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Sample records for light-emitting diodes formed

  1. Light-emitting Diodes

    Science.gov (United States)

    Opel, Daniel R.; Hagstrom, Erika; Pace, Aaron K.; Sisto, Krisanne; Hirano-Ali, Stefanie A.; Desai, Shraddha

    2015-01-01

    Background: In the early 1990s, the biological significance of light-emitting diodes was realized. Since this discovery, various light sources have been investigated for their cutaneous effects. Study design: A Medline search was performed on light-emitting diode lights and their therapeutic effects between 1996 and 2010. Additionally, an open-label, investigator-blinded study was performed using a yellow light-emitting diode device to treat acne, rosacea, photoaging, alopecia areata, and androgenetic alopecia. Results: The authors identified several case-based reports, small case series, and a few randomized controlled trials evaluating the use of four different wavelengths of light-emitting diodes. These devices were classified as red, blue, yellow, or infrared, and covered a wide range of clinical applications. The 21 patients the authors treated had mixed results regarding patient satisfaction and pre- and post-treatment evaluation of improvement in clinical appearance. Conclusion: Review of the literature revealed that differing wavelengths of light-emitting diode devices have many beneficial effects, including wound healing, acne treatment, sunburn prevention, phototherapy for facial rhytides, and skin rejuvenation. The authors’ clinical experience with a specific yellow light-emitting diode device was mixed, depending on the condition being treated, and was likely influenced by the device parameters. PMID:26155326

  2. 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.

  3. ORGANIC LIGHT EMITTING DIODE (OLED

    Directory of Open Access Journals (Sweden)

    Aririguzo Marvis Ijeaku

    2015-09-01

    Full Text Available An Organic Light Emitting Diode (OLED is a device composed of an organic layer that emits lights in response to an electrical current. Organic light emitting diodes have advanced tremendously over the past decades. The different manufacturing processes of the OLED itself to several advantages over flat panel displays made with LCD technology which includes its light weight and flexible plastic substrates, wider viewing angles, improved brightness, better power efficiency and quicker response time. However, its drawbacks include shorter life span, poor color balance, poor outdoor performance, susceptibility to water damage etc.The application of OLEDs in electronics is on the increase on daily basics from cameras to cell phones to OLED televisions, etc. Although OLEDs provides prospects for thinner, smarter, lighter and ultraflexible electronics displays, however, due to high cost of manufacturing, it is not yet widely used.

  4. Light emitting diode with high aspect ratio submicron roughness for light extraction and methods of forming

    Science.gov (United States)

    Li, Ting

    2013-08-13

    The surface morphology of an LED light emitting surface is changed by applying a reactive ion etch (RIE) process to the light emitting surface. High aspect ratio, submicron roughness is formed on the light emitting surface by transferring a thin film metal hard-mask having submicron patterns to the surface prior to applying a reactive ion etch process. The submicron patterns in the metal hard-mask can be formed using a low cost, commercially available nano-patterned template which is transferred to the surface with the mask. After subsequently binding the mask to the surface, the template is removed and the RIE process is applied for time duration sufficient to change the morphology of the surface. The modified surface contains non-symmetric, submicron structures having high aspect ratio which increase the efficiency of the device.

  5. In-Situ Formed Type I Nanocrystalline Perovskite Film for Highly Efficient Light-Emitting Diode.

    Science.gov (United States)

    Lee, Jin-Wook; Choi, Yung Ji; Yang, June-Mo; Ham, Sujin; Jeon, Sang Kyu; Lee, Jun Yeob; Song, Young-Hyun; Ji, Eun Kyung; Yoon, Dae-Ho; Seo, Seongrok; Shin, Hyunjung; Han, Gil Sang; Jung, Hyun Suk; Kim, Dongho; Park, Nam-Gyu

    2017-03-28

    Excellent color purity with a tunable band gap renders organic-inorganic halide perovskite highly capable of performing as light-emitting diodes (LEDs). Perovskite nanocrystals show a photoluminescence quantum yield exceeding 90%, which, however, decreases to lower than 20% upon formation of a thin film. The limited photoluminescence quantum yield of a perovskite thin film has been a formidable obstacle for development of highly efficient perovskite LEDs. Here, we report a method for highly luminescent MAPbBr3 (MA = CH3NH3) nanocrystals formed in situ in a thin film based on nonstoichiometric adduct and solvent-vacuum drying approaches. Excess MABr with respect to PbBr2 in precursor solution plays a critical role in inhibiting crystal growth of MAPbBr3, thereby forming nanocrystals and creating type I band alignment with core MAPbBr3 by embedding MAPbBr3 nanocrystals in the unreacted wider band gap MABr. A solvent-vacuum drying process was developed to preserve nanocrystals in the film, which realizes a fast photoluminescence lifetime of 3.9 ns along with negligible trapping processes. Based on a highly luminescent nanocrystalline MAPbBr3 thin film, a highly efficient green LED with a maximum external quantum efficiency of 8.21% and a current efficiency of 34.46 cd/A was demonstrated.

  6. Vertical nonpolar growth templates for light emitting diodes formed with GaN nanosheets

    Science.gov (United States)

    Yeh, Ting-Wei; Lin, Yen-Ting; Ahn, Byungmin; Stewart, Lawrence S.; Daniel Dapkus, P.; Nutt, Steven R.

    2012-01-01

    We demonstrate that nonpolar m-plane surfaces can be generated on uniform GaN nanosheet arrays grown vertically from the (0001)-GaN bulk material. InGaN/GaN multiple quantum wells (MQWs) grown on the facets of these nanosheets are demonstrated by cross-sectional transmission electron microscopy. Owing to the high aspect ratio of the GaN nanosheet structure, the MQWs predominantly grow on nonpolar GaN planes. The results suggest that GaN nanosheets provide a conduction path for device fabrication and also a growth template to reduce the piezoelectric field inside the active region of InGaN-based light emitting diodes.

  7. 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…

  8. Light-Emitting Diodes: Solving Complex Problems

    Science.gov (United States)

    Planinšic, Gorazd; Etkina, Eugenia

    2015-01-01

    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 paper provided…

  9. 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…

  10. 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…

  11. 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.

  12. 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…

  13. Red Blood Cell Forms in Acne and their Complex Treatment with Application of Light-Emitting Diode Influences

    Directory of Open Access Journals (Sweden)

    Farhad F. Khashimov

    2014-12-01

    Full Text Available The efficiency of the laser light-emitting diode (LED that is used in the complex treatment of acne was studied with light microscopy, scanning electron microscopy, and planimetry. It was found that the light emission of the photon matrix by A.Korobov–B.Korobov “Barva-Fleks/BIR” (λ1=470nm and λ2=940 nm combined with the drug treatment are an effective means for the treatment of acne.

  14. Safety of light emitting diodes in toys.

    Science.gov (United States)

    Higlett, M P; O'Hagan, J B; Khazova, M

    2012-03-01

    Light emitting diodes (LEDs) are increasingly being used in toys. An assessment methodology is described for determining the accessible emission limits for the optical radiation from the toys, which takes account of expected use and reasonably foreseeable misuse of toys. Where data are available, it may be possible to assess the toy from the data sheet alone. If this information is not available, a simple measurement protocol is proposed.

  15. Near infrared polymer light-emitting diodes

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong; YANG Jian; HOU Qiong; MO Yueqi; PENG Junbiao; CAO Yong

    2005-01-01

    High efficiency of near infrared polymer light-emitting diodes with bilayer structure was obtained. The diode structure is ITO/PEDOT/L1/L2/Ba/Al, where L1 is phenyl-substituted poly [p-phenylphenylene vinylene] derivative (P-PPV), L2 is 9,9-dioctylfluorene (DOF) and 4,7- bis(3-hexylthiophen)-2-yl-2,1,3-naphthothiadiazole (HDNT) copolymer (PFHDNT10). The electroluminescence (EL) spectrum of diodes from PFHDNT10 is at 750 nm located in the range of near infrared. The maximum external quantum efficiency is up to 2.1% at the current density of 35 mA/cm2. The improvement of the diode's performances was considered to be the irradiative excitons confined in the interface between L1 and L2 layers.

  16. Logarithmic current electrometer using light emitting diodes

    Science.gov (United States)

    Acharya, Y. B.; Aggarwal, A. K.

    1996-02-01

    The limit of low current measurement using logarithmic current to voltage converter is improved by 6 - 7 orders of magnitude with the use of diodes of large band gap as compared with silicon diodes. Low cost commercially available light emitting diodes (LEDs) have been used for this purpose. A theoretical study and experimental measurement of device constant and reverse saturation currents of the whole class of commercially available LEDs has been carried out. A circuit has been developed which makes use of a new technique for temperature compensation and its performance is compared with the technique in common use. The performance of the amplifier is found to be stable in the temperature range 5 - 600957-0233/7/2/005/img5 for both polarity of signals from 0957-0233/7/2/005/img6 to 0957-0233/7/2/005/img7 A.

  17. Atomically thin quantum light-emitting diodes

    Science.gov (United States)

    Palacios-Berraquero, Carmen; Barbone, Matteo; Kara, Dhiren M.; Chen, Xiaolong; Goykhman, Ilya; Yoon, Duhee; Ott, Anna K.; Beitner, Jan; Watanabe, Kenji; Taniguchi, Takashi; Ferrari, Andrea C.; Atatüre, Mete

    2016-09-01

    Transition metal dichalcogenides are optically active, layered materials promising for fast optoelectronics and on-chip photonics. We demonstrate electrically driven single-photon emission from localized sites in tungsten diselenide and tungsten disulphide. To achieve this, we fabricate a light-emitting diode structure comprising single-layer graphene, thin hexagonal boron nitride and transition metal dichalcogenide mono- and bi-layers. Photon correlation measurements are used to confirm the single-photon nature of the spectrally sharp emission. These results present the transition metal dichalcogenide family as a platform for hybrid, broadband, atomically precise quantum photonics devices.

  18. 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

  19. High-resolution patterns of quantum dots formed by electrohydrodynamic jet printing for light-emitting diodes.

    Science.gov (United States)

    Kim, Bong Hoon; Onses, M Serdar; Lim, Jong Bin; Nam, Sooji; Oh, Nuri; Kim, Hojun; Yu, Ki Jun; Lee, Jung Woo; Kim, Jae-Hwan; Kang, Seung-Kyun; Lee, Chi Hwan; Lee, Jungyup; Shin, Jae Ho; Kim, Nam Heon; Leal, Cecilia; Shim, Moonsub; Rogers, John A

    2015-02-11

    Here we demonstrate materials and operating conditions that allow for high-resolution printing of layers of quantum dots (QDs) with precise control over thickness and submicron lateral resolution and capabilities for use as active layers of QD light-emitting diodes (LEDs). The shapes and thicknesses of the QD patterns exhibit systematic dependence on the dimensions of the printing nozzle and the ink composition in ways that allow nearly arbitrary, systematic control when exploited in a fully automated printing tool. Homogeneous arrays of patterns of QDs serve as the basis for corresponding arrays of QD LEDs that exhibit excellent performance. Sequential printing of different types of QDs in a multilayer stack or in an interdigitated geometry provides strategies for continuous tuning of the effective, overall emission wavelengths of the resulting QD LEDs. This strategy is useful to efficient, additive use of QDs for wide ranging types of electronic and optoelectronic devices.

  20. 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.

  1. 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.

  2. The role of graphene formed on silver nanowire transparent conductive electrode in ultra-violet light emitting diodes

    Science.gov (United States)

    Seo, Tae Hoon; Lee, Seula; Min, Kyung Hyun; Chandramohan, S.; Park, Ah Hyun; Lee, Gun Hee; Park, Min; Suh, Eun-Kyung; Kim, Myung Jong

    2016-07-01

    This paper reports a highly reliable transparent conductive electrode (TCE) that integrates silver nanowires (AgNWs) and high-quality graphene as a protecting layer. Graphene with minimized defects and large graphene domains has been successfully obtained through a facile two-step growth approach. Ultraviolet light emitting diodes (UV-LEDs) were fabricated with AgNWs or hybrid electrodes where AgNWs were combined with two-step grown graphene (A-2GE) or conventional one-step grown graphene (A-1GE). The device performance and reliability of the UV-LEDs with three different electrodes were compared. The A-2GE offered high figure of merit owing to the excellent UV transmittance and reduced sheet resistance. As a consequence, the UV-LEDs made with A-2GE demonstrated reduced forward voltage, enhanced electroluminescence (EL) intensity, and alleviated efficiency droop. The effects of joule heating and UV light illumination on the electrode stability were also studied. The present findings prove superior performance of the A-2GE under high current injection and continuous operation of UV LED, compared to other electrodes. From our observation, the A-2GE would be a reliable TCE for high power UV-LEDs.

  3. Bipolar Host Materials for Organic Light-Emitting Diodes.

    Science.gov (United States)

    Yook, Kyoung Soo; Lee, Jun Yeob

    2016-02-01

    It is important to balance holes and electrons in the emitting layer of organic light-emitting diodes to maximize recombination efficiency and the accompanying external quantum efficiency. Therefore, the host materials of the emitting layer should transport both holes and electrons for the charge balance. From this perspective, bipolar hosts have been popular as the host materials of thermally activated delayed fluorescent devices and phosphorescent organic light-emitting diodes. In this review, we have summarized recent developments of bipolar hosts and suggested perspectives of host materials for organic light-emitting diodes.

  4. Organic light-emitting diodes: High-throughput virtual screening

    Science.gov (United States)

    Hirata, Shuzo; Shizu, Katsuyuki

    2016-10-01

    Computer networks, trained with data from delayed-fluorescence materials that have been successfully used in organic light-emitting diodes, facilitate the high-speed prediction of good emitters for display and lighting applications.

  5. Organic light emitting diode with surface modification layer

    Energy Technology Data Exchange (ETDEWEB)

    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).

  6. Organic light emitting diode with light extracting electrode

    Energy Technology Data Exchange (ETDEWEB)

    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).

  7. Perovskite Materials for Light-Emitting Diodes and Lasers.

    Science.gov (United States)

    Veldhuis, Sjoerd A; Boix, Pablo P; Yantara, Natalia; Li, Mingjie; Sum, Tze Chien; Mathews, Nripan; Mhaisalkar, Subodh G

    2016-08-01

    Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices.

  8. 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.

  9. 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…

  10. Hybrid Light-Emitting Diode Enhanced With Emissive Nanocrystals

    DEFF Research Database (Denmark)

    Kopylov, Oleksii

    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...... 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...

  11. 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....

  12. Degradation of light emitting diodes: a proposed methodology*

    Institute of Scientific and Technical Information of China (English)

    Sau Koh; Willem Van Driel; G.Q.Zhang

    2011-01-01

    Due to their long lifetime and high efficacy, light emitting diodes have the potential to revolutionize the illumination industry. However, self heat and high environmental temperature which will lead to increased junction temperature and degradation due to electrical overstress can shorten the life of the light emitting diode. In this research, a methodology to investigate the degradation of the LED emitter has been proposed. The epoxy lens of the emitter can be modelled using simplified Eyring methods whereas an equation has been proposed for describing the degradation of the LED emitters.

  13. Theory of piezo-phototronics for light-emitting diodes.

    Science.gov (United States)

    Zhang, Yan; Wang, Zhong Lin

    2012-09-04

    Devices fabricated by using the inner-crystal piezopotential as a "gate" voltage to tune/control the carrier generation, transport, and recombination processes at the vicinity of a p-n junction are named piezo-phototronics. Here, the theory of the photon emission and carrier transport behavior in piezo-phototronic devices is investigated as a p-n junction light-emitting diode. Numerical calculations are given for predicting the photon emission and current-voltage characteristics of a general piezo-phototronic light-emitting diode.

  14. 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.

  15. Optical communications. V - Light emitting diodes /LED/

    Science.gov (United States)

    Best, S. W.

    1980-10-01

    The process of assembling diode chips is discussed, along with their application in optical communications. Metal plating is performed with an evaporation technique using primarily AuGe on the back side and Al or AuZn on the front side. The assembling of LED-chips with metal casings is illustrated. The chip is mounted on a flat bottom plate and electrical contact is established by means of an alloying or adhesion procedure. A glass fiber can be attached to the diode and then fitted with a casing, or the diode can be assembled with a metal cap and a lense, or with an open cap that is sealed with a clear synthetic resin plastic. The typical emission spectra of an LED and a semiconductor laser are compared. Limitations in the operation of an LED in a photoconductor are examined, taking into account spectral line width and radiated power criteria.

  16. Toward inkjet printing of small molecule organic light emitting diodes

    NARCIS (Netherlands)

    Gorter, H.; Coenen, M.J.J.; Slaats, M.W.L.; Ren, M.; Lu, W.; Kuijpers, C.J.; Groen, W.A.

    2013-01-01

    Thermal evaporation is the current standard for the manufacture of small molecule organic light emitting diodes (smOLEDs), but it requires vacuum process, complicated shadow masks and is inefficient in material utilization, resulting in high cost of ownership. As an alternative, wet solution deposit

  17. 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 gre

  18. Silicon light-emitting diode antifuse: properties and devices

    NARCIS (Netherlands)

    Le Minh, P.; Holleman, J.

    2006-01-01

    This paper reviews our research on the silicon light-emitting diode antifuse, a tiny source featuring a full white-light spectrum. Optical and electrical properties of the device are discussed together with the modelling of the spectral emission, explaining the emitting mechanism of the device. An e

  19. Atom probe tomography of a commercial light emitting diode

    Science.gov (United States)

    Larson, D. J.; Prosa, T. J.; Olson, D.; Lefebvre, W.; Lawrence, D.; Clifton, P. H.; Kelly, T. F.

    2013-11-01

    The atomic-scale analysis of a commercial light emitting diode device purchased at retail is demonstrated using a local electrode atom probe. Some of the features are correlated with transmission electron microscopy imaging. Subtle details of the structure that are revealed have potential significance for the design and performance of this device.

  20. Organic light emitting diodes with spin polarized electrodes

    NARCIS (Netherlands)

    Arisi, E.; Bergenti, I.; Dediu, V.; Loi, M.A.; Muccini, M.; Murgia, M.; Ruani, G.; Taliani, C.; Zamboni, R.

    2003-01-01

    Electrical and optical properties of Alq3 based organic light emitting diodes with normal and spin polarized electrodes are presented. Epitaxial semitransparent highly spin polarized La0.7Sr0.3MnO3 were used as hole injector, substituting the traditional indium tin oxide electrode. A comparison of e

  1. 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…

  2. Toward inkjet printing of small molecule organic light emitting diodes

    NARCIS (Netherlands)

    Gorter, H.; Coenen, M.J.J.; Slaats, M.W.L.; Ren, M.; Lu, W.; Kuijpers, C.J.; Groen, W.A.

    2013-01-01

    Thermal evaporation is the current standard for the manufacture of small molecule organic light emitting diodes (smOLEDs), but it requires vacuum process, complicated shadow masks and is inefficient in material utilization, resulting in high cost of ownership. As an alternative, wet solution deposit

  3. 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

  4. 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

  5. Frequency Response of Modulated Electroluminescence of Light-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    FENG Lie-Feng; LI Yang; LI Ding; WANG Cun-Da; ZHANG Guo-Yi; YAO Dong-Sheng; LIU Wei-Fang; XING Peng-Fei

    2011-01-01

    Frequency responses of modulated electroluminescence (EL) of light-emitting diodes were measured using a testing setup.With increasing frequency of the ac signal,the relative light intensity (RLI) clearly decreases.Furthermore,a peculiar asynchrony between the RLI and ac small-signal is observed.At frequencies higher than 10kHz,the RLI clearly lags behind the ac signal and the absolute value of the lagging angle is nearly proportional to the signal frequency.Using the classical recombination model of light-emitting diodes under ac small-signal modulation,these abnormal characteristics of modulated EL can be clearly explained.High-power light-emitting diodes (LEDs) have received great attention recently owing to their applications in energy-saving lights,display items and many other fields;therefore,the optical and electrical characteristics of LEDs at forward bias hold significant potential for research.[1-4] However,for a new kind of light emission device,the general research on its performance focuses on the light emission and dc currentvoltage (I-V) characteristics.%Frequency responses of modulated electroluminescence (EL) of light-emitting diodes were measured using a testing setup. With increasing frequency of the ac signal, the relative light intensity (RLI) clearly decreases. Furthermore, a peculiar asynchrony between the RLI and ac small-signal is observed. At frequencies higher than 10kHz, the RLI clearly lags behind the ac signal and the absolute value of the lagging angle is nearly proportional to the signal frequency. Using the classical recombination model of light-emitting diodes under ac small-signal modulation, these abnormal characteristics of modulated EL can be clearly explained.

  6. Design of vertically-stacked polychromatic light-emitting diodes.

    Science.gov (United States)

    Hui, K N; Wang, X H; Li, Z L; Lai, P T; Choi, H W

    2009-06-01

    A new design for a polychromatic light-emitting diode (LED) is proposed and demonstrated. LED chips of the primary colors are physically stacked on top of each other. Light emitted from each layer of the stack passes through each other, and thus is mixed naturally without additional optics. As a color-tunable device, a wide range of colors can be generated, making it suitable for display purposes. As a phosphor-free white light LED, luminous efficacy of 30 lm/watt was achieved.

  7. 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.

  8. Forming the graded-refractive-index antireflection layers on light-emitting diodes to enhance the light extraction.

    Science.gov (United States)

    Cho, Joong-Yeon; Byeon, Kyeong-Jae; Lee, Heon

    2011-08-15

    Distributed antireflection (AR) layers with different composition ratios of ITO and SiO(2) formed on an ITO electrode of GaN-based LEDs provide substantial enhancement in light-extraction efficiency. By using the coradio frequency magnetron sputtering deposition, four 50 nm thick AR layers with graduated refractive indices were fabricated. The effect of the AR layers on enhancing the efficiency of the LED device was analyzed by electroluminescence (EL) and I-V measurements. As a result, the EL intensity of the LED device grown on the patterned sapphire substrate with AR layers was increased by up to 13% compared to the conventional patterned sapphire substrate-applied LED device without AR layers at a drive current of 20 mA. The AR layers on top of the LED device gradually changed the refractive indices between ITO (n=2.1) and air (n=1.0), which minimized the total internal reflection of generated light. And no degradation in the electrical characteristic of the LEDs was observed according to the I-V measurements.

  9. 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.

  10. 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").

  11. Flip-chip light emitting diode with resonant optical microcavity

    Science.gov (United States)

    Gee, James M.; Bogart, Katherine H.A.; Fischer, Arthur J.

    2005-11-29

    A flip-chip light emitting diode with enhanced efficiency. The device structure employs a microcavity structure in a flip-chip configuration. The microcavity enhances the light emission in vertical modes, which are readily extracted from the device. Most of the rest of the light is emitted into waveguided lateral modes. Flip-chip configuration is advantageous for light emitting diodes (LEDs) grown on dielectric substrates (e.g., gallium nitride LEDs grown on sapphire substrates) in general due to better thermal dissipation and lower series resistance. Flip-chip configuration is advantageous for microcavity LEDs in particular because (a) one of the reflectors is a high-reflectivity metal ohmic contact that is already part of the flip-chip configuration, and (b) current conduction is only required through a single distributed Bragg reflector. Some of the waveguided lateral modes can also be extracted with angled sidewalls used for the interdigitated contacts in the flip-chip configuration.

  12. 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 (efficiently inject carriers in all the QWs, are preferred.

  13. Organic light emitting diodes with structured electrodes

    Science.gov (United States)

    Mao, Samuel S.; Liu, Gao; Johnson, Stephen G.

    2012-12-04

    A cathode that contain nanostructures that extend into the organic layer of an OLED has been described. The cathode can have an array of nanotubes or a layer of nanoclusters extending out from its surface. In another arrangement, the cathode is patterned and etched to form protruding nanostructures using a standard lithographic process. Various methods for fabricating these structures are provided, all of which are compatible with large-scale manufacturing. OLEDs made with these novel electrodes have greatly enhanced electron injection, have good environmental stability.

  14. 77 FR 21038 - Energy Conservation Program: Test Procedures for Light-Emitting Diode Lamps

    Science.gov (United States)

    2012-04-09

    ... Parts 429 and 430 RIN 1904-AC67 Energy Conservation Program: Test Procedures for Light-Emitting Diode... light-emitting diode (LED) lamps to support implementation of labeling provisions by the Federal Trade... procedures. This rulemaking establishes test procedures that manufacturers of light-emitting diode (LED...

  15. Light-emitting diode technology in vitreoretinal surgery.

    Science.gov (United States)

    Dithmar, Stefan; Hoeh, Alexandra E; Amberger, Roman; Ruppenstein, Mira; Ach, Thomas

    2011-05-01

    Systems for vitreoretinal illumination during surgery usually consist of an external light source and a light fiber. We introduce a new illumination system for vitreoretinal surgery based on the light-emitting diode technology, with an embedded light source in the handle of the light fiber, making a separate light source unnecessary. A prototype of a new illumination system for vitreoretinal surgery (ocuLED; Geuder, Heidelberg, Germany) was tested. This system consists of a handle with a built-in light-emitting diode, supported by an external power source. The OcuLED was analyzed in regards to wavelength, maximum radiant power, and maximum irradiance and was compared with three commercially available vitreoretinal illumination systems. Furthermore, the first intraoperative application and handling were evaluated. The ocuLED system works with a cool white or a neutral white light-emitting diode and is powered externally. The wavelength spectrum shows a maximum at 565 nm and a second peak at 455 nm. Compared with other light sources, the proportion of potentially harmful blue light is low. Maximum radiant power and irradiance are in line with xenon and mercury vapor light sources. The intrasurgical light is bright and offers good visibility. The handle of ocuLED is slightly wider than commonly used light fiber handles, which do not affect its use during surgery. Technical progress in light-emitting diode technology allows minimizing the equipment for vitreoretinal illumination. The OcuLED provides bright illumination without an external light source. Wavelength spectrum, maximum radiant power, and irradiance are safe from the risk of phototoxic damage. Intrasurgical handling is identical to conventional light fibers.

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

    OpenAIRE

    Andre F. S. Guedes; Vilmar P. Guedes; Simone Tartari; Mônica L. Souza; Idaulo J. Cunha

    2014-01-01

    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,...

  17. CRITICAL ASSESSMENT: Gallium nitride based visible light emitting diodes

    OpenAIRE

    Oliver, Rachel A.

    2016-01-01

    This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Maney Publishing. Solid state lighting based on light-emitting diodes (LEDs) is a technology with the potential to drastically reduce energy usage, made possible by the development of gallium nitride and its alloys. However, the nitride materials family exhibits high defect densities and, in the equilibrium wurtzite crystal phase, large piezo-electric and polarisation fields arising a...

  18. Fabrication of natural DNA-containing organic light emitting diodes

    Science.gov (United States)

    Gomez, Eliot F.; Spaeth, Hans D.; Steckl, Andrew J.; Grote, James G.

    2011-09-01

    The process of creating natural DNA-containing bio-organic light emitting diodes is a fascinating journey from salmon fish to the highly-efficient BiOLED. DNA from salmon sperm is used as a high-performance electron blocking layer, to enhance the efficiency of the BiOLED over its conventional OLED counterpart. An overview of the BiOLED fabrication process and its key steps are presented in this paper.

  19. Study on electroluminescence from porous silicon light-emitting diode

    Institute of Scientific and Technical Information of China (English)

    Yajun Yang; Qingshan Li; Xianyun Liu

    2006-01-01

    @@ Porous silicon (PS) light-emitting diode (LED) with an ITO/PS/p-Si/Al structure was fabricated by anodic oxidation method. Photoluminescence (PL) of the PS LED was measured with a peak at 593 nm, and electroluminescence (EL) was measured with a peak at 556 nm under the conditions of 7.5-V forward bias and 210-mA current intensity. The spectral width of EL was measured to be about 160 nm.

  20. Growth and properties of wide spectral white light emitting diodes

    Institute of Scientific and Technical Information of China (English)

    Xie Zi-Li; Shi Yi; Zheng You-Dou; Zhang Rong; Fu De-Yi; Liu Bin; Xiu Xiang-Qian; Hua Xue-Mei; Zhao Hong; Chen Peng; Han Ping

    2011-01-01

    Wide spectral white light emitting diodes have been designed and grown on a sapphire substrate by using a metal-organic chemical vapor deposition system.Three quantum wells with blue-light-emitting,green-light-emitting and red-light-emitting structures were grown according to the design.The surface morphology of the film was observed by using atomic force microscopy. The films were characterized by their photoluminescence measurements. X-ray diffraction θ/2θ scan spectroscopy was carried out on the multi-quantum wells.The secondary fringes of the symmetric ω/2θ X-ray diffraction scan peaks indicate that the thicknesses and the alloy compositions of the individual quantum wells are repeatable throughout the active region.The room temperature photolumineecence spectra of the structures indicate that the white light emission of the multi-quantum wells is obtained.The light spectrum covers 400-700 nm,which is almost the whole visible light spectrum.

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

    Science.gov (United States)

    Yang, Zhenyu; Voznyy, Oleksandr; Liu, Mengxia; Yuan, Mingjian; Ip, Alexander H; Ahmed, Osman S; Levina, Larissa; Kinge, Sachin; Hoogland, Sjoerd; Sargent, Edward H

    2015-12-22

    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.

  3. Response time of light emitting diode-logarithmic electrometer

    Science.gov (United States)

    Acharya, Y. B.; Vyavahare, P. D.

    1998-02-01

    In a logarithmic electrometer which uses a transistor as a nonlinear element, a capacitance is generally connected across the feedback element of the operational amplifier. This stabilizes the loop but degrades the response at low current levels. However the stability problem is not so serious when a junction diode is used. In the present work an attempt was made to study the response time of a logarithmic electrometer which uses a light emitting diode (LED) as a nonlinear element and without external capacitance. The calculated values of rise time are based on an equivalent circuit with a depletion layer capacitance and voltage dependent conductance. These values are found to be in reasonable agreement with the experimentally measured values. This study will be useful in the estimation of dynamical errors in logarithmic electrometers using junction diode/LED, LED photometers and will be helpful in the techniques for improvements of the response time of logarithmic electrometers using a junction diode, particularly at low currents.

  4. Bright light-emitting diodes based on organometal halide perovskite.

    Science.gov (United States)

    Tan, Zhi-Kuang; Moghaddam, Reza Saberi; Lai, May Ling; Docampo, Pablo; Higler, Ruben; Deschler, Felix; Price, Michael; Sadhanala, Aditya; Pazos, Luis M; Credgington, Dan; Hanusch, Fabian; Bein, Thomas; Snaith, Henry J; Friend, Richard H

    2014-09-01

    Solid-state light-emitting devices based on direct-bandgap semiconductors have, over the past two decades, been utilized as energy-efficient sources of lighting. However, fabrication of these devices typically relies on expensive high-temperature and high-vacuum processes, rendering them uneconomical for use in large-area displays. Here, we report high-brightness light-emitting diodes based on solution-processed organometal halide perovskites. We demonstrate electroluminescence in the near-infrared, green and red by tuning the halide compositions in the perovskite. In our infrared device, a thin 15 nm layer of CH3NH3PbI(3-x)Cl(x) perovskite emitter is sandwiched between larger-bandgap titanium dioxide (TiO2) and poly(9,9'-dioctylfluorene) (F8) layers, effectively confining electrons and holes in the perovskite layer for radiative recombination. We report an infrared radiance of 13.2 W sr(-1) m(-2) at a current density of 363 mA cm(-2), with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. In our green light-emitting device with an ITO/PEDOT:PSS/CH3NH3PbBr3/F8/Ca/Ag structure, we achieved a luminance of 364 cd m(-2) at a current density of 123 mA cm(-2), giving external and internal quantum efficiencies of 0.1% and 0.4%, respectively. We show, using photoluminescence studies, that radiative bimolecular recombination is dominant at higher excitation densities. Hence, the quantum efficiencies of the perovskite light-emitting diodes increase at higher current densities. This demonstration of effective perovskite electroluminescence offers scope for developing this unique class of materials into efficient and colour-tunable light emitters for low-cost display, lighting and optical communication applications.

  5. Electron-enhanced hole injection in blue polyfluorene-based polymer light-emitting diodes

    NARCIS (Netherlands)

    Woudenbergh, T. van; Wildeman, J.; Blom, P.W.M.; Bastiaansen, J.J.A.M.; Langeveld-Voss, B.M.W.

    2004-01-01

    It has recently been reported that, after electrical conditioning, an ohmic hole contact is formed in poly(9,9-dioctylfluorene) (PFO)-based polymer light-emitting diodes (PLED), despite the large hole-injection barrier obtained with a poly(styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiophene

  6. Neodymium YAG lasers pumped by light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Bilak, V.I.; Goldobin, I.S.; Zverev, G.M.; Kuratev, I.I.; Pashkov, V.A.; Stel' makh, M.F.; Tsvetkov, Y.V.; Solov' eva, N.M.

    1981-11-01

    The results are presented of theoretical and experimental investigations of room-temperature YAG:Nd lasers pumped by light-emitting diodes. The lasing characteristics of a laser operated at the 1.06 and 1.32 ..mu.. wavelengths were investigated in the cw and pulsed regimes and dependences of its parameters on the temperature, pulse repetition frequency, and other factors were studied. In the pulsed regime the laser efficiency was 0.2% and in the cw regime the radiation power reached 50 and 17 mW at the 1.06 and 1.32 ..mu.. wavelengths, respectively.

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

    DEFF Research Database (Denmark)

    Hansen, René Skov

    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 the experiment consists of a 3mm high x 5mm wide slice of green colored gelatine overlaid by a 3cm layer of colorless gelatine. The light pulses from the LED is focused on the green gelatine. The photoacoustic response from the green gelatine is detected by a single transducer on the opposite (top) surface...

  8. High efficiency III-nitride light-emitting diodes

    Science.gov (United States)

    Crawford, Mary; Koleske, Daniel; Cho, Jaehee; Zhu, Di; Noemaun, Ahmed; Schubert, Martin F; Schubert, E. Fred

    2013-05-28

    Tailored doping of barrier layers enables balancing of the radiative recombination among the multiple-quantum-wells in III-Nitride light-emitting diodes. This tailored doping enables more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop in high-power III-Nitride LEDs. Mitigation of the efficiency droop in III-Nitride LEDs may enable the pervasive market penetration of solid-state-lighting technologies in high-power lighting and illumination.

  9. 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)

  10. Stability study of saturated red polymer light-emitting diodes

    Institute of Scientific and Technical Information of China (English)

    XU Wei; PENG JunBiao; XU YunHua; WANG Jian; HUANG Zhe; NIU QiaoLi; CAO Yong

    2007-01-01

    Saturated red polymer light-emitting diodes have been fabricated with a single emitting polymer blend layer of poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene](MEH-PPV)and poly[9,9-dioctylfluorene-co-4,7-di-2-thienyl-2,1,3-benzothiadiazole](PFO-DBT15).Saturated red emission with the Commission Internationale de I'Eclairage(CIE)coordinates of(0.67,0.33)was obtained.The device stability was investigated.The results showed that energy transfer occurred from MEH-PPV to PFO-DBT15,and MEH-PPV improved the hole injection and transportation.

  11. Camera vibration measurement using blinking light-emitting diode array.

    Science.gov (United States)

    Nishi, Kazuki; Matsuda, Yuichi

    2017-01-23

    We present a new method for measuring camera vibrations such as camera shake and shutter shock. This method successfully detects the vibration trajectory and transient waveforms from the camera image itself. We employ a time-varying pattern as the camera test chart over the conventional static pattern. This pattern is implemented using a specially developed blinking light-emitting-diode array. We describe the theoretical framework and pattern analysis of the camera image for measuring camera vibrations. Our verification experiments show that our method has a detection accuracy and sensitivity of 0.1 pixels, and is robust against image distortion. Measurement results of camera vibrations in commercial cameras are also demonstrated.

  12. Light-Emitting Diodes in the Solid-State Lighting Systems

    CERN Document Server

    Sparavigna, Amelia Carolina

    2014-01-01

    Red and green light-emitting diodes (LEDs) had been produced for several decades before blue emitting diodes, suitable for lighting applications, were widely available. Today, we have the possibility of combining the three fundamental colours to have a bright white light. And therefore, a new form of lighting, the solid-state lighting, has now become a reality. Here we discuss LEDs and some of their applications in displays and lamps.

  13. 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.

  14. Selective-area nanoheteroepitaxy for light emitting diode (LED) applications

    Science.gov (United States)

    Wildeson, Isaac H.

    Over 20% of the electricity in the United States is consumed for lighting, and the majority of this energy is wasted as heat during the lighting process. A solid-state (or light emitting diode (LED)-based) light source has the potential of saving the United States billions of dollars in electricity and reducing megatons of global CO2 emissions annually. While white light LEDs are currently on the market with efficiencies that are superior to incandescent and fluorescent light sources, their high up-front cost is inhibiting mass adoption. One reason for the high cost is the inefficiency of green and amber LEDs that can used to make white light. The inefficiency of green and amber LEDs results in more of these chips being required, and thus a higher cost. Improvements in the performance of green and amber LEDs is also required in order to realize the full potential of solid-state lighting. Nanoheteroepitaxy is an interesting route towards achieving efficient green and amber LEDs as it resolves major challenges that are currently plaguing III-nitride LEDs such as high dislocation densities and limited active region critical thicknesses. A method for fabricating III-nitride nanopyramid LEDs is presented that employs conventional processing used in industry. The present document begins with an overview of the current challenges in III-nitride LEDs and the benefits of nanoheteroepitaxy. A process for controlled selective-area growth of nanopyramid LEDs by organometallic vapor phase epitaxy has been developed throughout the course of this work. Dielectric templates used for the selective-area growth are patterned by two methods, namely porous anodic alumina and electron-beam lithography. The dielectric templates serve as efficient dislocation filters; however, planar defects are initiated during lower temperature growth on the nanopyramids. The quantum wells outline six semipolar planes that form each hexagonal pyramid. Quantum wells grown on these semipolar planes

  15. Organic light-emitting diodes based on a series of new polythienothiophene complexes and highly luminescent quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Vashchenko, A. A. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Goriachiy, D. O., E-mail: goryachii@phystech.edu [Moscow Institute of Physics and Technology (Russian Federation); Vitukhnovsky, A. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Tananaev, P. N. [Dukhov Research Institute of Automation (Russian Federation); Vasnev, V. A.; Rodlovskaya, E. N. [Russian Academy of Sciences, Nesmeyanov Institute of Organoelement Compounds (Russian Federation)

    2016-01-15

    Experimental samples of organic light-emitting diodes with transport layers based on polythienothiophenes and using CdSe/CdS/ZnS semiconductor quantum dots with an internal quantum efficiency up to 85% in the emitting layer are investigated. It is shown that solubility and film-forming properties are key for using polythienothiophenes in light-emitting diodes. The most promising polythienothiophenes are identified on the basis of the results obtained.

  16. High Efficiency SEPIC Converter For High Brightness Light Emitting Diodes (LEDs) System

    OpenAIRE

    Qin, Yaxiao

    2012-01-01

    ABSTRACT This thesis presents an investigation into the characteristics of and driving methods for light emitting diode (LED) lamp system. A comprehensive overview on the lighting development is proposed. The characteristic of the light emitting diode (LED) lamp is described and the requirements of the ballast for the light emitting diode (LED) lamp are presented. Although LED lamps have longer lifetime than fluorescent lamps, the short lifetime limitation of LED driver imposed by ele...

  17. DNA Bases Thymine and Adenine in Bio-Organic Light Emitting Diodes

    Science.gov (United States)

    2014-11-24

    DNA Bases Thymine and Adenine in Bio-Organic Light Emitting Diodes Eliot F. Gomez1, Vishak Venkatraman1, James G. Grote2 & Andrew J. Steckl1...45433-7707 USA. We report on the use of nucleic acid bases (NBs) in organic light emitting diodes (OLEDs). NBs are small molecules that are the basic...polymer has been a frequent natural material integrated in electronic devices. DNA has been used in organic light - emitting diodes (OLEDs)4,5,7–14

  18. LIGHT-EMITTING DIODE TECHNOLOGY IMPROVES INSECT TRAPPING

    Science.gov (United States)

    GILLEN, JONATHON I.; MUNSTERMANN, LEONARD E.

    2008-01-01

    In a climate of increased funding for vaccines, chemotherapy, and prevention of vector-borne diseases, fewer resources have been directed toward improving disease and vector surveillance. Recently developed light-emitting diode (LED) technology was applied to standard insect-vector traps to produce a more effective lighting system. This approach improved phlebotomine sand fly capture rates by 50%, and simultaneously reduced the energy consumption by 50–60%. The LEDs were incorporated into 2 lighting designs, 1) a LED combination bulb for current light traps and 2) a chip-based LED design for a modified Centers for Disease Control and Prevention light trap. Detailed descriptions of the 2 designs are presented. PMID:18666546

  19. Light emitting diodes (LEDs) applied to microalgal production.

    Science.gov (United States)

    Schulze, Peter S C; Barreira, Luísa A; Pereira, Hugo G C; Perales, José A; Varela, João C S

    2014-08-01

    Light-emitting diodes (LEDs) will become one of the world's most important light sources and their integration in microalgal production systems (photobioreactors) needs to be considered. LEDs can improve the quality and quantity of microalgal biomass when applied during specific growth phases. However, microalgae need a balanced mix of wavelengths for normal growth, and respond to light differently according to the pigments acquired or lost during their evolutionary history. This review highlights recently published results on the effect of LEDs on microalgal physiology and biochemistry and how this knowledge can be applied in selecting different LEDs with specific technical properties for regulating biomass production by microalgae belonging to diverse taxonomic groups. Copyright © 2014 Elsevier Ltd. All rights reserved.

  20. 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...

  1. 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...... 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...... 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...

  2. Acceptor impurity activation in III-nitride light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Römer, Friedhard, E-mail: froemer@uni-kassel.de; Witzigmann, Bernd, E-mail: bernd.witzigmann@uni-kassel.de [Department of Electrical Engineering, University of Kassel, 34121 Kassel (Germany)

    2015-01-12

    In this work, the role of the acceptor doping and the acceptor activation and its impact on the internal quantum efficiency (IQE) of a Gallium Nitride (GaN) based multi-quantum well light emitting diode is studied by microscopic simulation. Acceptor impurities in GaN are subject to a high activation energy which depends on the presence of proximate dopant atoms and the electric field. A combined model for the dopant ionization and activation barrier reduction has been developed and implemented in a semiconductor carrier transport simulator. By model calculations, we demonstrate the impact of the acceptor activation mechanisms on the decay of the IQE at high current densities, which is known as the efficiency droop. A major contributor to the droop is the electron leakage which is largely affected by the acceptor doping.

  3. TCNQ Interlayers for Colloidal Quantum Dot Light-Emitting Diodes.

    Science.gov (United States)

    Koh, Weon-kyu; Shin, Taeho; Jung, Changhoon; Cho, Dr-Kyung-Sang

    2016-04-18

    CdSe/CdS/ZnS quantum dot light-emitting diodes (QD-LEDs) show increased brightness (from ca. 18 000 to 27 000 cd m(-2) ) with 7,7,8,8-tetracyanoquinodimethane (TCNQ) between the QD and electron-transfer layers of ZnO nanoparticles. As QD/ZnO layers are known to have interface defects, our finding leads to the importance of interface engineering for QD-LEDs. Although the photoluminescent intensity and decay lifetime of ZnO/TCNQ/QD layers are similar to those of ZnO/QD layers, cyclic voltammetry suggests improved charge transfer of TCNQ/ZnO layers compared to that of pure ZnO layers. This helps us to understand the mechanism of electrically driven QD-LED behavior, which differs from that of conventional solid-state LEDs, and enables the rational design of QD-based optoelectronic devices.

  4. 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...

  5. Recent Progress toward white organic light emitting diodes

    Institute of Scientific and Technical Information of China (English)

    Tao Yu-Tai

    2004-01-01

    An efficient and stable white organic light emitting diode (WOLED) is highly desirable in potential applications such as lighting, background light source, and full color display.A series of highly fluorescent dyes based on a dipyrazolopyridine skeleton,1,7-diphenyl-l,7-dihydrodipyrazolo[3,4-b,4′,3′-e]pyridine, were synthesized and evaluated as emitting as well as charge-transporting material in the fabrication of electroluminescent devices.Several of the blue derivatives are found to be useful as the source of blue emission in fabricating bright white-emitting devices. The choice of dopants, cathode materials, electron-transporting materials as well as the device configurations greatly affect the emission profile, efficiencies, as well as the device lifetime. The latest progress in achieving a more efficient, color stable, durable white light device will be discussed.

  6. Application of Surface Plasmonics for Semiconductor Light-Emitting Diodes

    DEFF Research Database (Denmark)

    Fadil, Ahmed

    This thesis addresses the lack of an efficient semiconductor light source at green emission colours. Considering InGaN based quantum-well (QW) light-emitters and light-emitting diodes (LEDs), various ways of applying surface plasmonics and nano-patterning to improve the efficiency, are investigated....... By placing metallic thin films or nanoparticles (NPs) in the near-field of QW light-emitters, it is possible to improve their internal quantum efficiency (IQE) through the Purcell enhancement effect. It has been a general understanding that in order to achieve surface plasmon (SP) coupling with QWs...... is presented to obtain light extraction efficiency (LEE) improvement through nano-patterning, and IQE improvement through SP-QW coupling. Considering the fabrication process aspect, dry-etching damage on the semiconductor light-emitters from the nano-patterning is also addressed. Different ion-damage treatment...

  7. Thermal resistance of light emitting diode PCB with thermal vias.

    Science.gov (United States)

    Lee, Hyo Soo; Shin, Hyung Won; Jung, Seung Boo

    2012-04-01

    Light emitting diodes (LEDs) are already familiar for use as lighting sources in various electronic devices and displays. LEDs have many advantages such as long life, low power consumption, and high reliability. In the future, as an alternative to fluorescent lighting, LEDs are certain to receive much attention. However, in components related to advanced LED packages or modules there has been an issue regarding the heat from the LED chip. The LED chip is still being developed for use in high-power devices which generate more heat. In this study, we investigate the variation of thermal resistance in LED modules embedded with thermal vias. Through the analysis of thermal resistance with various test vehicles, we obtained the concrete relationship between thermal resistance and the thermal via structure.

  8. Resonance Raman measurements of carotenoids using light emitting diodes

    CERN Document Server

    Bergeson, S D; Eyring, N J; Fralick, J F; Stevenson, D N; Ferguson, S B

    2008-01-01

    We report on the development of a compact commercial instrument for measuring carotenoids in skin tissue. The instrument uses two light emitting diodes (LEDs) for dual-wavelength excitation and four photomultiplier tubes for multichannel detection. Bandpass filters are used to select the excitation and detection wavelengths. The f/1.3 optical system has high optical throughput and single photon sensitivity, both of which are crucial in LED-based Raman measurements. We employ a signal processing technique that compensates for detector drift and error. The sensitivity and reproducibility of the LED Raman instrument compares favorably to laser-based Raman spectrometers. This compact, portable instrument is used for non-invasive measurement of carotenoid molecules in human skin with a repeatability better than 10%.

  9. Simulations of charge transport in organic light emitting diodes

    CERN Document Server

    Martin, S J

    2002-01-01

    In this thesis, two approaches to the modelling of charge transport in organic light emitting diodes (OLEDs) are presented. The first is a drift-diffusion model, normally used when considering conventional crystalline inorganic semiconductors (e.g. Si or lll-V's) which have well defined energy bands. In this model, electron and hole transport is described using the current continuity equations and the drift-diffusion current equations, and coupled to Poisson's equation. These equations are solved with the appropriate boundary conditions, which for OLEDs are Schottky contacts; carriers are injected by thermionic emission and tunnelling. The disordered nature of the organic semiconductors is accounted for by the inclusion of field-dependent carrier mobilities and Langevin optical recombination. The second approach treats the transport of carriers in disordered organic semi-conductors as a hopping process between spatially and energetically disordered sites. This method has been used previously to account for th...

  10. A Pair of Light Emitting Diodes for Absorbance Measurement

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Dongyong; Eom, Inyong [Catholic Univ. of Daegu, Gyeongsan (Korea, Republic of)

    2013-10-15

    Two same wavelength LEDs (i. e. an emitter LED and a detector LED, respectively) were successfully used to measure absorbance of BTB solution. A linear calibration with r-squared value of 0.9945 was achieved. 0.03 μM of LOD was observed with a noise level of 2 Χ 10{sup -4} absorbance unit. We are now examining relative sensitivities of different LEDs with distinct wavelength. In the future, building a spectrophotometer equipped with LEDs is quite interesting both in scientifically and pedagogically (i. e. undergraduate lab course). Light emitting diodes (LEDs) have a semiconductor chip (∼1 mm{sup 2} area) mounted on a concave mirror and emit narrow band of wavelengths when forward biased. LEDs have been widely used in many fields. Conventional light bulbs are being replaced by LED bulbs.

  11. Organic Light-Emitting Diodes Driven by Organic Transistors

    Institute of Scientific and Technical Information of China (English)

    胡远川; 董桂芳; 王立铎; 梁琰; 邱勇

    2004-01-01

    Organic thin-film field-effect transistors (OTFTs) with pentacene as the semiconductor have been fabricated for driving an organic light-emitting diode (OLED). The driving circuit includes two OTFTs and one storage capacitor. The field-effect mobility of the transistors in the driving circuit is more than 0.3 cm2/Vs, and the on/off ratio is larger than 104. The light-emission area of the OLED is 0. 04mm2 and the brightness is larger than 400cd/m2 when the selected line voltage, data line voltage and drive voltage all are -40 V. The responding characteristics and holding characteristics are also researched when the selected line voltage and the date line voltage are changed.

  12. Model for Triplet State Engineering in Organic Light Emitting Diodes

    CERN Document Server

    Prodhan, Suryoday; Ramasesha, S

    2014-01-01

    Engineering the position of the lowest triplet state (T1) relative to the first excited singlet state (S1) is of great importance in improving the efficiencies of organic light emitting diodes and organic photovoltaic cells. We have carried out model exact calculations of substituted polyene chains to understand the factors that affect the energy gap between S1 and T1. The factors studied are backbone dimerisation, different donor-acceptor substitutions and twisted geometry. The largest system studied is an eighteen carbon polyene which spans a Hilbert space of about 991 million. We show that for reverse intersystem crossing (RISC) process, the best system involves substituting all carbon sites on one half of the polyene with donors and the other half with acceptors.

  13. Resonant cavity light-emitting diodes: modeling, design, and optimization

    Science.gov (United States)

    Dumitrescu, Mihail M.; Sipila, Pekko; Vilokkinen, Ville; Toikkanen, L.; Melanen, Petri; Saarinen, Mika J.; Orsila, Seppo; Savolainen, Pekka; Toivonen, Mika; Pessa, Markus

    2000-02-01

    Monolithic top emitting resonant cavity light-emitting diodes operating in the 650 and 880 nm ranges have been prepared using solid-source molecular beam epitaxy growth. Transfer matrix based modeling together with a self- consistent model have been sued to optimize the devices' performances. The design of the layer structure and doping profile was assisted by computer simulations that enabled many device improvements. Among the most significant ones intermediate-composition barrier-reduction layers were introduced in the DBR mirrors for improving the I-V characteristics and the cavity and mirrors were detuned aiming at maximum extraction efficiency. The fabricated devices showed line widths below 15 nm, CW light power output of 8 and 22.5 mW, and external quantum efficiencies of 3 percent and 14.1 percent in the 650 nm and 880 nm ranges, respectively - while the simulations indicate significant performance improvement possibilities.

  14. Kinetics of transient electroluminescence in organic light emitting diodes

    Science.gov (United States)

    Shukla, Manju; Kumar, Pankaj; Chand, Suresh; Brahme, Nameeta; Kher, R. S.; Khokhar, M. S. K.

    2008-08-01

    Mathematical simulation on the rise and decay kinetics of transient electroluminescence (EL) in organic light emitting diodes (OLEDs) is presented. The transient EL is studied with respect to a step voltage pulse. While rising, for lower values of time, the EL intensity shows a quadratic dependence on (t - tdel), where tdel is the time delay observed in the onset of EL, and finally attains saturation at a sufficiently large time. When the applied voltage is switched off, the initial EL decay shows an exponential dependence on (t - tdec), where tdec is the time when the voltage is switched off. The simulated results are compared with the transient EL performance of a bilayer OLED based on small molecular bis(2-methyl 8-hydroxyquinoline)(triphenyl siloxy) aluminium (SAlq). Transient EL studies have been carried out at different voltage pulse amplitudes. The simulated results show good agreement with experimental data. Using these simulated results the lifetime of the excitons in SAlq has also been calculated.

  15. Dr. Harry Whelan With the Light Emitting Diode Probe

    Science.gov (United States)

    1999-01-01

    The red light from the Light Emitting Diode (LED) probe shines through the fingers of Dr. Harry Whelan, a pediatric neurologist at the Children's Hospital of Wisconsin in Milwaukee. Dr. Whelan uses the long waves of light from the LED surgical probe to activate special drugs that kill brain tumors. Laser light previously has been used for this type of surgery, but the LED light illuminates through all nearby tissues, reaching parts of tumors 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. Also, it can be used for hours at a time while still remaining cool to the touch. The probe was developed for photodynamic cancer therapy under a NASA Small Business Innovative Research Program grant. The program is part of NASA's Technology Transfer Department at the Marshall Space Flight Center.

  16. 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.

  17. Electroluminescence property of organic light emitting diode (OLED)

    Energy Technology Data Exchange (ETDEWEB)

    Özdemir, Orhan; Kavak, Pelin; Saatci, A. Evrim; Gökdemir, F. Pınar; Menda, U. Deneb; Can, Nursel; Kutlu, Kubilay [Yıldız Technical University, Department of Physics, Esenler, Istanbul (Turkey); Tekin, Emine; Pravadalı, Selin [National Metrology Instıtute of Turkey (TUBİTAK-UME), Kocaeli (Turkey)

    2013-12-16

    Transport properties of electrons and holes were investigated not only in a anthracene-containing poly(p-phenylene-ethynylene)- alt - poly(p-phenylene-vinylene) (PPE-PPV) polymer (AnE-PVstat) light emitting diodes (OLED) but also in an ITO/Ag/polymer/Ag electron and ITO/PEDOT:PSS/polymer/Au hole only devices. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer.

  18. Escaped and Trapped Emission of Organic Light-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    LIANG Shi-Xiong; WU Zhao-Xin; ZHAO Xuan-Ke; HOU Xun

    2012-01-01

    By locating the emitters around the first and second antinode of the metal electrode, the escaped and trapped emission of small molecule based bottom emission organic light-emitting diodes is investigated by using an integrating sphere, a fiber spectrometer and a glass hemisphere. It is found that the external coupling ratio by locating the emitters at the second antinode (at a distance of 220 nm from the cathode) is 70%, which is higher than that of an emitter at the first antinode (60 nm from the cathode) in theory and experiment. Extending the "half-space" dipole model by taking the dipole radiation pattern into account, we also calculate the optical coupling efficiency for the emitter at both the first and second antinode. Our experimental and theoretical results will benefit the optimization of device structures for the higher out-coupling efficiency.%By locating the emitters around the first and second antinode of the metal electrode,the escaped and trapped emission of small molecule based bottom emission organic light-emitting diodes is investigated by using an integrating sphere,a fiber spectrometer and a glass hemisphere.It is found that the external coupling ratio by locating the emitters at the second antinode (at a distance of 220 nm from the cathode) is 70%,which is higher than that of an emitter at the first antinode (60nm from the cathode) in theory and experiment.Extending the "half-space" dipole model by taking the dipole radiation pattern into account,we also calculate the optical coupling efficiency for the emitter at both the first and second antinode.Our experimental and theoretical results will benefit the optimization of device structures for the higher out-coupling efficiency.

  19. 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.

  20. Ontology-based Patent Licensing and Litigation Strategic Knowledge System for the Light Emitting Diode Industry

    OpenAIRE

    Trappey, Amy J. C.; Yu-Hui Wang; Charles V. Trappey; Chun-Yi Wu; Tzu-Hsuan Lin

    2013-01-01

    This research studies the patents, intellectual properties and licensing landscape of the Light Emitting Diode (LED) industry. The ontology of LED technology is described and defined as four major sub-technology domains. The finding provides LED companies with consistent knowledge of their own and their competitors’ patents and intellectual property rights (IPR) ownership. Major LED companies often use their IPRs to gain and protect their market competitiveness, to form alliances, and to crea...

  1. Molecularly controlled interfacial layer strategy toward highly efficient simple-structured organic light-emitting diodes.

    Science.gov (United States)

    Han, Tae-Hee; Choi, Mi-Ri; Woo, Seong-Hoon; Min, Sung-Yong; Lee, Chang-Lyoul; Lee, Tae-Woo

    2012-03-15

    A highly efficient simplified organic light-emitting diode (OLED) with a molecularly controlled strategy to form near-perfect interfacial layer on top of the anode is demonstrated. A self-organized polymeric hole injection layer (HIL) is exploited increasing hole injection, electron blocking, and reducing exciton quenching near the electrode or conducting polymers; this HIL allows simplified OLED comprised a single small-molecule fluorescent layer to exhibits a high current efficiency (∼20 cd/A).

  2. Dye concentration study in PVK based light emitting diodes

    Science.gov (United States)

    Gautier-Thianche, E.; Sentein, C.; Nunzi, J.-M.; Lorin, A.; Denis, C.; Raimond, P.

    1998-06-01

    Light emitting diodes made of a single spin-coated layer of poly(9-vinylcarbazole) doped with coumarin-515 dye have been prepared. The influence of dye concentration on emission and electrical characteristics is evidenced. Two different regimes are identified. At low concentrations, hole injection barrier raises, holes are trapped and mobility decreases. External quantum efficiency increases with concentration. At concentrations larger than 10 per electron. Coumarin in a single-layer diode improves electron-hole injection and recombination balance more than an additional hole-blocking layer. Nous avons étudié des DEL constituées d'une monocouche de poly(9-vinylcarbazole) (PVK) dopée avec un colorant laser : la coumarine 515. Le taux de dopage en colorant influe sur les caractéristiques courant - tension et sur le rendement quantique d'électroluminescence. Aux faibles taux de dopage, la hauteur de la barrière d'injection des trous augmente, les trous sont piégés dans la matrice et leur mobilité décroît. Le rendement quantique externe augmente avec la concentration de dopant. Aux concentrations supérieures à 10 photoluminescence chute mais le rendement quantique externe augmente jusqu'à 0.1 recombinaison électron-trou bien mieux qu'une couche supplémentaire bloquant l'injection des trous.

  3. 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.

  4. 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.

  5. Active Matrix Organic Light Emitting Diode (AMOLED) Environmental Test Report

    Science.gov (United States)

    Salazar, George A.

    2013-01-01

    This report focuses on the limited environmental testing of the AMOLED display performed as an engineering evaluation by The NASA Johnson Space Center (JSC)-specifically. EMI. Thermal Vac, and radiation tests. The AMOLED display is an active-matrix Organic Light Emitting Diode (OLED) technology. The testing provided an initial understanding of the technology and its suitability for space applications. Relative to light emitting diode (LED) displays or liquid crystal displays (LCDs), AMOLED displays provide a superior viewing experience even though they are much lighter and smaller, produce higher contrast ratio and richer colors, and require less power to operate than LCDs. However, AMOLED technology has not been demonstrated in a space environment. Therefore, some risks with the technology must be addressed before they can be seriously considered for human spaceflight. The environmental tests provided preliminary performance data on the ability of the display technology to handle some of the simulated induced space/spacecraft environments that an AMOLED display will see during a spacecraft certification test program. This engineering evaluation is part of a Space Act Agreement (SM) between The NASA/JSC and Honeywell International (HI) as a collaborative effort to evaluate the potential use of AMOLED technology for future human spaceflight missions- both government-led and commercial. Under this SM, HI is responsible for doing optical performance evaluation, as well as temperature and touch screen studies. The NASA/JSC is responsible for performing environmental testing comprised of EMI, Thermal Vac, and radiation tests. Additionally, as part of the testing, limited optical data was acquired to assess performance as the display was subjected to the induced environments. The NASA will benefit from this engineering evaluation by understanding AMOLED suitability for future use in space as well as becoming a smarter buyer (or developer) of the technology. HI benefits

  6. 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.

  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. Highly efficient light-emitting diodes based on intramolecular rotation

    CERN Document Server

    Di, Dawei; Yang, Le; Jones, Saul; Friend, Richard H; Linnolahti, Mikko; Bochmann, Manfred; Credgington, Dan

    2016-01-01

    The efficiency of an organic light-emitting diode (OLED) is fundamentally governed by the spin of recombining electron-hole pairs (singlet and triplet excitons), since triplets cannot usually emit light. The singlet-triplet energy gap, a key factor for efficient utilization of triplets, is normally positive. Here we show that in a family of materials with amide donor and carbene acceptor moieties linked by a metal, this energy gap for singlet and triplet excitons with charge-transfer character can be tuned from positive to negative values via the rotation of donor and acceptor about the metal-amide bond. When the gap is close to zero, facile intersystem crossing is possible, enabling efficient emission from singlet excitons. We demonstrate solution-processed LEDs with exceptionally high quantum efficiencies (near-100% internal and >27% external quantum efficiencies), and current and power efficiencies (87 cd/A and 75 lm/W) comparable to, or exceeding, those of state-of-the-art vacuum-processed OLEDs and quant...

  9. Temperature-dependent photoluminescence in light-emitting diodes

    Science.gov (United States)

    Lu, Taiping; Ma, Ziguang; Du, Chunhua; Fang, Yutao; Wu, Haiyan; Jiang, Yang; Wang, Lu; Dai, Longgui; Jia, Haiqiang; Liu, Wuming; Chen, Hong

    2014-01-01

    Temperature-dependent photoluminescence (TDPL), one of the most effective and powerful optical characterisation methods, is widely used to investigate carrier transport and localized states in semiconductor materials. Resonant excitation and non-resonant excitation are the two primary methods of researching this issue. In this study, the application ranges of the different excitation modes are confirmed by analysing the TDPL characteristics of GaN-based light-emitting diodes. For resonant excitation, the carriers are generated only in the quantum wells, and the TDPL features effectively reflect the intrinsic photoluminescence characteristics within the wells and offer certain advantages in characterising localized states and the quality of the wells. For non-resonant excitation, both the wells and barriers are excited, and the carriers that drift from the barriers can contribute to the luminescence under the driving force of the built-in field, which causes the existing equations to become inapplicable. Thus, non-resonant excitation is more suitable than resonant excitation for studying carrier transport dynamics and evaluating the internal quantum efficiency. The experimental technique described herein provides fundamental new insights into the selection of the most appropriate excitation mode for the experimental analysis of carrier transport and localized states in p-n junction devices. PMID:25139682

  10. Optimized Performances of Thick Film Organic Lighting-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    WANG Xiu-Ru; ZHANG Zhi-Qiang; MA Dong-Ge; SUN Run-Guang

    2008-01-01

    @@ The performance of organic light-emitting diodes (OLEDs) with thick film is optimized.The alternative vana-dium oxide (V2O5) and N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) layers are used to enhance holes in the emissive region, and 4,7-dipheny-1,10-phenanthroline (Bphen) doped 8-tris-hydroxyquinoline alu-minium (Alq3) is used to enhance electrons is the emissive region, thus ITO/V2O5 (8nm)/NPB (52nm)/V2O5 (8nm)/NPB (52 nm)/Alq3 (30 and 45 nm)/Alq3:Bphen (30wt%, 30 and 45 nm)/LiF (1 nm)/Al (120nm) devices are fabricated.The thick-film devices show the turn-on voltage of about 3 V and the maximal power efficiency of 4.51m/W, which is 1.46 times higher than the conventional thin-film OLEDs.

  11. 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.

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

    Science.gov (United States)

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

    2016-12-01

    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. Highly Bright White Organic Light-Emitting Diode

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@ A highly bright white organic light-emitting diode (OLED) was realized by using a highly bright blue emitting layer, 1,7-diphenyl-4-biphenyl-3,5-dimethyl-l,7-dihydrodipyrazolo[3,4-b;4',3'-e]pyridine (PAP-Ph), together with a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM)-doped Alq [tris(8-hydroxyquinolinato) aluminum (Ⅲ)] layer to provide the blue, red and green emission for color mixing. With appropriate thickness control, the white-light OLED has a performance that reaches 24700 cd/m2 at 15 V, 1.93 lm/W at 6.5 V, and >300 cd/m2 at 7.7 mA/em2. The Commission Internationale de l'Eclairage (CIE) coordinates of the emitted light vary in a very small range, from (0.35, 0.34) to (0.34, 0.35), when forward voltages change from 6 to 12 V.

  14. Highly Bright White Organic Light-Emitting Diode

    Institute of Scientific and Technical Information of China (English)

    KO; C.; W.

    2001-01-01

    A highly bright white organic light-emitting diode (OLED) was realized by using a highly bright blue emitting layer, 1,7-diphenyl-4-biphenyl-3,5-dimethyl-l,7-dihydrodipyrazolo[3,4-b;4',3'-e]pyridine (PAP-Ph), together with a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM)-doped Alq [tris(8-hydroxyquinolinato) aluminum (Ⅲ)] layer to provide the blue, red and green emission for color mixing. With appropriate thickness control, the white-light OLED has a performance that reaches 24700 cd/m2 at 15 V, 1.93 lm/W at 6.5 V, and >300 cd/m2 at 7.7 mA/em2. The Commission Internationale de l'Eclairage (CIE) coordinates of the emitted light vary in a very small range, from (0.35, 0.34) to (0.34, 0.35), when forward voltages change from 6 to 12 V.  ……

  15. Kinetics of transient electroluminescence in organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Shukla, Manju; Brahme, Nameeta [School of Studies in Physics, Pt. Ravishanker Shukla University, Raipur (Congo, The Democratic Republic of the) 492010 (India); Kumar, Pankaj; Chand, Suresh [Center for Organic Electronics, National Physical Laboratory, Dr K S Krishnan Road, New Delhi-110012 (India); Kher, R S [Department of Physics, Government Science PG College, Bilaspur (Congo, The Democratic Republic of the) 495006 (India); Khokhar, M S K [Department of Rural Technology, GuruGhasidas University Bilaspur (Congo, The Democratic Republic of the) 495009 (India)], E-mail: manjushukla2003@gmail.com

    2008-08-21

    Mathematical simulation on the rise and decay kinetics of transient electroluminescence (EL) in organic light emitting diodes (OLEDs) is presented. The transient EL is studied with respect to a step voltage pulse. While rising, for lower values of time, the EL intensity shows a quadratic dependence on (t - t{sub del}), where t{sub del} is the time delay observed in the onset of EL, and finally attains saturation at a sufficiently large time. When the applied voltage is switched off, the initial EL decay shows an exponential dependence on (t - t{sub dec}), where t{sub dec} is the time when the voltage is switched off. The simulated results are compared with the transient EL performance of a bilayer OLED based on small molecular bis(2-methyl 8-hydroxyquinoline)(triphenyl siloxy) aluminium (SAlq). Transient EL studies have been carried out at different voltage pulse amplitudes. The simulated results show good agreement with experimental data. Using these simulated results the lifetime of the excitons in SAlq has also been calculated.

  16. 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).

  17. 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.

  18. Emission characteristics of light-emitting diodes by confocal microscopy

    Science.gov (United States)

    Cheung, W. S.; Choi, H. W.

    2016-03-01

    The emission profiles of light-emitting diodes have typically be measured by goniophotometry. However this technique suffers from several drawbacks, including the inability to generate three-dimensional intensity profiles as well as poor spatial resolution. These limitations are particularly pronounced when the technique is used to compared devices whose emission patterns have been modified through surface texturing at the micrometer and nanometer scales,. In view of such limitations, confocal microscopy has been adopted for the study of emission characteristics of LEDs. This enables three-dimensional emission maps to be collected, from which two-dimensional cross-sectional emission profiles can be generated. Of course, there are limitations associated with confocal microscopy, including the range of emission angles that can be measured due to the limited acceptance angle of the objective. As an illustration, the technique has been adopted to compare the emission profiles of LEDs with different divergence angles using an objective with a numerical aperture of 0.8. It is found that the results are consistent with those obtained by goniophotometry when the divergence angle is less that the acceptance angle of the objective.

  19. Curing efficacy of light emitting diodes of dental curing units

    Directory of Open Access Journals (Sweden)

    Seyd Mostafa Mousavinasab

    2009-03-01

    Full Text Available Background and aims. The aim of the present study was to compare the efficacy of quartz tungsten halogen (QTH and light emitting diode (LED curing lights on polymerization of resin composite. Materials and Methods. A hybrid resin composite was used to prepare samples which were cured using two QTH and ten LED light curing sources. Twelve groups, each containing ten samples, were prepared using each light source. The cured depth of the resin was determined using ISO 4049 method and Vickers hardness values were determined at 1.0 mm intervals. Data was analyzed by ANOVA and Tukey test. Results. Data analysis demonstrated a significant difference between light sources for depth of cure. At 1.0 mm below the surface all the tested light sources and at 2.0-mm intervals all light sources except two (Optilux 501 and LEDemetron I and at 3.0-mm intervals only two light sources (PenCure and LEDemetron II could produce hardness values higher than 80% of superficial layer values. Conclusion. This study showed that a variety of LED light sources used in the present study are as effective as the high-intensity QTH lights in polymerization of resin composite.

  20. A standardized light-emitting diode device for photoimmunotherapy.

    Science.gov (United States)

    de Boer, Esther; Warram, Jason M; Hartmans, Elmire; Bremer, Peter J; Bijl, Ben; Crane, Lucia M A; Nagengast, Wouter B; Rosenthal, Eben L; van Dam, Gooitzen M

    2014-11-01

    Antibody-based photodynamic therapy-photoimmunotherapy (PIT)-is an ideal modality to improve cancer treatment because of its selective and tumor-specific mode of therapy. Because the use of PIT for cancer treatment is continuing to be described, there is great need to characterize a standardized light source for PIT application. In this work, we designed and manufactured a light-emitting diode (LED)/PIT device and validated the technical feasibility, applicability, safety, and consistency of the system for cancer treatment. To outline the characteristics and photobiologic safety of the LED device, multiple optical measurements were performed in accordance with a photobiologic safety standard. A luciferase-transfected breast cancer cell line (2LMP-Luc) in combination with panitumumab-IRDye 700DX (pan-IR700) was used to validate the in vitro and in vivo performance of our LED device. Testing revealed the light source to be safe, easy to use, and independent of illumination and power output (mW cm(-2)) variations over time. For in vitro studies, an LED dose (2, 4, 6 J cm(-2))-dependent cytotoxicity was observed using propidium iodide exclusion and annexin V staining. Dose-dependent blebbing was also observed during microscopic analysis. Bioluminescence signals of tumors treated with 0.3 mg of pan-IR700 and 50 J cm(-2) decreased significantly (>80%) compared with signals of contralateral nontreated sites at 4 h and at 1 d after PIT. To our knowledge, a normalized and standardized LED device has not been explicitly described or developed. In this article, we introduce a standardized light source and validate its usability for PIT applications. © 2014 by the Society of Nuclear Medicine and Molecular Imaging, Inc.

  1. Effect of polarized light emitting diode irradiation on wound healing.

    Science.gov (United States)

    Tada, Kaoru; Ikeda, Kazuo; Tomita, Katsuro

    2009-11-01

    We propose a new phototherapy using polarized light from light emitting diode (LED). The purpose of this study is to clarify the effect of polarized LED irradiation on wound healing. Five groups were classified: control (C), unpolarized (U), linearly polarized (L), right circularly polarized (RC), and left circularly polarized (LC) LED irradiation. In vitro study, fibroblast cell cultures were irradiated, and cellular proliferation was evaluated with a WST-8 assay. In vivo study, full-thickness skin defect of 20 mm diameter was created on the dorsal side of rats. The ratio of the residual wound area was measured, and expression of type 1 and type 3 procollagen mRNA in granulation tissue was determined by real-time reverse transcription polymerase chain reaction method. The cellular proliferation rates of group RC and L were significantly higher than other groups. The ratio of the residual wound area of group RC and L was significantly reduced than group C and U. Expression of type 1 procollagen mRNA in group RC was found to be significantly increased about 1.5-fold in comparison with the group C. There were no significant differences for type 3 procollagen. The right circularly polarized light and linearly polarized light promoted the process of wound healing by increasing the proliferation of fibroblasts, and the right circularly polarized light increased the expression of type 1 procollagen mRNA. The effectiveness of right circularly polarized light suggests that some optical active material, which has a circular dichroic spectrum, takes part in a biochemical reaction.

  2. Focus Issue: Organic light-emitting diodes-status quo and current developments.

    Science.gov (United States)

    List, Emil J W; Koch, Norbert

    2011-11-01

    The guest editors introduce the Optics Express Energy Express supplement Focus Issue, "Organic Light-Emitting Diodes," which includes six invited articles addressing the challenges of light outcoupling and light management in OLEDs.

  3. 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. Assimilation

  4. A Device Model for Polymer Light-Emitting Diodes with Mobile Ions

    NARCIS (Netherlands)

    Jong, M.J.M. de; Blom, P.W.M.

    1996-01-01

    A model is presented for the device operation of a polymer light-emitting diode (PLED) with mobile ions. It is calculated that the low efficiency of a PLED with a high injection barrier increases as the ions migrate.

  5. Efficient light-emitting diodes based on nanocrystalline perovskite in a dielectric polymer matrix.

    Science.gov (United States)

    Li, Guangru; Tan, Zhi-Kuang; Di, Dawei; Lai, May Ling; Jiang, Lang; Lim, Jonathan Hua-Wei; Friend, Richard H; Greenham, Neil C

    2015-04-08

    Electroluminescence in light-emitting devices relies on the encounter and radiative recombination of electrons and holes in the emissive layer. In organometal halide perovskite light-emitting diodes, poor film formation creates electrical shunting paths, where injected charge carriers bypass the perovskite emitter, leading to a loss in electroluminescence yield. Here, we report a solution-processing method to block electrical shunts and thereby enhance electroluminescence quantum efficiency in perovskite devices. In this method, a blend of perovskite and a polyimide precursor dielectric (PIP) is solution-deposited to form perovskite nanocrystals in a thin-film matrix of PIP. The PIP forms a pinhole-free charge-blocking layer, while still allowing the embedded perovskite crystals to form electrical contact with the electron- and hole-injection layers. This modified structure reduces nonradiative current losses and improves quantum efficiency by 2 orders of magnitude, giving an external quantum efficiency of 1.2%. This simple technique provides an alternative route to circumvent film formation problems in perovskite optoelectronics and offers the possibility of flexible and high-performance light-emitting displays.

  6. 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....

  7. 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

  8. Evaluation of light-emitting diodes for signage applications

    Science.gov (United States)

    Freyssinier, Jean Paul; Zhou, Yutao; Ramamurthy, Vasudha; Bierman, Andrew; Bullough, John D.; Narendran, Nadarajah

    2004-01-01

    This paper outlines two parts of a study designed to evaluate the use of light-emitting diodes (LEDs) in channel-letter signs. The first part of the study evaluated the system performance of red LED signs and white LED signs against reference neon and cold-cathode signs. The results show a large difference between the actual performance and potential savings from red and white LEDs. Depending on the configuration, a red LED sign could use 20% to 60% less power than a neon sign at the same light output. The light output of the brightest white LED sign tested was 15% lower than the cold-cathode reference, but its power was 53% higher. It appears from this study that the most efficient white LED system is still 40% less efficient than the cold-cathode system tested. One area that offers a great potential for further energy savings is the acrylic diffuser of the signs. The acrylic diffusers measured absorb between 60% and 66% of the light output produced by the sign. Qualitative factors are also known to play an important role in signage systems. One of the largest issues with any new lighting technology is its acceptance by the end user. Consistency of light output and color among LEDs, even from the same manufacturing batch, and over time, are two of the major issues that also could affect the advantages of LEDs for signage applications. To evaluate different signage products and to identify the suitability of LEDs for this application, it is important to establish a criterion for brightness uniformity. Building upon this information, the second part of the study used human factors evaluations to determine a brightness-uniformity criterion for channel-letter signs. The results show that the contrast modulation between bright and dark areas within a sign seems to elicit the strongest effect on how people perceive uniformity. A strong monotonic relationship between modulation and acceptability was found in this evaluation. The effect of contrast seems to be stronger

  9. 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

  10. 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…

  11. Theory Promises Brighter Perspective for Polymeric Light-Emitting-Diodes

    Institute of Scientific and Technical Information of China (English)

    2004-01-01

    @@ A new take on the theory of light-emitting polymers suggests that their efficiency can be largely increased, a development that would boost the introduction of flexible displays and possibly reduce the cost of flat panel displays which currently depend on very expansive materials.

  12. Study of electrical fatigue by defect engineering in organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Gassmann, Andrea, E-mail: gassmann@e-mat.tu-darmstadt.de [Technische Universität Darmstadt, Materials Science and Geoscience Department, Electronic Materials Division, Alarich-Weiss-Str. 2, 64287 Darmstadt (Germany); Yampolskii, Sergey V. [Technische Universität Darmstadt, Materials Science and Geoscience Department, Materials Modeling Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Klein, Andreas [Technische Universität Darmstadt, Materials Science and Geoscience Department, Surface Science Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Albe, Karsten [Technische Universität Darmstadt, Materials Science and Geoscience Department, Materials Modeling Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Vilbrandt, Nicole [Technische Universität Darmstadt, Chemistry Department, Ernst Berl Institute for Macromolecular Research, Alarich-Weiss-Str. 4, 64287 Darmstadt (Germany); Pekkola, Oili [Technische Universität Darmstadt, Materials Science and Geoscience Department, Electronic Materials Division, Alarich-Weiss-Str. 2, 64287 Darmstadt (Germany); Genenko, Yuri A. [Technische Universität Darmstadt, Materials Science and Geoscience Department, Materials Modeling Division, Jovanka-Bontschits-Str. 2, 64287 Darmstadt (Germany); Rehahn, Matthias [Technische Universität Darmstadt, Chemistry Department, Ernst Berl Institute for Macromolecular Research, Alarich-Weiss-Str. 4, 64287 Darmstadt (Germany); Seggern, Heinz von [Technische Universität Darmstadt, Materials Science and Geoscience Department, Electronic Materials Division, Alarich-Weiss-Str. 2, 64287 Darmstadt (Germany)

    2015-02-15

    Graphical abstract: - Highlights: • Electrical fatigue is investigated in PPV-based polymer light-emitting diodes. • Bromide defects remaining from Gilch synthesis limit PLED lifetime. • Electrical stress yields lower hole mobility and transition to dispersive transport. • Triplet excitons reduce lifetime and EL-emission-induced degradation observed. • Self-consistent drift-diffusion model for charge carrier injection and transport. - Abstract: In this work the current knowledge on the electrical degradation of polymer-based light-emitting diodes is reviewed focusing especially on derivatives of poly(p-phenylene-vinylene) (PPV). The electrical degradation will be referred to as electrical fatigue and is understood as mechanisms, phenomena and material properties that change during continuous operation of the device at constant current. The focus of this review lies especially on the effect of chemical synthesis on the transport properties of the organic semiconductor and the device lifetimes. In addition, the prominent transparent conductive oxide indium tin oxide as well as In{sub 2}O{sub 3} will be reviewed and how their properties can be altered by the processing conditions. The experiments are accompanied by theoretical modeling shining light on how the change of injection barriers, charge carrier mobility or trap density influence the current–voltage characteristics of the diodes and on how and which defects form in transparent conductive oxides used as anode.

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

    Science.gov (United States)

    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. %.

  14. Selective scattering polymer dispersed liquid crystal film for light enhancement of organic light emitting diode.

    Science.gov (United States)

    Jiang, Jinghua; McGraw, Greg; Ma, Ruiqing; Brown, Julie; Yang, Deng-Ke

    2017-02-20

    We developed a novel light enhancing film for an organic light emitting diode (OLED) based on polymer dispersed liquid crystal (PDLC). In the film, the liquid crystal droplets are unidirectionally aligned along the film normal direction and exhibit selective scattering. The film scatters light emitted only in directions with large incident angles but not light emitted in directions with small incident angles. When the light is scattered, it changes propagation direction and exits the OLED. The PDLC film reduces the total internal reflection and thus can significantly increase the light efficiency of the OLED.

  15. Hybrid light emitting diodes based on solution processed polymers, colloidal quantum dots, and colloidal metal nanoparticles

    Science.gov (United States)

    Ma, Xin

    This dissertation focuses on solution-processed light-emitting devices based on polymer, polymer/PbS quantum dot, and polymer/silver nanoparticle hybrid materials. Solution based materials and organic/inorganic hybrid light emitting diodes attracted significant interest recently due to many of their advantages over conventional light emitting diodes (LEDs) including low fabrication cost, flexible, high substrate compatibility, as well as tunable emission wavelength of the quantum dot materials. However, the application of these novel solution processed materials based devices is still limited due to their low performances. Material properties and fabrication parameters need to be carefully examined and understood for further device improvement. This thesis first investigates the impact of solvent property and evaporation rate on the polymer molecular chain morphology and packaging in device structures. Solvent is a key component to make the active material solution for spin coating fabrication process. Their impacts are observed and examined on both polymer blend system and mono-polymer device. Secondly, PbS colloidal quantum dot are introduced to form hybrid device with polymer and to migrate the device emission into near-IR range. As we show, the dithiol molecules used to cross-link quantum dots determine the optical and electrical property of the resulting thin films. By choosing a proper ligand for quantum dot ligand exchange, a high performance polymer/quantum dot hybrid LED is fabricated. In the end, the interaction of polymer exciton with surface plasmon mode in colloidal silver nanoparticles and the use of this effect to enhance solution processed LEDs' performances are investigated.

  16. Nanotexturing of GaN light-emitting diode material through mask-less dry etching

    Energy Technology Data Exchange (ETDEWEB)

    Dylewicz, Rafal; Khokhar, Ali Z; Rahman, Faiz [School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow G12 8LT (United Kingdom); Wasielewski, Radoslaw; Mazur, Piotr, E-mail: Faiz.Rahman@glasgow.ac.uk [Institute of Experimental Physics, University of Wroclaw, plac Maxa Borna 9, 50-204 Wroclaw (Poland)

    2011-02-04

    We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

  17. Nanotexturing of GaN light-emitting diode material through mask-less dry etching

    Science.gov (United States)

    Dylewicz, Rafal; Khokhar, Ali Z.; Wasielewski, Radoslaw; Mazur, Piotr; Rahman, Faiz

    2011-02-01

    We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

  18. Integration of a Novel Microfluidic Device with Silicon Light Emitting Diode-Antifuse and Photodetector

    NARCIS (Netherlands)

    LeMinh, P.; Holleman, J.; Berenschot, J.W.; Tas, N.R.; Berg, van den A.

    2002-01-01

    Light emitting diode antifuse has been integrated into a microfluidic device that is realized with extended standard CMOS technological steps. The device comprises of a microchannel sandwiched between a photodiode detector and a nanometer-scale diode antifuse light emitter. In this chapter, the devi

  19. Monolithic Integration of a Novel Microfluidic Device with Silicon Light Emitting Diode-Antifuse and Photodetector

    NARCIS (Netherlands)

    LeMinh, P.; Holleman, J.; Berenschot, J.W.; Tas, N.R.; Berg, van den A.

    2002-01-01

    Light emitting diode antifuse has been integrated into a microfluidic device that is realized with extended standard CMOS technological steps. The device comprises of a microchannel sandwiched between a photodiode detector and a nanometer-scale diode antifuse light emitter. Within this contribution,

  20. Novel recycle technology for recovering rare metals (Ga, In) from waste light-emitting diodes.

    Science.gov (United States)

    Zhan, Lu; Xia, Fafa; Ye, Qiuyu; Xiang, Xishu; Xie, Bing

    2015-12-15

    This work develops a novel process of recycling rare metals (Ga, In) from waste light-emitting diodes using the combination of pyrolysis, physical disaggregation methods and vacuum metallurgy separation. Firstly, the pure chips containing InGaN/GaN are adopted to study the vacuum separation behavior of rare metals, which aims to provide the theoretical foundation for recycling gallium and indium from waste light-emitting diodes. In order to extract the rare-metal-rich particles from waste light-emitting diodes, pyrolysis and physical disaggregation methods (crushing, screening, grinding and secondly screening) are studied respectively, and the operating parameters are optimized. With low boiling points and high saturation vapor pressures under vacuum, gallium and indium are separated from rare-metal-rich particles by the process of evaporation and condensation. By reference to the separating parameters of pure chips, gallium and indium in waste light-emitting diodes are recycled with the recovery efficiencies of 93.48% and 95.67% under the conditions as follows: heating temperature of 1373 K, vacuum pressure of 0.01-0.1 Pa, and holding time of 60 min. There are no secondary hazardous materials generated in the whole processes. This work provides an efficient and environmentally friendly process for recycling rare metals from waste light-emitting diodes.

  1. High-Efficiency Light-Emitting Diodes of Organometal Halide Perovskite Amorphous Nanoparticles.

    Science.gov (United States)

    Xing, Jun; Yan, Fei; Zhao, Yawen; Chen, Shi; Yu, Huakang; Zhang, Qing; Zeng, Rongguang; Demir, Hilmi Volkan; Sun, Xiaowei; Huan, Alfred; Xiong, Qihua

    2016-07-26

    Organometal halide perovskite has recently emerged as a very promising family of materials with augmented performance in electronic and optoelectronic applications including photovoltaic devices, photodetectors, and light-emitting diodes. Herein, we propose and demonstrate facile solution synthesis of a series of colloidal organometal halide perovskite CH3NH3PbX3 (X = halides) nanoparticles with amorphous structure, which exhibit high quantum yield and tunable emission from ultraviolet to near-infrared. The growth mechanism and photoluminescence properties of the perovskite amorphous nanoparticles were studied in detail. A high-efficiency green-light-emitting diode based on amorphous CH3NH3PbBr3 nanoparticles was demonstrated. The perovskite amorphous nanoparticle-based light-emitting diode shows a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W, and an external quantum efficiency of 3.8%, which is 3.5 times higher than that of the best colloidal perovskite quantum-dot-based light-emitting diodes previously reported. Our findings indicate the great potential of colloidal perovskite amorphous nanoparticles in light-emitting devices.

  2. Silicon light-emitting diodes and lasers photon breeding devices using dressed photons

    CERN Document Server

    Ohtsu, Motoichi

    2016-01-01

    This book focuses on a novel phenomenon named photon breeding. It is applied to realizing light-emitting diodes and lasers made of indirect-transition-type silicon bulk crystals in which the light-emission principle is based on dressed photons. After presenting physical pictures of dressed photons and dressed-photon phonons, the principle of light emission by using dressed-photon phonons is reviewed. A novel phenomenon named photon breeding is also reviewed. Next, the fabrication and operation of light emitting diodes and lasers are described The role of coherent phonons in these devices is discussed. Finally, light-emitting diodes using other relevant crystals are described and other relevant devices are also reviewed.

  3. Enhanced Light Extraction from a GaN-based Light Emitting Diode with Triangle Grating Structure

    Directory of Open Access Journals (Sweden)

    Li Cheng

    2013-05-01

    Full Text Available We propose a simple method to improve the light extraction in GaN based light emitting diode. Conventional light emitting diode has an extraction limitation due to the total internal reflection which occurs at the interface between GaN and air. By using periodic grating etched at the GaN layer, we can couple more emitting light out of the active layer. Tapering the grating structure would facilitate the impedance matching between GaN light emitting diode and air, which can enhance broadband light extraction. We use finite difference time domain method to numerically find the best tapering grating structure. The numerical experiment demonstrate an enhance factor 4 of our proposed structure compared with the conventional one over broad band specctrum.

  4. A device of comparison of light-emitting diodes for a light stream.

    Directory of Open Access Journals (Sweden)

    G. A. Mirskikh

    2011-03-01

    Full Text Available The simple method of comparison of light-emitting diodes after a light stream and possible construction of setting of this method are presented in this article. Parabolic mirrors are specially entered in a construction, as directing concentrators of light stream, and vibromotor with automatic control. Near one focus of mirrors set a light-emitting diode which is envisaged on a vibromotor, and on an opposite mirror in focus fasten fotodetector. After including to the vibromotor, by oscillation vibrations a light-emitting diode in one of moments is combined with focus of parabolic mirror. Whereupon, a light stream is directed by a parabolic mirror on opposite and gathers in focus last, where and registered by fotodetector. The entered vibration imitates the frequent measuring of stream that saves time on realization of measuring.

  5. Phototoxic action of light emitting diode in the in vitro viability of Trichophyton rubrum.

    Science.gov (United States)

    Amorim, José Cláudio Faria; Soares, Betania Maria; Alves, Orley Araújo; Ferreira, Marcus Vinícius Lucas; Sousa, Gerdal Roberto; Silveira, Lívio de Barros; Piancastelli, André Costa Cruz; Pinotti, Marcos

    2012-01-01

    Trichophyton rubrum is the most common agent of superficial mycosis of the skin and nails causing long lasting infections and high recurrence rates. Current treatment drawbacks involve topical medications not being able to reach the nail bed at therapeutic concentrations, systemic antifungal drugs failing to eradicate the fungus before the nails are renewed, severe side effects and selection of resistant fungal isolates. Photodynamic therapy (PDT) has been a promising alternative to conventional treatments. This study evaluated the in vitro effectiveness of toluidine blue O (TBO) irradiated by Light emitting diode (LED) in the reduction of T. rubrum viability. The fungal inoculums' was prepared and exposed to different TBO concentrations and energy densities of Light emitting diode for evaluate the T. rubrum sensibility to PDT and production effect fungicidal after photodynamic treatment. In addition, the profiles of the area and volume of the irradiated fungal suspensions were also investigated. A small reduction, in vitro, of fungal cells was observed after exposition to 100 µM toluidine blue O irradiated by 18 J/cm² Light emitting diode. Fungicidal effect occurred after 25 µM toluidine blue O irradiation by Light emitting diode with energy density of 72 J/cm². The analysis showed that the area and volume irradiated by the Light emitting diode were 52.2 mm² and 413.70 mm³, respectively. The results allowed to conclude that Photodynamic therapy using Light emitting diode under these experimental conditions is a possible alternative approach to inhibit in vitro T. rubrum and may be a promising new treatment for dermatophytosis caused by this fungus.

  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. Investigations of thin p-GaN light-emitting diodes

    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....

  8. Emission properties of an organic light-emitting diode patterned by a photoinduced autostructuration process

    Science.gov (United States)

    Hubert, C.; Fiorini-Debuisschert, C.; Hassiaoui, I.; Rocha, L.; Raimond, P.; Nunzi, J.-M.

    2005-11-01

    The photoluminescence properties of a periodically structured organic light-emitting diode are presented. Patterning is achieved using an original single-step autostructuration technique based on photoinduced effects in azo-polymer films. We show that single beam laser irradiation can lead to the induction of regular two-dimensional surface relief gratings. The waveguide properties of these microstructures as well as their effect on the emission properties of a light-emitting material are studied. We demonstrate a new straightforward technique to improve external light emission efficiency by outcoupling part of the light that was initially guided into the different diode layers.

  9. Inkjet printing the three organic functional layers of two-colored organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Coenen, Michiel J.J., E-mail: Michiel.Coenen@tmc.nl [Holst Centre, PO BOX 8550, 5605 KN Eindhoven (Netherlands); Slaats, Thijs M.W.L.; Eggenhuisen, Tamara M. [Holst Centre, PO BOX 8550, 5605 KN Eindhoven (Netherlands); Groen, Pim [Holst Centre, PO BOX 8550, 5605 KN Eindhoven (Netherlands); Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629HS Delft (Netherlands)

    2015-05-29

    Inkjet printing allows for the roll-2-roll fabrication of organic electronic devices at an industrial scale. In this paper we demonstrate the fabrication of two-colored organic light emitting diodes (OLEDs) in which three adjacent organic device layers were inkjet printed from halogen free inks. The resulting devices demonstrate the possibilities offered by this technique for the fabrication of OLEDs for signage and personalized electronics. - Highlights: • Two-colored organic light emitting diodes with 3 inkjet printed device layers were fabricated. • All materials were printed from halogen free inks. • Inkjet printing of emissive materials is suitable for signage applications.

  10. 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....

  11. Performance of GaN-on-Si-based vertical light-emitting diodes using silicon nitride electrodes with conducting filaments: correlation between filament density and device reliability.

    Science.gov (United States)

    Kim, Kyeong Heon; Kim, Su Jin; Lee, Tae Ho; Lee, Byeong Ryong; Kim, Tae Geun

    2016-08-08

    Transparent conductive electrodes with good conductivity and optical transmittance are an essential element for highly efficient light-emitting diodes. However, conventional indium tin oxide and its alternative transparent conductive electrodes have some trouble with a trade-off between electrical conductivity and optical transmittance, thus limiting their practical applications. Here, we present silicon nitride transparent conductive electrodes with conducting filaments embedded using the electrical breakdown process and investigate the dependence of the conducting filament density formed in the transparent conductive electrode on the device performance of gallium nitride-based vertical light-emitting diodes. Three gallium nitride-on-silicon-based vertical light-emitting diodes using silicon nitride transparent conductive electrodes with high, medium, and low conducting filament densities were prepared with a reference vertical light-emitting diode using metal electrodes. This was carried to determine the optimal density of the conducting filaments in the proposed silicon nitride transparent conductive electrodes. In comparison, the vertical light-emitting diodes with a medium conducting filament density exhibited the lowest optical loss, direct ohmic behavior, and the best current injection and distribution over the entire n-type gallium nitride surface, leading to highly reliable light-emitting diode performance.

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

    Energy Technology Data Exchange (ETDEWEB)

    David P. Norton; Stephen Pearton; Fan Ren

    2007-09-30

    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

  13. Reduction of Concentration Quenching in a Nondoped DCM Organic Light-Emitting Diode

    Institute of Scientific and Technical Information of China (English)

    LIU Zhen-Gang; CHEN Zhi-Jian; GONG Qi-Huang

    2005-01-01

    @@ We obtain a nondoped red organic light-emitting diode (OLED) structure ITO/pc-PPV (~30 nm)/DCM (~30 nm)/BCP (~30nm)/Mg:Ag, where DCM refers to 4-(dicyanomethylene)-2-methyl-6-[(4-dimethylaninostyryl)-4-H-pyran]. The OLED shows pure and stable red luminescence depending on the driving voltages. The maximum luminance is 330 Cd/m2 and the turn-on voltage is as low as ~2 V. The reason why the concentration quenching of DCM could be reduced in this structure is investigated. In the preparation process, both the hole-transporting layer and the emitter layer are formed by the spin-coated method. It is believed that this method can lead to a new way to avoid the concentration quenching of red-emitting materials.

  14. 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.

  15. 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.

  16. 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...

  17. Nd:YAG solid-state ring laser pumped by a light-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Belozerov, S.A.; Kornienko, L.S.; Kravtsov, N.V.; Kuratev, I.I.; Rusakov, S.I.; Stel' makh, M.F.; Shelaev, A.A.; Shelaev, A.I.

    1984-01-01

    This letter reports lasing in an Nd:YAG solid-state laser (lambda = 1.06 ..mu..m) pumped either in pulses or continuously by a light-emitting diode. We report the first experimental results on this laser.(AIP)

  18. 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…

  19. 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...

  20. 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

  1. Light-emitting diodes based on polythiophene : Influence of the metal workfunction on rectification properties

    NARCIS (Netherlands)

    Garten, F; Vrijmoeth, J; Schlatmann, AR; Gill, RE; Klapwijk, TM; Hadziioannou, G

    1996-01-01

    Light emission and current-voltage characteristics of conjugated polymer poly(3-octylthiophene) (P3OT) light-emitting diodes (LEDs) are discussed for two types of top electrodes. On changing the workfunction of the top contact by 0.9 eV from 4.3 (Al) to 5.2 eV (Au) we find that the main direction of

  2. Hole-enhanced electron injection from ZnO in inverted polymer light-emitting diodes

    NARCIS (Netherlands)

    Lu, Mingtao; de Bruyn, Paul; Nicolai, Herman T.; Wetzelaer, Gert-Jan A. H.; Blom, Paul W. M.

    Metal oxides as ZnO provide an interesting alternative for conventional low work function metals as electron injection layer in organic light-emitting diodes (OLEDs). However, for most state-of-the-art OLED materials the high work function of ZnO leads to a large injection barrier for electrons. As

  3. 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.

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

    DEFF Research Database (Denmark)

    Thorseth, Anders

    2012-01-01

    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...... boundaries mapping the capabilities of the simulated lighting system....

  5. Patterning of Flexible Organic Light Emitting Diode (FOLED) stack using an ultrafast laser

    NARCIS (Netherlands)

    Mandamparambil, R.; Fledderus, H.; Steenberge, G.V.; Dietzel, A.H.

    2010-01-01

    A femtosecond laser has been successfully utilized for patterning thin Flexible Organic Light Emitting Diode (FOLED) structures of individual layer thickness around 100nm. The authors report in this paper a step-like ablation behavior at the layer interfaces which accounts for a local removal of ent

  6. Determination of the trap-assisted recombination strength in polymer light emitting diodes

    NARCIS (Netherlands)

    Kuik, M.; Nicolai, H.T.; Lenes, M.; Wetzelaer, G.-J.A.H.; Lu, M.; Blom, P.W.M.

    2011-01-01

    The recombination processes in poly(p -phenylene vinylene) based polymer light-emitting diodes (PLEDs) are investigated. Photogenerated current measurements on PLED device structures reveal that next to the known Langevin recombination also trap-assisted recombination is an important recombination c

  7. Hole transport in polymeric field-effect transistors and light-emitting diodes

    NARCIS (Netherlands)

    Tanase, C; Blom, PWM; Meijer, EJ; de Leeuw, DM; Dimitrakopoulos, CD; Dodabalapur, A

    2003-01-01

    The hole transport in the amorphous poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (OC1C10-PPV) and in the more ordered poly[2,5-bis(3',7'-dimethyloctyloxy)-p-phenylene vinylene] (OC10C10-PPV) has been investigated both in field-effect transistors (FETs) and light-emitting diodes (L

  8. Polymer solar cells and infrared light emitting diodes : Dual function low bandgap polymer

    NARCIS (Netherlands)

    Winder, C.; Mühlbacher, D.; Neugebauer, H.; Sariciftci, N.S.; Brabec, C.J.; Janssen, R.A.J.; Hummelen, J.C.

    2002-01-01

    Conjugated Polymers with a HOMO-LUMO transition <2eV, i.e. a low bandgap, respectively, have interesting and desired properties for some thin film optoelectronic devices like light emitting diodes and solar cells. In this contribution we present the implementation of the novel copolymer PTPTB,

  9. Polymer solar cells and infrared light emitting diodes : Dual function low bandgap polymer

    NARCIS (Netherlands)

    Winder, C.; Mühlbacher, D.; Neugebauer, H.; Sariciftci, N.S.; Brabec, C.J.; Janssen, R.A.J.; Hummelen, J.C.

    2002-01-01

    Conjugated Polymers with a HOMO-LUMO transition <2eV, i.e. a low bandgap, respectively, have interesting and desired properties for some thin film optoelectronic devices like light emitting diodes and solar cells. In this contribution we present the implementation of the novel copolymer PTPTB, consi

  10. Patterning of Flexible Organic Light Emitting Diode (FOLED) stack using an ultrafast laser

    NARCIS (Netherlands)

    Mandamparambil, R.; Fledderus, H.; Steenberge, G.V.; Dietzel, A.H.

    2010-01-01

    A femtosecond laser has been successfully utilized for patterning thin Flexible Organic Light Emitting Diode (FOLED) structures of individual layer thickness around 100nm. The authors report in this paper a step-like ablation behavior at the layer interfaces which accounts for a local removal of ent

  11. 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.

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

    Science.gov (United States)

    Sun, Liangfeng; Choi, Joshua J; Stachnik, David; Bartnik, Adam C; Hyun, Byung-Ryool; Malliaras, George G; Hanrath, Tobias; Wise, Frank W

    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.

  13. Response of adult mosquitoes to light emitting diodes placed in resting boxes and in the field.

    Science.gov (United States)

    Resting boxes are passive devices used to attract and capture mosquitoes seeking shelter. Increasing the attractiveness of these devices could improve their effectiveness. Light emitting diodes (LEDs) can be attractive to mosquitoes when used together with other trapping devices. Therefore restin...

  14. 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…

  15. 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

  16. Patterning of Flexible Organic Light Emitting Diode (FOLED) stack using an ultrafast laser

    NARCIS (Netherlands)

    Mandamparambil, R.; Fledderus, H.; Steenberge, G.V.; Dietzel, A.H.

    2010-01-01

    A femtosecond laser has been successfully utilized for patterning thin Flexible Organic Light Emitting Diode (FOLED) structures of individual layer thickness around 100nm. The authors report in this paper a step-like ablation behavior at the layer interfaces which accounts for a local removal of

  17. Modeling Ultraviolet (UV) Light Emitting Diode (LED) Energy Propagation in Reactor Vessels

    Science.gov (United States)

    2014-03-27

    urban wastewater effluent than a single wavelength used alone (Chevremont, Farnet, Coulomb, & Boudenne, 2012; Oguma, Kita, Sakai, Murakami ...j.jcrysgro.2004.04.071 Oguma, K., Kita, R., Sakai, H., Murakami , M., & Takizawa, S. (2013). Application of UV light emitting diodes to batch and flow

  18. InP/ZnS nanocrystals for colour conversion in white light emitting diodes

    DEFF Research Database (Denmark)

    Shirazi, Roza

    In this work a comprehensive study of a colloidal InP/ZnS nanocrystals (NC) as the colour conversion material for white light emitting diodes (WLED) is shown. Studied nanocrystals were synthesised by wet chemistry using one pot, hot injection method. A quantum efficiency (QE) of photoluminescence...

  19. 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

  20. 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

  1. 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…

  2. Indium contamination from the indium-tin-oxide electrode in polymer light-emitting diodes

    NARCIS (Netherlands)

    Schlatmann, A.R.; Floet, D.W.; Hilberer, A; Garten, F; Smulders, P.J M; Klapwijk, T.M; Hadziioannou, G

    1996-01-01

    We have found that polymer light-emitting diodes (LEDs) contain high concentrations of metal impurities prior to operation. Narrow peaks in the electroluminescence spectrum unambiguously demonstrate the presence of atomic indium and aluminum. Rutherford backscattering spectroscopy (RBS) and x-ray ph

  3. 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…

  4. 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

  5. Hole-enhanced electron injection from ZnO in inverted polymer light-emitting diodes

    NARCIS (Netherlands)

    Lu, Mingtao; de Bruyn, Paul; Nicolai, Herman T.; Wetzelaer, Gert-Jan A. H.; Blom, Paul W. M.

    2012-01-01

    Metal oxides as ZnO provide an interesting alternative for conventional low work function metals as electron injection layer in organic light-emitting diodes (OLEDs). However, for most state-of-the-art OLED materials the high work function of ZnO leads to a large injection barrier for electrons. As

  6. 77 FR 45377 - Certain Light-Emitting Diodes and Products Containing the Same; Notice of Request for Statements...

    Science.gov (United States)

    2012-07-31

    ... COMMISSION Certain Light-Emitting Diodes and Products Containing the Same; Notice of Request for Statements... limited exclusion order (``LEO'') against light-emitting diodes (``LEDs'') found to infringe claims 1, 3... attachments, concerning the public interest in light of the administrative law judge's Recommended...

  7. 77 FR 807 - Certain Light-Emitting Diodes and Products Containing the Same; Determination Not To Review...

    Science.gov (United States)

    2012-01-06

    ... COMMISSION Certain Light-Emitting Diodes and Products Containing the Same; Determination Not To Review... importation, sale for importation, and sale within the United States after importation of certain light-emitting diodes and products containing same by ] reason of infringement of certain claims of U.S. Patent...

  8. 76 FR 77552 - Certain Light-Emitting Diodes and Products Containing Same; Determination Not To Review an...

    Science.gov (United States)

    2011-12-13

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Certain Light-Emitting Diodes and Products Containing Same; Determination Not To Review an Initial... importation of certain light-emitting diodes and products containing same by reason of infringement of certain...

  9. 77 FR 56672 - Certain Light-Emitting Diodes and Products Containing the Same; Determination To Review a Final...

    Science.gov (United States)

    2012-09-13

    ... Light-Emitting Diodes and Products Containing the Same; Determination To Review a Final Initial... importation of certain light-emitting diodes and products containing same by reason of infringement of certain... Office (see RX-118) and USPTO (see RX-10002), show that JP 609 teaches a ``partial conversion'' of light...

  10. 77 FR 75446 - Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant...

    Science.gov (United States)

    2012-12-20

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant... importation of certain light-emitting diodes and products containing same by reason of infringement of certain...

  11. 76 FR 60082 - In the Matter of Certain Light-Emitting Diodes and Products Containing Same; Notice of Commission...

    Science.gov (United States)

    2011-09-28

    ... investigation on July 11, 2011, based on a complaint filed by OSRAM GmbH of Munich, Germany. 76 FR 40745 (Jul... COMMISSION In the Matter of Certain Light-Emitting Diodes and Products Containing Same; Notice of Commission... within the United States after importation of certain light-emitting diodes and products containing...

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

    Science.gov (United States)

    2015-03-26

    used as a surrogate organic compound . Low pressure Mercury -based lamps currently used in the treatment of water pose potential health risks if...emitted diode (UV LED). Tartrazine was used as a surrogate organic compound . Low pressure Mercury -based lamps currently used in the treatment of...and longer operating life compared to the mercury -based lamps. The apparent first order reaction rate constant for tartrazine degradation

  13. Phosphor-free polychromatic emission InGaN light-emitting diode

    OpenAIRE

    Feng, Cong; 冯聪

    2016-01-01

    Broadband white light is indispensable for applications involving general illumination and displaying, a task conventionally fulfilled by fluorescent light sources. Light-emitting diodes (LEDs) based on the Group-III nitrides have been taking over that role in recent years, despite the fact that LEDs are inherently monochromatic sources with spectral line-widths in the range of 20 to 50nm. The most adopted industrial solution is to shift part of the light emitted by a blue InGaN chip into lon...

  14. High-Efficiency Saturated Red Bilayer Light-Emitting Diodes: Comparative Studies with Devices from Blend of the Same Light-Emitting Polymers

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong; HOU Qiong; MO Yue-Qi; PENG Jun-Biao; CAO Yong

    2006-01-01

    @@ High-efficient saturated red light-emitting diodes are realized based on a bilayer of phenyl-substituted poly [p-phenylene vinylene] derivative (P-PPV) and copolymer (PFO-DBT15) of 9,9-dioctylfluorene (DOF) and 4,7-di2-thienyl-2,1,3-benzothiadiazole (DBT).

  15. Synthesis and optical properties of cadmium selenide quantum dots for white light-emitting diode application

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Xianmei; Wang, Yilin; Gule, Teri; Luo, Qiang [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China); Zhou, Liya, E-mail: zhouliyatf@163.com [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China); Gong, Fuzhong [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China)

    2013-03-15

    Highlights: ► Stable CdSe QDs were synthesized by the one-step and two-level process respectively. ► The fabricated white LEDs show good white balance. ► CdSe QDs present well green to yellow band luminescence. ► CdSe QDs displayed a broad excitation band. - Abstract: Yellow light-emitting cadmium selenide quantum dots were synthesized using one-step and two-step methods in an aqueous medium. The structural luminescent properties of these quantum dots were investigated. The obtained cadmium selenide quantum dots displayed a broad excitation band suitable for blue or near-ultraviolet light-emitting diode applications. White light-emitting diodes were fabricated by coating the cadmium selenide samples onto a 460 nm-emitting indium gallium nitrite chip. Both samples exhibited good white balance. Under a 20 mA working current, the white light-emitting diode fabricated via the one-step and two-step methods showed Commission Internationale de l’Éclairage coordinates at (0.27, 0.23) and (0.27, 0.33), respectively, and a color rendering index equal to 41 and 37, respectively. The one-step approach was simpler, greener, and more effective than the two-step approach. The one-step approach can be enhanced by combining cadmium selenide quantum dots with proper phosphors.

  16. Role of electron blocking layer in III-nitride laser diodes and light-emitting diodes

    Science.gov (United States)

    Kuo, Yen-Kuang; Chang, Jih-Yuan; Chen, Mei-Ling

    2010-02-01

    A high energy bandgap electron blocking layer (EBL) just behind the active region is conventionally used in the nitride-based laser diodes (LDs) and light-emitting diodes (LEDs) to improve the confinement capability of electrons within the quantum wells. Nevertheless, the EBL may also act as a potential barrier for the holes and cause non-uniform distribution of holes among quantum wells. A most recent study by Han et al. (Appl. Phys. Lett. 94, 231123, 2009) reported that, because of the blocking effect for holes, the InGaN LED device without an EBL has slighter efficiency droop and higher light output at high level of current injection when compared with the LED device with an EBL. This result seems to contradict with the original intention of using the EBL. Furthermore, findings from our previous studies (IEEE J. Lightwave Technol. 26, 329, 2008; J. Appl. Phys. 103, 103115, 2008; Appl. Phys. Lett. 91, 201118, 2007) indicated that the utilization of EBL is essential for the InGaN laser diodes. Thus, in this work, the optical properties of the InGaN LDs and LEDs are explored numerically with the LASTIP simulation program and APSYS simulation program, respectively. The analyses focus particularly on the light output power, energy band diagrams, recombination rates, distribution of electrons and holes in the active region, and electron overflow. This study will then conclude with a discussion of the effect of EBL on the optical properties of the InGaN LDs and LEDs.

  17. 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.

  18. 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.

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

    Science.gov (United States)

    Young, Erin C.; Yonkee, Benjamin P.; Wu, Feng; Oh, Sang Ho; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.

    2016-02-01

    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.

  20. 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.

  1. CoPt ferromagnetic injector in light-emitting Schottky diodes based on InGaAs/GaAs nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Zdoroveyshchev, A. V., E-mail: zdorovei@gmail.com; Dorokhin, M. V.; Demina, P. B. [Lobachevsky State University of Nizhny Novgorod, Physical–Technical Research Institute (Russian Federation); Kudrin, A. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Vikhrova, O. V. [Lobachevsky State University of Nizhny Novgorod, Physical–Technical Research Institute (Russian Federation); Ved’, M. V.; Danilov, Yu. A. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Erofeeva, I. V. [Lobachevsky State University of Nizhny Novgorod, Physical–Technical Research Institute (Russian Federation); Krjukov, R. N.; Nikolichev, D. E. [Lobachevsky State University of Nizhny Novgorod (Russian Federation)

    2015-12-15

    The possibility of fabricating a ferromagnetic injector based on a near-equiatomic CoPt alloy with pronounced perpendicular magnetization anisotropy in the InGaAs/GaAs spin light-emitting diode is shown. The physical properties of experimental spin light-emitting diode prototypes are comprehensively studied. Circularly polarized electroluminescence of fabricated diodes is obtained in zero magnetic field due to the remanent magnetization of CoPt layers.

  2. Organic light emitting diode with light extracting layer

    Science.gov (United States)

    Lu, Songwei

    2016-06-14

    A light extraction substrate includes a glass substrate having a first surface and a second surface. A light extraction layer is formed on at least one of the surfaces. The light extraction layer is a coating, such as a silicon-containing coating, incorporating nanoparticles.

  3. 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......In multilayer white organic light-emitting diodes the electronic processes in the various layers--injection and motion of charges as well as generation, diffusion and radiative decay of excitons--should be concerted such that efficient, stable and colour-balanced electroluminescence can occur. Here...... are shown to agree well with experiment. The experimental emission profile was obtained with nanometre resolution from the measured angle- and polarization-dependent emission spectra. The simulations elucidate the crucial role of exciton transfer from green to red and the efficiency loss due to excitons...

  4. Electrical and optical measurements of the bandgap energy of a light-emitting diode

    Science.gov (United States)

    Petit, Matthieu; Michez, Lisa; Raimundo, Jean-Manuel; Dumas, Philippe

    2016-03-01

    Semiconductor materials are at the core of electronics. Most electronic devices are made of semiconductors. The operation of these components is well described by quantum physics which is often a difficult concept for students to understand. One of the intrinsic parameters of semiconductors is their bandgap energy {{E}\\text{g}} . In the case of light-emitting diodes (LEDs) {{E}\\text{g}} fixes the colour of the light emitted by the diodes. In this article we propose an experiment to compare {{E}\\text{g}} of a green LED obtained by both electrical and optical measurements. The two slightly different results can be explained by the theoretical knowledge of students on solid physics and the internal structure of electronic devices.

  5. 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.

  6. High luminous efficacy green light-emitting diodes with AlGaN cap layer.

    Science.gov (United States)

    Alhassan, Abdullah I; Farrell, Robert M; Saifaddin, Burhan; Mughal, Asad; Wu, Feng; DenBaars, Steven P; Nakamura, Shuji; Speck, James S

    2016-08-01

    We demonstrate very high luminous efficacy green light-emitting diodes employing Al0.30Ga0.70N cap layer grown on patterned sapphire substrates by metal organic chemical vapor deposition. The peak external quantum efficiency and luminous efficacies were 44.3% and 239 lm/w, respectively. At 20 mA (20 A/cm2) the light output power was 14.3 mW, the forward voltage was 3.5 V, the emission wavelength was 526.6 nm, and the external quantum efficiency was 30.2%. These results are among the highest reported luminous efficacy values for InGaN based green light-emitting diodes.

  7. Multifunctional graphene sheets embedded in silicone encapsulant for superior performance of light-emitting diodes.

    Science.gov (United States)

    Lee, Seungae; Hong, Jin-Yong; Jang, Jyongsik

    2013-07-23

    Graphene nanosheets with uniform shape are successfully incorporated into a silicone encapsulant of a light-emitting diode (LED) using a solvent-exchange approach which is a facile and straightforward method. The graphene nanosheets embedded in the silicone encapsulant have a multifunctional role which improves the performance of light-emitting diodes. The presence of graphene gives rise to effective heat dissipation, improvement of protection ability from external stimuli, such as moisture and hazardous gas, and enhancement of mechanical properties such as elastic modulus and fracture toughness. Consequently, the LEDs composed of a graphene-embedded silicone encapsulant exhibit long-term stability without loss of luminous efficiency by addition of relatively small amounts of graphene. This novel strategy offers a feasible candidate for their practical or industrial applications.

  8. High-quality distributed Bragg reflectors for resonant-cavity light-emitting diode applications

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez, S.; Naranjo, F.B.; Calle, F.; Sanchez-Garcia, M.A.; Calleja, E. [ISOM, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Vennegues, P. [CHREA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France)

    2002-08-16

    Efficient distributed Bragg reflectors based on Al{sub x}Ga{sub 1} {sub -} {sub x}N/GaN multilayer stacks have been grown by plasma-assisted molecular-beam epitaxy on GaN/Al{sub 2}O{sub 3} templates. The final goal is to incorporate these reflectors as bottom mirrors in a backside (sapphire) resonant-cavity light-emitting diode at 510 nm. The reflectors have been characterised by atomic force microscopy, high-resolution X-ray diffraction and high-resolution transmission electron microscopy. Reflectivity measurements have also been performed, obtaining values between 30% and 50%, depending on the Al content used. The incorporation of the Al{sub x}Ga{sub 1} {sub -} {sub x}N/GaN Bragg reflector as bottom mirror in a RCLED structure improves the output power by a factor of 12 compared with conventional light-emitting diodes. (Abstract Copyright[2002], Wiley Periodicals, Inc.)

  9. Ultraviolet Photodissociation Induced by Light-Emitting Diodes in a Planar Ion Trap.

    Science.gov (United States)

    Holden, Dustin D; Makarov, Alexander; Schwartz, Jae C; Sanders, James D; Zhuk, Eugene; Brodbelt, Jennifer S

    2016-09-26

    The first application of light-emitting diodes (LEDs) for ultraviolet photodissociation (UVPD) mass spectrometry is reported. LEDs provide a compact, low cost light source and have been incorporated directly into the trapping cell of an Orbitrap mass spectrometer. MS/MS efficiencies of over 50 % were obtained using an extended irradiation period, and UVPD was optimized by modulating the ion trapping parameters to maximize the overlap between the ion cloud and the irradiation volume.

  10. Near-infrared organic light-emitting diodes for biosensing with high operating stability

    Science.gov (United States)

    Yamanaka, Takahiko; Nakanotani, Hajime; Hara, Shigeo; Hirohata, Toru; Adachi, Chihaya

    2017-07-01

    We demonstrate highly stable NIR organic light-emitting diodes (OLEDs) based on a system using excitonic energy transfer from thermally activated delay fluorescence molecules to NIR fluorophores. The NIR OLEDs showed an electroluminescence peak at 780 nm and robust operational stability with 2% loss of the initial radiant flux after 1000 h under a constant current density of 10 mA/cm2. The variation of hemoglobin oxygen saturation can be detected using the NIR OLEDs as a light source.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Highly Efficient Perovskite Nanocrystal Light-Emitting Diodes Enabled by a Universal Crosslinking Method.

    Science.gov (United States)

    Li, Guangru; Rivarola, Florencia Wisnivesky Rocca; Davis, Nathaniel J L K; Bai, Sai; Jellicoe, Tom C; de la Peña, Francisco; Hou, Shaocong; Ducati, Caterina; Gao, Feng; Friend, Richard H; Greenham, Neil C; Tan, Zhi-Kuang

    2016-05-01

    The preparation of highly efficient perovskite nanocrystal light-emitting diodes is shown. A new trimethylaluminum vapor-based crosslinking method to render the nanocrystal films insoluble is applied. The resulting near-complete nanocrystal film coverage, coupled with the natural confinement of injected charges within the perovskite crystals, facilitates electron-hole capture and give rise to a remarkable electroluminescence yield of 5.7%.

  13. Highly Efficient, Simplified, Solution-Processed Thermally Activated Delayed-Fluorescence Organic Light-Emitting Diodes.

    Science.gov (United States)

    Kim, Young-Hoon; Wolf, Christoph; Cho, Himchan; Jeong, Su-Hun; Lee, Tae-Woo

    2016-01-27

    Highly efficient, simplified, solution-processed thermally activated delayed-fluorescence organic light-emitting diodes can be realized by using pure-organic thermally activated delayed fluorescence emitters and a multifunctional buffer hole-injection layer, in which high EQE (≈24%) and current efficiency (≈73 cd A(-1) ) are demonstrated. High-efficiency fluorescence red-emitting and blue-emitting devices can also be fabricated in this manner.

  14. Bright Light-Emitting Diodes Based on Organometal Halide Perovskite Nanoplatelets.

    Science.gov (United States)

    Ling, Yichuan; Yuan, Zhao; Tian, Yu; Wang, Xi; Wang, Jamie C; Xin, Yan; Hanson, Kenneth; Ma, Biwu; Gao, Hanwei

    2016-01-13

    Bright light-emitting diodes based on solution-processable organometal halide perovskite nanoplatelets are demonstrated. The nanoplatelets created using a facile one-pot synthesis exhibit narrow-band emissions at 529 nm and quantum yield up to 85%. Using these nanoparticles as emitters, efficient electroluminescence is achieved with a brightness of 10 590 cd m(-2) . These ligand-capped nanoplatelets appear to be quite stable in moisture, allowing out-of-glovebox device fabrication.

  15. Enhancement of Stability of Polymer Light-Emitting Diodes by Post Annealing

    Institute of Scientific and Technical Information of China (English)

    YAO Bing; XIE Zhi-Yuan; YANG Jun-Wei; CHENG Yan-Xiang; WANG Li-Xiang

    2007-01-01

    We investigate the effect of thermal annealing before and after cathode deposition on the stability of polymer light-emitting diodes (PLEDs) based on green fluorescent polyfluorene derivative. The annealed PLEDs exhibit improved charge transport and red-shift emission compared to the as-fabricated device. The stability of the PLEDs is largely enhanced by post-annealing before and after Ca deposition, which is attributed to the enhanced charge transport and the intimate contact between the cathode and the emissive layer.

  16. 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.

  17. Dislocation related droop in InGaN/GaN light emitting diodes investigated via cathodoluminescence

    OpenAIRE

    Pozina, Galia; Ciechonski, Rafal; Bi, Zhaoxia; SAMUELSON, Lars; Monemar, Bo

    2015-01-01

    Todays energy saving solutions for general illumination rely on efficient white light emitting diodes (LEDs). However, the output efficiency droop experienced in InGaN based LEDs with increasing current injection is a serious limitation factor for future development of bright white LEDs. We show using cathodoluminescence (CL) spatial mapping at different electron beam currents that threading dislocations are active as nonradiative recombination centers only at high injection conditions. At lo...

  18. Confocal microscopic analysis of optical crosstalk from micro-pixel light-emitting diodes

    OpenAIRE

    2015-01-01

    Self-illuminating displays comprising two-dimensional arrays of micro-emitters are superior over conventional backlight-illuminated liquid-crystal displays (LCD) in many aspects, including lower power consumptions, thinner profiles, higher image contrasts, wider viewing angles, and broader operating temperatures. There still are several technical challenges prevent self-illuminating organic light-emitting diodes (OLEDs) from becoming a dominant commercial product in the field of image display...

  19. Influence of Energy Level Matching on Device Performances of Organic Light-emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    LIU Chen; ZOU Xue-cheng; YIN Sheng

    2004-01-01

    Through experiments and computer simulation, the influence of the energy levels of organic materials and electrode materials in the organic light-emitting diodes (OLEDs) on the device performances is discussed. Results show that the device performances are influenced by not only the carrier injection barriers at the electrode interface but also the barriers at the organic heterojunction interface. This result is helpful to the selection of the organic materials and their arrangement in the optimal design of OLEDs.

  20. Pulsed operation of high power light emitting diodes for flow velocimetry

    OpenAIRE

    Willert, Christian; Mößner, Steffen; Klinner, Joachim

    2009-01-01

    High powered light emitting diodes (LED) are investigated for possible uses as light sources in flow diagnostics, in particular, as an alternative to laser-based illumination in particle imaging flow velocimetry. Recent developments in solid state illumination resulted in mass-produced LEDs that provide average radiant power in excess of 10 Watt. By operating these LEDs with short duration, pulsed currents that are considerably beyond their continuous current damage th...

  1. Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

    OpenAIRE

    Willert, Christian; Stasicki, Boleslaw; Klinner, Joachim; Moessner, S.

    2010-01-01

    High-powered light emitting diodes (LED) are investigated for possible uses as light sources in flow diagnostics, in particular, as an alternative to laser-based illumination in particle imaging flow velocimetry in side-scatter imaging arrangements. Recent developments in solid state illumination resulted in mass-produced LEDs that provide average radiant power in excess of 10 W. By operating these LEDs with short duration, pulsed currents that are considerably beyond their continuous c...

  2. Super-Lattice Light Emitting Diodes (SLEDS) on GaAs

    Science.gov (United States)

    2016-03-31

    done using multiple techniques . Some of these techniques are thermocompression bonding , glass frit bonding , and adhesive bonding . It was decided to...method on predesigned GaAs RIIC that would drive the SLEDS. New developments showed that wafer bonding can be another succesful aproch to GSLEDS...infrared light emitting diodes (LEDs). Typically, the LED arrays are mated with CMOS read-in integrated circuit (RIIC) chips using flip-chip bonding . In

  3. Photo thermal efficacy of green light emitting diode and gold nano spheres for malignancy

    Science.gov (United States)

    Gananathan, Poorani; Prakasa Rao, Aruna; Ganesan, Singaravelu; Manickan, Elanchezhiyan

    2016-03-01

    The effect of 30nm Gold Nanoparticles (GNP) based on concentration and incubation time with respect to their cellular uptake kinetics was studied with Vero and HeLa cells . Photoirradiation effect of GNPs in combination with light emitting diode(LED) found to be remarkable and this work concentrates on optimizing concentration and light source. The effect of Gold nanoparticles alone and in combination with LED in malignant and normal cells lines were studied.

  4. 10 Mb/s visible light transmission system using a polymer light-emitting diode with orthogonal frequency division multiplexing.

    Science.gov (United States)

    Le, Son T; Kanesan, T; Bausi, F; Haigh, P A; Rajbhandari, S; Ghassemlooy, Z; Papakonstantinou, I; Popoola, W O; Burton, A; Le Minh, H; Cacialli, F; Ellis, A D

    2014-07-01

    We present a newly designed polymer light-emitting diode with a bandwidth of ~350  kHz for high-speed visible light communications. Using this new polymer light-emitting diode as a transmitter, we have achieved a record transmission speed of 10  Mb/s for a polymer light-emitting diode-based optical communication system with an orthogonal frequency division multiplexing technique, matching the performance of single carrier formats using multitap equalization. For achieving such a high data-rate, a power pre-emphasis technique was adopted.

  5. Light-emitting diode-generated red light inhibits keloid fibroblast proliferation.

    Science.gov (United States)

    Mamalis, Andrew; Jagdeo, Jared

    2015-01-01

    Red light is part of the visible light spectrum that does not generate DNA adducts associated with skin cancer and photoaging and may represent a safer therapeutic modality for treatment of keloid scars and other fibrotic skin diseases. Our laboratory previously demonstrated that light-emitting diode-generated red light (LED-RL) inhibits proliferation of skin fibroblasts. The effects of LED-RL on keloidal skin are not well characterized. To determine the effect of LED-RL on keloid-derived fibroblast proliferation and viability in vitro. Irradiation of primary keloid-derived human skin fibroblasts using LED-RL panels was performed in vitro, and modulation of proliferation and viability was quantified using trypan blue dye exclusion assay. Statistical analysis was performed using analysis of variance to compare treatment arms and the Student t-test to compare each treatment arm with the paired bench control arm. Keloid fibroblasts treated with LED-RL 240, 320, and 480 J/cm demonstrated statistically significant dose-dependent decreases in relative proliferation rate of 12.4%, 16.5%, and 28.9%, respectively, compared with matched nonirradiated controls (p Light-emitting diode-generated red light can inhibit keloid fibroblast proliferation in a dose-dependent manner without altering viability. Light-emitting diode-generated red light has the potential to contribute to the treatment of keloids and other fibrotic skin diseases and is worthy of further translational and clinical investigation.

  6. Structural Investigation of Cesium Lead Halide Perovskites for High-Efficiency Quantum Dot Light Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Van Le, Quyet; Beom Kim, Jong; Kim, Soo Young; Lee, Byeongdu; Lee, Dong Ryeol

    2017-08-16

    We have investigated the effect of reaction temperature of hot-injection method on the structural properties of CsPbX3 (X: Br, I, Cl) perovskite nanocrystals (NCs) using the small- and wide-angle X-ray scattering. It is confirmed that the size of the NCs decreased as the reaction temperature decreased, resulting stronger quantum confinement. The cubic-phase perovskite NCs were formed despite the reaction temperatures increased from 140 to 180 °C. However, monodispersive NC cubes which are required for densely packing self-assembly film were only formed at lower temperatures. From the X-ray scattering measurements, the spin-coated film from more monodispersive perovskite nanocubes synthesized at lower temperatures resulted in more preferred orientation. This dense-packing perovskite film with preferred orientation yielded efficient light-emitting diode (LED) performance. Thus, the dense-packing structure of NC assemblies formed after spin-coating should be considered for high-efficient LEDs based on perovskite quantum dots in addition to quantum confinement effect of the quantum dots.

  7. Selective-area growth of periodic nanopyramid light-emitting diode arrays on GaN/sapphire templates patterned by multiple-exposure colloidal lithography.

    Science.gov (United States)

    Xiong, Zhuo; Wei, Tongbo; Zhang, Yonghui; Zhang, Xiang; Yang, Chao; Liu, Zhiqiang; Yuan, Guodong; Li, Jinmin; Wang, Junxi

    2017-03-17

    Gallium nitride-based nanopyramid light-emitting diodes are a promising technology to achieve highly efficient solid-state lighting and beyond. Here, periodic nanopyramid light-emitting diode arrays on gallium nitride/sapphire templates were fabricated by selective-area metalorganic chemical vapor deposition and multiple-exposure colloidal lithography. The electric field intensity distribution of incident light going through polystyrene microspheres and photoresist are simulated using finite-different time-domain method. Nitrogen as the carrier gas and a low V/III ratio (ratio of molar flow rate of group-V to group-III sources) are found to be important in order to form gallium nitride nanopyramid. In addition, a broad yellow emission in photoluminescence and cathodoluminescence spectra were observed. This phenomena showed the potential of nanopyramid light-emitting diodes to realize long wavelength visible emissions.

  8. Selective-area growth of periodic nanopyramid light-emitting diode arrays on GaN/sapphire templates patterned by multiple-exposure colloidal lithography

    Science.gov (United States)

    Xiong, Zhuo; Wei, Tongbo; Zhang, Yonghui; Zhang, Xiang; Yang, Chao; Liu, Zhiqiang; Yuan, Guodong; Li, Jinmin; Wang, Junxi

    2017-03-01

    Gallium nitride-based nanopyramid light-emitting diodes are a promising technology to achieve highly efficient solid-state lighting and beyond. Here, periodic nanopyramid light-emitting diode arrays on gallium nitride/sapphire templates were fabricated by selective-area metalorganic chemical vapor deposition and multiple-exposure colloidal lithography. The electric field intensity distribution of incident light going through polystyrene microspheres and photoresist are simulated using finite-different time-domain method. Nitrogen as the carrier gas and a low V/III ratio (ratio of molar flow rate of group-V to group-III sources) are found to be important in order to form gallium nitride nanopyramid. In addition, a broad yellow emission in photoluminescence and cathodoluminescence spectra were observed. This phenomena showed the potential of nanopyramid light-emitting diodes to realize long wavelength visible emissions.

  9. Midinfrared InAsSbN/InAs Multiquantum Well Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    P. J. Carrington

    2011-01-01

    Full Text Available Electroluminescence is reported from dilute nitride InAsSbN/InAs multiquantum well light-emitting diodes grown using nitrogen plasma source molecular beam epitaxy. The diodes exhibited bright emission in the midinfrared peaking at 3.56 μm at room temperature. Emission occurred from a type I transition from electrons in the InAsSbN to confined heavy and light hole states in the QW. Analysis of the temperature- and current-dependent electroluminescence shows that thermally activated hole leakage and Auger recombination are the performance limiting factors in these devices.

  10. Temperature-dependent electroluminescence from GeSn heterojunction light-emitting diode on Si substrate

    Science.gov (United States)

    Chang, Chiao; Li, Hui; Huang, Ssu-Hsuan; Lin, Li-Chien; Cheng, Hung-Hsiang

    2016-04-01

    The electroluminescence from a Ge/GeSn/Ge p-i-n light-emitting diode on Si was investigated under different temperatures ranging from 25 to 150 K. The diode was operated at a low injection current density of 13 A/cm2. We obtained no-phonon- and phonon-assisted replicas in emission spectra. Also, the relationship between indirect bandgap energy and temperature was investigated. The temperature-dependent bandgap energy followed Varshni’s empirical expression with α = 4.884 × 10-4 eV/K and β = 130 K.

  11. Flexible Substrates with Polyimide Buffer Layers for Organic Light-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    常春; 王立铎; 李扬; 段炼; 邱勇

    2004-01-01

    We report a new method to enhance the properties of the polyethyleneterephthalate (PET) substrates for flexible organic light-emitting diodes (OLEDs). By spin-coating a polyimide (PI) film between the PET and the indiumtin-oxide anode, the flexible substrate with a smooth surface, high transmission over the visible spectrum and good adhesion are achieved. We also compare the flexible OLEDs on different substrates. The diodes on the substrates with polyimide buffer layers exhibit a brightness of 7280cd/m2 at 15 V and the maximum efficiency of 2.64 cd/A.

  12. Background story of the invention of efficient blue InGaN light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura, Shuji [University of California, Santa Barbara, CA (United States)

    2015-06-15

    Shuji Nakamura discovered p-type doping in Gallium Nitride (GaN) and developed blue, green, and white InGaN based light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid-state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize in Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. A Comparison Between Magnetic Field Effects in Excitonic and Exciplex Organic Light-Emitting Diodes

    Science.gov (United States)

    Sahin Tiras, Kevser; Wang, Yifei; Harmon, Nicholas J.; Wohlgenannt, Markus; Flatte, Michael E.

    In flat-panel displays and lighting applications, organic light emitting diodes (OLEDs) have been widely used because of their efficient light emission, low-cost manufacturing and flexibility. The electrons and holes injected from the anode and cathode, respectively, form a tightly bound exciton as they meet at a molecule in organic layer. Excitons occur as spin singlets or triplets and the ratio between singlet and triplet excitons formed is 1:3 based on spin degeneracy. The internal quantum efficiency (IQE) of fluorescent-based OLEDs is limited 25% because only singlet excitons contribute the light emission. To overcome this limitation, thermally activated delayed fluorescent (TADF) materials have been introduced in the field of OLEDs. The exchange splitting between the singlet and triplet states of two-component exciplex systems is comparable to the thermal energy in TADF materials, whereas it is usually much larger in excitons. Reverse intersystem crossing occurs from triplet to singlet exciplex state, and this improves the IQE. An applied small magnetic field can change the spin dynamics of recombination in TADF blends. In this study, magnetic field effects on both excitonic and exciplex OLEDs will be presented and comparison similarities and differences will be made.

  14. Preparation of organic light-emitting diode using coal tar pitch, a low-cost material, for printable devices

    National Research Council Canada - National Science Library

    Yamaoka, Miki; Asami, Shun-Suke; Funaki, Nayuta; Kimura, Sho; Yingjie, Liao; Fukuda, Takeshi; Yamashita, Makoto

    2013-01-01

    We have identified coal tar pitch, a very cheap organic material made from coal during the iron-making process, as a source from which could be obtained emissive molecules for organic light-emitting diodes...

  15. Wearable red-green-blue quantum dot light-emitting diode array using high-resolution intaglio transfer printing

    National Research Council Canada - National Science Library

    Choi, Moon Kee; Yang, Jiwoong; Kang, Kwanghun; Kim, Dong Chan; Choi, Changsoon; Park, Chaneui; Kim, Seok Joo; Chae, Sue In; Kim, Tae-Ho; Kim, Ji Hoon; Hyeon, Taeghwan; Kim, Dae-Hyeong

    2015-01-01

    Deformable full-colour light-emitting diodes with ultrafine pixels are essential for wearable electronics, which requires the conformal integration on curvilinear surface as well as retina-like high-definition displays...

  16. Large magnetic field effects in electrochemically doped organic light-emitting diodes

    Science.gov (United States)

    van Reenen, S.; Kersten, S. P.; Wouters, S. H. W.; Cox, M.; Janssen, P.; Koopmans, B.; Bobbert, P. A.; Kemerink, M.

    2013-09-01

    Large negative magnetoconductance (MC) of ˜12% is observed in electrochemically doped polymer light-emitting diodes at sub-band-gap bias voltages (Vbias). Simultaneously, a positive magnetoefficiency (Mη) of 9% is observed at Vbias = 2 V. At higher bias voltages, both the MC and Mη diminish while a negative magnetoelectroluminescence (MEL) appears. The negative MEL effect is rationalized by triplet-triplet annihilation that leads to delayed fluorescence, whereas the positive Mη effect is related to competition between spin mixing and exciton formation leading to an enhanced singlet:triplet ratio at nonzero magnetic field. The resultant reduction in triplet exciton density is argued to reduce detrapping of polarons in the recombination zone at low-bias voltages, explaining the observed negative MC. Regarding organic magnetoresistance, this study provides experimental data to verify existing models describing magnetic field effects in organic semiconductors, which contribute to better understanding hereof. Furthermore, we present indications of strong magnetic field effects related to interactions between trapped carriers and excitons, which specifically can be studied in electrochemically doped organic light-emitting diodes (OLEDs). Regarding light-emitting electrochemical cells (LECs), this work shows that delayed fluorescence from triplet-triplet annihilation substantially contributes to the electroluminescence and the device efficiency.

  17. Influence of Yellow Light-Emitting Diodes at 590 nm on Storage of Apple, Tomato and Bell Pepper Fruit

    OpenAIRE

    2016-01-01

    The objective of this study is to investigate the effects 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 ...

  18. Research data supporting "InGaAs spin light emitting diodes measured in the Faraday and oblique Hanle geometries"

    OpenAIRE

    Mansell, R; Laloë, J-B.; Holmes, S. N.; Petrou, A.; Farrer, I.; Jones, G. A. C.; Ritchie, D A; Barnes, C. H. W.

    2016-01-01

    Supporting data for 'InGaAs spin light emitting diodes measured in the Faraday and oblique Hanle geometries' published as JPhysD 49 165103 (2016). Contains underlying data for figures 1 and 3. This research data supports “InGaAs spin light emitting diodes measured in the Faraday and oblique Hanle geometries” which has been published in “Journal of Physics D: Applied Physics”. This work was supported by the EPSRC [grant number EPSRC DTA award].

  19. Realization of Red-Organic-Light Emitting Diode by Introducing the Double Emitting Zone

    Institute of Scientific and Technical Information of China (English)

    姜文龙; 侯晶莹; 赵毅; 刘式墉

    2003-01-01

    A saturated red-organic-light emitting diode (OLED) has been realized by doping an emitting material both in the hole-transporting layer (HTL) and the electron-transporting layer (ETL) to form double emitting zone. The red dopant, 4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyraan (DCJTB), was doped into the N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) layer and the tris (8-quinolinolate)aluminium (Alq3) layer, both of which act as the emitting layers. The optimal device, with a structure of ITO/CuPc/NPB/NPB:DCJTB/Alqa:DCJTB/Alqa/LiF/Al, showed good chromaticity coordinates (x = 0.63,y = 0.36) at 8 V. Uniquely, the current efficiency of the device was relatively independent of the drive voltage in a wide range from 8 V to 20 V. That may be helpful to ameliorate the lifetime of the organic electroluminescent devices and to adjust the grey-scale for the future full-colour display panel.

  20. Perovskite light-emitting diodes based on solution-processed self-organized multiple quantum wells

    Science.gov (United States)

    Wang, Nana; Cheng, Lu; Ge, Rui; Zhang, Shuting; Miao, Yanfeng; Zou, Wei; Yi, Chang; Sun, Yan; Cao, Yu; Yang, Rong; Wei, Yingqiang; Guo, Qiang; Ke, You; Yu, Maotao; Jin, Yizheng; Liu, Yang; Ding, Qingqing; di, Dawei; Yang, Le; Xing, Guichuan; Tian, He; Jin, Chuanhong; Gao, Feng; Friend, Richard H.; Wang, Jianpu; Huang, Wei

    2016-11-01

    Organometal halide perovskites can be processed from solutions at low temperatures to form crystalline direct-bandgap semiconductors with promising optoelectronic properties. However, the efficiency of their electroluminescence is limited by non-radiative recombination, which is associated with defects and leakage current due to incomplete surface coverage. Here we demonstrate a solution-processed perovskite light-emitting diode (LED) based on self-organized multiple quantum wells (MQWs) with excellent film morphologies. The MQW-based LED exhibits a very high external quantum efficiency of up to 11.7%, good stability and exceptional high-power performance with an energy conversion efficiency of 5.5% at a current density of 100 mA cm-2. This outstanding performance arises because the lower bandgap regions that generate electroluminescence are effectively confined by perovskite MQWs with higher energy gaps, resulting in very efficient radiative decay. Surprisingly, there is no evidence that the large interfacial areas between different bandgap regions cause luminescence quenching.

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

    Science.gov (United States)

    Zhu, Peifen

    2016-02-01

    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 TiO2 sphere in 0.30 μm PS layer with optimized in-coupling efficiency, out-coupling efficiency and cavity effect.

  2. Efficient perovskite light-emitting diodes featuring nanometre-sized crystallites

    Science.gov (United States)

    Xiao, Zhengguo; Kerner, Ross A.; Zhao, Lianfeng; Tran, Nhu L.; Lee, Kyung Min; Koh, Tae-Wook; Scholes, Gregory D.; Rand, Barry P.

    2017-01-01

    Organic-inorganic hybrid perovskite materials are emerging as highly attractive semiconductors for use in optoelectronics. In addition to their use in photovoltaics, perovskites are promising for realizing light-emitting diodes (LEDs) due to their high colour purity, low non-radiative recombination rates and tunable bandgap. Here, we report highly efficient perovskite LEDs enabled through the formation of self-assembled, nanometre-sized crystallites. Large-group ammonium halides added to the perovskite precursor solution act as a surfactant that dramatically constrains the growth of 3D perovskite grains during film forming, producing crystallites with dimensions as small as 10 nm and film roughness of less than 1 nm. Coating these nanometre-sized perovskite grains with longer-chain organic cations yields highly efficient emitters, resulting in LEDs that operate with external quantum efficiencies of 10.4% for the methylammonium lead iodide system and 9.3% for the methylammonium lead bromide system, with significantly improved shelf and operational stability.

  3. Extended structural defects and their influence on the electroluminescence in efficient Si light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Sobolev, N.A.; Emel' yanov, A.M.; Shek, E.I.; Vdovin, V.I

    2003-12-31

    We report our results on electroluminescence (EL) in the range of 1.0-1.6 {mu}m, structural defects and electrophysical properties of light-emitting diodes fabricated by implantation of B and P ions into Si substrates with a subsequent thermal annealing at 700-1200 deg. C in argon. A band-to-band emission peak dominates in the EL spectra of all the samples at 80-500 K. The internal quantum efficiency of the band-to-band EL, {eta}{sub int}, and the minority carrier lifetime, {tau}{sub p}, increase with annealing temperature to 1100 deg. C, with the efficiency practically proportional to the lifetime. The maximum {eta}{sub int} was registered after annealing at 1100 deg. C, when there are no extended structural defects. Rod-like defects, partial Frank and perfect prismatic dislocation loops are formed after annealing at lower temperatures. No correlation between the quantum efficiency and the defect structure was revealed with the variation of the annealing temperature. An increase of the value {tau}{sub p}/{eta}{sub int}, proportional to the radiative lifetime, with an increasing temperature has been observed.

  4. A charge inverter for III-nitride light-emitting diodes

    Science.gov (United States)

    Zhang, Zi-Hui; Zhang, Yonghui; Bi, Wengang; Geng, Chong; Xu, Shu; Demir, Hilmi Volkan; Sun, Xiao Wei

    2016-03-01

    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 SiO2 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 SiO2 insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO2 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 μm2 LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.

  5. Exploring the Potential of Nucleic Acid Bases in Organic Light Emitting Diodes.

    Science.gov (United States)

    Gomez, Eliot F; Venkatraman, Vishak; Grote, James G; Steckl, Andrew J

    2015-12-01

    Naturally occurring biomolecules have increasingly found applications in organic electronics as a low cost, performance-enhancing, environmentally safe alternative. Previous devices, which incorporated DNA in organic light emitting diodes (OLEDs), resulted in significant improvements in performance. In this work, nucleobases (NBs), constituents of DNA and RNA polymers, are investigated for integration into OLEDs. NB small molecules form excellent thin films by low-temperature evaporation, enabling seamless integration into vacuum deposited OLED fabrication. Thin film properties of adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U) are investigated. Next, their incorporation as electron-blocking (EBL) and hole-blocking layers (HBL) in phosphorescent OLEDs is explored. NBs affect OLED performance through charge transport control, following their electron affinity trend: G < A < C < T < U. G and A have lower electron affinity (1.8-2.2 eV), blocking electrons but allowing hole transport. C, T, and U have higher electron affinities (2.6-3.0 eV), transporting electrons and blocking hole transport. A-EBL-based OLEDs achieve current and external quantum efficiencies of 52 cd A(-1) and 14.3%, a ca. 50% performance increase over the baseline device with conventional EBL. The combination of enhanced performance, wide diversity of material properties, simplicity of use, and reduced cost indicate the promise of nucleobases for future OLED development.

  6. Bright luminescence from pure DNA-curcumin–based phosphors for bio hybrid light-emitting diodes

    Science.gov (United States)

    Reddy, M. Siva Pratap; Park, Chinho

    2016-08-01

    Recently, significant advances have occurred in the development of phosphors for bio hybrid light-emitting diodes (Bio-HLEDs), which have created brighter, metal-free, rare-earth phosphor-free, eco-friendly, and cost-competitive features for visible light emission. Here, we demonstrate an original approach using bioinspired phosphors in Bio-HLEDs based on natural deoxyribonucleic acid (DNA)-curcumin complexes with cetyltrimethylammonium (CTMA) in bio-crystalline form. The curcumin chromophore was bound to the DNA double helix structure as observed using field emission tunnelling electron microscopy (FE-TEM). Efficient luminescence occurred due to tightly bound curcumin chromophore to DNA duplex. Bio-HLED shows low luminous drop rate of 0.0551 s‑1. Moreover, the solid bio-crystals confined the activating bright luminescence with a quantum yield of 62%, thereby overcoming aggregation-induced quenching effect. The results of this study herald the development of commercially viable large-scale hybrid light applications that are environmentally benign.

  7. Stretchable active-matrix organic light-emitting diode display using printable elastic conductors

    Science.gov (United States)

    Sekitani, Tsuyoshi; Nakajima, Hiroyoshi; Maeda, Hiroki; Fukushima, Takanori; Aida, Takuzo; Hata, Kenji; Someya, Takao

    2009-06-01

    Stretchability will significantly expand the applications scope of electronics, particularly for large-area electronic displays, sensors and actuators. Unlike for conventional devices, stretchable electronics can cover arbitrary surfaces and movable parts. However, a large hurdle is the manufacture of large-area highly stretchable electrical wirings with high conductivity. Here, we describe the manufacture of printable elastic conductors comprising single-walled carbon nanotubes (SWNTs) uniformly dispersed in a fluorinated rubber. Using an ionic liquid and jet-milling, we produce long and fine SWNT bundles that can form well-developed conducting networks in the rubber. Conductivity of more than 100Scm-1 and stretchability of more than 100% are obtained. Making full use of this extraordinary conductivity, we constructed a rubber-like stretchable active-matrix display comprising integrated printed elastic conductors, organic transistors and organic light-emitting diodes. The display could be stretched by 30-50% and spread over a hemisphere without any mechanical or electrical damage.

  8. Ontology-based Patent Licensing and Litigation Strategic Knowledge System for the Light Emitting Diode Industry

    Directory of Open Access Journals (Sweden)

    Amy J.C. Trappey

    2013-08-01

    Full Text Available This research studies the patents, intellectual properties and licensing landscape of the Light Emitting Diode (LED industry. The ontology of LED technology is described and defined as four major sub-technology domains. The finding provides LED companies with consistent knowledge of their own and their competitors’ patents and intellectual property rights (IPR ownership. Major LED companies often use their IPRs to gain and protect their market competitiveness, to form alliances, and to create patent licensing or cross-licensing strategies. Newly established LED technology companies competing with global industry leaders face many challenges unaddressed in the research literature. This research focuses on the empirical and quantitative analysis of historical IP and patent related conduct in relation to corporate strategy. Based on the heuristic rules derived from historical conduct, the research establishes a standardized analytical procedure to use in the evaluation of patent licensing and litigation. The results help researchers effectively and consistently analyze their technical capabilities, evaluate their patent licensing strategies, and review litigation in view of the LED-related IP and patent marketplace.

  9. Light extraction enhancement from organic light-emitting diodes with randomly scattered surface fixture

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Dong-Ying; Shi, Xiao-Bo; Gao, Chun-Hong; Cai, Shi-Duan; Jin, Yue; Liao, Liang-Sheng, E-mail: lsliao@suda.edu.cn

    2014-09-30

    Graphical abstract: - Highlights: • A combination of scattering layer and roughened substrate is used for light extraction from OLEDs. • The scattering layer is readily achieved by spin-coating the TiO{sub 2} sol. • The enhancement relying scattering depends on the size of TiO{sub 2} nano particles. • With the light extraction techniques the uniform emission is achieved. - Abstract: A combination of a scattering medium layer and a roughened substrate was proposed to enhance the light extraction efficiency of organic light-emitting diodes (OLEDs). Comparing with a reference OLED without any scattering layer, 65% improvement in the forward emission has been achieved with a scattering layer formed on an intentionally roughened external substrate surface of the OLED by spin-coating a sol–gel fabricated matrix containing well dispersed titania (TiO{sub 2}) particles. Such a combination method not only demonstrated efficient extraction of the light trapped in the glass substrate but also achieved homogenous emission from the OLED panel. The proposed technique, convenient and inexpensive, is believed to be suitable for the large area OLED production in lighting applications.

  10. Design rules for charge-transport efficient host materials for phosphorescent organic light-emitting diodes.

    Science.gov (United States)

    May, Falk; Al-Helwi, Mustapha; Baumeier, Björn; Kowalsky, Wolfgang; Fuchs, Evelyn; Lennartz, Christian; Andrienko, Denis

    2012-08-22

    The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a π-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole-Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities.

  11. 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.

  12. Sodium bromide additive improved film morphology and performance in perovskite light-emitting diodes

    Science.gov (United States)

    Li, Jinghai; Cai, Feilong; Yang, Liyan; Ye, Fanghao; Zhang, Jinghui; Gurney, Robert S.; Liu, Dan; Wang, Tao

    2017-07-01

    Organometal halide perovskite is a promising material to fabricate light-emitting diodes (LEDs) via solution processing due to its exceptional optoelectronic properties. However, incomplete precursor conversion and various defect states in the perovskite light-emitting layer lead to low luminance and external quantum efficiency of perovskite LEDs. We show here the addition of an optimum amount of sodium bromide in the methylammonium lead bromide (MAPbBr3) precursor during a one-step perovskite solution casting process can effectively improve the film coverage, enhance the crystallinity, and passivate ionic defects on the surface of MAPbBr3 crystal grains, resulting in LEDs with a reduced turn-on voltage from 2.8 to 2.3 V and an enhanced maximum luminance from 1059 to 6942 Cd/m2 when comparing with the pristine perovskite-based device.

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

    Energy Technology Data Exchange (ETDEWEB)

    Abbaszadeh, D.; Wetzelaer, G. A. H. [Molecular Electronics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG, Groningen (Netherlands); Dutch Polymer Institute, P.O. Box 902, 5600 AX, Eindhoven (Netherlands); Nicolai, H. T. [TNO/Holst Centre, High Tech Campus 31, 5605 KN, Eindhoven (Netherlands); Blom, P. W. M., E-mail: blom@mpip-mainz.mpg.de [Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah (Saudi Arabia)

    2014-12-14

    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 recombination zone shifts from the cathode to the anode with increasing voltage. The exciton quenching at the anode at higher voltages leads to an efficiency roll-off. The voltage dependence of the luminous efficiency is reproduced by a drift-diffusion model under the condition that quenching of excitons at the PEDOT:PSS anode and metallic cathode is of equal strength. Experimentally, the efficiency roll-off at high voltages due to anode quenching is eliminated by the use of an electron-blocking layer between the anode and the light-emitting polymer.

  14. An Improved Blue Polymer Light-Emitting Diode by Using Sodium Hydroxide/Ca/Al Cathode

    Institute of Scientific and Technical Information of China (English)

    MA Liang; XIE Zhi-Yuan; LIU Jun; YANG Jun-Wei; CHENG Yan-Xiang; WANG Li-Xiang; WANG Fo-Song

    2005-01-01

    @@ The performance of blue polymer light-emitting diodes (PLEDs) based on poly(9,9-dioctylfluorene) (PFO) is improved by introducing a thin layer of sodium hydroxide (NaOH) between the calcium cathode and the PFO emissive layer. By replacing the commonly used Ca/Al cathode by a NaOH (2.5nm)/Ca (10 nm)/Al cathode,the driving voltage is reduced from 8.3 V to 5.4 V and the light-emitting efficiency is enhanced from 0.46cd/A to 0. 72 cd/A for achieving a luminance of 500 cd/m2, respectively. Moreover, the device with NaOH/Ca/Al cathode shows a pure blue emission of (0.17, 0. 12) at high brightnesses. These improvements are attributed to introduction of a thin layer of NaOH that can lower the interfacial barrier and facilitate electron injection.

  15. Emitter Orientation as a Key Parameter in Organic Light-Emitting Diodes

    Science.gov (United States)

    Schmidt, Tobias D.; Lampe, Thomas; Sylvinson, Daniel M. R.; Djurovich, Peter I.; Thompson, Mark E.; Brütting, Wolfgang

    2017-09-01

    The distinct preferential alignment, i.e., horizontal orientation with respect to the substrate plane, of the optical transition dipole moment vectors (TDMVs) of organic dye molecules is of paramount importance for extracting the internally generated power of organic light-emitting diodes (OLEDs) to the outside world. This feature is one of the most promising approaches for the enhancement of the electrical efficacy in state-of-the-art OLEDs, as their internal quantum efficiencies are already close to the ultimate limit. If one can achieve complete horizontal orientation of the TDMVs, it is possible to increase the efficiency by at least 50% because alignment strongly influences the power dissipation into the different optical modes present in such a thin-film device. Thus, this feature of organic light-emitting molecules can lead to advanced performance for future applications. Therefore, we present here a review of recent achievements, ongoing research, and future tasks in this particular area of organic electronics.

  16. Thin Film Encapsulation of Light-Emitting Diodes with Photopolymerized Polyacrylate and Silver Films

    Institute of Scientific and Technical Information of China (English)

    WANG Li-Duo; WU Zhao-Xin; LI Yang; QIU Yong

    2005-01-01

    @@ A thin film encapsulation of organic light-emitting diodes (OLEDs) is investigated with a multi-layer stack of polyacrylate-Ag-polyacrylate-Ag-polyacrylate-Ag-polyacrylate (PAPAPAP). It is shown that the fabrication of polyacrylate films by a wet process does not affect the electroluminescent (EL) characteristics of the devices and polyacrylate films together with the silver layers can perform to minimize oxygen and water diffusion into the organic light-emitting device. The structure of polyacrylate(20 μm)-Ag(200nm)-polyacrylate(20 μm)-Ag(200nm)-polyacrylate(20μm)-Ag(200nm)-polyacrylate(20μm) is demonstrated to enhance dramatically the lifetime of OLEDs.

  17. Junction temperature measurements in deep-UV light-emitting diodes.

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, Arthur Joseph; Crawford, Mary Hagerott; Gessmann, Th. (Rensselaer Polytechnic Institute, Troy, NY); Shah, J. M. (Rensselaer Polytechnic Institute, Troy, NY); Xi, J.-Q. (Rensselaer Polytechnic Institute, Troy, NY); Xi, Y. (Rensselaer Polytechnic Institute, Troy, NY); Allerman, Andrew Alan; Schubert, E. Fred; Bogart, Katherine Huderle Andersen

    2004-12-01

    The junction temperature of AlGaN/GaN ultraviolet (UV) Light-Emitting Diodes (LEDs) emitting at 295 nm is measured by using the temperature coefficients of the diode forward volt-age and emission peak energy. The high-energy slope of the spectrum is explored to measure the carrier temperature. A linear relation between junction temperature and current is found. Analysis of the experimental methods reveals that the diode-forward voltage is the most accurate method (,,b 3 ,,aC). A theoretical model for the dependence of the diode junction voltage (Vj) on junction temperature (T) is developed that takes into account the temperature dependence of the energy gap. A thermal resistance of 87.6 K/W is obtained with the AlGaN/GaN LED sample mounted with thermal paste on a heat sink.

  18. 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 %.

  19. Excited states structure and processes: Understanding organic light-emitting diodes at the molecular level

    Energy Technology Data Exchange (ETDEWEB)

    Shuai, Zhigang, E-mail: zgshuai@tsinghua.edu.cn [MOE Key Laboratory of Organic OptoElectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, 100084 Beijing (China); Peng, Qian, E-mail: qpeng@iccas.ac.cn [Beijing National Laboratory for Molecular Science (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, 100190 Beijing (China)

    2014-04-01

    Photo- or electro-excited states in polyatomic molecules, aggregates, and conjugated polymers are at the center of organic light-emitting diodes (OLEDs). These can decay radiatively or non-radiatively, determining the luminescence quantum efficiency of molecular materials. According to Kasha’s rule, light-emission is dictated by the lowest-lying excited state. For conjugated polymers, the electron correlation effect can lead the lowest-lying excited state to the even-parity 2A{sub g} state which is non-emissive. To understand the nature of the low-lying excited state structure, we developed the density matrix renormalization group (DMRG) theory and its symmetrization scheme for quantum chemistry applied to calculate the excited states structure. We found there are three types of 1B{sub u}/2A{sub g} crossover behaviors: with electron correlation strength U, with bond length alternation, and with conjugation length. These directly influence the light-emitting property. For the electro-excitation, carriers (electron and hole) are injected independently, forming both singlet and triplet excited bound states with statistically 25% and 75% portions, respectively. We found that the exciton formation rate can depend on spin manifold, and for conjugated polymers, the singlet exciton can have larger formation rate leading to the internal electroluminescence quantum efficiency larger than the 25% spin statistical limit. It is originated from the interchain electron correlation as well as intrachain lattice relaxation. For the dipole allowed emissive state, the radiative decay process via either spontaneous emission or stimulated emission can be computed from electronic structure plus vibronic couplings. The challenging issue lies in the non-radiative decay via non-adiabatic coupling and/or spin–orbit coupling. We developed a unified correlation function formalism for the excited state radiative and non-radiative decay rates. We emphasized the low-frequency mode mixing

  20. Inactivation of Pseudomonas aeruginosa biofilm after ultraviolet light-emitting diode treatment: a comparative study between ultraviolet C and ultraviolet B

    DEFF Research Database (Denmark)

    Argyraki, Aikaterini; Markvart, Merete; Bjørndal, Lars

    2017-01-01

    GaN light-emitting diodes (LEDs) was used to deliver UV irradiation on the biofilms. The effectiveness of the UVB at 296 nm and UVC at 266 nm irradiations was quantified by counting colony-forming units. The survival of less mature biofilms (24 h grown) was studied as a function of UV-radiant exposure. All...

  1. Comparison between blue lasers and light-emitting diodes for future solid-state lighting: Comparison between blue lasers and light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Wierer, Jonathan J. [Sandia National Laboratories, Albuquerque NM 87185 USA; Tsao, Jeffrey Y. [Sandia National Laboratories, Albuquerque NM 87185 USA; Sizov, Dmitry S. [Corning Incorporated, One Science Center Dr., Corning NY 14831 USA

    2013-08-01

    Solid-state lighting (SSL) is now the most efficient source of high color quality white light ever created. Nevertheless, the blue InGaN light-emitting diodes (LEDs) that are the light engine of SSL still have significant performance limitations. Foremost among these is the decrease in efficiency at high input current densities widely known as “efficiency droop.” Efficiency droop limits input power densities, contrary to the desire to produce more photons per unit LED chip area and to make SSL more affordable. Pending a solution to efficiency droop, an alternative device could be a blue laser diode (LD). LDs, operated in stimulated emission, can have high efficiencies at much higher input power densities than LEDs can. In this article, LEDs and LDs for future SSL are explored by comparing: their current state-of-the-art input-power-density-dependent power-conversion efficiencies; potential improvements both in their peak power-conversion efficiencies and in the input power densities at which those efficiencies peak; and their economics for practical SSL.

  2. Diamond based light-emitting diode for visible single-photon emission at room temperature

    Science.gov (United States)

    Lohrmann, A.; Pezzagna, S.; Dobrinets, I.; Spinicelli, P.; Jacques, V.; Roch, J.-F.; Meijer, J.; Zaitsev, A. M.

    2011-12-01

    Diamond-based p-i-n light-emitting diodes capable of single-photon emission in the visible spectral region at room temperature are discussed. The diodes were fabricated on a high quality single crystal diamond grown by chemical vapor deposition. Implantation of boron and phosphorus ions followed by annealing at a temperature of 1600 °C has been used for doping p-type and n-type areas, respectively. Electrical characterization of the devices demonstrates clear diode behavior. Spectra of electroluminescence generated in the i-area reveal sole emission from the neutral nitrogen-vacancy (NV) defects. Photon antibunching implies single-photon character of this emission when generated by individual NV defects.

  3. P-doping-free III-nitride high electron mobility light-emitting diodes and transistors

    Energy Technology Data Exchange (ETDEWEB)

    Li, Baikui; Tang, Xi; Chen, Kevin J., E-mail: eekjchen@ust.hk [Department of Electronic and Computer Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Wang, Jiannong [Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2014-07-21

    We report that a simple metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet emission at 3.4 eV at a small forward bias larger than ∼2 V at room temperature. Based on the surface states distribution of AlGaN, a mature impact-ionization-induced Fermi-level de-pinning model is proposed to explain the underlying mechanism of the electroluminescence (EL) process. By experimenting with different Schottky metals, Ni/Au and Pt/Au, we demonstrated that this EL phenomenon is a “universal” property of metal-AlGaN/GaN Schottky diodes. Since this light-emitting Schottky diode shares the same active structure and fabrication processes as the AlGaN/GaN high electron mobility transistors, straight-forward and seamless integration of photonic and electronic functional devices has been demonstrated on doping-free III-nitride heterostructures. Using a semitransparent Schottky drain electrode, an AlGaN/GaN high electron mobility light-emitting transistor is demonstrated.

  4. Frequency-Downconversion Stability of PMMA Coatings in Hybrid White Light-Emitting Diodes

    Science.gov (United States)

    Caruso, Fulvio; Mosca, Mauro; Rinella, Salvatore; Macaluso, Roberto; Calì, Claudio; Saiano, Filippo; Feltin, Eric

    2016-01-01

    We report on the properties of a poly(methyl methacrylate)-based coating used as a host for an organic dye in hybrid white light-emitting diodes. The device is composed by a pump source, which is a standard inorganic GaN/InGaN blue light-emitting diode (LED) emitting at around 450 nm, and a spin-coated conversion layer making use of Lumogen® F Yellow 083. Under prolonged irradiation, the coating exhibits significant bleaching, thus degrading the color rendering performance of the LED. We present experimental results that confirm that the local temperature rise of the operating diode does not affect the conversion layer. It is also proven that, during the test, the photostability of the organic dye is compromised, resulting in a chromatic shift from Commission Internationale de l'Eclairage (CIE) ( x; y) coordinates (0.30;0.39) towards the color of the pump (0.15;0.04). Besides photodegradation of the dye, we address a phenomenon attributed to modification of the polymer matrix activated by the LED's blue light energy as confirmed by ultraviolet-visible and Fourier-transform infrared spectroscopic analyses. Three methods for improving the overall stability of the organic coating are presented.

  5. Blue InGaN light-emitting diodes with dip-shaped quantum wells

    Institute of Scientific and Technical Information of China (English)

    Lu Tai-Ping; Wang Hai-Long; Yang Xiao-Dong; LiShu-Ti; Zhang Kang; Liu Chao; Xiao Guo-Wei; Zhou Yu-Gang; ZhengShu-Wen; Yin Yi-An; Wu Le-Juan

    2011-01-01

    InGaN based light-emitting diodes (LEDs) with dip-shaped quantum wells and conventional rectangular quantum wells are numerically investigated by using the APSYS simulation software.It is found that the structure with dipshaped quantum wells shows improved light output power,lower current leakage and less efficiency droop.Based on numerical simulation and analysis,these improvements on the electrical and the optical characteristics are attributed mainly to the alleviation of the electrostatic field in dip-shaped InGaN/GaN multiple quantum wells (MQWs).

  6. Patterning of flexible organic light emitting diode (FOLED) stack using an ultrafast laser.

    Science.gov (United States)

    Mandamparambil, Rajesh; Fledderus, Henri; Van Steenberge, Geert; Dietzel, Andreas

    2010-04-12

    A femtosecond laser has been successfully utilized for patterning thin Flexible Organic Light Emitting Diode (FOLED) structures of individual layer thickness around 100nm. The authors report in this paper a step-like ablation behavior at the layer interfaces which accounts for a local removal of entire layers. Various surface analyzing techniques are used to investigate the morphologies and chemical compositions within and in the vicinity of the ablation areas. This study opens a new avenue in selectively ablating different layers from a multilayer stack on flexible substrates using fs lasers allowing post deposition structuring of large area flexible organic electronic devices.

  7. Fluorescent SiC and its application to white light-emitting diodes*

    Institute of Scientific and Technical Information of China (English)

    Satoshi Kamiyama; Motoaki Iwaya; Tetsuya Takeuchi; Isamu Akasaki; Mikael Syv(a)j(a)rvi; Rositza Yakimova

    2011-01-01

    Fluorescent-SiC (f-SiC), which contains donor and acceptor impurities with optimum concentrations,has high conversion efficiency from NUV to visible light caused by donor-acceptor-pair (DAP) recombination.This material can be used as a substrate for a nearUV light-emitting diode (LED) stack, and leads to monolithic white LED device with suitable spectral property for general lighting applications. In this paper, we describe basic technologies of the white LED, such as optical properties of f-SiC substrate, and epitaxial growth of NUV stack on the f-SiC substrate.

  8. Molecular hosts for triplet emitters in organic light-emitting diodes and the corresponding working principle

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    This paper summarizes the mechanism and routes for excitation of triplet emitters in dopant emission based phosphorescent organic light-emitting diodes (PhOLEDs),providing a comprehensive overview of recent progress in molecular hosts for triplet emitters in PhOLEDs.Particularly,based on the nature of different hosts,e.g.,hole transporting,electron transporting or bipolar materials,in which the dopant emitters can be hosted to generate phosphorescence,the respective device performances are summarized and compared.Highlights are given to the relationships among the molecular structure,thermal stability,triplet energy,carrier mobility,molecular orbital energy level and their corresponding device performances.

  9. Room temperature spin relaxation length in spin light-emitting diodes

    Science.gov (United States)

    Soldat, Henning; Li, Mingyuan; Gerhardt, Nils C.; Hofmann, Martin R.; Ludwig, Arne; Ebbing, Astrid; Reuter, Dirk; Wieck, Andreas D.; Stromberg, Frank; Keune, Werner; Wende, Heiko

    2011-08-01

    We investigate the spin relaxation length in GaAs spin light-emitting diode devices under drift transport at room temperature. The spin-polarised electrons are injected through a MgO tunnel barrier from a Fe/Tb multilayer in magnetic remanence. The decrease in circular polarization with increasing injection path length is investigated and found to be exponential, supporting drift-based transport. The spin relaxation length in our samples is 26 nm, and a lower bound for the spin injection efficiency at the spin injector/GaAs interface is estimated to be 25 ± 2%.

  10. Versatile light-emitting-diode-based spectral response measurement system for photovoltaic device characterization.

    Science.gov (United States)

    Hamadani, Behrang H; Roller, John; Dougherty, Brian; Yoon, Howard W

    2012-07-01

    An absolute differential spectral response measurement system for solar cells is presented. The system couples an array of light emitting diodes with an optical waveguide to provide large area illumination. Two unique yet complementary measurement methods were developed and tested with the same measurement apparatus. Good agreement was observed between the two methods based on testing of a variety of solar cells. The first method is a lock-in technique that can be performed over a broad pulse frequency range. The second method is based on synchronous multifrequency optical excitation and electrical detection. An innovative scheme for providing light bias during each measurement method is discussed.

  11. Electrically driven green, olivine, and amber color nanopyramid light emitting diodes.

    Science.gov (United States)

    Chang, Shih-Pang; Chang, Jet-Rung; Sou, Kuok-Pan; Liu, Mei-Chun; Cheng, Yuh-Jen; Kuo, Hao-Chung; Chang, Chun-Yen

    2013-10-07

    We report the fabrication and studies of electrically driven green, olivine, and amber color nanopyramid GaN light emitting diodes (LEDs). InGaN/GaN multiple quantum wells (MQWs) were grown on the nanopyramid semipolar facets. Compared with the commonly used (0001) c-plane MQWs, the semipolar facet has lower piezoelectric field, resulting in much faster radiative recombination efficiency. This is important for high In content MQWs. The measured internal quantum efficiencies for green, olivine, and amber color LED are 30%, 25%, and 21%, respectively. The radiative and non-radiative lifetime of the semipolar MQWs are also investigated.

  12. Confocal microphotoluminescence of InGaN-based light-emitting diodes

    OpenAIRE

    Okamoto, K.; Kaneta, A; Kawakami, Y.; Fujita, S; Choi, J.; Terazima, M; Mukai, T

    2005-01-01

    Spatially resolved photoluminescence (PL) of InGaN/GaN/AlGaN-based quantum-well-structured light-emitting diodes (LEDs) with a yellow-green light (530 nm) and an amber light (600 nm) was measured by using confocal microscopy. Submicron-scale spatial inhomogeneities of both PL intensities and spectra were found in confocal micro-PL images. We also found clear correlations between PL intensities and peak wavelength for both LEDs. Such correlations for yellow-green and amber LEDs were differen...

  13. Interface modification and material synthesis of organic light-emitting diodes using plasma technology

    Science.gov (United States)

    Liang, Rongqing; Ou, Qiongrong; Yang, Cheng; He, Kongduo; Yang, Xilu; Zhong, Shaofeng; plasma application Team

    2015-09-01

    Organic light-emitting diodes (OLEDs), due to their unique properties of solution processability, compatibility with flexible substrates and with large-scale printing technology, attract huge interest in the field of lighting. The integration of plasma technology into OLEDs provides a new route to improve their performance. Here we demonstrate the modification of indium-tin-oxide (ITO) work function by plasma treatment, synthesis of thermally activated delayed fluorescence (TADF) materials using plasma grafting (polymerisation), and multi-layer solution processing achieved by plasma cross-linking.

  14. Bromination of hydrocarbons with CBr4, initiated by light-emitting diode irradiation

    Directory of Open Access Journals (Sweden)

    Yuta Nishina

    2013-08-01

    Full Text Available The bromination of hydrocarbons with CBr4 as a bromine source, induced by light-emitting diode (LED irradiation, has been developed. Monobromides were synthesized with high efficiency without the need for any additives, catalysts, heating, or inert conditions. Action and absorption spectra suggest that CBr4 absorbs light to give active species for the bromination. The generation of CHBr3 was confirmed by NMR spectroscopy and GC–MS spectrometry analysis, indicating that the present bromination involves the homolytic cleavage of a C–Br bond in CBr4 followed by radical abstraction of a hydrogen atom from a hydrocarbon.

  15. Enhanced Electroluminescent Efficiency Based on Functionalized Europium Complexes in Polymer Light-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yong; WANG Lei; LI Chun; ZENG Wen-Jin; SHI Hua-Hong; CAO Yong

    2007-01-01

    Efficient red polymer light-emitting diodes are fabricated with the single active layer from the blends of poly (Nvinylcarbazole) (PVK) in the presence of 30wt.% electron-transporting compound 2-(4-biphenylyl)-5-(p-tertbutylphenyl)-1,3,4-oxadiazole (PBD) and europium complexes. The polyphenylene functionalized europium complex shows an enhanced electroluminescent efficiency due to the large site-isolation effect. For the polyphenylene functionalized europium complex, the maximum external quantum efficiency of 1.90% and luminous efficiency of 2.01 cd A-1 are achieved with emission peak at 612nm. The maximum brightness is more than 300cd m-2.

  16. The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

    Institute of Scientific and Technical Information of China (English)

    Guo Xia; Shen Guang-Di

    2008-01-01

    The scalability of the tunnel-regenerated multi-active-region (TRMAR) structure has been investigated for the application in light-emitting diodes (LEDs).The use of the TRMAR structure was proved theoretically to have unique advantages over conventional single-active-layer structures in virtually every aspect,such as high quantum efficiency,high power and low leakage.Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.

  17. Ultraviolet light-emitting diodes with polarization-doped p-type layer

    Science.gov (United States)

    Hu, Wenxiao; Qin, Ping; Song, Weidong; Zhang, Chongzhen; Wang, Rupeng; Zhao, Liangliang; Xia, Chao; Yuan, Songyang; Yin, Yian; Li, Shuti

    2016-09-01

    We report ultraviolet light emitting diode (LEDs) with polarization doped p-type layer. Fabricated LEDs with polarization doped p-type layer exhibited reduced forward voltage and enhanced light output power, compared to those with traditional p-type AlGaN layer. The improvement is attributed to improved hole concentration and the smooth valence band by the polarization enhanced p-type doping. Our simulated results reveal that this p-type layer can further enhance the performance of ultraviolet LEDs by removing the electron blocking layer (EBL).

  18. Low Level Light Therapy with Light-Emitting Diodes for the Aging Face.

    Science.gov (United States)

    Calderhead, R Glen; Vasily, David B

    2016-07-01

    Low level light therapy (LLLT) with light-emitting diodes (LEDs) is emerging from the mists of black magic as a solid medico-scientific modality, with a substantial buildup of corroborative bodies of evidence for its efficacy and elucidation of the modes of action. Reports are appearing from many different specialties; however, of particular interest to plastic surgeons treating the aging face is the proven action of LED-LLLT on skin cells in both the epidermis and dermis and enhanced blood flow. Thus, LED-LLLT is a safe and effective stand-alone therapy for patients who are prepared to wait until the final effect is perceived.

  19. Spectral variation of light-emitting diodes based on organic molecules doped polymer

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Organic light-emitting diodes based on naphthylimine-gallium complexes doped into a PPV derivative have been fabricated by a spin coating method.Color variation from green to blue with increase of the applied voltage has been observed.And the electroluminescent intensity of the blend samples is much stronger than that of the samples containing the complexes only.The results have been attributed to the variation of the recombination zone and the charge transfer between the materials.The process of the charge transport has been analyzed in detail.

  20. Color temperature tunable white light emitting diodes packaged with an omni-directional reflector.

    Science.gov (United States)

    Su, Jung-Chieh; Lu, Chun-Lin

    2009-11-23

    This study proposed a correlated color temperature (CCT) tunable phosphor-converted white light emitting diode (LED) with an omni-directional reflector (ODR). Applying current to each individual InGaN based ultraviolet, purple and blue source LED chip of the white LED package, we can achieve the CCT tunability. The optimum color properties of the resulting white light are (0.3347, 0.3384), 5398 K, 81, 3137-8746 K for color coordinates, CCT, color rendering index (CRI) and CCT tuning range, respectively. Roughening the ODR substrate, we solve the non-uniformity color distribution caused by the reflectance of the ODR and positioning of source LED chips.

  1. Phosphor-free white light-emitting diode with laterally distributed multiple quantum wells

    Science.gov (United States)

    Park, Il-Kyu; Kim, Ja-Yeon; Kwon, Min-Ki; Cho, Chu-Young; Lim, Jae-Hong; Park, Seong-Ju

    2008-03-01

    A phosphor-free white light-emitting diode (LED) was fabricated with laterally distributed blue and green InGaN /GaN multiple quantum wells (MQWs) grown by a selective area growth method. Photoluminescence and electroluminescence (EL) spectra of the LED showed emission peaks corresponding to the individual blue and green MQWs. The integrated EL intensity ratio of green to blue emission varied from 2.5 to 6.5 with the injection current below 300mA, but remained constant at high injection currents above 300mA. The stability of the emission color at high currents is attributed to parallel carrier injection into both MQWs.

  2. Light-emitting diodes for solid-state lighting: searching room for improvements

    Science.gov (United States)

    Karpov, Sergey Y.

    2016-03-01

    State-of-the art light-emitting diodes (LEDs) for solid-state lighting (SSL) are reviewed with the focus on their efficiency and ways for its improvement. Mechanisms of the LED efficiency losses are considered on the heterostructure, chip, and device levels, including high-current efficiency droop, recombination losses, "green gap", current crowding, Stokes losses, etc. Materials factors capable of lowering the LED efficiency, like composition fluctuations in InGaN alloys and plastic stress relaxation in device heterostructures, are also considered. Possible room for the efficiency improvement is discussed along with advanced schemes of color mixing and LED parameters optimal for generation of high-quality white light.

  3. Geometrical design and measurement of light-emitting diode for lighting

    OpenAIRE

    Cheung, Wing-shing; 章永聖

    2015-01-01

    Year 2014 is a milestone in the history of LEDs industry. Isamu Akasaki, Hiroshi Amano and Shuji Nakamura were awarded the Nobel Prize in Physics 2014 for their contribution in the application of “bright and energy-saving white light sources” with invention of efficient blue indium gallium nitrate (InGaN) light-emitting diodes (LED) [1]. This can be treated as an admission of the impotence of LED lighting in the modern human civilization. Although the LED- related technologies had been we...

  4. 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%.

  5. Graded Heterojunction of AlGaInP High-brightness Light Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    LIU Lu; FAN Guang-han; LIAO Chang-jun

    2004-01-01

    A simple model of the graded heterojunction in AlGaInP compound semiconductors was introduced to analyze the band profile. The band profiles are analyzed with the different grading ways but the same grading length and under the different doping densities. The effect of the different grading lengths on the surplus of the potential of the spike to the potential of N region are also analyzed under the different doping densities.Through the experiments,it proves that the performances of high brightness light emitting diodes can be improved by the effects of the graded heterojunction.

  6. Plastic cup traps equipped with light-emitting diodes for monitoring adult Bemisia tabaci (Homoptera: Aleyrodidae).

    Science.gov (United States)

    Chu, Chang-Chi; Jackson, Charles G; Alexander, Patrick J; Karut, Kamil; Henneberry, Thomas J

    2003-06-01

    Equipping the standard plastic cup trap, also known as the CC trap, with lime-green light-emitting diodes (LED-plastic cup trap) increased its efficacy for catching Bemisia tabaci by 100%. Few Eretmocerus eremicus Rose and Zolnerowich and Encarsia formosa Gahan were caught in LED-plastic cup traps. The LED-plastic cup traps are less expensive than yellow sticky card traps for monitoring adult whiteflies in greenhouse crop production systems and are more compatible with whitefly parasitoids releases for Bemisia nymph control.

  7. Energy-recycling pixel for active-matrix organic light-emitting diode display

    Science.gov (United States)

    Yang, Che-Yu; Cho, Ting-Yi; Chen, Yen-Yu; Yang, Chih-Jen; Meng, Chao-Yu; Yang, Chieh-Hung; Yang, Po-Chuan; Chang, Hsu-Yu; Hsueh, Chun-Yuan; Wu, Chung-Chih; Lee, Si-Chen

    2007-06-01

    The authors report a pixel structure for active-matrix organic light-emitting diode (OLED) displays that has a hydrogenated amorphous silicon solar cell inserted between the driving polycrystalline Si thin-film transistor and the pixel OLED. Such an active-matrix OLED pixel structure not only exhibits a reduced reflection (and thus improved contrast) compared to conventional OLEDs but also is capable of recycling both incident photon energies and internally generated OLED radiation. Such a feature of energy recycling may be of use for portable/mobile electronics, which are particularly power aware.

  8. Flexible organic light-emitting diodes with poly-3,4-ethylenedioxythiophene as transparent anode

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The flexible oragnic light-emitting diodes (OLEDs) fabricated on poly-3,4-ethylenedioxythiophene/poly- styrenesulfonate (PEDOT/PSS) coated substrates were demonstrated. How the fabricating processes and the device structure will affect the device performance was studied and the atomic force microscopy was employed to analyze the mophorlogy of the conducting polymer anode. Under optimized conditions, flexible OLEDs with PEDOT anode showed the brightness up to 2760 cd/m2 and maximum external quantum efficiency of 1.4%. These data are comparable to those of conventional flexible OLEDs with ITO anode.

  9. 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.)

  10. Transparent Heat-Resistant PMMA Copolymers for Packing Light-Emitting Diode Materials

    Directory of Open Access Journals (Sweden)

    Shu-Ling Yeh

    2015-07-01

    Full Text Available Transparent and heat-resistant poly(methyl methacrylate copolymers were synthesized by bulk polymerizing methyl methacrylate (MMA, isobornyl methacrylate (IBMA, and methacrylamide (MAA monomers. Copolymerization was performed using a chain transfer agent to investigate the molecular weight changes of these copolymers, which exhibited advantages including a low molecular weight distribution, excellent optical properties, high transparency, high glass transition temperature, low moisture absorption, and pellets that can be readily mass produced by using extrusion or jet injection for packing light-emitting diode materials.

  11. 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 measured......, the colorimetric values were calculated, and a visual comparison using Gretagmacbeth colorcharts was performed. The visual comparison showed that the LED bulb was better to render colors despite a low color rendering index (CRI). Furthermore, the LED bulb was tested in a photolithography room...

  12. 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.

  13. 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.

  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. Transparent conductive PVP/AgNWs films for flexible organic light emitting diodes by spraying method

    Science.gov (United States)

    Hu, Jun-tao; Mei, Wen-juan; Ye, Kang-li; Wei, Qing-qing; Hu, Sheng

    2016-05-01

    In this study, a simple spraying method is used to prepare the transparent conductive films (TCFs) based on Ag nanowires (AgNWs). Polyvinylpyrrolidone (PVP) is introduced to modify the interface of substrate. The transmittance and bending performance are improved by optimizing the number of spraying times and the solution concentration and controlling the annealing time. The spraying times of 20, the concentration of 2 mg/mL and the annealing time of 10 min are chosen to fabricate the PVP/AgNWs films. The transmittance of PVP/AgNWs films is 53.4%—67.9% at 380—780 nm, and the sheet resistance is 30 Ω/□ which is equivalent to that of commercial indium tin oxide (ITO). During cyclic bending tests to 500 cycles with bending radius of 5 mm, the changes of resistivity are negligible. The performance of PVP/AgNW transparent electrodes has little change after being exposed to the normal environment for 1 000 h. The adhesion to polymeric substrate and the ability to endure bending stress in AgNWs network films are both significantly improved by introducing PVP. Spraying method makes AgNWs form a stratified structure on large-area polymer substrates, and the vacuum annealing method is used to weld the AgNWs together at junctions and substrates, which can improve the electrical conductivity. The experimental results indicate that PVP/AgNW transparent electrodes can be used as transparent conductive electrodes in flexible organic light emitting diodes (OLEDs).

  16. 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.

  17. Microwave assisted transformation of N,N-diphenylamine as precursors of organic light emitting diodes (OLED)

    Science.gov (United States)

    Jefri, Wahyuningrum, Deana

    2015-09-01

    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, CDCl3) 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.

  18. 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.

  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. Identifying Dosage Effect of Light-Emitting Diode Therapy on Muscular Fatigue in Quadriceps.

    Science.gov (United States)

    Hemmings, Thomas J; Kendall, Kristina L; Dobson, John L

    2017-02-01

    Hemmings, TJ, Kendall, KL, and Dobson, JL. Identifying dosage effect of light-emitting diode therapy on muscular fatigue in quadriceps. J Strength Cond Res 31(2): 395-402, 2017-The purpose of this study was to compare the effects of various dosages of light-emitting diode therapy (LEDT) on muscle fatigue while performing a single-leg extension to exhaustion. A total of 34 recreationally resistance-trained athletes between the ages of 18 and 26 participated in 4 trials. Each trial included pre-exercise/postexercise blood lactate measurements and 2 sets of 3 maximal voluntary isometric contractions (MVICs), followed by LEDT on 6 points across the superficial quadriceps. Each randomized trial consisted of a placebo, 30, 60, or 120 seconds on each point on the quadriceps. Three minutes after LEDT, the participants performed an eccentric leg extension with 120% of MVIC until fatigue. There was significant increase in the number of repetitions performed between the placebo treatment and 60 seconds (p = 0.023), as well as placebo and 120 seconds (p = 0.004) of irradiation on each point. There were no significant differences in blood lactate levels between any of the 4 trials. In conclusion, LEDT had a positive effect on performance when irradiating 6 points on the superficial quadriceps for 60 and 120 seconds before an eccentric leg extension.

  1. An Alkane-Soluble Dendrimer as Electron-Transport Layer in Polymer Light-Emitting Diodes.

    Science.gov (United States)

    Zhong, Zhiming; Zhao, Sen; Pei, Jian; Wang, Jian; Ying, Lei; Peng, Junbiao; Cao, Yong

    2016-08-10

    Polymer light-emitting diodes (PLEDs) have attracted broad interest due to their solution-processable properties. It is well-known that to achieve better performance, organic light-emitting diodes require multilayer device structures. However, it is difficult to realize multilayer device structures by solution processing for PLEDs. Because most semiconducting polymers have similar solubility in common organic solvents, such as toluene, xylene, chloroform, and chlorobenzene, the deposition of multilayers can cause layers to mix together and damage each layer. Herein, a novel semiorthogonal solubility relationship was developed and demonstrated. For the first time, an alkane-soluble dendrimer is utilized as the electron-transport layer (ETL) in PLEDs via a solution-based process. With the dendrimer ETL, the external quantum efficiency increases more than threefold. This improvement in the device performance is attributed to better exciton confinement, improved exciton energy transfer, and better charge carrier balance. The semiorthogonal solubility provided by alkane offers another process dimension in PLEDs. By combining them with water/alcohol-soluble polyelectrolytes, more exquisite multilayer devices can be fabricated to achieve high device performance, and new device structures can be designed and realized.

  2. 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

    2012-05-27

    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.

  3. The electrodeposition of multilayers on a polymeric substrate in Flexible Organic Light Emitting Diode (OLED)

    Science.gov (United States)

    Guedes, Andre F. S.; Guedes, Vilmar P.; Tartari, Simone; Cunha, Idaulo Jose

    2016-09-01

    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, Poly(p-phenylenevinylene), PPV, 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 PET/ITO/PEDOT/PPV/PANI-X1/Al 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 1200 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.

  4. Improved heat dissipation in gallium nitride light-emitting diodes with embedded graphene oxide pattern.

    Science.gov (United States)

    Han, Nam; Cuong, Tran Viet; Han, Min; Ryu, Beo Deul; Chandramohan, S; Park, Jong Bae; Kang, Ji Hye; Park, Young-Jae; Ko, Kang Bok; Kim, Hee Yun; Kim, Hyun Kyu; Ryu, Jae Hyoung; Katharria, Y S; Choi, Chel-Jong; Hong, Chang-Hee

    2013-01-01

    The future of solid-state lighting relies on how the performance parameters will be improved further for developing high-brightness light-emitting diodes. Eventually, heat removal is becoming a crucial issue because the requirement of high brightness necessitates high-operating current densities that would trigger more joule heating. Here we demonstrate that the embedded graphene oxide in a gallium nitride light-emitting diode alleviates the self-heating issues by virtue of its heat-spreading ability and reducing the thermal boundary resistance. The fabrication process involves the generation of scalable graphene oxide microscale patterns on a sapphire substrate, followed by its thermal reduction and epitaxial lateral overgrowth of gallium nitride in a metal-organic chemical vapour deposition system under one-step process. The device with embedded graphene oxide outperforms its conventional counterpart by emitting bright light with relatively low-junction temperature and thermal resistance. This facile strategy may enable integration of large-scale graphene into practical devices for effective heat removal.

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

    Science.gov (United States)

    Mesta, Murat; Carvelli, Marco; de Vries, Rein J.; van Eersel, Harm; van der Holst, Jeroen J. M.; Schober, Matthias; Furno, Mauro; Lüssem, Björn; Leo, Karl; Loebl, Peter; Coehoorn, Reinder; Bobbert, Peter A.

    2013-07-01

    In multilayer white organic light-emitting diodes the electronic processes in the various layers—injection and motion of charges as well as generation, diffusion and radiative decay of excitons—should be concerted such that efficient, stable and colour-balanced electroluminescence can occur. Here 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 are shown to agree well with experiment. The experimental emission profile was obtained with nanometre resolution from the measured angle- and polarization-dependent emission spectra. The simulations elucidate the crucial role of exciton transfer from green to red and the efficiency loss due to excitons generated in the interlayer between the green and blue layers. The perpendicular and lateral confinement of the exciton generation to regions of molecular-scale dimensions revealed by this study demonstrate the necessity of molecular-scale instead of conventional continuum simulation.

  6. Stacking multiple connecting functional materials in tandem organic light-emitting diodes

    Science.gov (United States)

    Zhang, Tao; Wang, Deng-Ke; Jiang, Nan; Lu, Zheng-Hong

    2017-01-01

    Tandem device is an important architecture in fabricating high performance organic light-emitting diodes and organic photovoltaic cells. The key element in making a high performance tandem device is the connecting materials stack, which plays an important role in electric field distribution, charge generation and charge injection. For a tandem organic light-emitting diode (OLED) with a simple Liq/Al/MoO3 stack, we discovered that there is a significant current lateral spreading causing light emission over an extremely large area outside the OLED pixel when the Al thickness exceeds 2 nm. This spread light emission, caused by an inductive electric field over one of the device unit, limits one’s ability to fabricate high performance tandem devices. To resolve this issue, a new connecting materials stack with a C60 fullerene buffer layer is reported. This new structure permits optimization of the Al metal layer in the connecting stack and thus enables us to fabricate an efficient tandem OLED having a high 155.6 cd/A current efficiency and a low roll-off (or droop) in current efficiency. PMID:28225028

  7. 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.

  8. Fabrication of white light-emitting diodes based on UV light-emitting diodes with conjugated polymers-(CdSe/ZnS) quantum dots as hybrid phosphors.

    Science.gov (United States)

    Jung, Hyunchul; Chung, Wonkeun; Lee, Chang Hun; Kim, Sung Hyun

    2012-07-01

    White light-emitting diodes (LEDs) were fabricated using GaN-based 380-nm UV LEDs precoated with the composite of blue-emitting polymer (poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(2-methoxy-5-{2-ethylhexyloxy)-1 ,4-phenylene)]), yellow green-emitting polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)]), and 605-nm red-emitting quantum dots (QDs). CdSe cores were obtained by solvothermal route using CdO, Se precursors and ZnS shells were synthesized by using diethylzinc, and hexamethyldisilathiane precursors. The optical properties of CdSe/ZnS QDs were characterized by UV-visible and photoluminescence (PL) spectra. The structural data and composition of the QDs were transmission electron microscopy (TEM), and EDX technique. The quantum yield and size of the QDs were 58.7% and about 6.7 nm, respectively. Three-band white light was generated by hybridizing blue (430 nm), green (535 nm), and red (605 nm) emission. The color-rendering index (CRI) of the device was extremely improved by introducing the QDs. The CIE-1931 chromaticity coordinate, color temperature, and CRI of a white LED at 20 mA were (0.379, 0.368), 3969 K, and 90, respectively.

  9. Characterization of four-color multi-package white light-emitting diodes combined with various green monochromatic phosphor-converted light-emitting diodes

    Science.gov (United States)

    Oh, Ji Hye; Lee, Keyong Nam; Do, Young Rag

    2012-03-01

    In this study, several combinations of multi-package white light-emitting diodes (LEDs), which combine an InGaN blue LED with green, amber, and red phosphor-converted LEDs (pc-LEDs), were characterized by changing the peak wavelength of green pc-LEDs between 515nm and 560nm (515, 521, 530, 540, 550, 560nm) in color temperature of 6,500K and 3,500K. Various green monochromatic pc-LEDs were fabricated by capping a long-wave pass-filter (LWPF) on top of pc-LEDs to improve luminous efficacy and color purity. LWPF-capped green monochromatic pc-LED can address the drawback of green semiconductor-type III-V LED, such as low luminous efficacy in the region of green gap wavelength. Luminous efficacy and color rendering index (CRI) of multi-package white LEDs are compared with changing the driving current of individual LED in various multi-package white LEDs. This study provides a best combination of four-color multi-package white LEDs which has high luminous efficacy and good CRI.

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

    DEFF Research Database (Denmark)

    Bak, Jimmy; Ladefoged, S.D.; Tvede, M.

    2010-01-01

    , 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...... in the range of 5 x 10(5)-1.3 x 10(9) CFU ml(-1), with disinfection rates in the range 96-100%. The applied UVC doses corresponded to treatment times between 15 and 300 min. Disinfection (100%) was obtained in 10 cm Teflon tubes exposed for 30 min (detection limit...

  11. 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

    , 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...... in the range of 5 x 10(5)-1.3 x 10(9) CFU ml(-1), with disinfection rates in the range 96-100%. The applied UVC doses corresponded to treatment times between 15 and 300 min. Disinfection (100%) was obtained in 10 cm Teflon tubes exposed for 30 min (detection limit...

  12. Origin of magnetic field effect enhancement by electrical stress in organic light emitting diodes

    Science.gov (United States)

    Bagnich, S. A.; Niedermeier, U.; Melzer, C.; Sarfert, W.; von Seggern, H.

    2009-06-01

    Recently, it has been discovered that the magnetic field effect (MFE) in organic light emitting diodes (OLEDs) based on poly(para-phenylene vinylene) can be enhanced by exposing the diode to moderate electrical stress. Here, we disclose the mechanism behind this way of improving the MFE. We first show that electronic traps in general play an important role for the MFE. Optical depletion of available trap states by infrared illumination leads to a decrease in the MFE. Furthermore, we demonstrate that annealing of the OLED at high temperatures eliminates the MFE improvement of the previously performed electrical conditioning. However, the improvement can be restored by subsequent conditioning at higher current or voltage. Thus it is likely that electrical stress is accompanied by a transformation of the polymer morphology or conformation resulting in a formation of energetic traps for charge carriers.

  13. Substrate-Free InGaN/GaN Nanowire Light-Emitting Diodes.

    Science.gov (United States)

    Neplokh, Vladimir; Messanvi, Agnes; Zhang, Hezhi; Julien, Francois H; Babichev, Andrey; Eymery, Joel; Durand, Christophe; Tchernycheva, Maria

    2015-12-01

    We report on the demonstration of substrate-free nanowire/polydimethylsiloxane (PDMS) membrane light-emitting diodes (LEDs). Metal-organic vapour-phase epitaxy (MOVPE)-grown InGaN/GaN core-shell nanowires were encapsulated into PDMS layer. After metal deposition to p-GaN, a thick PDMS cap layer was spin-coated and the membrane was manually peeled from the sapphire substrate, flipped upside down onto a steel holder, and transparent indium tin oxide (ITO) contact to n-GaN was deposited. The fabricated LEDs demonstrate rectifying diode characteristics. For the electroluminescence (EL) measurements, the samples were manually bonded using silver paint. The EL spectra measured at different applied voltages demonstrate a blue shift with the current increase. This shift is explained by the current injection into the InGaN areas of the active region with different average indium content.

  14. Blue Superluminescent Light-Emitting Diodes with Output Power above 100 mW for Picoprojection

    Science.gov (United States)

    Kopp, Fabian; Eichler, Christoph; Lell, Alfred; Tautz, Sönke; Ristić, Jelena; Stojetz, Bernhard; Höß, Christine; Weig, Thomas; Schwarz, Ulrich T.; Strauss, Uwe

    2013-08-01

    We present a blue InGaN research and development superluminescent light-emitting diode (SLED) that is suitable for picoprojection. The SLED reaches an output power of >100 mW with a peak wavelength of 443 nm and a spectral bandwidth of >2.6 nm as well as a single-mode far-field driven in cw mode at 25 °C. In order to figure out an optimized waveguide design, which enables such a high output power at lowest operation current, we compare the performance of diodes with curved and tilted shaped ridges in detail, using the lasing threshold current as a criterion for lasing or superluminescence, respectively.

  15. Properties of CoPt ferromagnetic layers for application in spin light-emitting diodes

    Science.gov (United States)

    Zdoroveyshchev, A. V.; Dorokhin, M. V.; Vikhrova, O. V.; Demina, P. B.; Kudrin, A. V.; Temiryazev, A. G.; Temiryazeva, M. P.

    2016-11-01

    The magnetic properties of Co45Pt55 films deposited by electron-beam evaporation in vacuum have been studied. The measurements of the Faraday and Kerr magnetooptical effects confirm the presence of the easy-magnetization axis perpendicular to the Co45Pt55 surface. It is shown that the perpendicular magnetic anisotropy and the residual magnetization are retained at 300 K for a long time. The magnetic characteristics of the Co45Pt55 layer surface have been studied by magnetic force microscopy, and "circular" mobile magnetic structures have been detected. The spin light-emitting diodes based on In(Ga)As/GaAs heteronanostructures with Co45Pt55 contact layers were fabricated. These diodes emit circularly-polarized light in the absence of an external magnetic field.

  16. 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...

  17. 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.

  18. 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.

  19. Evaluation of inorganic and organic light-emitting diode displays for signage application

    Science.gov (United States)

    Sharma, Pratibha; Kwok, Harry

    2006-08-01

    High-brightness, inorganic light-emitting diodes (LEDs) have been successfully utilized for edge-lighting of large displays for signage. Further interest in solid-state lighting technology has been fueled with the emergence of small molecule and polymer-based organic light-emitting diodes (OLEDs). In this paper, edgelit inorganic LED-based displays and state-of-the-art OLED-based displays are evaluated on the basis of electrical and photometric measurements. The reference size for a signage system is assumed to be 600 mm x 600mm based on the industrial usage. With the availability of high power light-emitting diodes, it is possible to develop edgelit signage systems of the standard size. These displays possess an efficacy of 18 lm/W. Although, these displays are environmentally friendly and efficient, they suffer from some inherent limitations. Homogeneity of displays, which is a prime requirement for illuminated signs, is not accomplished. A standard deviation of 3.12 lux is observed between the illuminance values on the surface of the display. In order to distribute light effectively, reflective gratings are employed. Reflective gratings aid in reducing the problem but fail to eliminate it. In addition, the overall cost of signage is increased by 50% with the use of these additional components. This problem can be overcome by the use of a distributed source of light. Hence, the organic-LEDs are considered as a possible contender. In this paper, we experimentally determine the feasibility of using OLEDs for signage applications and compare their performance with inorganic LEDs. Passive matrix, small-molecule based, commercially available OLEDs is used. Design techniques for implementation of displays using organic LEDs are also discussed. It is determined that tiled displays based on organic LEDs possess better uniformity than the inorganic LED-based displays. However, the currently available OLEDs have lower light-conversion efficiency and higher costs than the

  20. Using Pre-Exercise Photobiomodulation Therapy Combining Super-Pulsed Lasers and Light-Emitting Diodes to Improve Performance in Progressive Cardiopulmonary Exercise Tests

    National Research Council Canada - National Science Library

    Miranda, Eduardo Foschini; Vanin, Adriane Aver; Tomazoni, Shaiane Silva; Grandinetti, Vanessa dos Santos; de Paiva, Paulo Roberto Vicente; Machado, Caroline dos Santos Monteiro; Monteiro, Kadma Karênina Damasceno Soares; Casalechi, Heliodora Leão; de Tarso, Paulo; de Carvalho, Camillo; Leal-Junior, Ernesto Cesar Pinto

    2016-01-01

    ...) combining superpulsed lasers (low-level laser therapy) and light-emitting diodes (LEDs) on muscle performance during a progressive cardiopulmonary treadmill exercise test. Crossover study. Laboratory...

  1. Low temperature solution process-based defect-induced orange-red light emitting diode

    Science.gov (United States)

    Biswas, Pranab; Baek, Sung-Doo; Hoon Lee, Sang; Park, Ji-Hyeon; Jeong Lee, Su; Il Lee, Tae; Myoung, Jae-Min

    2015-01-01

    We report low-temperature solution-processed p-CuO nanorods (NRs)/n-ZnO NRs heterojunction light emitting diode (LED), exploiting the native point defects of ZnO NRs. ZnO NRs were synthesized at 90 °C by using hydrothermal method while CuO NRs were synthesized at 100 °C by using microwave reaction system. The electrical properties of newly synthesized CuO NRs revealed a promising p-type nature with a hole concentration of 9.64 × 1018 cm−3. The current-voltage characteristic of the heterojunction showed a significantly high rectification ratio of 105 at 4 V with a stable current flow. A broad orange-red emission was obtained from the forward biased LED with a major peak at 610 nm which was attributed to the electron transition from interstitial zinc to interstitial oxygen point defects in ZnO. A minor shoulder peak was also observed at 710 nm, corresponding to red emission which was ascribed to the transition from conduction band of ZnO to oxygen vacancies in ZnO lattice. This study demonstrates a significant progress toward oxide materials based, defect-induced light emitting device with low-cost, low-temperature methods. PMID:26648420

  2. Origin of the Electroluminescence from Annealed-ZnO/GaN Heterojunction Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Kai-Chiang Hsu

    2015-11-01

    Full Text Available This paper addressed the effect of post-annealed treatment on the electroluminescence (EL of an n-ZnO/p-GaN heterojunction light-emitting diode (LED. The bluish light emitted from the 450 °C-annealed LED became reddish as the LED annealed at a temperature of 800 °C under vacuum atmosphere. The origins of the light emission for these LEDs annealed at various temperatures were studied using measurements of electrical property, photoluminescence, and Auger electron spectroscopy (AES depth profiles. A blue-violet emission located at 430 nm was associated with intrinsic transitions between the bandgap of n-ZnO and p-GaN, the green-yellow emission at 550 nm mainly originating from the deep-level transitions of native defects in the n-ZnO and p-GaN surfaces, and the red emission at 610 nm emerging from the Ga-O interlayer due to interdiffusion at the n-ZnO/p-GaN interface. The above-mentioned emissions also supported the EL spectra of LEDs annealed at 700 °C under air, nitrogen, and oxygen atmospheres, respectively.

  3. 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.

  4. Comparison of organic light emitting diodes with different mixed layer structures

    Energy Technology Data Exchange (ETDEWEB)

    Kee, Y.Y.; Siew, W.O. [Faculty of Engineering, Multimedia University, 63100 Cyberjaya (Malaysia); Yap, S.S. [Faculty of Engineering, Multimedia University, 63100 Cyberjaya (Malaysia); Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur (Malaysia); Tou, T.Y., E-mail: tytou@mmu.edu.my [Faculty of Engineering, Multimedia University, 63100 Cyberjaya (Malaysia)

    2014-11-03

    A mixed-source thermal evaporation method was used to fabricate organic light emitting diodes (OLEDs) with uniformly mixed (UM), continuously graded mixed (CGM) and step-wise graded, mixed (SGM) light-emitting layers. N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine and Tris-(8-hydroxyquinoline)aluminum were used, respectively, as the hole- and electron-transport materials. As compared to the conventional, heterojunction OLED, the maximum brightness of UM-, CGM- and SGM-OLEDs without charge injection layers were improved by 2.2, 3.8 and 2.1 times, respectively, while the maximum power efficiencies improved by 1.5, 3.2 and 1.9 times. These improvements were discussed in terms of more distributed recombination zone and removal of interfacial barrier. - Highlights: • Fabrication of OLEDs using a mixed-source evaporation technique • Three different types of mixed-host OLEDs with better brightness • Improved electroluminescence and power efficiencies as compared to conventional OLED.

  5. 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.

  6. Radiation Damage Effects in Heterostructure Light Emitting Diodes (HLEDs under Proton Irradiation Fields

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2012-05-01

    Full Text Available In the present paper, we have been analyzed the high temperature variations testing in order to be used to determine light emitting diode lifetime, even though laser diode failure mechanisms are more sensitive to increases in current density. As a measured parameter of degradation, the current density is of great significance when searching for failure modes in a laser diode. Raising the current density however, is not really indicative of lifetime since it is more likely a situation to be avoided than one that simulates normal lifetime degradation. The reliability of semiconductor sources is very dependent on the degradation modes. This paper has investigated some of the degradation modes and capabilities of typical LEDs currently used in many communication and sensing systems over wide range of the affecting parameters. LED’s are typically used in multimode transmission systems where data rates no larger than 50 Mbit/sec are required. They have larger spectral widths and can add to the problem of dispersion in communications systems. Laser diodes are used in systems that require coherent and often single mode light such as high data rate communications and sensing applications.

  7. 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

  8. 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.

  9. Local indium segregation and band structure in high efficiency green light emitting InGaN/GaN diodes

    OpenAIRE

    Jinschek, Joerg R.; Erni, Rolf; Gardner, Nathan F.; Kim, Andrew Y.; Kisielowski, Christian

    2004-01-01

    GaN/InGaN light emitting diodes (LEDs) are commercialized for lighting applications because of the cost efficient way that they produce light of high brightness1,2. Nevertheless, there is significant room for improving their external emission efficiency3 from typical values below 10 percent4 to more than 50 percent5, which are obtainable by use of other materials systems that, however, do not cover the visible spectrum. In particular, green-light emitting diodes fall short in this respec...

  10. Mixed polarity in polarization-induced p-n junction nanowire light-emitting diodes.

    Science.gov (United States)

    Carnevale, Santino D; Kent, Thomas F; Phillips, Patrick J; Sarwar, A T M G; Selcu, Camelia; Klie, Robert F; Myers, Roberto C

    2013-07-10

    Polarization-induced nanowire light emitting diodes (PINLEDs) are fabricated by grading the Al composition along the c-direction of AlGaN nanowires grown on Si substrates by plasma-assisted molecular beam epitaxy (PAMBE). Polarization-induced charge develops with a sign that depends on the direction of the Al composition gradient with respect to the [0001] direction. By grading from GaN to AlN then back to GaN, a polarization-induced p-n junction is formed. The orientation of the p-type and n-type sections depends on the material polarity of the nanowire (i.e., Ga-face or N-face). Ga-face material results in an n-type base and a p-type top, while N-face results in the opposite. The present work examines the polarity of catalyst-free nanowires using multiple methods: scanning transmission electron microscopy (STEM), selective etching, conductive atomic force microscopy (C-AFM), and electroluminescence (EL) spectroscopy. Selective etching and STEM measurements taken in annular bright field (ABF) mode demonstrate that the preferred orientation for catalyst-free nanowires grown by PAMBE is N-face, with roughly 10% showing Ga-face orientation. C-AFM and EL spectroscopy allow electrical and optical differentiation of the material polarity in PINLEDs since the forward bias direction depends on the p-n junction orientation and therefore on nanowire polarity. Specifically, C-AFM reveals that the direction of forward bias for individual nanowire LEDs changes with the polarity, as expected, due to reversal of the sign of the polarization-induced charge. Electroluminescence measurements of mixed polarity PINLEDs wired in parallel show ambipolar emission due to the mixture of p-n and n-p oriented PINLEDs. These results show that, if catalyst-free III-nitride nanowires are to be used to form polarization-doped heterostructures, then it is imperative to understand their mixed polarity and to design devices using these nanowires accordingly.

  11. 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 CsPbBr3 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-CsPbBr3 nanostructure studied here provides a novel strategy on the road to the future development of perovskite LEDs.

  12. 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.

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

    Science.gov (United States)

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

    2015-10-01

    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.

  14. 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.

  15. AlGaInP-Si glue bonded high performance light emitting diodes

    Institute of Scientific and Technical Information of China (English)

    Chen Yi-Xin; Shen Guang-Di; Guo Wei-Ling; Gao Zhi-Yuan

    2011-01-01

    We propose a new method of using conductive glue to agglutinate GaAs based AlGaInP light emitting diodes (LEDs)onto silicon substrate,and the absorbing GaAs layer is subsequently removed by grinding and selective wet etching.It was found that AIGainP-Si glue agglutinated LEDs have larger saturation current and luminous intensity than the conventional LEDs working at the same injected current.The luminous intensity of the new device is as much as 1007.4 mcd at a saturation current of 125 mA without being encapsulated,while the conventional LEDs only have 266.2 mcd at a saturation current of 105 mA.The luminescence intensity is also found to increase by about 3.2% after working at 50 mA for 768 h.This means that the new structured LEDs have good reliability performance.

  16. Increased mycelial biomass production by Lentinula edodes intermittently illuminated by green light emitting diodes.

    Science.gov (United States)

    Glukhova, Lubov B; Sokolyanskaya, Ludmila O; Plotnikov, Evgeny V; Gerasimchuk, Anna L; Karnachuk, Olga V; Solioz, Marc; Karnachuk, Raisa A

    2014-11-01

    Fungi possess a range of light receptors to regulate metabolism and differentiation. To study the effect of light on Lentinula edodes (the shiitake mushroom), mycelial cultures were exposed to blue, green, and red fluorescent lights and light-emitting diodes, as well as green laser light. Biomass production, morphology, and pigment production were evaluated. Exposure to green light at intervals of 1 min/d at 0.4 W/m(2) stimulated biomass production by 50-100 %, depending on the light source. Light intensities in excess of 1.8 W/m(2) or illumination longer than 30 min/d did not affect biomass production. Carotenoid production and morphology remained unaltered during increased biomass production. These observations provide a cornerstone to the study of photoreception by this important fungus.

  17. 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

    (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......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...... 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...

  18. Visualization of trap dilution in polyfluorene based light-emitting diodes

    Science.gov (United States)

    Khodabakhshi, Elham; Michels, Jasper J.; Blom, Paul W. M.

    2017-07-01

    The effects of electron trapping and resulting trap-assisted recombination can be strongly suppressed by diluting a semiconducting polymer with a large band gap polymer such as polystyrene. Polyfluorene (PFO)-based light-emitting diodes (PLEDs) are an excellent model system to visualize this trap dilution effect. The blue emission from the pristine PFO backbone is accompanied by a broad, featureless green emission band originating from monomeric ketone defects that act as an electron trap. We demonstrate that the green emission from radiative trap-assisted recombination at these ketone defects is nearly eliminated upon dilution. The ratio between bimolecular blue emission and trap-assisted green emission as a function of dilution is shown to be in quantitative agreement with model predictions.

  19. Selective Patterning of Organic Light-Emitting Diodes by Physical Vapor Deposition of Photosensitive Materials

    Science.gov (United States)

    Muroyama, Masakazu; Saito, Ichiro; Yokokura, Seiji; Tanaka, Kuniaki; Usui, Hiroaki

    2009-04-01

    A novel method of patterning polymeric thin films by the vapor deposition of a photosensitive layer followed by photopolymerization and development was proposed. This method was applied to the patterning of the emissive layer (EML) of an organic light-emitting diode (OLED). For the hole transport layer (HTL), N,N,N'-triphenyl-N'-(4-vinylphenyl)-biphenyl-4,4'-diamine (vTPD) and a zinc acrylate (ZnAc) crosslinker were coevaporated. The film was polymerized by postdeposition annealing to yield a polymeric HTL with a high resistance to organic solvents. On this HTL, the photosensitive EML was prepared by coevaporating a 9H-carbazole-9-ethylmethacrylate (CEMA) host material and 4-(dimethylamino)benzophenone (DABP) photoinitiator. UV irradiation on the EML through a photomask initiated radical polymerization, leaving a negative pattern of the irradiated region after immersion in tetrahydrofuran (THF). The photopatterning process was found to cause no damage to the film morphology or the device characteristics.

  20. Diffusion voltage in polymer light emitting diodes measured with electric field induced second harmonic generation

    Science.gov (United States)

    Kristensen, P. K.; Rafaelsen, J.; Pedersen, T. G.; Pedersen, K.

    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.

  1. 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.

  2. 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.

  3. Colorimetric characterization models based on colorimetric characteristics evaluation for active matrix organic light emitting diode panels.

    Science.gov (United States)

    Gong, Rui; Xu, Haisong; Tong, Qingfen

    2012-10-20

    The colorimetric characterization of active matrix organic light emitting diode (AMOLED) panels suffers from their poor channel independence. Based on the colorimetric characteristics evaluation of channel independence and chromaticity constancy, an accurate colorimetric characterization method, namely, the polynomial compensation model (PC model) considering channel interactions was proposed for AMOLED panels. In this model, polynomial expressions are employed to calculate the relationship between the prediction errors of XYZ tristimulus values and the digital inputs to compensate the XYZ prediction errors of the conventional piecewise linear interpolation assuming the variable chromaticity coordinates (PLVC) model. The experimental results indicated that the proposed PC model outperformed other typical characterization models for the two tested AMOLED smart-phone displays and for the professional liquid crystal display monitor as well.

  4. Detection of Single Molecules Illuminated by a Light-Emitting Diode

    CERN Document Server

    Gerhardt, Ilja; Lamas-Linares, Antia; Kurtsiefer, Christian

    2011-01-01

    Optical detection and spectroscopy of single molecules has become an indispensable tool in biological imaging and sensing. Its success is based on fluorescence of organic dye molecules under carefully engineered laser illumination. In this paper we demonstrate optical detection of single molecules on a wide-field microscope with an illumination based on a commercially available, green light-emitting diode. The results are directly compared with laser illumination in the same experimental configuration. The setup and the limiting factors, such as light transfer to the sample, spectral filtering and the resulting signal-to-noise ratio are discussed. A theoretical and an experimental approach to estimate these parameters are presented. The results can be adapted to other single emitter and illumination schemes.

  5. Current-voltage characteristics of light-emitting diodes under optical and electrical excitation

    Institute of Scientific and Technical Information of China (English)

    Wen Jing; Wen Yumei; Li Ping; Li Lian

    2011-01-01

    The factors influencing the current-voltage (Ⅰ-Ⅴ) characteristics of light-emitting diodes (LEDs) are investigated to reveal the connection of Ⅰ-Ⅴ characteristics under optical excitation and those under electrical excitation.By inspecting the Ⅰ-Ⅴ curves under optical and electrical excitation at identical injection current,it has been found that the Ⅰ-Ⅴ curves exhibit apparent differences in voltage values.Furthermore,the differences are found to originate from the junction temperatures in diverse excitation ways.Experimental results indicate that if the thermal effect of illuminating spot is depressed to an ignorable extent by using pulsed light,the junction temperature will hardly deflect from that under optical excitation,and then the Ⅰ-Ⅴ characteristics under two diverse excitation ways will be the same.

  6. Quantum mechanical modeling the emission pattern and polarization of nanoscale light emitting diodes.

    Science.gov (United States)

    Wang, Rulin; Zhang, Yu; Bi, Fuzhen; Frauenheim, Thomas; Chen, GuanHua; Yam, ChiYung

    2016-07-21

    Understanding of the electroluminescence (EL) mechanism in optoelectronic devices is imperative for further optimization of their efficiency and effectiveness. Here, a quantum mechanical approach is formulated for modeling the EL processes in nanoscale light emitting diodes (LED). Based on non-equilibrium Green's function quantum transport equations, interactions with the electromagnetic vacuum environment are included to describe electrically driven light emission in the devices. The presented framework is illustrated by numerical simulations of a silicon nanowire LED device. EL spectra of the nanowire device under different bias voltages are obtained and, more importantly, the radiation pattern and polarization of optical emission can be determined using the current approach. This work is an important step forward towards atomistic quantum mechanical modeling of the electrically induced optical response in nanoscale systems.

  7. 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.

  8. One-step Double-layer Thermal Evaporation Method for Organic Light Emitting Diodes

    Science.gov (United States)

    Kee, Y. Y.; Yong, T. K.; Ong, D. S.; Tou, T. Y.

    2011-03-01

    A new one-step double-layer thermal evaporation method was used to fabricate organic light emitting diodes (OLEDs) with device structure of: ITO (anode)/N,N_-diphenyl-N,N_-bis(3-methylphenyl)-1,1_-diphenyl-4,4_-diamine (TPD) /tris-(8-hydroxyquinoline)aluminum(3) (Alq3)/Al (cathode). These OLEDs were fabricated in cleanroom on the ITO-coated glass with a sheet resistivity of 20Ω/sq and an optical transmittance of 90%. The I-V and brightness characteristic showed that the new method could produce better performance achieving lower turn-on voltage (-2V), higher peak current efficiency (+29%) and higher brightness (+36%).

  9. Near-infrared broad-band cavity enhanced absorption spectroscopy using a superluminescent light emitting diode.

    Science.gov (United States)

    Denzer, W; Hamilton, M L; Hancock, G; Islam, M; Langley, C E; Peverall, R; Ritchie, G A D

    2009-11-01

    A fibre coupled near-infrared superluminescent light emitting diode that emits approximately 10 mW of radiation between 1.62 and 1.7 microm is employed in combination with a broad-band cavity enhanced spectrometer consisting of a linear optical cavity with mirrors of reflectivity approximately 99.98% and either a dispersive near-infrared spectrometer or a Fourier transform interferometer. Results are presented on the absorption of 1,3-butadiene, and sensitivities are achieved of 6.1 x 10(-8) cm(-1) using the dispersive spectrometer in combination with phase-sensitive detection, and 1.5 x 10(-8) cm(-1) using the Fourier transform interferometer (expressed as a minimum detectable absorption coefficient) over several minutes of acquisition time.

  10. Employment of gold-coated silver nanowires as transparent conductive electrode for organic light emitting diodes

    Science.gov (United States)

    Kim, Sunho; Kim, Bongsung; Im, Inseob; Kim, Dongjae; Lee, Haeseong; Nam, Jaewook; Chung, Ho Kyoon; Lee, Hoo-Jeong; Cho, Sung Min

    2017-08-01

    This study proposes a simple method of Au coating on silver nanowires (Ag NWs) transparent conductive films as the anode of organic light emitting diodes (OLED) to increase the work function of the film and thus enhance hole transport. We carefully engineer the process conditions (pretreatment, solution concentrations, and coating number) of the coating using a diluted HAuCl4 solution on the Ag NWs film to minimize etching damage on Ag NWs accompanying the galvanic replacement reaction. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy show work function increase of Ag NWs upon Au coating. OLED devices based on Au-coated Ag NWs show a lower turn-on voltage and higher luminance, compared with pristine Ag NWs device. Although the Ag NWs device displays poor efficiencies in the low luminance range due to a high leakage, some of the Au-coated Ag NWs devices showed efficiencies higher than those of the ITO device in a high luminance.

  11. Novel Strategy for Photopatterning Emissive Polymer Brushes for Organic Light Emitting Diode Applications

    Science.gov (United States)

    2017-01-01

    A light-mediated methodology to grow patterned, emissive polymer brushes with micron feature resolution is reported and applied to organic light emitting diode (OLED) displays. Light is used for both initiator functionalization of indium tin oxide and subsequent atom transfer radical polymerization of methacrylate-based fluorescent and phosphorescent iridium monomers. The iridium centers play key roles in photocatalyzing and mediating polymer growth while also emitting light in the final OLED structure. The scope of the presented procedure enables the synthesis of a library of polymers with emissive colors spanning the visible spectrum where the dopant incorporation, position of brush growth, and brush thickness are readily controlled. The chain-ends of the polymer brushes remain intact, affording subsequent chain extension and formation of well-defined diblock architectures. This high level of structure and function control allows for the facile preparation of random ternary copolymers and red–green–blue arrays to yield white emission. PMID:28691078

  12. 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.

  13. Monolithic photonic integration of suspended light emitting diode, waveguide and photodetector

    CERN Document Server

    Wang, Yongjin; Gao, Xumin; Cai, Wei; Xu, Yin; Yuan, Jialei; Zhu, Guixia; Yang, Yongchao; Cao, Xun; Zhu, Hongbo; Gruenberg, Peter

    2015-01-01

    We report here a monolithic photonic integration of light emitting diode (LED) with waveguide and photodetector to build a highly-integrated photonic system to perform functionalities on the GaN-on-silicon platform. Suspended p-n junction InGaN/GaN multiple quantum wells (MQWs) are used for device fabrication. Part of the LED emission is coupled into suspended waveguide and then, the guided light laterally propagates along the waveguide and is finally sensed by the photodetector. Planar optical communication experimentally demonstrates that the proof-of-concept monolithic photonic integration system can achieve the on-chip optical interconnects. This work paves the way towards novel active electro-optical sensing system and planar optical communication in the visible range.

  14. Nanoporous silicon tubes: the role of geometry in nanostructure formation and application to light emitting diodes

    Science.gov (United States)

    Vukajlović Pleština, Jelena; Đerek, Vedran; Francaviglia, Luca; Amaduzzi, Francesca; Potts, Heidi; Ivanda, Mile; Morral, Anna Fontcuberta i.

    2017-07-01

    Obtaining light emission from silicon has been the holy grail of optoelectronics over the last few decades. One of the most common methods for obtaining light emission from silicon is to reduce it to a nanoscale structure, for example by producing porous silicon. Here, we present a method for the large-area fabrication of porous silicon microtubes by the stain etching of silicon micropillar arrays. We explain and model how the formation of the microtubes is influenced by the morphology of the substrate, especially the concave or convex character of the 3D features. Light emission is demonstrated at the micro- and nanoscale respectively by photo- and cathodoluminescence. Finally, we demonstrate a 0.55 cm2 device that can work as a photodetector with 2.3% conversion efficiency under one sun illumination, and also as a broadband light emitting diode, illustrating the applicability of our results for optoelectronic applications.

  15. Polymer Light-Emitting Diodes Efficiency Dependence on Bipolar Charge Traps Concentration

    Directory of Open Access Journals (Sweden)

    Luis Morgado

    2009-01-01

    Full Text Available The efficiency of light-emitting diodes (LEDs based on poly[(9,9-dioctylfluorenyl-2,7-diyl-alt-1,4-benzo-{2,1′-3}-thiadiazole], F8BT, is optimized upon simultaneous doping with a hole and an electron trapping molecule, namely, N,N′-Bis(3-methylphenyl-N,N′-diphenylbenzidine and 2-(4-biphenylyl-5-(4-tert-butylphenyl-1,3,4-oxadiazole, respectively. It is shown that, for devices with poly(3,4-ethylene dioxythiophene doped with polystyrene sulfonic acid as hole-injection layer material and magnesium cathodes, the efficiency is nearly doubled (from ca. 2.5 to 3.7 cd/A upon doping with ca. 0.34% by weight of both compounds.

  16. 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.

  17. 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.

  18. 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.

  19. Color three-dimensional display with omnidirectional view based on a light-emitting diode projector.

    Science.gov (United States)

    Yan, Caijie; Liu, Xu; Li, Haifeng; Xia, Xinxing; Lu, Haixia; Zheng, Wenting

    2009-08-01

    A three-dimensional (3D) color display with 360 degrees omnidirectional views is developed by use of a high frame rate digital micromirror device projector and three-color light-emitting diodes as the light source. The high-speed projector can project a series of color images on a rotating anisotropic diffusing mirror that controls the reflective light in a designed angular region. Observers around the display scene can watch autostereoscopic views from the ominidirectional 360 deg view around the 3D display. The vivid 3D scene can be obtained with perfect color effect and correct parallax, projection effect, and occlusion. The principle of the omnidirectional view 3D color display is analyzed in detail and experimental results of a 3D color object are presented.

  20. Flip-Chip GaN-Based Light-Emitting Diodes with Mesh-Contact Electrodes

    Institute of Scientific and Technical Information of China (English)

    ZHU Yan-Xu; XU Chen; HAN Jun; SHEN Guang-Di

    2007-01-01

    @@ GaN-based light-emitting diodes (LEDs) with mesh-contact electrodes have been developed. The p-type ohmic contact layer is composed of oxidized Ni/Au mesh and NiO overlay (20 (A)). An Ag (3000 (A)) omni-directional reflector covers the p-type contact. The n-type contact is a Ti/Al planar film with a 10-μm-width Ti/Al stripe.The Ti/Al stripe surrounds the centre of LED mesa. With a 20-mA current injection, the light output power of GaN-based LEDs with mesh-contact electrodes is 23% higher than that of the conventional LEDs.

  1. Correlated Color Temperature Tunable Multi-chip Light Emitting Diodes Light Source Design

    Institute of Scientific and Technical Information of China (English)

    SHEN Hai-ping; PAN Jian-gen; FENG Hua-jun

    2008-01-01

    One of the methods to derive white light from light emitting diodes(LEDs) is the multi-chip white LED technology, which mixes the light from red, green and blue LEDs. Introduced is an optimal algorithm for the spectrum design of the multi-chip white LEDs in this paper. It optimizes the selection of single color LEDs and drive current controlling, so that the multi-chip white LED achieves the target correlated color temperature(CCT), as well as high luminous efficacy and good color rendering. A CCT tunable LED light source with four high-power LEDs is realized based on the above optimal design. Test results show that it maintains satisfactory color rendering and stable luminous efficacy across the whole CCT tuning range. Finally, discussed are the design improvement and the prospect of the future applications of the CCT tunable LED light source.

  2. Solar-powered light emitting diode power line avoidance marker design

    Science.gov (United States)

    Snook, Ellen H.; Rash, Clarence E.; Martin, John S.; Levine, Richard R.; Johnson, Parley P.

    1992-12-01

    In-flight wire strikes are a constant threat to U.S. Army Aviation during all-weather, daytime and nighttime helicopter operations. Despite routine training on wire avoidance techniques, wire strikes continue to occur, with a majority of the mishaps historically occurring during training and maneuvering over familiar sites. In an effort to increase the conspicuity of suspended cables and wires, the aviation training community at Fort Rucker, Alabama, currently employs a passive wire marking system which consists of international-orange colored spheres suspended from cables and wires in heavily trafficked airspace. During a previous evaluation of wire marker visibility, a solar-powered wire marker design was developed. This new design incorporates retroreflective material and light emitting diodes (LED's) to provide greater range visibility and detectability during aided and unaided flight.

  3. 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.

  4. 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.

  5. Improved calibration technique of the infrared imaging bolometer using ultraviolet light-emitting diodes.

    Science.gov (United States)

    Drapiko, E; Peterson, B; Alekseev, A; Seo, D C

    2010-10-01

    The technique used until recently utilizing the Ne-He laser for imaging bolometer foils calibration [B. J. Peterson et al., J. Plasma Fusion Res. 2, S1018 (2007)] has showed several issues. The method was based on irradiation of 1 cm spaced set of points on a foil by the laser beam moved by set of mirrors. Issues were the nonuniformity of laser power due to the vacuum window transmission nonuniformity and high reflection coefficient for the laser. Also, due to the limited infrared (IR) window size, it was very time consuming. The new methodology uses a compact ultraviolet (uv) light-emitting diodes installed inside the vacuum chamber in a fixed position and the foil itself will be moved in the XY directions by two vacuum feedthroughs. These will help to avoid the above mentioned issues due to lack of a vacuum window, fixed emitters, higher uv power absorption, and a fixed IR camera position.

  6. Green semipolar III-nitride light-emitting diodes grown by limited area epitaxy

    Science.gov (United States)

    Pynn, C. D.; Kowsz, S. J.; Oh, S. H.; Gardner, H.; Farrell, R. M.; Nakamura, S.; Speck, J. S.; DenBaars, S. P.

    2016-07-01

    The performance of multiple quantum well green and yellow semipolar light-emitting diodes (LEDs) is limited by relaxation of highly strained InGaN-based active regions and the subsequent formation of nonradiative defects. Limited area epitaxy was used to block glide of substrate threading dislocations and to reduce the density of misfit dislocations (MDs) directly beneath the active region of (20 2 ¯ 1 ) LEDs. Devices were grown and fabricated on a 1D array of narrow substrate mesas to limit the MD run length. Reducing the mesa width from 20 μm to 5 μm lowered the density of basal plane and non-basal plane MDs on the mesas and limited the number of defect-generating dislocation intersections. This improvement in material quality yielded a 73% enhancement in peak external quantum efficiency for the devices with the narrowest mesas compared to the devices with the widest mesas.

  7. 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.

  8. Aligning the Band Structures of Polymorphic Molybdenum Oxides and Organic Emitters in Light-Emitting Diodes

    Science.gov (United States)

    Yun, Jongmin; Jang, Woosun; Lee, Taehun; Lee, Yonghyuk; Soon, Aloysius

    2017-02-01

    Heavy transition-metal oxides are widely studied for key applications in electronics and energy technologies. In cutting-edge organic-light-emitting-diode (OLED) devices, there remain scientific challenges to achieve an efficient transfer of charges between electrodes and the organic layer. Recently, polymorphic MoO3 has been actively investigated to exploit its unique high work-function values, especially for its use in the electrode buffer layer to effectively transfer the charges in OLED devices. However, no systematic fundamental studies of its electronic structure are available. Thus, in this study, we use first-principles density-functional theory to investigate both the crystal structure and the electronic structure of the MoO3 polymorphs, and we conclude with a simple perspective to screen the best candidate for OLED applications via a hole transport-barrier descriptor.

  9. White Organic Light-Emitting Diodes with fine chromaticity tuning via ultrathin layer position shifting

    CERN Document Server

    Choukri, H; Forget, S; Chenais, S; Castex, M C; Ades, D; Siove, A; Geffroy, B; Choukri, Hakim; Fischer, Alexis; Forget, Sebastien; Chenais, Sebastien; Castex, Marie-Claude; Ades, Dominique; Siove, Alain; Geffroy, Bernard

    2006-01-01

    Non-doped white organic light-emitting diodes using an ultrathin yellow-emitting layer of rubrene (5,6,11,12-tetraphenylnaphtacene) inserted on either side of the interface between a hole-transporting NPB (4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl) layer and a blue-emitting DPVBi (4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl) layer are described. Both the thickness and the position of the rubrene layer allow fine chromaticity tuning from deep-blue to pure-yellow via bright-white with CIE coordinates (x= 0.33, y= 0.32), a external quantum efficiency of 1.9%, and a color rendering index of 70. Such a structure also provides an accurate sensing tool to measure the exciton diffusion length in both DPVBi and NPB (8.7 and 4.9 nm respectively).

  10. An Electroluminescence Delay Time Model of Bilayer Organic Light-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    LI Hong-Jian; ZHU Ru-Hui; LI Xue-Yong; YANG Bing-Chu

    2007-01-01

    @@ Based on the mechanism of injection, transport and recombination of the charge carriers, we develop a model to calculate the delay time of electroluminescence (EL) from bilayer organic light emitting diodes. The effect of injection, transport and recombination processes on the EL delay time is discussed, and the relationship between the internal interface barrier and the recombination time is revealed. The results show that the EL delay time is dominated by the recombination process at lower applied voltage and by the transport process at higher applied voltage. When the internal interface barrier varies from 0.15 eV to 0.3 eV, the recombination delay time increases rapidly, while the internal interface barrier exceeds about 0.3eV, the dependence of the recombination delay time on applied voltage is almost undiversified, which may serve as a guideline for designing of a high-speed EL response device.

  11. The effects of sodium in ITO by pulsed laser deposition on organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Yong, Thian Khok [Multimedia University, Faculty of Engineering, Cyberjaya, Selangor (Malaysia); Universiti Tunku Abdul Rahman, Faculty of Engineering and Science, Kuala Lumpur (Malaysia); Kee, Yeh Yee; Tan, Sek Sean; Siew, Wee Ong; Tou, Teck Yong [Multimedia University, Faculty of Engineering, Cyberjaya, Selangor (Malaysia); Yap, Seong Shan [Multimedia University, Faculty of Engineering, Cyberjaya, Selangor (Malaysia); Norwegian University of Science and Technology, Department of Physics, Trondheim (Norway)

    2010-12-15

    The depth profile of ITO on glass was measured by the time-of-flight secondary ion mass spectroscopy (TOFSIMS) which revealed high sodium (Na) ion concentration at the ITO surface as well as at the ITO-glass interface as a result of out diffusion with substrate heating. Effects of Na ions on the performance of organic light-emitting diode (OLED) were studied by etching away a few tens of nanometers off the ITO surface with a dilute aquaregia solution of HNO{sub 3}:HCl:H{sub 2}O. A single-layer, molecularly doped ITO/(PVK+TPD+Alq{sub 3})/Al OLEDs were fabricated on bare and etched ITO samples. Although the removal of a 10-nm layer of ITO surface increased the voltage range, brightness, and lifetime, it was insufficient to correlate these improvements with solely to the Na ion reduction without considering the surface roughness. (orig.)

  12. Triarylboron-Based Fluorescent Organic Light-Emitting Diodes with External Quantum Efficiencies Exceeding 20 .

    Science.gov (United States)

    Suzuki, Katsuaki; Kubo, Shosei; Shizu, Katsuyuki; Fukushima, Tatsuya; Wakamiya, Atsushi; Murata, Yasujiro; Adachi, Chihaya; Kaji, Hironori

    2015-12-01

    Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron-accepting properties arising from the vacant p orbitals on the boron atoms. In this study, we design and synthesize new donor-acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky-blue to green emission and high photoluminescence quantum yields of 87-100 % in host matrices. Organic light-emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0-22.8 %, which originate from efficient up-conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states.

  13. Tuning the Microcavity of Organic Light Emitting Diodes by Solution Processable Polymer-Nanoparticle Composite Layers.

    Science.gov (United States)

    Preinfalk, Jan B; Schackmar, Fabian R; Lampe, Thomas; Egel, Amos; Schmidt, Tobias D; Brütting, Wolfgang; Gomard, Guillaume; Lemmer, Uli

    2016-02-01

    In this study, we present a simple method to tune and take advantage of microcavity effects for an increased fraction of outcoupled light in solution-processed organic light emitting diodes. This is achieved by incorporating nonscattering polymer-nanoparticle composite layers. These tunable layers allow the optimization of the device architecture even for high film thicknesses on a single substrate by gradually altering the film thickness using a horizontal dipping technique. Moreover, it is shown that the optoelectronic device parameters are in good agreement with transfer matrix simulations of the corresponding layer stack, which offers the possibility to numerically design devices based on such composite layers. Lastly, it could be shown that the introduction of nanoparticles leads to an improved charge injection, which combined with an optimized microcavity resulted in a maximum luminous efficacy increase of 85% compared to a nanoparticle-free reference device.

  14. Radiation-damage-induced phasing: a case study using UV irradiation with light-emitting diodes.

    Science.gov (United States)

    de Sanctis, Daniele; Zubieta, Chloe; Felisaz, Franck; Caserotto, Hugo; Nanao, Max H

    2016-03-01

    Exposure to X-rays, high-intensity visible light or ultraviolet radiation results in alterations to protein structure such as the breakage of disulfide bonds, the loss of electron density at electron-rich centres and the movement of side chains. These specific changes can be exploited in order to obtain phase information. Here, a case study using insulin to illustrate each step of the radiation-damage-induced phasing (RIP) method is presented. Unlike a traditional X-ray-induced damage step, specific damage is introduced via ultraviolet light-emitting diodes (UV-LEDs). In contrast to UV lasers, UV-LEDs have the advantages of small size, low cost and relative ease of use.

  15. High-Resolution Organic Light-Emitting Diodes Patterned via Contact Printing.

    Science.gov (United States)

    Li, Jinhai; Xu, Lisong; Tang, Ching W; Shestopalov, Alexander A

    2016-07-01

    In this study, we report a contact printing technique that uses polyurethane-acrylate (PUA) polymers as the printing stamps to pattern electroluminescent layers of organic light emitting diodes (OLEDs). We demonstrate that electroluminescent thin films can be printed with high uniformity and resolution. We also show that the performance of the printed devices can be improved via postprinting thermal annealing, and that the external quantum efficiency of the printed devices is comparable with the efficiency of the vacuum-deposited OLEDs. Our results suggest that the PUA-based contact printing can be used as an alternative to the traditional shadow mask deposition, permitting manufacturing of OLED displays with the resolution up to the diffraction limit of visible-light emission.

  16. Fully Printed Halide Perovskite Light-Emitting Diodes with Silver Nanowire Electrodes.

    Science.gov (United States)

    Bade, Sri Ganesh R; Li, Junqiang; Shan, Xin; Ling, Yichuan; Tian, Yu; Dilbeck, Tristan; Besara, Tiglet; Geske, Thomas; Gao, Hanwei; Ma, Biwu; Hanson, Kenneth; Siegrist, Theo; Xu, Chengying; Yu, Zhibin

    2016-02-23

    Printed organometal halide perovskite light-emitting diodes (LEDs) are reported that have indium tin oxide (ITO) or carbon nanotubes (CNTs) as the transparent anode, a printed composite film consisting of methylammonium lead tribromide (Br-Pero) and poly(ethylene oxide) (PEO) as the emissive layer, and printed silver nanowires as the cathode. The fabrication can be carried out in ambient air without humidity control. The devices on ITO/glass have a low turn-on voltage of 2.6 V, a maximum luminance intensity of 21014 cd m(-2), and a maximum external quantum efficiency (EQE) of 1.1%, surpassing previous reported perovskite LEDs. The devices on CNTs/polymer were able to be strained to 5 mm radius of curvature without affecting device properties.

  17. Charge injection and accumulation in organic light-emitting diode with PEDOT:PSS anode

    Energy Technology Data Exchange (ETDEWEB)

    Weis, Martin, E-mail: martin.weis@stuba.sk [Institute of Electronics and Photonics, Slovak University of Technology, Ilkovičova 3, Bratislava 81219 (Slovakia); Otsuka, Takako; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa, E-mail: iwamoto@ome.pe.titech.ac.jp [Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8552 (Japan)

    2015-04-21

    Organic light-emitting diode (OLED) displays using flexible substrates have many attractive features. Since transparent conductive oxides do not fit the requirements of flexible devices, conductive polymer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) has been proposed as an alternative. The charge injection and accumulation in OLED devices with PEDOT:PSS anodes are investigated and compared with indium tin oxide anode devices. Higher current density and electroluminescence light intensity are achieved for the OLED device with a PEDOT:PSS anode. The electric field induced second-harmonic generation technique is used for direct observation of temporal evolution of electric fields. It is clearly demonstrated that the improvement in the device performance of the OLED device with a PEDOT:PSS anode is associated with the smooth charge injection and accumulation.

  18. Very low color-temperature organic light-emitting diodes for lighting at night

    Science.gov (United States)

    Jou, Jwo-Huei; Tang, Ming-Chun; Chen, Pin-Chu; Chen, Szu-Hao; Shen, Shih-Ming; Chen, Chien-Chih; Wang, Ching-Chiun; Chen, Chien-Tien

    2011-12-01

    Light sources with low color temperature (CT) are essential for their markedly less suppression effect on the secretion of melatonin, and high power efficiency is crucial for energy-saving. To provide visual comfort, the light source should also have a reasonably high color rendering index (CRI). In this report, we demonstrate the design and fabrication of low CT and high efficiency organic light-emitting diodes. The best resultant device exhibits a CT of 1,880 K, much lower than that of incandescent bulbs (2,000-2,500 K) and even as low as that of candles, (1,800-2,000 K), a beyond theoretical limit external quantum efficiency 22.7 %, and 36.0 lm/W at 100 cd/m 2. The high efficiency of the proposed device may be attributed to its interlayer, which helps effectively distribute the entering carriers into the available recombination zones.

  19. Analysis of thermal degradation of organic light-emitting diodes with infrared imaging and impedance spectroscopy.

    Science.gov (United States)

    Kwak, Kiyeol; Cho, Kyoungah; Kim, Sangsig

    2013-12-02

    We propose a route to examine the thermal degradation of organic light-emitting diodes (OLEDs) with infrared (IR) imaging and impedance spectroscopy. Four different OLEDs with tris (8-hydroxyquinolinato) aluminum are prepared in this study for the analysis of thermal degradation. Our comparison of the thermal and electrical characteristics of these OLEDs reveals that the real-time temperatures of these OLEDs obtained from the IR images clearly correlate with the electrical properties and lifetimes. The OLED with poor electrical properties shows a fairly high temperature during the operation and a considerably short lifetime. Based on the correlation of the real-time temperature and the performance of the OLEDs, the impedance results suggest different thermal degradation mechanisms for each of the OLEDs. The analysis method suggested in this study will be helpful in developing OLEDs with higher efficiency and longer lifetime.

  20. 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.

  1. Studies of light-emitting diode sources for photobiomodulation on cells

    Science.gov (United States)

    Liu, Jiang; Liu, Timon Cheng-Yi; Deng, Xiao-Yuan; Fan, Guang-Han; Liu, Song-Hao

    2006-01-01

    Light-emitting diode (LED), smaller and less expensive, requires less power than laser does, is more and more popular in studying photobiomodulation. Three new LED systems with different intensity have been designed in this paper. The three LED systems consist of a set of lens to expand the beam of light or/and to focus the rays of light, and an array of LEDs set in the sphere connected with Fresnel lens. The intensity of the three LED systems ranges from: 0.002 to 1.465 W/m2 with the spot diameter 40 mm; 0.358 to 11.229 W/m2 with the spot diameter 60 mm; 17.626 to 115.371 W/m2 with the spot diameter 80 mm. Their experimental formulae for calculating intensity were obtained by SPSS.

  2. Evaluation of InGaN/GaN light-emitting diodes of circular geometry.

    Science.gov (United States)

    Wang, X H; Fu, W Y; Lai, P T; Choi, H W

    2009-12-07

    Blue GaN light emitting diodes (LEDs) in the shape of cuboids and circular disks have been fabricated by laser micromachining. The proposed circular geometry serves to enhance overall light extraction on a macro-scale and to improve uniformity of the emission pattern due to the rotational symmetry of the chip. Analysis of the chip shaping effect is carried out by ray-tracing simulations and further supported with mathematical modeling using ideal LED models, and subsequently verified with fabricated devices. In comparison, a 10% improvement in overall emission was observed for circular LEDs over the regular cuboids, consistent with simulations and calculations. The measured emission pattern from the circular LED confirms the axial symmetry of the emission beam.

  3. Evaluation of an organic light-emitting diode display for precise visual stimulation.

    Science.gov (United States)

    Ito, Hiroyuki; Ogawa, Masaki; Sunaga, Shoji

    2013-06-11

    A new type of visual display for presentation of a visual stimulus with high quality was assessed. The characteristics of an organic light-emitting diode (OLED) display (Sony PVM-2541, 24.5 in.; Sony Corporation, Tokyo, Japan) were measured in detail from the viewpoint of its applicability to visual psychophysics. We found the new display to be superior to other display types in terms of spatial uniformity, color gamut, and contrast ratio. Changes in the intensity of luminance were sharper on the OLED display than those on a liquid crystal display. Therefore, such OLED displays could replace conventional cathode ray tube displays in vision research for high quality stimulus presentation. Benefits of using OLED displays in vision research were especially apparent in the fields of low-level vision, where precise control and description of the stimulus are needed, e.g., in mesopic or scotopic vision, color vision, and motion perception.

  4. 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.

  5. Room-temperature direct band-gap electroluminescence from germanium (111)-fin light-emitting diodes

    Science.gov (United States)

    Tani, Kazuki; Saito, Shin-ichi; Oda, Katsuya; Miura, Makoto; Wakayama, Yuki; Okumura, Tadashi; Mine, Toshiyuki; Ido, Tatemi

    2017-03-01

    Germanium (Ge) (111) fins of 320 nm in height were successfully fabricated using a combination of flattening sidewalls of a silicon (Si) fin structure by anisotropic wet etching with tetramethylammonium hydroxide, formation of thin Ge fins by selective Si oxidation in SiGe layers, and enlargement of Ge fins by Ge homogeneous epitaxial growth. The excellent electrical characteristics of Ge(111) fin light-emitting diodes, such as an ideality factor of 1.1 and low dark current density of 7.1 × 10‑5 A cm‑2 at reverse bias of ‑2 V, indicate their good crystalline quality. A tensile strain of 0.2% in the Ge fins, which originated from the mismatch of the thermal expansion coefficients between Ge and the covering SiO2 layers, was expected from the room-temperature photoluminescence spectra, and room-temperature electroluminescence corresponding to the direct band-gap transition was observed from the Ge fins.

  6. Note: A flexible light emitting diode-based broadband transient-absorption spectrometer

    Science.gov (United States)

    Gottlieb, Sean M.; Corley, Scott C.; Madsen, Dorte; Larsen, Delmar S.

    2012-05-01

    This Note presents a simple and flexible ns-to-ms transient absorption spectrometer based on pulsed light emitting diode (LED) technology that can be incorporated into existing ultrafast transient absorption spectrometers or operate as a stand-alone instrument with fixed-wavelength laser sources. The LED probe pulses from this instrument exhibit excellent stability (˜0.5%) and are capable of producing high signal-to-noise long-time (>100 ns) transient absorption signals either in a broadband multiplexed (spanning 250 nm) or in tunable narrowband (20 ns) operation. The utility of the instrument is demonstrated by measuring the photoinduced ns-to-ms photodynamics of the red/green absorbing fourth GMP phosphodiesterase/adenylyl cyclase/FhlA domain of the NpR6012 locus of the nitrogen-fixing cyanobacterium Nostoc punctiforme.

  7. Modeling of organic light emitting diodes: from molecular to device properties (Conference Presentation)

    Science.gov (United States)

    Andrienko, Denis; Kordt, Pascal; May, Falk; Badinski, Alexander; Lennartz, Christian

    2016-09-01

    We will review the progress in modeling of charge transport in disordered organic semiconductors on various length-scales, from atomistic to macroscopic. This includes evaluation of charge transfer rates from first principles, parametrization of coarse-grained lattice and off-lattice models, and solving the master and drift-diffusion equations. Special attention is paid to linking the length-scales and improving the efficiency of the methods. All techniques will be illustrated on an amorphous organic semiconductor, DPBIC, a hole conductor and electron blocker used in state of the art organic light emitting diodes (OLEDs). The outlined multiscale scheme can be used to predict OLED properties without fitting parameters, starting from chemical structures of compounds.

  8. Single nanowire green InGaN/GaN light emitting diodes

    Science.gov (United States)

    Zhang, Guogang; Li, Ziyuan; Yuan, Xiaoming; Wang, Fan; Fu, Lan; Zhuang, Zhe; Ren, Fang-Fang; Liu, Bin; Zhang, Rong; Tan, Hark Hoe; Jagadish, Chennupati

    2016-10-01

    Single nanowire (NW) green InGaN/GaN light-emitting diodes (LEDs) were fabricated by top-down etching technology. The electroluminescence (EL) peak wavelength remains approximately constant with an increasing injection current in contrast to a standard planar LED, which suggests that the quantum-confined Stark effect is significantly reduced in the single NW device. The strain relaxation mechanism is studied in the single NW LED using Raman scattering analysis. As compared to its planar counterpart, the EL peak of the NW LED shows a redshift, due to electric field redistribution as a result of changes in the cavity mode pattern after metallization. Our method has important implication for single NW optoelectronic device applications.

  9. Ultrastrong light-matter coupling in electrically doped microcavity organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Mazzeo, M., E-mail: marco.mazzeo@unisalento.it [Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, Via Monteroni, 73100 Lecce (Italy); NNL, Istituto Nanoscienze - CNR, Via Arnesano, 73100 Lecce (Italy); Genco, A. [Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, Via Monteroni, 73100 Lecce (Italy); Gambino, S. [NNL, Istituto Nanoscienze - CNR, Via Arnesano, 73100 Lecce (Italy); CBN, Istituto Italiano Tecnologia, Via Barsanti 1, 73010 Lecce (Italy); Ballarini, D.; Mangione, F.; Sanvitto, D. [NNL, Istituto Nanoscienze - CNR, Via Arnesano, 73100 Lecce (Italy); Di Stefano, O.; Patanè, S.; Savasta, S. [Dipartimento di Fisica e Scienze della Terra, Università di Messina, Viale F. Stagno d' Alcontres 31, 98166 Messina (Italy); Gigli, G. [Dipartimento di Matematica e Fisica “Ennio De Giorgi”, Università del Salento, Via Monteroni, 73100 Lecce (Italy); NNL, Istituto Nanoscienze - CNR, Via Arnesano, 73100 Lecce (Italy); CBN, Istituto Italiano Tecnologia, Via Barsanti 1, 73010 Lecce (Italy)

    2014-06-09

    The coupling of the electromagnetic field with an electronic transition gives rise, for strong enough light-matter interactions, to hybrid states called exciton-polaritons. When the energy exchanged between light and matter becomes a significant fraction of the material transition energy an extreme optical regime called ultrastrong coupling (USC) is achieved. We report a microcavity embedded p-i-n monolithic organic light emitting diode working in USC, employing a thin film of squaraine dye as active layer. A normalized coupling ratio of 30% has been achieved at room temperature. These USC devices exhibit a dispersion-less angle-resolved electroluminescence that can be exploited for the realization of innovative optoelectronic devices. Our results may open the way towards electrically pumped polariton lasers.

  10. Long-term stability improvement of light-emitting diode using highly transparent graphene oxide paste.

    Science.gov (United States)

    Lee, Seungae; Kim, Yun Ki; Jang, Jyongsik

    2016-10-14

    A highly transparent paste adhesive is successfully fabricated by introducing graphene oxide (GO) to silicone paste adhesive by using a solvent-exchange method. The GO incorporated in the paste adhesive has a significant role in improving thermal conductivity, transparency and adhesive strength. The GO-embedded silicone paste is applied as a die-attach paste to light-emitting diodes (LEDs) in order to enhance the optical quality of the LEDs. The presence of GO in the die-attach layer of the LEDs gives rise to the enhancement of luminous intensity, effective heat dissipation, improvement of moisture barrier property as well as high adhesive strength. Consequently, the LEDs with the GO-embedded die-attach paste exhibit enhanced long-term stability. This novel approach provides a feasible and effective strategy for improving LED performance.

  11. Organic oxide/Al composite cathode in small molecular organic light-emitting diodes

    Science.gov (United States)

    Guo, Tzung-Fang; Yang, Fuh-Shun; Tsai, Zen-Jay; Wen, Ten-Chin; Wu, Ching-In; Chung, Chia-Tin

    2006-07-01

    This study addresses the feasibility of using an organic oxide/Al composite cathode to fabricate the small molecular organic light-emitting diodes (OLEDs). A supplementary organic buffer film is placed at the interface between the tris(8-hydroxyquinoline) aluminum (Alq3) and the organic oxide/Al complex layers. Incorporating the rubrene/poly(ethylene glycol) dimethyl ether (PEGDE) buffer layers into the composite cathode structure markedly improves the performance of devices. The luminous efficiencies of Alq3-based OLEDs biased at ˜100mA /cm2 are 4.8 and 5.1cd/A for rubrene (50Å)/PEGDE (15Å)/Al and rubrene (50Å)/PEGDE (15Å)/LiF (5Å)/Al cathode devices, and 1.3 and 3.8cd/A for devices with Al and LiF (5Å)/Al cathodes, respectively.

  12. Dislocation related droop in InGaN/GaN light emitting diodes investigated via cathodoluminescence

    Science.gov (United States)

    Pozina, Galia; Ciechonski, Rafal; Bi, Zhaoxia; Samuelson, Lars; Monemar, Bo

    2015-12-01

    Today's energy saving solutions for general illumination rely on efficient white light emitting diodes (LEDs). However, the output efficiency droop experienced in InGaN based LEDs with increasing current injection is a serious limitation factor for future development of bright white LEDs. We show using cathodoluminescence (CL) spatial mapping at different electron beam currents that threading dislocations are active as nonradiative recombination centers only at high injection conditions. At low current, the dislocations are inactive in carrier recombination due to local potentials, but these potentials are screened by carriers at higher injection levels. In CL images, this corresponds to the increase of the dark contrast around dislocations with the injection (excitation) density and can be linked with droop related to the threading dislocations. Our data indicate that reduction of droop in the future efficient white LED can be achieved via a drastic reduction of the dislocation density by using, for example, bulk native substrates.

  13. Tunability of InGaN/GaN quantum well light emitting diodes through current

    Science.gov (United States)

    Biswas, Dipankar; Panda, Siddhartha

    2013-07-01

    In the recent years, InGaN/GaN quantum well (QW) light emitting diodes (LEDs) have gathered much importance through the introduction of white LEDs and dual wavelength LEDs. However, the continuous tunability of InGaN/GaN QW LEDs has not been well addressed or discussed. In this paper, we introduce the tunability of an InGaN/GaN QW LED having a well width of 4 nm and In mole fraction of 0.3. The results, obtained from self-consistent solutions of the Schrödinger and Poisson equations, show that the transition energy of the LED may be continuously tuned by the device current. A prominent nonlinearity of the transition energy with the device current is generated, which should be of interest to the research workers in the field of optoelectronics.

  14. Dichromatic color tuning with InGaN-based light-emitting diodes

    Science.gov (United States)

    Fellows, Natalie N.; Sato, Hitoshi; Lin, You-da; Chung, Roy B.; DenBaars, Steven P.; Nakamura, Shuji

    2008-09-01

    Color tuning GaN based light-emitting diodes (LEDs) both electrically and optically was investigated. Color mixing of two LED dies, one nonpolar (λp=467 nm) and one semipolar (λp=574 nm), produced white light. Electrically, the correct current was supplied to each die in order to change its correlated color temperature and Commission Internationale de l'Eclairage (CIE) chromaticity coordinates from 3287 K and (0.425, 0.413) to 7242 K and (0.303, 0.315). The optical polarization anisotropy inherent in nonpolar and semipolar wurtzite GaN allowed color tuning optically with the use of a polarizer. Several regions of the CIE diagram were explored using this method and are discussed.

  15. Phosphor-Free, Color-Tunable Monolithic InGaN Light-Emitting Diodes

    Science.gov (United States)

    Li, Hongjian; Li, Panpan; Kang, Junjie; Li, Zhi; Li, Zhicong; Li, Jing; Yi, Xiaoyan; Wang, Guohong

    2013-10-01

    We have demonstrated phosphor-free color-tunable monolithic GaN-based light-emitting diodes (LEDs) by inserting an ultrathin 1-nm-thick InGaN shallow quantum well (QW) between deep InGaN QWs and GaN barriers. Without using any phosphors, this monolithic LED chip can be tuned to realize wide-range multicolor emissions from red to yellow under different injection currents. In partical, when the injection current reaches an upper level above 100 mA, the LEDs will achieve white emission with a very high color rending index (CRI) of 85.6. This color-tunable characteristic is attributed to the carrier redistribution in the shallow/deep QWs and the energy band filling effect as well.

  16. Polarized light emitting diode by long-range nanorod self-assembling on a water surface.

    Science.gov (United States)

    Rizzo, Aurora; Nobile, Concetta; Mazzeo, Marco; De Giorgi, Milena; Fiore, Angela; Carbone, Luigi; Cingolani, Roberto; Manna, Liberato; Gigli, Giuseppe

    2009-06-23

    We demonstrate a straightforward strategy to fabricate a multilayer inorganic/organic polarized light-emitting diode device based on highly ordered arrays of rod-shaped nanocrystals as the active species. We have developed a simple and effective method that allows colloidal CdSe/CdS core/shell nanorods to be laterally aligned in smectic or nematic phases on the surface of water. A floating film of such ordered nanorods has been collected by a poly(dimethylsiloxane) (PDMS) stamp pad and transferred by contact printing onto previously evaporated organic layers. Thanks to the lateral nanorod alignment the as-prepared film exhibited strong polarized photoluminescence and it has been used as emissive layer in the polarized electroluminescent device.

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

    Science.gov (United States)

    He, Kongduo; Liu, Yang; Gong, Junyi; Zeng, Pan; Kong, Xun; Yang, Xilu; Yang, Cheng; Yu, Yan; Liang, Rongqing; Ou, Qiongrong

    2016-09-01

    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.

  18. 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.

  19. Whole device printing for full colour displays with organic light emitting diodes

    Science.gov (United States)

    Choi, Jun-ho; Kim, Kyung-Ho; Choi, Se-Jin; Lee, Hong H.

    2006-05-01

    Whole device printing is presented for realizing full colour displays with red (R), green (G) and blue (B) organic light emitting diodes (OLEDs). In this process, the whole OLED structure is transferred from a patterned mould to a glass substrate. Therefore, a simple step and repeat of the transfer of each of R, G and B OLED for RGB pixels completes the fabrication of the full colour display over a given area. A difference in the work of adhesion at two interfaces enables the transfer. A 'rigiflex' mould is used for the printing. It is rigid enough to allow sub-100 nm resolution and yet flexible enough for intimate contact with the glass substrate, which permits large area application.

  20. Photonic effects in microstructured conjugated polymer films and light emitting diodes

    CERN Document Server

    Matterson, B J

    2002-01-01

    metal layers that are used as electrodes in the LED does not adversely affect the electrical properties of the LED. It is demonstrated that grating in the LED is able to substantially increase the light emission without using extra electrical power. The emission spectra from LEDs are observed to vary with angle, and exhibit considerable polarization. This thesis reports an investigation into the photonic effects caused by wavelength scale microstructure patterned onto films of conjugated polymers. The efficiency of light emitting diodes (LEDs) made from conjugated polymers is limited in part by the trapping of light into waveguide modes caused by the high refractive index of these materials. Waveguide modes in films of poly(p,-phenylene vinylene) (PPV) and poly(2-methoxy, 5-(2'ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) are analysed and the refractive index of these materials is calculated. The photoluminescence of conjugated polymer films that have been spun onto textured substrates is analysed. It is fou...

  1. 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.

  2. Light extraction enhancement of organic light-emitting diodes using aluminum zinc oxide embedded anodes.

    Science.gov (United States)

    Hsu, Ching-Ming; Lin, Bo-Ting; Zeng, Yin-Xing; Lin, Wei-Ming; Wu, Wen-Tuan

    2014-12-15

    Aluminum zinc oxide (AZO) has been embedded onto indium tin oxide (ITO) anode to enhance the light extraction from an organic light-emitting diode (OLED). The embedded AZO provides deflection and scattering interfaces on the newly generated AZO/organics and AZO/ITO interfaces rather than the conventional ITO/organic interface. The current efficiency of AZO embedded OLEDs was enhanced by up to 64%, attributed to the improved light extraction by additionally created reflection and scattering of emitted light on the AZO/ITO interfaces which was roughed in AZO embedding process. The current efficiency was found to increase with the increasing AZO embedded area ratio, but limited by the accompanying increases in haze and electrical resistance of the AZO embedded ITO film.

  3. Luminescent Tungsten(VI) Complexes: Photophysics and Applicability to Organic Light-Emitting Diodes and Photocatalysis.

    Science.gov (United States)

    Yeung, Kwan-Ting; To, Wai-Pong; Sun, Chenyue; Cheng, Gang; Ma, Chensheng; Tong, Glenna So Ming; Yang, Chen; Che, Chi-Ming

    2017-01-02

    The synthesis, excited-state dynamics, and applications of two series of air-stable luminescent tungsten(VI) complexes are described. These tungsten(VI) complexes show phosphorescence in the solid state and in solutions with emission quantum yields up to 22 % in thin film (5 % in mCP) at room temperature. Complex 2 c, containing a 5,7-diphenyl-8-hydroxyquinolinate ligand, displays prompt fluorescence (blue-green) and phosphorescence (red) of comparable intensity, which could be used for ratiometric luminescent sensing. Solution-processed organic light-emitting diodes (OLEDs) based on 1 d showed a stable yellow emission with an external quantum efficiency (EQE) and luminance up to 4.79 % and 1400 cd m(-2) respectively. These tungsten(VI) complexes were also applied in light-induced aerobic oxidation reactions. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Efficient distributed control of light-emitting diode array lighting systems.

    Science.gov (United States)

    Dong, Jianfei; Pandharipande, Ashish

    2012-07-15

    We consider illumination rendering with distributed control of a lighting system with an array of light-emitting diodes (LEDs). As low-cost microprocessors become standard components in LED drivers, distributing the computation of the control signals to individual LED drivers becomes attractive. Common distributed control algorithms require each individual controller to exchange information with all the others and process it. This incurs too large a communication and processing overhead for a low-cost local controller. In this Letter, we propose a distributed control algorithm for achieving global illumination rendering, wherein a controller only needs to communicate within a selected neighborhood. We present design criteria for defining the communication neighborhood and study its impact on rendering performance.

  5. Heterogeneous integration of gallium nitride light-emitting diodes on diamond and silica by transfer printing.

    Science.gov (United States)

    Trindade, A J; Guilhabert, B; Xie, E Y; Ferreira, R; McKendry, J J D; Zhu, D; Laurand, N; Gu, E; Wallis, D J; Watson, I M; Humphreys, C J; Dawson, M D

    2015-04-06

    We report the transfer printing of blue-emitting micron-scale light-emitting diodes (micro-LEDs) onto fused silica and diamond substrates without the use of intermediary adhesion layers. A consistent Van der Waals bond was achieved via liquid capillary action, despite curvature of the LED membranes following release from their native silicon growth substrates. The excellence of diamond as a heat-spreader allowed the printed membrane LEDs to achieve optical power output density of 10 W/cm(2) when operated at a current density of 254 A/cm(2). This high-current-density operation enabled optical data transmission from the LEDs at 400 Mbit/s.

  6. Recent developments in photocatalytic dye degradation upon irradiation with energy-efficient light emitting diodes

    Institute of Scientific and Technical Information of China (English)

    Wan-Kuen Jo; Rajesh J.Tayade

    2014-01-01

    Light emitting diodes (LEDs) are gaining recognition as a convenient and energy-efficient light source for photocatalytic application. This review focuses on recent progress in the research and development of the degradation of dyes in water under LED light irradiation and provides a brief overview of photocatalysis, details of the LEDs commonly employed, a discussion of the advantages of LEDs over traditional ultraviolet sources and their application to photocatalytic dye degradation. We also discuss the experimental conditions used, the reported mechanisms of dye degradation and the various photocatalytic reactor designs and pay attention to the different types of LEDs used, and their power consumption. Based on a literature survey, the feasibility, benefits, limitations, and future prospects of LEDs for use in photocatalytic dye degradation are discussed in detail.

  7. Improved Carrier Transfer in Red Organic Light Emitting Diodes Doped with Rubrene

    Institute of Scientific and Technical Information of China (English)

    刘宏宇; 高文宝; 杨开霞; 刘式墉

    2002-01-01

    A red organic light emitting diode doped with rubrene is constructed with the configuration of ITO/NPB/Alq3:rubrene:DCM/Alq3/LiF/Al. In the device, N,N'-bis-(1-naphthl)-N,N:diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) is used as the hole-transporting layer, tris(8-quinolinolato) aluminium (Alq3) as the electron-transporting layer and Alq3 doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) and 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) as the emitting layer. When the doping concentration of rubrene is 6% and that of DCM is 4%, red purity of the device is improved effectively. The experimental phenomena are explained as the result of the improved carrier transfer from rubrene to DCM.

  8. White organic light-emitting diodes with fine chromaticity tuning via ultrathin layer position shifting

    Science.gov (United States)

    Choukri, Hakim; Fischer, Alexis; Forget, Sébastien; Chénais, Sébastien; Castex, Marie-Claude; Adès, Dominique; Siove, Alain; Geffroy, Bernard

    2006-10-01

    Nondoped white organic light-emitting diodes using an ultrathin yellow-emitting layer of rubrene (5,6,11,12-tetraphenylnaphtacene) inserted on either side of the interface between a hole-transporting 4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (α-NPB) layer and a blue-emitting 4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl (DPVBi) layer are described. Both the thickness and the position of the rubrene layer allow fine chromaticity tuning from deep blue to pure yellow via bright white with CIE coordinates (x =0.33, y =0.32), an ηext of 1.9%, and a color rendering index of 70. Such a structure also provides an accurate sensing tool to measure the exciton diffusion length in both DPVBi and NPB (8.7 and 4.9nm, respectively).

  9. 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.

  10. Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

    Science.gov (United States)

    Willert, C.; Stasicki, B.; Klinner, J.; Moessner, S.

    2010-07-01

    High-powered light emitting diodes (LED) are investigated for possible uses as light sources in flow diagnostics, in particular, as an alternative to laser-based illumination in particle imaging flow velocimetry in side-scatter imaging arrangements. Recent developments in solid state illumination resulted in mass-produced LEDs that provide average radiant power in excess of 10 W. By operating these LEDs with short duration, pulsed currents that are considerably beyond their continuous current damage threshold, light pulses can be generated that are sufficient to illuminate and image micron-sized particles in flow velocimetry. Time-resolved PIV measurements in water at a framing rate of 2kHz are presented. The feasibility of LED-based PIV measurements in air is also demonstrated.

  11. Novel Digital Driving Method Using Dual Scan for Active Matrix Organic Light-Emitting Diode Displays

    Science.gov (United States)

    Jung, Myoung Hoon; Choi, Inho; Chung, Hoon-Ju; Kim, Ohyun

    2008-11-01

    A new digital driving method has been developed for low-temperature polycrystalline silicon, transistor-driven, active-matrix organic light-emitting diode (AM-OLED) displays by time-ratio gray-scale expression. This driving method effectively increases the emission ratio and the number of subfields by inserting another subfield set into nondisplay periods in the conventional digital driving method. By employing the proposed modified gravity center coding, this method can be used to effectively compensate for dynamic false contour noise. The operation and performance were verified by current measurement and image simulation. The simulation results using eight test images show that the proposed approach improves the average peak signal-to-noise ratio by 2.61 dB, and the emission ratio by 20.5%, compared with the conventional digital driving method.

  12. Thermal analysis of high intensity organic light-emitting diodes based on a transmission matrix approach

    Science.gov (United States)

    Qi, Xiangfei; Forrest, Stephen R.

    2011-12-01

    We use a general transmission matrix formalism to determine the thermal response of organic light-emitting diodes (OLEDs) under high currents normally encountered in ultra-bright illumination conditions. This approach, based on Laplace transforms, facilitates the calculation of transient coupled heat transfer in a multi-layer composite characteristic of OLEDs. Model calculations are compared with experimental data on 5 cm × 5 cm green and red-emitting electrophosphorescent OLEDs under various current drive conditions. This model can be extended to study other complex optoelectronic structures under a wide variety of conditions that include heat removal via conduction, radiation, and convection. We apply the model to understand the effects of using high-thermal- conductivity substrates, and the transient thermal response under pulsed-current operation.

  13. Driving technology for improving motion quality of active-matrix organic light-emitting diode display

    Science.gov (United States)

    Kim, Jongbin; Kim, Minkoo; Kim, Jong-Man; Kim, Seung-Ryeol; Lee, Seung-Woo

    2014-09-01

    This paper reports transient response characteristics of active-matrix organic light emitting diode (AMOLED) displays for mobile applications. This work reports that the rising responses look like saw-tooth waveform and are not always faster than those of liquid crystal displays. Thus, a driving technology is proposed to improve the rising transient responses of AMOLED based on the overdrive (OD) technology. We modified the OD technology by combining it with a dithering method because the conventional OD method cannot successfully enhance all the rising responses. Our method can improve all the transitions of AMOLED without modifying the conventional gamma architecture of drivers. A new artifact is found when OD is applied to certain transitions. We propose an optimum OD selection method to mitigate the artifact. The implementation results show the proposed technology can successfully improve motion quality of scrolling texts as well as moving pictures in AMOLED displays.

  14. Voltage Drop Compensation Method for Active Matrix Organic Light Emitting Diode Displays

    Science.gov (United States)

    Choi, Sang-moo; Ryu, Do-hyung; Kim, Keum-nam; Choi, Jae-beom; Kim, Byung-hee; Berkeley, Brian

    2011-03-01

    In this paper, the conventional voltage drop compensation methods are reviewed and the novel design and driving scheme, the advanced power de-coupled (aPDC) driving method, is proposed to effectively compensate the voltage IR drop of active matrix light emitting diode (AMOLED) displays. The advanced PDC driving scheme can be applied to general AMOLED pixel circuits that have been developed with only minor modification or without requiring modification in pixel circuit. A 14-in. AMOLED panel with the aPDC driving scheme was fabricated. Long range uniformity (LRU) of the 14-in. AMOLED panel was improved from 43% without the aPDC driving scheme, to over 87% at the same brightness by using the scheme and the layout complexity of the panel with new design scheme is less than that of the panel with the conventional design scheme.

  15. Bi2+-doped strontium borates for white-light-emitting diodes.

    Science.gov (United States)

    Peng, Mingying; Wondraczek, Lothar

    2009-10-01

    We report on Bi(2+)-doped SrB(4)O(7) and SrB(6)O(10) as orange and red phosphors for white-light-emitting diodes. In both compounds, absorption due to (2)P(1/2)-->(2)S(1/2) in Bi(2+) could be observed and quantified. The emission redshift from SrB(4)O(7) to SrB(6)O(10) and their different phonon satellite spectra are attributed to the enhancement of phonon-electron interaction. Investigation of the reduction mechanism of Bi(3+) to Bi(2+) suggests that in oxidizing atmosphere, Bi(2+) can be stabilized on Sr(2+) sites only in such lattices that are dominated by tetrahedrally coordinated boron.

  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. A randomly nano-structured scattering layer for transparent organic light emitting diodes.

    Science.gov (United States)

    Huh, Jin Woo; Shin, Jin-Wook; Cho, Doo-Hee; Moon, Jaehyun; Joo, Chul Woong; Park, Seung Koo; Hwang, Joohyun; Cho, Nam Sung; Lee, Jonghee; Han, Jun-Han; Chu, Hye Yong; Lee, Jeong-Ik

    2014-09-21

    A random scattering layer (RSL) consisting of a random nano-structure (RNS) and a high refractive index planarization layer (HRI PL) is suggested and demonstrated as an efficient internal light-extracting layer for transparent organic light emitting diodes (TOLEDs). By introducing the RSL, a remarkable enhancement of 40% and 46% in external quantum efficiency (EQE) and luminous efficacy (LE) was achieved without causing deterioration in the transmittance. Additionally, with the use of the RSL, the viewing angle dependency of EL spectra was reduced to a marginal degree. The results were interpreted as the stronger influence of the scattering effect over the microcavity. The RSL can be applied widely in TOLEDs as an effective light-extracting layer for extracting the waveguide mode of confined light at the indium tin oxide (ITO)/OLED stack without introducing spectral changes in TOLEDs.

  18. Plasmonic phototherapy using gold nanospheres and gold nanorods irradiated with light-emitting diodes

    Science.gov (United States)

    Poorani, Gananathan; Rao, Aruna Prakasa; Singaravelu, Ganesan; Manickam, Elanchezhiyan

    2016-04-01

    Gold nanoparticles (GNPs) provide different modes of therapeutic responses in cells depending on their size and shape. We have studied two modifications of GNPs exhibiting surface plasmon resonances (SPRs) with phototherapeutic effects in nonmalignant Vero and malignant HeLa cell lines. The cells were treated with 30-nm-size gold nanospheres (GNSs) (having SPR at a wavelength of 530 nm) and with gold nanorods (GNRs) (having SPR at 630 nm). The plasmonic phototherapy effect in cells was provided by irradiating them with green and red light-emitting diodes (LEDs). The cytotoxicities of GNPs were determined by MTT assay. Both the GNSs and GNRs were found to be biocompatible and have efficient phototherapeutic activity with LEDs.

  19. Optical Interference Effects by Metal Cathode in Organic Light-Emitting Diodes

    Institute of Scientific and Technical Information of China (English)

    WU Zhao-Xin; WANG Li-Duo; QIU Yong

    2004-01-01

    The dependence of light intensities of organic light-emitting diodes (OLEDs) on the distance of emission zone to metal cathode is investigated numerically. The investigation is based on the half-space optical model that accounts for optical interference effects of metal cathode. We find that light intensities of OLEDs are functions of the distance of emission zone from the metal cathode because of the effect of interference of the metal cathode.This interference leads to an optimal location of emission zone in OLEDs for the maximum of light intensities.Optimal locations of emission zone are numerically shown in various emitting colour OLEDs with different metal cathodes and these results are expected to give insight into the preparation of high efficiency full colour or white light OLEDs.

  20. 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.

  1. Dislocation related droop in InGaN/GaN light emitting diodes investigated via cathodoluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Pozina, Galia [Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden); Ciechonski, Rafal [GLO AB, Scheelevägen 22, SE-22363 Lund (Sweden); Bi, Zhaoxia [Solid State Physics, Lund University, Box 118, SE-22100 Lund (Sweden); Samuelson, Lars [GLO AB, Scheelevägen 22, SE-22363 Lund (Sweden); Solid State Physics, Lund University, Box 118, SE-22100 Lund (Sweden); Monemar, Bo [Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden); Solid State Physics, Lund University, Box 118, SE-22100 Lund (Sweden); TokyoUniversity of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

    2015-12-21

    Today's energy saving solutions for general illumination rely on efficient white light emitting diodes (LEDs). However, the output efficiency droop experienced in InGaN based LEDs with increasing current injection is a serious limitation factor for future development of bright white LEDs. We show using cathodoluminescence (CL) spatial mapping at different electron beam currents that threading dislocations are active as nonradiative recombination centers only at high injection conditions. At low current, the dislocations are inactive in carrier recombination due to local potentials, but these potentials are screened by carriers at higher injection levels. In CL images, this corresponds to the increase of the dark contrast around dislocations with the injection (excitation) density and can be linked with droop related to the threading dislocations. Our data indicate that reduction of droop in the future efficient white LED can be achieved via a drastic reduction of the dislocation density by using, for example, bulk native substrates.

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

    DEFF Research Database (Denmark)

    Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

    fluorescent Boron-Nitrogen co-doped 6H SiC is optimized in terms of source material, growth condition, dopant concentration, and carrier lifetime by using photoluminescence, pump-probe spectroscopy etc. The internal quantum efficiency is measured and the methods to increase the efficiency have been explored......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...

  3. 3D thermal analysis of rectangular microscale inorganic light-emitting diodes in a pulsed operation

    Science.gov (United States)

    Cui, Y.; Bian, Z.; Li, Y.; Xing, Y.; Song, J.

    2016-10-01

    Microscale inorganic light-emitting diodes (µ-ILEDs) have attracted much attention due to their excellent performance in biointegrated applications such as optogenetics. The thermal behaviors of µ-ILEDs are critically important since a certain temperature increase may degrade the LED performance and cause tissue lesion. The µ-ILEDs in a pulsed operation offer an advantage in thermal management. In this paper, a 3D analytic model, as validated by finite element analysis, is developed to study the thermal response of rectangular µ-ILEDs in a pulsed operation. A scaling law for the maximum normalized temperature increase of rectangular µ-ILEDs in terms of non-dimensional parameters is established. The influences of geometric (i.e. shape factor) and loading parameters (e.g. duty cycle and period) on the temperature increase are systematically investigated. These results are very helpful in designing µ-ILEDs by providing guidelines to avoid adverse thermal effects.

  4. 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.

  5. A hole accelerator for InGaN/GaN light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Wang, Liancheng; Zhu, Binbin; Zhang, Yiping; Lu, Shunpeng; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei, E-mail: EXWSUN@ntu.edu.sg, E-mail: VOLKAN@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Demir, Hilmi Volkan, E-mail: EXWSUN@ntu.edu.sg, E-mail: VOLKAN@stanfordalumni.org [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800 Ankara (Turkey)

    2014-10-13

    The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED.

  6. A light emitting diode based photoelectrochemical screener for distributed combinatorial materials discovery.

    Science.gov (United States)

    Winkler, Gates R; Winkler, Jay R

    2011-11-01

    Combinatorial approaches for targeted discovery of new materials require rapid screening systems to evaluate large numbers of new material compositions. High-throughput combinatorial materials discovery is a capital-intensive undertaking requiring sophisticated robotic sample preparation and rapid screening assays. A distributed approach to combinatorial materials discovery can achieve similar goals by increasing the breadth of participation and reducing the size of the capital investment. The discovery of new photoactive materials for solar fuels production demands a screening device to probe materials for electrochemical current production upon irradiation with visible light. We have developed a system that uses an array of pulsed light-emitting diodes (LEDs) synchronized with a two-electrode potentiostat that can measure the photoelectrochemical responses of combinatorial sample arrays deposited on conducting glass plates. Compared to raster scanning methods, this LED system trades spatial resolution for a substantial reduction in scan time. © 2011 American Institute of Physics

  7. Light-emitting diode spherical packages: an equation for the light transmission efficiency

    CERN Document Server

    Moreno, Ivan; Avendano-Alejo, Maximino; 10.1364/AO.49.000012

    2011-01-01

    Virtually all light-emitting diodes (LEDs) are encapsulated with a transparent epoxy or silicone-gel. In this paper we analyze the optical efficiency of spherical encapsulants. We develop a quasi-radiometric equation for the light transmission efficiency, which incorporates some ideas of Monte-Carlo ray tracing into the context of radiometry. The approach includes the extended source nature of the LED chip, and the chip radiance distribution. The equation is an explicit function of the size and the refractive index of the package, and also of several chip parameters such as shape, size, radiance, and location inside the package. To illustrate the use of this equation, we analyze several packaging configurations of practical interest; for example, a hemispherical dome with multiple chips, a flat encapsulation as a special case of the spherical package, and approximate calculations of an encapsulant with a photonic crystal LED or with a photonic quasi crystal LED. These calculations are compared with Monte-Carl...

  8. Substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes

    Science.gov (United States)

    Chung, Seungjun; Lee, Jae-Hyun; Jeong, Jaewook; Kim, Jang-Joo; Hong, Yongtaek

    2009-06-01

    We report substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes (OLEDs). Heat dissipation behavior of top-emission OLEDs fabricated on silicon, glass, and planarized stainless steel substrates was measured by using an infrared camera. Peak temperature measured from the backside of each substrate was saturated to be 21.4, 64.5, and 40.5 °C, 180 s after the OLED was operated at luminance of 10 000 cd/m2 and 80% luminance lifetime was about 198, 31, and 96 h, respectively. Efficient heat dissipation through the highly thermally conductive substrates reduced temperature increase, resulting in much improved OLED lifetime.

  9. Light extraction from organic light-emitting diodes for lighting applications by sand-blasting substrates.

    Science.gov (United States)

    Chen, Shuming; Kwok, Hoi Sing

    2010-01-04

    Light extraction from organic light-emitting diodes (OLEDs) by scattering the light is one of the effective methods for large-area lighting applications. In this paper, we present a very simple and cost-effective method to rough the substrates and hence to scatter the light. By simply sand-blasting the edges and back-side surface of the glass substrates, a 20% improvement of forward efficiency has been demonstrated. Moreover, due to scattering effect, a constant color over all viewing angles and uniform light pattern with Lambertian distribution has been obtained. This simple and cost-effective method may be suitable for mass production of large-area OLEDs for lighting applications.

  10. Color optimization of conjugated-polymer/InGaN hybrid white light emitting diodes by incomplete energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Chi-Jung, E-mail: changcj@fcu.edu.tw [Department of Chemical Engineering, Feng Chia University, 100, Wenhwa Road, Seatwen, Taichung 40724, Taiwan (China); Lai, Chun-Feng [Department of Photonics, Feng Chia University, 100, Wenhwa Road, Seatwen, Taichung 40724, Taiwan (China); Madhusudhana Reddy, P.; Chen, Yung-Lin; Chiou, Wei-Yung [Department of Chemical Engineering, Feng Chia University, 100, Wenhwa Road, Seatwen, Taichung 40724, Taiwan (China); Chang, Shinn-Jen [Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu 300, Taiwan (China)

    2015-04-15

    By using the wavelength conversion method, white light emitting diodes (WLEDs) were produced by applying mixtures of polysiloxane and fluorescent polymers on InGaN based light emitting diodes. UV curable organic–inorganic hybrid materials with high refractive index (1.561), compromised optical, thermal and mechanical properties was used as encapsulants. Red light emitting fluorescent FABD polymer (with 9,9-dioctylfluorene (F), anthracene (A) and 2,1,3-benzothiadiazole (B), and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (D) repeating units) and green light emitting fluorescent FAB polymer were used as wavelength converters. The encapsulant/fluorescent polymer mixture and InGaN produce the white light by incomplete energy transfer mechanism. WLEDs with high color rendering index (CRI, about 93), and tunable correlated color temperature (CCT) properties can be produced by controlling the composition and chemical structures of encapsulating polymer and fluorescent polymer in hybrid materials, offering cool-white and neutral-white LEDs. - Highlights: • Highly efficient white light-emitting diodes (WLEDs) were produced. • Conjugated-polymer/InGaN hybrid WLEDs by incomplete energy transfer mechanism. • WLEDs with high color-rendering index and tunable correlated color temperature. • Polysiloxane encapsulant with superior optical, mechanical and thermal properties.

  11. 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 CO2 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.

  12. 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.

  13. Positive and negative innate immune responses in zebrafish under light emitting diodes conditions.

    Science.gov (United States)

    Zheng, Jia-Lang; Yuan, Shuang-Shuang; Li, Wei-Ye; Wu, Chang-Wen

    2016-09-01

    Certain light emitting diodes (LEDs) have become popular in fish farming beacause of a promoting effect on growth and reproduction. However, little information is available on innate immune responses in related tissues under LEDs conditions. The present study assessed the effects of a white fluorescent bulb (the control) and two different light-emitting diodes (LEDs: blue, LDB, peak at 450 nm; red, LDR, 630 nm) on growth and innate immune responses in the serum, liver and ovary of zebrafish for 8 weeks. LDB significantly enhanced specific growth rate (SGR), food intake (FI), and serum globulin levels. In contrast, LDR sharply inhibited SGR, FI, and the levels of albumin and globulin. Under LDB condition, there was an increase in protein levels of alkaline phophatase (AKP) and protein and activity levels of lysozyme (LZM) in the liver, and the levels of mRNA, protein, and activity of LZM in the ovary. Under LDR condition, LZM was dramatically down-regulated at mRNA, protein and activity levels in the ovary, suggesting that LZM was regulated at a transcriptional level. In the liver of the LDR group, though AKP mRNA levels sharply increased, its protein and activity levels significantly declined, indicating that AKP was regulated at translational level. Furthermore, a positive correlation between transcription factor NF-κB RelA mRNA levels and expression levels of AKP and LZM was observed in the liver and ovary, implying a transcriptional regulation of NF-κB RelA. In conclusion, the present study demonstrated a positive effect of LDB and negative effect of LDR on fish growth and innate immune responses, possibly associated with modifications at transcriptional, translational, and post-translational levels, and the transcriptional regulation of the NF-κB signaling molecule.

  14. 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

  15. Optical-Fiber-Matrix Exposure Using Light-Emitting-Diode Sources

    Science.gov (United States)

    Horiuchi, Toshiyuki; Mirumachi, Naofumi; Ooshima, Yuki

    2007-09-01

    A new projection exposure method without using reticles was proposed, and the feasibility of printing arbitrary patterns was investigated. The preparation of expensive reticles is not favorable for the small-volume production of micro-electro-mechanical systems (MEMS), optomechanical systems, and their components. On the other hand, long turnaround time (TAT) becomes a fatal bottleneck preventing the rapid follow-up of various design changes. As a countermeasure, we previously proposed a new exposure method named optical-fiber-matrix exposure. In this method, patterns are delineated by superimposing light spots from an optical-fiber matrix, and expensive reticles are not necessary. Therefore, patterns are easily changeable by controlling the pattern delineation program. However, in the previous method, light rays from one intensive lamp were divided and switched using small mechanical shutters placed at each fiber entrance, and the shutters were not sufficiently reliable. For this reason, violet light-emitting diodes (LEDs) were used in this research in place of the lamp source and mechanical shutters, and the light or dark state at each optical fiber end was controlled using a microcomputer that switched each LED attached to each fiber entrance one by one. Since the illuminance of each LED was different, LEDs with approximately the same illuminance were selectively used, and each illuminance was adjusted to be uniform by inserting an individual color filter. Thus, the widths of patterns printed by scanning different fiber elements were homogenized. Since line-and-space patterns and various alphabet patterns were successfully printed, the feasibility of fabricating a large-scale optical-fiber matrix was also investigated. An optical-fiber line matrix composed of more than 330 fibers was fabricated without including any gaps between neighbor fibers. There will probably be no fatal problems to enlarge the matrix scale. Although the exposure speed should be improved

  16. Laser-induced forward transfer of polymer light-emitting diode pixels with increased charge injection.

    Science.gov (United States)

    Shaw-Stewart, James; Lippert, Thomas; Nagel, Matthias; Nüesch, Frank; Wokaun, Alexander

    2011-02-01

    Laser-induced forward transfer (LIFT) has been used to print 0.6 mm × 0.5 mm polymer light-emitting diode (PLED) pixels with poly[2-methoxy, 5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) as the light-emitting polymer. The donor substrate used in the LIFT process is covered by a sacrificial triazene polymer (TP) release layer on top of which the aluminium cathode and functional MEH-PPV layers are deposited. To enhance electron injection into the MEH-PPV layer, a thin poly(ethylene oxide) (PEO) layer on the Al cathode or a blend of MEH-PPV and PEO was used. These donor substrates have been transferred onto both plain indium tin oxide (ITO) and bilayer ITO/PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) blend) receiver substrates to create the PLED pixels. For comparison, devices were fabricated in a conventional manner on ITO substrates coated with a PEDOT:PSS hole-transporting layer. Compared to multilayer devices without PEO, devices with ITO/PEDOT:PSS/MEH-PPV:PEO blend/Al architecture show a 100 fold increase of luminous efficiency (LE) reaching a maximum of 0.45 cd/A for the blend at a brightness of 400 cd/m(2). A similar increase is obtained for the polymer light-emitting diode (PLED) pixels deposited by the LIFT process, although the maximum luminous efficiency only reaches 0.05 cd/A for MEH-PPV:PEO blend, which we have attributed to the fact that LIFT transfer was carried out in an ambient atmosphere. For all devices, we confirm a strong increase in device performance and stability when using a PEDOT:PSS film on the ITO anode. For PLEDs produced by LIFT, we show that a 25 nm thick PEDOT:PSS layer on the ITO receiver substrate considerably reduces the laser fluence required for pixel transfer from 250 mJ/cm(2) without the layer to only 80 mJ/cm(2) with the layer.

  17. A highly efficient white-light-emitting diode based on a two-component polyfluorene/quantum dot composite

    Science.gov (United States)

    Dayneko, S. V.; Samokhvalov, P. S.; Lypenko, D.; Nosova, G. I.; Berezin, I. A.; Yakimanskii, A. V.; Chistyakov, A. A.; Nabiev, I.

    2017-01-01

    Organic light-emitting diodes (OLEDs) are attracting great interest of the scientific community and industry because they can be grown on flexible substrates using relatively simple and inexpensive technologies (solution processes). However, a problem in the fabrication of white OLEDs is that it is difficult to achieve a balance between the intensities of individual emission components in the blue, green, and red spectral regions. In this work, we try to solve this problem by creating a two-component light-emitting diode based on modified polyfluorene (PF-BT), which efficiently emits in the blue-green region, and CdSe/ZnS/CdS/ZnS semiconductor quantum dots emitting in the orange-red region with a fluorescence quantum yield exceeding 90%. By changing the mass ratio of components in the active light-emitting composite within 40-50%, it is possible to transform the diode emission spectrum from cold to warm white light without loss of the diode efficiency. It is very likely that optimization of the morphology of multilayer light-emitting diodes will lead to further improvement of their characteristics.

  18. Light-emitting diode-based multiwavelength diffuse optical tomography system guided by ultrasound

    Science.gov (United States)

    Yuan, Guangqian; Alqasemi, Umar; Chen, Aaron; Yang, Yi; Zhu, Quing

    2014-01-01

    Abstract. Laser diodes are widely used in diffuse optical tomography (DOT) systems but are typically expensive and fragile, while light-emitting diodes (LEDs) are cheaper and are also available in the near-infrared (NIR) range with adequate output power for imaging deeply seated targets. In this study, we introduce a new low-cost DOT system using LEDs of four wavelengths in the NIR spectrum as light sources. The LEDs were modulated at 20 kHz to avoid ambient light. The LEDs were distributed on a hand-held probe and a printed circuit board was mounted at the back of the probe to separately provide switching and driving current to each LED. Ten optical fibers were used to couple the reflected light to 10 parallel photomultiplier tube detectors. A commercial ultrasound system provided simultaneous images of target location and size to guide the image reconstruction. A frequency-domain (FD) laser-diode-based system with ultrasound guidance was also used to compare the results obtained from those of the LED-based system. Results of absorbers embedded in intralipid and inhomogeneous tissue phantoms have demonstrated that the LED-based system provides a comparable quantification accuracy of targets to the FD system and has the potential to image deep targets such as breast lesions. PMID:25473884

  19. Color-converted remote phosphor prototype of a multiwavelength excitable borosilicate glass for white light-emitting diodes

    Institute of Scientific and Technical Information of China (English)

    Tian Hua; Liu Ji-Wen; Qiu Kun; Song Jun; Wang Da-Jian

    2012-01-01

    We report a unique red light-emitting Eu-doped borosilicate glass to convert color for warm white light-emitting diodes.This glass can be excited from 394 nm-peaked near ultraviolet light,466 nm-peaked blue light,to 534 nm-peaked green light to emit the desired red light with an excellent transmission in the wavelength range of 400-700 nm which makes this glass suitable for color conversion without a great cost of luminous power loss.In particular,when assembling this glass for commercial white light-emitting diodes,the tested results show that the color rendering index is improved to 84 with a loss of luminous power by 12 percent at average,making this variety of glass promising for inorganic "remote-phosphor" color conversion.

  20. Solution-processable deep red-emitting supramolecular phosphorescent polymer with novel iridium complex for organic light-emitting diodes

    Science.gov (United States)

    Liang, Aihui; Huang, Gui; Wang, Zhiping; Wu, Wenjin; Zhong, Yu; Zhao, Shan

    2016-09-01

    A novel bis(dibenzo-24-crown-8)-functionalized iridium complex with an emission peak at 665 nm was synthesized. Several deep red-emitting supramolecualr phosphorescent polymers (SPPs) as a class of solutionprocessable electroluminescent (EL) emitters were formed by utilizing the efficient non-bonding self-assembly between the resulting iridium complex and bis(dibenzylammonium)-tethered monomers. These SPPs show an intrinsic glass transition with a T g of ca. 90 °C. The photophysical and electroluminescent properties are strongly dependent on the hosts' structures of the supramolecular phosphorescent polymers. The polymer light-emitting diode based on SPP3 displayed a maximal external quantum efficiency (EQE) of 2.14% ph·el-1 and the Commission Internationale de L'Eclairage (CIE) coordinates of (0.70, 0.29).

  1. Localized surface plasmon enhanced emission of organic light emitting diode coupled to DBR-cathode microcavity by using silver nanoclusters.

    Science.gov (United States)

    Khadir, Samira; Chakaroun, Mahmoud; Belkhir, Abderrahmane; Fischer, Alexis; Lamrous, Omar; Boudrioua, Azzedine

    2015-09-01

    In this work, we aim to increase the emission of the standard guest-host organic light emitting diode (OLED) thanks to localized surface plasmon and to investigate this effect in a microcavity. As a first step, we consider thermal deposition of silver clusters within an OLED guest-host stack. We investigate both the influence of the size of silver nanoparticles (Ag-NPs) and their position within the OLED heterostructure. Secondly, we study the optimized OLED within a microcavity formed by Al-cathode top mirror and a Distributed Bragg Reflector (DBR) bottom mirror. The experimental results show a substantial enhancement of the electroluminescence (EL) intensity as well as a reduction of the spectral width at a half maximum.

  2. Molecular beam epitaxial growth and characterization of Al(Ga)N nanowire deep ultraviolet light emitting diodes and lasers

    Science.gov (United States)

    Mi, Z.; Zhao, S.; Woo, S. Y.; Bugnet, M.; Djavid, M.; Liu, X.; Kang, J.; Kong, X.; Ji, W.; Guo, H.; Liu, Z.; Botton, G. A.

    2016-09-01

    We report on the detailed molecular beam epitaxial growth and characterization of Al(Ga)N nanowire heterostructures on Si and their applications for deep ultraviolet light emitting diodes and lasers. The nanowires are formed under nitrogen-rich conditions without using any metal catalyst. Compared to conventional epilayers, Mg-dopant incorporation is significantly enhanced in nearly strain- and defect-free Al(Ga)N nanowire structures, leading to efficient p-type conduction. The resulting Al(Ga)N nanowire LEDs exhibit excellent performance, including a turn-on voltage of ∼5.5 V for an AlN nanowire LED operating at 207 nm. The design, fabrication, and performance of an electrically injected AlGaN nanowire laser operating in the UV-B band is also presented.

  3. Embedded Touch Sensing Circuit Using Mutual Capacitance for Active-Matrix Organic Light-Emitting Diode Display

    Science.gov (United States)

    Park, Young-Ju; Seok, Su-Jeong; Park, Sang-Ho; Kim, Ohyun

    2011-03-01

    We propose and simulate an embedded touch sensing circuit for active-matrix organic light-emitting diode (AMOLED) displays. The circuit consists of three thin-film transistors (TFTs), one fixed capacitor, and one variable capacitor. AMOLED displays do not have a variable capacitance characteristic, so we realized a variable capacitor to detect touches in the sensing pixel by exploiting the change in the mutual capacitance between two electrodes that is caused by touch. When a dielectric substance approaches two electrodes, the electric field is shunted so that the mutual capacitance decreases. We use the existing TFT process to form the variable capacitor, so no additional process is needed. We use advanced solid-phase-crystallization TFTs because of their stability and uniformity. The proposed circuit detects multi-touch points by a scanning process.

  4. Enhancing the performance of blue GaN-based light emitting diodes with double electron blocking layers

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yao; Liang, Meng; Fu, Jiajia; Liu, Zhiqiang, E-mail: spring@semi.ac.cn, E-mail: lzq@semi.ac.cn; Yi, Xiaoyan, E-mail: spring@semi.ac.cn, E-mail: lzq@semi.ac.cn; Wang, Junxi; Wang, Guohong; Li, Jinmin [R and D Center for Semiconductor Lighting, Chinese Academy of Sciences, Beijing 100083 (China)

    2015-03-15

    In this work, novel double Electron Blocking Layers for InGaN/GaN multiple quantum wells light-emitting diodes were proposed to mitigate the efficiency droop at high current density. The band diagram and carriers distributions were investigated numerically. The results indicate that due to a newly formed holes stack in the p-GaN near the active region, the hole injection has been improved and an uniform carriers distribution can be achieved. As a result, in our new structure with double Electron Blocking Layers, the efficiency droop has been reduced to 15.5 % in comparison with 57.3 % for the LED with AlGaN EBL at the current density of 100 A/cm{sup 2}.

  5. Electro-optical properties of a polymer light-emitting diode with an injection-limited hole contact

    NARCIS (Netherlands)

    van Woudenbergh, T; Blom, PWM; Huiberts, JN

    2003-01-01

    The electro-optical characteristics of a polymer light-emitting diode with a strongly reduced hole injection have been investigated. A silver contact on poly-dialkoxy-p-phenylene vinylene decreases the hole injection by five orders of magnitude, resulting in both a highly reduced light output and cu

  6. 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.

  7. Manipulating the local light emission in organic light-emitting diodes by using patterned self-assembled monolayers

    NARCIS (Netherlands)

    Mathijssen, Simon G. J.; van Hal, Paul A.; van den Biggelaar, Ton J. M.; Smits, Edsger C. P.; de Boer, Bert; Kemerink, Martijn; Janssen, Rene A. J.; de Leeuw, Dago M.

    2008-01-01

    Patterned organic light-emitting diodes are fabricated by using microcontactDrinted self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a

  8. A polymer based miniature loop heat pipe with silicon substrate and temperature sensors for high brightness light-emitting diodes

    NARCIS (Netherlands)

    Ye, H.; Sokolovskij, R.; Zeijl, H.W. van; Gielen, A.W.J.; Zhang, G.

    2014-01-01

    Solid State Lighting (SSL) systems, powered by light-emitting diodes (LEDs), are revolutionizing the lighting industry with energy saving and enhanced performance compared to traditional light sources. However, around 70%-80% of the electric power will still be transferred to heat. As the elevated t

  9. Demonstration Assessment of Light-Emitting Diode (LED) Post-Top Lighting at Central Park in New York City

    Energy Technology Data Exchange (ETDEWEB)

    Myer, Michael; Goettel, Russell T.; Kinzey, Bruce R.

    2012-09-30

    A review of five post-top light-emitting diode (LED) pedestrian luminaires installed in New York City's Central Park for possible replacement to the existing metal halide post-top luminaire. This report reviews the energy savings potential and lighting delivered by the LED post-top luminaires.

  10. Manipulating the Local Light Emission in Organic Light-Emitting Diodes by using Patterned Self-Assembled Monolayers

    NARCIS (Netherlands)

    Mathijssen, S.G.J.; Hal, P.A. van; Biggelaar, T.J.M. van den; Smits, E.C.P.; Boer, B. de; Kemerink, M.; Janssen, R.A.J.; Leeuw, D.M. de

    2008-01-01

    In organic light-emitting diodes (OLEDs), interface dipoles play an important role in the process of charge injection from the metallic electrode into the active organic layer.[1,2] An oriented dipole layer changes the effective work function of the electrode because of its internal electric field.

  11. High-Efficiency Blue Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence from Phenoxaphosphine and Phenoxathiin Derivatives.

    Science.gov (United States)

    Lee, Sae Youn; Adachi, Chihaya; Yasuda, Takuma

    2016-06-01

    High-efficiency blue thermally activated delayed fluorescence (TADF) molecules, consisting of phenoxaphosphine oxide and phenoxathiin dioxide as acceptor units and 9,9-dimethylacridan as a donor unit, are reported. Maximum external electroluminescence quantum efficiencies of up to 20.5% are achieved in blue organic light-emitting diodes (OLEDs) by employing these materials as TADF emitters.

  12. Fluorescent Organic Planar pn Heterojunction Light-Emitting Diodes with Simplified Structure, Extremely Low Driving Voltage, and High Efficiency.

    Science.gov (United States)

    Chen, Dongcheng; Xie, Gaozhan; Cai, Xinyi; Liu, Ming; Cao, Yong; Su, Shi-Jian

    2016-01-13

    Fluorescent organic light-emitting diodes capable of radiative utilization of both singlet and triplet excitons are achieved via a simple double-layer planar pn hetero-junction configuration without a conventional emission layer, leading to high external quantum efficiency above 10% and extremely low driving voltages close to the theoretical minima.

  13. Solution-Processable Graphene Oxide as an Efficient Hole Injection Layer for High Luminance Organic Light-Emitting Diodes

    OpenAIRE

    Shi, Shengwei; Sadhu, Veera; Moubah, Reda; Schmerber, Guy; Bao, Qinye; Silva, S. Ravi P.

    2014-01-01

    The application of solution-processable graphene oxide (GO) as hole injection layer in organic light-emitting diodes (OLEDs) is demonstrated. High luminance of over 53,000 cd m-2 is obtained at only 10 V. The results will unlock a route of applying GO in flexible OLEDs and other electrode applications.

  14. A polymer based miniature loop heat pipe with silicon substrate and temperature sensors for high brightness light-emitting diodes

    NARCIS (Netherlands)

    Ye, H.; Sokolovskij, R.; Zeijl, H.W. van; Gielen, A.W.J.; Zhang, G.

    2014-01-01

    Solid State Lighting (SSL) systems, powered by light-emitting diodes (LEDs), are revolutionizing the lighting industry with energy saving and enhanced performance compared to traditional light sources. However, around 70%-80% of the electric power will still be transferred to heat. As the elevated

  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. Improved Performance of Organic Light-Emitting Diodes with MgF2 as the Anode Buffer Layer

    Institute of Scientific and Technical Information of China (English)

    XIE Jing; ZHANG De-Qiang; WANG Li-Duo; DUAN Lian; QIAO Juan; QIU Yong

    2006-01-01

    @@ Organic light-emitting diodes (OLEDs) based on N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) and tris (8-hydroxyquinoline) aluminium (Alq3) are improved by using a thin MgF2 buffer layer sandwiched between the indium tin oxide (ITO) anode and hole transporting layer (HTL) of NPB.

  17. Methods and apparatus of spatially resolved electroluminescence of operating organic light-emitting diodes using conductive atomic force microscopy

    Science.gov (United States)

    Hersam, Mark C. (Inventor); Pingree, Liam S. C. (Inventor)

    2008-01-01

    A conductive atomic force microscopy (cAFM) technique which can concurrently monitor topography, charge transport, and electroluminescence with nanometer spatial resolution. This cAFM approach is particularly well suited for probing the electroluminescent response characteristics of operating organic light-emitting diodes (OLEDs) over short length scales.

  18. 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.

  19. 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 non-radiat

  20. CURRENT STATE OF AUTOMOTIVE LIGHTING EQUIPMENT WITH NON-REPLACEABLE LIGHT SOURCES ON BASIS OF LIGHT-EMITTING DIODE TECHNOLOGIES

    Directory of Open Access Journals (Sweden)

    S. Sernov

    2012-01-01

    Full Text Available The paper contains information on the current state of automotive lighting equipment. Different designs of automotive lighting devices, their merits and demerits are described in the paper. The paper includes a substantiation of expediency of developing light-emitting diode lighting and proposes recommendations about optimization of their design.

  1. Effect of arylamine hole-transport units on the performance of blue polyspirobifulorene light-emitting diodes

    NARCIS (Netherlands)

    Abbaszadeh, D.; Nicolai, H.T.; Crəciun, N.I.; Blom, P.W.M.

    2014-01-01

    The operation of blue light-emitting diodes based on polyspirobifluorene with a varying number of N,N,N′,N′ tetraaryldiamino biphenyl (TAD) hole-transport units (HTUs) is investigated. Assuming that the electron transport is not affected by the incorporation of TAD units, model calculations predict

  2. 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...

  3. 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 lar

  4. Light-Emitting Diodes with Hierarchical and Multifunctional Surface Structures for High Light Extraction and an Antifouling Effect.

    Science.gov (United States)

    Leem, Young-Chul; Park, Jung Su; Kim, Joon Heon; Myoung, NoSoung; Yim, Sang-Youp; Jeong, Sehee; Lim, Wantae; Kim, Sung-Tae; Park, Seong-Ju

    2016-01-13

    Bioinspired hierarchical structures on the surface of vertical light-emitting diodes (VLEDs) are demonstrated by combining a self-assembled dip-coating process and nanopatterning transfer method using thermal release tape. This versatile surface structure can efficiently reduce the total internal reflection and add functions, such as superhydrophobicity and high oleophobicity, to achieve an antifouling effect for VLEDs.

  5. 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.

  6. Analytical correction of temperature in a logarithmic electrometer using light-emitting diodes

    Science.gov (United States)

    Acharya, Y. B.; Aggarwal, A. K.

    1996-05-01

    The current-voltage characteristics of logarithmic amplifiers depend considerably on the ambient temperature. A theoretical correction has been estimated considering the temperature dependence of various parameters in the diode equation. A log electrometer using light-emitting diodes has been fabricated and its I-V characteristics are obtained experimentally for calibration and also to determine the device constant. If a measurement is obtained at a temperature other than the one for which calibration has been done, the theoretical correction can be applied to get the correct value. It has been shown that the theoretically corrected readings lie within ±4% of the experimentally obtained data in the temperature range of 5-60 °C for the operating current range of 10-12-10-4 A. The alternative can be to introduce temperature compensation circuitry into the logarithmic amplifier. However, this makes the electrometer circuit more complex. The proposed theoretical correction method may find applications where space and power are at a premium and the accuracy requirement is not very stringent.

  7. 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.

  8. Preparation of organic light-emitting diode using coal tar pitch, a low-cost material, for printable devices.

    Directory of Open Access Journals (Sweden)

    Miki Yamaoka

    Full Text Available We have identified coal tar pitch, a very cheap organic material made from coal during the iron-making process, as a source from which could be obtained emissive molecules for organic light-emitting diodes. Coal tar pitch was separated by simple dissolution in organic solvent, and subsequent separation by preparative thin-layer chromatography was used to obtain emissive organic molecules. The retardation factor of preparative thin-layer chromatography played a major role in deciding the emission characteristics of the solution as photoluminescence spectra and emission-excitation matrix spectra could be controlled by modifying the solution preparation method. In addition, the device characteristics could be improved by modifying the solution preparation method. Two rounds of preparative thin-layer chromatography separation could improve the luminance of organic light-emitting diodes with coal tar pitch, indicating that less polar components are favorable for enhancing the luminance and device performance. By appropriate choice of the solvent, the photoluminescence peak wavelength of separated coal tar pitch could be shifted from 429 nm (cyclohexane to 550 nm (chloroform, and consequently, the optical properties of the coal tar pitch solution could be easily tuned. Hence, the use of such multicomponent materials is advantageous for fine-tuning the net properties at a low cost. Furthermore, an indium tin oxide/poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate/coal tar pitch/LiF/Al system, in which the emissive layer was formed by spin-coating a tetrahydrofuran solution of coal tar pitch on the substrate, showed a luminance of 176 cd/m(2. In addition, the emission spectrum of coal tar pitch was narrowed after the preparative thin-layer chromatography process by removing the excess emissive molecules.

  9. Preparation of organic light-emitting diode using coal tar pitch, a low-cost material, for printable devices.

    Science.gov (United States)

    Yamaoka, Miki; Asami, Shun-Suke; Funaki, Nayuta; Kimura, Sho; Yingjie, Liao; Fukuda, Takeshi; Yamashita, Makoto

    2013-01-01

    We have identified coal tar pitch, a very cheap organic material made from coal during the iron-making process, as a source from which could be obtained emissive molecules for organic light-emitting diodes. Coal tar pitch was separated by simple dissolution in organic solvent, and subsequent separation by preparative thin-layer chromatography was used to obtain emissive organic molecules. The retardation factor of preparative thin-layer chromatography played a major role in deciding the emission characteristics of the solution as photoluminescence spectra and emission-excitation matrix spectra could be controlled by modifying the solution preparation method. In addition, the device characteristics could be improved by modifying the solution preparation method. Two rounds of preparative thin-layer chromatography separation could improve the luminance of organic light-emitting diodes with coal tar pitch, indicating that less polar components are favorable for enhancing the luminance and device performance. By appropriate choice of the solvent, the photoluminescence peak wavelength of separated coal tar pitch could be shifted from 429 nm (cyclohexane) to 550 nm (chloroform), and consequently, the optical properties of the coal tar pitch solution could be easily tuned. Hence, the use of such multicomponent materials is advantageous for fine-tuning the net properties at a low cost. Furthermore, an indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/coal tar pitch/LiF/Al system, in which the emissive layer was formed by spin-coating a tetrahydrofuran solution of coal tar pitch on the substrate, showed a luminance of 176 cd/m(2). In addition, the emission spectrum of coal tar pitch was narrowed after the preparative thin-layer chromatography process by removing the excess emissive molecules.

  10. Highly luminescent colloidal CdS quantum dots with efficient near-infrared electroluminescence in light-emitting diodes

    OpenAIRE

    Bansal, Ashu Kumar; Antolini, F.; Zhang, Shuyue; Stroea, L.; Orlotani, L; Lanzi, M; Serra, E; Allard, S; Scherf, U.; Samuel, Ifor David William

    2016-01-01

    We acknowledge financial support from FP7 project “Laser Induced Synthesis of Polymeric Nanocomposite Materials and Development of Micro-Patterned Hybrid Light Emitting Diodes (LED) and Transistors (LET)”-LAMP (Project G.A.247928). A.K.B. and I.D.W.S. also acknowledge financial support from EPSRC Programme “Challenging the Limits of Photonics: Structured Light” Grant EP/J01771X/1. Quantum dots are of growing interest as emissive materials in light emitting devices. Here first we report the fo...

  11. Novel donor-acceptor materials for organic light-emitting diodes based on {alpha}-cinnamoyl cyclic ketene dithioacetals

    Energy Technology Data Exchange (ETDEWEB)

    Peng Ping [Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun 130023 (China); Sun Shaoguang [Department of Chemistry, Northeast Normal University, Changchun 130024 (China); Zhao Yixin [Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun 130023 (China); Wu Weicai [Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun 130023 (China); Xia Haijian [Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun 130023 (China); Tian Wenjing [Key Laboratory for Supramolecular Structure and Materials of Ministry of Education, Jilin University, Changchun 130023 (China)]. E-mail: wjtian@mail.jlu.edu.cn; Liu Qun [Department of Chemistry, Northeast Normal University, Changchun 130024 (China)

    2007-10-15

    A new family of {alpha}-cinnamoyl cyclic ketene dithioacetals (CCKDA) based on a typical donor-{pi}-acceptor structure were designed and synthesized. These unsymmetrical {pi}-conjugated molecules consisted of different electron-donating moiety and the same ketene dithioacetals acceptor. The introduction of different donor moieties changed energy level parameters of the molecules and allowed a fine tuning of their optical and electrical properties. It is promising to apply these compounds in organic light-emitting diodes (OLED) as light-emitting and electron-transporting materials.

  12. High power visible light emitting diodes as pulsed excitation sources for biomedical photoacoustics.

    Science.gov (United States)

    Allen, Thomas J; Beard, Paul C

    2016-04-01

    The use of visible light emitting diodes (LEDs) as an alternative to Q-switched lasers conventionally used as photoacoustic excitation sources has been explored. In common with laser diodes, LEDs offer the advantages of compact size, low cost and high efficiency. However, laser diodes suitable for pulsed photoacoustic generation are typically available only at wavelengths greater than 750nm. By contrast, LEDs are readily available at visible wavelengths below 650nm where haemoglobin absorption is significantly higher, offering the prospect of increased SNR for superficial vascular imaging applications. To demonstrate feasibility, a range of low cost commercially available LEDs operating in the 420-620nm spectral range were used to generate photoacoustic signals in physiologically realistic vascular phantoms. Overdriving with 200ns pulses and operating at a low duty cycle enabled pulse energies up to 10µJ to be obtained with a 620nm LED. By operating at a high pulse repetition frequency (PRF) in order to rapidly signal average over many acquisitions, this pulse energy was sufficient to generate detectable signals in a blood filled tube immersed in an Intralipid suspension (µs' = 1mm(-1)) at a depth of 15mm using widefield illumination. In addition, a compact four-wavelength LED (460nm, 530nm, 590nm, 620nm) in conjunction with a coded excitation scheme was used to illustrate rapid multiwavelength signal acquisition for spectroscopic applications. This study demonstrates that LEDs could find application as inexpensive and compact multiwavelength photoacoustic excitation sources for imaging superficial vascular anatomy. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

  13. Visible Red Light Emitting Diode Photobiomodulation for Skin Fibrosis: Key Molecular Pathways.

    Science.gov (United States)

    Mamalis, Andrew; Siegel, Daniel; Jagdeo, Jared

    Skin fibrosis, also known as skin scarring, is an important global health problem that affects an estimated 100 million persons per year worldwide. Current therapies are associated with significant side effects and even with combination therapy, progression, and recurrence is common. Our goal is to review the available published data available on light-emitting diode-generated (LED) red light phototherapy for treatment of skin fibrosis. A search of the published literature from 1 January 2000 to present on the effects of visible red light on skin fibrosis, and related pathways was performed in January 2016. A search of PubMed and EMBASE was completed using specific keywords and MeSH terms. "Fibrosis" OR "skin fibrosis" OR "collagen" was combined with ("light emitting diode," "LED," "laser," or "red light"). The articles that were original research studies investigating the use of visible red light to treat skin fibrosis or related pathways were selected for inclusion. Our systematic search returned a total of 1376 articles. Duplicate articles were removed resulting in 1189 unique articles, and 133 non-English articles were excluded. From these articles, we identified six articles related to LED effects on skin fibrosis and dermal fibroblasts. We augmented our discussion with additional in vitro data on related pathways. LED phototherapy is an emerging therapeutic modality for treatment of skin fibrosis. There is a growing body of evidence demonstrating that visible LED light, especially in the red spectrum, is capable of modulating key cellular characteristic associated with skin fibrosis. We anticipate that as the understanding of LED-RL's biochemical mechanisms and clinical effects continue to advance, additional therapeutic targets in related pathways may emerge. We believe that the use of LED-RL, in combination with existing and new therapies, has the potential to alter the current treatment paradigm of skin fibrosis. There is a current lack of clinical trials

  14. Organic light-emitting diodes incorporating nanometer thick films of europium-cored complexes

    Science.gov (United States)

    Phelan, Gregory D.; Carlson, Brenden; Jiang, Xuezhong; Jen, Alex K. Y.; Dalton, Larry R.

    2002-11-01

    Europium cored complexes may be used as a source of red emission in light emitting diodes. Novel europium cored complexes have been synthesized and incorporated into organic light emitting diodes (OLED's). These complexes emit red light at 615 nm with a full width half maximum (FWHM) of less than 5 nm. The europium complexes consist of one equivalent of europium chelated to three equivalents of a nonsymmetrical β-diketone ligand. The Claissen condensation of a polycyclic aromatic sensitizer and an ester of a fluorinated carboxylic acid create the ligands. The use of a sensitizer such as phenanthrene results in a ligand that has an emission band that directly overlaps with the absorption band of europium. The use of fluorinated chains improves the overall processibility as well as the charge transfer capability of the resulting metal cored complex. The europium core is further encapsulated by the inclusion of an additional polycyclic aromatic compound such as 4, 7 diphenyl - 1, 10 phenanthroline. Emission of 615 nm light is accomplished through excitation of the ligand and efficient Forrester energy transfer to the europium complex. A multiple layer device consisting of a substrate of indium tin oxide, followed by thin layers of BTPD-PFCB (with a thickness of 20nm), a polymer blend containing the europium complex (30 nm), followed by a layer of calcium (50nm) and finally a protective layer of silver (120 nm). The polymer blends were either poly(n-vinyl carbazole)(PVK) or poly vinyl naphthalene (PVN). The device performance was further improved by the incorporation of another lanthanide metal complex. These complexes were based upon similar ligands surrounding gadolinium. In these devices, there is a Dexter energy transfer as well as the Forster energy transfer. For the devices that are based on a PVN:PBD as a polymer host, the lowest turn on voltage was 12.0 volts. The devices that use PVK:TPD devices was 178 cd/m2 with an external quantum efficiency of 0.61%.For

  15. Synthesis, characterization and properties of novel blue light emitting discrete π-functional polymer consisting of carbazole and anthracene units and their applications in polymer light emitting diodes

    Science.gov (United States)

    Gopal, Ram; Huang, Yi-Chiang; Lee, Hsu-Feng; Chang, Ming-Sien; Huang, Wen-Yao

    2017-03-01

    A new novel blue light emitting polymer containing carbazole and anthracene derivatives has been successfully synthesized via polycondensation chemical reaction of diol and difluoro monomers. An effort has been made to raise the band gap of blue light emitter by lowering the conjugation extent in the backbone. The synthesized blue polymer exhibits decent solubility, good process ability, high thermal stability, high glass transition temperature (272 °C) and the decomposition temperature of 358 °C. The UV-vis absorption spectra and photoluminescence spectra depict that the light emission lies in blue region. The solid state photoluminescence (PL) spectra of the polymer (λPL=456 nm) shows red shift (Δλ = 37 nm) as compared with the corresponding solution PL spectra, presumably due to lower intermolecular distance in solid state. The multi-layered polymer light emitting diode was fabricated, using blue polymer with ITO/PEDOT: PSS/BP/LiF/Al architecture. The luminance-voltage (L-V) and current density-voltage (J-V) curves show a maximum luminance of 7544 cd m-2, a maximum emission efficiency of 4.2 cd A-1, a maximum current density of 453 mA cm-2 at a turn-on voltage of 4.5 V. Moreover, the PLED instigate pure blue EL emission, stable at 436 nm with outstanding CIE coordinates of (x = 0.15, y = 0.08), which is close to the pure NTSC blue coordinates of (0.14, 0.08). [Figure not available: see fulltext.

  16. Platinum (II) azatetrabenzoporphyrins for near-infrared organic light emitting diodes

    Science.gov (United States)

    Huang, L.; Park, C. D.; Fleetham, T.; Li, J.

    2016-12-01

    This article describes a series of platinum (II) azatetrabenzoporphyrin emitters for near-infrared (NIR) organic light emitting diode (OLED) applications. Platinum (II) aza-triphenyltetrabenzoporphyrin (PtNTBP) results in a 72 nm shift in the photoluminescent (PL) emission spectrum to 842 nm compared to 770 nm of the platinum (II) tetraphenyltetrabenzoporphyrin (PtTPTBP). Also, the full width at half maximum of the emission spectrum of PtNTBP was significantly narrowed to 27 nm compared to 40 nm for PtTPTBP. The multilayer devices fabricated by thermal vacuum evaporation process employing PtTPTBP, PtNTBP, and cis-PtN2TBP exhibit electroluminescent (EL) emission peak at 770 nm, 848 nm, and 846 nm with the peak external quantum efficiency (EQE) of 8.0%, 2.8%, and 1.5%, respectively. Even with the decrease in EQE of devices employing PtNTBP and cis-PtN2TBP compared with those employing PtTPTBP, the combination of the spectral narrowing and the bathochromic shift to lower energy EL emission demonstrates the promise of PtNTBP for NIR applications. In the meanwhile, the solution-processed single-layer device using PtNTBP demonstrates the EQE of 0.33% and the peak EL emission at 844 nm.

  17. 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.

  18. Recent advances in light outcoupling from white organic light-emitting diodes

    Science.gov (United States)

    Gather, Malte C.; Reineke, Sebastian

    2015-01-01

    Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ˜100% yield. However, the extraction of photons remains rather inefficient (typically <30%). Here, we provide an introduction to the underlying physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal-metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.

  19. 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

    2017-03-07

    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) Csx PbBr3 (FA = CH(NH2 )2 ). By detailed characterization of their morphological, optical, and physicochemical properties, it is found that the emission property of the perovskite, FA(1-x) Csx PbBr3 , 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 FA0.8 Cs0.2 PbBr3 , 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.

  20. High-performance perovskite light-emitting diodes via morphological control of perovskite films.

    Science.gov (United States)

    Yu, Jae Choul; Kim, Da Bin; Jung, Eui Dae; Lee, Bo Ram; Song, Myoung Hoon

    2016-04-07

    Solution-processable perovskite materials have garnered tremendous attention because of their excellent charge carrier mobility, possibility of a tunable optical bandgap, and high photoluminescence quantum efficiency (PLQE). In particular, the uniform morphology of a perovskite film is the most important factor in realizing perovskite light-emitting diodes (PeLEDs) with high efficiency and full-coverage electroluminescence (EL). In this study, we demonstrate highly efficient PeLEDs that contain a perovskite film with a uniform morphology by introducing HBr into the perovskite precursor. The introduction of HBr into the perovskite precursor results in a perovskite film with a uniform, continuous morphology because the HBr increases the solubility of the inorganic component in the perovskite precursor and reduces the crystallization rate of the perovskite film upon spin-coating. Moreover, PeLEDs fabricated using perovskite films with a uniform, continuous morphology, which were deposited using 6 vol% HBr in a dimethylformamide (DMF)/hydrobromic acid (HBr) cosolvent, exhibited full coverage of the green EL emission. Finally, the optimized PeLEDs fabricated with perovskite films deposited using the DMF/HBr cosolvent exhibited a maximum luminance of 3490 cd m(-2) (at 4.3 V) and a luminous efficiency of 0.43 cd A(-1) (at 4.3 V).

  1. Fabrication of an Organic Light-Emitting Diode from New Host π Electron Rich Zinc Complex

    Science.gov (United States)

    Jafari, Mohammad Reza; Janghouri, Mohammad; Shahedi, Zahra

    2016-09-01

    A new π electron rich zinc complex was used as a fluorescent material in organic light-emitting diodes (OLEDs). Devices with a structure of indium tin oxide/poly (3,4-ethylenedi-oxythiophene):poly(styrenesulfonate) (PEDOT: PSS) (50 nm)/polyvinylcarbazole (60 nm)/Zn: %2 porphyrin derivatives (45 nm)/Al (150 nm) were fabricated. Porphyrin derivatives accounting for 2 wt.% in the π electron rich zinc complex were used as a host. The electroluminescence (EL) spectra of porphyrin derivatives indicated a red shift, as π electron rich zinc complex EL spectra. The device (4) has also a luminance of 3420 cd/m2 and maximum efficiency of 1.58 cd/A at 15 V, which are the highest values among four devices. The result of Commission International del'Eclairage (CIE) (X, Y) coordinate and EL spectrum of device (3) indicated that it is more red shifted compared to other devices. Results of this work indicate that π electron rich zinc complex is a promising host material for high efficiency red OLEDs and has a simple structure compared to Alq3-based devices.

  2. Patternless light outcoupling enhancement method for top-emission organic light-emitting diodes

    Science.gov (United States)

    Kim, Doo-Hoon; Lee, Ho-Nyeon

    2016-11-01

    An increase of 65% in the luminous flux of a top-emission organic light-emitting diode (TE-OLED) was obtained by fabricating a stacked N,N‧-bis(naphthalen-1-yl)-N,N‧-bis(phenyl)benzidine (NPB) (0.2 µm)/CaF2 (2.5 µm) light outcoupling layer on the TE-OLED. The high-refractive-index NPB layer extracted the trapped light energy in the TE-OLED for input into the light outcoupling layer and protected the top cathode of the TE-OLED from damage due to the CaF2 layer. The surface morphology of the CaF2 layer had an irregular shape consisting of randomly dispersed pyramids; the irregular structure scattered the waveguide mode energy into air. By combining the effects of the NPB and CaF2 layers, the external quantum efficiency of the TE-OLED was increased significantly. The light outcoupling layer can be fabricated using a thermal evaporation process without patterning and, hence, provides a practical solution for the enhancement of TE-OLED light outcoupling using a patternless fabrication process.

  3. Broadband Midwave Infrared InAs/GaSb Superlattice Light-Emitting Diodes

    Science.gov (United States)

    Ricker, Russell; Provence, Sydney; Norton, Dennis; Prineas, John; Boggess, Thomas

    Broadband (3.0 μm to 5.0 μm) emission is reported from InAs/GaSb superlattice light-emitting diodes grown via molecular beam epitaxy . Stacked active regions, each with a different emission wavelength, were connected with tunnel junctions, resulting in multiple emission wavelengths in a monolithic structure. Eight active regions provided eight overlapping emission spectra, simulating a broadband spectrum. Chips with mesas of sizes ranging from 24 μm x 24 μm to 400 μm x 400 μm were fabricated and wire bonded to a leadless chip carrier (LCC). The LCC was mounted in a liquid nitrogen cryostat. At low input currents, distinct peaks were observed at 3.3 μm, 3.6 μm, 3.9 μm, 4.2 μm, 4.5 μm, 4.9 μm, and 5.3 μm. At high input currents a continuous spectrum was observed with a peak near 3.8 μm and with a full-width at half-maximum of 1.42 μm. In quasi-continuous operation at 77 K, radiances exceeding 0.35 W/cm2-sr in a Lambertian profile were achieved. Current dependent electroluminescent spectra measured at liquid nitrogen temperatures demonstrate the blending of the various colors from each stage into one smooth spectrum at high currents.

  4. Use of anodes with tunable work function for improving organic light-emitting diode performance

    Science.gov (United States)

    Li, Meng-Chi; Lo, Yen-Ming; Liao, Shih-Fang; Chen, Hsi-Chao; Chang, Hsin-Hua; Lee, Cheng-Chung; Kuo, Chien-Cheng

    2015-12-01

    The effect of reactive gases-oxygen and hydrogen-on the tunable work function of Al-doped ZnO (AZO) films was studied. An increase in the work function with an increase in the oxygen flow rate was mainly interpreted as reflecting a decrease in the carrier concentration, which was attributed to the filling of oxygen vacancies. However, a decrease in the carrier concentration would result in the resistivity increasing sharply. This article presents a new concept for improving the performance of organic light-emitting diodes (OLEDs) through easy and effective hole injection from a multilayer AZO anode to the organic layer. A bilayer AZO film prepared using a tunable work function technique was used to modify the surface of AZO anodes and to ensure that the anodes had low resistivity. The AZO anode stacked with high-work-function AZO films, similar to hole transport buffer layers, had a low turn-on voltage of 2.89 V, and its luminance efficiency and power efficiency were 5.01% and 6.1% greater than those of tin-doped indium oxide anodes used in OLEDs.

  5. Lifetime improvement mechanism in organic light-emitting diodes with mixed materials at a heterojunction interface

    Science.gov (United States)

    Minagawa, Masahiro; Takahashi, Noriko

    2016-02-01

    To investigate the lifetime improvement mechanism caused by mixing at the heterojunction interface, organic light-emitting diodes (OLEDs) with stacked and mixed 4,4‧-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD)/tris(8-hydroxyquinoline)aluminum (Alq3) interfaces were fabricated, and changes in their displacement current due to continuous operation were measured. A decrease in accumulated holes at the α-NPD/Alq3 interface was observed in the stacked configuration devices over longer operations. These results indicate that the injected hole density was reduced during continuous operation, implying that the carrier balance became uneven in the emission region. However, few accumulated holes and changes in the displacement current due to continuous operation were observed in the devices having the mixed layer. Therefore, it was deduced that the number of holes concentrated between the α-NPD and Alq3 layers was decreased by mixing at the heterojunction interface, and that the change in the number of holes was smaller during continuous operation, resulting in less degradation.

  6. Enhanced performance of blue polymer light-emitting diodes by a self-assembled thin interlayer.

    Science.gov (United States)

    Kim, Yun Ho; Lee, Wonjoo; Cai, Gangri; Baek, Su Jin; Han, Sung-Hwan; Lee, Soo-Hyoung

    2008-09-01

    High efficiency and long lifetime, blue polymer light-emitting diodes were obtained by adding a thin interlayer, which was fabricated by a layer-by-layer self-assembly technique between poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonic acid) (PEDOT:PSS) hole transporting and emissive polymer layers in the device configuration of indium tin oxide (ITO)/PEDOT:PSS (65 nm)/interlayer (10-30 nm)/emissive polymer (70 nm)/BaF2 (2 nm)/Ca (50 nm)/Al (300 nm). The interlayer, (PPV/PSS)n, consisted of self-assembled multilayers of the conjugated polymer, poly (p-phenylenevinylene) (PPV), and the polyelectrolyte, poly (styrene sulfonic acid) (PSS). Electroluminescence (EL) characteristics such as luminescence and current efficiency of the devices were enhanced by the addition of the interlayer. Furthermore, the devices with interlayer showed longer lifetime than those without interlayer. The maximum device performance was obtained from the device with (PPV/PSS)3 interlayer.

  7. 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.

  8. 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.

  9. The activation of directional stem cell motility by green light-emitting diode irradiation.

    Science.gov (United States)

    Ong, Wei-Kee; Chen, How-Foo; Tsai, Cheng-Ting; Fu, Yun-Ju; Wong, Yi-Shan; Yen, Da-Jen; Chang, Tzu-Hao; Huang, Hsien-Da; Lee, Oscar Kuang-Sheng; Chien, Shu; Ho, Jennifer Hui-Chun

    2013-03-01

    Light-emitting diode (LED) irradiation is potentially a photostimulator to manipulate cell behavior by opsin-triggered phototransduction and thermal energy supply in living cells. Directional stem cell motility is critical for the efficiency and specificity of stem cells in tissue repair. We explored that green LED (530 nm) irradiation directed the human orbital fat stem cells (OFSCs) to migrate away from the LED light source through activation of extracellular signal-regulated kinases (ERK)/MAP kinase/p38 signaling pathway. ERK inhibitor selectively abrogated light-driven OFSC migration. Phosphorylation of these kinases as well as green LED irradiation-induced cell migration was facilitated by increasing adenosine triphosphate (ATP) production in OFSCs after green LED exposure, and which was thermal stress-independent mechanism. OFSCs, which are multi-potent mesenchymal stem cells isolated from human orbital fat tissue, constitutionally express three opsins, i.e. retinal pigment epithelium-derived rhodopsin homolog (RRH), encephalopsin (OPN3) and short-wave-sensitive opsin 1 (OPN1SW). However, only two non-visual opsins, i.e. RRH and OPN3, served as photoreceptors response to green LED irradiation-induced OFSC migration. In conclusion, stem cells are sensitive to green LED irradiation-induced directional cell migration through activation of ERK signaling pathway via a wavelength-dependent phototransduction. Copyright © 2012 Elsevier Ltd. All rights reserved.

  10. Manipulation and control of the interfacial polarization in organic light-emitting diodes by dipolar doping

    Science.gov (United States)

    Jäger, Lars; Schmidt, Tobias D.; Brütting, Wolfgang

    2016-09-01

    Most of the commonly used electron transporting materials in organic light-emitting diodes exhibit interfacial polarization resulting from partially aligned permanent dipole moments of the molecules. This property modifies the internal electric field distribution of the device and therefore enables an earlier flat band condition for the hole transporting side, leading to improved charge carrier injection. Recently, this phenomenon was studied with regard to different materials and degradation effects, however, so far the influence of dilution has not been investigated. In this paper we focus on dipolar doping of the hole transporting material 4,4-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) with the polar electron transporting material tris-(8-hydroxyquinolate) aluminum (Alq3). Impedance spectroscopy reveals that changes of the hole injection voltage do not scale in a simple linear fashion with the effective thickness of the doped layer. In fact, the measured interfacial polarization reaches a maximum value for a 1:1 blend. Taking the permanent dipole moment of Alq3 into account, an increasing degree of dipole alignment is found for decreasing Alq3 concentration. This observation can be explained by the competition between dipole-dipole interactions leading to dimerization and the driving force for vertical orientation of Alq3 dipoles at the surface of the NPB layer.

  11. Stress-induced piezoelectric field in GaN-based 450-nm light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Tawfik, Wael Z. [Department of Materials Science and Engineering, Chonnam National University, Yongbong 300 Gwangju 500-757 (Korea, Republic of); Department of Physics, Faculty of Science, Beni-Suef University, Beni-Suef 62511 (Egypt); Hyeon, Gil Yong; Lee, June Key, E-mail: junekey@chonnam.ac.kr [Department of Materials Science and Engineering, Chonnam National University, Yongbong 300 Gwangju 500-757 (Korea, Republic of)

    2014-10-28

    We investigated the influence of the built-in piezoelectric field induced by compressive stress on the characteristics of GaN-based 450-nm light-emitting diodes (LEDs) prepared on sapphire substrates of different thicknesses. As the sapphire substrate thickness was reduced, the compressive stress in the GaN layer was released, resulting in wafer bowing. The wafer bowing-induced mechanical stress altered the piezoelectric field, which in turn reduced the quantum confined Stark effect in the InGaN/GaN active region of the LED. The flat-band voltage was estimated by measuring the applied bias voltage that induced a 180° phase shift in the electro-reflectance (ER) spectrum. The piezoelectric field estimated by the ER spectra changed by ∼110 kV/cm. The electroluminescence spectral peak wavelength was blue-shifted, and the internal quantum efficiency was improved by about 22% at a high injection current of 100 mA. The LED on the 60-μm-thick sapphire substrate exhibited the highest light output power of ∼59 mW at an injection current of 100 mA, with the operating voltage unchanged.

  12. Waveguide-integrated microdisk light-emitting diode and photodetector based on Ge quantum dots.

    Science.gov (United States)

    Xu, Xuejun; Maruizumi, Takuya; Shiraki, Yasuhiro

    2014-02-24

    Microdisk integrated with a bus waveguide is fabricated on silicon-on-insulator substrate containing Ge self-assembled quantum dots as active medium. The device is demonstrated to be operated as both light-emitting diode and photodetector. At forward bias, carriers are injected into the microdisk and light emission at 1.45-1.6 μm is extracted through the waveguide via microdisk-waveguide coupling. Sharp resonant peaks with Q-factor as high as 1350 are obtained in the electroluminescence spectra, corresponding to whispering gallery modes of the microdisk. At reverse bias, the device functions as a resonant cavity enhanced photodetector with wavelength-selective photo-response. The photo-current at resonant wavelength of 1533.65 nm is 50 times larger than that at non-resonant wavelength. The dark current density of the photodetector is as low as 0.29 mA/cm2 up to -10 V bias and the peak responsivity is 5.645 mA/W.

  13. Reliability analysis of CaN-based light emitting diodes for solid state illumination

    Institute of Scientific and Technical Information of China (English)

    Yang Ling; Ma Xiao-Hua; Feng Qian; Hao Yue

    2008-01-01

    In this paper, we have discussed the effect of electrical stress on GaN light emitting diode (LED). With the lapse of time, the LED with an applied large current stress can reduce its current more than without such a stress under a large forward-voltage drop. Its scanning electron microscopy (SEM) image shows that there exist several pits on the surface of the p-metal. With an electrical stress applied, the number of pits greatly increases. We also find that the degradation of GaN LED is related to the oxidized Ni/Au ohmic contact to p-GaN. The electrical activation of H-passivated Mg acceptors is described in detail. Annealing is performed in ambient air for 10min and the differential resistances at a forward-voltage drop of 5V are taken to evaluate the activation of the Mg acceptors. These results suggest some mechanisms of degradation responsible for these phenomena, which are described in the paper.

  14. 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.)

  15. Organic Light Emitting Diodes with Lithium Contained Alq3 as Electron Injection Layer

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Novel lithium doped tris-8-hydroxylquinoline aluminium (Alq3:Li) layer is deposited between emission layer and electron injection aluminium electrode as an electron injection assistant layer in different organic light emitting diodes(OLED) to lower the electron injection barrier. In these devices, Alq3 is used as emission layer, and a bilayer film of N, N' -bis- ( 1-naphhyl)-N, N' -diphenyl- 1,1' -biphenyle-4,4" -diamine (NPB) and 4,4' , 4" -tris (3-methyl-phenylphenylamino) triphenylamine(m-MTDATA) used as hole transport layer(HTL). The electroluminescent performance of devices with different thicknesses of Alq3: Li shows that the insertion of the lithium doped Alq3 layer can reduce the turn on voltage by at least 2 volts, and the stability of devices with this lithium doped Alq3 layer is improved too. It can also change the efficiency of devices. Compared with an ultra-thin lithium fluoride(IiF) layer, Alq3 : Li sheet gives similar effects but higher efficiency and can be much thicker and hence it is easier to control the deposition.

  16. 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.

  17. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Daibo, M [Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan); Kamiwano, D [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Kurosawa, T [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Yoshizawa, M [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Tayama, N [Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551 (Japan)

    2006-06-01

    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.

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

    Science.gov (United States)

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

    2015-09-01

    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 dielectric. Uncured polymer is then rinsed away, leaving a patterned dielectric layer that conforms to the shape of the grid lines. To enhance the accuracy of the alignment, heat conduction into the substrate and the transparent electrode is limited by using short current pulses instead of a constant current. Excellent alignment accuracy of the dielectric layer on printed metal grid lines has been achieved, with a typical 4-μm dielectric overhang. In addition to good accuracy, pulsed Joule heating significantly cuts down process time and energy consumption compared to heating with a constant current. The feasibility of using a printed current distribution grid and Joule heating was demonstrated in an OLED device.

  20. Remanent spin injection and spin relaxation in quantum dot light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Soldat, Henning; Li, Mingyuan; Gerhardt, Nils C.; Hofmann, Martin R. [Lehrstuhl fuer Photonik und Terahertztechnologie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Ludwig, Arne; Wieck, Andreas D.; Reuter, Dirk [Lehrstuhl fuer Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany); Stromberg, Frank; Keune, Werner; Wende, Heiko [Fakultaet fuer Physik, Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, D-47048 Duisburg (Germany)

    2011-07-01

    The study of spin-controlled optoelectronic devices has been a field of intensive research over the past few years. We investigate spin injection in remanence into InAs quantum dot (QD) light emitting diodes (LEDs). Our samples are spin LEDs with a Fe/Tb injector with out-of-plane remanent magnetization and a MgO tunnel barrier at the ferromagnetic metal/semiconductor interface to overcome the conductivity mismatch. The active region is an ensemble of InAs QDs. Intrinsic GaAs layers of variable thickness have been implemented between this active region and the spin injector to investigate the influence of transport path length on spin polarization. We have measured the circular polarization of the LED emission in remanence. By investigating the different injection path lengths for the samples we have determined the spin diffusion length in undoped GaAs along with the spin polarization at the injector interface. Additionally, the spin injection efficiency at the MgO tunnel barrier has been investigated.