper, electroluminescence from organic light-emitting diodes based on 2-(4'-biphenyl)-5-(4{sup ''}-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) is reported. Based on the exciplex emission from the TPD/PBD interface under high electric fields, the influence of the TPD/PBD interface on exciplex emission was investigated by increasing the number of TPD/PBD interfaces while keeping both the total thickness of the TPD layer and the PBD layer constant in the multiple quantum-wells (MQW) device ITO/TPD/[PBD/TPD]{sub n}/PBD/Al (n is the well number that was varied from 0 to 3). Our experimental data shows that exciplex emission can be enhanced by suitably increasing the well number of this kind of MQW-like device. (orig.)

  5. Differential carrier lifetime and transport effects in electrically injected III-nitride light-emitting diodes

    Science.gov (United States)

    Rashidi, A.; Nami, M.; Monavarian, M.; Aragon, A.; DaVico, K.; Ayoub, F.; Mishkat-Ul-Masabih, S.; Rishinaramangalam, A.; Feezell, D.

    2017-07-01

    This work describes a small-signal microwave method for determining the differential carrier lifetime and transport effects in electrically injected InGaN/GaN light-emitting diodes (LEDs). By considering the carrier diffusion, capture, thermionic escape, and recombination, the rate equations are used to derive an equivalent small-signal electrical circuit for the LEDs, from which expressions for the input impedance and modulation response are obtained. The expressions are simultaneously fit to the experimental data for the input impedance and modulation response for nonpolar InGaN/GaN micro-LEDs on free-standing GaN substrates. The fittings are used to extract the transport related circuit parameters and differential carrier lifetimes. The dependence of the parameters on the device diameter and current density is reported. We also derive approximations for the modulation response under low and high injection levels and show that the transport of carriers affects the modulation response of the device, especially at low injection levels. The methods presented are relevant to the design of high-speed LEDs for visible-light communication.

  6. High-Power Genuine Ultraviolet Light-Emitting Diodes Based On Colloidal Nanocrystal Quantum Dots.

    Science.gov (United States)

    Kwak, Jeonghun; Lim, Jaehoon; Park, Myeongjin; Lee, Seonghoon; Char, Kookheon; Lee, Changhee

    2015-06-10

    Thin-film ultraviolet (UV) light-emitting diodes (LEDs) with emission wavelengths below 400 nm are emerging as promising light sources for various purposes, from our daily lives to industrial applications. However, current thin-film UV-emitting devices radiate not only UV light but also visible light. Here, we introduce genuine UV-emitting colloidal nanocrystal quantum dot (NQD) LEDs (QLEDs) using precisely controlled NQDs consisting of a 2.5-nm-sized CdZnS ternary core and a ZnS shell. The effective core size is further reduced during the shell growth via the atomic diffusion of interior Cd atoms to the exterior ZnS shell, compensating for the photoluminescence red shift. This design enables us to develop CdZnS@ZnS UV QLEDs with pure UV emission and minimal parasitic peaks. The irradiance is as high as 2.0-13.9 mW cm(-2) at the peak wavelengths of 377-390 nm, several orders of magnitude higher than that of other thin-film UV LEDs.

  7. Application of ultraviolet light-emitting diodes (UV-LEDs) for water disinfection: A review.

    Science.gov (United States)

    Song, Kai; Mohseni, Madjid; Taghipour, Fariborz

    2016-05-01

    Ultraviolet (UV) disinfection is an effective technology for the inactivation of pathogens in water and is of growing interest for industrial application. A new UV source - ultraviolet light-emitting diode (UV-LED) - has emerged in the past decade with a number of advantages compared to traditional UV mercury lamps. This promising alternative raises great interest in the research on application of UV-LEDs for water treatment. Studies on UV-LED water disinfection have increased during the past few years. This article presents a comprehensive review of recent studies on UV-LEDs with various wavelengths for the inactivation of different microorganisms. Many inconsistent and incomparable data were found from published studies, which underscores the importance of establishing a standard protocol for studying UV-LED inactivation of microorganisms. Different UV sensitivities to UV-LEDs and traditional UV lamps were observed in the literature for some microorganisms, which requires further investigation for a better understanding of microorganism response to UV-LEDs. The unique aspects of UV-LEDs improve inactivation effectiveness by applying LED special features, such as multiple wavelengths and pulsed illumination; however, more studies are needed to investigate the influencing factors and mechanisms. The special features of UV-LEDs offer the flexibility of novel reactor designs for a broad application of UV-LED reactors. Copyright © 2016 Elsevier Ltd. All rights reserved.

  8. Comparative effectiveness of light emitting diodes (LEDs) and Lasers in near infrared photoimmunotherapy.

    Science.gov (United States)

    Sato, Kazuhide; Watanabe, Rira; Hanaoka, Hirofumi; Nakajima, Takahito; Choyke, Peter L; Kobayashi, Hisataka

    2016-03-22

    Near infrared photoimmunotherapy (NIR-PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by photosensitizers after exposure to near infrared (NIR) light. Herein we compare two NIR-light sources; light emitting diodes (LEDs) and Lasers, for their effectiveness in NIR-PIT. A photosensitizer, IRDye-700DX, conjugated to panitumumab (pan-IR700), was incubated with EGFR-expressing A431 and MDA-MB-468-luc cells. NIR-light was provided by LEDs or Lasers at the same light dose. Laser-light produced more cytotoxicity and greater reductions in IR700-fluorescence intensity than LED-light. Laser-light also produced more cytotoxicity in vivo in both cell lines. Assessment of super-enhanced permeability and retention (SUPR) effects were stronger with Laser than LED. These results suggest that Laser-light produced significantly more cytotoxic effects compared to LEDs. Although LED is less expensive, Laser-light produces superior results in NIR-PIT.

  9. Structural design and optimization of near-ultraviolet light-emitting diodes with wide wells

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, Yen-Kuang, E-mail: ykuo@cc.ncue.edu.tw [Department of Physics, National Changhua University of Education, Changhua 500, Taiwan (China); Chen, Fang-Ming [Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan (China); Chang, Jih-Yuan [Center for Teacher Education, National Changhua University of Education, Changhua 500, Taiwan (China); Shih, Ya-Hsuan [Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan (China)

    2016-03-07

    The characteristics of the near-ultraviolet (NUV) light-emitting diodes (LEDs) with wide (14-nm-thick) and narrow (2-nm-thick) wells under the situations of different numbers of wells and degree of polarization are systematically investigated. The simulation results show that the Auger recombination can be efficiently suppressed with the increase of number of wells in NUV LEDs. For the LEDs with wide wells, the quantum-confined Stark effect and Shockley–Read–Hall recombination play an important role when the number of wells increases, especially when the LED is under low current injection or high degree of polarization. In order to take the advantage of using wide wells, it is proposed that the quaternary Al{sub 0.1}In{sub 0.05}Ga{sub 0.85}N barriers be used in wide-well NUV LEDs along with the use of Al{sub 0.3}Ga{sub 0.7}N/Al{sub 0.1}Ga{sub 0.9}N superlattice electron-blocking layer to mitigate the polarization effect and electron overflow. With this band-engineering structural design, the optical performance of the wide-well NUV LEDs is much better than its thin-well counterpart even under the situation of high degree of polarization.

  10. Injection and detection of a spin-polarized current in a light-emitting diode

    Science.gov (United States)

    Fiederling, R.; Keim, M.; Reuscher, G.; Ossau, W.; Schmidt, G.; Waag, A.; Molenkamp, L. W.

    1999-12-01

    The field of magnetoelectronics has been growing in practical importance in recent years. For example, devices that harness electronic spin-such as giant-magnetoresistive sensors and magnetoresistive memory cells-are now appearing on the market. In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts, but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a non-magnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.

  11. NANOSTRUCTURED HIGH PERFORMANCE ULTRAVIOLET AND BLUE LIGHT EMITTING DIODES FOR SOLID STATE LIGHTING

    Energy Technology Data Exchange (ETDEWEB)

    Arto V. Nurmikko; Jung Han

    2004-10-01

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the first 12 month contract period include (1) new means of synthesizing zero- and one-dimensional GaN nanostructures, (2) establishment of the building blocks for making GaN-based microcavity devices, and (3) demonstration of top-down approach to nano-scale photonic devices for enhanced spontaneous emission and light extraction. These include a demonstration of eight-fold enhancement of the external emission efficiency in new InGaN QW photonic crystal structures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  12. Efficient light emitting diodes by photon recycling and their application in pixelless infrared imaging devices

    Science.gov (United States)

    Dupont, E.; Chiu, S.

    2000-02-01

    The success of the pixelless imaging concept using a quantum well infrared photodetector integrated with a light emitting diode (QWIP-LED) depends critically on the extent of spatial lateral spreading of both photocurrent generated in the QWIP and near infrared (NIR) photons emitted by the LED as they escape from the device layers. According to the photon recycling model proposed by Schnitzer et al. [Appl. Phys. Lett. 62, 131 (1993)] there appears to be a trade-off between a high LED external quantum efficiency and a small photon lateral spread, the former being a necessary condition for achieving high detector sensitivity. This lateral spreading due to multireflections and reincarnations of the NIR photons could potentially degrade the image quality or resolution of the device. By adapting Schnitzer's model to the QWIP-LED structure, we have identified device parameters that could potentially influence the NIR photon lateral spread and the LED external efficiency. In addition, we have developed a simple sequential model to estimate the crosstalk between the incoming far infrared image and the up-converted NIR image. We have found that the thickness of the LED is an important parameter that needs to be optimized in order to maximize the external efficiency and to minimize the crosstalk. A 6000-Å-thick LED active layer should give a resolution of ˜30 μm and an external efficiency of ˜10%.

  13. Investigation of Mechanical Properties of Silicone/Phosphor Composite Used in Light Emitting Diodes Package

    Directory of Open Access Journals (Sweden)

    Yongjun Pan

    2018-02-01

    Full Text Available Mass fraction of phosphor in silicone and aging time play important roles in the optics and mechanical performance of the silicone that is used in the light emitting diode (LED package. In this paper, the mechanical properties of silicone/phosphor composites are investigated experimentally by separate tensile and compression tests. Distribution of the phosphors is observed by scanning electron microscopy (SEM to ensure the homogeneity of the samples. Different loading rates are applied to study the silicone material’s rate-dependent properties. The experimental results of the tensile and compression test show that the Young’s modulus increases with the mass fraction of phosphor in silicone. Longer aging time stiffens the silicone composite and weakens the ductility of the materials. A three-dimensional model used cohesive zone material (CZM between the interface of the phosphor particles, and matrix silicone is built up to study the degradation mechanism at a micro-scale level. The simulation results indicate that the diameter of particles in silicone also impacts its interface debonding and crack growth. The theoretical results concerning the mass fraction of phosphor are in good agreement with the experiments.

  14. Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Liping; Chen, Jiangshan; Ma, Dongge, E-mail: mdg1014@ciac.ac.cn [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Changchun 130022 (China)

    2015-11-07

    We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency, and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m{sup 2} luminance. The critical current density is as high as 210 mA/cm{sup 2}. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.

  15. Efficient green phosphorescent tandem organic light emitting diodes with solution processable mixed hosts charge generating layer

    Energy Technology Data Exchange (ETDEWEB)

    Talik, N.A.; Yeoh, K.H.; Ng, C.Y.B [Low Dimensional Research Center, Department of Physics, University Malaya, 50603 Kuala Lumpur (Malaysia); ItraMAS Corporation. Sdn. Bhd., 542A-B Mukim 1, Lorong Perusahaan Baru 2, Kawasan Perindustrian, Perai 13600, Penang (Malaysia); Yap, B.K. [Center of Microelectronic and Nanotechnology Engineering (CeMNE), College of Engineering, Universiti Tenaga Nasional, Jln. Uniten-Ikram, 4300 Kajang, Selangor (Malaysia); Woon, K.L., E-mail: ph7klw76@um.edu.my [Low Dimensional Research Center, Department of Physics, University Malaya, 50603 Kuala Lumpur (Malaysia)

    2014-10-15

    A novel solution processable charge generating layer (CGL) that consists of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN{sub 6})/Poly(N-vinylcarbazole) (PVK): 1,1-bis-(4-bis(4-tolyl)-aminophenyl) cyclohexene (TAPC) for a tandem green phosphorescent organic light emitting diode (PHOLED) is demonstrated. The use of orthogonal solvent to dissolve HATCN{sub 6} and PVK:TAPC is the key to overcome the interface erosion problem for the solution processed CGL. The current efficiency of the 2 wt% TAPC mixed with PVK is the highest at 24.2 cd/A, which is more than three-folds higher than that of the single device at 1000 cd/m{sup 2}. - Highlights: • A solution processable tandem OLED is built using a novel charge generating layer. • HATCN{sub 6} and PVK:TAPC are shown to be effective charge generating layers. • The turn on voltages for tandem devices are almost similar to single unit. • 2 wt% TAPC blended with PVK exhibits three-folds increase in efficiency.

  16. Exciplex-Forming Cohost for High Efficiency and High Stability Phosphorescent Organic Light-Emitting Diodes.

    Science.gov (United States)

    Shih, Chun-Jen; Lee, Chih-Chien; Chen, Ying-Hao; Biring, Sajal; Kumar, Gautham; Yeh, Tzu-Hung; Sen, Somaditya; Liu, Shun-Wei; Wong, Ken-Tsung

    2018-01-17

    An exciplex forming cohost system is employed to achieve a highly efficient organic light-emitting diode (OLED) with good electroluminescent lifetime. The exciplex is formed at the interfacial contact of a conventional star-shaped carbazole hole-transporting material, 4,4',4″-tris(N-carbazolyl)-triphenylamine (TCTA), and a triazine electron-transporting material, 2,4,6-tris[3-(1H-pyrazol-1-yl)phenyl]-1,3,5-triazine (3P-T2T). The excellent combination of TCTA and 3P-T2T is applied as the cohost of a common green phosphorescent emitter with almost zero energy loss. When Ir(ppy) 2 (acac) is dispersed in such exciplex cohost system, OLED device with maximum external quantum efficiency of 29.6%, the ultrahigh power efficiency of 147.3 lm/W, and current efficiency of 107 cd/A were successfully achieved. More importantly, the OLED device showed a low-efficiency roll-off and an operational lifetime (τ 80 ) of ∼1020 min with the initial brightness of 2000 cd/m 2 , which is 56 times longer than the reference device. The significant difference of device stability was attributed to the degradation of exciplex system for energy transfer process, which was investigated by the photoluminescence aging measurement at room temperature and 100 K, respectively.

  17. Role of wide bandgap host in the degradation of blue phosphorescent organic light-emitting diodes

    Science.gov (United States)

    Yang, R. Y.; Li, X. M.; Cao, X. A.

    2017-08-01

    Accelerated reliability tests of blue phosphorescent organic light-emitting diodes (OLEDs) comprising bis[(4,6-difluorophenyl)pyridinato-N,C2](picolinato)-iridium(III) (FIrpic) doped in four different wide bandgap hosts were conducted. The half-life of the OLEDs stressed under a high current density of 100 mA/cm2 varied in a wide range, revealing an important role of the host. Pulsed current stressing with a 1% duty cycle was performed to suppress self-heating, but only extended the lifetime by 2-3.2×. For blue OLEDs with a host favoring hole transport, current stressing caused a shift of the recombination zone toward the anode, turning the emission color to greenish blue. These results suggest that device degradation was mainly caused by charge-trapping defects generated within a narrow zone close to the electron-transport layer. It is expected that the lifetime of blue phosphorescent OLEDs can be effectively extended by selecting an appropriate host which has good stability, enables efficient charge injection and balanced charge transport in the emissive layer.

  18. Hot excited state management for long-lived blue phosphorescent organic light-emitting diodes

    Science.gov (United States)

    Lee, Jaesang; Jeong, Changyeong; Batagoda, Thilini; Coburn, Caleb; Thompson, Mark E.; Forrest, Stephen R.

    2017-05-01

    Since their introduction over 15 years ago, the operational lifetime of blue phosphorescent organic light-emitting diodes (PHOLEDs) has remained insufficient for their practical use in displays and lighting. Their short lifetime results from annihilation between high-energy excited states, producing energetically hot states (>6.0 eV) that lead to molecular dissociation. Here we introduce a strategy to avoid dissociative reactions by including a molecular hot excited state manager within the device emission layer. Hot excited states transfer to the manager and rapidly thermalize before damage is induced on the dopant or host. As a consequence, the managed blue PHOLED attains T80=334+/-5 h (time to 80% of the 1,000 cd m-2 initial luminance) with a chromaticity coordinate of (0.16, 0.31), corresponding to 3.6+/-0.1 times improvement in a lifetime compared to conventional, unmanaged devices. To our knowledge, this significant improvement results in the longest lifetime for such a blue PHOLED.

  19. Abrupt change of luminescence spectrum in single-layer phosphorescent polymer light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, X.; Lee, D.-H.; Chae, H. [School of Chemical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Cho, S.M., E-mail: sungmcho@skku.edu [School of Chemical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Advanced Materials and Process Research Center for IT, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2012-01-15

    PVK-based single-layer phosphorescent polymer OLEDs (organic light emitting diodes) with different rubrene concentrations were fabricated and examined for the Foerster energy transfer from phosphorescent FIrpic dye to rubrene. We found out that at a certain rubrene concentration the energy transfer occurs abruptly and the transfer shows an abnormal evolution of electroluminescence (EL) spectrum due to the coincidence of peak wavelengths of bis[(4,6-difluorophenyl)-pyridinato-N,C{sup 2'}](picolinate) iridium(III) (FIrpic) emission and 5,6,11,12-tetraphenylnaphthacene (rubrene) absorption. With the calculation of Foerster radius and average distance between FIrpic molecules, we have related the calculated ratio between the number of FIrpic molecules within to that out of Foerster radius with the degree of Foerster energy transfer from EL spectra measured in the experiment. Experimental results were found to fit well with the predicted results especially at low rubrene concentrations. - Highlights: > Foerster energy transfer between FIrpic and rubrene. > Energy transfer shows an abnormal evolution of emission spectrum. > Calculated Foerster radius and degree of energy transfer by a simple model.

  20. Improved efficiency in blue phosphorescent organic light-emitting diodes by the stepwise doping structure

    Science.gov (United States)

    Yang, Liping; Wang, Xiaoping; Kou, Zhiqi; Ji, Changyan

    2017-04-01

    The electro-optical properties of the blue phosphorescent organic light-emitting diodes (PHOLEDs) can be affected by the stepwise doping structure in the emitting layer (EML). A series of multi-EML devices with different doping concentration of blue dopant (FIrpic) are fabricated. The effect of the stepwise doping structure close to the electron transport layer is more obvious than that close to the hole transport layer. When the doping concentration increases gradually from the hole injection side to the electron injection side, the maximum values of the luminance, current and power efficiency can reach to 9745 cd/m2 (at 9 V), 32.0 cd/A and 25.1 lm/W in the device with the asymmetric tri-EML structure, which is improved by about 10% compared with that in the bi-EML device. When the number of the EML is four, the performance of the device becomes worse because of the interface effect resulting from different concentration of dopant.

  1. Multiple night-time light-emitting diode lighting strategies impact grassland invertebrate assemblages.

    Science.gov (United States)

    Davies, Thomas W; Bennie, Jonathan; Cruse, Dave; Blumgart, Dan; Inger, Richard; Gaston, Kevin J

    2017-07-01

    White light-emitting diodes (LEDs) are rapidly replacing conventional outdoor lighting technologies around the world. Despite rising concerns over their impact on the environment and human health, the flexibility of LEDs has been advocated as a means of mitigating the ecological impacts of globally widespread outdoor night-time lighting through spectral manipulation, dimming and switching lights off during periods of low demand. We conducted a three-year field experiment in which each of these lighting strategies was simulated in a previously artificial light naïve grassland ecosystem. White LEDs both increased the total abundance and changed the assemblage composition of adult spiders and beetles. Dimming LEDs by 50% or manipulating their spectra to reduce ecologically damaging wavelengths partially reduced the number of commoner species affected from seven to four. A combination of dimming by 50% and switching lights off between midnight and 04:00 am showed the most promise for reducing the ecological costs of LEDs, but the abundances of two otherwise common species were still affected. The environmental consequences of using alternative lighting technologies are increasingly well established. These results suggest that while management strategies using LEDs can be an effective means of reducing the number of taxa affected, averting the ecological impacts of night-time lighting may ultimately require avoiding its use altogether. © 2017 John Wiley & Sons Ltd.

  2. Optical fluence modelling for ultraviolet light emitting diode-based water treatment systems.

    Science.gov (United States)

    Simons, R; Gabbai, U E; Moram, M A

    2014-12-01

    This work presents a validated optical fluence rate model optimised for ultraviolet light-emitting diodes (UV-LEDs), which allow a very wide range of emission wavelengths and source geometries to be used in water treatment units. The model is based on a Monte Carlo approach, in which an incremental ray-tracing algorithm is used to calculate the local volumetric rate of energy absorption and subsequently convert it to the local fluence rate distribution for an UV-LED water treatment chamber of arbitrary design. The model includes contributions from optical reflections and scattering by treatment chamber walls and from scattering due to particulates and/or microorganisms. The model successfully predicts optical fluence rates in point-of-use water treatment units, as verified using biodosimetry with MS-2 bacteriophage at a UV-LED emission wavelength of 254 nm. The effects of chamber geometry are also modelled effectively and are consistent with the inactivation data for E. coli at 254 nm. The data indicate that this model is suitable for application in the design and optimisation of UV-LED-based water treatment systems. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Determination of the optical constants of polymer light-emitting diode films from single reflection measurements

    International Nuclear Information System (INIS)

    Zhu Dexi; Shen Weidong; Ye Hui; Liu Xu; Zhen Hongyu

    2008-01-01

    We present a simple and fast method to determine the optical constant and physical thickness of polymer films from a single reflectivity measurement. A self-consistent dispersion formula of the Forouhi-Bloomer model was introduced to fit the measured spectral curves by a modified 'Downhill' simplex algorithm. Four widely used polymer light-emitting diodes materials: poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene], poly(9,9-dioctylfluoreny-2,7-diyl) (PFO), poly(N-vinyl carbazole) and poly(3,4-ethylene dioxythiophene) : poly(styrenesulfonate) were investigated by this technique. The refractive indices over the whole visible region as well as the optical band gap extracted by this method agree well with those reported in the literature. The determined physical thicknesses present a deviation less than 4% compared with the experimental values measured by the stylus profiler. The influence of scattering loss on the fitted results is discussed to demonstrate the applicability of this technology for polymer films.

  4. A charge inverter for III-nitride light-emitting diodes

    International Nuclear Information System (INIS)

    Zhang, Zi-Hui; Zhang, Yonghui; Bi, Wengang; Geng, Chong; Xu, Shu; Demir, Hilmi Volkan; Sun, Xiao Wei

    2016-01-01

    In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO 2 insulator layer on the p + -GaN surface of a LED structure before growing the p-electrode. When the LED is forward-biased, a weak inversion layer can be obtained at the interface between the p + -GaN and SiO 2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO 2 layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p + -GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm 2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.

  5. Organic Light-Emitting Diodes with Highly Conductive Polymer Electrodes as Anode and Their Stress Tolerance

    Science.gov (United States)

    Kajii, Hirotake; Ohmori, Yutaka; Maki, Hideki; Sekimoto, Yasuhiro; Shigeno, Yasuhiro; Takehara, Naoya; Nakagawa, Hiroshi

    2008-01-01

    The fabrication and characteristics of organic light-emitting diodes (OLEDs) with highly conductive polymer electrodes as an anode and the stress tolerance of the devices fabricated on polymeric substrates were studied. By inserting a wet-processed organic layer between a polymer electrode and a dry-processed hole-transport layer, the surface emission pattern from an OLED was markedly improved. For the device with a wet-processed organic layer (methoxy-substituted 1,3,5-tris[4-(diphenylamino)phenyl]benzene), the uniform surface emission resulted from the uniform applied electric field in the emissive layer and the improvement in interface adherence. The OLED with a wet-processed layer as a hole injection layer showed a maximum luminance and a maximum efficiency of 10,000 cd/m2 and 3.5 cd/A, respectively. For the device fabricated on a polymeric substrate, the impact testing of the OLEDs with highly conductive polymer electrodes [poly(ethylenedioxythiophene):poly(styrene sulfonic acid)] as an anode revealed that the emission lasted for more than several ten thousand steps. A highly conductive polymer electrode had a sufficient tolerance to mechanical stress, as determined by comparing devices with indium tin oxide and a highly conductive polymer as anodes.

  6. Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting

    Energy Technology Data Exchange (ETDEWEB)

    Arto V. Nurmikko; Jung Han

    2005-09-30

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the second 12 month contract period include (i) new means of synthesizing AlGaN and InN quantum dots by droplet heteroepitaxy, (ii) synthesis of AlGaInN nanowires as building blocks for GaN-based microcavity devices, (iii) progress towards direct epitaxial alignment of the dense arrays of nanowires, (iv) observation and measurements of stimulated emission in dense InGaN nanopost arrays, (v) design and fabrication of InGaN photonic crystal emitters, and (vi) observation and measurements of enhanced fluorescence from coupled quantum dot and plasmonic nanostructures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  7. The effect of Indium metal nanoparticles on the electronic properties of organic light emitting diodes (OLEDs)

    Energy Technology Data Exchange (ETDEWEB)

    Kalhor, Davood, E-mail: d_kalhor@sbu.ac.ir [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran 1983963113 (Iran, Islamic Republic of); Department of Physics, Damghan University, POB 3671941167, Damghan (Iran, Islamic Republic of); Mohajerani, Ezeddin, E-mail: e-mohajerani@sbu.ac.ir [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran 1983963113 (Iran, Islamic Republic of); Hashemi Pour, Omid, E-mail: HashemiPour@sbu.ac.ir [Department of Electrical and Computer Engineering, Shahid Beheshti University, G.C., Tehran 1983963113 (Iran, Islamic Republic of)

    2015-11-15

    In this paper the effect of Indium nanoparticles (NPs) on the electronic properties of organic light emitting diodes (OLEDs) is experimentally investigated. The metal NPs which are added to the hole transfer layer can be considered as a blocker layer for injected electrons. By optimizing hole and electron ratio, current density and voltage can be decreased. In order to study this effect, among various fabricated devices, a specific structure, namely ITO/PEDOT:PSS (50 nm)/TPD (45 nm)/NPs (x nm)/Alq{sub 3} (50 nm)/Ag (80 nm) has been used. Also, the experiment is investigated for Au and Cu as different cathode the results of structures are compared with Ag cathode. A manually controllable shutter was used for vacuum deposition process to prepare the same structures and to avoid any disturbing effects. It is observed that specific Indium NPs reduce current density and turn on voltage of the device. - Highlights: • The effect of In NPs on the electronic properties of OLEDs is investigated. • Current density and voltage may be reduced by optimizing electron hole ratio. • In NPs reduce the current density and turn on voltage of the device.

  8. Double surface plasmon enhanced organic light-emitting diodes by gold nanoparticles and silver nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Chia-Yuan; Chen, Ying-Chung [Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan (China); Chen, Kan-Lin [Department of Electronic Engineering, Fortune Institute of Technology, Kaohsiung, Taiwan (China); Huang, Chien-Jung, E-mail: chien@nuk.edu.tw [Department of Applied Physics, National University of Kaohsiung, Kaohsiung, Taiwan (China)

    2015-12-30

    Graphical abstract: - Highlights: • The buffer layer is inserted between PEDOT: PSS and the emitting layer in order to avoid that the nonradiative decay process of exciton is generated. • The silver nanoclusters will generate surface plasmon resonance effect, resulting that the localized electric field around the silver nanoclusters is enhanced. • When the recombination region of the excitons is too close to the nanoparticles of the hole-transport layer, the nonradiative quenching of excitons is generated. - Abstract: The influence of gold nanoparticles (GNPs) and silver nanoclusters (SNCs) on the performance of organic light-emitting diodes is investigated in this study. The GNPs are doped into (poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate)) (PEDOT: PSS) and the SNCs are introduced between the electron-injection layer and cathode alumina. The power efficiency of the device, at the maximum luminance, with double surface plasmon resonance and buffer layer is about 2.15 times higher than that of the device without GNPs and SNCs because the absorption peaks of GNPs and SNCs are as good as the photoluminescence peak of the emission layer, resulting in strong surface plasmon resonance effect in the device. In addition, the buffer layer is inserted between PEDOT: PSS and the emitting layer in order to avoid that the nonradiative decay process of exciton is generated.

  9. Energy down converting organic fluorophore functionalized mesoporous silica hybrids for monolith-coated light emitting diodes

    Directory of Open Access Journals (Sweden)

    Markus Börgardts

    2017-04-01

    Full Text Available The covalent attachment of organic fluorophores in mesoporous silica matrices for usage as energy down converting phosphors without employing inorganic transition or rare earth metals is reported in this article. Triethoxysilylpropyl-substituted derivatives of the blue emitting perylene, green emitting benzofurazane, and red emitting Nile red were synthesized and applied in the synthesis of mesoporous hybrid materials by postsynthetic grafting to commercially available MCM-41. These individually dye-functionalized hybrid materials are mixed in variable ratios to furnish a powder capable of emitting white light with CIE chromaticity coordinates of x = 0.33, y = 0.33 and an external quantum yield of 4.6% upon irradiation at 410 nm. Furthermore, as a proof of concept two different device setups of commercially available UV light emitting diodes, are coated with silica monoliths containing the three triethoxysilylpropyl-substituted fluorophore derivatives. These coatings are able to convert the emitted UV light into light with correlated color temperatures of very cold white (41100 K, 10700 K as well as a greenish white emission with correlated color temperatures of about 5500 K.

  10. Efficiency Control in Iridium Complex-Based Phosphorescent Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Boucar Diouf

    2012-01-01

    Full Text Available Key factors to control the efficiency in iridium doped red and green phosphorescent light emitting diodes (PhOLEDs are discussed in this review: exciton confinement, charge trapping, dopant concentration and dopant molecular structure. They are not independent from each other but we attempt to present each of them in a situation where its specific effects are predominant. A good efficiency in PhOLEDs requires the triplet energy of host molecules to be sufficiently high to confine the triplet excitons within the emitting layer (EML. Furthermore, triplet excitons must be retained within the EML and should not drift into the nonradiative levels of the electron or hole transport layer (resp., ETL or HTL; this is achieved by carefully choosing the EML’s adjacent layers. We prove how reducing charge trapping results in higher efficiency in PhOLEDs. We show that there is an ideal concentration for a maximum efficiency of PhOLEDs. Finally, we present the effects of molecular structure on the efficiency of PhOLEDs using red iridium complex dopant with different modifications on the ligand to tune its highest occupied molecular orbital (HOMO and lowest unoccupied molecular orbital (LUMO energies.

  11. Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Kai Ding

    2017-10-01

    Full Text Available We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV light-emitting diodes (LEDs, with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances in the methods for the growth of bulk single crystal AlN intended as a native substrate together with a discussion of its UV transparency. It should be stated, however, that due to the high-cost of bulk AlN substrates at the time of writing, the growth of DUV LEDs on foreign substrates such as sapphire still dominates the field. On the deposition front, the heteroepitaxial growth approaches incorporate high-temperature metal organic chemical vapor deposition (MOCVD and pulsed-flow growth, a variant of MOCVD, with the overarching goal of enhancing adatom surface mobility, and thus epitaxial lateral overgrowth which culminates in minimization the effect of lattice- and thermal-mismatches. This is followed by addressing the benefits of pseudomorphic growth of strained high Al-molar fraction AlGaN on AlN. Finally, methods utilized to enhance both p- and n-type conductivity of high Al-molar fraction AlGaN are reviewed.

  12. EDGE EFFECT MODELING AND STUDY FOR THREE-CHIP RGB LIGHT-EMITTING DIODES

    Directory of Open Access Journals (Sweden)

    A. I. Podosinnikov

    2015-03-01

    Full Text Available Subject of study. The paper deals with light quality improvement of multi–chip RGB light-emitting diodes (LEDs and luminaries on their basis. In particular, we have studied the issues of the edge effect reducing, which is non–uniformity of color when observing the source of light under different angles as well as non-uniformity of color distribution on the illuminated surface. Methods. Experimental study of the edge effect has been performed, namely, the analysis of the halo at the periphery of the illuminated area and the non–uniformity of area at the surface of the screen illuminated with RGB LEDs with and without light concentrators. Modeling of illumination distribution at various distances from the source for the system containing four RGB LEDs with reflectors by ZEMAX software has been carried out. Assessment of the uniformity for light distribution via calculating the chromaticity coordinates has been performed. Main results. The possibility of modeling application at the stage of a luminary design is shown on the example of RGB LEDs for assessing the efficiency of light flux usage and colorimetric parameters. Suggested method simplifies significantly the design of luminaries and reduces associated costs. Practical relevance. The findings can be used in the design of luminaries based on RGB LEDs, including the ones with secondary optics elements.

  13. Modeling of light-emitting diode wavefronts for the optimization of transmission holograms.

    Science.gov (United States)

    Karthaus, Daniela; Giehl, Markus; Sandfuchs, Oliver; Sinzinger, Stefan

    2017-06-20

    The objective of applying transmission holograms in automotive headlamp systems requires the adaptation of holograms to divergent and polychromatic light sources like light-emitting diodes (LEDs). In this paper, four different options to describe the scalar light waves emitted by a typical automotive LED are regarded. This includes a new approach to determine the LED's wavefront from interferometric measurements. Computer-generated holograms are designed considering the different LED approximations and recorded into a photopolymer. The holograms are reconstructed with the LED and the resulting images are analyzed to evaluate the quality of the wave descriptions. In this paper, we show that our presented new approach leads to better results in comparison to other wave descriptions. The enhancement is evaluated by the correlation between reconstructed and ideal images. In contrast to the next best approximation, a spherical wave, the correlation coefficient increased by 0.18% at 532 nm, 1.69% at 590 nm, and 0.75% at 620 nm.

  14. Red/near-infrared light-emitting diode therapy for traumatic brain injury

    Science.gov (United States)

    Naeser, Margaret A.; Martin, Paula I.; Ho, Michael D.; Krengel, Maxine H.; Bogdanova, Yelena; Knight, Jeffrey A.; Yee, Megan K.; Zafonte, Ross; Frazier, Judith; Hamblin, Michael R.; Koo, Bang-Bon

    2015-05-01

    This invited paper reviews our research with scalp application of red/near-infrared (NIR) light-emitting diodes (LED) to improve cognition in chronic, traumatic brain injury 1. Application of red/NIR light improves mitochondrial function (especially hypoxic/compromised cells) promoting increased ATP, important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. Eleven chronic, mTBI participants with closed-head injury and cognitive dysfunction received 18 outpatient treatments (MWF, 6 Wks) starting at 10 Mo. to 8 Yr. post-mTBI (MVA, sports-related, IED blast injury). LED therapy is non-invasive, painless, non-thermal (FDA-cleared, non-significant risk device). Each LED cluster head (2.1" diameter, 500mW, 22.2mW/cm2) was applied 10 min (13J/cm2) to 11 scalp placements: midline, from front-to-back hairline; and bilaterally on dorsolateral prefrontal cortex, temporal, and parietal areas. Testing performed pre- and post-LED (+1 Wk, 1 and 2 Mo post- 18th treatment) showed significant linear trend for LED effect over time, on improved executive function and verbal memory. Fewer PTSD symptoms were reported. New studies at VA Boston include TBI patients treated with transcranial LED (26J/cm2); or treated with only intranasal red, 633nm and NIR, 810nm diodes placed into the nostrils (25 min, 6.5mW, 11.4J/cm2). Intranasal LEDs are hypothesized to deliver photons to hippocampus. Results are similar to Naeser et al. (2014). Actigraphy sleep data show increased sleep time (average, +1 Hr/night) post-18th transcranial or intranasal LED treatment. LED treatments may be self-administered at home (Naeser et al., 2011). A shamcontrolled study with Gulf War Illness Veterans is underway.

  15. Soluble Flavanthrone Derivatives: Synthesis, Characterization, and Application to Organic Light-Emitting Diodes.

    Science.gov (United States)

    Kotwica, Kamil; Bujak, Piotr; Data, Przemyslaw; Krzywiec, Wojciech; Wamil, Damian; Gunka, Piotr A; Skorka, Lukasz; Jaroch, Tomasz; Nowakowski, Robert; Pron, Adam; Monkman, Andrew

    2016-06-01

    Simple modification of benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine-8,16-dione, an old and almost-forgotten vat dye, by reduction of its carbonyl groups and subsequent O-alkylation, yields solution-processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and -3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16-dioctyloxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine (FC-8), the most promising compound, was solved. It crystallizes in space group P1‾ and forms π-stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC-8 have a strong tendency to self-organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16-Dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80 %. They show efficient electroluminescence, and can be used as guest molecules with a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl host in guest/host-type organic light-emitting diodes. The best fabricated diodes showed a luminance of about 1900 cd m(-12) , a luminance efficiency of about 3 cd A(-1) , and external quantum efficiencies exceeding 0.9 %. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Fabrication of an organic light-emitting diode inside a liquid crystal display

    International Nuclear Information System (INIS)

    Lee, Jiun-Haw; Chang, Wei-Fu; Wu, Cheng-Che; Lin, Chi-Feng; Lee, Jiunn-Yih; Chiu, Tien-Lung

    2013-01-01

    The fabrication of a hybrid device architecture fully integrating a transparent organic light-emitting diode (OLED) and a liquid crystal display (LCD) within two glass substrates is reported in this study. The transparent OLED was fabricated on the inner surface of the glass substrate. Twisted nematic liquid crystal (LC) materials were used to fill the space between the two glass substrates. The OLED was driven by an indium-tin oxide (ITO) anode on the glass substrate and a thin bi-metal (Al/Ag) cathode, which also served as the electrode of the LCD. The other electrode for the LCD-mode operation was the ITO on the other glass substrate. A commercially available ultraviolet (UV)-curable resin was spun onto the thin Al/Ag as the passivation layer to protect the OLED from attacks by the following polyimide layer (serving as the alignment layer of the LCD), rubbing process and LC materials. In this device structure, the electrical characteristic of the OLED-mode operation was almost the same as that of the control device. Current efficiency (in terms of cd/A) of the hybrid device from top-emission (towards the LCD) decreased by 26.5% due to optical interference effect, whereas efficiency from bottom-emission remained the same. The driving voltage of the LCD-mode operation increased by 1.6 V due to the insertion of the passivation layer between the two electrodes. The contrast ratio decreased from 150 to 25 due to the reflection of the thin Al/Ag layer. Compared with that of the control device, the storage lifetime of the OLED increased as a result of filling the encapsulated cavity with LC materials, which helped repel ambient water and oxygen. - Highlights: • Organic light emitting device (OLED) was fabricated inside liquid crystal device (LCD). • LCD protected OLED from the attack of ambient oxygen and moisture. • OLED functions were not affected by LCD process with suitable treatment

  17. Resonant cavity light-emitting diodes based on dielectric passive cavity structures

    Science.gov (United States)

    Ledentsov, N.; Shchukin, V. A.; Kropp, J.-R.; Zschiedrich, L.; Schmidt, F.; Ledentsov, N. N.

    2017-02-01

    A novel design for high brightness planar technology light-emitting diodes (LEDs) and LED on-wafer arrays on absorbing substrates is proposed. The design integrates features of passive dielectric cavity deposited on top of an oxide- semiconductor distributed Bragg reflector (DBR), the p-n junction with a light emitting region is introduced into the top semiconductor λ/4 DBR period. A multilayer dielectric structure containing a cavity layer and dielectric DBRs is further processed by etching into a micrometer-scale pattern. An oxide-confined aperture is further amended for current and light confinement. We study the impact of the placement of the active region into the maximum or minimum of the optical field intensity and study an impact of the active region positioning on light extraction efficiency. We also study an etching profile composed of symmetric rings in the etched passive cavity over the light emitting area. The bottom semiconductor is an AlGaAs-AlAs multilayer DBR selectively oxidized with the conversion of the AlAs layers into AlOx to increase the stopband width preventing the light from entering the semiconductor substrate. The approach allows to achieve very high light extraction efficiency in a narrow vertical angle keeping the reasonable thermal and current conductivity properties. As an example, a micro-LED structure has been modeled with AlGaAs-AlAs or AlGaAs-AlOx DBRs and an active region based on InGaAlP quantum well(s) emitting in the orange spectral range at 610 nm. A passive dielectric SiO2 cavity is confined by dielectric Ta2O5/SiO2 and AlGaAs-AlOx DBRs. Cylindrically-symmetric structures with multiple ring patterns are modeled. It is demonstrated that the extraction coefficient of light to the air can be increased from 1.3% up to above 90% in a narrow vertical angle (full width at half maximum (FWHM) below 20°). For very small oxide-confined apertures 100nm the narrowing of the FWHM for light extraction can be reduced down to 5

  18. Mobility balance in the light-emitting layer governs the polaron accumulation and operational stability of organic light-emitting diodes

    Science.gov (United States)

    Kim, Jae-Min; Lee, Chang-Heon; Kim, Jang-Joo

    2017-11-01

    Organic light-emitting diode (OLED) displays are lighter and more flexible, have a wider color gamut, and consume less power than conventional displays. Stable materials and the structural design of the device are important for OLED longevity. Control of charge transport and accumulation in the device is particularly important because the interaction of excitons and polarons results in material degradation. This research investigated the charge dynamics of OLEDs experimentally and by drift-diffusion modeling. Parallel capacitance-voltage measurements of devices provided knowledge of charge behavior at different driving voltages. A comparison of exciplex-forming co-host and single host structures established that the mobility balance in the emitting layers determined the amount of accumulated polarons in those layers. Consequently, an exciplex-forming co-host provides a superior structure in terms of device lifetime and efficiency because of its well-balanced mobility. Minimizing polaron accumulation is key to achieving long OLED device lifetimes. This is a crucial aspect of device physics that must be considered in the device design structure.

  19. Stacking layered structure of polymer light emitting diodes prepared by evaporative spray deposition using ultradilute solution for improving carrier balance

    International Nuclear Information System (INIS)

    Aoki, Youichi; Shakutsui, Masato; Fujita, Katsuhiko

    2009-01-01

    Polymer light-emitting diodes (PLEDs) with staking layered structures are prepared by the evaporative spray deposition using ultradilute solution (ESDUS) method, which has enabled forming a polymer layer onto another polymer layer even if both polymers are soluble in a solvent used for the preparation. By this method, polymers having various HOMO and LUMO levels can be stacked as a hole transport layer, an emitting layer and an electron transport layer as commonly employed in small molecule-based organic light emitting diodes. Here we demonstrated that a PLED having a tri-layer structure using three kinds of polymers showed significant improvement in quantum efficiency compared with those having a single or bi-layer structure of corresponding polymers.

  20. An indole derivative as a high triplet energy hole transport material for blue phosphorescent organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Park, Min Su; Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr

    2013-12-02

    A thermally stable high triplet energy material derived from an indoloacridine core and indole hole transport units, 8,8-bis(4-(1H-indol-1-yl)phenyl)-8H-indolo[3,2,1-de]acridine (BIPIA), was synthesized as the hole transport material for deep blue phosphorescent organic light-emitting diodes. The BIPIA hole transport material showed a high triplet energy of 2.95 eV and high glass transition temperature of 142 °C. A high quantum efficiency of 19.3% was obtained in the deep blue device using BIPIA as the high triplet energy hole transport material. - Highlights: • A high triplet energy hole transport material derived from an indole • High quantum efficiency of 19.3% in deep blue phosphorescent organic light-emitting diodes • Good thermal stability with a high glass transition temperature of 142 °C.

  1. High quantum efficiency in solution processed blue phosphorescent organic light-emitting diodes based on an asymmetric benzothienopyridine host

    Energy Technology Data Exchange (ETDEWEB)

    Yook, Kyoung Soo; Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr

    2014-09-15

    Highly efficient blue phosphorescent organic light-emitting diodes were developed using a benzothienopyridine based host material with an asymmetric molecular structure. 3-(3-(9H-carbazol-9-yl)phenyl)benzothieno[2,3-b]pyridine (BTP1) was used as the asymmetric host material for the solution processed blue devices. The BTP1 host showed a smooth morphology with a surface roughness of 0.30 nm and high quantum efficiency of 14.5% in blue phosphorescent organic light-emitting diodes. - Highlights: • High quantum efficiency in solution processed blue devices. • Smooth film morphology with a low surface roughness. • Benzothienopyridine based asymmetric host material for solution process.

  2. Ordered and ultrathin reduced graphene oxide LB films as hole injection layers for organic light-emitting diode.

    Science.gov (United States)

    Yang, Yajie; Yang, Xiaojie; Yang, Wenyao; Li, Shibin; Xu, Jianhua; Jiang, Yadong

    2014-01-01

    In this paper, we demonstrated the utilization of reduced graphene oxide (RGO) Langmuir-Blodgett (LB) films as high performance hole injection layer in organic light-emitting diode (OLED). By using LB technique, the well-ordered and thickness-controlled RGO sheets are incorporated between the organic active layer and the transparent conducting indium tin oxide (ITO), leading to an increase of recombination between electrons and holes. Due to the dramatic increase of hole carrier injection efficiency in RGO LB layer, the device luminance performance is greatly enhanced comparable to devices fabricated with spin-coating RGO and a commercial conducting polymer PEDOT:PSS as the hole transport layer. Furthermore, our results indicate that RGO LB films could be an excellent alternative to commercial PEDOT:PSS as the effective hole transport and electron blocking layer in light-emitting diode devices.

  3. High-efficiency pyrene-based blue light emitting diodes: Aggregation suppression using a calixarene 3D-scaffold

    KAUST Repository

    Chan, Khaileok

    2012-01-01

    An efficient blue light emitting diode based on solution processable pyrene-1,3-alt-calix[4]arene is demonstrated, providing a record current efficiency of 10.5 cd A -1 in a simple non-doped OLED configuration. Complete suppression of pyrene aggregation in the solid state is achieved by controlling chromophore dispersion using the 1,3-alt-calix[4]arene scaffold. © 2012 The Royal Society of Chemistry.

  4. GaN-Based Multiple-Quantum-Well Light-Emitting Diodes Employing Nanotechnology for Photon Management

    KAUST Repository

    Hsiao, Yu Hsuan

    2015-03-01

    Nanostructures have been proved to be an efficient way of modifying/improving the performance of GaN-based light-emitting diodes (LEDs). The achievements in photon management include strain relaxation, light extraction enhancement, radiation pattern control, and white-light devices. In this paper, we discuss the impact and the underlying physics of applying nanotechnology on LEDs. A variety of nanostructures are introduced, as well as the fabrication techniques. © 1972-2012 IEEE.

  5. Investigation regarding prevention of insufficiency fractures in children with severe cerebral palsy by Light-Emitting Diode (LED) irradiation

    OpenAIRE

    Asagai, Yoshimi; Yamamoto, Kengo; Ohshiro, Toshio; Ohshiro, Takafumi

    2014-01-01

    Bone metabolism in children with severe fractures was examined, risk factors for fractures were characterized, and effects of LED (light-emitting diode) irradiation on the risk factors for fractures were investigated. Since insufficiency fracture in children with severe cerebral palsy can be caused without obvious external force in daily care, it is sometimes handled as a medical accident and can lead to a lawsuit. It is very important to explain the possibility of an insufficiency fracture t...

  6. Time effectiveness of Ultraviolet C light (UVC) emitted by Light Emitting Diodes (LEDs) in reducing stethoscope contamination

    OpenAIRE

    Messina, Gabriele; Fattorini, Mattia; Nante, Nicola; Rosadini, Daniele; Serafini, Andrea; Tani, Marco; Cevenini, Gabriele

    2016-01-01

    Today it is well demonstrated that stethoscopes can be as contaminated as hands, which are a recognized source of Health-Care Associated Infections (HCAIs). Ultraviolet C (UVC) light has proven disinfection capacity and the innovative UVC technology of Light Emitting Diode (LED) shows several potential benefits. To verify whether the use of UVC LEDs is effective and reliable in stethoscope membrane disinfection after prolonged use, a pre-post intervention study was conducted. A total of 1668 ...

  7. Antibacterial Mechanism of 405-Nanometer Light-Emitting Diode against Salmonella at Refrigeration Temperature.

    Science.gov (United States)

    Kim, Min-Jeong; Yuk, Hyun-Gyun

    2017-03-01

    The aim of this study was to elucidate the antibacterial mechanism of 405 ± 5-nm light-emitting diode (LED) illumination against Salmonella at 4°C in phosphate-buffered saline (PBS) by determining endogenous coproporphyrin content, DNA oxidation, damage to membrane function, and morphological change. Gene expression levels, including of oxyR , recA , rpoS , sodA , and soxR , were also examined to understand the response of Salmonella to LED illumination. The results showed that Salmonella strains responded differently to LED illumination, revealing that S. enterica serovar Enteritidis (ATCC 13076) and S. enterica subsp. enterica serovar Saintpaul (ATCC 9712) were more susceptible and resistant, respectively, than the 16 other strains tested. There was no difference in the amounts of endogenous coproporphyrin in the two strains. Compared with that in nonilluminated cells, the DNA oxidation levels in illuminated cells increased. In illuminated cells, we observed a loss of efflux pump activity, damage to the glucose uptake system, and changes in membrane potential and integrity. Transmission electron microscopy revealed a disorganization of chromosomes and ribosomes due to LED illumination. The levels of the five genes measured in the nonilluminated and illuminated S Saintpaul cells were upregulated in PBS at a set temperature of 4°C, indicating that increased gene expression levels might be due to a temperature shift and nutrient deficiency rather than to LED illumination. In contrast, only oxyR in S Enteritidis cells was upregulated. Thus, different sensitivities of the two strains to LED illumination were attributed to differences in gene regulation. IMPORTANCE Bacterial inactivation using visible light has recently received attention as a safe and environmentally friendly technology, in contrast with UV light, which has detrimental effects on human health and the environment. This study was designed to understand how 405 ± 5-nm light-emitting diode (LED

  8. Visualization Enhancement of Dentinal Defects by Using Light-Emitting Diode Transillumination.

    Science.gov (United States)

    Coelho, Marcelo Santos; Card, Steven J; Tawil, Peter Z

    2016-07-01

    Several recent studies have evaluated the presence of dentinal defects after root canal preparation in extracted human teeth by using the root sectioning methodology. The objective of this research was to investigate whether light-emitting diode (LED) transillumination enhances the visualization of dentinal defects by using a root sectioning methodology. Forty mesial roots of mandibular molars were sectioned at 3, 6, and 9 mm from the apex with a low-speed saw under water cooling. Microscopic pictures of the specimens were taken by using ×19.2 magnification for the 3-mm slice and ×12.8 magnification for the 6- and 9-mm slices. The LED transillumination was done by positioning an LED probe at 4 different locations (mesial, distal, buccal, and lingual). The root canal lumen was masked, and 2 independent evaluators assessed the presence of dentinal defects on the non-LED and LED images. The number of dentinal defects was recorded, and χ(2) test was used for statistical analysis (P < .05). The number of slices presenting dentinal defects at 3, 6, and 9 mm were 2 (5%), 1 (2.5%), and 1 (2.5%), respectively, for the non-LED assessment and 8 (20%), 10 (25%), and 9 (22.5%), respectively, for the LED assessment. Overall, 4 of the specimens (10%) presented dentinal defects without LED evaluation, and 19 of the specimens (47.5%) presented dentinal defects with LED evaluation. This difference was statistically significant (P < .05). LED transillumination enhanced the visualization of dentinal defects in uninstrumented roots. The results from previous studies that used the traditional non-LED sectioning methodology should be evaluated with caution. Copyright © 2016 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

  9. Light-emitting diode assessment of dentinal defects: the role of presumed extraction forces

    Directory of Open Access Journals (Sweden)

    Marcelo Santos Coelho

    2017-07-01

    Full Text Available Objectives The evaluation of iatrogenic dentinal defects in extracted teeth may be influenced by extraction forces and prolonged dry times. The purpose of this study was to compare the presence of dentinal defects in freshly extracted, periodontally compromised teeth with those in a group of teeth with uncontrolled extraction forces and storage time. Materials and Methods The experimental group consisted of eighteen roots obtained from teeth extracted due to periodontal reasons with class II or III mobility. They were kept in saline and sectioned within 1 hour following extraction. The control group consisted of matched root types obtained from an anonymous tooth collection, consistent with previous dentinal defect studies. The slices were obtained at 3, 6, and 9 mm from the apex. The imaging process exposed all specimens to no more than 60 seconds of dry time. The × 12.8 magnification was used for the 9 mm slices and × 19.2 magnification for the 3 mm and 6 mm slices under light-emitting diode (LED transillumination. The root canal spaces and periodontal tissues were masked to minimize extraneous factors that might influence the evaluators. Chi-square test was used for statistical analysis. Results Dentinal defects were detected in 17% of the experimental group teeth, compared to 61% of control teeth (p = 0.015. Conclusions LED transillumination assessment of freshly extracted roots with class II or III mobility showed smaller number of dentinal defects than roots with uncontrolled storage time and extraction forces. The use of freshly extracted roots with mobility should be considered for future dental defect assessment studies.

  10. Degradation mechanism of AlInGaP light emitting diodes during PMMA encapsulation and operation

    Energy Technology Data Exchange (ETDEWEB)

    Preuss, S.

    2007-11-15

    In this thesis we investigate the degradation mechanism of AlInGaP light emitting diodes (LEDs) during encapsulation and operation. The AlInGaP LEDs are encapsulated using an injection moulding tool. The molded part acts as physical housing as well as tailors the radiation pattern. Thus a narrow light beam with a spread angle of {alpha}=10 has been observed. The LED temperature has been measured by the voltage variation of the LED which is caused by the temperature change at a constant current. Thus the thermal load of the LED chips during the encapsulation process is investigated. To verify the temperature measurement a simulation based on the finite element method has been carried out. The experimental and theoretical data are in good agreement. The LED properties are investigated before and after the encapsulation. The results are compared and we found a reduction of the serial resistance and an enhanced luminous efficiency. The peak emission energy remained constant, but a peak broadening of {delta}E=9meV has been observed. A slight polarisation of the emitted light is an indication for a polarization effect of the polymethylmethacrylat (PMMA) housing. Accelerated degradation experiments using high forward currents are performed to estimate the lifetime of the PMMA encapsulated LEDs. A diffusion model is presented to explain the decay in luminous flux versus degradation time and degradation current. We believe that the reduction of quantum efficiency is caused by p-type dopant diffusion into the active layer where it acts as a non-radiative recombination centre. Using this model we determine the lifetime under the recommended drive current of I=20mA. The resulting lifetime is t=1.5.10{sup 6}h using a reduction of 50% in the luminous flux as failure criteria. (orig.)

  11. Relationships between junction temperature, electroluminescence spectrum and ageing of light-emitting diodes

    Science.gov (United States)

    Vaskuri, Anna; Kärhä, Petri; Baumgartner, Hans; Kantamaa, Olli; Pulli, Tomi; Poikonen, Tuomas; Ikonen, Erkki

    2018-04-01

    We have developed spectral models describing the electroluminescence spectra of AlGaInP and InGaN light-emitting diodes (LEDs) consisting of the Maxwell-Boltzmann distribution and the effective joint density of states. One spectrum at a known temperature for one LED specimen is needed for calibrating the model parameters of each LED type. Then, the model can be used for determining the junction temperature optically from the spectral measurement, because the junction temperature is one of the free parameters. We validated the models using, in total, 53 spectra of three red AlGaInP LED specimens and 72 spectra of three blue InGaN LED specimens measured at various current levels and temperatures between 303 K and 398 K. For all the spectra of red LEDs, the standard deviation between the modelled and measured junction temperatures was only 2.4 K. InGaN LEDs have a more complex effective joint density of states. For the blue LEDs, the corresponding standard deviation was 11.2 K, but it decreased to 3.5 K when each LED specimen was calibrated separately. The method of determining junction temperature was further tested on white InGaN LEDs with luminophore coating and LED lamps. The average standard deviation was 8 K for white InGaN LED types. We have six years of ageing data available for a set of LED lamps and we estimated the junction temperatures of these lamps with respect to their ageing times. It was found that the LEDs operating at higher junction temperatures were frequently more damaged.

  12. Disinfection of Spacecraft Potable Water Systems by Photocatalytic Oxidation Using UV-A Light Emitting Diodes

    Science.gov (United States)

    Birmele, Michele N.; O'Neal, Jeremy A.; Roberts, Michael S.

    2011-01-01

    Ultraviolet (UV) light has long been used in terrestrial water treatment systems for photodisinfection and the removal of organic compounds by several processes including photoadsorption, photolysis, and photocatalytic oxidation/reduction. Despite its effectiveness for water treatment, UV has not been explored for spacecraft applications because of concerns about the safety and reliability of mercury-containing UV lamps. However, recent advances in ultraviolet light emitting diodes (UV LEDs) have enabled the utilization of nanomaterials that possess the appropriate optical properties for the manufacture of LEDs capable of producing monochromatic light at germicidal wavelengths. This report describes the testing of a commercial-off-the-shelf, high power Nichia UV-A LED (250mW A365nnJ for the excitation of titanium dioxide as a point-of-use (POD) disinfection device in a potable water system. The combination of an immobilized, high surface area photocatalyst with a UV-A LED is promising for potable water system disinfection since toxic chemicals and resupply requirements are reduced. No additional consumables like chemical biocides, absorption columns, or filters are required to disinfect and/or remove potentially toxic disinfectants from the potable water prior to use. Experiments were conducted in a static test stand consisting of a polypropylene microtiter plate containing 3mm glass balls coated with titanium dioxide. Wells filled with water were exposed to ultraviolet light from an actively-cooled UV-A LED positioned above each well and inoculated with six individual challenge microorganisms recovered from the International Space Station (ISS): Burkholderia cepacia, Cupriavidus metallidurans, Methylobacterium fujisawaense, Pseudomonas aeruginosa, Sphingomonas paucimobilis and Wautersia basilensis. Exposure to the Nichia UV-A LED with photocatalytic oxidation resulted in a complete (>7-log) reduction of each challenge bacteria population in <180 minutes of contact

  13. High color rendering index white organic light-emitting diode using levofloxacin as blue emitter

    Science.gov (United States)

    Miao, Yan-Qin; Gao, Zhi-Xiang; Zhang, Ai-Qin; Li, Yuan-Hao; Wang, Hua; Jia, Hu-Sheng; Liu, Xu-Guang; Tsuboi, Taijuf

    2015-05-01

    Levofloxacin (LOFX), which is well-known as an antibiotic medicament, was shown to be useful as a 452-nm blue emitter for white organic light-emitting diodes (OLEDs). In this paper, the fabricated white OLED contains a 452-nm blue emitting layer (thickness of 30 nm) with 1 wt% LOFX doped in CBP (4,4’-bis(carbazol-9-yl)biphenyl) host and a 584-nm orange emitting layer (thickness of 10 nm) with 0.8 wt% DCJTB (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran) doped in CBP, which are separated by a 20-nm-thick buffer layer of TPBi (2,2’,2”-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole). A high color rendering index (CRI) of 84.5 and CIE chromaticity coordinates of (0.33, 0.32), which is close to ideal white emission CIE (0.333, 0.333), are obtained at a bias voltage of 14 V. Taking into account that LOFX is less expensive and the synthesis and purification technologies of LOFX are mature, these results indicate that blue fluorescence emitting LOFX is useful for applications to white OLEDs although the maximum current efficiency and luminance are not high. The present paper is expected to become a milestone to using medical drug materials for OLEDs. Project supported by the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-13-0927), the International Science & Technology Cooperation Program of China (Grant No. 2012DFR50460), the National Natural Science Foundation of China (Grant Nos. 21101111 and 61274056), and the Shanxi Provincial Key Innovative Research Team in Science and Technology, China (Grant No. 2012041011).

  14. Potential environmental impacts of light-emitting diodes (LEDs): metallic resources, toxicity, and hazardous waste classification.

    Science.gov (United States)

    Lim, Seong-Rin; Kang, Daniel; Ogunseitan, Oladele A; Schoenung, Julie M

    2011-01-01

    Light-emitting diodes (LEDs) are advertised as environmentally friendly because they are energy efficient and mercury-free. This study aimed to determine if LEDs engender other forms of environmental and human health impacts, and to characterize variation across different LEDs based on color and intensity. The objectives are as follows: (i) to use standardized leachability tests to examine whether LEDs are to be categorized as hazardous waste under existing United States federal and California state regulations; and (ii) to use material life cycle impact and hazard assessment methods to evaluate resource depletion and toxicity potentials of LEDs based on their metallic constituents. According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5). However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), Pb (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous. The environmental burden associated with resource depletion potentials derives primarily from gold and silver, whereas the burden from toxicity potentials is associated primarily with arsenic, copper, nickel, lead, iron, and silver. Establishing benchmark levels of these substances can help manufacturers implement design for environment through informed materials substitution, can motivate recyclers and waste management teams to recognize resource value and occupational hazards, and can inform policymakers who establish waste management policies for LEDs.

  15. Multi-solution processes of small molecule for flexible white organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Yu-Sheng, E-mail: ystsai@nfu.edu.tw [Institute of Electro-optical and Materials Science, National Formosa University, Yunlin 63201, Taiwan, ROC (China); Chittawanij, Apisit; Hong, Lin-Ann; Guo, Siou-Wei [Institute of Electro-optical and Materials Science, National Formosa University, Yunlin 63201, Taiwan, ROC (China); Wang, Ching-Chiun [Department of Solid State Lighting Technology, Mechanical and Systems Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan, ROC (China); Juang, Fuh-Shyang [Institute of Electro-optical and Materials Science, National Formosa University, Yunlin 63201, Taiwan, ROC (China); Lai, Shih-Hsiang [Department of Solid State Lighting Technology, Mechanical and Systems Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan, ROC (China); Lin, Yang-Ching [Institute of Electro-optical and Materials Science, National Formosa University, Yunlin 63201, Taiwan, ROC (China)

    2016-04-01

    Most small molecule organic light emitting diode (SM-OLED) device structures are made in one layer using solution-based processing because the solution is usually a high dissolvent material that easily attacks the layer below it. We demonstrate a simple and reliable stamping technique for fabricating multi-solution process flexible white SM-OLEDs. The structure is anode/spin-hole injection layer/spin-emitting layer/stamping-electron transport layer/cathode. Poly(di-methyl silane) (PDMS) stamp is used for transferring electron transport layer. An intermediate ultraviolet-ozone surface treatment is introduced to temporarily modify the PDMS stamp surface. Then, the solution-based electron transport layer film can therefore be uniformly formed on top of the PDMS surface. After that the electron transport layer film on the PDMS stamp is transfer-printed onto the emitting layer with suitable heating and pressing. A solution-based processing is successfully established to efficiently fabricate flexible white SM-OLEDs. The SM-OLEDs were obtained at the current density of 20 mA/cm{sup 2}, luminance of 1062 cd/m{sup 2}, current efficiency of 5.57 cd/A, and Commission internationale de l'éclairage coordinate of (0.32, 0.35). - Highlights: • All solution-processed small molecule materials (emitting layer, electron transport layer). • Poly(di-methylsilane) (PDMS) stamp is subsequently used for stamping transfer. • The flexible white SM-OLEDs are based on solution-processes with a low-cost method.

  16. High-performance light-emitting diodes encapsulated with silica-filled epoxy materials.

    Science.gov (United States)

    Li, Tian; Zhang, Jie; Wang, Huiping; Hu, Zhongnan; Yu, Yingfeng

    2013-09-25

    Packaging materials have a great impact on the performance and reliability of light-emitting diodes (LEDs). In this study, we have prepared high performance LED devices through encapsulating LEDs by epoxy materials incorporated with filler powders. A set of evaluation methods have also been established to characterize the reliability of LED devices. No delamination or internal cracking between packaging materials and lead frames has been found for the encapsulated high performance LED devices after the package saturation with moisture and subsequent exposure to high-temperature solder reflow and thermal cycling. Four kinds of inorganic silica fillers, namely, quartz, fused silica, cristobalite, and spherical silica, and one kind of organic filler, that is, spherical silicone powder, were incorporated into the epoxy packaging materials to compare their effects on performance of LED devices. The properties of epoxy packaging materials and LED devices were studied by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), dynamic mechanical analysis (DMA), thermomechanical analyzer (TMA), ultravioletvisible spectrophotometer (UV-vis), scanning acoustic microscopy (SAM), and scanning electron microscopy (SEM). Except the spherical silicone powder filled epoxy materials, all the other filled systems showed lower equilibrium water sorption content and smaller water diffusion coefficient in both water sorption and moisture sorption tests. The coefficient of thermal expansion (CTE) values were also decreased with the addition of fillers, and the systems filled with quartz, fused, and filled with spherical silica gave the best performance, which exhibited the reduced CTE values both below and above Tg. The results of TGA essentially showed no difference between filled and unfilled systems. The glass transition temperature changed little for all the filled systems, except the one incorporated with spherical silicone. The modulus at room temperature

  17. Analysis of light extraction efficiency of GaN-based light-emitting diodes

    International Nuclear Information System (INIS)

    Wang Pei; Cao Bin; Gan Zhiyin; Liu Sheng

    2011-01-01

    GaN-based light emitting diodes (LEDs) as one of the most important light source in next-generation solid-state lighting have been extensively studied and remarkable progress has been obtained. However, the light extraction efficiency (LEE) is not sufficient to satisfy application requirements. Most of the photons generated in multiple quantum well (MQW) always are trapped inside the semiconductor because both the reflection index of GaN and InGaN are higher than that of air, which results in total internal reflection (TIR). Great efforts were made in enhancing light extraction of LEDs experimentally in previous investigation. However, detailed theoretical studies in predicting the LEE of different types of LEDs are not available. In this paper the light extraction efficiency(LEE) of conventional chip (CC), flip chip (FC) and vertical chip (VC) is investigated using Monte Carlo ray tracing method is presented in conventional chip (CC). Monte Carlo ray tracing simulation based on statistics is known to be one of the most suitable methods to analyze the dependence of the light extraction efficiency of LEDs on the variety of the device parameters. Diffused bottom surface was found to be better for improvement of LEE than the perfect mirror surface. When there is a material with higher refraction index on the top surface the VC structure has the highest LEE no matter the bottom surface is perfect mirror or diffuse surface, which is above 80%. It is indicated that VC is potential in high-power GaN-based LEDs from the results.

  18. Influence of Light Emitting Diode-Derived Blue Light Overexposure on Mouse Ocular Surface.

    Science.gov (United States)

    Lee, Hyo Seok; Cui, Lian; Li, Ying; Choi, Ji Suk; Choi, Joo-Hee; Li, Zhengri; Kim, Ga Eon; Choi, Won; Yoon, Kyung Chul

    2016-01-01

    To investigate the influence of overexposure to light emitting diode (LED)-derived light with various wavelengths on mouse ocular surface. LEDs with various wavelengths were used to irradiate C57BL/6 mice at an energy dose of 50 J/cm2, twice a day, for 10 consecutive days. The red, green, and blue groups represented wavelengths of 630 nm, 525 nm, and 410 nm, respectively. The untouched group (UT) was not exposed to LED light and served as the untreated control. Tear volume, tear film break-up time (TBUT), and corneal fluorescein staining scores were measured on days 1, 3, 5, 7, and 10. Levels of interferon (IFN)-γ, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α were measured in the cornea and conjunctiva using a multiplex immunobead assay at day 10. Levels of malondialdehyde (MDA) were measured with an enzyme-linked immunosorbent assay. Flow cytometry, 2'7'-dichlorofluorescein diacetate (DCF-DA) assay, histologic analysis, immunohistochemistry with 4-hydroxynonenal, and terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) staining were also performed. TBUT of the blue group showed significant decreases at days 7 and 10, compared with the UT and red groups. Corneal fluorescein staining scores significantly increased in the blue group when compared with UT, red, and green groups at days 5, 7, and 10. A significant increase in the corneal levels of IL-1β and IL-6 was observed in the blue group, compared with the other groups. The blue group showed significantly increased reactive oxygen species production in the DCF-DA assay and increased inflammatory T cells in the flow cytometry. A significantly increased TUNEL positive cells was identified in the blue group. Overexposure to blue light with short wavelengths can induce oxidative damage and apoptosis to the cornea, which may manifest as increased ocular surface inflammation and resultant dry eye.

  19. Curing performance of a new-generation light-emitting diode dental curing unit.

    Science.gov (United States)

    Wiggins, Kim M; Hartung, Martin; Althoff, Olaf; Wastian, Christine; Mitra, Sumita B

    2004-10-01

    BACKGROUND; Recent technological advances have resulted in the marketing of high-powered, or HP, battery-operated light-emitting diode, or LED, dental curing lights. The authors examine the curing efficiency and peak polymerization temperature, or Tp, of a new HP LED curing light. The authors studied four visible light-curing, or VLC, units: HP LED (A), first-generation LED (B), conventional halogen (C) and high-intensity halogen (D). They determined the depth of cure, or DOC; adhesion; and Tp of three types of VLC resin-based composites after exposure to each light. The exposure times for units A and D were one-half those for units B and C. The power density of unit A was 1,000 milliwatts per square centimeter, which was comparable to that of unit D with turbo charge. The DOC and adhesion attained for all three resin-based composites after being light cured by unit A for a 10-second exposure time were equivalent to those after being light cured by unit D for a 10-second exposure time and to those after being light cured by units B and C for 20-second exposure times. The resin-based composites light cured by unit A attained significantly lower Tps than did those light cured by unit D at equivalent cure, or exposure, times and by unit C at twice the cure time. The authors found that Unit A effectively cured the resin-based composites at one-half the cure time of units B and C and at the same time as unit D, while maintaining low Tp. The battery-operated HP LED curing light might be an effective, time-saving alternative for clinicians to use in light curing resin-based composites.

  20. Fabrication and Characterization of Micro-membrane GaN Light Emitting Diodes

    KAUST Repository

    Liao, Hsien-Yu

    2015-05-01

    Developing etching of GaN material system is the key to device fabrications. In this thesis, we report on the fabrication of high throughput lift-off of InGaN/GaN based micro-membrane light emitting diode (LED) from sapphire substrate using UV-assisted photoelectroless chemical (PEsC) etching. Unlike existing bandgap selective etching based on unconventional sacrificial layer, the current hydrofluoric acid based wet etching process enables the selective etching of undoped GaN layer already incorporated in standard commercial LED structures, thus attaining the leverage on high performance device design, and facile wet process technology. The lift-off micro-membrane LED showed 16% alleviated quantum efficiency droop under 200 mA/cm2 current injection, demonstrating the advantage of LED epitaxy exfoliation from the lattice-mismatched sapphire substrate. The origin of the performance improvement was investigated based on non-destructive characterization methods. Photoluminescence (PL) characterization showed a 7nm peak emission wavelength shift in the micro-membrane LED compared to the GaN-on-Sapphire LED. The Raman spectroscopy measurements correlate well with the PL observation that a 0.86 GPa relaxed compressive biaxial strain was achieved after the lift-off process. The micro-membrane LED technology enables further heterogeneous integration for forming pixelated red, green, blue (RGB) display on flexible and transparent substrate. The development of discrete and membrane LEDs using nano-fiber paper as the current spreading layer was also explored for such integration.

  1. Light-Emitting Diode (LED) Traps Improve the Light-Trapping of Anopheline Mosquitoes.

    Science.gov (United States)

    Costa-Neta, B M; da Silva, A A; Brito, J M; Moraes, J L P; Rebêlo, J M M; Silva, F S

    2017-11-07

    Numerous advantages over the standard incandescent lamp favor the use of light-emitting diodes (LEDs) as an alternative and inexpensive light source for sampling medically important insects in surveillance studies. Previously published studies examined the response of mosquitoes to different wavelengths, but data on anopheline mosquito LED attraction are limited. Center for Disease Control and Prevention-type light traps were modified by replacing the standard incandescent lamp with 5-mm LEDs, one emitting at 520 nm (green) and the other at 470 nm (blue). To test the influence of moon luminosity on LED catches, the experiments were conducted during the four lunar phases during each month of the study period. A total of 1,845 specimens representing eight anopheline species were collected. Anopheles (Nyssorhynchus) evansae (35.2%) was the most frequently collected, followed by An. (Nys.) triannulatus (21.9%), An. (Nys.) goeldii (12.9%), and An. (Nys.) argyritarsis (11.5%). The green LED was the most attractive light source, accounting for 43.3% of the individuals collected, followed by the blue (31.8%) and control (24.9%) lights. The LED traps were significantly more attractive than the control, independent of the lunar phase. Light trapping of anopheline mosquitoes was more efficient when the standard incandescent lamp was replaced with LEDs, regardless of the moon phase. The efficiency of LEDs improves light trapping results, and it is suggested that the use of LEDs as an attractant for anopheline mosquitoes should be taken into consideration when sampling anopheline mosquitoes. © The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  2. Retinal endoilluminator toxicity of xenon and light-emitting diode (LED) light source: rabbit model.

    Science.gov (United States)

    Aydin, Bahri; Dinç, Erdem; Yilmaz, S Necat; Altiparmak, U Emrah; Yülek, Fatma; Ertekin, Sevda; Yilmaz, Mustafa; Yakın, Mehmet

    2014-09-01

    This study evaluates retinal toxicity due to endoillumination with the light-emitting diode (LED) light source in comparison to endoillumination with xenon light source. Twenty-five eyes of 14 New Zealand pigmented rabbits were used in the study. The LED light (Omesis Medical Systems, Turkey) group was composed of 7 right eyes, while the other 7 right eyes constituted the xenon group (420 nm filter, 357mW/cm(2)) (Bright Star; DORC, Zuidland, Netherlands). Eleven untreated left eyes composed the control group. Twenty gauge pars plana incision 1.5 mm behind the limbus was performed in the right eyes. Twenty gauge bullet type fiberoptic endoilluminator was inserted into the eye from the incision without any pars plana vitrectomy. Fiberoptic endoilluminator was placed in such a way that it was directed toward visual streak of the rabbit retina with a 5 mm distance to retinal surface. Endoillumination was then applied for 20 min with a maximum light intensity for LED and xenon light. In left control eyes, no surgical procedure and no endoillumination were performed. One week after the endoillumination procedure, both eyes of the rabbits were enucleated following electroretinography. Sections stained with hematoxylin and eosin to evaluate morphologic changes. Retina tissues were assessed by active caspase-3 staining. There was no difference in the shape of the waveforms recorded in the eyes endoilluminated with LED light and xenon light sources compared to control eyes both before and after endoillumination application (p > 0.05). Microscopic evaluation of the retinas with hematoxylin and eosin staining demonstrated that all study groups have normal histologic properties similar to control group. No apoptosis positive cells were found within all sections in all groups. When the LED light source is used with maximum power and limited duration for endoillumination in rabbit eyes it does not produce phototoxic effects that may be detectable by electrophysiology

  3. Multi-solution processes of small molecule for flexible white organic light-emitting diodes

    International Nuclear Information System (INIS)

    Tsai, Yu-Sheng; Chittawanij, Apisit; Hong, Lin-Ann; Guo, Siou-Wei; Wang, Ching-Chiun; Juang, Fuh-Shyang; Lai, Shih-Hsiang; Lin, Yang-Ching

    2016-01-01

    Most small molecule organic light emitting diode (SM-OLED) device structures are made in one layer using solution-based processing because the solution is usually a high dissolvent material that easily attacks the layer below it. We demonstrate a simple and reliable stamping technique for fabricating multi-solution process flexible white SM-OLEDs. The structure is anode/spin-hole injection layer/spin-emitting layer/stamping-electron transport layer/cathode. Poly(di-methyl silane) (PDMS) stamp is used for transferring electron transport layer. An intermediate ultraviolet-ozone surface treatment is introduced to temporarily modify the PDMS stamp surface. Then, the solution-based electron transport layer film can therefore be uniformly formed on top of the PDMS surface. After that the electron transport layer film on the PDMS stamp is transfer-printed onto the emitting layer with suitable heating and pressing. A solution-based processing is successfully established to efficiently fabricate flexible white SM-OLEDs. The SM-OLEDs were obtained at the current density of 20 mA/cm 2 , luminance of 1062 cd/m 2 , current efficiency of 5.57 cd/A, and Commission internationale de l'éclairage coordinate of (0.32, 0.35). - Highlights: • All solution-processed small molecule materials (emitting layer, electron transport layer). • Poly(di-methylsilane) (PDMS) stamp is subsequently used for stamping transfer. • The flexible white SM-OLEDs are based on solution-processes with a low-cost method.

  4. Heating of Newborn Infants due to Blue Light-Emitting Diode Fibreoptic Phototherapy Pads.

    Science.gov (United States)

    Ng, Pei Ling; Carlisle, Tony; Ly, Marleesa; Morris, Scott Adam

    2017-01-01

    Surface temperatures of fibreoptic phototherapy pads using a high intensity blue light-emitting diode (LED) light source have not been studied. The aim of this study was to measure the temperature of LED fibreoptic phototherapy pads during phototherapy in a bench-top study, and to determine temperature effects on babies during phototherapy. A commercially available LED fibreoptic phototherapy system was tested. In a bench-top setting, pad surface temperatures were measured before, during and after a 12-h period of phototherapy (10 different LED light box-pad combinations). A prospective, cohort study of well babies at >34 weeks' gestation receiving phototherapy was then conducted to determine changes in pad and body temperatures during a 90-min phototherapy period. In the bench-top study, the mean (95% CI) pad temperature was 21.8°C (21.5-22.1) before lights, 27.0°C (26.5-27.5) after 12 h of lights, and 22.1°C (21.9-22.4) 8 h after turning off the lights (F = 366.1, p phototherapy was linearly correlated with irradiance (r = 0.89, p phototherapy was 38.9°C. Axillary temperature increased by a mean (95% CI) of 0.3°C (0.1-0.5), p LED fibreoptic phototherapy pads are heated by high-intensity blue light. The thermal environment and temperature of babies should be monitored closely during LED fibreoptic phototherapy. A temperature probe placed between the skin and the pad will not accurately reflect the core temperature during fibreoptic phototherapy. © 2017 S. Karger AG, Basel.

  5. Is light-emitting diode phototherapy (LED-LLLT) really effective?

    Science.gov (United States)

    Kim, Won-Serk; Calderhead, R Glen

    2011-01-01

    Low level light therapy (LLLT) has attracted attention in many clinical fields with a new generation of light-emitting diodes (LEDs) which can irradiate large targets. To pain control, the first main application of LLLT, have been added LED-LLLT in the accelerated healing of wounds, both traumatic and iatrogenic, inflammatory acne and the patient-driven application of skin rejuvenation. Rationale and Applications: The rationale behind LED-LLLT is underpinned by the reported efficacy of LED-LLLT at a cellular and subcellular level, particularly for the 633 nm and 830 nm wavelengths, and evidence for this is presented. Improved blood flow and neovascularization are associated with 830 nm. A large variety of cytokines, chemokines and macromolecules can be induced by LED phototherapy. Among the clinical applications, non-healing wounds can be healed through restoring the collagenesis/collagenase imbalance in such examples, and 'normal' wounds heal faster and better. Pain, including postoperative pain, postoperative edema and many types of inflammation can be significantly reduced. Experimental and clinical evidence: Some personal examples of evidence are offered by the first author, including controlled animal models demonstrating the systemic effect of 830 nm LED-LLLT on wound healing and on induced inflammation. Human patients are presented to illustrate the efficacy of LED phototherapy on treatment-resistant inflammatory disorders. Provided an LED phototherapy system has the correct wavelength for the target cells, delivers an appropriate power density and an adequate energy density, then it will be at least partly, if not significantly, effective. The use of LED-LLLT as an adjunct to conventional surgical or nonsurgical indications is an even more exciting prospect. LED-LLLT is here to stay.

  6. Low frequency noise of gallium nitride-based deep ultraviolet light emitting diodes

    Science.gov (United States)

    Sawyer, Shayla Maya Louise

    This study covers the investigation of deep UV GaN-based light emitting diodes using low frequency noise characterization. Using this technique, device improvements were analyzed as feedback to developers and practical parameters were created for system use. AlGaN LEDs emit wavelengths into the deep UV spectral region (lambda food and water sterilization, non-line-of-sight short range communication, counterfeit identification, photolithography, and general white lighting. The current technological trend demonstrates a decrease in material quality and device performance with decreasing wavelength. However, progress has allowed for its commercialization in a relatively short period of time. Characterization of material and device improvements provides feedback for changes in development. Secondly, methods to determine the reliability and stability of these devices are essential to the applications for which they are used. One such method is through optical and current low frequency noise (LFN) measurements in which both system related parameters such as a signal-to-noise ratio for light sources and insight into the fundamental physics within the devices can be determined. The quality of the device can be compared before costly integration into systems that require low noise, high reliability, and optical stability. It not only quantifies performance limiting noise levels, but it is known to be a sensitive, nondestructive measure of material quality and reliability. The research highlighted in this thesis demonstrates a new measurement technique in analyzing the light intensity fluctuations through low frequency optical noise. From this work, a proposed figure-of-merit is presented. Low frequency current noise was performed as a well known indicator of material quality. Each technique compares LEDs grown by SET Inc. LEDs of varying wavelengths along the UV spectrum, with different growth methods and device structures. The cross-correlation between optical and current

  7. Optical diffraction tomography microscopy with transport of intensity equation using a light-emitting diode array

    Science.gov (United States)

    Li, Jiaji; Chen, Qian; Zhang, Jialin; Zhang, Zhao; Zhang, Yan; Zuo, Chao

    2017-08-01

    Optical diffraction tomography (ODT) is an effective label-free technique for quantitatively refractive index imaging, which enables long-term monitoring of the internal three-dimensional (3D) structures and molecular composition of biological cells with minimal perturbation. However, existing optical tomographic methods generally rely on interferometric configuration for phase measurement and sophisticated mechanical systems for sample rotation or beam scanning. Thereby, the measurement is suspect to phase error coming from the coherent speckle, environmental vibrations, and mechanical error during data acquisition process. To overcome these limitations, we present a new ODT technique based on non-interferometric phase retrieval and programmable illumination emitting from a light-emitting diode (LED) array. The experimental system is built based on a traditional bright field microscope, with the light source replaced by a programmable LED array, which provides angle-variable quasi-monochromatic illumination with an angular coverage of ±37 degrees in both x and y directions (corresponding to an illumination numerical aperture of ∼0.6). Transport of intensity equation (TIE) is utilized to recover the phase at different illumination angles, and the refractive index distribution is reconstructed based on the ODT framework under first Rytov approximation. The missing-cone problem in ODT is addressed by using the iterative non-negative constraint algorithm, and the misalignment of the LED array is further numerically corrected to improve the accuracy of refractive index quantification. Experiments on polystyrene beads and thick biological specimens show that the proposed approach allows accurate refractive index reconstruction while greatly reduced the system complexity and environmental sensitivity compared to conventional interferometric ODT approaches.

  8. Computational diffraction tomographic microscopy with transport of intensity equation using a light-emitting diode array

    Science.gov (United States)

    Li, Jiaji; Chen, Qian; Zhang, Jialin; Zuo, Chao

    2017-10-01

    Optical diffraction tomography (ODT) is an effective label-free technique for quantitatively refractive index imaging, which enables long-term monitoring of the internal three-dimensional (3D) structures and molecular composition of biological cells with minimal perturbation. However, existing optical tomographic methods generally rely on interferometric configuration for phase measurement and sophisticated mechanical systems for sample rotation or beam scanning. Thereby, the measurement is suspect to phase error coming from the coherent speckle, environmental vibrations, and mechanical error during data acquisition process. To overcome these limitations, we present a new ODT technique based on non-interferometric phase retrieval and programmable illumination emitting from a light-emitting diode (LED) array. The experimental system is built based on a traditional bright field microscope, with the light source replaced by a programmable LED array, which provides angle-variable quasi-monochromatic illumination with an angular coverage of +/-37 degrees in both x and y directions (corresponding to an illumination numerical aperture of ˜ 0.6). Transport of intensity equation (TIE) is utilized to recover the phase at different illumination angles, and the refractive index distribution is reconstructed based on the ODT framework under first Rytov approximation. The missing-cone problem in ODT is addressed by using the iterative non-negative constraint algorithm, and the misalignment of the LED array is further numerically corrected to improve the accuracy of refractive index quantification. Experiments on polystyrene beads and thick biological specimens show that the proposed approach allows accurate refractive index reconstruction while greatly reduced the system complexity and environmental sensitivity compared to conventional interferometric ODT approaches.

  9. Microwave assisted transformation of N,N-diphenylamine as precursors of organic light emitting diodes (OLED)

    Energy Technology Data Exchange (ETDEWEB)

    Jefri,; Wahyuningrum, Deana, E-mail: deana@chem.itb.ac.id [Organic Chemistry Research Division, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jalan Ganesha 10, Bandung 40132 (Indonesia)

    2015-09-30

    In this research, study on the transformation of N,N-diphenylamine (DPA) using iodine (I2) utilizing solid state Microwave Assisted Organic Synthesis (MAOS) method has been carried out. The reaction was performed by variations of three parameters namely the mole of reagents, the amount and type of solid support (alumina/Al2O3), and the reaction conditions. Experimental results showed that neutral-alumina was a better solid support than basic-alumina. The optimum temperature for the reaction was approximately at 125-133 °C with reaction time of 15 minutes and microwave reactor power at 500-600 W. The separation of the yellowish green product solution with preparative Thin Layer Chromatography (TLC) method using n-hexane:ethyl acetate = 4:1 (v/v) as eluent yielded two fractions (I and II) and both fractions can undergo fluorescence under 365 nm UV light. Based on the LC chromatogram with methanol:water = 95:5 (v/v) as eluent and its corresponding mass spectra (ESI+), fraction I contained three compounds, which were tetracarbazole A, triphenylamine, and impurities in the form of plasticizer such as bis(2-ethylhexyl) phthalate. Fraction II also contained three compounds, which were tetracarbazole C, tetraphenylhydrazine, and plasticizer such as bis(2-ethylhexyl) phthalate. Both FT-IR (KBr disks) and NMR (500 MHz, CDCl{sub 3}) spectra of fraction I and II confirmed the aromatic amine groups in those compounds. The observed fluorescence colors of fraction I and II were violet and violet-blue, respectively. Based on their structures and fluorescence characters, the compounds in fraction I and II have the potential to be used as Organic Light Emitting Diode (OLED) compound precursors.

  10. Recent development of organic light-emitting diode utilizing energy transfer from exciplex to phosphorescent emitter

    Science.gov (United States)

    Seo, Satoshi; Shitagaki, Satoko; Ohsawa, Nobuharu; Inoue, Hideko; Suzuki, Kunihiko; Nowatari, Hiromi; Takahashi, Tatsuyoshi; Hamada, Takao; Watabe, Takeyoshi; Yamada, Yui; Mitsumori, Satomi

    2016-09-01

    This study investigates an organic light-emitting diode (OLED) utilizing energy transfer from an excited complex (exciplex) comprising donor and acceptor molecules to a phosphorescent dopant. An exciplex has a very small energy gap between the lowest singlet and triplet excited states (S1 and T1). Thus, both S1 and T1 energies of the exciplex can be directly transferred to the T1 of the phosphorescent dopant by adjusting the emission energy of the exciplex to the absorption-edge energy of the dopant. Such an exciplex‒triplet energy transfer (ExTET) achieves high efficiency at low drive voltage because the electrical excitation energy of the exciplex approximates the T1 energy of the dopant. Furthermore, the efficiency of the reverse intersystem crossing (RISC) of the exciplex does not affect the external quantum efficiency (EQE) of the ExTET OLED. The RISC of the exciplex is inhibited when the T1 energy of either donor or acceptor molecules is close to or lower than that of the exciplex itself. Even in this case, however, the ExTET OLED maintains its high efficiency because the T1 energy of each component of the exciplex or the T1 energy of the exciplex itself can be transferred to the dopant. We also varied the emission colors of ExTET OLEDs from sky-blue to red by introducing various phosphorescent dopants. These devices achieved high EQEs (≍30%), low drive voltages (≍3 V), and extremely long lifetimes (e.g., 1 million hours for the orange OLED) at a luminance of 1,000 cd/m2.

  11. Simplified efficient phosphorescent organic light-emitting diodes by organic vapor phase deposition

    Science.gov (United States)

    Pfeiffer, P.; Beckmann, C.; Stümmler, D.; Sanders, S.; Simkus, G.; Heuken, M.; Vescan, A.; Kalisch, H.

    2017-12-01

    The most efficient phosphorescent organic light-emitting diodes (OLEDs) are comprised of complex stacks with numerous organic layers. State-of-the-art phosphorescent OLEDs make use of blocking layers to confine charge carriers and excitons. On the other hand, simplified OLEDs consisting of only three organic materials have shown unexpectedly high efficiency when first introduced. This was attributed to superior energy level matching and suppressed external quantum efficiency (EQE) roll-off. In this work, we study simplified OLED stacks, manufactured by organic vapor phase deposition, with a focus on charge balance, turn-on voltage (Von), and efficiency. To prevent electrons from leaking through the device, we implemented a compositionally graded emission layer. By grading the emitter with the hole transport material, charge confinement is enabled without additional blocking layers. Our best performing organic stack is composed of only three organic materials in two layers including the emitter Ir(ppy)3 and yields a Von of 2.5 V (>1 cd/m2) and an EQE of 13% at 3000 cd/m2 without the use of any additional light extraction techniques. Changes in the charge balance, due to barrier tuning or adjustments in the grading parameters and layer thicknesses, are clearly visible in the current density-voltage-luminance (J-V-L) measurements. As charge injection at the electrodes and organic interfaces is of great interest but difficult to investigate in complex device structures, we believe that our simplified organic stack is not only a potent alternative to complex state-of-the-art OLEDs but also a well suited test vehicle for experimental studies focusing on the modification of the electrode-organic semiconductor interface.

  12. Scalable Light Module for Low-Cost, High-Efficiency Light- Emitting Diode Luminaires

    Energy Technology Data Exchange (ETDEWEB)

    Tarsa, Eric [Cree, Inc., Goleta, CA (United States)

    2015-08-31

    During this two-year program Cree developed a scalable, modular optical architecture for low-cost, high-efficacy light emitting diode (LED) luminaires. Stated simply, the goal of this architecture was to efficiently and cost-effectively convey light from LEDs (point sources) to broad luminaire surfaces (area sources). By simultaneously developing warm-white LED components and low-cost, scalable optical elements, a high system optical efficiency resulted. To meet program goals, Cree evaluated novel approaches to improve LED component efficacy at high color quality while not sacrificing LED optical efficiency relative to conventional packages. Meanwhile, efficiently coupling light from LEDs into modular optical elements, followed by optimally distributing and extracting this light, were challenges that were addressed via novel optical design coupled with frequent experimental evaluations. Minimizing luminaire bill of materials and assembly costs were two guiding principles for all design work, in the effort to achieve luminaires with significantly lower normalized cost ($/klm) than existing LED fixtures. Chief project accomplishments included the achievement of >150 lm/W warm-white LEDs having primary optics compatible with low-cost modular optical elements. In addition, a prototype Light Module optical efficiency of over 90% was measured, demonstrating the potential of this scalable architecture for ultra-high-efficacy LED luminaires. Since the project ended, Cree has continued to evaluate optical element fabrication and assembly methods in an effort to rapidly transfer this scalable, cost-effective technology to Cree production development groups. The Light Module concept is likely to make a strong contribution to the development of new cost-effective, high-efficacy luminaries, thereby accelerating widespread adoption of energy-saving SSL in the U.S.

  13. Effects of Nanoscale V-Shaped Pits on GaN-Based Light Emitting Diodes.

    Science.gov (United States)

    Chen, Shuo-Wei; Li, Heng; Chang, Chia-Jui; Lu, Tien-Chang

    2017-01-28

    This paper reviews the formation of nanoscale V-shaped pits on GaN-based light emitting diodes (LEDs) grown by the metal organic chemical vapor deposition (MOCVD) system and studies the effect of V-shaped pits on quantum efficiency. Since V-pits could provide potential barriers around threading dislocations to lessen non-radiative recombinations in such a high defect environment. In our study, multiple InGaN/GaN quantum well samples with different emission wavelengths of 380, 420, 460, and 500 nm were grown, each with different nanoscale V-shaped pits of three diameters for 150, 200, and 250 nm, respectively. It was found that the multiple quantum well (MQW) sample with larger V-pits had a lower pit density, but a relatively larger total V-pits defected area. The optimum diameter of V-pits showing the highest quantum efficiency from the MQW sample depended on the emission wavelength. MQW samples with wavelengths of 380 and 500 nm exhibited the best internal quantum efficiency (IQE) performance at the smallest V-pits area; however, the best performance for MQW samples with wavelength around 420 and 460 nm occurred when large V-pit areas were presented. Photoluminescence (PL) peak shifts and Raman shifts can provide a relationship between quantum-confined Stark effect (QCSE) and IQE, as well as a comparison between strain and IQE. The results obtained in this phenomenological study shall provide a useful guide line in making high-performance GaN-based LEDs with wide emission spectra.

  14. Molecular beam deposition and polymerization of parylene-N ultrathin films: Effective buffers in organic light emitting diodes

    International Nuclear Information System (INIS)

    Hu, Y.M.; Li, R.H.; He, Y.; Zhang, X.Q.; Li, M.Q.; Zhu, Y.; Yi, J.H.; Fu, R.Ch.

    2014-01-01

    Highlights: • Parylene-N (PPXN) films prepared by using a home-made Knudsen Cell were identified and characterized. • 1 nm PPXN thin films were inserted at different locations in the hole transport layers of organic light emitting diodes. • For an optimized PPXN inserted organic light emitting diodes, current efficiency improvement of 11% was achieved. • The device current efficiency improvement and the current density variation under operation were discussed. - Abstract: Ultrathin Parylene-N (PPXN) films were prepared by using a home-made Knudsen Cell (KC). The PPXN films were identified by infrared (IR) spectra. The morphology and insulativity of PPXN films were measured by atomic force microscope (AFM) and current density versus voltage (j–V) characteristics. Well controlled 1-nm-thick PPXN thin films were inserted at different locations in the N′-bis(naphthalene-1-yl)-N, N′-bis(phenyl) benzidine (NPB) layers of organic light emitting diodes (OLEDs) with the structure of ITO/NPB/tris (8-hydroxyquinolato) aluminum (Alq 3 )/LiF/Al. For an optimized PPXN inserted structure, current efficiency of 6.27 cd/A was achieved, 11% higher than the 5.64 cd/A of the control one with 1-nm-thick PPXN buffer inserted at the anode interface. The device current efficiency improvement is due to the electron blocking of PPXN buffers, and the current density variation of devices under operation was explained by tunneling barrier reduction

  15. Degradation of phosphorescent blue organic light-emitting diodes (OLED); Degradation der phosphoreszenten blauen organischen Leuchtdioden

    Energy Technology Data Exchange (ETDEWEB)

    Chiu, Chien-Shu

    2011-07-01

    Phosphorescent organic materials harvest singlet and triplet excitons through inter-system crossing and improve the efficiency of organic light-emitting diodes (OLEDs). This improvement increases the potential of OLEDs, particularly white phosphorescent OLEDs (PHOLEDs), for lighting application. Although much progress has been made in the development of white PHOLEDs, the lifetime of phosphorescent emitters, especially the blue emitter, still needs to be improved. This thesis discusses the developments of blue PHOLEDs and investigations of degradation mechanisms. For development of blue PHOLEDs, two phosphorescent blue emitters were investigated: commercially available FIrpic and B1 provided by BASF. By varying the matrix and blocker materials, diode efficiency and lifetime have been investigated and improved. Blue PHOLEDs with emitter B1 show better efficiency and lifetime than devices with FIrpic. From lifetime measurement with constant DC current density, intrinsic degradation including luminance loss and voltage increase on both FIrpic and B1 PHOLEDs was observed. Photoluminescence measurement shows degradation in the emitting layers. To investigate the degradation of emitter layers, single-carrier devices with emitter systems or pure matrix materials were fabricated. Degradation on these devices was investigated by applying constant DC current, UV-irradiation and combination of both. We found that due to excited states (excitons), FIrpic molecules become unstable and polarons would enhance the degradation of FIrpic during DC operation and UV-excitation. To investigate the impact the exciton formation and exciton decay have on the degradation of FIrpic molecules, red phosphorescent emitter Ir(MDQ){sub 2}(acac) was doped in blue emitter layer TCTA:20% FIrpic. The doping concentration of Ir(MDQ){sub 2}(acac) was much lower than FIrpic to ensure that most of the exciton formation occurred on FIrpic molecules. Lower triplet energy of Ir(MDQ){sub 2}(acac) molecules

  16. High performance inkjet printed phosphorescent organic light emitting diodes based on small molecules commonly used in vacuum processes

    Energy Technology Data Exchange (ETDEWEB)

    Jung, Sung-Hoon [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Kim, Jang-Joo, E-mail: jjkim@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Kim, Hyong-Jun, E-mail: hkim@kongju.ac.kr [Department of Chemical Engineering, Kongju National University, Cheonan, 330-717 (Korea, Republic of)

    2012-09-30

    High efficiency phosphorescent organic light emitting diodes (OLEDs) are realized by inkjet printing based on small molecules commonly used in vacuum processes in spite of the limitation of the limited solubility. The OLEDs used the inkjet printed 5 wt.% tris(2-phenylpyridine)iridium(III) (Ir(ppy){sub 3}) doped in 4,4 Prime -Bis(carbazol-9-yl)biphenyl (CBP) as the light emitting layer on various small molecule based hole transporting layers, which are widely used in the fabrication of OLEDs by vacuum processes. The OLEDs resulted in the high power and the external quantum efficiencies of 29.9 lm/W and 11.7%, respectively, by inkjet printing the CBP:Ir(ppy){sub 3} on a 40 nm thick 4,4 Prime ,4 Double-Prime -tris(carbazol-9-yl)triphenylamine layer. The performance was very close to a vacuum deposited device with a similar structure. - Highlights: Black-Right-Pointing-Pointer Effective inkjet printed organic light emitting diode (OLED) technique is explored. Black-Right-Pointing-Pointer Solution process on commonly used hole transporting material (HTM) is demonstrated. Black-Right-Pointing-Pointer Triplet energy overlap of HTM and emitting material is the key to the performance. Black-Right-Pointing-Pointer Simple inkjet printed OLED provides the high current efficiency of 40 cd/A.

  17. Trap-state-assisted white light emission from a CdSe nanocrystal integrated hybrid light-emitting diode.

    Science.gov (United States)

    Chandramohan, S; Ryu, Beo Deul; Kim, Hyun Kyu; Hong, Chang-Hee; Suh, Eun-Kyung

    2011-03-15

    This Letter reports on the fabrication of hybrid white-light-emitting diodes made of semiconductor nanocrystals (NCs) integrated on InGaN/GaN LEDs. Using core type and core/shell type CdSe NCs, the white light properties are systematically engineered for white light generation with high color rendering index (CRI). Unlike CdSe/ZnS core/shell NCs, which exhibited a unique narrowband edge emission, core type CdSe NCs offered extended broad emission toward orange/red wavelengths associated with deep trap states. Consequently, the light-emitting properties of the devices showed strong dependence on the type of NCs used, and devices with CdSe NCs offered admirable characteristics, such as Commission Internationale d'Eclairage coordinates of (0.356, 0.330) and a CRI as high as 87.4.

  18. Moisture exposure to different layers in organic light-emitting diodes and the effect on electroluminescence characteristics

    International Nuclear Information System (INIS)

    Liao, L. S.; Tang, C. W.

    2008-01-01

    Moisture effect on electroluminescence characteristics, including current density versus voltage, luminance versus voltage, luminous efficiency versus current density, dark spot formation, and operational stability of organic light-emitting diodes, has been systematically investigated by exposing each layer of the devices to moisture at room temperature. Moisture has a different effect on each of the interfaces or surfaces, and the influence increases as exposure time increases. There is a slight effect on the electroluminescence characteristics after the anode surface has been exposed to moisture. However, severe luminance decrease, dark spot formation, and operational stability degradation take place after the light-emitting layer or the electron-transporting layer is exposed to moisture. It is also demonstrated that the effect of moisture can be substantially reduced if the exposure to moisture is in a dark environment

  19. Warm White Light-Emitting Diodes Based on a Novel Orange Cationic Iridium(III) Complex.

    Science.gov (United States)

    Tang, Huaijun; Meng, Guoyun; Chen, Zeyu; Wang, Kaimin; Zhou, Qiang; Wang, Zhengliang

    2017-06-16

    A novel orange cationic iridium(III) complex [(TPTA)₂Ir(dPPOA)]PF₆ (TPTA: 3,4,5-triphenyl-4 H -1,2,4-triazole, dPPOA: N,N-diphenyl-4-(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)aniline) was synthesized and used as a phosphor in light-emitting diodes (LEDs). [(TPTA)₂Ir(dPPOA)]PF₆ has high thermal stability with a decomposition temperature ( T d ) of 375 °C, and its relative emission intensity at 100 °C is 88.8% of that at 25°C. When only [(TPTA)₂Ir(dPPOA)]PF₆ was used as a phosphor at 6.0 wt % in silicone and excited by a blue GaN (GaN: gallium nitride) chip (450 nm), an orange LED was obtained. A white LED fabricated by a blue GaN chip (450 nm) and only yellow phosphor Y₃Al₅O 12 :Ce 3+ (YAG:Ce) (1.0 wt % in silicone) emitted cold white light, its CIE (CIE: Commission International de I'Eclairage ) value was (0.32, 0.33), color rendering index (CRI) was 72.2, correlated color temperature (CCT) was 6877 K, and luminous efficiency ( η L ) was 128.5 lm∙W -1 . Such a cold white LED became a neutral white LED when [(TPTA)₂Ir(dPPOA)]PF₆ was added at 0.5 wt %; its corresponding CIE value was (0.35, 0.33), CRI was 78.4, CCT was 4896 K, and η L was 85.2 lm∙W -1 . It further became a warm white LED when [(TPTA)₂Ir(dPPOA)]PF₆ was added at 1.0 wt %; its corresponding CIE value was (0.39, 0.36), CRI was 80.2, CCT was 3473 K, and η L was 46.1 lm∙W -1 . The results show that [(TPTA)₂Ir(dPPOA)]PF₆ is a promising phosphor candidate for fabricating warm white LEDs.

  20. Electroluminescence dependence of the simplified green light organic light emitting diodes on in situ thermal treatment

    Energy Technology Data Exchange (ETDEWEB)

    Mu, Haichuan, E-mail: hcmu@ecust.edu.cn [Department of Physics, School of Science, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Rao, Lu [Department of Physics, School of Science, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China); Li, Weiling; Wei, Bin [Key Laboratory of Advanced Display and System Applications, Ministry of Education, School of Mechanics Engineering and Automation, Shanghai University, 149 Yanchang Road, Shanghai 200072 (China); Wang, Keke; Xie, Haifen [Department of Physics, School of Science, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237 (China)

    2015-12-01

    Highlights: • In-situ thermal treating the organic tri-layer (CBP/CBP:Ir(ppy){sub 3}/TPBi) of the green light PHOLED under various temperatures during the organic materials evaporation. • Investigating the effect of in situ thermal treatment on the electroluminescence (EL) performance of the green light PHOLED with tri-layer structures. • Provide an easy and practical way to improve the EL performance of the OLEDs without major modification of the organic materials and OLEDs structures required. - Abstract: Simplified multilayer green light phosphorescent organic light emitting diodes (PHOLED) with the structure of ITO/MoO{sub 3}(1 nm)/CBP(20 nm)/CBP:Ir(ppy){sub 3} (1 wt%) (15 nm)/TPBi(60 nm)/LiF(0.5 nm)/Al were fabricated via thermal evaporation and in situ thermal treatment (heating the OLED substrates to certain temperatures during the thermal evaporation of the organic materials) was performed. The effect of the in situ thermal treatment on the electroluminescence (EL) performance of the PHOLED was investigated. It was found that the OLED exhibited strong EL dependence on the thermal treatment temperatures, and their current efficiency was improved with the increasing temperature from room temperature (RT) to 69 °C and deteriorated with the further increasing temperature to 105 °C. At the brightness of 1000 cd/m{sup 2}, over 80% improvement of the current efficiency at the optimal thermal treatment temperature of 69 °C (64 cd/A) was demonstrated compared to that at RT (35 cd/A). Meanwhile, the tremendous influences of the in situ thermal treatment on the morphology of the multilayer CBP/CBP:Ir(ppy){sub 3}/TPBi were also observed. At the optimal thermal treatment temperature of 69 °C, the improvement of the EL performance could be ascribed to the enhancement of the electron and hole transporting in the CBP:Ir(ppy){sub 3} emitting layer, which suppressed the triplets self-quenching interactions and promoted the charge balance and excitons formation. The

  1. Growing lettuce under multispectral light-emitting diodes lamps with adjustable light intensity

    Directory of Open Access Journals (Sweden)

    Giacomo Tosti

    2017-09-01

    Full Text Available Light-emitting diodes (LEDs technology offers vast possibilities in plant lighting due to its ability to mix different light frequencies, high energy use efficiency and low heat production combined to long lifespan. In particular, the combined effect of the Blue:Red (B:R ratio and other frequencies in the central part of the PAR spectrum (CGA, i.e. cyan, green and amber may be very important, though literature information is scarce. In this paper, the effects of six light spectra from LED technology were tested, i.e.: i B:R=0.82 (i.e. similar to sunlight with CGA (treatment T0; ii B:R=0.82 without CGA (T1; iii red prevalence (B:R=0.25 without CGA (T2; iv blue prevalence (B:R=4 without CGA (T3; v red prevalence with CGA (T4; and vi blue prevalence with CGA (T5. The experiment was carried out in a walk-in climatic chamber with controlled temperature and relative humidity and an incident PAR photon flux density (PFD of 300 μmol m–2 s–1 (14/10 light/dark photoperiod, generated by multispectral LED lamps with adjustable light intensity. Smooth leaved lettuce (Lactuca sativa L. cv Gentilina was used as the test plant and biomass yield (DW, g m–2, LAI, soil coverage proportion (SC%, energy-biomass conversion efficiency (E-BCE, kWh g–1 and radiation use efficiency (RUE, g mol–1 photons were determined. Treatments with red predominance (T2 and T4 showed the highest SC% rates, while those with blue predominance (T3 and T5 showed the lowest. Light spectrum also affected leaf size (i.e. mean leaf area. The highest DW and RUE were observed in T2 and T4, followed by T0, while biomass in T3 and T5 was significantly lower (similar to T1. LAI values were generally high, but treatments with blue predominance showed the lowest LAI values (both with or without CGA. The introduction of intermediate wavelengths (green, cyan and amber did not bring about significant improvement in DW or RUE, but resulted in reduced energy-biomass conversion efficiency

  2. Plant experiments with light-emitting diode module in Svet space greenhouse

    Science.gov (United States)

    Ilieva, Iliana; Ivanova, Tania; Naydenov, Yordan; Dandolov, Ivan; Stefanov, Detelin

    2010-10-01

    Light is necessary for photosynthesis and shoot orientation in the space plant growth facilities. Light modules (LM) must provide sufficient photosynthetic photon flux for optimal efficiency of photosynthetic processes and also meet the constraints for power, volume and mass. A new LM for Svet space greenhouse using Cree® XLamp® 7090 XR light-emitting diodes (LEDs) was developed. Monochromic LEDs emitting in the red, green, and blue regions of the spectrum were used. The LED-LM contains 36 LED spots - 30 LED spots with one red, green and blue LED and 6 LED spots with three red LEDs. Digital Multiplex Control Unit controls the LED spots and can set 231 levels of light intensity thus achieving Photosynthetic Photon Flux Density (PPFD) in the range 0-400 μmol m -2 s -1 and different percentages of the red, green and blue light, depending on the experimental objectives. Two one-month experiments with plants - lettuce and radicchio were carried out at 400 μmol m -2 s -1 PPFD (high light - HL) and 220 μmol m -2 s -1 PPFD (low light - LL) and 70% red, 20% green and 10% blue light composition. To evaluate the efficiency of photosynthesis, in vivo modulated chlorophyll fluorescence was measured by Pulse Amplitude Modulation (PAM) fluorometer on leaf discs and the following parameters: effective quantum yield of Photosystem II ( ΦPSII) and non-photochemical quenching (NPQ) were calculated. Both lettuce and radicchio plants grown at LL express higher photochemical activity of Photosystem II (PSII) than HL grown plants, evaluated by ΦPSII. Accelerated rise in NPQ in both LL grown plants was observed, while steady state NPQ values were higher in LL grown lettuce plants and did not differ in LL and HL grown radicchio plants. The extent of photoinhibition process in both plants was evaluated by changes in malonedialdehyde (MDA) concentration, peroxidase (POX) activity and hydrogen peroxide (H 2O 2) content. Accumulation of high levels of MDA and increased POX activity

  3. New Materials and Device Designs for Organic Light-Emitting Diodes

    Science.gov (United States)

    O'Brien, Barry Patrick

    Research and development of organic materials and devices for electronic applications has become an increasingly active area. Display and solid-state lighting are the most mature applications and, and products have been commercially available for several years as of this writing. Significant efforts also focus on materials for organic photovoltaic applications. Some of the newest work is in devices for medical, sensor and prosthetic applications. Worldwide energy demand is increasing as the population grows and the standard of living in developing countries improves. Some studies estimate as much as 20% of annual energy usage is consumed by lighting. Improvements are being made in lightweight, flexible, rugged panels that use organic light emitting diodes (OLEDs), which are particularly useful in developing regions with limited energy availability and harsh environments. Displays also benefit from more efficient materials as well as the lighter weight and ruggedness enabled by flexible substrates. Displays may require different emission characteristics compared with solid-state lighting. Some display technologies use a white OLED (WOLED) backlight with a color filter, but these are more complex and less efficient than displays that use separate emissive materials that produce the saturated colors needed to reproduce the entire color gamut. Saturated colors require narrow-band emitters. Full-color OLED displays up to and including television size are now commercially available from several suppliers, but research continues to develop more efficient and more stable materials. This research program investigates several topics relevant to solid-state lighting and display applications. One project is development of a device structure to optimize performance of a new stable Pt-based red emitter developed in Prof Jian Li's group. Another project investigates new Pt-based red, green and blue emitters for lighting applications and compares a red/blue structure with a red

  4. Light-emitting diode 585nm photomodulation inhibiting melanin synthesis and inducing autophagy in human melanocytes.

    Science.gov (United States)

    Chen, Li; Xu, Zhongyi; Jiang, Min; Zhang, Chengfeng; Wang, Xuan; Xiang, Leihong

    2018-01-01

    Melasma is a common hyperpigmentation skin disease on face. Light-emitting diode (LED) photomodulation (585nm) is reported to be effective for the treatment of melasma. However, whether and how LED photomodulation would influence melanogenesis of human epidermal melanocytes (HEMs) is unknown. To evaluate the effects of LED photomodulation (585nm) on melanogenesis in HEMs. HEMs were irradiated with fluences of 0, 5, 10 and 20J/cm 2 585nm LED light. After 5-day treatment, cell viability was analyzed by CCK-8 assay, and apoptosis was assessed by Annexin V APC assay. Melanin content and tyrosinase activity were measured by spectrophotometer. Melanosome stage and autophagosomes were determined under transmission electron microscope (TEM). The formation of autophagic punctate structures was observed under confocal microscope. RT-PCR and western blotting were used to assess the expression of relative mRNA and protein levels. Yellow light LED 585nm had no effects on HEMs cell viability and apoptosis. Treatment with LED 585nm from 5J/cm 2 to 20J/cm 2 inhibited melanosome maturation, decreased melanin content and tyrosinase activity. Inhibition was accompanied by the decreased expression of tyrosinase (TYR), tyrosinase-related protein-1 (TRP-1) and microphthalmia-associated transcription factor (MITF) on both mRNA and protein levels. Autophagosomes were observed under TEM. Autophagic punctate structures of microtubule-associated protein light chain 3 (LC3) proteins were induced by LED 585nm light. The configuration change of LC3 from LC3-I to LC3-II, and the degradation of p62 protein were observed after LED 585nm. Furthermore, we also revealed that the anti-melanogenic effect of LED 585nm photomodulation was reversed by 3-Methyladenine (3-MA), which inhibits autophagy by blocking autophagosome formation via the inhibition of type III Phosphatidylinositol 3-kinases (PI-3K). Our finding demonstrated that LED photomodulation with 585nm wavelength suppressed melanin content in

  5. Transient electroluminescence spikes in small molecular organic light-emitting diodes

    Science.gov (United States)

    Liu, Rui; Gan, Zhengqing; Shinar, Ruth; Shinar, Joseph

    2011-06-01

    We present a comprehensive study of transient nanosecond electroluminescence (EL) spikes that exceed the dc level and microseconds-long EL tails following a bias pulse in guest-host small molecular organic light-emitting diodes (SMOLEDs), including relatively efficient devices, which elucidates carrier and exciton dynamics in such devices. The transient EL is strongly dependent, among other parameters, on device materials and structure. At low temperatures, all measured devices, with the exception of Pt octaethylporphyrin (PtOEP)-doped tris(8-hydroxyquinoline) Al (Alq3) SMOLEDs, exhibit the spikes at ˜70-300 ns. At room temperature (RT), however, only those with a hole injection barrier, carrier-trapping guest-host emitting layer, and no strong electron-transporting and hole-blocking layer [such as 4,7-diphenyl-1,10-phenanthroline (BPhen)] exhibit strong spikes. These narrow and appear earlier under postpulse reverse bias. To further elucidate the origin of the spikes, we monitored their dependence on the pulsed bias width and voltage, the doped layer thickness, and its location within the OLED structure. The characteristics of the microseconds-long tails were also evaluated through the effect of the postpulse voltage. A model based on the recombination of correlated charge pairs (CCPs) and on charge detrapping is presented; the model agrees well with the experimental data. The results suggest that reduced electric-field-induced dissociative quenching of singlet excitons is responsible for the spikes’ amplitude exceeding the on-pulse dc EL level. The long tails are attributed to recombination of charges detrapped from a distribution of shallow, mostly host, sites, reminiscent of the detrapping and recombination processes that yield the thermally stimulated luminescence of such materials. The comprehensive transient EL measurements in guest-host devices demonstrate the generality of the strong spike phenomenon in devices with charge trapping in the emitting guest

  6. Investigation of quinoline-based materials for organic light-emitting diode (OLED) applications

    Science.gov (United States)

    Chen, Changqing

    Blue electroluminescent materials are essential for the development of full-color displays. A blue-emitting quinoline-based material 8,8' -dimethoxy-5,5'-bisquinoline (DMeOBQ) was synthesized and characterized. This material is sublimable and has significantly improved hydrolytic stability as well as promising electron transporting and emitting properties. A blue organic light-emitting diode (OLED) was made with this material. The device configuration is indium tin oxide/NPB/DMeOBQ/CsF/Al. N, N'-bis-(1-naphthyl)-N, N'-diphenyl-1,1 '-biphenyl-4, 4'-diamine (NPB) was used as the hole transporting material, DMeOBQ as the electron transporting and blue emitting material, and CsF/Al as the cathode. The device showed a bright blue emission with a peak wavelength of 425nm (CIE coordinates: x = 0.155, y = 0.10) and narrow EL band (FWHM = 63 nm). The device also showed a low turn on voltage of 2.8 ev. Tris-(8-hydroxyquinoline) aluminum (Alq3) has become one of the most widely used electroluminescent materials in OLEDs because of its good stability and luminescence properties. The existence of various isomers (meridianal and facial) as well as left- and right-handed enantiomers of the meridianal isomer could potentially contribute to structure randomization of Alq3, thereby qualitatively addressing the microcrystaline nature of this material. We studied exchange dynamics of the three inequivalent ligands and the enantiomers in Alq3 complexes. Liquid state NMR spectroscopy was used to quantify the interchange of the three ligands, the temperature dependence of this process and the enantiomers of Alq3 in the presence of a chiral shift reagent. The three inequivalent ligands were found to exchange following a first-order kinetic model. Activation parameters were obtained from the temperature dependence of the reaction rate constants. The activation energies for the flip of the three inequivalent ligands were found to be around 100 kJ/mol. The existence of the two enantiomers of

  7. Bactericidal effects of 310 nm ultraviolet light-emitting diode irradiation on oral bacteria.

    Science.gov (United States)

    Takada, Ayuko; Matsushita, Kenji; Horioka, Satoru; Furuichi, Yasushi; Sumi, Yasunori

    2017-06-06

    Ultraviolet (UV) light is used for phototherapy in dermatology, and UVB light (around 310 nm) is effective for treatment of psoriasis and atopic dermatitis. In addition, it is known that UVC light (around 265 nm) has a bactericidal effect, but little is known about the bactericidal effect of UVB light. In this study, we examined the bactericidal effects of UVB-light emitting diode (LED) irradiation on oral bacteria to explore the possibility of using a 310 nm UVB-LED irradiation device for treatment of oral infectious diseases. We prepared a UVB (310 nm) LED device for intraoral use to examine bactericidal effects on Streptococcus mutans, Streptococcus sauguinis, Porphyromonas gingivalis, and Fusobacterium nucleatum and also to examine the cytotoxicity to a human oral epithelial cell line (Ca9-22). We also examined the production of nitric oxide and hydrogen peroxide from Ca9-22 cells after irradiation with UVB-LED light. Irradiation with the 310 nm UVB-LED at 105 mJ/cm 2 showed 30-50% bactericidal activity to oral bacteria, though 17.1 mJ/cm 2 irradiation with the 265 nm UVC-LED completely killed the bacteria. Ca9-22 cells were strongly injured by irradiation with the 265 nm UVC-LED but were not harmed by irradiation with the 310 nm UVB-LED. Nitric oxide and hydrogen peroxide were produced by Ca9-22 cells with irradiation using the 310 nm UVB-LED. P. gingivalis was killed by applying small amounts of those reactive oxygen species (ROS) in culture, but other bacteria showed low sensitivity to the ROS. Narrowband UVB-LED irradiation exhibited a weak bactericidal effect on oral bacteria but showed low toxicity to gingival epithelial cells. Its irradiation also induces the production of ROS from oral epithelial cells and may enhance bactericidal activity to specific periodontopathic bacteria. It may be useful as a new adjunctive therapy for periodontitis.

  8. Effects of ultraviolet light emitting diodes (LEDs) on microbial and enzyme inactivation of apple juice.

    Science.gov (United States)

    Akgün, Merve Pelvan; Ünlütürk, Sevcan

    2017-11-02

    In this study, the effects of Ultraviolet light-emitting diodes (UV-LEDs) on the inactivation of E. coli K12 (ATCC 25253), an indicator organism of E. coli O157:H7, and polyphneoloxidase (PPO) in cloudy apple juice (CAJ) were investigated. The clear (AJ) and cloudy apple juice were exposed to UV rays for 40min by using a UV device composed of four UV-LEDs with peak emissions at 254 and 280nm and coupled emissions as follows: 254/365, 254/405, 280/365, 280/405 and 254/280/365/405nm. UV-LEDs at 254nm achieved 1.6±0.1 log 10 CFU/mL inactivation of E. coli K12 at UV dose of 707.2mJ/cm 2 . The highest inactivation of E. coli K12 (2.0±0.1log 10 CFU/mL and 2.0±0.4log 10 CFU/mL) was achieved when the cloudy apple juice was treated with both 280nm and 280/365nm UV-LEDs. For clear apple juice the highest inactivation 4.4log 10 CFU/mL obtained for E. coli K12 was achieved using 4 lamps emitting light at 280nm for 40min exposure time. For the same treatment time, the experiments using a combination of lamps emitting light at 280 and 365nm (2lamp/2lamp) were resulted in 3.9±0.2log 10 CFU/mL reductions. UV-A and UV-C rays in combination showed a better inactivation effect on PPO than UV-C rays used separately. Residual activity of PPO in CAJ was reduced to 32.58% when treated with UV-LED in combination of UV-C (280nm) and UV-A (365nm) rays. Additionally, the total color change (ΔE) of CAJ subjected to combined UV-LED irradiation at 280/365nm was the lowest compared to other studied processing conditions. This study provides key implications for the future application of UV-LEDs to fruit juice pasteurization. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Feasibility of Ultraviolet Light Emitting Diodes as an Alternative Light Source for Photocatalysis

    Science.gov (United States)

    Levine, Langanf H.; Richards, Jeffrey T.; Soler, Robert; Maxik, Fred; Coutts, Janelle; Wheeler, Raymond M.

    2011-01-01

    The objective of this study was to determine whether ultraviolet light emitting diodes (UV-LEDs) could serve as an alternative photon source efficiently for heterogeneous photocatalytic oxidation (PCO). An LED module consisting of 12 high-power UV-A LEDs was designed to be interchangeable with a UV-A fluorescent black light blue (BLB) lamp in a Silica-Titania Composite (STC) packed bed annular reactor. Lighting and thermal properties were characterized to assess the uniformity and total irradiant output. A forward current of (I(sub F)) 100 mA delivered an average irradiance of 4.0 m W cm(exp -2), which is equivalent to the maximum output of the BLB, but the irradiance of the LED module was less uniform than that of the BLB. The LED- and BLB-reactors were tested for the oxidization of 50 ppmv ethanol in a continuous flow-through mode with 0.94 sec space time. At the same irradiance, the UV-A LED reactor resulted in a lower PCO rate constant than the UV-A BLB reactor (19.8 vs. 28.6 nM CO2 sec-I), and consequently lower ethanol removal (80% vs. 91%) and mineralization efficiency (28% vs. 44%). Ethanol mineralization increased in direct proportion to the irradiance at the catalyst surface. This result suggests that reduced ethanol mineralization in the LED- reactor could be traced to uneven irradiance over the photocatalyst, leaving a portion of the catalyst was under-irradiated. The potential of UV-A LEDs may be fully realized by optimizing the light distribution over the catalyst and utilizing their instantaneous "on" and "off' feature for periodic irradiation. Nevertheless, the current UV-A LED module had the same wall plug efficiency (WPE) of 13% as that of the UV-A BLB. These results demonstrated that UV-A LEDs are a viable photon source both in terms of WPE and PCO efficiency.

  10. Point-of-use water disinfection using ultraviolet and visible light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Lui, Gough Yumu, E-mail: gough@student.unsw.edu.au [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); School of Photovoltaics and Renewable Energy Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Roser, David, E-mail: djroser@unsw.edu.au [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Corkish, Richard, E-mail: r.corkish@unsw.edu.au [School of Photovoltaics and Renewable Energy Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); Ashbolt, Nicholas J., E-mail: ashbolt@ualberta.ca [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia); School of Public Health, South Academic Building, University of Alberta, Edmonton, Alberta T6G 2G7 (Canada); Stuetz, Richard, E-mail: r.stuetz@unsw.edu.au [UNSW Water Research Centre, School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052 (Australia)

    2016-05-15

    Improvements in point-of-use (POU) drinking water disinfection technologies for remote and regional communities are urgently needed. Conceptually, UV-C light-emitting diodes (LEDs) overcome many drawbacks of low-pressure mercury tube based UV devices, and UV-A or visible light LEDs also show potential. To realistically evaluate the promise of LED disinfection, our study assessed the performance of a model 1.3 L reactor, similar in size to solar disinfection bottles. In all, 12 different commercial or semi-commercial LED arrays (270–740 nm) were compared for their ability to inactivate Escherichia coli K12 ATCC W3110 and Enterococcus faecalis ATCC 19433 over 6 h. Five log{sub 10} and greater reductions were consistently achieved using the 270, 365, 385 and 405 nm arrays. The output of the 310 nm array was insufficient for useful disinfection while 430 and 455 nm performance was marginal (≈ 4.2 and 2.3-log{sub 10}s E. coli and E. faecalis over the 6 h). No significant disinfection was observed with the 525, 590, 623, 660 and 740 nm arrays. Delays in log-phase inactivation of E. coli were observed, particularly with UV-A wavelengths. The radiation doses required for > 3-log{sub 10} reduction of E. coli and E. faecalis differed by 10 fold at 270 nm but only 1.5–2.5 fold at 365–455 nm. Action spectra, consistent with the literature, were observed with both indicators. The design process revealed cost and technical constraints pertaining to LED electrical efficiency, availability and lifetime. We concluded that POU LED disinfection using existing LED technology is already technically possible. UV-C LEDs offer speed and energy demand advantages, while UV-A/violet units are safer. Both approaches still require further costing and engineering development. Our study provides data needed for such work. - Highlights: • Disinfection of E. coli and E. faecalis achieved with 270 and 365–455 nm LEDs • No significant disinfection was found with 310 and > 455 nm LEDs

  11. Measuring the Photocatalytic Breakdown of Crystal Violet Dye using a Light Emitting Diode Approach

    Science.gov (United States)

    Ryan, Robert E.; Underwood, Lauren W.; O'Neal, Duane; Pagnutti, Mary; Davis, Bruce A.

    2009-01-01

    A simple method to estimate the photocatalytic reactivity performance of spray-on titanium dioxide coatings for transmissive glass surfaces was developed. This novel technique provides a standardized method to evaluate the efficiency of photocatalytic material systems over a variety of illumination levels. To date, photocatalysis assessments have generally been conducted using mercury black light lamps. Illumination levels for these types of lamps are difficult to vary, consequently limiting their use for assessing material performance under a diverse range of simulated environmental conditions. This new technique uses an ultraviolet (UV) gallium nitride (GaN) light emitting diode (LED) array instead of a traditional black light to initiate and sustain photocatalytic breakdown. This method was tested with a UV-resistant dye (crystal violet) applied to a titanium dioxide coated glass slide. Experimental control is accomplished by applying crystal violet to both titanium dioxide coated slides and uncoated control slides. A slide is illuminated by the UV LED array, at various light levels representative of outdoor and indoor conditions, from the dye side of the slide. To monitor degradation of the dye over time, a temperature-stabilized white light LED, whose emission spectrum overlaps with the dye absorption spectrum, is used to illuminate the opposite side of the slide. Using a spectrometer, the amount of light from the white light LED transmitted through the slide as the dye degrades is monitored as a function of wavelength and time and is subsequently analyzed. In this way, the rate of degradation for photocatalytically coated versus uncoated slide surfaces can be compared. Results demonstrate that the dye absorption decreased much more rapidly on the photocatalytically coated slides than on the control uncoated slides, and that dye degradation is dependent on illumination level. For photocatalytic activity assessment purposes, this experimental configuration and

  12. Development and Utilization of Host Materials for White Phosphorescent Organic Light-Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Ching; Chen, Shaw

    2013-05-31

    Our project was primarily focused on the MYPP 2015 goal for white phosphorescent organic devices (PhOLEDs or phosphorescent organic light-emitting diodes) for solid-state lighting with long lifetimes and high efficiencies. Our central activity was to synthesize and evaluate a new class of host materials for blue phosphors in the PhOLEDs, known to be a weak link in the device operating lifetime. The work was a collaborative effort between three groups, one primarily responsible for chemical design and characterization (Chen), one primarily responsible for device development (Tang) and one primarily responsible for mechanistic studies and degradation analysis (Rothberg). The host materials were designed with a novel architecture that chemically links groups with good ability to move electrons with those having good ability to move “holes” (positive charges), the main premise being that we could suppress the instability associated with physical separation and crystallization of the electron conducting and hole conducting materials that might cause the devices to fail. We found that these materials do prevent crystallization and that this will increase device lifetimes but that efficiencies were reduced substantially due to interactions between the materials creating new low energy “charge transfer” states that are non-luminescent. Therefore, while our proposed strategy could in principle improve device lifetimes, we were unable to find a materials combination where the efficiency was not substantially compromised. In the course of our project, we made several important contributions that are peripherally related to the main project goal. First, we were able to prepare the proposed new family of materials and develop synthetic routes to make them efficiently. These types of materials that can transport both electrons and holes may yet have important roles to play in organic device technology. Second we developed an important new method for controlling the

  13. SPECTRAL CHARACTERISTICS OF MID-INFRARED LIGHT-EMITTING DIODES BASED ON InAs (Sb,P

    Directory of Open Access Journals (Sweden)

    N. K. Zhumashev

    2016-01-01

    Full Text Available Subject of Study. We consider spectral characteristics of mid-infrared light-emitting diodes with heterostructures based on InAs(Sb,P emitting at T=300 K in the wavelength range 3.4–4.1 micrometers. The aim of the study was to search for the ways of increasing the diode efficiency. Methods. The heterostructures were grown from metal-organic chemical compounds with the use of vapor-phase epitaxial technique. The spectra were recorded under pulse excitation with the use of computer-controlled installation employing MDR-23 grating monochromator and a lock-in amplifier. InSb photodiode was used as a detector. Comparative study of electroluminescence spectra of the diodes was carried out at the temperatures equal to 300 K and 77 K. We compared the obtained data with the calculation results of the band diagrams of the heterostructures. Main Results. As a result of comparative study of the electroluminescence spectra of the diodes recorded at 300 K and 77 K we have established that increasing of their efficiency is hindered by substantial influence of Auger recombination. For the first time at 77 К we have observed the effect of stimulated emission from InAsSb active layer in light-emitting structures made of InAs/InAsSb/InAsSbP. For heterostructures with quantum wells InAs/(InAs/InAsSb/InAsSbP we have found out that at 77 К the carrier recombination occurs outside quantum wells, which points out to the insufficient carrier localization in the active layer. Thus, we have shown that the efficiency of mid-infrared light-emitting diodes based on InAs(Sb,P can be increased via suppression of Auger-recombination and improvement of carrier localization in the active region. Practical Relevance. The results of the study can be used for development of heterostructures for mid-infrared light-emitting diodes.

  14. Design and geometry of hybrid white light-emitted diodes for efficient energy transfer from the quantum well to the nanocrystals

    DEFF Research Database (Denmark)

    Kopylov, Oleksii; Huck, Alexander; Shirazi, Roza

    2013-01-01

    We demonstrate light color conversion in patterned InGaN light-emitting diodes (LEDs), which is enhanced via nonradiative exciton resonant energy transfer (RET) from the electrically driven diode to colloidal semiconductor nanocrystals (NCs). Patterning of the diode is essential for the coupling ...

  15. Development of Radiation-Resistant In-Water Wireless Transmission System Using Light Emitting Diodes and Photo Diodes

    Science.gov (United States)

    Takeuchi, T.; Shibata, H.; Otsuka, N.; Uehara, T.; Tsuchiya, K.; Shibagaki, T.; Komanome, H.

    2016-10-01

    Several kinds of commercially available light emitting diodes (LED) and photo diodes (PD) were irradiated with 60Co gamma ray up to 1 MGy for development of a radiation-resistant in-water wireless transmission system using visible light. The lens parts of the LEDs turned brown by the irradiation and their colors became dark with the absorbed dose. The total luminous fluxes decreased with the absorbed dose and the LED with shorter emission wavelength had the higher decrease rate. Meanwhile, the current-voltage characteristics hardly changed. These results indicate that the decreases of the total luminous flux of the LEDs were mainly caused not by the degradation of the semiconductor parts but by the coloring of the lens parts by the irradiation. On the other hand, the light sensitivities of the PDs decreased with the absorbed dose. The PDs with the window part which turned a darker color had the higher decrease rate. These results indicate that the decreases of light sensitivities of the PDs were also mainly caused by the coloring of the resin parts by the irradiation. If the wireless transmission is performed using the candidate LED and PD between 5 meters in water, using a few LEDs and PDs, the PD's output current generated by the emission light of the LED is estimated to be detectable even considering the effects of the absorption of the light in water and the increased dark current by the irradiation. Therefore, a radiation resistant in-water transmission system can be constructed using commercially available LEDs and PDs in principle.

  16. Charge transport and recombination in polyspirobifluorene blue light-emitting diodes

    NARCIS (Netherlands)

    Nicolai, H.T.; Hof, A.; Oosthoek, J.L.M.; Blom, P.W.M.

    2011-01-01

    The charge transport in blue light-emitting polyspirobifluorene is investigated by both steady-state current-voltage measurements and transient electroluminescence. Both measurement techniques yield consistent results and show that the hole transport is space-charge limited. The electron current is

  17. Current Spreading Layer with High Transparency and Conductivity for near-ultraviolet light emitting diodes

    DEFF Research Database (Denmark)

    Lin, Li; Jensen, Flemming; Herstrøm, Berit

    Transparent conductive aluminum-doped zinc oxide (AZO) layer was deposited on GaN-based near-ultraviolet (NUV) light emitting epitaxial wafers as current spreading layer by a sputtering process. Efforts were made to improve the electrical properties of AZO in order to produce ohmic contact....

  18. Colloidal metal oxide nanocrystals as charge transporting layers for solution-processed light-emitting diodes and solar cells.

    Science.gov (United States)

    Liang, Xiaoyong; Bai, Sai; Wang, Xin; Dai, Xingliang; Gao, Feng; Sun, Baoquan; Ning, Zhijun; Ye, Zhizhen; Jin, Yizheng

    2017-03-21

    Colloidal metal oxide nanocrystals offer a unique combination of excellent low-temperature solution processability, rich and tuneable optoelectronic properties and intrinsic stability, which makes them an ideal class of materials as charge transporting layers in solution-processed light-emitting diodes and solar cells. Developing new material chemistry and custom-tailoring processing and properties of charge transporting layers based on oxide nanocrystals hold the key to boosting the efficiency and lifetime of all-solution-processed light-emitting diodes and solar cells, and thereby realizing an unprecedented generation of high-performance, low-cost, large-area and flexible optoelectronic devices. This review aims to bridge two research fields, chemistry of colloidal oxide nanocrystals and interfacial engineering of optoelectronic devices, focusing on the relationship between chemistry of colloidal oxide nanocrystals, processing and properties of charge transporting layers and device performance. Synthetic chemistry of colloidal oxide nanocrystals, ligand chemistry that may be applied to colloidal oxide nanocrystals and chemistry associated with post-deposition treatments are discussed to highlight the ability of optimizing processing and optoelectronic properties of charge transporting layers. Selected examples of solution-processed solar cells and light-emitting diodes with oxide-nanocrystal charge transporting layers are examined. The emphasis is placed on the correlation between the properties of oxide-nanocrystal charge transporting layers and device performance. Finally, three major challenges that need to be addressed in the future are outlined. We anticipate that this review will spur new material design and simulate new chemistry for colloidal oxide nanocrystals, leading to charge transporting layers and solution-processed optoelectronic devices beyond the state-of-the-art.

  19. Self-assembly surface modified indium-tin oxide anodes for single-layer light-emitting diodes

    CERN Document Server

    Morgado, J; Charas, A; Matos, M; Alcacer, L; Cacialli, F

    2003-01-01

    We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.

  20. On-chip cavity-enhanced absorption spectroscopy using a white light-emitting diode and polymer mirrors.

    Science.gov (United States)

    Rushworth, Cathy M; Jones, Gareth; Fischlechner, Martin; Walton, Emma; Morgan, Hywel

    2015-02-07

    We have developed a disposable microfluidic chip with integrated cavity mirrors comprised of two pieces of 3M Vikuiti™ enhanced specular reflector II (ESRII) film, for performing cavity-enhanced absorption spectroscopy with a white light-emitting diode (LED). Compared to measurements made with a chip without cavity mirrors, the absorption path length is enhanced by a maximum factor of 28 at 544 nm, and the sensitivity is enhanced by approximately 5 times, enabling micromolar range detection limits to be achieved in an optical path length of only 50 μm.

  1. Light-emitting diode street lights reduce last-ditch evasive manoeuvres by moths to bat echolocation calls

    Science.gov (United States)

    Wakefield, Andrew; Stone, Emma L.; Jones, Gareth; Harris, Stephen

    2015-01-01

    The light-emitting diode (LED) street light market is expanding globally, and it is important to understand how LED lights affect wildlife populations. We compared evasive flight responses of moths to bat echolocation calls experimentally under LED-lit and -unlit conditions. Significantly, fewer moths performed ‘powerdive’ flight manoeuvres in response to bat calls (feeding buzz sequences from Nyctalus spp.) under an LED street light than in the dark. LED street lights reduce the anti-predator behaviour of moths, shifting the balance in favour of their predators, aerial hawking bats. PMID:26361558

  2. Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

    Energy Technology Data Exchange (ETDEWEB)

    Qian, L., E-mail: qian_lei@126.com; Xu, Z.; Teng, F.; Duan, X.-X. [Beijing Jiaotong University, Institute of Optoelectronic Technology (China); Jin, Z.-S.; Du, Z.-L. [Henan University, Key Laboratory on special functional materials (China); Li, F.-S.; Zheng, M.-J. [State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, Peking University, Department of Physics (China); Wang, Y.-S. [Beijing Jiaotong University, Institute of Optoelectronic Technology (China)

    2007-06-15

    Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

  3. Infrared light-emitting diode radiation causes gravitropic and morphological effects in dark-grown oat seedlings

    Science.gov (United States)

    Johnson, C. F.; Brown, C. S.; Wheeler, R. M.; Sager, J. C.; Chapman, D. K.; Deitzer, G. F.

    1996-01-01

    Oat (Avena sativa cv Seger) seedlings were irradiated with IR light-emitting diode (LED) radiation passed through a visible-light-blocking filter. Infrared LED irradiated seedlings exhibited differences in growth and gravitropic response when compared to seedlings grown in darkness at the same temperature. Thus, the oat seedlings in this study were able to detect IR LED radiation. These findings call into question the use of IR LED as a safe-light for some photosensitive plant response experiments. These findings also expand the defined range of wavelengths involved in radiation-gravity (light-gravity) interactions to include wavelengths in the IR region of the spectrum.

  4. Quantitative and depth-resolved deep level defect distributions in InGaN/GaN light emitting diodes.

    Science.gov (United States)

    Armstrong, A; Henry, T A; Koleske, D D; Crawford, M H; Lee, S R

    2012-11-05

    Deep level defects in the multi-quantum well (MQW) region of InGaN/GaN light emitting diodes (LEDs) were investigated. InGaN quantum well and GaN quantum barrier defect states were distinguished using bias-dependent steady-state photocapacitance and deep level optical spectroscopy, and their possible physical origin and potential impact on LED performance is considered. Lighted capacitance-voltage measurements provided quantitative and nanoscale depth profiling of the deep level concentration within the MQW region. The concentration of every observed deep level varied strongly with depth in the MQW region, which indicates evolving mechanisms for defect incorporation during MQW growth.

  5. Phototransferred thermoluminescence from alpha-Al sub 2 O sub 3 :C using blue light emitting diodes

    CERN Document Server

    Bulur, E

    1999-01-01

    Phototransferred thermoluminescence (PTTL) from alpha-Al sub 2 O sub 3 :C single crystals was studied using a blue light emitting diode (LED) for phototransfer of charges from deep traps to the main dosimetry trap. The dose response was found to be linear in the region from approx 5 mGy to approx 5 Gy. It was observed that the corresponding deep traps were located near 500 deg. C and heating to temperatures >600 deg. C removes the PTTL effect induced by the light from the blue LED. The thermal activation energy of the source traps involved in the PTTL production was calculated as 3.23 eV.

  6. Enhanced light emission in blue light-emitting diodes by multiple Mie scattering from embedded silica nanosphere stacking layers.

    Science.gov (United States)

    Park, Young Jae; Kang, Ji Hye; Kim, Hee Yun; Lysak, Volodymyr V; Chandramohan, S; Ryu, Jae Hyoung; Kim, Hyun Kyu; Han, Nam; Jeong, Hyun; Jeong, Mun Seok; Hong, Chang-Hee

    2011-11-07

    We demonstrate enhanced light emission in blue light-emitting diodes (LEDs) by multiple Mie scattering from embedded silica nanosphere stacking layers (SNSL). A honeycomb cone structure is introduced in the GaN epilayer to confine a maximum number of silica nanospheres (SNs). We found that the light is predominantly directed vertically by scattering and geometrical effect in SNSL embedded LEDs. Consequently, the light output power is enhanced by 2.7 times, which we attribute to the improvement in light extraction efficiency due to the multiple Mie scattering of light from the embedded SNSL. The experimental results are verified by simulation using finite difference time domain method (FDTD).

  7. Self-assembly surface modified indium-tin oxide anodes for single-layer light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Morgado, Jorge [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Barbagallo, Nunzio [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Charas, Ana [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Matos, Manuel [Departamento de Engenharia Quimica, Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emidio Navarro-1, P-1949-001 Lisbon (Portugal); Alcacer, Luis [Instituto de Telecomunicacoes and Departamento de Engenharia Quimica, Instituto Superior Tecnico, Avenida Rovisco Pais, P-1049-001 Lisbon (Portugal); Cacialli, Franco [Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT (United Kingdom)

    2003-03-07

    We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.

  8. Paired emitter-detector light emitting diodes for the measurement of lead(II) and cadmium(II)

    International Nuclear Information System (INIS)

    Lau, K.-T.; McHugh, Eimear; Baldwin, Susan; Diamond, Dermot

    2006-01-01

    A transmittance mode optical device based on using a reverse biased light emitting diode (LED) as light detector has been developed for colorimetric analysis. This new optical device was validated with bromocresol green dye for absorbance measurements before being employed for detecting cadmium(II) and lead(II) in water. Results show that the performance of this LED-based device is comparable to much more expensive bench top UV-vis instruments, but with the advantages of being low cost, low power and simple to operate

  9. Direct evaluation of reflector effects on radiant flux from InGaN-based light-emitting diodes

    Science.gov (United States)

    Masui, Hisashi; Fellows, Natalie N.; Sato, Hitoshi; Asamizu, Hirokuni; Nakamura, Shuji; Denbaars, Steven P.

    2007-08-01

    A metal layer formed on the backside of InGaN/sapphire-based light-emitting diodes deteriorates the inherent optical power output. An experimental approach of a suspended die is employed to study the effects of such metal layers via a direct comparison in radiant flux from a discrete die with and without a reflector. A sphere package that employs no reflector is proposed and fabricated. Light extraction of the sphere design is discussed; a light source in the sphere package would not have to be either an ideal point or placed at the center of the sphere, due to a finite critical angle at the sphere/air interface.

  10. 270 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Over 60 mW Continuous Wave Output Power

    Science.gov (United States)

    Grandusky, James R.; Chen, Jianfeng; Gibb, Shawn R.; Mendrick, Mark C.; Moe, Craig G.; Rodak, Lee; Garrett, Gregory A.; Wraback, Michael; Schowalter, Leo J.

    2013-03-01

    In this letter, the achievement of over 60 mW output power from pseudomorphic ultraviolet light-emitting diodes in continuous wave operation is reported. Die thinning and encapsulation improved the photon extraction efficiency to over 15%. Improved thermal management and a high characteristic temperature resulted in a low thermal rolloff up to 300 mA injection current with an output power of 67 mW, an external quantum efficiency (EQE) of 4.9%, and a wall plug efficiency (WPE) of 2.5% for a single-chip device emitting at 271 nm in continuous wave operation.

  11. Efficient white phosphorescent organic light-emitting diodes consisting of orange ultrathin and blue mixed host emission layers

    Science.gov (United States)

    Sheng, Ren; Zuo, Liangmei; Xue, Kaiwen; Duan, Yu; Chen, Ping; Cheng, Gang; Zhao, Yi

    2016-08-01

    We have successfully demonstrated highly efficient white phosphorescent organic light-emitting diodes (OLEDs) by inserting an ultrathin non-doped orange layer within blue mixed host emission layer. The key feature of the novel device is the employment of blue mixed host and orange ultrathin layers, resulting in an extended recombination region and more balanced charge carrier. The maximum efficiencies of 33.8 lm W-1 and 32.2 cd A-1 are obtained. Moreover, the resulting white device achieves a slight efficiency roll-off and a high luminance at low operating voltage. Our versatile concept suggests a promising simple method to achieve high performance white OLEDs.

  12. Effects of Charge Balance and Exciton Confinement on the Operational Lifetime of Blue Phosphorescent Organic Light-Emitting Diodes

    Science.gov (United States)

    Coburn, Caleb; Forrest, Stephen R.

    2017-04-01

    We measure the contribution of loss of charge balance and exciton confinement in the emission zone to the operational lifetime of blue phosphorescent organic light-emitting diodes (PHOLEDs). Charge balance and exciton confinement are monitored as functions of time by measuring the emission intensity of either phosphorescent or fluorescent red-emitting "sensing" layers embedded within the charge-transport layers outside of the emission zone. We find no significant change in charge balance over the lifetime of the device, while loss of exciton confinement accounts for <5 % of luminance loss, confirming that degradation is primarily due to decomposition of molecular constituents within the emission layer of the PHOLED.

  13. Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

    International Nuclear Information System (INIS)

    Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

    2007-01-01

    Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased

  14. Electrical spin injection using GaCrN in a GaN based spin light emitting diode

    Science.gov (United States)

    Banerjee, D.; Adari, R.; Sankaranarayan, S.; Kumar, A.; Ganguly, S.; Aldhaheri, R. W.; Hussain, M. A.; Balamesh, A. S.; Saha, D.

    2013-12-01

    We have demonstrated electrical spin-injection from GaCrN dilute magnetic semiconductor (DMS) in a GaN-based spin light emitting diode (spin-LED). The remanent in-plane magnetization of the thin-film semiconducting ferromagnet has been used for introducing the spin polarized electrons into the non-magnetic InGaN quantum well. The output circular polarization obtained from the spin-LED closely follows the normalized in-plane magnetization curve of the DMS. A saturation circular polarization of ˜2.5% is obtained at 200 K.

  15. Demonstration Assessment of Light-Emitting Diode (LED) Parking Lot Lighting in Leavenworth, KS

    Energy Technology Data Exchange (ETDEWEB)

    Myer, Michael; Kinzey, Bruce R.; Curry, Ku' uipo

    2011-05-06

    This report describes the process and results of a demonstration of solid-state lighting (SSL) technology in a commercial parking lot lighting application, under the U.S. Department of Energy (DOE) Solid-State Lighting Technology GATEWAY Demonstration Program. The parking lot is for customers and employees of a Walmart Supercenter in Leavenworth, Kansas and this installation represents the first use of the LED Parking Lot Performance Specification developed by the DOE’s Commercial Building Energy Alliance. The application is a parking lot covering more than a half million square feet, lighted primarily by light-emitting diodes (LEDs). Metal halide wall packs were installed along the building facade. This site is new construction, so the installed baseline(s) were hypothetical designs. It was acknowledged early on that deviating from Walmart’s typical design would reduce the illuminance on the site. Walmart primarily uses 1000W pulse-start metal halide (PMH) lamps. In order to provide a comparison between both typical design and a design using conventional luminaires providing a lower illuminance, a 400W PMH design was also considered. As mentioned already, the illuminance would be reduced by shifting from the PMH system to the LED system. The Illuminating Engineering Society of North America (IES) provides recommended minimum illuminance values for parking lots. All designs exceeded the recommended illuminance values in IES RP-20, some by a wider margin than others. Energy savings from installing the LED system compared to the different PMH systems varied. Compared to the 1000W PMH system, the LED system would save 63 percent of the energy. However, this corresponds to a 68 percent reduction in illuminance as well. In comparison to the 400W PMH system, the LED system would save 44 percent of the energy and provide similar minimum illuminance values at the time of relamping. The LED system cost more than either of the PMH systems when comparing initial costs

  16. Device Engineering and Degradation Mechanism Study of All-Phosphorescent White Organic Light-Emitting Diodes

    Science.gov (United States)

    Xu, Lisong

    As a possible next-generation solid-state lighting source, white organic light-emitting diodes (WOLEDs) have the advantages in high power efficiency, large area and flat panel form factor applications. Phosphorescent emitters and multiple emitting layer structures are typically used in high efficiency WOLEDs. However due to the complexity of the device structure comprising a stack of multiple layers of organic thin films, ten or more organic materials are usually required, and each of the layers in the stack has to be optimized to produce the desired electrical and optical functions such that collectively a WOLED of the highest possible efficiency can be achieved. Moreover, device degradation mechanisms are still unclear for most OLED systems, especially blue phosphorescent OLEDs. Such challenges require a deep understanding of the device operating principles and materials/device degradation mechanisms. This thesis will focus on achieving high-efficiency and color-stable all-phosphorescent WOLEDs through optimization of the device structures and material compositions. The operating principles and the degradation mechanisms specific to all-phosphorescent WOLED will be studied. First, we investigated a WOLED where a blue emitter was based on a doped mix-host system with the archetypal bis(4,6-difluorophenyl-pyridinato-N,C2) picolinate iridium(III), FIrpic, as the blue dopant. In forming the WOLED, the red and green components were incorporated in a single layer adjacent to the blue layer. The WOLED efficiency and color were optimized through variations of the mixed-host compositions to control the electron-hole recombination zone and the dopant concentrations of the green-red layers to achieve a balanced white emission. Second, a WOLED structure with two separate blue layers and an ultra-thin red and green co-doped layer was studied. Through a systematic investigation of the placement of the co-doped red and green layer between the blue layers and the material

  17. OLED Fundamentals: Materials, Devices, and Processing of Organic Light-Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Blochwitz-Nimoth, Jan; Bhandari, Abhinav; Boesch, Damien; Fincher, Curtis R.; Gaspar, Daniel J.; Gotthold, David W.; Greiner, Mark T.; Kido, Junji; Kondakov, Denis; Korotkov, Roman; Krylova, Valentina A.; Loeser, Falk; Lu, Min-Hao; Lu, Zheng-Hong; Lussem, Bjorn; Moro, Lorenza; Padmaperuma, Asanga B.; Polikarpov, Evgueni; Rostovtsev, Vsevolod V.; Sasabe, Hisahiro; Silverman, Gary; Thompson, Mark E.; Tietze, Max; Tyan, Yuan-Sheng; Weaver, Michael; Xin , Xu; Zeng, Xianghui

    2015-05-26

    What is an organic light emitting diode (OLED)? Why should we care? What are they made of? How are they made? What are the challenges in seeing these devices enter the marketplace in various applications? These are the questions we hope to answer in this book, at a level suitable for knowledgeable non-experts, graduate students and scientists and engineers working in the field who want to understand the broader context of their work. At the most basic level, an OLED is a promising new technology composed of some organic material sandwiched between two electrodes. When current is passed through the device, light is emitted. The stack of layers can be very thin and has many variations, including flexible and/or transparent. The organic material can be polymeric or composed small molecules, and may include inorganic components. The electrodes may consist of metals, metal oxides, carbon nanomaterials, or other species, though of course for light to be emitted, one electrode must be transparent. OLEDs may be fabricated on glass, metal foils, or polymer sheets (though polymeric substrates must be modified to protect the organic material from moisture or oxygen). In any event, the organic material must be protected from moisture during storage and operation. A control circuit, the exact nature of which depends on the application, drives the OLED. Nevertheless, the control circuit should have very stable current control to generate uniform light emission. OLEDs can be designed to emit a single color of light, white light, or even tunable colors. The devices can be switched on and off very rapidly, which makes them suitable for displays or for general lighting. Given the amazing complexity of the technical and design challenges for practical OLED applications, it is not surprising that applications are still somewhat limited. Although organic electroluminescence is more than 50 years old, the modern OLED field is really only about half that age – with the first high

  18. Solution processed, white emitting tandem organic light-emitting diodes with inverted device architecture.

    Science.gov (United States)

    Höfle, Stefan; Schienle, Alexander; Bernhard, Christoph; Bruns, Michael; Lemmer, Uli; Colsmann, Alexander

    2014-08-13

    Fully solution processed monochromatic and white-light emitting tandem or multi-photon polymer OLEDs with an inverted device architecture have been realized by employing WO3 /PEDOT:PSS/ZnO/PEI charge carrier generation layers. The luminance of the sub-OLEDs adds up in the stacked device indicating multi-photon emission. The white OLEDs exhibit a CRI of 75. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. A review on organic spintronic materials and devices: II. Magnetoresistance in organic spin valves and spin organic light emitting diodes

    Directory of Open Access Journals (Sweden)

    Rugang Geng

    2016-09-01

    Full Text Available In the preceding review paper, Paper I [Journal of Science: Advanced Materials and Devices 1 (2016 128–140], we showed the major experimental and theoretical studies on the first organic spintronic subject, namely organic magnetoresistance (OMAR in organic light emitting diodes (OLEDs. The topic has recently been of renewed interest as a result of a demonstration of the magneto-conductance (MC that exceeds 1000% at room temperature using a certain type of organic compounds and device operating condition. In this report, we will review two additional organic spintronic devices, namely organic spin valves (OSVs where only spin polarized holes exist to cause magnetoresistance (MR, and spin organic light emitting diodes (spin-OLEDs where both spin polarized holes and electrons are injected into the organic emissive layer to form a magneto-electroluminescence (MEL hysteretic loop. First, we outline the major advances in OSV studies for understanding the underlying physics of the spin transport mechanism in organic semiconductors (OSCs and the spin injection/detection at the organic/ferromagnet interface (spinterface. We also highlight some of outstanding challenges in this promising research field. Second, the first successful demonstration of spin-OLEDs is reviewed. We also discuss challenges to achieve the high performance devices. Finally, we suggest an outlook on the future of organic spintronics by using organic single crystals and aligned polymers for the spin transport layer, and a self-assembled monolayer to achieve more controllability for the spinterface.

  20. Growth and characterization of air annealing Tb-doped YAG:Ce single crystal for white-light-emitting diode

    International Nuclear Information System (INIS)

    Gong, Maogao; Xiang, Weidong; Liang, Xiaojuan; Zhong, Jiasong; Chen, Daqin; Huang, Jun; Gu, Guorui; Yang, Cheng; Xiang, Run

    2015-01-01

    Highlights: • We report preparation of transparent Ce,Tb:YAG single crystal by Czochralski method. • The effect of annealing on Ce,Tb:YAG single crystal had been investigated. • The Ce,Tb:YAG single crystal after annealing exhibited better optical performance. • The Ce,Tb:YAG single crystal could be used as an ideal candidate for WLED. - Abstract: We report the preparation of transparent Ce and Tb co-doped Y 3 Al 5 O 12 single crystal by the Czochralski method. The characterization of the resulting single crystal was accomplished by using X-ray powder diffractometer, scanning electron microscopy and energy dispersive X-ray spectroscopy. Absorption peak of the single crystal at about 460 nm has been obtained from ultraviolet–visible absorption spectrometer and their intensity is changed with different annealing condition. Its optical properties also have been investigated using fluorescence spectrometer. What’s more, its photoelectric parameters were studied by LED fast spectrometer. The constructed single crystal based white-light-emitting diode exhibits a high luminous efficiency of 140.89 lm/W, and a correlated color temperature of 4176 K as well as a color rendering index of 56.7, which reveal the prominent feasibility of the present single crystal material in white-light-emitting diode application

  1. Influence of TiO2 Nanoparticles on Enhancement of Optoelectronic Properties of PFO-Based Light Emitting Diode

    Directory of Open Access Journals (Sweden)

    Bandar Ali Al-Asbahi

    2013-01-01

    Full Text Available Improvement on optoelectronic properties of poly (9,9′-di-n-octylfluorenyl-2.7-diyl- (PFO- based light emitting diode upon incorporation of TiO2 nanoparticles (NPs is demonstrated. The PFO/TiO2 nanocomposites with different weight ratios between 5 and 35 wt.% were prepared using solution blending method before they were spin coated onto Indium Tin Oxide substrate. Then a thin Al layer was deposited onto the nanocomposite layer to act as top electrode. The nanocomposites were tested as emissive layer in organic light emitting diodes (OLEDs. The TiO2 NPs played the most crucial role in facilitating charge transport and electrical injection and thus improved device performance in terms of turn-on voltage, electroluminescence spectra (EL, luminance, and luminance efficiency. The best composition was OLED with 5 wt.% TiO2 NPs content having moderate surface roughness and well distribution of NPs. The device performance was reduced at higher TiO2 NPs content due to higher surface roughness and agglomeration of TiO2 NPs. This work demonstrated the importance of optimum TiO2 NPs content with uniform distribution and controlled surface roughness of the emissive layer for better device performance.

  2. Electroluminescence of colloidal quasi-two-dimensional semiconducting CdSe nanostructures in a hybrid light-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Selyukov, A. S., E-mail: vslebedev.mobile@gmail.com; Vitukhnovskii, A. G.; Lebedev, V. S.; Vashchenko, A. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Vasiliev, R. B.; Sokolikova, M. S. [Moscow State University (Russian Federation)

    2015-04-15

    We report on the results of studying quasi-two-dimensional nanostructures synthesized here in the form of semiconducting CdSe nanoplatelets with a characteristic longitudinal size of 20–70 nm and a thick-ness of a few atomic layers. Their morphology is studied using TEM and AFM and X-ray diffraction analysis; the crystal structure and sizes are determined. At room and cryogenic temperatures, the spectra and kinetics of the photoluminescence of such structures (quantum wells) are investigated. A hybrid light-emitting diode operating on the basis of CdSe nanoplatelets as a plane active element (emitter) is developed using the organic materials TAZ and TPD to form electron and hole transport layers, respectively. The spectral and current-voltage characteristics of the constructed device with a radiation wavelength λ = 515 nm are obtained. The device triggering voltage is 5.5 V (visible glow). The use of quasi-two-dimensional structures of this type is promising for hybrid light-emitting diodes with pure color and low operating voltages.

  3. Molecular absorption measurements with an optical fibre coupled array of ultra-violet light-emitting diodes.

    Science.gov (United States)

    Bui, Duy Anh; Kraiczek, Karsten G; Hauser, Peter C

    2017-09-15

    A photometric detector based on eight different light-emitting diodes covering the ultraviolet range from 255 nm to 350 nm is described. These are coupled with fused silica optical fibres to a conventional cuvette with 1 cm optical path length or to a low volume flow through cell for detection in high-performance liquid chromatography. Photodiodes are employed for the measurement of the transmitted intensity as well as of a reference signal and the photocurrents are processed with a log-ratio amplifier to obtain a voltage proportional to absorbance values. The wavelength desired for the measurement at hand is selected by electronically switching on the requisite light-emitting diode. The detector was found to have a low noise level of 80 μAU. In batch-wise measurements as well as in detection for high-performance liquid chromatography dynamic ranges of 2-3 orders of magnitude were possible. Reproducibilities in peak areas for the latter application were better than 1%. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Effect of Stepwise Doping on Lifetime and Efficiency of Blue and White Phosphorescent Organic Light Emitting Diodes.

    Science.gov (United States)

    Lee, Song Eun; Lee, Ho Won; Lee, Seok Jae; Koo, Ja-ryong; Lee, Dong Hyung; Yang, Hyung Jin; Kim, Hye Jeong; Yoon, Seung Soo; Kim, Young Kwan

    2015-02-01

    We investigated a light emission mechanism of blue phosphorescent organic light emitting diodes (PHOLEDs), using a stepwise doping profile of 2, 8, and 14 wt.% within the emitting layer (EML). We fabricated several blue PHOLEDs with phosphorescent blue emitter iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,C2]picolinate doped in N,N'-dicarbazolyl-3,5-benzene as a p-type host material. A blue PHOLED with the highest doping concentration as part of the EML close to an electron transporting layer showed a maximum luminous efficiency of 20.74 cd/A, and a maximum external quantum efficiency of 10.52%. This can be explained by effective electron injection through a highly doped EML side. Additionally, a white OLED based on the doping profile was fabricated with two thin red EMLs within a blue EML maintaining a thickness of 30 nm for the entire EML. Keywords: Blue Phosphorescent Organic Light Emitting Diodes, Stepwise Doping Structure, Charge Trapping Effect.

  5. A New Lridium(III) Complex as a Deep-Red Phosphorescent Emitter in Organic Light-Emitting Diodes.

    Science.gov (United States)

    Kim, Hee Un; Jang, Jae-Ho; Xu, Fei; Lee, Jun Yeob; Hwang, Do-Hoon

    2016-03-01

    We synthesized a novel red-emitting iridium(III) complex, bis[2-(5-(9H-carbazole-9-yl)thiophene-2-yl)benzo[d]thiazole]iridium(III)acetylacetonate ([(CTBT)21 r(acac)]), for use in phosphorescent organic light-emitting diodes. The photophysical and electrochemical properties of [(CTBT)2Ir(acac)] were characterized using photoluminescence (PL) and cyclic voltammetry. The photophysical properties of [(CTBT)2Ir(acac)] included PL emission at 630 nm. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of [(CTBT)2Ir(acac)] were calculated to be -5.14 and -2.83 eV, respectively. Phosphorescent organic light-emitting diodes with a configuration of ITO/PEDOT:PSS (30 nm)/TAPC (30 nm)/TPBi (12.5 nm):TCTA (12.5 nm):dopant (3%, 5%, 10%)/TSPO1 (35 nm)/LiF (1 nm)/Al (100 nm) were fabricated and characterized. The fabricated device doped with 5% [(CTBT)2Ir(acac)] showed a high luminous efficiency of 2.06 cd/A, maximum external quantum efficiency of 4.32% at 4 V, maximum outstanding luminance of 398.8 cd/m2, and maximum power efficiency of 1.79 lm/W with Commission Internationale de L'Eclairage (CIE) coordinates of (0.69, 0.31).

  6. Influence of Yellow Light-Emitting Diodes at 590 nm on Storage of Apple, Tomato and Bell Pepper Fruit

    Directory of Open Access Journals (Sweden)

    Janez Hribar

    2016-01-01

    Full Text Available The objective of this study is to investigate the eff ects of irradiation from light-emitting diodes (LEDs on several fruits during storage. To improve storage and increase the contents of some bioactive compounds, apple, tomato and red bell pepper fruits were exposed to yellow light emitted from the diodes at 590 nm. The contents of ascorbic acid, total phenolics, total flavonoids and several pigments were investigated, along with the antioxidant potential. The colour parameters (L*, a* and b* and firmness of the fruit were also determined. After 7 days of LED light irradiation, there was significantly higher total phenolic content and antioxidant potential in apple peel extracts. The irradiated fruit of tomato had significantly higher levels of total phenolic compounds, and the fruit of red bell pepper had significantly higher antioxidant potential. LED light had no effects on the colour parameters, although there was a tendency to accelerate colour development. Apple fruit irradiated with LED light was significantly less firm. Among twelve analysed pigments, significantly more β-carotene was detected in LED light-irradiated apple and bell pepper fruit, more α-tocopherol and γ-tocopherol in bell pepper fruit, and more lutein in apple peel and bell pepper fruit. The applied LED light slightly accelerated the ripening of the studied fruit, and affected the synthesis of some of the secondary metabolites.

  7. Low-level light emitting diode (LED) therapy suppresses inflammasome-mediated brain damage in experimental ischemic stroke.

    Science.gov (United States)

    Lee, Hae In; Lee, Sae-Won; Kim, Nam Gyun; Park, Kyoung-Jun; Choi, Byung Tae; Shin, Yong-Il; Shin, Hwa Kyoung

    2017-11-01

    Use of photostimulation including low-level light emitting diode (LED) therapy has broadened greatly in recent years because it is compact, portable, and easy to use. Here, the effects of photostimulation by LED (610 nm) therapy on ischemic brain damage was investigated in mice in which treatment started after a stroke in a clinically relevant setting. The mice underwent LED therapy (20 min) twice a day for 3 days, commencing at 4 hours post-ischemia. LED therapy group generated a significantly smaller infarct size and improvements in neurological function based on neurologic test score. LED therapy profoundly reduced neuroinflammatory responses including neutrophil infiltration and microglia activation in the ischemic cortex. LED therapy also decreased cell death and attenuated the NLRP3 inflammasome, in accordance with down-regulation of pro-inflammatory cytokines IL-1β and IL-18 in the ischemic brain. Moreover, the mice with post-ischemic LED therapy showed suppressed TLR-2 levels, MAPK signaling and NF-kB activation. These findings suggest that by suppressing the inflammasome, LED therapy can attenuate neuroinflammatory responses and tissue damage following ischemic stroke. Therapeutic interventions targeting the inflammasome via photostimulation with LED may be a novel approach to ameliorate brain injury following ischemic stroke. Effect of post-ischemic low-level light emitting diode therapy (LED-T) on infarct reduction was mediated by inflammasome suppression. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Detection of composite resin restorations using an ultraviolet light-emitting diode flashlight during forensic dental identification.

    Science.gov (United States)

    Guzy, Gerald; Clayton, Mary Ann

    2013-06-01

    With the increased use of composite resin and the decreased use of amalgam as a dental restorative material, the forensic dental identification of unidentified human remains has become more difficult. Various methods have been used to detect the presence of composite resin restorations including dyes, forensic alternative light sources, quantitative light-induced fluorescence, and ultraviolet lights. Although these methods may be helpful, the expense of the equipment, the electrical requirements, and the need for water to wash the dye from the mouth may make these methods impractical especially in a temporary morgue situation during a mass disaster. The fluorescent properties of composite resins, when exposed to ultraviolet light, are well documented. Standard tube ultraviolet lights have been used to detect the presence of composite resin, but these lights are large and bulky, and the tubes are fragile. The development of ultraviolet light emitting diode flashlights has provided forensic odontologists with a tool that is small, inexpensive, and battery operated. The two forensic dental identification cases described here demonstrate the value of ultraviolet light emitting diode flashlights as an adjunct to a careful clinical and radiographic examination.

  9. Highly efficient exciplex organic light-emitting diodes using thermally activated delayed fluorescent emitters as donor and acceptor materials

    Science.gov (United States)

    Jeon, Sang Kyu; Yook, Kyoung Soo; Lee, Jun Yeob

    2016-06-01

    Highly efficient exciplex type organic light-emitting diodes were developed using thermally activated delayed fluorescent emitters as donors and acceptors of an exciplex. Blue emitting bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) was a donor and 9,9‧-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9H-carbazole) (DDCzTrz) and 9,9‧,9″-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzene-1,2,3-triyl)tris(9H-carbazole) (TCzTrz) were acceptor materials. The exciplexes of DMAC-DPS:TCzTrz and DMAC-DPS:DDCzTrz resulted in high photoluminescence quantum yield and high quantum efficiency in the green exciplex organic light-emitting diodes. High quantum efficiencies of 13.4% and 15.3% were obtained in the DMAC-DPS:DDCzTrz and DMAC-DPS:TCzTrz exciplex devices.

  10. Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

    Science.gov (United States)

    Shervin, Shahab; Oh, Seung Kyu; Park, Hyun Jung; Lee, Keon-Hwa; Asadirad, Mojtaba; Kim, Seung-Hwan; Kim, Jeomoh; Pouladi, Sara; Lee, Sung-Nam; Li, Xiaohang; Kwak, Joon Seop; Ryou, Jae-Hyun

    2018-03-01

    We report a new route to improve quantum efficiencies of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency is enhanced higher than three times, when the DUV LEDs are moderately bent with concave curvatures. Furthermore, an efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

  11. Fabrication Methods and Luminescent Properties of ZnO Materials for Light-Emitting Diodes

    OpenAIRE

    Lee, Ching-Ting

    2010-01-01

    Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high optical gain of 320 cm−1 at room temperature. Its luminescent properties have been intensively investigated for samples, in the form of bulk, thin film, or nanostructure, prepared by various methods and doped with different impur...

  12. New fluorescent dipolar pyrazine derivatives for non-doped red organic light-emitting diodes

    International Nuclear Information System (INIS)

    Gao Baoxiang; Zhou Quanguo; Geng Yanhou; Cheng Yanxiang; Ma Dongge; Xie Zhiyuan; Wang Lixiang; Wang Fosong

    2006-01-01

    Dipolar fluorescent compounds containing electron-accepting pyrazine-2,3-dicarbonitrile and electron-donating arylamine moiety have been designed and synthesized. The optical and electrochemical properties of these compounds can be adjusted by changing π-bridge length and the donor (D) strength. Organic light-emitting devices based on these compounds are fabricated. Saturated red emission of (0.67, 0.33) and the external quantum efficiency as high as 1.41% have been demonstrated for one of these compounds

  13. Understanding the role of ultra-thin polymeric interlayers in improving efficiency of polymer light emitting diodes

    Science.gov (United States)

    Bailey, Jim; Wright, Edward N.; Wang, Xuhua; Walker, Alison B.; Bradley, Donal D. C.; Kim, Ji-Seon

    2014-05-01

    Insertion of ultra-thin polymeric interlayers (ILs) between the poly(3,4-ethylenedioxythiophene):polystyrene sulphonate hole injection and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) light emission layers of polymer light emitting diodes (PLEDs) can significantly increase their efficiency. In this paper, we investigate experimentally a broad range of probable causes of this enhancement with an eye to determining which IL parameters have the most significant effects. The importance of hole injection and electron blocking was studied through varying the IL material (and consequently its electronic energy levels) for both PLED and hole-only diode structures. The role of IL conductivity was examined by introducing a varying level of charge-transfer doping through blending the IL materials with a strong electron-accepting small molecule in concentrations from 1% to 7% by weight. Depositing ILs with thicknesses below the exciton diffusion length of ˜15 nm allowed the role of the IL as a physical barrier to exciton quenching to be probed. IL containing PLEDs was also fabricated with Lumation Green Series 1300 (LG 1300) light emission layers. On the other hand, the PLEDs were modeled using a 3D multi-particle Kinetic Monte Carlo simulation coupled with an optical model describing how light is extracted from the PLED. The model describes charge carrier transport and interactions between electrons, holes, singlets, and triplets, with the current density, luminance, and recombination zone (RZ) locations calculated for each PLED. The model shows F8BT PLEDs have a narrow charge RZ adjacent to the anode, while LG 1300 PLEDs have a wide charge RZ that is evenly distributed across the light emitting layer. Varying the light emitting layer from F8BT to Lumation Green Series 1300, we therefore experimentally examine the dependence of the IL function, specifically in regard to anode-side exciton quenching, on the location of the RZ. We found an exponential dependence of F8

  14. Thermally stable aromatic amine derivative with symmetrically substituted double spirobifluorene core as a hole transport material for green phosphorescent organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Yong Joo; Lee, Jun Yeob, E-mail: leej17@dankook.ac.kr

    2012-11-01

    A thermally stable aromatic amine derivative with a symmetrically substituted double spirobifluorene core was synthesized as a hole transport material for green phosphorescent organic light-emitting diodes. A high glass transition temperature of 142 Degree-Sign C was obtained and a film morphology of the hole transport material was kept stable up to 120 Degree-Sign C. The hole transport material showed a high triplet energy of 2.53 eV and a quantum efficiency of 17.4% in green phosphorescent organic light-emitting diodes. - Highlights: Black-Right-Pointing-Pointer Synthesis of symmetrically substituted double spirobifluorene core Black-Right-Pointing-Pointer Stable film morphology up to 120 Degree-Sign C Black-Right-Pointing-Pointer High quantum efficiency in green phosphorescent organic light emitting diode.

  15. Fabrication Methods and Luminescent Properties of ZnO Materials for Light-Emitting Diodes

    Science.gov (United States)

    Lee, Ching-Ting

    2010-01-01

    Zinc oxide (ZnO) is a potential candidate material for optoelectronic applications, especially for blue to ultraviolet light emitting devices, due to its fundamental advantages, such as direct wide band gap of 3.37 eV, large exciton binding energy of 60 meV, and high optical gain of 320 cm−1 at room temperature. Its luminescent properties have been intensively investigated for samples, in the form of bulk, thin film, or nanostructure, prepared by various methods and doped with different impurities. In this paper, we first review briefly the recent progress in this field. Then a comprehensive summary of the research carried out in our laboratory on ZnO preparation and its luminescent properties, will be presented, in which the involved samples include ZnO films and nanorods prepared with different methods and doped with n-type or p-type impurities. The results of ZnO based LEDs will also be discussed.

  16. Improved efficiencies in organic light emitting diodes made with CdSe/ZnS quantum dots and a semiconducting polymer.

    Science.gov (United States)

    Lee, Chih-Wen; Yang, Sheng-Hsiung; Hsu, Chain-Shu; Meng, Hsin-Fei

    2009-03-01

    In this study, we report the fabrication and characterization of organic/inorganic hybrid polymer light emitting diodes (PLEDs) made with ZnS-capped CdSe core/shell type nanocrystals and a light-emitting polymer poly[2-phenyl-3-(9,9-dihexylfluoren-2-yl)-1,4-phenylene vinylene]-co-[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene]. The device using pristine polymer as active layer emitted yellow light with a maximum brightness of 3949 cd/m2 and maximum external quantum efficiency of 0.27 cd/A at 10 V. After blending with the CdSe/ZnS quantum dots (QDs), the device showed a much higher brightness of 8192 cd/m2 and external quantum efficiency of 1.27 cd/A at 7 V, while the driving voltage was lowered. The experimental results revealed that CdSe/ZnS QDs act as a hole-blocker in the devices. More efficient electron-hole recombination process inside polymer layer results in large improvement in luminescence and efficiency.

  17. Improvement in luminance of light-emitting diode using InP/ZnS quantum dot with 1-dodecanethiol ligand

    Science.gov (United States)

    Fukuda, Takeshi; Sasaki, Hironao

    2018-03-01

    We present the synthesis protocol of a red emissive InP/ZnS quantum dot with a 1-dodecanthiol ligand and its application to a quantum dot light-emitting diode. The ligand change from oleylamine to 1-dodecanthiol, which were connected around the InP/ZnS quantum dot, was confirmed by Fourier-transform infrared spectroscopy and thermal analysis. The absorption peak was blue-shifted by changing 1-dodecanthiol ligands from oleylamine ligands to prevent the unexpected nucleation of the InP core. In addition, the luminance of the light-emitting device was improved by using the InP/ZnS quantum dot with 1-dodecanthiol ligands, and the maximum current efficiency of 7.2 × 10‑3 cd/A was achieved. The 1-dodecanthiol ligand is often used for capping to reduce the number of surface defects and/or prevent unexpected core growth, resulting in reduced Auger recombination. This result indicates that 1-dodecanthiol ligands prevent the deactivation of excitons while injecting carriers by applying a voltage, resulting in a high luminance efficiency.

  18. White polymer light-emitting diodes co-doped with phosphorescent iridium complexes bearing the same cyclometalated ligand

    Energy Technology Data Exchange (ETDEWEB)

    Ikawa, Shigeru; Yagi, Shigeyuki; Maeda, Takeshi; Nakazumi, Hiroyuki [Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan)

    2012-12-15

    In order to develop white organic light-emitting devices, we fabricated poly(9-vinylcarbazole)-based polymer light-emitting diodes (PLEDs) using blue- and orange-phosphorescent bis-cyclometalated iridium(III) complexes Ir-1a and Ir-1b as emitting co-dopants, both of which possess the same cyclometalated ligand. The PLED co-doped with Ir-1a and Ir-1b in a single emitting layer (WPLED-1) yielded the optimized white electroluminescence with a Commission Internationale de L'Eclairage (CIE) chromaticity coordinate of (0.33, 0.46), although the value of the color rendering index (CRI) was very poor (CRI = 58). Thus, in order to improve the color rendering properties of WPLED-1, the deep red-phosphorescent iridium(III) complex Ir-2 was employed as an additional co-dopant. In the PLED co-doped with Ir-1a, Ir-1b and Ir-2 (WPLED-2), tuning the ratio of the three emitting co-dopants allowed us to obtain white electroluminescence with high color rendering properties (CRI = 82), where the CIE chromaticity coordinate of (0.38, 0.44) was obtained. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  19. Micro-light-emitting diodes with III–nitride tunnel junction contacts grown by metalorganic chemical vapor deposition

    Science.gov (United States)

    Hwang, David; Mughal, Asad J.; Wong, Matthew S.; Alhassan, Abdullah I.; Nakamura, Shuji; DenBaars, Steven P.

    2018-01-01

    Micro-light-emitting diodes (µLEDs) with tunnel junction (TJ) contacts were grown entirely by metalorganic chemical vapor deposition. A LED structure was grown, treated with UV ozone and hydrofluoric acid, and reloaded into the reactor for TJ regrowth. The silicon doping level of the n++-GaN TJ was varied to examine its effect on voltage. µLEDs from 2.5 × 10‑5 to 0.01 mm2 in area were processed, and the voltage penalty of the TJ for the smallest µLED at 20 A/cm2 was 0.60 V relative to that for a standard LED with indium tin oxide. The peak external quantum efficiency of the TJ LED was 34%.

  20. Carbon nanotube-graphene composite film as transparent conductive electrode for GaN-based light-emitting diodes

    KAUST Repository

    Kang, Chun Hong

    2016-08-23

    Transparent conductive electrodes (TCE) made of carbon nanotube (CNT) and graphene composite for GaN-based light emitting diodes (LED) are presented. The TCE with 533-Ω/□ sheet resistance and 88% transmittance were obtained when chemical-vapor-deposition grown graphene was fused across CNT networks. With an additional 2-nm thin NiOx interlayer between the TCE and top p-GaN layer of the LED, the forward voltage was reduced to 5.12 V at 20-mA injection current. Four-fold improvement in terms of light output power was observed. The improvement can be ascribed to the enhanced lateral current spreading across the hybrid CNT-graphene TCE before injection into the p-GaN layer.