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Sample records for heterojunction light-emitting diodes

  1. 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...

  2. Electron-hole capture in polymer heterojunction light-emitting diodes

    Science.gov (United States)

    Greenham, Neil

    2005-03-01

    Polymer light-emitting diodes based on blends of polyfluorene derivatives show very high efficiencies and low drive voltages. Electron-hole capture in these devices directly produces long-lived exciplex states where the electron and hole are predominantly localized on opposite sides of the heterojunction. The exciplex may then be thermally excited to form an intra-chain exciton, which can itself either emit, or be recycled to reform the exciplex. I will review the physics of exciplex formation and emission in these devices, and will show that exciplex formation rates are consistent with low free charge densities at the heterojunction. I will present evidence that the rate of charge transfer at polyfluorene heterojunctions can be modulated with an applied electric field, leading in some cases to an increase in photoluminescence efficiency with applied field. I will also present recent results showing enhanced triplet exciton formation after photoexcitation in polyfluorene blends, and will discuss the implications of the results for polymer light-emitting and photovoltaic devices.

  3. 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

  4. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-04-15

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

  6. Light-emitting diode.

    Science.gov (United States)

    Gold, Michael H

    2011-01-01

    Light-emitting diode (LED) photomodulation has become a recognized player in the world of lasers and light sources. It is used to treat a variety of clinical entities, including photorejuvenation, erythema-induced injury following laser and other cosmetic procedures, and acne vulgaris. Its use has increased and will increase further as our understanding of LED devices deepens. Copyright © 2011 S. Karger AG, Basel.

  7. Light Emitting Diode (LED)

    Science.gov (United States)

    1997-01-01

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

  8. Single ZnO nanowire/p-type GaN heterojunctions for photovoltaic devices and UV light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Bie, Ya-Qing; Liao, Zhi-Min; Wang, Peng-Wei; Zhou, Yang-Bo; Han, Xiao-Bing; Ye, Yu; Zhao, Qing; Wu, Xiao-Song; Dai, Lun; Xu, Jun; Sang, Li-Wen; Deng, Jun-Jing; Laurent, K.; Yu, Da-Peng [State Key Laboratory for Mesoscopic Physics, Department of Physics, Peking University, Beijing 100871 (China); Leprince-Wang, Y. [Laboratoire de Physique des Materiaux Divises et Interfaces (LPMDI), CNRS-UMR 8108, Universite Paris-Est., Marne la Vallee Cedex 2, 77454, (France)

    2010-10-08

    We fabricate heterojunctions consisting of a single n-type ZnO nanowire and a p-type GaN film. The photovoltaic effect of heterojunctions exhibits open-circuit voltages ranging from 2 to 2.7 V, and a maximum output power reaching 80 nW. Light-emitting diodes with UV electroluminescence based on the heterojunctions are demonstrated. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  9. A Flexible Blue Light-Emitting Diode Based on ZnO Nanowire/Polyaniline Heterojunctions

    Directory of Open Access Journals (Sweden)

    Y. Y. Liu

    2013-01-01

    Full Text Available An organic/inorganic light-emitting diode (LED consisting of n-type vertically aligned ZnO nanowires (NWs and p-type proton acid doped polyaniline (PANi is reported. The device was fabricated on flexible indium-tin-oxide (ITO coated polyethylene terephthalate (PET substrate. A broad blue light emission band ranging from 390 nm to 450 nm was observed in the electroluminescence (EL spectra of the device, which was related to the interface recombination of electrons in the conduction band of ZnO NWs and holes in the polaron level of PANi. The turn-on voltage of the device is ~3.5 V, lower than most of ZnO NWs based LED devices. In combination with the easy fabrication, flexibility, low power consumption, and mechanical robustness, this novel device is very promising in the application of blue LEDs.

  10. 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.

  11. Electroluminescence from nonpolar n-ZnO/p-AlGaN heterojunction light-emitting diode on r-sapphire

    Science.gov (United States)

    Chen, Jingwen; Zhang, Jun; Dai, Jiangnan; Wu, Feng; Wang, Shuai; Chen, Cheng; Long, Hanling; Liang, Renli; Zhao, Chong; Chen, Changqing; Tang, Zhiwu; Cheng, Hailing; He, Yunbin; Li, Mingkai

    2017-03-01

    Nonpolar a-plane n-ZnO/p-AlGaN heterojunction light-emitting diodes (LEDs) have been prepared on r-sapphire substrate using metal organic chemical vapor deposition and a pulsed laser deposition method. The dominant electroluminescence emission at 390 nm from the interband transition in n-ZnO layer under a forward bias was observed. Interestingly, electroluminescence with emission at 385 nm based on an avalanche mechanism was also achieved under reverse bias. The mechanisms of both the electroluminescence and I-V characteristics are discussed in detail by considering the avalanche effect. It is demonstrated that the crystalline quality of n-ZnO, not the p-AlGaN, is what affects the performance of the nonpolar ZnO based avalanche LED.

  12. Influence of heterojunction interface on exciplex emission from organic light-emitting diodes under electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Shengyi; Zhang, Xiulong; Lou, Zhidong; Hou, Yanbing [Beijing Jiaotong University, Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing (China)

    2008-03-15

    In this paper, electroluminescence from organic light-emitting diodes based on 2-(4'-biphenyl)-5-(4{sup ''}-tert-butylphenyl)-1,3,4-oxadiazole (PBD) and N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) is reported. Based on the exciplex emission from the TPD/PBD interface under high electric fields, the influence of the TPD/PBD interface on exciplex emission was investigated by increasing the number of TPD/PBD interfaces while keeping both the total thickness of the TPD layer and the PBD layer constant in the multiple quantum-wells (MQW) device ITO/TPD/[PBD/TPD]{sub n}/PBD/Al (n is the well number that was varied from 0 to 3). Our experimental data shows that exciplex emission can be enhanced by suitably increasing the well number of this kind of MQW-like device. (orig.)

  13. Managing excitons for high performance hybrid white organic light-emitting diodes by using a simple planar heterojunction interlayer

    Science.gov (United States)

    Shi, Changsheng; Sun, Ning; Wu, Zhongbin; Chen, Jiangshan; Ahamad, Tansir; Alshehri, Saad M.; Ma, Dongge

    2018-01-01

    High performance hybrid white organic light-emitting diodes (WOLEDs) were fabricated by inserting a planar heterojunction interlayer between the fluorescent and phosphorescent emitting layers (EMLs). The maximum external quantum efficiency (EQE) of 19.3%, current efficiency of 57.1 cd A-1, and power efficiency (PE) of 66.2 lm W-1 were achieved in the optimized device without any light extraction enhancement. At the luminance of 1000 cd m-2, the EQE and PE remained as high as 18.9% and 60 lm W-1, respectively, showing the reduced efficiency-roll. In order to disclose the reason for such high performance, the distribution of excitons was analyzed by using ultra-thin fluorescent and phosphorescent layers as sensors. It was found that the heterojunction interlayer can efficiently separate the singlet and triplet excitons, preventing the triplet excitons from being quenched by the fluorescent emitter. The introduction of the heterojunction interlayer between the fluorescent and phosphorescent EMLs should offer a simple and efficient route to fabricate the high performance hybrid WOLEDs.

  14. Solution-processed n-ZnO nanorod/p-Co3O4 nanoplate heterojunction light-emitting diode

    Science.gov (United States)

    Kim, Jong-Woo; Lee, Su Jeong; Biswas, Pranab; Lee, Tae Il; Myoung, Jae-Min

    2017-06-01

    A heterojunction light-emitting diode (LED) based on p-type cobalt oxide (Co3O4) nanoplates (NPs)/n-type zinc oxide (ZnO) nanorods (NRs) is demonstrated. Using a low-temperature aqueous solution process, the n-type ZnO NRs were epitaxially grown on Co3O4 NPs which were two-dimensionally assembled by a modified Langmuir-Blodgett process. The heterojunction LEDs exhibited a typical rectifying behavior with a turn-on voltage of about 2 V and emitted not only reddish-orange light at 610 nm but also violet light at about 400 nm. From the comparative analyses of electroluminescence and photoluminescence, it was determined that the reddish-orange light emission was related to the electronic transitions from zinc interstitials (Zni) to oxygen interstitials (Oi) or conduction-band minimum (CBM) to oxygen vacancies (VO), and the violet light emission was attribute to the transition from CBM to valence-band maximum (VBM) or Zni to zinc vacancies (VZn).

  15. Determination of band offsets at strained NiO and MgO heterojunction for MgO as an interlayer in heterojunction light emitting diode applications

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S.D., E-mail: devsh@rrcat.gov.in [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Nand, Mangla [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ajimsha, R.S.; Upadhyay, Anuj; Kamparath, Rajiv; Mukherjee, C.; Misra, P.; Sinha, A.K. [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Jha, S.N. [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ganguli, Tapas [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India)

    2016-12-15

    Highlights: • Valence band offset at NiO/MgO heterojunction is experimentally determined. • Experimentally determined value of 2.3 ± 0.4 eV is significantly larger than the predicted from theoretical calculations. • The value of valence band offset is in corroboration with that estimated from the band transitivity model. • Our result can be used to predict accurately carrier transport and electroluminescence mechanisms for heterojunction LEDs. - Abstract: Valence band offset of 2.3 ± 0.4 eV at strained NiO/MgO heterojunction is determined from photoelectron spectroscopy (PES) measurements. The determined value of valence band offset is larger than that is predicted from first principle calculations, but is in corroboration with that obtained from band transitivity rule. Our PES result indicates a larger value of the valence band offset at strained NiO/MgO heterojunction and can be used to predict accurately carrier transport and electroluminescence mechanisms for n-ZnO/MgO/p-NiO and p-NiO/MgO/n-GaN heterojunction light emitting diodes.

  16. Nanostructured Materials for Organic Light Emitting Diodes

    OpenAIRE

    Dinh, Nguyen Nang

    2010-01-01

    We have given an overview of the recent works on nanocomposites used for optoelectronic devices. From the review it is seen that a very rich publication has been issued regarding the nanostructured composites and nano-hybrid layers or heterojunctions which can be applied for different practical purposes. Among them there are organic light emitting diodes (OLED) and excitonic or organic solar cells (OSC). Our recent achievements on the use of nanocomposites for OLEDs were also presented. There...

  17. A two-colour heterojunction unipolar nanowire light-emitting diode by tunnel injection

    Science.gov (United States)

    Zimmler, Mariano A.; Bao, Jiming; Shalish, Ilan; Yi, Wei; Narayanamurti, Venkatesh; Capasso, Federico

    2007-10-01

    We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices.

  18. Broadband light-emitting diode

    Science.gov (United States)

    Fritz, Ian J.; Klem, John F.; Hafich, Michael J.

    1998-01-01

    A broadband light-emitting diode. The broadband light-emitting diode (LED) comprises a plurality of III-V compound semiconductor layers grown on a semiconductor substrate, with the semiconductor layers including a pair of cladding layers sandwiched about a strained-quantum-well active region having a plurality of different energy bandgaps for generating light in a wavelength range of about 1.3-2 .mu.m. In one embodiment of the present invention, the active region may comprise a first-grown quantum-well layer and a last-grown quantum-well layer that are oppositely strained; whereas in another embodiment of the invention, the active region is formed from a short-period superlattice structure (i.e. a pseudo alloy) comprising alternating thin layers of InGaAs and InGaAlAs. The use a short-period superlattice structure for the active region allows different layers within the active region to be simply and accurately grown by repetitively opening and closing one or more shutters in an MBE growth apparatus to repetitively switch between different growth states therein. The broadband LED may be formed as either a surface-emitting LED or as an edge-emitting LED for use in applications such as chemical sensing, fiber optic gyroscopes, wavelength-division-multiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft.

  19. Quantum Dot Light Emitting Diode

    Energy Technology Data Exchange (ETDEWEB)

    Keith Kahen

    2008-07-31

    The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, and environmental stability between that of LEDs and OLEDs. At the end of the project the Recipient shall gain an understanding of the device physics and properties of Quantum-Dot LEDs (QD-LEDs), have reliable and accurate nanocrystal synthesis routines, and have formed green-yellow emitting QD-LEDs with a device efficiency greater than 3 lumens/W, a brightness greater than 400 cd/m2, and a device operational lifetime of more than 1000 hours. Thus the aim of the project is to break the current cost-efficiency paradigm by creating novel low cost inorganic LEDs composed of inorganic nanoparticles.

  20. Quantum Dot Light Emitting Diode

    Energy Technology Data Exchange (ETDEWEB)

    Kahen, Keith

    2008-07-31

    The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, and environmental stability between that of LEDs and OLEDs. At the end of the project the Recipient shall gain an understanding of the device physics and properties of Quantum-Dot LEDs (QD-LEDs), have reliable and accurate nanocrystal synthesis routines, and have formed green-yellow emitting QD-LEDs with a device efficiency greater than 3 lumens/W, a brightness greater than 400 cd/m{sup 2}, and a device operational lifetime of more than 1000 hours. Thus the aim of the project is to break the current cost-efficiency paradigm by creating novel low cost inorganic LEDs composed of inorganic nanoparticles.

  1. Use of the Thermal Chemical Vapor Deposition to Fabricate Light-Emitting Diodes Based on ZnO Nanowire/p-GaN Heterojunction

    Directory of Open Access Journals (Sweden)

    Sheng-Po Chang

    2011-01-01

    Full Text Available The fabrication and characteristics of grown ZnO nanowire/p-GaN heterojunction light-emitting diodes are reported. Vertically aligned ZnO nanowire arrays were grown on a p-GaN substrate by thermal chemical vapor deposition in quartz tube. The rectifying current-voltage characteristics indicate that a p-n junction was formed with a heterostructure of n-ZnO nanowire/p-GaN. The room temperature electroluminescent emission peak at 425 nm was attributed to the band offset at the interface between the n-ZnO nanowire and p-GaN and to defect-related emission from GaN; it was also found that the there exist the yellow band in the hetrojunction. It would be attributed to the deep defect level in the heterojunction.

  2. Near white electroluminescence from self-supporting ZnO nanocone array based heterojunction light-emitting diodes

    Science.gov (United States)

    Wang, Haoning; Long, Hao; Mo, Xiaoming; Chen, Zhao; Li, Songzhan; Huang, Huihui; Liu, Yuping; Fang, Guojia

    2015-03-01

    Self-supporting ZnO nanocone arrays (NCAs) were fabricated by a low temperature and substrate-free hydrothermal process in open air, and near white electroluminescence (EL) devices with a structure of n-ZnO NCAs/p-Si heterojunction were fabricated. Different EL performances were achieved by controlling the growth time of ZnO nanocone layer and the chromaticity coordinates of the obtained diodes are tunable and can be changed from (0.36, 0.41) to (0.29, 0.32), which is close to (0.33, 0.33) of standard white light. The mechanism of the EL emission phenomenon was discussed.

  3. Hydrothermal growth of n-ZnO films on a patterned p-GaN epilayer and its application in heterojunction light-emitting diodes

    Science.gov (United States)

    Ko, Rong-Ming; Wang, Shui-Jinn; Chen, Ching-Yi; Wu, Cheng-Han; Lin, Yan-Ru; Lo, Hsin-Ming

    2017-04-01

    The hydrothermal growth (HTG) of crystalline n-ZnO films on both the nonpatterned and patterned p-GaN epilayers with a honeycomb array of etched holes is demonstrated, and its application in n-ZnO/p-GaN heterojunction light-emitting diodes (HJ-LEDs) is reported. The results reveal that an HTG n-ZnO film on a patterned p-GaN layer exhibits a high-quality single crystal with FWHMs of 0.463 and 0.983° obtained from a ω-rocking curve and a ϕ-scan pattern, respectively, which are much better than those obtained on a nonpatterned p-GaN layer. In addition, the n-ZnO/patterned p-GaN HJ-LED exhibited a much better rectifying diode behavior owing to having a higher n-ZnO film crystallinity quality and an improved interface with the p-GaN layer. Strong violet and violet-blue lights emitted from the n-ZnO/patterned p-GaN HJ-LED at around 405, 412, and 430 nm were analyzed.

  4. Effect of interface voids on electroluminescence colors for ZnO microdisk/p-GaN heterojunction light-emitting diodes

    Science.gov (United States)

    Mo, Ran; Choi, Ji Eun; Kim, Hyeong Jin; Jeong, Junseok; Kim, Jong Chan; Kim, Yong-Jin; Jeong, Hu Young; Hong, Young Joon

    2017-10-01

    This study investigates the influence of voids on the electroluminescence (EL) emission color of ZnO microdisk/p-GaN heterojunction light-emitting diodes (LEDs). For this study, position-controlled microdisk arrays were fabricated on patterned p-GaN via wet chemical epitaxy of ZnO, and specifically, the use of trisodium citrate dihydrate (TCD) yielded high-density voids at the bottom of the microdisk. Greenish yellow or whitish blue EL was emitted from the microdisk LEDs formed with or without TCD, respectively, at reverse-bias voltages. Such different EL colors were found to be responsible for the relative EL intensity ratio between indigo and yellow emission peaks, which were originated from radiative recombination at p-GaN and ZnO, respectively. The relative EL intensity between dichromatic emissions is discussed in terms of (i) junction edge effect provoked by interfacial voids and (ii) electron tunneling probability depending on the depletion layer geometry.

  5. Photon recycling semiconductor light-emitting diode

    Science.gov (United States)

    Guo, Xiaoyun; Graff, John W.; Schubert, E. F.; Karlicek, Robert F., Jr.

    2000-04-01

    A new white light emitting diode, the photon recycling semiconductor light emitting diode (PRS-LED) is demonstrated. The device consists of a GaInN/GaN LED emitting in the blue spectral range and an AlGaInP photon recycling semiconductor emitting at the complementary color. Thus the PRS-LED has two emission peaks, one in the blue and one in the amber wavelength range. The theoretical luminous performance of the PRS-LED exceeds 300 lm/W, higher than the performance of phosphor-based white LEDs.

  6. Solution-processed n-ZnO nanorod/p-Co{sub 3}O{sub 4} nanoplate heterojunction light-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jong-Woo; Lee, Su Jeong; Biswas, Pranab [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722 (Korea, Republic of); Lee, Tae Il [Department of BioNano Technology, Gachon University, 1342 Seongnam Daero, Seongnam 13120 (Korea, Republic of); Myoung, Jae-Min, E-mail: jmmyoung@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722 (Korea, Republic of)

    2017-06-01

    Highlights: • The n-ZnO nanorods were epitaxially grown on p-Co{sub 3}O{sub 4} nanoplates. • The heteroepitaxial p-n junction was fabricated by using hydrothermal process. • The LEDs emitted reddish-orange and violet light related to ZnO point defects. • The Co{sub 3}O{sub 4} nanoplates function as a hole injection layer. • Junction between 1D NRs and 2D NPs provides a new approach to design nanostructures. - Abstract: A heterojunction light-emitting diode (LED) based on p-type cobalt oxide (Co{sub 3}O{sub 4}) nanoplates (NPs)/n-type zinc oxide (ZnO) nanorods (NRs) is demonstrated. Using a low-temperature aqueous solution process, the n-type ZnO NRs were epitaxially grown on Co{sub 3}O{sub 4} NPs which were two-dimensionally assembled by a modified Langmuir-Blodgett process. The heterojunction LEDs exhibited a typical rectifying behavior with a turn-on voltage of about 2 V and emitted not only reddish-orange light at 610 nm but also violet light at about 400 nm. From the comparative analyses of electroluminescence and photoluminescence, it was determined that the reddish-orange light emission was related to the electronic transitions from zinc interstitials (Zn{sub i}) to oxygen interstitials (O{sub i}) or conduction-band minimum (CBM) to oxygen vacancies (V{sub O}), and the violet light emission was attribute to the transition from CBM to valence-band maximum (VBM) or Zn{sub i} to zinc vacancies (V{sub Zn}).

  7. Fluorescence lifetime imaging using light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, Gordon T; Munro, Ian; Poher, Vincent; French, Paul M W; Neil, Mark A A [Blackett Laboratory, Imperial College London, South Kensington Campus, London SW7 2AZ (United Kingdom); Elson, Daniel S [Institute of Biomedical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ (United Kingdom); Hares, Jonathan D [Kentech Instruments Ltd, Unit 9, Hall Farm Workshops, South Moreton, Didcot, Oxfordshire, OX11 9AG (United Kingdom)], E-mail: gordon.kennedy@imperial.ac.uk

    2008-05-07

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

  8. 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…

  9. Highly efficient silicon light emitting diode

    NARCIS (Netherlands)

    Le Minh, P.; Holleman, J.; Wallinga, Hans

    2002-01-01

    In this paper, we describe the fabrication, using standard silicon processing techniques, of silicon light-emitting diodes (LED) that efficiently emit photons with energy around the silicon bandgap. The improved efficiency had been explained by the spatial confinement of charge carriers due to a

  10. 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…

  11. 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…

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

    Science.gov (United States)

    2004-01-01

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

  13. 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

  14. 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.

  15. Laterally injected light-emitting diode and laser diode

    Science.gov (United States)

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

    2015-06-16

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

  16. Printing of organic light emitting diodes on textile

    OpenAIRE

    Verboven, Inge; Gilissen, Koen; Vandevenne, Glen; Troia, Mariagrazia; Leins, Martina; Walker, Matthias; Schulz, Andreas; Deferme, Wim

    2015-01-01

    Smart textiles with light-emitting properties open a whole new world of innovative textile applications such as indoor and outdoor design and safety clothing. To achieve light-emitting properties on textiles, organic light emitting diodes are printed or integrated onto textile substrates. The advantage of this approach is that typical textile properties like flexibility and drapabilty are maintained. The authors would like to thank the research and funding partners of the European CORNET p...

  17. Plant Growth Under Light Emitting Diode Irradiation.

    Science.gov (United States)

    Tennessen, Daniel John

    Plant growth under light emitting diodes (LEDs) was investigated to determine if LEDs would be useful to provide radiant energy for two plant processes, photosynthesis and photomorphogenesis. Photosynthesis of tomato (Lycopersicon esculentum L.) and Kudzu (Pueraria lobata (Willd) Ohwi.) was measured using photons from LEDs to answer the following: (1) Are leaves able to use red LED light for photosynthesis? and (2) Is the efficiency of photosynthesis in pulsed light equal to that of continuous light? In 175 Pa CO _2, or in response to changes in CO _2,tomato (Lycopersicon esculentum Mill.) and transformed tobacco and tomato (expressing oat phytochrome-A) was assessed by growing plants under red LED lamps in an attempt to answer the following: (1) What is the developmental response of non-transformed and transformed tobacco to red LED light? and (2) Can tomato plants that grow tall and spindly in red LED light be made to grow short by increasing the amount of phytochrome-A? The short phenotype of transformed tobacco was not evident when plants were grown in LED light. Addition of photons of far-red or blue light to red light resulted in short transformed tobacco. Tomato plants grew three times as tall and lacked leaf development in LED versus white light, but transformed tomato remained short and produced fruit under LED light. I have determined that the LED photons are useful for photosynthesis and that the photon efficiency of photosynthesis is the same in pulsed as in continuous light. From responses of tobacco, I concluded that the P_{ rm r} form of phytochrome-A and the phytochrome cycling rate mediate responses. In tomato, increased amounts of Phytochrome-A prevented stem elongation and caused chlorophyll accumulation in LED light.

  18. Evaluation of light-emitting diode beacon light fixtures.

    Science.gov (United States)

    2009-12-01

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

  19. 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).

  20. 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).

  1. Highly efficient charge generation and electron injection of m-MTDATA/m-MTDATA:HAT-CN/HAT-CN organic heterojunction on ITO cathode for high efficiency inverted white organic light-emitting diodes

    Science.gov (United States)

    Wang, Xiaoli; Shi, Changsheng; Guo, Qingxun; Chen, Jiangshan; Qiao, Xianfeng; Ma, Dongge; Ahamad, Tansir; Alshehri, Saad M.; Bae, Sang Soon

    2017-09-01

    The charge generation and electron injection characteristics of m-MTDATA/m-MTDATA:HAT-CN/HAT-CN organic heterojunction made of 4,4',4″-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA) p-type organic semiconductor and 1,4,5,8,9,12-hexaazatriphenylene-hexacarbonitrile (HAT-CN) n-type semiconductor were well studied. It was found that m-MTDATA/m-MTDATA:HAT-CN/HAT-CN organic heterojunction showed better charge generation ability than m-MTDATA/HAT-CN organic heterojuntion, and realized highly efficient electron injection when using it as charge generator on indium tin oxide (ITO) cathode. The investigations of capacitance-frequency and current density-voltage characteristics of the electron-only devices based on m-MTDATA/m-MTDATA:HAT-CN/HAT-CN organic heterojunction demonstrated that the amounts of the injected electrons were dependent on the properties of the used n-doping electron transporting layer (n-ETL). Therefore, by optimization, high efficiency inverted white organic light-emitting diodes (OLEDs) with ITO as cathode were successfully fabricated using m-MTDATA/m-MTDATA:HAT-CN/HAT-CN organic heterojunction as charge injector and lithium carbonate (Li2CO3) doped bathophenanthroline (BPhen) as n-ETL. The resulting inverted white OLEDs achieved the maximum external quantum efficiency of 12.9%, current efficiency of 42.6 cd/A and power efficiency of 50.5 lm/W, and still remained 12.5%, 41.0 cd/A and 45.0 lm/W at the luminance of 1000 cd/m2, respectively, exhibiting extremely low efficiency roll-off.

  2. 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…

  3. 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....

  4. C70/C70:pentacene/pentacene organic heterojunction as the connecting layer for high performance tandem organic light-emitting diodes: Mechanism investigation of electron injection and transport

    Science.gov (United States)

    Guo, Qingxun; Yang, Dezhi; Chen, Jiangshan; Qiao, Xianfeng; Ahamad, Tansir; Alshehri, Saad M.; Ma, Dongge

    2017-03-01

    A high performance tandem organic light-emitting diode (OLED) is realized by employing a C70/C70:pentacene/pentacene organic heterojunction as the efficient charge generation layer (CGL). Not only more than two time enhancement of external quantum efficiency but also significant improvement in both power efficiency and lifetime are well achieved. The mechanism investigations find that the electron injection from the CGL to the adjacent electron transport layer (ETL) in tandem devices is injection rate-limited due to the high interface energy barrier between the CGL and the ETL. By the capacitance-frequency (C-F) and low temperature current density-voltage (J-V) characteristic analysis, we confirm that the electron transport is a space-charge-limited current process with exponential trap distribution. These traps are localized states below the lowest unoccupied molecular orbital edge inside the gap and would be filled with the upward shift of the Fermi level during the n-doping process. Furthermore, both the trap density (Ht) and the activation energy (Ea) could be carefully worked out through low temperature J-V measurements, which is very important for developing high performance tandem OLEDs.

  5. 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

  6. Gallium-Nitride-Based Light-Emitting Diodes

    Indian Academy of Sciences (India)

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

  7. 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

  8. 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

  9. 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…

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

    DEFF Research Database (Denmark)

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

    2017-01-01

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

  11. 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

  12. 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

  13. Admittance spectroscopy on polymer light-emitting diodes

    NARCIS (Netherlands)

    Blom, PWM; Martens, HCF; Brom, HB; Huiberts, JN; Jabbour, GE; Sariciftci, NS

    2002-01-01

    From admittance spectroscopy measurements on poly(p-phenylene vinylene) based light-emitting diodes various relaxation processes can be observed. At low bias inductive contributions due to the transit of charge carriers dominate, at high bias capacitive contributions as a result of charge

  14. Device physics of white polymer light-emitting diodes

    NARCIS (Netherlands)

    Nicolai, H.T.; Hof, A.; Blom, P.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

  15. Fabrication and characterization of Zn O:Zn(n{sup +})/porous-silicon/Si(p) heterojunctions for white light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Vasquez A, M. A. [INAOE, Department of Electronics, 72840 Puebla, Pue. (Mexico); Romero P, G.; Pena S, R. [IPN, Centro de Investigacion y de Estudios Avanzados, Departamento de Ingenieria Electrica, SEES, Av. Intituto Politecnico Nacional No. 2508, Col. San Pedro Zacatenco, 07360 Ciudad de Mexico (Mexico); Andraca A, J. A. [IPN, Centro de Nanociencias y Micro y Nanotecnologias, Av. Luis Enrique Erro s/n, Col. San Pedro Zacatenco, 07738 Ciudad de Mexico (Mexico)

    2016-11-01

    The fabrication and characterization of electro luminescent Zn O:Zn(n{sup +})/porous silicon/Si(p) heterojunctions is presented. Highly conductive Zn O films (Zn O:Zn(n{sup +})) were produced by applying a temperature annealing at 400 degrees Celsius by 5 min to the Zn O/Zn/Zn O arrange formed by DC sputtering, and the porous silicon (PS) films were prepared on p-type (100) Si wafers by anodic etching. The Zn O: Zn(n{sup +})/PS/Si(p) heterojunction is accomplished by applying a brief temperature annealing stage to the entire Zn O/Zn/Zn O/PS/Si structure to preserve the PS luminescent characteristics. The Zn O:Zn(n{sup +}) films were characterized by X-ray diffraction and Hall-van der Pauw measurements. The PS and Zn O:Zn(n{sup +}) films were also studied by photoluminescence (Pl) measurements. The current-voltage characteristics of the heterojunctions showed well defined rectifying behavior with a turn-on voltage of 1.5 V and ideality factor of 5.4. The high ideality factor is explained by the presence of electron tunneling transport aided by energy levels related to the defects at the heterojunction interface and into the PS film. The saturation current and the series resistance of the heterostructure were 4 x 10{sup -7} A/cm{sup 2} and 16 Ω-cm{sup 2}, respectively. White color electroluminescence is easily observed at the naked eye when excited with square wave pulses of 8 V and 1 Khz. (Author)

  16. 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...... was less than 10nm. Analysis of the results shows that in order to achieve sufficient for the white LED color conversion, better surface passivation and nanocrystals with shorter exciton lifetimes and weaker Auger recombination and needed....

  17. 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.

  18. Amplified spontaneous emission from ZnO in n-ZnO/ZnO nanodots-SiO(2) composite/p-AlGaN heterojunction light-emitting diodes.

    Science.gov (United States)

    Shih, Ying Tsang; Wu, Mong Kai; Li, Wei Chih; Kuan, Hon; Yang, Jer Ren; Shiojiri, Makoto; Chen, Miin Jang

    2009-04-22

    This study demonstrates amplified spontaneous emission (ASE) of the ultraviolet (UV) electroluminescence (EL) from ZnO at lambda~380 nm in the n-ZnO/ZnO nanodots-SiO(2) composite/p- Al(0.12)Ga(0.88)N heterojunction light-emitting diode. A SiO(2) layer embedded with ZnO nanodots was prepared on the p-type Al(0.12)Ga(0.88)N using spin-on coating of SiO(2) nanoparticles followed by atomic layer deposition (ALD) of ZnO. An n-type Al-doped ZnO layer was deposited upon the ZnO nanodots-SiO(2) composite layer also by the ALD technique. High-resolution transmission electron microscopy (HRTEM) reveals that the ZnO nanodots embedded in the SiO(2) matrix have diameters of 3-8 nm and the wurtzite crystal structure, which allows the transport of carriers through the thick ZnO nanodots-SiO(2) composite layer. The high quality of the n-ZnO layer was manifested by the well crystallized lattice image in the HRTEM picture and the low-threshold optically pumped stimulated emission. The low refractive index of the ZnO nanodots-SiO(2) composite layer results in the increase in the light extraction efficiency from n-ZnO and the internal optical feedback of UV EL into n-ZnO layer. Consequently, significant enhancement of the UV EL intensity and super-linear increase in the EL intensity, as well as the spectral narrowing, with injection current were observed owing to ASE in the n-ZnO layer.

  19. High extraction efficiency ultraviolet light-emitting diode

    Science.gov (United States)

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

    2015-11-24

    Ultraviolet light-emitting diodes with tailored AlGaN quantum wells can achieve high extraction efficiency. For efficient bottom light extraction, parallel polarized light is preferred, because it propagates predominately perpendicular to the QW plane and into the typical and more efficient light escape cones. This is favored over perpendicular polarized light that propagates along the QW plane which requires multiple, lossy bounces before extraction. The thickness and carrier density of AlGaN QW layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. At Al>0.3, thinner QW layers (<2.5 nm are preferred) result in light preferentially polarized parallel to the QW plane. Also, active regions consisting of six or more QWs, to reduce carrier density, and with thin barriers, to efficiently inject carriers in all the QWs, are preferred.

  20. 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.

  1. 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").

  2. The heating effect on different light emitting diodes chips materials

    Science.gov (United States)

    Chu, K. K.; Hambali, N. A. M. A.; Ariffin, S. N.; Wahid, M. H. A.; Shahimin, M. M.; Ali, Norshamsuri

    2017-09-01

    In this paper, simulation of non-radiative recombination heating and Joule heating effects based on different material of a light emitting diodes chip for Gallium Nitride, Indium Nitride, Zinc Oxide, Zinc Selenide and Titanium Dioxide are demonstrated. Among the light emitting diodes chips materials, Indium Nitride, Zinc Oxide and Zinc Selenide has the capability to produce the highest non-radiative recombination heating which the heating value is potential up to ×1012 to ×1013 W/m3. Meanwhile, Titanium Dioxide has the capability to generate higher value of non-radiative recombination heating with lowest value of electron carriers concentration. For the joule heating effect, the Titanium Dioxide shows the fast heating behavior as compared with other materials.

  3. Cubic-phase GaN light-emitting diodes

    Science.gov (United States)

    Yang, Hui; Zheng, L. X.; Li, J. B.; Wang, X. J.; Xu, D. P.; Wang, Y. T.; Hu, X. W.; Han, P. D.

    1999-04-01

    The feasibility of growing device-quality cubic GaN/GaAs(001) films by metal organic chemical vapor deposition has been demonstrated. The optical quality of the GaN films was characterized by room-temperature photoluminescence measurements, which shows a full width at half maximum of 46 meV. The structural quality of the films was investigated by transmission electron microscopy. There are submicron-size grains free from threading dislocations and stacking faults. More importantly, a cubic-phase GaN blue light-emitting diode has been fabricated. The device process, which is very simple and compatible with current GaAs technology, indicates a promising future for the blue light-emitting diode.

  4. 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.

  5. Absorbance based light emitting diode optical sensors and sensing devices

    OpenAIRE

    Dermot Diamond; Martina O’Toole

    2008-01-01

    The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied i...

  6. DNA electron injection interlayers for polymer light-emitting diodes.

    Science.gov (United States)

    Zalar, Peter; Kamkar, Daniel; Naik, Rajesh; Ouchen, Fahima; Grote, James G; Bazan, Guillermo C; Nguyen, Thuc-Quyen

    2011-07-27

    Introduction of a DNA interlayer adjacent to an Al cathode in a polymer light-emitting diode leads to lower turn-on voltages, higher luminance efficiencies, and characteristics comparable to those observed using a Ba electrode. The DNA serves to improve electron injection and also functions as a hole-blocking layer. The temporal characteristics of the devices are consistent with an interfacial dipole layer adjacent to the electrode being responsible for the reduction of the electron injection barrier.

  7. 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.

  8. 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.

  9. Light emitting diodes as a plant lighting source

    Energy Technology Data Exchange (ETDEWEB)

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

    1994-12-31

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

  10. Top-emitting organic light-emitting diodes.

    Science.gov (United States)

    Hofmann, Simone; Thomschke, Michael; Lüssem, Björn; Leo, Karl

    2011-11-07

    We review top-emitting organic light-emitting diodes (OLEDs), which are beneficial for lighting and display applications, where non-transparent substrates are used. The optical effects of the microcavity structure as well as the loss mechanisms are discussed. Outcoupling techniques and the work on white top-emitting OLEDs are summarized. We discuss the power dissipation spectra for a monochrome and a white top-emitting OLED and give quantitative reports on the loss channels. Furthermore, the development of inverted top-emitting OLEDs is described.

  11. Light outcoupling enhanced flexible organic light-emitting diodes.

    Science.gov (United States)

    Ou, Qing-Dong; Xu, Lu-Hai; Zhang, Wen-Yue; Li, Yan-Qing; Zhang, Yi-Bo; Zhao, Xin-Dong; Chen, Jing-De; Tang, Jian-Xin

    2016-03-21

    Flexible organic light-emitting diodes (OLEDs) are emerging as a leading technology for rollable and foldable display applications. For the development of high-performance flexible OLEDs on plastic substrate, we report a transparent nanocomposite electrode with superior mechanical, electrical, and optical properties, which is realized by integrating the nanoimprinted quasi-random photonic structures into the ultrathin metal/dielectric stack to collectively optimize the electrical conduction and light outcoupling capabilities. The resulting flexible OLEDs with green emission yield the enhanced device efficiency, reaching the maximum external quantum efficiency of 43.7% and luminous efficiency of 154.9 cd/A, respectively.

  12. Efficiency droop in nitride-based light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Piprek, Joachim [NUSOD Institute LLC, Newark, Delaware 19714-7204 (United States)

    2010-10-15

    Nitride-based light-emitting diodes (LEDs) suffer from a reduction (droop) of the internal quantum efficiency with increasing injection current. This droop phenomenon is currently the subject of intense research worldwide, as it delays general lighting applications of GaN-based LEDs. Several explanations of the efficiency droop have been proposed in recent years, but none is widely accepted. This feature article provides a snapshot of the present state of droop research, reviews currently discussed droop mechanisms, contextualizes them, and proposes a simple yet unified model for the LED efficiency droop. Illustration of LED efficiency droop. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  13. 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.

  14. 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)

  15. Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices.

    Science.gov (United States)

    O'Toole, Martina; Diamond, Dermot

    2008-04-07

    The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements.

  16. 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...

  17. Fabrication and characterization of a germanium nanowire light emitting diode

    Science.gov (United States)

    Greil, Johannes; Bertagnolli, Emmerich; Salem, Bassem; Baron, Thierry; Gentile, Pascal; Lugstein, Alois

    2017-12-01

    In this letter, we demonstrate the feasibility of a germanium nanowire light emitting diode as a reasonable approach for downscaling of CMOS compatible light sources. We show room-temperature direct bandgap electroluminescence from axial p-n junction nanowire devices. The electron population in the Γ valley, necessary for direct bandgap emission, is achieved by high injection current densities. Carrier temperature is consistently found to be higher than the lattice temperature, indicating inhibited carrier cooling in small diameter wires. Strong polarization of the emission parallel to the nanowire axis is observed and attributed to dielectric contrast phenomena.

  18. 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.

  19. 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.

  20. 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.

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

    Science.gov (United States)

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

    2017-12-01

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

  2. Doping of nanostructures for light emitting diode applications

    Energy Technology Data Exchange (ETDEWEB)

    Han, S. U.; Jeon, J. S.; Park, C. I.; Kim, B. H. [Chonbuk National University, Jeonju (Korea, Republic of)

    2009-04-15

    Lighting Emitting Diodes have been widely studied and developed for practical applications and the LED market in the world has been dramatically expended. GaN-based materials are mostly used for LED applications. However, for diverse application, we should first solved several problems in the GaN-based LEDs, thermal heating effects and low light emitting efficiency. In this project, we studied the possibility of ZnO nanomaterials as LEDs. We have developed a technique to fabricate ZnO nanorods on various substrates with a ZnO homo-buffer layer. We also systematically studied the doping of ZnO nanorods with the implantation method of protons and nitrogen ions. After the protons and N+ ions with various energy of 50-90 keV were implanted to pre-grown ZnO nanorods, the ZnO nanorods were analyzed with various techniques, XRD, EXAFS, SEM, TEM, PL, EDS, and others. Any strong impurity peak were observed in the PL spectra. This strongly suggests that the implanted ions capture the excitons.

  3. 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%.

  4. 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.

  5. 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

  6. 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...

  7. 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...

  8. 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.

  9. Indoor localization system utilizing two visible light emitting diodes

    Science.gov (United States)

    Mousa, Farag I. K.; Le-Minh, Hoa; Ghassemlooy, Zabih; Dai, Xuewu; Tran, Son T.; Boucouvalas, Anthony C.; Liaw, Shien-Kuei

    2016-11-01

    Indoor positioning or localization based on visible light communications (VLC) is an emerging technology with wide applications. In conventional localization schemes, the trilateration technique is widely used with at least three separate lighting sources to determine the user's location. An indoor VLC positioning scheme based on the optical power distributions of only two light emitting diodes (LEDs) is reported for different environments. We have used two received signal strength indications to determine the user's position based on the LEDs configuration offering less complexity. We propose comprehensive mathematical models for the VLC localization system considering the noise and its impact on the user's location, and numerically evaluated it over a range of signal-to-noise ratios (SNRs). In addition, it is compared to the results with the exiting trilateration technique. The performance of the proposed system is evaluated with a reported accuracy of 13 dB.

  10. Quantum key distribution with an entangled light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-28

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

  11. 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...

  12. Light-emitting diodes enhanced by localized surface plasmon resonance.

    Science.gov (United States)

    Gu, Xuefeng; Qiu, Teng; Zhang, Wenjun; Chu, Paul K

    2011-03-08

    Light-emitting diodes [LEDs] are of particular interest recently as their performance is approaching fluorescent/incandescent tubes. Moreover, their energy-saving property is attracting many researchers because of the huge energy crisis we are facing. Among all methods intending to enhance the efficiency and intensity of a conventional LED, localized surface plasmon resonance is a promising way. The mechanism is based on the energy coupling effect between the emitted photons from the semiconductor and metallic nanoparticles fabricated by nanotechnology. In this review, we describe the mechanism of this coupling effect and summarize the common fabrication techniques. The prospect, including the potential to replace fluorescent/incandescent lighting devices as well as applications to flat panel displays and optoelectronics, and future challenges with regard to the design of metallic nanostructures and fabrication techniques are discussed.

  13. Light-emitting diodes enhanced by localized surface plasmon resonance

    Directory of Open Access Journals (Sweden)

    Zhang Wenjun

    2011-01-01

    Full Text Available Abstract Light-emitting diodes [LEDs] are of particular interest recently as their performance is approaching fluorescent/incandescent tubes. Moreover, their energy-saving property is attracting many researchers because of the huge energy crisis we are facing. Among all methods intending to enhance the efficiency and intensity of a conventional LED, localized surface plasmon resonance is a promising way. The mechanism is based on the energy coupling effect between the emitted photons from the semiconductor and metallic nanoparticles fabricated by nanotechnology. In this review, we describe the mechanism of this coupling effect and summarize the common fabrication techniques. The prospect, including the potential to replace fluorescent/incandescent lighting devices as well as applications to flat panel displays and optoelectronics, and future challenges with regard to the design of metallic nanostructures and fabrication techniques are discussed.

  14. 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.

  15. Light-emitting diodes enhanced by localized surface plasmon resonance

    Science.gov (United States)

    Gu, Xuefeng; Qiu, Teng; Zhang, Wenjun; Chu, Paul K.

    2011-12-01

    Light-emitting diodes [LEDs] are of particular interest recently as their performance is approaching fluorescent/incandescent tubes. Moreover, their energy-saving property is attracting many researchers because of the huge energy crisis we are facing. Among all methods intending to enhance the efficiency and intensity of a conventional LED, localized surface plasmon resonance is a promising way. The mechanism is based on the energy coupling effect between the emitted photons from the semiconductor and metallic nanoparticles fabricated by nanotechnology. In this review, we describe the mechanism of this coupling effect and summarize the common fabrication techniques. The prospect, including the potential to replace fluorescent/incandescent lighting devices as well as applications to flat panel displays and optoelectronics, and future challenges with regard to the design of metallic nanostructures and fabrication techniques are discussed.

  16. 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

  17. Recycling of guided mode light emission in planar microcavity light emitting diodes

    Science.gov (United States)

    De Neve, H.; Blondelle, J.; Van Daele, P.; Demeester, P.; Baets, R.; Borghs, G.

    1997-02-01

    Results are presented on planar microcavity light emitting diodes with different device diameters. A record external quantum efficiency of 20% is achieved for a 1.5 mm light emitting diode. The strong dependence of the quantum efficiency on current density and device size are compared with theoretical results. A good correspondence is obtained when spectral broadening and photon recycling are taken into account.

  18. 77 FR 75190 - Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To...

    Science.gov (United States)

    2012-12-19

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

  19. 77 FR 55499 - Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To...

    Science.gov (United States)

    2012-09-10

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-10-25

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

  1. The development of monolithic alternating current light-emitting diode

    Science.gov (United States)

    Yeh, Wen-Yung; Yen, Hsi-Hsuan; Chan, Yi-Jen

    2011-02-01

    The monolithic alternating current light emitting diode (ACLED) has been revealed for several years and was regarded as a potential device for solid state lighting. In this study, we will discuss the characteristics, development status, future challenges, and ITRI's development strategy about ACLED, especially focusing on the development progress of the monolithic GaN-based Schottky barrier diodes integrated ACLED (SBD-ACLED). The SBD-ACLED design can not only improve the chip area utilization ratio but also provide much higher reverse breakdown voltage by integrating four SBDs with the micro-LEDs array in a single chip, which was regarded as a good on-chip ACLED design. According to the experimental results, higher chip efficiency can be reached through SBD-ACLED design since the chip area utilization ratio was increased. Since the principle and the operation condition of ACLED is quite different from those of the typical DCLED, critical issues for ACLED like the current droops, the flicker phenomenon, the safety regulations, the measurement standards and the power fluctuation have been studied for getting a practical and reliable ACLED design. Besides, the "AC LED application and research alliance" (AARA) lead by ITRI in Taiwan for the commercialization works of ACLED has also been introduced.

  2. 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.

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

    Science.gov (United States)

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

    2010-11-01

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

  4. 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

  5. Tunnel-injected sub-260 nm ultraviolet light emitting diodes

    Science.gov (United States)

    Zhang, Yuewei; Krishnamoorthy, Sriram; Akyol, Fatih; Bajaj, Sanyam; Allerman, Andrew A.; Moseley, Michael W.; Armstrong, Andrew M.; Rajan, Siddharth

    2017-05-01

    We report on tunnel-injected deep ultraviolet light emitting diodes (UV LEDs) configured with a polarization engineered Al0.75Ga0.25 N/In0.2Ga0.8 N tunnel junction structure. Tunnel-injected UV LED structure enables n-type contacts for both bottom and top contact layers. However, achieving Ohmic contact to wide bandgap n-AlGaN layers is challenging and typically requires high temperature contact metal annealing. In this work, we adopted a compositionally graded top contact layer for non-alloyed metal contact and obtained a low contact resistance of ρc = 4.8 × 10-5 Ω cm2 on n-Al0.75Ga0.25 N. We also observed a significant reduction in the forward operation voltage from 30.9 V to 19.2 V at 1 kA/cm2 by increasing the Mg doping concentration from 6.2 × 1018 cm-3 to 1.5 × 1019 cm-3. Non-equilibrium hole injection into wide bandgap Al0.75Ga0.25 N with Eg>5.2 eV was confirmed by light emission at 257 nm. This work demonstrates the feasibility of tunneling hole injection into deep UV LEDs and provides a structural design towards high power deep-UV emitters.

  6. Applications of Light Emitting Diodes in Health Care.

    Science.gov (United States)

    Dong, Jianfei; Xiong, Daxi

    2017-09-25

    Light emitting diodes (LEDs) have become the main light sources for general lighting, due to their high lumen efficiency and long life time. Moreover, their high bandwidth and the availability of diverse wavelength contents ranging from ultraviolet to infrared empower them with great controllability in tuning brightness, pulse durations and spectra. These parameters are the essential ingredients of the applications in medical imaging and therapies. Despite the fast advances in both LED technologies and their applications, few reviews have been seen to link the controllable emission properties of LEDs to these applications. The objective of this paper is to bridge this gap by reviewing the main control techniques of LEDs that enable creating enhanced lighting patterns for imaging and generating effective photon doses for photobiomodulation. This paper also provides the basic mechanisms behind the effective LED therapies in treating cutaneous and neurological diseases. The emerging field of optogenetics is also discussed with a focus on the application of LEDs. The multidisciplinary topics reviewed in this paper can help the researchers in LEDs, imaging, light therapy and optogenetics better understand the basic principles in each other's field; and hence to stimulate the application of LEDs in health care.

  7. 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).

  8. Light-emitting diodes as a radiation source for plants

    Science.gov (United States)

    Bula, R. J.; Morrow, R. C.; Tibbitts, T. W.; Barta, D. J.; Ignatius, R. W.; Martin, T. S.

    1991-01-01

    Development of a more effective radiation source for use in plant-growing facilities would be of significant benefit for both research and commercial crop production applications. An array of light-emitting diodes (LEDs) that produce red radiation, supplemented with a photosynthetic photon flux (PPF) of 30 micromoles s-1 m-2 in the 400- to 500-nm spectral range from blue fluorescent lamps, was used effectively as a radiation source for growing plants. Growth of lettuce (Lactuca sativa L. Grand Rapids') plants maintained under the LED irradiation system at a total PPF of 325 micromoles s-1 m-2 for 21 days was equivalent to that reported in the literature for plants grown for the same time under cool-white fluorescent and incandescent radiation sources. Characteristics of the plants, such as leaf shape, color, and texture, were not different from those found with plants grown under cool-white fluorescent lamps. Estimations of the electrical energy conversion efficiency of a LED system for plant irradiation suggest that it may be as much as twice that published for fluorescent systems.

  9. Flexible fluorescent white organic light emitting diodes with ALD encapsulation

    Science.gov (United States)

    Tsai, Yu-Sheng; Chittawanij, Apisit; Juang, Fuh-Shyang; Lin, Pen-Chu; Hong, Lin-Ann; Tsai, Feng-Yu; Tseng, Ming-Hong; Wang, Ching-Chiun; Chen, Chien-Chih; Lin, Kung-Liang; Chen, Szu-Hao

    2015-08-01

    In this paper, the flexible white organic light-emitting diodes (WOLED) was fabricated on polyethylene naphthalate (PEN) with structure of ITO/EHI608 (75 nm)/HTG-1 (10 nm)/3% EB502:0.8% EY53 (5 nm)/3% EB502 (35 nm)/Alq3 (10 nm)/LiF (0.8 nm)/Al (150 nm) and was compared with glass substrate the same structure. It was seen that the performances of flexible and glass substrate are almost the same. The luminance, current efficiency, and CIE coordinates of flexible device is 6351 cd/m2, 12.7 cd/A, and (0.31, 0.38) at 50 mA/cm2, respectively. Then, an Al2O3/HfO2 film on polyethylene terephthalate (PET) was deposited using atomic layer deposition (ALD) as a thin film encapsulation layer have been described and compared, such as the characteristics of water permeability and lifetime of flexible WOLED. The results show that the PET/ALD film low value of about 0.04 g/m2d, and the PET film shows WVTR of about 3.8 g/m2/d. The lifetimes of PET/ALD and PET encapsulations are 840 min and 140 min, respectively. Simultaneous deposition of ALD film on PET film gave the lifetime of flexible WOLED is six times longer than device without ALD encapsulation.

  10. 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.

  11. White organic light-emitting diodes with fluorescent tube efficiency.

    Science.gov (United States)

    Reineke, Sebastian; Lindner, Frank; Schwartz, Gregor; Seidler, Nico; Walzer, Karsten; Lüssem, Björn; Leo, Karl

    2009-05-14

    The development of white organic light-emitting diodes (OLEDs) holds great promise for the production of highly efficient large-area light sources. High internal quantum efficiencies for the conversion of electrical energy to light have been realized. Nevertheless, the overall device power efficiencies are still considerably below the 60-70 lumens per watt of fluorescent tubes, which is the current benchmark for novel light sources. Although some reports about highly power-efficient white OLEDs exist, details about structure and the measurement conditions of these structures have not been fully disclosed: the highest power efficiency reported in the scientific literature is 44 lm W(-1) (ref. 7). Here we report an improved OLED structure which reaches fluorescent tube efficiency. By combining a carefully chosen emitter layer with high-refractive-index substrates, and using a periodic outcoupling structure, we achieve a device power efficiency of 90 lm W(-1) at 1,000 candelas per square metre. This efficiency has the potential to be raised to 124 lm W(-1) if the light outcoupling can be further improved. Besides approaching internal quantum efficiency values of one, we have also focused on reducing energetic and ohmic losses that occur during electron-photon conversion. We anticipate that our results will be a starting point for further research, leading to white OLEDs having efficiencies beyond 100 lm W(-1). This could make white-light OLEDs, with their soft area light and high colour-rendering qualities, the light sources of choice for the future.

  12. 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.

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

    Science.gov (United States)

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

    2018-01-30

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

  14. 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...

  15. 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.

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

    Science.gov (United States)

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

    2016-03-22

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

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

    Directory of Open Access Journals (Sweden)

    Jwo-Huei Jou

    2015-07-01

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

  18. Performance improvement of indoor positioning using light-emitting diodes and an image sensor for light-emitting diode communication

    Science.gov (United States)

    Hossen, Md. Sazzad; Park, Youngil; Kim, Ki-Doo

    2015-04-01

    Light-emitting diodes (LEDs) are expected to replace existing lighting technologies in the near future because of the potential dual function of LED light (i.e., wireless communication and lighting) in the context of visible light communication (VLC). We propose a highly precise indoor positioning algorithm using lighting LEDs, an image sensor, and VLC. In the proposed algorithm, three LEDs transmit their three-dimensional coordinate information, which is received and demodulated by a single image sensor at an unknown position. The unknown position is then calculated from the geometrical relations of the LED images created on the image sensor plane. We describe the algorithm in detail. A simulation of the proposed algorithm is presented in this paper. We also compare the performance of this algorithm with that of our previously proposed algorithm. The comparison indicates significant improvement in positioning accuracy because of the simple algorithmic structure and low computational complexity. This technique does not require any angular measurement, which is needed in the contemporary positioning algorithms using LEDs and image sensor. The simulation results show that the proposed system can estimate the unknown position to an accuracy of 0.001 m inside the approximate positioning area when the pixel value is >3000.

  19. 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.

  20. Influence of electron transport layer thickness on optical properties of organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Guohong; Liu, Yong; Li, Baojun; Zhou, Xiang, E-mail: stszx@mail.sysu.edu.cn [State Key Lab of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

    2015-06-07

    We investigate experimentally and theoretically the influence of electron transport layer (ETL) thickness on properties of typical N,N′-diphenyl-N,N′-bis(1-naphthyl)-[1,1′-biphthyl]-4,4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq{sub 3}) heterojunction based organic light-emitting diodes (OLEDs), where the thickness of ETL is varied to adjust the distance between the emitting zone and the metal electrode. The devices showed a maximum current efficiency of 3.8 cd/A when the ETL thickness is around 50 nm corresponding to an emitter-cathode distance of 80 nm, and a second maximum current efficiency of 2.6 cd/A when the ETL thickness is around 210 nm corresponding to an emitter-cathode distance of 240 nm. We adopt a rigorous electromagnetic approach that takes parameters, such as dipole orientation, polarization, light emitting angle, exciton recombination zone, and diffusion length into account to model the optical properties of devices as a function of varying ETL thickness. Our simulation results are accurately consistent with the experimental results with a widely varying thickness of ETL, indicating that the theoretical model may be helpful to design high efficiency OLEDs.

  1. Influence of electron transport layer thickness on optical properties of organic light-emitting diodes

    Science.gov (United States)

    Liu, Guohong; Liu, Yong; Li, Baojun; Zhou, Xiang

    2015-06-01

    We investigate experimentally and theoretically the influence of electron transport layer (ETL) thickness on properties of typical N,N'-diphenyl-N,N'-bis(1-naphthyl)-[1,1'-biphthyl]-4,4'-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3) heterojunction based organic light-emitting diodes (OLEDs), where the thickness of ETL is varied to adjust the distance between the emitting zone and the metal electrode. The devices showed a maximum current efficiency of 3.8 cd/A when the ETL thickness is around 50 nm corresponding to an emitter-cathode distance of 80 nm, and a second maximum current efficiency of 2.6 cd/A when the ETL thickness is around 210 nm corresponding to an emitter-cathode distance of 240 nm. We adopt a rigorous electromagnetic approach that takes parameters, such as dipole orientation, polarization, light emitting angle, exciton recombination zone, and diffusion length into account to model the optical properties of devices as a function of varying ETL thickness. Our simulation results are accurately consistent with the experimental results with a widely varying thickness of ETL, indicating that the theoretical model may be helpful to design high efficiency OLEDs.

  2. GaN doped with beryllium—An effective light converter for white light emitting diodes

    Science.gov (United States)

    Teisseyre, Henryk; Bockowski, Michal; Grzegory, Izabella; Kozanecki, Adrian; Damilano, Benjamin; Zhydachevskii, Yaroslav; Kunzer, Michael; Holc, Katarzyna; Schwarz, Ulrich T.

    2013-07-01

    So far, most of the studies on GaN doped with beryllium have mainly concentrated on possible p-type doping. Unfortunately, realization of p-type conductivity in such a way appeared to be very difficult. It seems, however, that bulk crystals doped with beryllium can be used as white light converters in the monolithic white light emitting diodes. To realize monolithic white light emitting diode, we used blue light emitting diodes and a single GaN:Be crystal as converter. High value of the Color Rendering Index gives hope for obtaining an effective light converter based on gallium nitride doped with beryllium.

  3. Efficient and bright organic light-emitting diodes on single-layer graphene electrodes

    Science.gov (United States)

    Li, Ning; Oida, Satoshi; Tulevski, George S.; Han, Shu-Jen; Hannon, James B.; Sadana, Devendra K.; Chen, Tze-Chiang

    2013-08-01

    Organic light-emitting diodes are emerging as leading technologies for both high quality display and lighting. However, the transparent conductive electrode used in the current organic light-emitting diode technologies increases the overall cost and has limited bendability for future flexible applications. Here we use single-layer graphene as an alternative flexible transparent conductor, yielding white organic light-emitting diodes with brightness and efficiency sufficient for general lighting. The performance improvement is attributed to the device structure, which allows direct hole injection from the single-layer graphene anode into the light-emitting layers, reducing carrier trapping induced efficiency roll-off. By employing a light out-coupling structure, phosphorescent green organic light-emitting diodes exhibit external quantum efficiency >60%, while phosphorescent white organic light-emitting diodes exhibit external quantum efficiency >45% at 10,000 cd m-2 with colour rendering index of 85. The power efficiency of white organic light-emitting diodes reaches 80 lm W-1 at 3,000 cd m-2, comparable to the most efficient lighting technologies.

  4. 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.

  5. Multicolor white light-emitting diodes for illumination applications

    Science.gov (United States)

    Chi, Solomon W. S.; Chen, Tzer-Perng; Tu, Chuan-Cheng; Chang, Chih-Sung; Tsai, Tzong-Liang; Hsieh, Mario C. C.

    2004-01-01

    Semiconductor light emitting diode (LED) has become a promising device for general-purpose illumination applications. LED has the features of excellent durability, long operation life, low power consumption, no mercury containing and potentially high efficiency. Several white LED technologies appear capable of meeting the technical requirements of illumination. In this paper we present a new multi-color white (MCW) LED as a high luminous efficacy, high color rendering index and low cost white illuminator. The device consists of two LED chips, one is AlInGaN LED for emitting shorter visible spectra, another is AlInGaP LED for emitting longer visible spectra. At least one chip in the MCW-LED has two or more transition energy levels used for emitting two or more colored lights. The multiple colored lights generated from the MCW-LED can be mixed into a full-spectral white light. Besides, there is no phosphors conversion layer used in the MCW-LED structure. Therefore, its color rendering property and illumination efficiency are excellent. The Correlated Color Temperature (CCT) of the MCW-LED may range from 2,500 K to over 10,000 K. The theoretical General Color Rendering Index (Ra) could be as high as 94, which is close to the incandescent and halogen sources, while the Ra of binary complementary white (BCW) LED is about 30 ~ 45. Moreover, compared to the expensive ternary RGB (Red AlInGaP + Green AlInGaN + Blue AlInGaN) white LED sources, the MCW-LED uses only one AlInGaN chip in combination with one cheap AlInGaP chip, to form a low cost, high luminous performance white light source. The MCW-LED is an ideal light source for general-purpose illumination applications.

  6. 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

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

    Science.gov (United States)

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

    1998-01-01

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

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

    Science.gov (United States)

    2014-03-27

    concern is through Advanced Oxidation Processes (AOP). One such process uses ultraviolet (UV) energy to decompose hydrogen peroxide ( H2O2 ) to create...MODELING ULTRAVIOLET (UV) LIGHT EMITTING DIODE (LED) ENERGY PROPAGATION IN REACTOR VESSELS THESIS...

  9. 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

  10. Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer

    National Research Council Canada - National Science Library

    Lee, Bo Ram; Jung, Eui Dae; Park, Ji Sun; Nam, Yun Seok; Min, Sa Hoon; Kim, Byeong-Su; Lee, Kyung-Min; Jeong, Jong-Ryul; Friend, Richard H; Kim, Ji-Seon; Kim, Sang Ouk; Song, Myoung Hoon

    2014-01-01

    .... Here, we improve the efficiency of inverted polymer light-emitting diodes by introducing a spontaneously formed ripple-shaped nanostructure of ZnO and applying an amine-based polar solvent treatment...

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

    Science.gov (United States)

    2009-12-01

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

  12. 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.

  13. 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....

  14. Device physics of polymer light-emitting diodes

    Science.gov (United States)

    Crone, Brian Keith

    Organic light emitting diodes have the structure metal_A/organic/metal_B. The physical processes which determine the operating characteristics of these devices are carrier injection into the organic material from the metal contacts, carrier transport through the organic, and carrier recombination in the organic layer. The philosophy employed here is to study these processes in simple situations where they can be studied independently to as large a degree as possible, and then to apply the understanding gained from simple systems to successively more complex systems. This is done by using experiments in parallel with a device model to describe the experimental results. First single carrier single layer devices are considered. Current voltage characteristics are measured for series of electron and hole only devices both as a function of device thickness and of energy barrier to carrier injection. These measurements were described by a device model and carrier mobilities were extracted. The energy barriers to injection were measured independently. Then the current voltage characteristics were measured for series of bipolar single layer devices both as a function of device thickness and energy barrier to carrier injection. These measurements were described by the carrier mobilities and energy barriers determined from single carrier experiments with no additional fitting parameters. The device model also gave a qualitative description of single layer device luminances. The calculated current voltage characteristics were found to be relatively insensitive to the magnitude of the recombination rate used in the device model. Organic materials which have desirable electroluminescence properties may not have the necessary physical characteristics to make an efficient single layer LED. Device model results are presented which show that if the injection or transport of one carrier is lacking in a material, an efficient device can be made by introducing a second material which

  15. 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

  16. Resonant-cavity light-emitting diodes for optical interconnects

    Science.gov (United States)

    Jin, Xu

    This dissertation addresses the issues related to external quantum efficiencies and light coupling efficiency of novel 1.3 mum Resonant-cavity light-emitting diodes (RCLEDs) on GaAs substrates. External quantum efficiency (QE) is defined as the number of extracted photons per injected electrons, i.e., the product of injection efficiency, internal QE, and light extraction efficiency. This study focuses on the latter two terms. Internal QE mainly depends on the properties of the active region quantum wells (QWs) used in the RCLEDs, such as composition, thickness, and strain compensation. GaAsSb/GaAs QW edge-emitting (EE) lasers are characterized experimentally to extract key parameters, such as internal QE and internal loss. With optimized QWs and a novel self-aligned EE lasers process, room temperature continuous wave (CW) operation of GaAsSb EE lasers has been demonstrated for the first time. The highest operational temperature for the EE lasers is 48°C at a wavelength as long as 1260 nm. This result is the best ever reported by a university group. In conventional LEDs, very little light generated by the active region, succeeds in escaping from the semiconductor material due to the small critical angle of total internal reflection. With the use of a resonant cavity, the light extraction efficiency of RCLEDs is significantly improved. Front and back reflectivities, detuning (offset) between resonant-cavity peak and electroluminescence, and electroluminescence linewidth have been identified as key factors influencing light extraction efficiency. Numerical simulations indicate that the fraction of luminescence transmitted through the top mirror of an optimized RCLED is around 9%, which is more than double that of conventional LEDs. This number will be larger when multiple reflections and photon recycling are considered; which are not included in the current model since they are structure dependent. The best GaAsSb/GaAs QW RCLEDs demonstrated in this work have shown

  17. 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

  18. 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…

  19. Method and apparatus for improving the performance of light emitting diodes

    Science.gov (United States)

    Lowery, Christopher H.; McElfresh, David K.; Burchet, Steve; Adolf, Douglas B.; Martin, James

    1996-01-01

    A method for increasing the resistance of a light emitting diode and other semiconductor devices to extremes of temperature is disclosed. During the manufacture of the light emitting diode, a liquid coating is applied to the light emitting die after the die has been placed in its lead frame. After the liquid coating has been placed on the die and its lead frames, a thermosetting encapsulant material is placed over the coating. The operation that cures the thermosetting material leaves the coating liquid intact. As the die and the encapsulant expand and contract at different rates with respect to changes in temperature, and as in known light emitting diodes the encapsulating material adheres to the die and lead frames, this liquid coating reduces the stresses that these different rates of expansion and contraction normally cause by eliminating the adherence of the encapsulating material to the die and frame.

  20. Thermally evaporated hybrid perovskite for hetero-structured green light-emitting diodes

    Science.gov (United States)

    Mariano, Fabrizio; Listorti, Andrea; Rizzo, Aurora; Colella, Silvia; Gigli, Giuseppe; Mazzeo, Marco

    2017-10-01

    Thermal evaporation of green-light emitting perovskite (MaPbBr3) films is reported. Morphological studies show that a soft thermal treatment is needed to induce an outstanding crystal growth and film organization. Hetero-structured light-emitting diodes, embedding as-deposited and annealed MAPbBr3 films as active layers, are fabricated and their performances are compared, highlighting that the perovskite evolution is strongly dependent on the growing substrate, too.

  1. Novel integration of a microchannel with a silicon light emitting diode antifuse

    NARCIS (Netherlands)

    Le Minh, P.; Holleman, J.; Wallinga, Hans; Berenschot, Johan W.; Tas, Niels Roelof; van den Berg, Albert

    Light emitting diode antifuses have been integrated into a microfluidic device that is realized with extended standard IC-compatible technological steps. The device comprises a microchannel sandwiched between a photodiode detector and a nanometre-scale diode antifuse light emitter. In this paper,

  2. Monolithic integration of a novel microfluidic device with silicon light emitting diode-antifuse and photodetector

    NARCIS (Netherlands)

    Le Minh, P.; Holleman, J.; Berenschot, Johan W.; Tas, Niels Roelof; van den Berg, Albert

    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,

  3. Integration of a novel microfluidic device with silicon light emitting diode-antifuse and photodetector

    NARCIS (Netherlands)

    Le Minh, P.; Holleman, J.; Berenschot, Johan W.; Tas, Niels Roelof; van den Berg, Albert

    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,

  4. Hole transport in poly(p-phenylene vinylene) based light-emitting diodes revisited

    NARCIS (Netherlands)

    Tanase, C; Blom, PWM; de Leeuw, DM; Kafafi, ZH; Lane, PA

    2004-01-01

    Understanding of the charge transport properties is of great importance for the operation and the efficiency of polymer based light-emitting diodes (LEDs). We investigate the charge transport in hole-only diodes based on poly(p-phenylene vinylene) (PPV) as function of temperature T, charge carrier

  5. Exciton dynamics of luminescent defects in aging organic light-emitting diodes

    Science.gov (United States)

    Ingram, Grayson L.; Zhao, Yong-Biao; Lu, Zheng-Hong

    2017-12-01

    Fundamental device physics of exciton dynamics is crucial to the design and fabrication of organic light-emitting diodes (OLEDs) with a long lifetime at high brightness. In this paper, we report a set of analytical equations which describe how and where defects form during exciton-driven degradation of an OLED and their impact on device operation. This set of equations allows us to quantify changes in the exciton and defect populations as a function of time in neat layers of 4,4'-Bis(carbazol-9-yl)biphenyl (CBP) in simple bilayer OLEDs. CBP produces luminescent defects which present a unique opportunity to quantify the exciton capturing dynamics of the defects. Through modeling of the time and current density dependence of both the CBP and defect emission, we clearly identify CBP singlet excitons as the source of OLED degradation. Further analysis of experimental data on devices with precisely positioned exciton capturing layers suggests that defects are formed near organic heterojunctions.

  6. Characteristics of organic light emitting diodes with copper iodide as injection layer

    Energy Technology Data Exchange (ETDEWEB)

    Stakhira, P., E-mail: stakhira@polynet.lviv.u [Lviv Polytechnic National University, S. Bandera, 12, Lviv, 79013 (Ukraine); Cherpak, V.; Volynyuk, D.; Ivastchyshyn, F. [Lviv Polytechnic National University, S. Bandera, 12, Lviv, 79013 (Ukraine); Hotra, Z. [Lviv Polytechnic National University, S. Bandera, 12, Lviv, 79013 (Ukraine); Rzeszow University of Technology, W. Pola 2, Rzeszow, 35-959 (Poland); Tataryn, V. [Lviv Polytechnic National University, S. Bandera, 12, Lviv, 79013 (Ukraine); Luka, G. [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland)

    2010-09-30

    We have studied the use of a thin copper iodide (CuI) film as an efficient injection layer of holes from indium tin oxide (ITO) anode in a light-emitting diode structure based on tris-8-hydroxyquinoline aluminium (Alq3). The results of impedance analysis of two types of diode structures, ITO/CuI/Alq3/poly(ethylene glycol) dimethyl ether/Al and ITO/Alq3/poly(ethylene glycol) dimethyl ether/Al, are presented. Comparative analysis of their current density-voltage, luminance-voltage and impedance characteristics shows that presence of CuI layer facilitates injection of holes from ITO anode into the light-emitting layer Alq3 and increases electroluminescence efficiency of the organic light emitting diodes.

  7. 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.

  8. 76 FR 51396 - Certain Light-Emitting Diodes and Products Containing Same; Notice of Institution of Investigation

    Science.gov (United States)

    2011-08-18

    ... COMMISSION Certain Light-Emitting Diodes and Products Containing Same; Notice of Institution of Investigation... importation, and the sale within the United States after importation of certain light-emitting diodes and...- emitting diodes and products containing same that infringe one or more of claims 1, 3, 5-10, and 13-16 of...

  9. 76 FR 52348 - Certain Light-Emitting Diodes and Products Containing Same; Corrected Notice of Institution of...

    Science.gov (United States)

    2011-08-22

    ... COMMISSION Certain Light-Emitting Diodes and Products Containing Same; Corrected Notice of Institution of... importation, or the sale within the United States after importation of certain light- emitting diodes and...-emitting diodes and products containing same by reason of infringement of certain claims of U.S. Patent No...

  10. Color tunable organic light emitting diodes using Eu complex doping

    Science.gov (United States)

    Li, W. X.; Hagen, J.; Jones, R.; Heikenfeld, J.; Steckl, A. J.

    2007-03-01

    A voltage-controlled color tunable organic light emitting device has been demonstrated by using a co-evaporated emissive layer of NPB [( N, N'-bis(naphthalene-1-yl)- N, N'-bis(phenyl)benzidine)] and an organic Eu complex. As a result of minimized energy transfer from the host (NPB) to the guest emitter (Eu complex), this device can vary the light emission from vivid red to deep blue with increasing bias. Optimal device performance is obtained for a 20 wt.% Eu doping in NPB. This doping concentration is able to yield x and y chromaticity coordinates in the range of 0.61-0.17 and 0.31-0.12, respectively.

  11. 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.

  12. Organic light emitting diode with a DNA biopolymer electron blocking layer

    Science.gov (United States)

    Hagen, Joshua A.; Grote, James G.; Li, Wayne X.; Steckl, Andrew J.; Diggs, Darnell E.; Zetts, John S.; Nelson, Robert L.; Hopkins, F. Kenneth

    2006-08-01

    Enhanced electroluminescent efficiency using a deoxyribonucleic acid (DNA)-based biopolymer complex as an electron blocking layer has been demonstrated in both green- and blue-emitting organic light emitting diodes. The resulting bio organic light emitting diodes, or BioLEDs, achieved a maximum luminous efficiency of 8.2 and 0.8 cd/A, respectively, resulting in as much as 10× higher efficiency, 30× brighter output and 3× longer lifetime than their OLED counterparts. In this paper we describe the device fabrication and present the performance of these new structures.

  13. 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....

  14. 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....

  15. 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

    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...

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

    Science.gov (United States)

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

    2017-05-09

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

  17. Slanted n-ZnO/p-GaN nanorod arrays light-emitting diodes grown by oblique-angle deposition

    Directory of Open Access Journals (Sweden)

    Ya-Ju Lee

    2014-05-01

    Full Text Available High-efficient ZnO-based nanorod array light-emitting diodes (LEDs were grown by an oblique-angle deposition scheme. Due to the shadowing effect, the inclined ZnO vapor-flow was selectively deposited on the tip surfaces of pre-fabricated p-GaN nanorod arrays, resulting in the formation of nanosized heterojunctions. The LED architecture composed of the slanted n-ZnO film on p-GaN nanorod arrays exhibits a well-behaving current rectification of junction diode with low turn-on voltage of 4.7 V, and stably emits bluish-white luminescence with dominant peak of 390 nm under the operation of forward injection currents. In general, as the device fabrication does not involve passivation of using a polymer or sophisticated material growth techniques, the revealed scheme might be readily applied on other kinds of nanoscale optoelectronic devices.

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

    Directory of Open Access Journals (Sweden)

    Qingkai Yao

    2017-07-01

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

  19. Efficient polymer light-emitting diode with air-stable aluminum cathode

    NARCIS (Netherlands)

    Abbaszadeh, Davood; Wetzelaer, G.A.H.; Doumon, Nutifafa Y.; Blom, P.W.M

    2016-01-01

    The fast degradation of polymer light-emitting diodes (PLEDs) in ambient conditions is primarily due to the oxidation of highly reactive metals, such as barium or calcium, which are used as cathode materials. Here, we report the fabrication of PLEDs using an air-stable partially oxidized aluminum

  20. Efficient electron injection from solution-processed cesium stearate interlayers in organic light-emitting diodes

    NARCIS (Netherlands)

    Wetzelaer, G. A. H.; Najafi, A.; Kist, R. J. P.; Kuik, M.; Blom, P. W. M.

    2013-01-01

    The electron-injection capability of solution-processed cesium stearate films in organic light-emitting diodes is investigated. Cesium stearate, which is expected to exhibit good solubility and film formation due to its long hydrocarbon chain, is synthesized using a straightforward procedure.

  1. 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...

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

    Science.gov (United States)

    Kamata, Masahiro; Abe, Mayumi

    2012-01-01

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

  3. Medical applications of space light-emitting diode technology-space station and beyond

    Science.gov (United States)

    Whelan, Harry T.; Houle, John M.; Donohoe, Deborah L.; Bajic, Dawn M.; Schmidt, Meic H.; Reichert, Kenneth W.; Weyenberg, George T.; Larson, David L.; Meyer, Glenn A.; Caviness, James A.

    1999-01-01

    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.

  4. Red for LED : New narrow band red phosphors for white light emitting diodes

    NARCIS (Netherlands)

    Senden, T.|info:eu-repo/dai/nl/37060217X

    2018-01-01

    White light emitting diodes (LEDs) are nowadays widely applied in general lighting and consumer electronics. Due to their superior energy efficiency and long operation lifetime, white LEDs are considered to be the light sources of the future, and it is anticipated that white LEDs will largely

  5. 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.

  6. Bias-dependent current efficiency in polymer light-emitting diodes

    NARCIS (Netherlands)

    van Woudenbergh, T; Wildeman, J; Blom, PWM

    The current efficiency (CE) of single-layer poly-p-phenylene vinylene-based light-emitting diodes (PLEDs) at low voltages is poor and strongly bias dependent, which has been attributed to the quenching of excitons at the metallic cathode. In the absence of exciton quenching the CE is expected to be

  7. 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

  8. 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

  9. 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

  10. 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....

  11. 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

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

    Indian Academy of Sciences (India)

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

  13. 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

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

    NARCIS (Netherlands)

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

    2014-01-01

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

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

    NARCIS (Netherlands)

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

    2014-01-01

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

  16. Color Shift Modeling of Light-Emitting Diode Lamps in Step-Loaded Stress Testing

    NARCIS (Netherlands)

    Cai, Miao; Yang, Daoguo; Huang, J.; Zhang, Maofen; Chen, Xianping; Liang, Caihang; Koh, S.W.; Zhang, G.Q.

    2017-01-01

    The color coordinate shift of light-emitting diode (LED) lamps is investigated by running three stress-loaded testing methods, namely step-up stress accelerated degradation testing, step-down stress accelerated degradation testing, and constant stress accelerated degradation testing. A power

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

    NARCIS (Netherlands)

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

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

  18. Outsmarting waveguide losses in thin-film light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Meerholz, K.; Mueller, D.C. [Muenchen Univ. (Germany). Chemistry Dept.

    2001-08-01

    Several attempts to overcome the problem of waveguide losses in light-emitting diodes (LEDs) have been made over past few years. This article summarizes the most important developments in this area and specifically highlights one attempt, achieved by Tsutsui et al. and published in the latest issue of Advanced Materials. (orig.)

  19. 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.

  20. 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

  1. Non-radiative recombination losses in polymer light-emitting diodes

    NARCIS (Netherlands)

    Kuik, M.; Koster, L.J.A.; Dijkstra, A.G.; Wetzelaer, G.A.H.; Blom, P.W.M.

    2012-01-01

    We present a quantitative analysis of the loss of electroluminescence in light-emitting diodes (LEDs) based on poly[2-methoxy-5-(2′-ethylhexyloxy)- p-phenylenevinylene] (MEH-PPV) due to the combination of non-radiative trap-assisted recombination and exciton quenching at the metallic cathode. It is

  2. 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,

  3. 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

  4. Trap-assisted and Langevin-type recombination in organic light-emitting diodes

    NARCIS (Netherlands)

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

    2011-01-01

    Trapping of charges is known to play an important role in the charge transport of organic semiconductors, but the role of traps in the recombination process has not been addressed. Here we show that the ideality factor of the current of organic light-emitting diodes (OLEDs) in the

  5. 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

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. All-silicon light-emitting diodes waveguide-integrated with superconducting single-photon detectors

    Science.gov (United States)

    Buckley, Sonia; Chiles, Jeffrey; McCaughan, Adam N.; Moody, Galan; Silverman, Kevin L.; Stevens, Martin J.; Mirin, Richard P.; Nam, Sae Woo; Shainline, Jeffrey M.

    2017-10-01

    We demonstrate cryogenic, electrically injected, waveguide-coupled Si light-emitting diodes (LEDs) operating at 1.22 μm. The active region of the LED consists of W centers implanted in the intrinsic region of a p-i-n diode. The LEDs are integrated on waveguides with superconducting nanowire single-photon detectors (SNSPDs). We demonstrate the scalability of this platform with an LED coupled to eleven SNSPDs in a single integrated photonic device.

  11. Investigation on light emission in light-emitting diodes constructed with n-ZnO and p-Si nanowires.

    Science.gov (United States)

    Kim, Kwangeun; Moon, Taeho; Kim, Sangsig

    2011-07-01

    The light emission was investigated in light-emitting diodes (LEDs) constructed with n-ZnO and p-Si nanowires (NWs). ZnO NWs were synthesized by thermal chemical vapor deposition and Si NWs were formed by crystallographic wet etching of a Si wafer. The LEDs were fabricated using the NWs via dielectrophoresis (DEP) and direct transfer methods. The DEP method enabled to align the ZnO NW at the position that led to p-n heterojunction diodes by crossing with the transferred Si NW. The I-V curve of the p-n heterojunction diode showed the well-defined current-rectifying characteristic, with a turn-on voltage of 3 V. The electroluminescence spectrum in the dark showed the strong emission at approximately 385 nm and the broad emission centered at approximately 510 nm, at a forward bias of 30 V. Under the illumination of 325-nm-wavelength light, the luminescence intensity at 385 nm was dramatically enhanced, compared to that in the dark, probably due to the electric-field-induced enhancement of luminescence.

  12. Tandem organic light-emitting diodes with buffer-modified C60/pentacene as charge generation layer

    Science.gov (United States)

    Wang, Zhen; Zheng, Xin; Liu, Fei; Wang, Pei; Gan, Lin; Wang, Jing-jing

    2017-09-01

    Buffer-modified C60/pentacene as charge generation layer (CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes (OLEDs) with multiple identical emissive units and using buffer-modified C60/pentacene organic semiconductor heterojunction (OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd·A-1 at 30 mA·cm-2 can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs2CO3/Al is an effective buffer for C60/pentacene-based tandem OLEDs.

  13. Solution-Grown ZnO Films toward Transparent and Smart Dual-Color Light-Emitting Diode.

    Science.gov (United States)

    Huang, Xiaohu; Zhang, Li; Wang, Shijie; Chi, Dongzhi; Chua, Soo Jin

    2016-06-22

    An individual light-emitting diode (LED) capable of emitting different colors of light under different bias conditions not only allows for compact device integration but also extends the functionality of the LED beyond traditional illumination and display. Herein, we report a color-switchable LED based on solution-grown n-type ZnO on p-GaN/n-GaN heterojunction. The LED emits red light with a peak centered at ∼692 nm and a full width at half-maximum of ∼90 nm under forward bias, while it emits green light under reverse bias. These two lighting colors can be switched repeatedly by reversing the bias polarity. The bias-polarity-switched dual-color LED enables independent control over the lighting color and brightness of each emission with two-terminal operation. The results offer a promising strategy toward transparent, miniaturized, and smart LEDs, which hold great potential in optoelectronics and optical communication.

  14. 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.

  15. Manufacturing polymer light emitting diode with high luminance efficiency by solution process

    Science.gov (United States)

    Kim, Miyoung; Jo, SongJin; Yang, Ho Chang; Yoon, Dang Mo; Kwon, Jae-Taek; Lee, Seung-Hyun; Choi, Ju Hwan; Lee, Bum-Joo; Shin, Jin-Koog

    2012-06-01

    While investigating polymer light emitting diodes (polymer-LEDs) fabricated by solution process, surface roughness influences electro-optical (E-O) characteristics. We expect that E-O characteristics such as luminance and power efficiency related to surface roughness and layer thickness of emitting layer with poly-9-Vinylcarbazole. In this study, we fabricated polymer organic light emitting diodes by solution process which guarantees easy, eco-friendly and low cost manufacturing for flexible display applications. In order to obtain high luminescence efficiency, E-O characteristics of these devices by varying parameters for printing process have been investigated. Therefore, we optimized process condition for polymer-LEDs by adjusting annealing temperatures of emission, thickness of emission layer showing efficiency (10.8 cd/A) at 10 mA/cm2. We also checked wavelength dependent electroluminescence spectrum in order to find the correlation between the variation of efficiency and the thickness of the layer.

  16. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-04-04

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

  18. 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.

  19. Carbon Nanotube Driver Circuit for 6 ? 6 Organic Light Emitting Diode Display

    OpenAIRE

    Jianping Zou; Kang Zhang; Jingqi Li; Yongbiao Zhao; Yilei Wang; Suresh Kumar Raman Pillai; Hilmi Volkan Demir; Xiaowei Sun; Chan-Park, Mary B.; Qing Zhang

    2015-01-01

    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 s...

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

    Science.gov (United States)

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

    2014-07-22

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

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

    OpenAIRE

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

    2018-01-01

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

  2. Continuous light-emitting Diode (LED) lighting for improving food quality

    OpenAIRE

    Lu, C.; Bian, Z.

    2016-01-01

    Lighting-emitting diodes (LEDs) have shown great potential for plant growth and development, with higher luminous efficiency and positive impact compared with other artificial lighting. The combined effects of red/blue or/and green, and white LED light on plant growth and physiology, including chlorophyll fluorescence, nitrate content and phytochemical concentration before harvest, were investigated. The results showed that continuous light (CL)\\ud exposure at pre-harvest can effectively redu...

  3. 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.

  4. Analysis of photon recycling in light emitting diodes with nonuniform injection

    Science.gov (United States)

    Tsutsui, N.; Khmyrova, I.; Ryzhii, V.; Ikegami, T.

    2000-09-01

    We studied the effect of photon recycling in double heterostructure light emitting diodes (LEDs) with relatively small area contact providing nonuniform injection of electrons. A simple phenomenological model of the electron and photon transport in the LED is used to calculate the spatial distributions of electrons and output radiation as well as the external quantum efficiency as functions of device parameters. It is shown that photon recycling is the governing factor of the operation of LEDs with nonuniform injection.

  5. Efficient GaAs light-emitting diodes by photon recycling

    Science.gov (United States)

    Dupont, E.; Liu, H. C.; Buchanan, M.; Chiu, S.; Gao, M.

    2000-01-01

    Heterostructure AlGaAs/GaAs light-emitting diodes (LEDs) with a thick active region have shown high external efficiencies, thanks to reabsorption in the active region. For high injection currents and low temperature, we report a 22% efficiency which corresponds to a 98% efficiency internally. We discuss the application of such LED when integrated with a quantum-well infrared photodetector for pixelless thermal imaging systems.

  6. 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.

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

    OpenAIRE

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

    2014-01-01

    We report on the use of nucleic acid bases (NBs) in organic light emitting diodes (OLEDs). NBs are small molecules that are the basic building blocks of the larger DNA polymer. NBs readily thermally evaporate and integrate well into the vacuum deposited OLED fabrication. Adenine (A) and thymine (T) were deposited as electron-blocking/hole-transport layers (EBL/HTL) that resulted in increases in performance over the reference OLED containing the standard EBL material NPB. A-based OLEDs reached...

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

    Science.gov (United States)

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

    2013-01-01

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

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

    Science.gov (United States)

    2017-11-01

    sent from light-emitting diodes (LEDs) of 5 colors (green, red, white , amber, and blue). Experiment 1 involved controlled laboratory measurements of...for operation at 12 VDC. Specifications for colored and white LEDs are in Table 1. * A picture of...520 nm Blue 15 mA 1000 mcd 465 nm White LED specifications Color Current draw Output Effective color temperature Cool white 20 mA 4100 mcd 6000 K

  10. First examples of organophosphorus-containing materials for light-emitting diodes.

    Science.gov (United States)

    Fave, Claire; Cho, Ting-Yi; Hissler, Muriel; Chen, Chieh-Wei; Luh, Tien-Yau; Wu, Chung-Chih; Réau, Régis

    2003-08-06

    Exploiting the reactivity of the P-atom of phosphole-based oligomers, we have achieved access to the first organophosphorus-containing organic light-emitting diode (OLED) materials. The versatility of these P-materials is demonstrated with the synthesis of a corresponding gold complex that has also been used as an OLED material. Optimization of the OLED devices by doping the phosphole layer with a red fluorescent dye is described.

  11. 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.

  12. Analytical devices based on light-emitting diodes--a review of the state-of-the-art.

    Science.gov (United States)

    Bui, Duy Anh; Hauser, Peter C

    2015-01-01

    A general overview of the development of the uses of light-emitting diodes in analytical instrumentation is given. Fundamental aspects of light-emitting diodes, as far as relevant for this usage, are covered in the first part. The measurement of light intensity is also discussed, as this is an essential part of any device based on light-emitting diodes as well. In the second part, applications are discussed, which cover liquid and gas-phase absorbance measurements, flow-through detectors for chromatography and capillary electrophoresis, sensors, as well as some less often reported methods such as photoacoustic spectroscopy. Copyright © 2014 Elsevier B.V. All rights reserved.

  13. 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.

  14. Highly Efficient Soluble Blue Delayed Fluorescent and Hyperfluorescent Organic Light-Emitting Diodes by Host Engineering.

    Science.gov (United States)

    Jeon, Sang Kyu; Park, Hee-Jun; Lee, Jun Yeob

    2018-01-30

    Solution-processed high-efficiency fluorescent organic light-emitting diodes with an external quantum efficiency over 18% were developed by engineering a host material and device structure designed for solution process. A high triplet energy host material designed for the solution process, (oxybis(3-(tert-butyl)-6,1-phenylene))bis(diphenylphosphine oxide) (DPOBBPE), worked efficiently as the host of blue fluorescent devices because of good solubility, high photoluminescence quantum yield, and good film properties. The DPOBBPE host enabled a high external quantum efficiency of 18.8% in the fluorescent organic light-emitting diodes by the solution process. Moreover, 25.8% external quantum efficiency in the soluble blue thermally activated delayed fluorescent devices was also realized. The 25.8% external quantum efficiency of the DPOBBPE delayed fluorescent device and 18.8% external quantum efficiency of the fluorescent device are the highest efficiency values achieved in the solution-processed blue fluorescent organic light-emitting diodes. Moreover, the solution-processed fluorescent device showed an improved blue color coordinate of (0.14, 0.20) compared to (0.17, 0.31) of the delayed fluorescent device.

  15. White organic light emitting diodes based on fluorene-carbazole dendrimers

    Energy Technology Data Exchange (ETDEWEB)

    Usluer, Özlem, E-mail: usluerozlem@yahoo.com.tr [Department of Chemistry, Muğla Sıtkı Koçman University, 48000 Muğla (Turkey); Demic, Serafettin [Department of Materials Science and Engineering, Izmir Katip Çelebi University, 35620 Çiğli, Izmir (Turkey); Kus, Mahmut, E-mail: mahmutkus1@gmail.com [Chemical Engineering Department and Advanced Technology R and D Center, Selçuk University, Konya (Turkey); Özel, Faruk [Chemical Engineering Department and Advanced Technology R and D Center, Selçuk University, Konya (Turkey); Serdar Sariciftci, Niyazi [Linz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes Kepler University, Altenbergerstr. 69, A-4040 Linz (Austria)

    2014-02-15

    In this paper, we report on theProd. Type: FTP fabrication and characterization of blue and white light emitting devices based on two fluorene-carbazole containing dendrimers and para-sexiphenyl (6P) oligomers. Blue light emitting diodes were fabricated using 9′,9″-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis-9′H-9,3′:6′,9″-tercarbazole (OFC-G2) and 9′,9″-(9,9′-spirobi[fluorene]-2,7-diyl)bis-9′H-9,3′:6′,9″-tercarbazole (SBFC-G2) dendrimers as a hole transport and emissive layer (EML) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as an electron transport layer. White light emitting diodes were fabricated using 6P and these two dendrimers as an EML. OLED device with the structure of ITO/PEDOT:PSS (50 nm)/OFC-G2 (40 nm)/6P (20 nm)/LiF:Al (0.5:100 nm) shows maximum luminance of nearly 1400 cd/m{sup 2} and a Commission Internationale de l'Eclairage chromaticity coordinates of (0.27, 0.30) at 12 V. -- Highlights: • White organic light emitting diodes have been fabricated using two fluorene-carbazole dendrimers and para-sexiphenyl (6P) oligomers. • When only these two dendrimers are used as EML, OLED devices are emitted blue light. • The emission colors of OLED devices change from blue to white when 6P is coated on dendrimer films.

  16. Comparison of intensive light-emitting diode and intensive compact fluorescent phototherapy in non-hemolytic jaundice

    National Research Council Canada - National Science Library

    Takcı, Sahin; Yiğit, Sule; Bayram, Gülperi; Korkmaz, Ayşe; Yurdakök, Murat

    2013-01-01

    ...: intensive compact fluorescent tube (CFT) and intensive light-emitting diode (LED) phototherapy. Forty-three infants over 35 weeks of gestation with severe non-hemolytic hyperbilirubinemia were enrolled in the prospective study...

  17. Usability of light-emitting diodes in precision approach path indicator systems by individuals with marginal color vision.

    Science.gov (United States)

    2014-05-01

    To save energy, the FAA is planning to convert from incandescent lights to light-emitting diodes (LEDs) in : precision approach path indicator (PAPI) systems. Preliminary work on the usability of LEDs by color vision-waivered pilots (Bullough, Skinne...

  18. Improving Light Distribution by Zoom Lens for Electricity Savings in a Plant Factory with Light-Emitting Diodes

    National Research Council Canada - National Science Library

    Li, Kun; Li, Zhipeng; Yang, Qichang

    2016-01-01

    The high energy consumption of a plant factory is the biggest issue in its rapid expansion, especially for lighting electricity, which has been solved to a large extent by light-emitting diodes (LED...

  19. Effect of gold wire bonding process on angular correlated color temperature uniformity of white light-emitting diode

    National Research Council Canada - National Science Library

    Wu, Bulong; Luo, Xiaobing; Zheng, Huai; Liu, Sheng

    2011-01-01

    Gold wire bonding is an important packaging process of lighting emitting diode (LED). In this work, we studied the effect of gold wire bonding on the angular uniformity of correlated color temperature...

  20. 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...

  1. Solution-processable organic light emitting diode on glass fibers for textile applications

    Energy Technology Data Exchange (ETDEWEB)

    Gruber, Bjoern; Kerstin, Schulze; Silvia, Janietz [Fraunhofer Institute for Applied Polymer Research, Geiselbergstr. 69, 14476 Potsdam-Golm (Germany)

    2011-07-01

    Electronic devices based on organic materials offers the possibility to be a low-cost production technology on large area in several years. As a special application organic devices could be used in the field of electronic-textiles in future, for example for safety applications or as smart textiles. Therefore the direct integration of the electronic devices on the textile fibers is interesting. In this work, organic light emitting diodes (OLEDs) have been manufactured and investigated on cylindrical and flexible substrates. Especially the cylindrical geometry of the substrate hinders a homogeneous deposition of organic layers. Here, we present first results using solution processes for the preparation of the organic materials of an organic light emitting diode on glass fibers. The OLEDs were prepared on thin glass fibers using thermally evaporated metals and dip-coated polymeric layers. We focus on the challenging preparation steps of these layers on cylindrical substrates resulting in working devices. Additionally a current density-voltage-characteristic of a light emitting device on a glass fiber is presented and analyzed.

  2. Novel organic electron injection layer for efficient and stable organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Grover, Rakhi [Center for Organic Electronics, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012 (India); Instrument Design Development Center, Indian Institute of Technology Delhi, New Delhi 110016 (India); Srivastava, Ritu, E-mail: ritu@mail.nplindia.ernet.in [Center for Organic Electronics, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012 (India); Kamalasanan, M.N. [Center for Organic Electronics, CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi 110012 (India); Mehta, D.S. [Instrument Design Development Center, Indian Institute of Technology Delhi, New Delhi 110016 (India)

    2014-02-15

    The efficiency of organic light-emitting diodes (OLEDs) was significantly improved by introducing a novel organic composition (4,7-diphyenyl-1,10-phenanthroline (BPhen): 20 wt% tetracyanoquinodimethane (TCNQ)) as an electron injection layer which could be uniformly deposited over a range of thicknesses. A highly injecting contact was obtained using 1.5 nm thick film of 20 wt% TCNQ mixed BPhen as the electron injection layer. High efficiency and stability of organic light emitting device are ascribed to improved electron injection and hence better charge carrier balance inside the OLEDs. -- Highlights: • • Highly conducting mixed BPhen films were used as electron injection layer in OLEDs for the first time. • Thickness of the proposed film has been optimized for best efficiency of OLEDs. • Proposed layer being organic could be deposited at relatively low temperatures. • TCNQ mixed BPhen films prove to be an efficient n-type layer in OLEDs.

  3. 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.

  4. 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.

  5. High-performance light-emitting diodes based on carbene-metal-amides

    Science.gov (United States)

    Di, Dawei; Romanov, Alexander S.; Yang, Le; Richter, Johannes M.; Rivett, Jasmine P. H.; Jones, Saul; Thomas, Tudor H.; Abdi Jalebi, Mojtaba; Friend, Richard H.; Linnolahti, Mikko; Bochmann, Manfred; Credgington, Dan

    2017-04-01

    Organic light-emitting diodes (OLEDs) promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed OLEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 nanoseconds at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, so that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of the donor and acceptor moieties about the bridge. Unlike other systems with low exchange energy, substantial oscillator strength is sustained at the singlet-triplet degeneracy point.

  6. Ultraviolet-enhanced light emitting diode employing individual ZnO microwire with SiO2 barrier layers

    Science.gov (United States)

    Xu, Yingtian; Xu, Li; Dai, Jun; Ma, Yan; Chu, Xianwei; Zhang, Yuantao; Du, Guotong; Zhang, Baolin; Yin, Jingzhi

    2015-05-01

    This paper details the fabrication of n-ZnO single microwire (SMW)-based high-purity ultraviolet light-emitting diodes (UV-LEDs) with an added SiO2 barrier layer on the p-Si substrate. However, the current-voltage (I-V) curve exhibited non-ideal rectifying characteristics. Under forward bias, both UV and visible emissions could be detected by electroluminescence (EL) measurement. When bias voltage reached 60 V at room temperature, a UV emission spike occurred at 390 nm originating from the n-ZnO SMW. Compared with the EL spectrum of the n-ZnO SMW/p-Si heterojunction device without the SiO2 barrier layer, we saw improved UV light extraction efficiency from the current-blocking effect of the SiO2 layer. The intense UV emission in the n-ZnO SMW/SiO2/p-Si heterojunction indicated that the SiO2 barrier layer can restrict the movement of electrons as expected and result in effective electron-hole recombination in ZnO SMW.

  7. Electrical and Optical Enhancement in Internally Nanopatterned Organic Light-Emitting Diodes

    Science.gov (United States)

    Fina, Michael Dane

    Organic light-emitting diodes (OLEDs) have made tremendous technological progress in the past two decades and have emerged as a top competitor for next generation light-emitting displays and lighting. State-of-the-art OLEDs have been reported in literature to approach, and even surpass, white fluorescent tube efficiency. However, despite rapid technological progress, efficiency metrics must be improved to compete with traditional inorganic light-emitting diode (LED) technology. Organic materials possess specialized traits that permit manipulations to the light-emitting cavity. Overall, as demonstrated within, these modifications can be used to improve electrical and optical device efficiencies. This work is focused at analyzing the effects that nanopatterned geometric modifications to the organic active layers play on device efficiency. In general, OLED efficiency is complicated by the complex, coupled processes which contribute to spontaneous dipole emission. A composite of three sub-systems (electrical, exciton and optical) ultimately dictate the OLED device efficiency. OLED electrical operation is believed to take place via a low-mobility-modified Schottky injection process. In the injection-limited regime, geometric effects are expected to modify the local electric field leading to device current enhancement. It is shown that the patterning effect can be used to enhance charge carrier parity, thereby enhancing overall recombination. Current density and luminance characteristics are shown to be improved by OLED nanopatterning from both the model developed within and experimental techniques. Next, the optical enhancement effects produced by the nanopatterned array are considered. Finite-difference time-domain (FDTD) simulations are used to determine positional, spectral optical enhancement for the nanopatterned device. The results show beneficial effects to the device performance. The optical enhancements are related to the reduction in internal radiative

  8. AlGaInN-based light emitting diodes with a transparent p-contact based on thin ITO films

    Energy Technology Data Exchange (ETDEWEB)

    Smirnova, I. P., E-mail: irina@quantum.ioffe.ru; Markov, L. K.; Pavlyuchenko, A. S. [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); Kukushkin, M. V. [ZAO Innovation Company ' TETIS' (Russian Federation)

    2012-03-15

    A method for obtaining transparent conductive ITO (indium-tin oxide) films aimed for use in light emitting diodes of the blue spectral range is developed. The peak external quantum efficiency of light-emitting diodes with a p-contact based on the obtained films reaches 25%, while for similar light-emitting diodes with a standard semitransparent metal contact, it is <10%. An observed increase in the direct voltage drop from 3.15 to 3.37 V does not significantly affect the possibility of applying these films in light-emitting diodes since the optical power of light-emitting diodes with a transparent p-contact based on ITO films exceeds that of chips with metal semitransparent p-contacts with a working current of 20 mA by a factor of almost 2.5. Light-emitting diodes with p-contacts based on ITO films successfully withstand a pumping current that exceeds their calculated working current by a factor of 5 without the appearance of any signs of degradation.

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

    Science.gov (United States)

    Liu, Daxin

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

  10. Molecular beam epitaxial growth and characterization of AlN nanowall deep UV light emitting diodes

    Science.gov (United States)

    Liu, Xianhe; Zhao, Songrui; Le, Binh Huy; Mi, Zetian

    2017-09-01

    We have demonstrated large area AlN nanowall light emitting diodes grown on a sapphire substrate, which operate at 214 nm. Through detailed temperature-dependent and power-dependent photoluminescence measurements and rate equation analysis, a relatively high internal quantum efficiency (˜60%) was derived for AlN nanowall structures at room-temperature. A consistent blueshift in the emission wavelengths was measured with decreasing nanowall widths due to the reduced tensile strain distribution. The devices exhibit excellent current-voltage characteristics, including a turn-on voltage of 7 V and current densities of >170 A/cm2 at 12 V.

  11. 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.)

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

    Science.gov (United States)

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

    2017-11-01

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

  13. 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.

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

    Science.gov (United States)

    David, Aurelien; Hurni, Christophe A.; Aldaz, Rafael I.; Cich, Michael J.; Ellis, Bryan; Huang, Kevin; Steranka, Frank M.; Krames, Michael R.

    2014-12-01

    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%.

  15. 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.

  16. Laser pumped light emitting diodes as broad area sources of coherent radiation

    Science.gov (United States)

    Rahman, Faiz; Sorel, Marc

    2006-08-01

    This paper describes the use of large area light emitting diodes, pumped with various laser sources, as extended area emitters of coherent radiation. The photon recycling takes place through the intermediary of electron hole pair formation and subsequent stimulated recombination. It is possible to generate both spontaneous and stimulated emission together and the two channels are then independent of each other. This allows the generation of a mixture of coherent and non-coherent radiation in any desired proportion. The technique described is a broad-band resonant process with diffusive feedback and can be used for generating non-collimated laser radiation for a variety of applications.

  17. Spontaneous emission model of lateral light extraction from heterostructure light-emitting diodes

    Science.gov (United States)

    Ochoa, D.; Houdré, R.; Stanley, R. P.; Ilegems, M.; Benisty, H.; Hanke, C.; Borchert, B.

    2000-05-01

    We investigate the extraction of light from semiconductor light-emitting diodes made of dielectric multilayer stacks with quantum-well sources. The model is a combination of a rigorous vertical model of dipole emission and an in-plane ray-tracing model. The vertical model is shown to conveniently provide the relevant horizontal decay length of the various kinds of in-plane propagating modes. The proposed combination of the two models accounts for the lateral extraction as well as light recycling in the active layers.

  18. Color-tunable light emitting diodes based on quantum dot suspension.

    Science.gov (United States)

    Luo, Zhenyue; Chen, Haiwei; Liu, Yifan; Xu, Su; Wu, Shin-Tson

    2015-04-01

    We propose a color-tunable light emitting diode (LED) consisting of a blue LED as the light source and quantum dot (QD) suspension as the color-conversion medium. The LED color temperature can be controlled by varying the liquid volume of each QD suspension with different photoluminescence colors. We simulate and optimize the light efficiency and color quality of the color-tunable LED and also fabricated a prototype to prove concept. The proposed color-tunable LED exhibits several advantages such as excellent color-rendering property, simple structure and driving mechanism, as well as high energy efficiency. Its potential applications include circadian rhythm regulation and healthy lighting.

  19. Electroluminescence and impedance analyses of organic light emitting diodes using anhydride materials as cathode interfacial layers

    Energy Technology Data Exchange (ETDEWEB)

    Nam, Eunkyoung [Department of Physics, Brain Korea 21 Physics Research Division, Institute of Basic Science, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of); Park, Hyungjun [School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of); Park, Keunhee; Moon, Mi Ran [Department of Physics, Brain Korea 21 Physics Research Division, Institute of Basic Science, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of); Sohn, Sunyoung [Korea Basic Science Institute, Dukjin Dong 664-14, Jeonju 561-756 (Korea, Republic of); Jung, Donggeun [Department of Physics, Brain Korea 21 Physics Research Division, Institute of Basic Science, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of); Yi, Junsin [School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of); Chae, Heeyeop [Department of Chemical Engineering, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of); Kim, Hyoungsub, E-mail: hsubkim@skku.ed [School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, 440-746 (Korea, Republic of)

    2009-05-29

    Pyromellitic dianhydride (PMDA) and trimellitic anhydride (TMA) were tried as cathode interfacial layers between tris-(8-hydroxyquinoline) aluminum (Alq{sub 3}) and Al in organic light emitting diodes (OLEDs). Both ultra-thin anhydride cathode interfacial layers improved the electroluminescence characteristics of OLEDs compared to those without any interfacial layer, and the PMDA interfacial layer showed the most significant enhancement of the device performance. According to impedance measurements and equivalent circuit analysis, the PMDA interfacial layer decreased the impedance, probably due to the increase in the injection efficiency of electrons from the Al cathode.

  20. A nearly ideal phosphor-converted white light-emitting diode

    Science.gov (United States)

    Allen, Steven C.; Steckl, Andrew J.

    2008-04-01

    A phosphor-converted light-emitting diode was obtained with nearly ideal blue-to-white conversion loss of only 1%. This is achieved using internal reflection to steer phosphor emission away from lossy surfaces, a reflector material with high reflectivity, and a remotely located organic phosphor having (1) unity quantum efficiency (ηq), (2) homogeneous refractive index to minimize scattering, and (3) refractive index-matched to the encapsulation to eliminate total internal reflection. An inorganic composite phosphor is also reported with a nearly homogeneous refractive index to minimize diffuse scattering of emitted light, thereby maximizing the effective phosphor ηq and light extraction.

  1. Red/blue electroluminescence from europium-doped organic light emitting diodes

    Science.gov (United States)

    Hagen, Joshua A.; Li, Wayne X.; Grote, James G.; Steckl, Andrew J.

    2006-02-01

    Red/Blue emitting organic light emitting diodes (OLED) devices have been obtained using a Europium-doped organic emitting layer (NPB:Eu). The Eu-doped OLEDs emit in 2 color ranges: a broad blue (~420-500nm) band due to NPB emission and a narrow red peak at 620nm due to Eu emission. The red/blue devices achieve a brightness ~13x more intense than a similarly structured green (Alq 3) emitting OLED. These NPB:Eu emitting structures also reach a maximum efficiency of 0.2 cd/A at brightnesses above 100 cd/m2.

  2. Surface recombination measurements on III-V candidate materials for nanostructure light-emitting diodes

    Science.gov (United States)

    Boroditsky, M.; Gontijo, I.; Jackson, M.; Vrijen, R.; Yablonovitch, E.; Krauss, T.; Cheng, Chuan-Cheng; Scherer, A.; Bhat, R.; Krames, M.

    2000-04-01

    Surface recombination is an important characteristic of an optoelectronic material. Although surface recombination is a limiting factor for very small devices it has not been studied intensively. We have investigated surface recombination velocity on the exposed surfaces of the AlGaN, InGaAs, and InGaAlP material systems by using absolute photoluminescence quantum efficiency measurements. Two of these three material systems have low enough surface recombination velocity to be usable in nanoscale photonic crystal light-emitting diodes.

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

    OpenAIRE

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

    2007-01-01

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

  4. 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.

  5. 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...... joined with a time resolved photoluminescence (TRPL) measurements of NCs covering the visible light spectrum range revealed a presence of a population of NCs that does not emit light upon photon absorption and it is significantly higher for a larger particles. By modifying local density of optical states...

  6. Efficient deep-blue organic light-emitting diodes using double-emitting layer.

    Science.gov (United States)

    Seo, Ji Hoon; Seo, Bo Min; Lee, Seok Jae; Lee, Kum Hee; Yoon, Seung Soo; Kim, Young Kwan

    2012-04-01

    Efficient deep-blue organic light-emitting diodes were demonstrated using 1,4-tetranaphthalene doped in double-emitting layers (D-EMLs) consisting of 2-methyl-9,10-di(2-naphthyl)anthracene and 4'-(dinaphthalen-2-yl)-1,1'-binaphthyl as blue hosts. The device with D-EML exhibits good confinement of holes and electrons, as well as a broad recombination zone. The optimized device showed a peak current efficiency of 3.67 cd/A, a peak external quantum efficiency of 3.97%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).

  7. Natural substrate lift-off technique for vertical light-emitting diodes

    Science.gov (United States)

    Lee, Chia-Yu; Lan, Yu-Pin; Tu, Po-Min; Hsu, Shih-Chieh; Lin, Chien-Chung; Kuo, Hao-Chung; Chi, Gou-Chung; Chang, Chun-Yen

    2014-04-01

    Hexagonal inverted pyramid (HIP) structures and the natural substrate lift-off (NSLO) technique were demonstrated on a GaN-based vertical light-emitting diode (VLED). The HIP structures were formed at the interface between GaN and the sapphire substrate by molten KOH wet etching. The threading dislocation density (TDD) estimated by transmission electron microscopy (TEM) was reduced to 1 × 108 cm-2. Raman spectroscopy indicated that the compressive strain from the bottom GaN/sapphire was effectively released through the HIP structure. With the adoption of the HIP structure and NSLO, the light output power and yield performance of leakage current could be further improved.

  8. A Substrate-Reclamation Technology for GaN-Based Lighting-Emitting Diodes Wafer

    Directory of Open Access Journals (Sweden)

    Shih-Yung Huang

    2017-03-01

    Full Text Available This study reports on the use of a substrate-reclamation technology for a gallium nitride (GaN-based lighting-emitting diode (LED wafer. There are many ways to reclaim sapphire substrates of scrap LED wafers. Compared with a common substrate-reclamation method based on chemical mechanical polishing, this research technology exhibits simple process procedures, without impairing the surface morphology and thickness of the sapphire substrate, as well as the capability of an almost unlimited reclamation cycle. The optical performances of LEDs on non-reclaimed and reclaimed substrates were consistent for 28.37 and 27.69 mcd, respectively.

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

    Science.gov (United States)

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

    2017-07-01

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

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

    Directory of Open Access Journals (Sweden)

    Francinaldo Soares Silva

    2015-09-01

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

  11. Staining-free malaria diagnostics by multispectral and multimodality light-emitting-diode microscopy.

    Science.gov (United States)

    Merdasa, Aboma; Brydegaard, Mikkel; Svanberg, Sune; Zoueu, Jeremie T

    2013-03-01

    We report an accurate optical differentiation technique between healthy and malaria-infected erythrocytes by quasi-simultaneous measurements of transmittance, reflectance, and scattering properties of unstained blood smears using a multispectral and multimode light-emitting diode microscope. We propose a technique for automated imaging, identification, and counting of malaria-infected erythrocytes for real-time and cost-effective parasitaemia diagnosis as an effective alternative to the manual screening of stained blood smears, now considered to be the gold standard in malaria diagnosis. We evaluate the performance of our algorithm against manual estimations of an expert and show a spectrally resolved increased scattering from malaria-infected blood cells.

  12. Influence of dehydrated nanotubed titanic acid on polymer light-emitting diodes with phosphorescent dye

    Science.gov (United States)

    Qian, L.; Zhang, T.; Wang, Y. S.; Xu, X. R.; Jin, Z. S.; Du, Z. L.

    2006-01-01

    In this letter, we demonstrate that hole injection and transport in polymer light-emitting diodes with phosphorescent dye Ir(ppy)3 can be significantly enhanced by doping p-type conductive dehydrated nanotubed titanic acid into poly(vinylcarbazole) (PVK) films at 2wt.%. At the same time, both energy transfer and exciton recombination efficiency are improved because of the open and straight conformation of the PVK molecule in the nanocomposite. The performance of these devices was greatly improved, showing higher luminance, enhanced efficiency, and a lower turn-on voltage.

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

    Directory of Open Access Journals (Sweden)

    Peter Juhasz

    2016-01-01

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

  14. 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.

  15. Two examples of organic opto-electronic devices: Light emitting diodes and solar cells

    Science.gov (United States)

    Maldonado, J. L.; Ramos-Ortíz, G.; Miranda, M. L.; Vázquez-Córdova, S.; Meneses-Nava, M. A.; Barbosa-García, O.; Ortíz-Gutiérrez, M.

    2008-12-01

    Organic and polymeric (plastic) opto-electronic devices have been developed over the past decade, and some of them have made the leap from the research laboratory to commercial use. We present a simple and inexpensive method of fabricating organic light emitting diodes and organic photovoltaic cells. The devices are fabricated by the deposition of solid films based on the fluorescent polymer MEH:PPV using the spin-coating technique. The films were sandwiched between electrodes, one of which was made of Bi-Pb-Cd-Sn alloy. An overview of these two devices is also provided.

  16. Design of a bike headlamp based on a power white-light-emitting diode

    Science.gov (United States)

    Lo, Yi-Chien; Chen, Cheng-Chien; Chou, Hung-Yu; Yang, Kai-Yu; Sun, Ching-Cherng

    2011-08-01

    In this letter, we present a new design for a light-emitting diode- based bike headlamp. The optical design contains two horizontal reflectors and a light pipe with two horizontal parallel mirrors. The designed illumination pattern in our simulations performs a contrast of 250 in the K-mark regulation, and it was measured to be 21 in the experiment with a not well-finished prototype, which was operated at 1 W. The contrast is higher than 5 as requested in the regulation.

  17. Noniterative algorithm for improving the accuracy of a multicolor-light-emitting-diode-based colorimeter

    Science.gov (United States)

    Yang, Pao-Keng

    2012-05-01

    We present a noniterative algorithm to reliably reconstruct the spectral reflectance from discrete reflectance values measured by using multicolor light emitting diodes (LEDs) as probing light sources. The proposed algorithm estimates the spectral reflectance by a linear combination of product functions of the detector's responsivity function and the LEDs' line-shape functions. After introducing suitable correction, the resulting spectral reflectance was found to be free from the spectral-broadening effect due to the finite bandwidth of LED. We analyzed the data for a real sample and found that spectral reflectance with enhanced resolution gives a more accurate prediction in the color measurement.

  18. Accuracy Improvement for Light-Emitting-Diode-Based Colorimeter by Iterative Algorithm

    Science.gov (United States)

    Yang, Pao-Keng

    2011-09-01

    We present a simple algorithm, combining an interpolating method with an iterative calculation, to enhance the resolution of spectral reflectance by removing the spectral broadening effect due to the finite bandwidth of the light-emitting diode (LED) from it. The proposed algorithm can be used to improve the accuracy of a reflective colorimeter using multicolor LEDs as probing light sources and is also applicable to the case when the probing LEDs have different bandwidths in different spectral ranges, to which the powerful deconvolution method cannot be applied.

  19. Design of an efficient light-emitting diode with 10 GHz modulation bandwidth

    Science.gov (United States)

    Fattal, D.; Fiorentino, M.; Tan, M.; Houng, D.; Wang, S. Y.; Beausoleil, Raymond G.

    2008-12-01

    We present a high-speed light-emitting-diode (LED) design for efficient modulation at speeds higher than 10 GHz. It relies on a tensile-strain GaAsP quantum well coupled with surface plasmon polaritons on a silver surface. We present optical pumping experiments showing a tenfold reduction in carrier lifetime when the quantum well is located 40 nm above the silver surface. We believe this represents the first step toward an efficient LED compatible with 10 GHz modulation speed for use in short distance optical communication systems.

  20. High-Efficiency Nitride-Based Light-Emitting Diodes with Moth-Eye Structure

    Science.gov (United States)

    Kasugai, Hideki; Miyake, Yasuto; Honshio, Akira; Mishima, Shunsuke; Kawashima, Takeshi; Iida, Kazuyoshi; Iwaya, Motoaki; Kamiyama, Satoshi; Amano, Hiroshi; Akasaki, Isamu; Kinoshita, Hiroyuki; Shiomi, Hiromu

    2005-10-01

    Nitride-based blue light-emitting diodes (LEDs) with a moth-eye structure on the back of a 6H-SiC substrate have been developed. The moth-eye LED has a roughness less than the optical wavelength at the back surface of the SiC substrate fabricated by reactive ion etching (RIE) with CF4 gas. The light extraction efficiency and corresponding output power have been increased to 3.8 times those of a LED with a conventional structure. The experimental findings agree with the results of a theoretical analysis of the effect of the moth-eye structure.

  1. Measurement of the water content in oil and oil products using IR light-emitting diode-photodiode optrons

    Science.gov (United States)

    Bogdanovich, M. V.; Kabanau, D. M.; Lebiadok, Y. V.; Shpak, P. V.; Ryabtsev, A. G.; Ryabtsev, G. I.; Shchemelev, M. A.; Andreev, I. A.; Kunitsyna, E. V.; Ivanov, E. V.; Yakovlev, Yu. P.

    2017-02-01

    The feasibility of using light-emitting devices, the radiation spectrum of which has maxima at wavelengths of 1.7, 1.9, and 2.2 μm for determining the water concentration in oil and oil products (gasoline, kerosene, diesel fuel) has been demonstrated. It has been found that the measurement error can be lowered if (i) the temperature of the light-emitting diode is maintained accurate to 0.5-1.0°C, (ii) by using a cell through which a permanently stirred analyte is pumped, and (iii) by selecting the repetition rate of radiation pulses from the light-emitting diodes according to the averaging time. A meter of water content in oil and oil products has been developed that is built around IR light-emitting device-photodiode optrons. This device provides water content on-line monitoring accurate to 1.5%.

  2. Flexible organic light-emitting diodes with transparent carbon nanotube electrodes: problems and solutions.

    Science.gov (United States)

    Hu, Liangbing; Li, Jianfeng; Liu, Jun; Grüner, George; Marks, Tobin

    2010-04-16

    We study in detail here the application of transparent, conductive carbon single-wall nanotube (SWNT) networks as electrodes in flexible organic light-emitting diodes (FOLEDs). Overall comparisons of these networks to the commonly used electrodes poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and indium tin oxide (ITO) are made, and SWNT networks are shown to have excellent optical and superior mechanical properties. The effects of protruding nanotubes, rough surface morphology, and SWNT network-adjacent layer dewetting are shown to be problematic, and approaches for addressing these issues are identified. The mechanical properties of SWNT networks and ITO are compared, and SWNT networks are shown to exhibit more durable sheet conductance under bending, which leads to bendable FOLEDs. We demonstrated FOLEDs with SWNT network anodes that exhibit outstanding light output and meet display requirements. SWNT-based FOLEDs show comparable lifetime performances to ITO-based devices. The promise and the remaining challenges for implementing SWNT networks in organic light-emitting diodes are discussed.

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

    Science.gov (United States)

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

    2010-09-28

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

  4. 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.

  5. 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.

  6. Effect of light-emitting diode colour temperature on magnifier reading performance of the visually impaired.

    Science.gov (United States)

    Wolffsohn, James S; Palmer, Eshmael; Rubinstein, Martin; Eperjesi, Frank

    2012-09-01

    As light-emitting diodes become more common as the light source for low vision aids, the effect of illumination colour temperature on magnifier reading performance was investigated. Reading ability (maximum reading speed, critical print size, threshold near visual acuity) using Radner charts and subjective preference was assessed for 107 participants with visual impairment using three stand magnifiers with light emitting diode illumination colour temperatures of 2,700 K, 4,500 K and 6,000 K. The results were compared with distance visual acuity, prescribed magnification, age and the primary cause of visual impairment. Reading speed, critical print size and near visual acuity were unaffected by illumination colour temperature (p > 0.05). Reading metrics decreased with worsening acuity and higher levels of prescribed magnification but acuity was unaffected by age. Each colour temperature was preferred and disliked by a similar number of patients and was unrelated to distance visual acuity, prescribed magnification and age (p > 0.05). Patients had better near acuity (p = 0.002), critical print size (p = 0.034) and maximum reading speed (p colour temperature illumination. A range of colour temperature illuminations should be offered to all visually impaired individuals prescribed with an optical magnifier for near tasks to optimise subjective and objective benefits. © 2012 The Authors. Clinical and Experimental Optometry © 2012 Optometrists Association Australia.

  7. ZnO light-emitting diodes fabricated on Si substrates with homobuffer layers

    Science.gov (United States)

    Ye, Z. Z.; Lu, J. G.; Zhang, Y. Z.; Zeng, Y. J.; Chen, L. L.; Zhuge, F.; Yuan, G. D.; He, H. P.; Zhu, L. P.; Huang, J. Y.; Zhao, B. H.

    2007-09-01

    ZnO homojunction light-emitting diodes (LEDs), comprised of N-Al codoped p-type ZnO and Al-doped n-type ZnO layers, were fabricated on Si substrates with homobuffer layers. The current-voltage measurements showed typical diode characteristic with a threshold voltage of about 3.3V. The electroluminescence (EL) bands at 110K consisted of a near-band-edge emission at 3.18eV and a deep level emission at 2.58eV. The EL emissions were assigned as radiative recombinations, presumably of donor-acceptor pairs, in the p-type layer of the LED. The quenching of EL with temperature was attributed to the degradation of p-type conducting of the ZnO:(N,Al) layer.

  8. 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......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...

  9. 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......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...

  10. Properties of a CdZnO/ZnO multiple quantum-well light-emitting diode

    Science.gov (United States)

    Liu, Zhan-Hui; Zhang, Li-Li; Li, Qing-Fang; Zhang, Rong; Xie, Zi-Li; Xiu, Xiang-Qian; Liu, Bin

    2016-10-01

    A CdZnO/ZnO multiple quantum-well light-emitting diode (LED) structure was successfully grown by using plasma-assisted molecular beam epitaxy on a p-GaN template that had been grown by using metal-organic chemical-vapor deposition on a c-sapphire substrate. The properties of the sample were characterized by using high-resolution X-ray diffraction, transmission electron microscopy, and temperature-dependent photoluminescence measurements. The light output performance of the CdZnO/ZnO QW LED device was also investigated in detail by using I-V and electroluminescence spectral measurements. The characterization showed that our CdZnO/ZnO QW LED structure had good crystalline quality and weaker carrier localization. Owing to the heterojunction structure, the I-V curve indicated that the LED device had a higher turn-on voltage and series resistance. The EL measurement demonstrated that for our LED device's optoelectronic characteristic, the carrier-screening effect played the dominant role in the emission-energy blue-shift mechanism, and the broadening of the emission energy width was mainly ascribed to the band-filling effect. Without a special heat sinking, the L-I curve exhibited slight efficiency droop after 30 mA.

  11. Quantum-Dot Light-Emitting Diodes with Nitrogen-Doped Carbon Nanodot Hole Transport and Electronic Energy Transfer Layer

    Science.gov (United States)

    Park, Young Ran; Jeong, Hu Young; Seo, Young Soo; Choi, Won Kook; Hong, Young Joon

    2017-04-01

    Electroluminescence efficiency is crucial for the application of quantum-dot light-emitting diodes (QD-LEDs) in practical devices. We demonstrate that nitrogen-doped carbon nanodot (N-CD) interlayer improves electrical and luminescent properties of QD-LEDs. The N-CDs were prepared by solution-based bottom up synthesis and were inserted as a hole transport layer (HTL) between other multilayer HTL heterojunction and the red-QD layer. The QD-LEDs with N-CD interlayer represented superior electrical rectification and electroluminescent efficiency than those without the N-CD interlayer. The insertion of N-CD layer was found to provoke the Förster resonance energy transfer (FRET) from N-CD to QD layer, as confirmed by time-integrated and -resolved photoluminescence spectroscopy. Moreover, hole-only devices (HODs) with N-CD interlayer presented high hole transport capability, and ultraviolet photoelectron spectroscopy also revealed that the N-CD interlayer reduced the highest hole barrier height. Thus, more balanced carrier injection with sufficient hole carrier transport feasibly lead to the superior electrical and electroluminescent properties of the QD-LEDs with N-CD interlayer. We further studied effect of N-CD interlayer thickness on electrical and luminescent performances for high-brightness QD-LEDs. The ability of the N-CD interlayer to improve both the electrical and luminescent characteristics of the QD-LEDs would be readily exploited as an emerging photoactive material for high-efficiency optoelectronic devices.

  12. [Hygienic aspects of the use of light-emitting diode sources in the communal artificial lighting systems].

    Science.gov (United States)

    Kuchma, V R; Teksheva, L M; Nadezhdin, D S; Zvezdina, I V

    2011-01-01

    To estimate the possibilities of using light-emitting diode energy-saving lighting in the residential and public houses, industrial buildings and structures is one of society's most important tasks. The concept of these researches was to study comparative psychophysiological and functional changes in the volunteers working under general lighting generated by light-emitting diodes and luminescent lamps. The results of the study permit one to recommend the use of light-emitting diodes in general lighting systems in the rooms wherein visual and mental load work is done, i.e. in the industrial, office, and public buildings intended for adult users for different purposes, as well as in rail transport objects.

  13. Transient measurement of light-emitting diode characteristic parameters for production lines.

    Science.gov (United States)

    Zhou, Shengjun; Liu, Sheng

    2009-09-01

    A new instrument has been developed for transient measurement of light-emitting diodes (LEDs), including photometric parameters, colorimetric parameters, and electrical parameters in a matter of milliseconds, by combining spectrometer with a human photopic vision detector and data acquisition card (DAQ). The instrument can provide communication interface for sorter to realize automatic sorting of measured LEDs samples. The light emitted from the measured LEDs, which are illuminated under pulse current operation condition, is captured by the spectrometer and the human photopic vision detector. The spectral power distributions of LEDs are recorded by spectrometer, and processed to provide colorimetric parameters. We employ two novel algorithms including look-up table method and curve fitting method to determine the dominant wavelength of LED. In combination with linear interpolation, the look-up table method can locate dominant wavelength with a resolution of 0.1 nm. A programmable constant current source/voltage source is designed for power supply to drive LED. The luminous intensity of LED can be derived by detecting the photocurrent of human photopic vision detector. We also describe the calibration of the human photopic vision detector. This calibration provides detector-specific correction factor that enables accurate extraction of luminous intensity of LED. The instrument has been used to measure and inspect the quality of packaging LED.

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

    Science.gov (United States)

    Saikia, Dhrubajyoti; Sarma, Ranjit

    2018-01-01

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

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

    Science.gov (United States)

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

    2017-11-01

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

  16. 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.

  17. 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.

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

    CERN Document Server

    Williams, E W; Pamplin, BR

    2013-01-01

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

  19. 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...

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

    DEFF Research Database (Denmark)

    Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

    Fluorescent SiC based white light-emitting diodes(LEDs) light source, as an innovative energy-efficient light source, would even have longer lifetime, better light quality and eliminated blue-tone effect, compared to the current phosphor based white LED light source. In this paper, the yellow....... At a device level, the focus is on improving the light extraction efficiency due to the rather high refractive index of SiC by nanostructuring the surface of SiC. Both periodic nanostructures made by e-beam lithography and nanosphere lithography and random nanostructures made by self-assembled Au nanosphere...... 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...

  1. 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.

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

    Science.gov (United States)

    Zou, Jianping; Zhang, Kang; Li, Jingqi; Zhao, Yongbiao; Wang, Yilei; Pillai, Suresh Kumar Raman; Volkan Demir, Hilmi; Sun, Xiaowei; Chan-Park, Mary B.; Zhang, Qing

    2015-06-01

    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.

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

    Science.gov (United States)

    Weis, Martin; Otsuka, Takako; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

    2015-04-01

    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.

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

    Directory of Open Access Journals (Sweden)

    Lirong Zhang

    2017-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Wen Jing; Wen Yumei; Li Ping; Li Lian, E-mail: wenjing@cqu.edu.cn [Key Laboratory for Opto-Electronic Technologies and Systems of Ministry of Education, College of Opto-Electronic Engineering, Chongqing University, Chongqing 400044 (China)

    2011-08-15

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

    Science.gov (United States)

    Jing, Wen; Yumei, Wen; Ping, Li; Lian, Li

    2011-08-01

    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.

  7. Design and Dynamic Analysis of a High-Speed Organic Light-Emitting Diode

    Science.gov (United States)

    Salehifar, Samira; Shayesteh, Mohammad Reza; Hashemian, Saeedeh

    2018-02-01

    We propose a structure of a high-speed multilayer organic light-emitting diode (OLED). The different organic materials have been chosen so that the barrier potential between two adjacent layers is smaller than 0.2 eV, which causes the charge carriers to move easily between layers to reach the emitting layer. The static and dynamic behaviors of the OLED have been analyzed numerically. The results from simulation show that the proposed OLED structure has an electroluminescence delay time of about 30 ns, and hence can respond to electrical pulses with a repetition rate of 2 MHz. Moreover, the device can provide good features such as high light emission efficiency, low voltage DC driving, and thermal stability.

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

    Directory of Open Access Journals (Sweden)

    Peng Xiao

    2018-02-01

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

  9. White Electroluminescence Using ZnO Nanotubes/GaN Heterostructure Light-Emitting Diode.

    Science.gov (United States)

    Sadaf, J R; Israr, Mq; Kishwar, S; Nur, O; Willander, M

    2010-04-04

    We report the fabrication of heterostructure white light-emitting diode (LED) comprised of n-ZnO nanotubes (NTs) aqueous chemically synthesized on p-GaN substrate. Room temperature electroluminescence (EL) of the LED demonstrates strong broadband white emission spectrum consisting of predominating peak centred at 560 nm and relatively weak violet-blue emission peak at 450 nm under forward bias. The broadband EL emission covering the whole visible spectrum has been attributed to the large surface area and high surface states of ZnO NTs produced during the etching process. In addition, comparison of the EL emission colour quality shows that ZnO nanotubes have much better quality than that of the ZnO nanorods. The colour-rendering index of the white light obtained from the nanotubes was 87, while the nanorods-based LED emit yellowish colour.

  10. A lamp light-emitting diode-induced fluorescence detector for capillary electrophoresis.

    Science.gov (United States)

    Xu, Jing; Xiong, Yan; Chen, Shiheng; Guan, Yafeng

    2008-07-15

    A light-emitting diode-induced fluorescence detector (LED-FD) for capillary electrophoresis was constructed and evaluated. A lamp LED with an enhanced emission spectrum and a band pass filter was used as the excitation light source. Refractive index matching fluid (RIMF) was used in the detection cell to reduce scattering light and the noise level. The limit of detection (LOD) for fluorescein was 1.5 nM (SNR=3). The system exhibited linear responses in the range of 1 x 10(-8) to 5 x 10(-6)M (R=0.999). Application of the lamp LED-FD for the analysis of FITC-labeled ephedra herb extract by capillary electrophoresis was demonstrated.

  11. Optical design of a light-emitting diode lamp for a maritime lighthouse.

    Science.gov (United States)

    Jafrancesco, D; Mercatelli, L; Sansoni, P; Fontani, D; Sani, E; Coraggia, S; Meucci, M; Francini, F

    2015-04-10

    Traffic signaling is an emerging field for light-emitting diode (LED) applications. This sustainable power-saving illumination technology can be used in maritime signaling thanks to the recently updated norms, where the possibility to utilize LED sources is explicitly cited, and to the availability of high-power white LEDs that, combined with suitable lenses, permit us to obtain well-collimated beams. This paper describes the optical design of a LED-based lamp that can replace a traditional lamp in an authentic marine lighthouse. This source recombines multiple separated LEDs realizing a quasi-punctual localized source. Advantages can be lower energy consumption, higher efficiency, longer life, fewer faults, slower aging, and minor maintenance costs. The proposed LED source allows us to keep and to utilize the old Fresnel lenses of the lighthouse, which very often have historical value.

  12. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2005-09-07

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

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

    Science.gov (United States)

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

    2017-12-01

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

  15. 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.

  16. 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.

  17. 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.

  18. Excellent photostability of phosphorescent nanoparticles and their application as a color converter in light emitting diodes.

    Science.gov (United States)

    Kim, Ok-Hee; Ha, Shin-Woo; Kim, Jae Il; Lee, Jin-Kyu

    2010-06-22

    The phosphorescent Ir(III) complexes were modified by allylation and consecutive hydrosilylation, and covalently incorporated into the silica nanoparticles by hydrolysis and condensation reaction with TEOS. These nanoparticles showed an excellent photochemical and thermal stability, and a very high luminescent efficiency due to the blocking of O(2) quenching and suppression of energy transfer through the amorphous silica solid solution. The limited mobility of complexes in the silica matrix also resulted in a decrease in the vibration relaxation and restrained the nonradiative decay. It is expected that these photostable and very efficient phosphorescent nanoparticles can be used in various fields ranging from nanobiotechnology to nanoengineering materials, where long-term stability with the high luminescent efficiency is required. As an example of the use of excellent photostability, a preliminary test result in which they are used as a color converter in a light emitting diode (LED) is also discussed.

  19. Efficiency of True-Green Light Emitting Diodes: Non-Uniformity and Temperature Effects.

    Science.gov (United States)

    Titkov, Ilya E; Karpov, Sergey Yu; Yadav, Amit; Mamedov, Denis; Zerova, Vera L; Rafailov, Edik

    2017-11-18

    External quantum efficiency of industrial-grade green InGaN light-emitting diodes (LEDs) has been measured in a wide range of operating currents at various temperatures from 13 K to 300 K. Unlike blue LEDs, the efficiency as a function of current is found to have a multi-peak character, which could not be fitted by a simple ABC-model. This observation correlated with splitting of LED emission spectra into two peaks at certain currents. The characterization data are interpreted in terms of non-uniformity of the LED active region, which is tentatively attributed to extended defects like V-pits. We suggest a new approach to evaluation of temperature-dependent light extraction and internal quantum efficiencies taking into account the active region non-uniformity. As a result, the temperature dependence of light extraction and internal quantum efficiencies have been evaluated in the temperature range mentioned above and compared with those of blue LEDs.

  20. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-06-15

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

  2. Reduced molybdenum oxide as an efficient electron injection layer in polymer light-emitting diodes

    Science.gov (United States)

    Vasilopoulou, Maria; Palilis, Leonidas C.; Georgiadou, Dimitra G.; Argitis, Panagiotis; Kennou, Stella; Sygellou, Labrini; Kostis, Ioannis; Papadimitropoulos, Giorgos; Konofaos, Nikos; Iliadis, Agis A.; Davazoglou, Dimitris

    2011-03-01

    We report a significant improvement in the performance of single layer polymer light-emitting diodes (PLEDs), based on the green emitting copolymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2, 1',3}-thiadiazole)], upon inserting a very thin layer of partially reduced molybdenum oxide (MoOx, where x=2.7) at the polymer/Al cathode interface. Both fully oxidized (x=3) and partially reduced (x=2.7) thin molybdenum oxide layers were investigated as electron injection layers and their influence on PLED device performance was examined. Improved current density, luminance, and efficiency was achieved only in the case of devices with a thin partially reduced MoO2.7 film as electron injection layer, as a result of improved electron injection and more facile transfer at the modified polymer/Al interface.

  3. Characteristic Evaluation of Organic Light-Emitting Diodes Prepared with Stamp Printing Technique

    Directory of Open Access Journals (Sweden)

    Apisit Chittawanij

    2017-01-01

    Full Text Available We have reported on a stamp printing technique that uses PET release film as a printing stamp to deposit TPBi thin film served as the electron transport layer of the organic light-emitting diodes. TPBi thin film was printed with a good uniformity and resolution. Effect of deposition conditions on optical and electrical properties and surface roughness of TPBi thin film have been studied under spectroscopy and atomic force microscopy, respectively. It is found that characteristic of TPBi thin film is improved via controlled stamp temperature and time. Since TPBi thin film exhibits the surface morphology comparable to that of conventional spin-coating thin film, our findings suggest that PET release film-based stamp printing approach is possible to use as an alternative deposition of the organic thin film as compared with a traditional one.

  4. Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts.

    Science.gov (United States)

    Cui, Lin-Song; Ruan, Shi-Bin; Bencheikh, Fatima; Nagata, Ryo; Zhang, Lei; Inada, Ko; Nakanotani, Hajime; Liao, Liang-Sheng; Adachi, Chihaya

    2017-12-21

    Organic light-emitting diodes have become a mainstream display technology because of their desirable features. Third-generation electroluminescent devices that emit light through a mechanism called thermally activated delayed fluorescence are currently garnering much attention. However, unsatisfactory device stability is still an unresolved issue in this field. Here we demonstrate that electron-transporting n-type hosts, which typically include an acceptor moiety in their chemical structure, have the intrinsic ability to balance the charge fluxes and broaden the recombination zone in delayed fluorescence organic electroluminescent devices, while at the same time preventing the formation of high-energy excitons. The n-type hosts lengthen the lifetimes of green and blue delayed fluorescence devices by > 30 and 1000 times, respectively. Our results indicate that n-type hosts are suitable to realize stable delayed fluorescence organic electroluminescent devices.

  5. 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.

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

    Science.gov (United States)

    Page, Zachariah A; Narupai, Benjaporn; Pester, Christian W; Bou Zerdan, Raghida; Sokolov, Anatoliy; Laitar, David S; Mukhopadhyay, Sukrit; Sprague, Scott; McGrath, Alaina J; Kramer, John W; Trefonas, Peter; Hawker, Craig J

    2017-06-28

    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.

  7. Drooping as a simple characterization tool for extraction efficiency and optical losses in light emitting diodes

    Science.gov (United States)

    Oksanen, Jani; Tulkki, Jukka

    2010-09-01

    We extend the previous droop models developed for InGaN light emitting diodes (LEDs) by accounting for the light extraction and show that drooping can be used to quantify both the extraction efficiency and the optical losses in LEDs. Our model allows very simple characterization of LEDs by an integrating sphere and therefore provides an attractive characterization tool to measure the most important loss parameters of various LED structures. In particular, the approach allows evaluation of the effects of various optical losses and photon recycling on the efficiency and consequently allows more efficient optimization of the LED structures. As an additional benefit, our measurement method does not necessarily require any fitting of the data.

  8. Enhanced lifetime in porous silicon light-emitting diodes with fluorine doped tin oxide electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Macedo, Andreia G. [Departamento de Fisica, Universidade Federal do Parana, 81531-990, Curitiba-PR (Brazil); Vasconcelos, Elder A. de [Departamento de Fisica, Universidade Federal de Pernambuco, Cidade Universitaria, 50670-901 Recife-PE (Brazil); Valaski, Rogerio [Flexitec Eletronica Organica Ltda, 81531-990 Curitiba-PR (Brazil); Muchenski, Fabio [Departamento de Fisica, Universidade Federal do Parana, 81531-990, Curitiba-PR (Brazil); Silva, Eronides F. da [Departamento de Fisica, Universidade Federal de Pernambuco, Cidade Universitaria, 50670-901 Recife-PE (Brazil); Silva, Antonio F. da [Instituto de Fisica, Universidade Federal da Bahia, Campus Ondina, 40210-340, Salvador-BA (Brazil); Roman, Lucimara S. [Departamento de Fisica, Universidade Federal do Parana, 81531-990, Curitiba-PR (Brazil)], E-mail: lsroman@fisica.ufpr.br

    2008-11-28

    We investigated the electrical and optical properties of porous Si (PS) light-emitting diodes using fluorinated tin oxide (FTO) as transparent electrodes. At high forward bias, the current-voltage characteristic is space charge limited. At low forward bias, it follows an exponential law. Whereas the electroluminescence (EL) in devices with non-fluorinated indium-tin oxide electrodes degrades in few minutes, EL intensity in devices with FTO electrodes shows little degradation after 1300 min of operation. This result indicates that the well known beneficial effects of fluorinated species in the improvement of resistance to irradiation and carrier injection degradation in metal-oxide-semiconductor devices might be also observed in PS devices.

  9. 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.

  10. 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.

  11. Phosphorescent white organic light-emitting diodes by electron transporting layer engineering.

    Science.gov (United States)

    Lee, Seok Jae; Koo, Ja Ryong; Lee, Dong Hyung; Lee, Ho Won; Lee, Kum Hee; Yoon, Seung Soo; Kim, Young Kwan

    2014-10-01

    The authors describe the fabrication of white organic light-emitting diodes (WOLEDs) with dual electron transporting layers (D-ETL) using 2,9-dimethyl-4,7-diphenyl-1,10-phenanhroline/ 4,7-diphenyl-1,10-phenanthroline (BPhen) and bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato) aluminum/BPhen. Stepwise D-ETL easily transports electrons easily to the emitting layer and reduces the leakage of electrons. Therefore, WOLEDs with D-ETL show higher external quantum efficiency (EQE) when compared to a control WOLED with a single ETL device. The optimized WOLEDs showed a peak EQE of 13.0%, luminous efficiency of 27.4 cd/A, and Commission Internationale de L'Eclairage coordinates of (0.40, 0.39) at 1000 cd/m2.

  12. Thermally stable conformal encapsulation material for high-power ultraviolet light-emitting diodes

    Science.gov (United States)

    Huang, Shun-Yuan; Wang, Jau-Sheng

    2017-07-01

    A conformal encapsulation material for use in high-power, thermally stable ultraviolet (UV) light-emitting diodes was successfully developed. For silicone, thermal degradation started at ˜200°C, and the transmittance was 85.5% at 365 nm. The transmittance decreased by 55% after thermal aging at 250°C for 72 h and it decreased further by 2.5%, even at room temperature, under continuous exposure to UV light at 365 nm for 72 h. By contrast, for the sol-gel material, thermal degradation started at ˜300°C, and the transmittance was 90% at 365 nm. The transmittance decreased negligibly after thermal aging at 250°C for 72 h and it did not decrease further even at 75°C under continuous exposure to UV light at 365 nm for 72 h.

  13. High brightness phosphorescent organic light emitting diodes on transparent and flexible cellulose films

    Science.gov (United States)

    Purandare, Sumit; Gomez, Eliot F.; Steckl, Andrew J.

    2014-03-01

    Organic light-emitting diodes (OLED) were fabricated on flexible and transparent reconstituted cellulose obtained from wood pulp. Cellulose is naturally available, abundant, and biodegradable and offers a unique substrate alternative for the fabrication of flexible OLEDs. Transparent cellulose material was formed by dissolution of cellulose in an organic solvent (dimethyl acetamide) at elevated temperature (165 °C) in the presence of a salt (LiCl). The optical transmission of 40-μm thick transparent cellulose sheet averaged 85% over the visible spectrum. High brightness and high efficiency thin film OLEDs were fabricated on transparent cellulose films using phosphorescent Ir(ppy)3 as the emitter material. The OLEDs achieved current and luminous emission efficiencies as high as 47 cd A-1 and 20 lm W-1, respectively, and a maximum brightness of 10 000 cd m-2.

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

    Science.gov (United States)

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

    2015-02-01

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

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

    Science.gov (United States)

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

    1977-01-01

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

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

    Science.gov (United States)

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

    2016-10-01

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

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

    Science.gov (United States)

    1997-01-01

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

  18. Light-emitting diode lamp design by Monte Carlo photon simulation

    Science.gov (United States)

    Lee, Song Jae

    2001-05-01

    In this presentation, basic elements of light-emitting diode (LED) lamp design are discussed. In practical applications of LED lamps, the far-field photon distribution pattern is one of the important considerations. Both the reflecting cup and lens surface profile employed in the design can be flexibly adjusted by a few parameters such that the far field photon distribution pattern is rather easily manipulated. For simulation of LED lamps, we have used Monte Carlo photon simulation method. Based on simulation results, we can verify or explain the effect of the various LED lamp design parameters on far-field patterns. Some of the important design examples are LED lamps with far-field patterns that are either tilted by certain angle in the vertical direction or double- lobed in the horizontal direction. LED lamps of this type of far-field patterns may find some application in some special outdoor displays, for instance, in a large stadium.

  19. 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.

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

    DEFF Research Database (Denmark)

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

    1999-01-01

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

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

    Science.gov (United States)

    Zeng, Xi; Mizuno, Yosuke; Nakamura, Kentaro

    2017-12-01

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

  2. APPLICATION OF LIGHT EMITTING DIODE IRRADIATION IN SURGERY AND OTHER FIELDS OF MEDICINE

    Directory of Open Access Journals (Sweden)

    Iskander Mukhamedovich Baybekov

    2017-05-01

    Full Text Available Goal. To study the experience of using Light Emitting Diode (LED in surgery and other areas of medicine. Methods and methodology. The methodological basis is the analysis of literature, synthesis of the results of experimental and clinical studies, as well as a modern interpretation of the mechanisms of action of low-intensity laser radiation and LED effects on the body. Special attention is paid to the experience of clinical and morphological studies LED of impacts at the Republican specialized center of surgery named academician V. Vahidov of the Ministry of health of the Republic of Uzbekistan. Results. Comparative features of LED and lasers, such as stimulation of reparative processes, their influence on healing of skin wounds and sternum after sternotomy, red blood cells and microcirculation are discussed. Conclusion. It has been suggested that LED is a worthy alternative to lasers. Their use is advisable in complex treatment of surgical diseases.

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

    CERN Document Server

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

    2000-01-01

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

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

    CERN Document Server

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

    2000-01-01

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

  5. Fabrication of Flexible White Light-Emitting Diodes from Photoluminescent Polymer Materials with Excellent Color Quality.

    Science.gov (United States)

    Lin, Huang-Yu; Sher, Chin-Wei; Lin, Chih-Hao; Tu, Hsien-Hao; Chen, Xin Yin; Lai, Yi-Chun; Lin, Chien-Chung; Chen, Huang-Ming; Yu, Peichen; Meng, Hsin-Fei; Chi, Gou-Chung; Honjo, Keiji; Chen, Teng-Ming; Kuo, Hao-Chung

    2017-10-11

    This study developed flexible light-emitting diodes (LEDs) with warm white and neutral white light. A simple ultraviolet flip-chip sticking process was adopted for the pumping source and combined with polymer and quantum dot (QD) films technology to yield white light. The polymer-blended flexible LEDs exhibited higher luminous efficiency than the QD-blended flexible LEDs. Moreover, the polymer-blended LEDs achieved excellent color-rendering index (CRI) values (Ra = 96 and R9 = 96), with high reliability, demonstrating high suitability for special applications like accent, down, or retrofit lights in the future. In places such as a museum, kitchen, or surgery room, its high R9 and high CRI characteristics can provide high-quality services.

  6. Organic materials for deep blue phosphorescent organic light-emitting diodes.

    Science.gov (United States)

    Yook, Kyoung Soo; Lee, Jun Yeob

    2012-06-26

    Recently, great progress has been made in the device performance of deep blue phosphorescent organic light-emitting diodes (PHOLEDs) by developing high triplet energy charge-transport materials, high triplet energy host and deep blue emitting phosphorescent dopant materials. A high quantum efficiency of over 25% and a high power efficiency of over 15 lm/W have already been achieved at 1000 cd m(-2) in the deep blue PHOLEDs with a y color coordinate less than 0.20. In this work, recent developments in organic materials for high efficiency deep blue PHOLEDs are reviewed and a future strategy for the development of high efficiency deep blue PHOLEDs is proposed. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Science.gov (United States)

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

    2017-11-01

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

  8. High-quality vertical light emitting diodes fabrication by mechanical lift-off technique

    Science.gov (United States)

    Tu, Po-Min; Hsu, Shih-Chieh; Chang, Chun-Yen

    2011-10-01

    We report the fabrication of mechanical lift-off high quality thin GaN with Hexagonal Inversed Pyramid (HIP) structures for vertical light emitting diodes (V-LEDs). The HIP structures were formed at the GaN/sapphire substrate interface under high temperature during KOH wet etching process. The average threading dislocation density (TDD) was estimated by transmission electron microscopy (TEM) and found the reduction from 2×109 to 1×108 cm-2. Raman spectroscopy analysis revealed that the compressive stress of GaN epilayer was effectively relieved in the thin-GaN LED with HIP structures. Finally, the mechanical lift-off process is claimed to be successful by using the HIP structures as a sacrificial layer during wafer bonding process.

  9. 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.

  10. 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.

  11. Fluorescent Silicon Carbide and its Applications in White Light-Emitting Diodes

    DEFF Research Database (Denmark)

    Ou, Yiyu

    This thesis focuses on the optical properties analysis of Donor-Acceptor-Pair (DAP) co-doped Fluorescent Silicon Carbide (f-SiC) as a wavelengthconversion material in white Light-Emitting Diodes (LEDs). Different methods of fabricating surface Antireflective Structures (ARS) on f-SiC to enhance its...... light extraction efficiency are presented. White LEDs are the most promising techniques to replace the conventional lighting sources. A typical white LED consists of a Gallium Nitride (GaN) blue or Ultraviolet (UV) LED stack and a wavelengthconversion material. Silicon Carbide (SiC) has a wide optical...... bandgap and could be tailored to emit light at different wavelength by introducing different dopants. Combined emitting spectra of two types of DAP co-doped f-SiC could cover the whole visible spectral range and make f-SiC as a good candidate of wavelength-conversion material. It has a better color...

  12. Unraveled Face-Dependent Effects of Multilayered Graphene Embedded in Transparent Organic Light-Emitting Diodes.

    Science.gov (United States)

    Lim, Jong Tae; Kim, Jaesu; Lee, Hyunkoo; Moon, Jaehyun; Kwon, Byoung-Hwa; Ahn, Seongdeok; Cho, Nam Sung; Ahn, Byung-Wook; Lee, Jeong-Ik; Ihm, Kyuwook; Lim, Seong Chu

    2017-12-13

    With increasing demand for transparent conducting electrodes, graphene has attracted considerable attention, owing to its high electrical conductivity, high transmittance, low reflectance, flexibility, and tunable work function. Two faces of single-layer graphene are indistinguishable in its nature, and this idea has not been doubted even in multilayered graphene (MLG) because it is difficult to separately characterize the front (first-born) and the rear face (last-born) of MLG by using conventional analysis tools, such as Raman and ultraviolet spectroscopy, scanning probe microscopy, and sheet resistance. In this paper, we report the striking difference of the emission pattern and performance of transparent organic light-emitting diodes (OLEDs) depending on the adopted face of MLG and show the resolved chemical and physical states of both faces by using depth-selected absorption spectroscopy. Our results strongly support that the interface property between two different materials rules over the bulk property in the driving performance of OLEDs.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-07-18

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

  14. A research on the reliability of light-emitting diode based on analyzing of chip image

    Directory of Open Access Journals (Sweden)

    Ruan Jian

    2016-01-01

    Full Text Available This paper proposes a new method for studying the reliability of high-power light-emitting diode (LED by analyzing chip images taken from a batch of LEDs which are selected to conduct the accelerated aging test lasting for 1400 hours. To exclude the disturbance of electrode in these images, an image processing algorithm based on projection is used to extract the interested section. An index called “dark point” which is related to non-radiative combination to describe the reliability of LED is proposed. The method is based on analyzing the variation trends of dark points in the extracted section of these images. The results show that the proportion of the dark point increases with aging time increasing. The lifetime of LED with higher increasing rate is shorter. Based on the increasing rate of dark point, the lifetime of the chip can be predicted in an easier way.

  15. Cyclometalated Iridium(III) Carbene Phosphors for Highly Efficient Blue Organic Light-Emitting Diodes.

    Science.gov (United States)

    Chen, Zhao; Wang, Liqi; Su, Sikai; Zheng, Xingyu; Zhu, Nianyong; Ho, Cheuk-Lam; Chen, Shuming; Wong, Wai-Yeung

    2017-11-22

    Five deep blue carbene-based iridium(III) phosphors were synthesized and characterized. Interestingly, one of them can be fabricated into deep blue, sky blue and white organic light-emitting diodes (OLEDs) through changing the host materials and exciton blocking layers. These deep and sky blue devices exhibit Commission Internationale de l'Éclairage (CIE) coordinates of (0.145, 0.186) and (0.152, 0.277) with external quantum efficiency (EQE) of 15.2% and 9.6%, respectively. The EQE of the deep blue device can be further improved up to 19.0% by choosing a host with suitable energy level of its lowest unoccupied molecular orbital (LUMO).

  16. 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.

  17. Wafer-bonding AlGaInP light emitting diodes with pyramidally patterned metal reflector

    Science.gov (United States)

    Zhiyuan, Zuo; Wei, Xia; Gang, Wang; Xiangang, Xu

    2015-02-01

    We demonstrate and introduce here a pyramidally patterned metal reflector into wafer-bonding AlGaInP light emitting diodes (LEDs) to improve the light extraction efficiency by using a photo-assisted chemical etched GaP:Mg layer. The pyramid patterns were fabricated employing a HF and H2O2 mixed solution in combination with a 532 nm laser on a GaP:Mg surface firstly, and then a gold reflector layer was evaporated onto the patterned GaP:Mg surface. After the whole chip process, the patterned gold reflector structure was confirmed to be efficient for light extraction and a 18.55% enhancement of the electroluminescent flux has been obtained by an integrating sphere, compared to the surface textured LEDs with flat reflectors.

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

    Science.gov (United States)

    Gao, Chia-Yuan; Chen, Ying-Chung; Chen, Kan-Lin; Huang, Chien-Jung

    2015-11-01

    The influence of gold nanoparticles (GNPs) with different sizes doped into (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)) (PEDOT:PSS) on the performance of organic light-emitting diodes is investigated in this study. The current efficiency of the device, at a current density of 145 mA/cm, with PEDOT:PSS doped with GNPs of 8 nm is about 1.57 times higher than that of the device with prime PEDOT:PSS because the absorption peak of GNPs is closest to the photoluminescence peak of the emission layer, resulting in maximum surface plasmon resonance effect in the device. In addition, the surface-enhanced Raman scattering spectroscopy also reveals the maximum surface plasmon resonance effect in the device when the mean particle size of GNPs is 8 nm.

  19. Enhanced quantum-dot light-emitting diodes using gold nanorods

    Science.gov (United States)

    Cho, Nam-Kwang; Lee, Sang Moo; Song, Kigook; Kang, Seong Jun

    2015-11-01

    Plasmon-enhanced quantum-dot light-emitting diodes (QLEDs) were fabricated by inserting gold (Au) nanorods at the interface of the QLEDs. The length of the nanorods was 60 nm, which corresponds to the plasmonic absorption of wavelengths in the range of 630 to 670 nm. CdSe/ZnS quantum dots (QDs) were used as emission layers with additional hole injection, transport, and electron transport layers. The maximum emission was observed at 630 nm, which is in the range of the plasmon resonance of the Au nanorods. The QLEDs with Au nanorods showed enhanced electroluminescence properties compared to the devices without the plasmonic nano-structure. A 172% increase in electroluminescent intensity was observed due to the plasmon coupling effect. The results demonstrate a promising method for developing high-performance QLEDs.

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

    Science.gov (United States)

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

    2017-09-01

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

  1. Enhanced optical output power of blue light-emitting diodes with quasi-aligned gold nanoparticles

    Science.gov (United States)

    Jin, Yuanhao; Li, Qunqing; Li, Guanhong; Chen, Mo; Liu, Junku; Zou, Yuan; Jiang, Kaili; Fan, Shoushan

    2014-01-01

    The output power of the light from GaN-based light-emitting diodes (LEDs) was enhanced by fabricating gold (Au) nanoparticles on the surface of p-GaN. Quasi-aligned Au nanoparticle arrays were prepared by depositing Au thin film on an aligned suspended carbon nanotube thin film surface and then putting the Au-CNT system on the surface of p-GaN and thermally annealing the sample. The size and position of the Au nanoparticles were confined by the carbon nanotube framework, and no other additional residual Au was distributed on the surface of the p-GaN substrate. The output power of the light from the LEDs with Au nanoparticles was enhanced by 55.3% for an injected current of 100 mA with the electrical property unchanged compared with the conventional planar LEDs. The enhancement may originate from the surface plasmon effect and scattering effect of the Au nanoparticles.

  2. 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.

  3. Surface plasmon resonance sensor utilizing an integrated organic light emitting diode.

    Science.gov (United States)

    Frischeisen, Jörg; Mayr, Christian; Reinke, Nils A; Nowy, Stefan; Brütting, Wolfgang

    2008-10-27

    A novel surface plasmon resonance (SPR) sensor based on an integrated planar and polychromatic light source is presented. The sensor comprises an organic light emitting diode (OLED) and a metallic sensing layer located on opposite sides of a glass prism. We successfully fabricated and tested prototype sensors based on this approach by the use of different prism geometries and OLEDs with blue, green and red emission color. We investigated the angular and wavelength dependent SPR dispersion relation for sensing layers consisting of silver and gold in contact with air. Further on we demonstrated the sensor function by real time monitoring of temperature changes inside an adjacent water reservoir as well as by recording the dissolving process of sodium chloride in water. The presented technique offers the advantage that there is no necessity to couple light from external bulky sources such as lasers or halogen lamps into the sensing device which makes it particularly interesting for miniaturization.

  4. Double surface plasmon enhanced organic light-emitting diodes by gold nanoparticles and silver nanoclusters

    Science.gov (United States)

    Gao, Chia-Yuan; Chen, Ying-Chung; Chen, Kan-Lin; Huang, Chien-Jung

    2015-12-01

    The influence of gold nanoparticles (GNPs) and silver nanoclusters (SNCs) on the performance of organic light-emitting diodes is investigated in this study. The GNPs are doped into (poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate)) (PEDOT: PSS) and the SNCs are introduced between the electron-injection layer and cathode alumina. The power efficiency of the device, at the maximum luminance, with double surface plasmon resonance and buffer layer is about 2.15 times higher than that of the device without GNPs and SNCs because the absorption peaks of GNPs and SNCs are as good as the photoluminescence peak of the emission layer, resulting in strong surface plasmon resonance effect in the device. In addition, the buffer layer is inserted between PEDOT: PSS and the emitting layer in order to avoid that the nonradiative decay process of exciton is generated.

  5. 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.

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

    Science.gov (United States)

    Baran, Timothy M; Mironov, Oleg; Sharma, Ashwani K; Foster, Thomas H

    2016-06-01

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

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

    Directory of Open Access Journals (Sweden)

    J. Asare

    2016-06-01

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

  8. 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.

  9. Effect of the thermal evaporation rate of Al cathodes on organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Hee Young; Suh, Min Chul, E-mail: mcsuh@khu.ac.kr

    2014-10-15

    Graphical abstract: - Highlights: • The TOF-SIMS analysis to investigate cathode diffusion during evaporation process. • Performance change of OLEDs prepared with different evaporation rate of Al cathode. • Change of electron transport behavior during thermal evaporation process. - Abstract: The relationship between the thermal evaporation rate of Al cathodes and the device performance of organic light-emitting diodes (OLEDs) was investigated to clarify the source of leakage current. Time-of-flight secondary ion mass spectrometry was applied to identify the diffusion of Li and Al fragments into the underlying organic layer during the thermal evaporation process. We prepared various OLEDs by varying the evaporation rates of the Al cathode to investigate different device performance. Interestingly, the leakage current level decreased when the evaporation rate reached ∼25 Å/s. In contrast, the best efficiency and operational lifetime was obtained when the evaporation rate was 5 Å/s.

  10. 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.

  11. Array of organic thin film transistors integrated with organic light emitting diodes on a plastic substrate

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, Gi-Seong [Division of Electrical and Electronics and Computer Engineering, Dong-A University, 840 Hadan-dong Saha-gu, Busan, 604-714 (Korea, Republic of); Choe, Ki-Beom [Division of Electrical and Electronics and Computer Engineering, Dong-A University, 840 Hadan-dong Saha-gu, Busan, 604-714 (Korea, Republic of); Song, Chung-Kun [Division of Electrical and Electronics and Computer Engineering, Dong-A University, 840 Hadan-dong Saha-gu, Busan, 604-714 (Korea, Republic of)]. E-mail: cksong@dau.ac.kr

    2006-08-30

    In order to demonstrate the possible application of an organic thin film transistor (OTFT) to a flexible active matrix organic light emitting diode (OLED) an array of 64 x 64 pixels was fabricated on a 4-in. size poly-ethylene-terephehalate substrate. Each pixel was composed of one OTFT integrated with one OLED. OTFTs successfully drove OLEDs by varying current in a wide range and some images were displayed on the array by emitting green light. The OTFTs used poly(4-vinylphenol) for the gate and pentacene for the semiconductor taking account compatibility with the PET substrate. The average mobility in the array was 0.2 cm{sup 2}/V.s, which was reduced from 1.0 cm{sup 2}/V.s in a single OTFT, and its variation over the entire substrate was 10%.

  12. 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

  13. 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/cm2, 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.

  14. 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.

  15. All-solution processed composite hole transport layer for quantum dot light emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiaoli [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Synergetic Innovation Center of Chemical Science and Engineering, Tianjin (China); Dai, Haitao, E-mail: htdai@tju.edu.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Zhao, Junliang; Wang, Shuguo [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, School of Science, Tianjin University, Tianjin 300072 (China); Sun, Xiaowei [Department of Electrical & Electronic Engineering, South University of Science and Technology of China, Tangchang Road 1088, Shenzhen, Guangdong 518055 (China)

    2016-03-31

    In the present work, poly-TPD and TCTA composite hole transport layer (HTL) was employed in solution processed CdSe/ZnS quantum dot light emitting diodes (QLEDs). As the doping level of TCTA can determine the carriers transport efficiency of HTL, the proper mixing ratio of TCTA and poly-TPD should be found to optimize the performance of composite HTL for QLEDs. The doping of poly-TPD by low TCTA content can make its HOMO level lower and then reduce the energy barrier height from HTL to quantum dots (QDs), whereas the doping of poly-TPD by the concentrated TCTA results in the degraded performance of QLEDs due to its decreased hole transport mobility. By using the optimized composition with poly-TPD:TCTA (3:1) as the hole transport layer, the luminescence of the device exhibits about double enhancement compared with that of poly-TPD based device. The improvement of luminescence is mainly attributed to the lower energy barrier of hole injection. The Förster resonant energy transfer (FRET) mechanism in the devices was investigated through theoretical and experimental analysis and the results indicate that the TCTA doping makes no difference on FRET. Therefore, the charge injection mechanism dominates the improved performance of the devices. - Highlights: • Quantum dot light emitting diodes (QLEDs) were fabricated by all solution method. • The performance of QLEDs was optimized by varying the composite hole transport layer. • The blend HTL could promote hole injection by optimizing HOMO levels. • The energy transfer mechanism was analyzed by studying Förster resonant energy transfer process.

  16. 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

  17. Frequency limits of high-efficiency non-resonant cavity light-emitting diodes

    Science.gov (United States)

    Heremans, Paul L.; Windisch, Reiner; Knobloch, Alexander; Potemans, J.; Dutta, Barundeb; Doehler, Gottfried H.; Borghs, Gustaaf

    1999-04-01

    In this paper, we present measurements of the switch-on times and of the switch-off times of non-resonant cavity light-emitting diodes, compared to those of conventional reference diodes. From this comparison, we infer that the high quantum efficiency of NRC-LED's is not achieved by photon recycling, but purely by efficient extraction of generated photons. This is further corroborated by the good matching that is achieved between the measured switch-on times and theoretical predictions of the switch-on times. The latter are calculated with a model that includes only the electrical charging of the active layer and assumes that photon recycling does not occur. It is furthermore shown that the switch-on can be made faster by switching the diode between a non-zero low-state and the required high state. Doing so, an open eye diagram is achieved at 622 Mbit/s for a NRC-LED having an external quantum efficiency of 17%.

  18. Anomalous temperature dependent magneto-conductance in organic light-emitting diodes with multiple emissive states

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Chen-xiao; Jia, Wei-yao; Huang, Ke-Xun; Zhang, Qiao-ming; Yang, Xiao-hui; Xiong, Zu-hong, E-mail: zhxiong@swu.edu.cn [School of Physical Science and Technology, MOE Key Laboratory on Luminescence and Real-Time Analysis, Southwest University, Chongqing 400715 (China)

    2015-07-13

    The temperature dependence of the magneto-conductance (MC) in organic electron donor-acceptor hybrid and layer heterojunction diodes was studied. The MC value increased with temperature in layer heterojunction and in 10 wt. % hybrid devices. An anomalous decrease of the MC with temperature was observed in 25 wt. %–50 wt. % hybrid devices. Further increasing donor concentration to 75 wt. %, the MC again increased with temperature. The endothermic exciplex-exciton energy transfer and the change in electroplex/exciton ratio caused by change in charge transport with temperature may account for these phenomena. Comparative studies of the temperature evolutions of the IV curves and the electroluminescence and photoluminescence spectra back our hypothesis.

  19. 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.

  20. High efficiency, high modulation bandwidth (Ga,Al)As:Te,Zn light-emitting diodes with graded band gap

    Science.gov (United States)

    Leibenzeder, S.; Rühle, W.; Hoffmann, L.; Weyrich, C.

    1985-05-01

    A new (Ga,Al)As light-emitting diode (λmax =660-880 nm) is presented which has several advantages: simple processing, high external quantum efficiencies (up to 12%), and short decay times (down to 12 ns). The importance of photon recycling and reduced self-absorption in the graded band gap is demonstrated.

  1. 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

  2. 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

  3. 76 FR 54254 - In the Matter of Certain Light Emitting Diodes and Products Containing Same; Notice of...

    Science.gov (United States)

    2011-08-31

    ... COMMISSION In the Matter of Certain Light Emitting Diodes and Products Containing Same; Notice of Institution... products containing same by reason of infringement of certain claims of U.S. Patent No. 7,928,465 (``the... products containing same that infringe one or more of claims 1, 2, 10, 11, 13-15, 17, 18, 20-23, 26-34, and...

  4. 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.

  5. Crossover from space-charge-limited to recombination-limited transport in polymer light-emitting diodes

    NARCIS (Netherlands)

    Martens, Henk; Pasveer, W.F.; Brom, H.B.; Huiberts, J.N.; Blom, P.W.M.; Martens, HCF

    2001-01-01

    By performing admittance spectroscopy as a function of frequency on polymer light-emitting diodes, inductive and capacitive charge-relaxation processes with different characteristic time scales are separated. The inductive contributions arise from the finite transit time of injected carriers, while

  6. 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.

  7. Microcontact printing of self-assembled monolayers to pattern the light-emission of polymeric light-emitting diodes

    NARCIS (Netherlands)

    Brondijk, J. J.; Li, X.; Akkerman, H. B.; Blom, P. W. M.; de Boer, B.

    By patterning a self-assembled monolayer (SAM) of thiolated molecules with opposing dipole moments on a gold anode of a polymer light-emitting diode (PLED), the charge injection and, therefore, the light-emission of the device can be controlled with a micrometer-scale resolution. Gold surfaces were

  8. 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.

  9. 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)

  10. Room temperature luminescence properties of fluorescent SiC as white light emitting diode medium

    Energy Technology Data Exchange (ETDEWEB)

    Sun, J.W., E-mail: jianwusun@gmail.com [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden); Jokubavicius, V.; Liljedahl, R.; Yakimova, R. [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden); Juillaguet, S. [Universite Montpellier 2, Laboratoire Charles Coulomb UMR 5221, F-34095, Montpellier (France); Camassel, J. [CNRS, Laboratoire Charles Coulomb UMR 5221, F-34095, Montpellier (France); Kamiyama, S. [Department of Materials Science and Engineering, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku, Nagoya 468-8502 (Japan); Syvaejaervi, M. [Department of Physics, Chemistry and Biology, Linkoeping University, 581 83 Linkoeping (Sweden)

    2012-11-01

    The high quantum efficiency of donor-acceptor-pair emission in N and B co-doped 6H-SiC opens the way for SiC to constitute as an efficient light-emitting medium for white light-emitting diodes. In this work, we evidence room temperature luminescence in N and B co-doped 6H-SiC fluorescent material grown by the Fast Sublimation Growth Process. Three series of samples, with eight different N and B doping levels, were investigated. In most samples, from photoluminescence measurements a strong N-B donor-acceptor-pair emission band was observed at room temperature, with intensity dependent on the nitrogen pressure in the growth chamber and boron doping level in the source. Low temperature photoluminescence spectra showed that N bound exciton peaks exhibited a continuous broadening with increasing N{sub 2} pressure during the growth, unambiguously indicating an opportunity to control the N doping in the epilayer by conveniently changing the N{sub 2} pressure. Finally, the crystal quality of the N and B doped 6H-SiC was evaluated by X-ray diffraction measurements. The {omega} rocking curves of (0006) Bragg diffractions from the samples grown with lower and higher N{sub 2} pressure show almost the same value of the full width at half maximum as that collected from the substrate. This suggests that the N and B doping, which is expected to give rise to an efficient donor-acceptor-pair emission at room temperature, does not degrade the crystal quality.

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

    Science.gov (United States)

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

    2017-07-25

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

  12. 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.

  13. 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.

  14. Absorbance detector based on a deep UV light emitting diode for narrow-column HPLC.

    Science.gov (United States)

    Bui, Duy Anh; Bomastyk, Benjamin; Hauser, Peter C

    2013-10-01

    A detector for miniaturized HPLC based on deep UV emitting diodes and UV photodiodes was constructed. The measurement is accomplished by the transverse passage of the radiation from the light-emitting diode (LED) through fused-silica tubing with an internal diameter of 250 μm. The optical cell allows flexible alignment of the LED, tubing, and photodiode for optimization of the light throughput and has an aperture to block stray light. A beam splitter was employed to direct part of the emitted light to a reference photodiode and the Lambert-Beer law was emulated with a log-ratio amplifier circuitry. The detector was tested with two LEDs with emission bands at 280 and 255 nm and showed noise levels as low as 0.25 and 0.22 mAU, respectively. The photometric device was employed successfully in separations using a column of 1 mm inner diameter in isocratic as well as gradient elution. Good linearities over three orders of magnitude in concentration were achieved, and the precision of the measurements was better than 1% in all cases. Detection down to the low micromolar range was possible. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Spot phosphor concept applied to a remote phosphor light-emitting diode light engine

    Science.gov (United States)

    Acuña, Paula; Meuret, Youri; Deconinck, Geert; Hanselaer, Peter

    2016-11-01

    Although remote phosphor technology outperforms conformal phosphor technology for midpower applications, one of the limiting factors due to its impact on the total cost is the amount of phosphor required. Furthermore, an important loss mechanism in remote phosphor light-emitting diode (LED) technology is the reabsorption of recycled, downconverted light by the phosphor. An obvious solution to this issue is to enable a light path for the converted light, such that further interactions with the phosphor element are avoided. We propose a spot phosphor concept to achieve this goal. To explore this configuration, a simulation model of a phosphor element is devised and validated. The optical input parameters are based on experimental data and the application of the inverse adding-doubling method. The resulting configuration, along with a long-pass filter, is shown to be a potential solution for reduction of phosphor usage. The moderate decrease in the light extraction ratio (LER) when applying the spot concept is partly attributed to the losses in the secondary optics needed to narrow the LED beam; the combination of the spot concept configuration with a directional light source such as a laser diode is shown to be a powerful combination for the enhancement of the LER.

  16. Study of a QCW light-emitting-diode (LED)-pumped solid-state laser

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kangin; Bae, Sangyoon; Gwag, Jinseog; Kwon, Jinhyuk; Yi, Jonghoon [Yeungnam University, Gyeungsan (Korea, Republic of)

    2011-11-15

    The lasing of solid-state lasers pumped by light emitting diodes (LEDs) was studied to replace the quasi-continuous-wave (QCW) laser diode in pulse laser pumping. The investigated solid-state gain media included Nd-doped solid-state materials (Nd:YAG, Nd:glass, Nd/Cr:YAG), Ti:sapphire, and solid dye. The gain medium was surrounded by arrays of LEDs very closely. The distribution of the LED radiation absorbed in the gain medium was calculated by using non-sequential ray tracing software. The calculated data transferred to the cavity analysis software and the lasing characteristics were simulated. The calculated results for the absorbed LED distribution and the absorption efficiency in the Nd:YAG rod were compared to experimentally measured fluorescence profile and the absorption efficiency and were found to be accurate within an error of 11%. Among the investigated gain media, Nd/Cr:YAG showed the lowest lasing threshold. We also found that the use of reflector in the pumping chamber could lower the lasing threshold of Nd:YAG to half the lasing threshold without the reflector.

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

    Science.gov (United States)

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

    2016-01-01

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

  18. Similarities and differences of alkali metal chlorides applied in organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Lue, Zhaoyue [Department of Physics, School of Science, East China University of Science and Technology, Shanghai 200237 (China); Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Deng, Zhenbo [Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Hou, Ying [Department of Physics, School of Science, East China University of Science and Technology, Shanghai 200237 (China); Xu, Haisheng, E-mail: hsxu@ecust.edu.cn [Department of Physics, School of Science, East China University of Science and Technology, Shanghai 200237 (China); Kunshan Hisense Electronics, Co., Ltd., Kunshan, Jiangsu 215300 (China)

    2012-12-15

    The similarities and differences of alkali metal chlorides (sodium chloride (NaCl), potassium chloride (KCl), rubidium chloride (RbCl) and cesium chloride (CsCl)) applied in organic light-emitting diodes (OLEDs) are investigated. The behavior is similar for the OLEDs with these four chlorides as electron injection layer (EIL). Their maximum luminance and efficiency at 100 mA/cm{sup 2} are within the ranges of 18 550 {+-} 600 (cd/m{sup 2}) with an error of 3.23% and 4.09 {+-} 0.15 (cd/A) within an error of 3.67%, respectively. The similar performance is due to almost identical electron injection barrier for NaCl, KCl, RbCl and CsCl as EIL. Interestingly, the properties are different for devices with chlorides inserted inside tris (8-hydroxyquinoline) aluminum at the position of 20 nm away from aluminum cathode, labeled as NaCl-, KCl-, RbCl- and CsCl- devices. The relation of luminance is CsCl- > RbCl- = KCl- > NaCl-, where '>' and '=' mean 'better than' and 'the same as', respectively. And the device efficiencies are decreased from CsCl to NaCl. That is, the sort order of the efficiencies is CsCl- > RbCl- > KCl- > NaCl-. The mechanism is explained by tunneling model in terms of various energy gaps estimated by optical electronegativity of NaCl, KCl, RbCl and CsCl. - Highlights: Black-Right-Pointing-Pointer Effects of NaCl, KCl, RbCl and CsCl in organic light-emitting diodes are compared. Black-Right-Pointing-Pointer The similar performance is due to almost identical electron injection barrier. Black-Right-Pointing-Pointer The different behavior of chlorides inside Alq{sub 3} is explained by tunneling model. Black-Right-Pointing-Pointer The different behavior is attributed to various energy gaps of different chlorides. Black-Right-Pointing-Pointer The efficiency of device with chlorides inside Alq{sub 3} is decreased from CsCl to NaCl.

  19. 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

  20. Color tuning of light-emitting-diodes by modulating the concentration of red-emitting silicon nanocrystal phosphors

    Science.gov (United States)

    Barillaro, G.; Strambini, L. M.

    2014-03-01

    Luminescent forms of nanostructured silicon have received significant attention in the context of quantum-confined light-emitting devices thanks to size-tunable emission wavelength and high-intensity photoluminescence, as well as natural abundance, low cost, and non-toxicity. Here, we show that red-emitting silicon nanocrystal (SiN) phosphors, obtained by electrochemical erosion of silicon, allow for effectively tuning the color of commercial light-emitting-diodes (LEDs) from blue to violet, magenta, and red, by coating the LED with polydimethylsiloxane encapsulating different SiN concentrations. High reliability of the tuning process, with respect to SiN fabrication and concentration, and excellent stability of the tuning color, with respect to LED bias current, is demonstrated through simultaneous electrical/optical characterization of SiN-modified commercial LEDs, thus envisaging exciting perspectives for silicon nanocrystals in the field of light-emitting applications.

  1. An Analysis of the Far-Field Radiation Pattern of the Ultraviolet Light-Emitting Diode (LED) Engin LZ4-00UA00 Diode with and without Beam Shaping Optics

    Science.gov (United States)

    2015-09-01

    SEP 2015 US Army Research Laboratory An Analysis of the Far-Field Radiation Pattern of the Ultraviolet Light - Emitting Diode (LED) Engin...Radiation Pattern of the Ultraviolet Light - Emitting Diode (LED) Engin LZ4-00UA00 Diode with and without Beam Shaping Optics 5a. CONTRACT NUMBER... light - emitting diode (LED), with and without beam shaping optics. This LED has 4 emitters arranged in a square pattern that are off-center from the

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

    Science.gov (United States)

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

    2014-04-01

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

  3. Influence of vacuum chamber impurities on the lifetime of organic light-emitting diodes.

    Science.gov (United States)

    Fujimoto, Hiroshi; Suekane, Takashi; Imanishi, Katsuya; Yukiwaki, Satoshi; Wei, Hong; Nagayoshi, Kaori; Yahiro, Masayuki; Adachi, Chihaya

    2016-12-13

    We evaluated the influence of impurities in the vacuum chamber used for the fabrication of organic light-emitting diodes on the lifetime of the fabricated devices and found a correlation between lifetime and the device fabrication time. The contact angle of the ITO substrates stored the chamber under vacuum were used to evaluate chamber cleanliness. Liquid chromatography-mass spectrometry was performed on Si wafers stored in the vacuum chamber before device fabrication to examine the impurities in the chamber. Surprisingly, despite the chamber and evaporation sources being at room temperature, a variety of materials were detected, including previously deposited materials and plasticizers from the vacuum chamber components. We show that the impurities, and not differences in water content, in the chamber were the source of lifetime variations even when the duration of exposure to impurities only varied before and after deposition of the emitter layer. These results suggest that the impurities floating in the vacuum chamber significantly impact lifetime values and reproducibility.

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

    Science.gov (United States)

    Mao, Zongzhen; Xu, Guodong; Yang, Yi

    2014-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-09-30

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

  6. Stacking illumination of a confocal reflector light emitting diode automobile headlamp with an asymmetric triangular prism.

    Science.gov (United States)

    Chen, Hsi-Chao; Zhou, Jia-Hao; Zhou, Yang

    2017-02-01

    A confocal reflector lamp with an asymmetric triangular prism was designed for a stacking illumination of a light emitting diode (LED) automobile headlamp fitting ECE R112 asymmetrical regulation. The optical system includes three 1st elliptic reflectors, three 2nd parabolic reflectors, and one asymmetric triangular prism. Three elliptic and parabolic reflectors were assembled with three confocal reflector modules; two modules projected the cut-off line of a 0° angle, and the other module projected the cut-off line of a 15° angle using of an asymmetric triangular prism. The ray tracing, optical simulation, and mockup experiment results exhibited that the illumination distribution met the regulation of ECE R112 class B, and the ideal efficiency could reach 96.8% in theory. The tolerance analysis showed the efficiency remained above 98% under the error values of ±0.2  mm of the position of the LED light source, and the y direction of the up-down movement was more sensitive than the x and z directions. The measurement results of the mockup sample safety factor were all larger than 1.15 and supported the regulation of the ECE R112 Class B.

  7. NANOSTRUCTURED HIGH PERFORMANCE ULTRAVIOLET AND BLUE LIGHT EMITTING DIODES FOR SOLID STATE LIGHTING

    Energy Technology Data Exchange (ETDEWEB)

    Arto V. Nurmikko; Jung Han

    2004-10-01

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the first 12 month contract period include (1) new means of synthesizing zero- and one-dimensional GaN nanostructures, (2) establishment of the building blocks for making GaN-based microcavity devices, and (3) demonstration of top-down approach to nano-scale photonic devices for enhanced spontaneous emission and light extraction. These include a demonstration of eight-fold enhancement of the external emission efficiency in new InGaN QW photonic crystal structures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  8. Improved performance of organic light-emitting diode with vanadium pentoxide layer on the FTO surface

    Science.gov (United States)

    Saikia, D.; Sarma, R.

    2017-06-01

    Vanadium pentoxide layer deposited on the fluorine-doped tin oxide (FTO) anode by vacuum deposition has been investigated in organic light-emitting diode (OLED). With 12 nm optimal thickness of V2O5, the luminance efficiency is increased by 1.66 times compared to the single FTO-based OLED. The improvement of current efficiency implies that there is a better charge injection and better controlling of hole current. To investigate the performance of OLED by the buffer layer, V2O5 films of different thicknesses were deposited on the FTO anode and their J- V and L- V characteristics were studied. Further analysis was carried out by measuring sheet resistance, optical transmittance and surface morphology with the FE-SEM images. This result indicates that the V2O5 (12 nm) buffer layer is a good choice for increasing the efficiency of FTO-based OLED devices within the tunnelling region. Here the maximum value of current efficiency is found to be 2.83 cd / A.

  9. Transparent perovskite light-emitting diodes by employing organic-inorganic multilayer transparent top electrodes

    Science.gov (United States)

    Liang, Junqing; Guo, Xiaoyang; Song, Li; Lin, Jie; Hu, Yongsheng; Zhang, Nan; Liu, Xingyuan

    2017-11-01

    Perovskite light-emitting diodes (PeLEDs) have attracted much attention in the past two years due to their high photoluminescence quantum efficiencies and wavelength tuneable characteristics. In this work, transparent PeLEDs (TPeLEDs) have been reported with organic-inorganic multilayer transparent top electrodes that have more convenient control of the organic/electrode interface. By optimizing the thickness of the MoO3 layer in the top electrode, the best average transmittance of 47.21% has been obtained in the TPeLED in the wavelength range of 380-780 nm. In addition, the TPeLED exhibits a maximum luminance of 6380 cd/m2, a maximum current efficiency (CE) of 3.50 cd/A, and a maximum external quantum efficiency (EQE) of 0.85% from the bottom side together with a maximum luminance of 3380 cd/m2, a maximum CE of 1.47 cd/A, and a maximum EQE of 0.36% from the top side. The total EQE of the TPeLED is about 86% of that of the reference device, indicating efficient TPeLED achieved in this work, which could have significant contribution to PeLEDs for see-through displays.

  10. High-performance flexible organic light-emitting diodes using embedded silver network transparent electrodes.

    Science.gov (United States)

    Zhou, Lei; Xiang, Heng-Yang; Shen, Su; Li, Yan-Qing; Chen, Jing-De; Xie, Hao-Jun; Goldthorpe, Irene A; Chen, Lin-Sen; Lee, Shuit-Tong; Tang, Jian-Xin

    2014-12-23

    Because of their mechanical flexibility, organic light-emitting diodes (OLEDs) hold great promise as a leading technology for display and lighting applications in wearable electronics. The development of flexible OLEDs requires high-quality transparent conductive electrodes with superior bendability and roll-to-roll manufacturing compatibility to replace indium tin oxide (ITO) anodes. Here, we present a flexible transparent conductor on plastic with embedded silver networks which is used to achieve flexible, highly power-efficient large-area green and white OLEDs. By combining an improved outcoupling structure for simultaneously extracting light in waveguide and substrate modes and reducing the surface plasmonic losses, flexible white OLEDs exhibit a power efficiency of 106 lm W(-1) at 1000 cd m(-2) with angular color stability, which is significantly higher than all other reports of flexible white OLEDs. These results represent an exciting step toward the realization of ITO-free, high-efficiency OLEDs for use in a wide variety of high-performance flexible applications.

  11. Wearable Electrocardiogram Monitor Using Carbon Nanotube Electronics and Color-Tunable Organic Light-Emitting Diodes.

    Science.gov (United States)

    Koo, Ja Hoon; Jeong, Seongjin; Shim, Hyung Joon; Son, Donghee; Kim, Jaemin; Kim, Dong Chan; Choi, Suji; Hong, Jong-In; Kim, Dae-Hyeong

    2017-10-24

    With the rapid advances in wearable electronics, the research on carbon-based and/or organic materials and devices has become increasingly important, owing to their advantages in terms of cost, weight, and mechanical deformability. Here, we report an effective material and device design for an integrative wearable cardiac monitor based on carbon nanotube (CNT) electronics and voltage-dependent color-tunable organic light-emitting diodes (CTOLEDs). A p-MOS inverter based on four CNT transistors allows high amplification and thereby successful acquisition of the electrocardiogram (ECG) signals. In the CTOLEDs, an ultrathin exciton block layer of bis[2-(diphenylphosphino)phenyl]ether oxide is used to manipulate the balance of charges between two adjacent emission layers, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) and bis(2-phenylquinolyl-N,C(2'))iridium(acetylacetonate), which thereby produces different colors with respect to applied voltages. The ultrathin nature of the fabricated devices supports extreme wearability and conformal integration of the sensor on human skin. The wearable CTOLEDs integrated with CNT electronics are used to display human ECG changes in real-time using tunable colors. These materials and device strategies provide opportunities for next generation wearable health indicators.

  12. Light-emitting diodes (LED) for domestic lighting: any risks for the eye?

    Science.gov (United States)

    Behar-Cohen, F; Martinsons, C; Viénot, F; Zissis, G; Barlier-Salsi, A; Cesarini, J P; Enouf, O; Garcia, M; Picaud, S; Attia, D

    2011-07-01

    Light-emitting diodes (LEDs) are taking an increasing place in the market of domestic lighting because they produce light with low energy consumption. In the EU, by 2016, no traditional incandescent light sources will be available and LEDs may become the major domestic light sources. Due to specific spectral and energetic characteristics of white LEDs as compared to other domestic light sources, some concerns have been raised regarding their safety for human health and particularly potential harmful risks for the eye. To conduct a health risk assessment on systems using LEDs, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), a public body reporting to the French Ministers for ecology, for health and for employment, has organized a task group. This group consisted physicists, lighting and metrology specialists, retinal biologist and ophthalmologist who have worked together for a year. Part of this work has comprised the evaluation of group risks of different white LEDs commercialized on the French market, according to the standards and found that some of these lights belonged to the group risk 1 or 2. This paper gives a comprehensive analysis of the potential risks of white LEDs, taking into account pre-clinical knowledge as well as epidemiologic studies and reports the French Agency's recommendations to avoid potential retinal hazards. Copyright © 2011. Published by Elsevier Ltd.

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

    KAUST Repository

    Janjua, Bilal

    2014-12-01

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

  14. Compact environmental spectroscopy using advanced semiconductor light-emitting diodes and lasers

    Energy Technology Data Exchange (ETDEWEB)

    Fritz, I.J.; Klem, J.F.; Hafich, M.J. [and others

    1997-04-01

    This report summarizes research completed under a Laboratory Directed Research and Development program funded for part of FY94, FY95 and FY96. The main goals were (1) to develop novel, compound-semiconductor based optical sources to enable field-based detection of environmentally important chemical species using miniaturized, low-power, rugged, moderate cost spectroscopic equipment, and (2) to demonstrate the utility of near-infrared spectroscopy to quantitatively measure contaminants. Potential applications would include monitoring process and effluent streams for volatile organic compound detection and sensing head-space gasses in storage vessels for waste management. Sensing is based on absorption in the 1.3-1.9 {mu}m band from overtones of the C-H, N-H and O-H stretch resonances. We describe work in developing novel broadband light-emitting diodes emitting over the entire 1.4-1.9 {mu}m wavelength range, first using InGaAs quantum wells, and second using a novel technique for growing digital-alloy materials in the InAlGaAs material system. Next we demonstrate the utility of near-infrared spectroscopy for quantitatively determining contamination of soil by motor oil. Finally we discuss the separability of different classes of organic compounds using near-infrared spectroscopic techniques.

  15. Estimation of carrier leakage in InGaN light emitting diodes from photocurrent measurements

    Science.gov (United States)

    Hafiz, Shopan; Zhang, Fan; Monavarian, Morteza; Okur, Serdal; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

    2014-02-01

    Carrier transport in double heterostructure (DH) InGaN light emitting diodes (LEDs) was investigated using photocurrent measurements performed under CW HeCd laser (325 nm wavelength) excitation. The effect of electron injector thicknesses was investigated by monitoring the excitation density and applied bias dependent escape of photogenerated carriers from the active region and through energy band structure and carrier transport simulations using Silvaco Atlas. For quad (4x) 3-nm DH LED structures incorporating staircase electron injectors (SEIs), photocurrent increased with SEI thickness due to reduced effective barrier opposing carrier escape from the active region as confirmed by simulations. The carrier leakage percentile at -3V bias and 280 Wcm-2 optical excitation density increased from 24 % to 55 % when In 0.04Ga0.96N + In0.08Ga0.92N SEI thickness was increased from 4 nm + 4 nm to 30 nm + 30 nm. The increased leakage with thicker SEI correlates with increased carrier overflow under forward bias.

  16. Electron injection into hole-transporting layer from emitting layer in organic light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Tsuboi, Taiju [Faculty of Engineering, Kyoto Sangyo University, Kamigamo (Japan); Kishimoto, Tadahi; Wako, Kazuhiro [Research Institute for Advanced Liquid Crystal Technology, Aomori (Japan); Matsuda, Kuniharu; Iguchi, Hirofumi [Tohoku Device Co., Ltd., Hanamaki, Iwate (Japan)

    2011-09-15

    Optical and electrical characteristics of organic light emitting diode devices with emitting layer of N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) doped with 0.2, 0.5, and 1.0% tris[1-phenylisoquinolinato-C2, N] iridium [Ir(piq){sub 3}] are presented. Tris(8-hydroxyquinoline) aluminum (Alq{sub 3}) and NPB were used as electron and hole transport layers, respectively. Emissions from Ir(piq){sub 3} dopant and Alq{sub 3} have been observed in all the devices. No emission from NPB host was observed even in device with 0.2% dopant concentration. This is understood by the high HOMO gap (0.8 eV) between NPB and Alq{sub 3} and by the very small HOMO gap (0.1 eV) between Ir(piq){sub 3} and Alq{sub 3}, which do not lead to injection of electrons from Alq{sub 3} electron transport layer into NPB host in emitting layer but lead to direct injection of electrons from Alq{sub 3} into Ir(piq){sub 3}. It was found that the driving voltage, external quantum efficiency, and luminous efficiency increase with increasing dopant concentration, but power efficiency decrease. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  17. Simulations of emission from microcavity tandem organic light-emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Biswas, Rana; Xu, Chun; Zhao, Weijun; Liu, Rui; Shinar, Ruth; Shinar, Joseph

    2011-01-01

    Microcavity tandem organic light-emitting diodes (OLEDs) are simulated and compared to experimental results. The simulations are based on two complementary techniques: rigorous finite element solutions of Maxwell's equations and Fourier space scattering matrix solutions. A narrowing and blue shift of the emission spectrum relative to the noncavity single unit OLED is obtained both theoretically and experimentally. In the simulations, a distribution of emitting sources is placed near the interface of the electron transport layer tris(8-hydroxyquinoline) Al (Alq{sub 3}) and the hole transport layer (N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine) ({alpha}-NPB). Far-field electric field intensities are simulated. The simulated widths of the emission peaks also agree with the experimental results. The simulations of the 2-unit tandem OLEDs shifted the emission to shorter wavelength, in agreement with experimental measurements. The emission spectra's dependence on individual layer thicknesses also agreed well with measurements. Approaches to simulate and improve the light emission intensity from these OLEDs, in particular for white OLEDs, are discussed.

  18. Investigation of organic light-emitting diodes with novel organic electron injection layers

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sunae; Sethuraman, Kunjithapatham; An, Jongdeok; Im, Chan [Konkuk University, Seoul (Korea, Republic of); Hwang, Boseon [Jinwoong Industrial Co. Ltd., Seoul (Korea, Republic of)

    2012-03-15

    1-(diphenyl-phosphinoyl)-4-(2,2-diphenyl-vinyl)-benzene (DpDvB) and 4-(diphenyl-phosphinoyl)-4'-(2,2-diphenyl-vinyl)-biphenyl (DpDvBp) have been prepared and used as efficient electron injection layers (EILs) between aluminum cathode and tris (8-hydroxyquinoline) aluminum organic light emitting diodes (OLED). The performances of devices with different thicknesses of DpDvB and DpDvBp were investigated. Experimental results show that the turn-on voltage of the devices was decreased and the luminance of the devices was enhanced with increasing thickness of the EILs. Power efficiencies of 1.07 lm/W and 0.97 lm/W were obtained by inserting a 3-nm-thick EIL of DpDvB and a 5 nm thick EIL of DpDvBp, respectively. These efficiencies are comparable to that of the device using LiF as an EIL. The results prove that DpDvB and DpDvBp layers are also suitable for efficient EILs in OLEDs.

  19. Semitransparent quantum dot light-emitting diodes by cadmium-free colloidal quantum dots.

    Science.gov (United States)

    Kim, Yohan; Ippen, Christian; Greco, Tonino; Oh, Min Suk; Chul, Jong Han; Lee, Jeongno; Wedel, Armin; Kim, Jiwan

    2014-11-01

    The InP/ZnSe/ZnS multishell colloidal quantum dots (QDs) were prepared by convenient heating-up method for an emission layer of semitransparent quantum dot light-emitting diodes (QD-LEDs). The synthesized InP/ZnSe/ZnS multishell QDs exhibited an emission peak at 545 nm for clear green color with a full-width at half-maximum (FWHM) of 50 nm, and photoluminescent (PL) quantum yield (QY) of 45%. The multishell on the indium phosphide (InP) core helped increasing QY and stability by reducing interfacial defects. Using a Ca/Ag cathode, the whole QD-LEDs were semitransparent throughout the visible wavelengths. The maximum brightness and currernt efficiency of semitransparent QD-LEDs reached 587 cd/m2 and 1.52 cd/A by controlling the thickness of Ca/Ag cathode, which is comparable to the device with opaque LiF/Al cathode (1444 cd/m2 and 1.98 cd/A). The performance of our semitransparent and eco-friendly device is not matched with traditional cadmium (Cd) based QD-LEDs yet, but it shows the great potential for various window-type information displays.

  20. Near-infrared roll-off-free electroluminescence from highly stable diketopyrrolopyrrole light emitting diodes

    Science.gov (United States)

    Sassi, Mauro; Buccheri, Nunzio; Rooney, Myles; Botta, Chiara; Bruni, Francesco; Giovanella, Umberto; Brovelli, Sergio; Beverina, Luca

    2016-09-01

    Organic light emitting diodes (OLEDs) operating in the near-infrared spectral region are gaining growing relevance for emerging photonic technologies, such as lab-on-chip platforms for medical diagnostics, flexible self-medicated pads for photodynamic therapy, night vision and plastic-based telecommunications. The achievement of efficient near-infrared electroluminescence from solution-processed OLEDs is, however, an open challenge due to the low photoluminescence efficiency of most narrow-energy-gap organic emitters. Diketopyrrolopyrrole-boron complexes are promising candidates to overcome this limitation as they feature extremely high photoluminescence quantum yield in the near-infrared region and high chemical stability. Here, by incorporating suitably functionalized diketopyrrolopyrrole derivatives emitting at ~760 nm in an active matrix of poly(9,9-dioctylfluorene-alt-benzothiadiazole) and without using complex light out-coupling or encapsulation strategies, we obtain all-solution-processed NIR-OLEDs with external quantum efficiency as high as 0.5%. Importantly, our test-bed devices show no efficiency roll-off even for high current densities and high operational stability, retaining over 50% of the initial radiant emittance for over 50 hours of continuous operation at 10 mA/cm2, which emphasizes the great applicative potential of the proposed strategy.

  1. 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.

  2. Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes

    Science.gov (United States)

    Kyu Kim, Jung; Bae, Sukang; Yi, Yeonjin; Jin Park, Myung; Jin Kim, Sang; Myoung, Nosoung; Lee, Chang-Lyoul; Hee Hong, Byung; Hyeok Park, Jong

    2015-06-01

    Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions.

  3. Blue emitting 1,8-naphthalimides with electron transport properties for organic light emitting diode applications

    Science.gov (United States)

    Ulla, Hidayath; Kiran, M. Raveendra; Garudachari, B.; Ahipa, T. N.; Tarafder, Kartick; Adhikari, Airody Vasudeva; Umesh, G.; Satyanarayan, M. N.

    2017-09-01

    In this article, the synthesis, characterization and use of two novel naphthalimides as electron-transporting emitter materials for organic light emitting diode (OLED) applications are reported. The molecules were obtained by substituting electron donating chloro-phenoxy group at the C-4 position. A detailed optical, thermal, electrochemical and related properties were systematically studied. Furthermore, theoretical calculations (DFT) were performed to get a better understanding of the electronic structures. The synthesized molecules were used as electron transporters and emitters in OLEDs with three different device configurations. The devices with the molecules showed blue emission with efficiencies of 1.89 cdA-1, 0.98 lmW-1, 0.71% at 100 cdm-2. The phosphorescent devices with naphthalimides as electron transport materials displayed better performance in comparison to the device without any electron transporting material and were analogous with the device using standard electron transporting material, Alq3. The results demonstrate that the naphthalimides could play a significant part in the progress of OLEDs.

  4. 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.

  5. 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.

  6. Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting

    Energy Technology Data Exchange (ETDEWEB)

    Arto V. Nurmikko; Jung Han

    2007-03-31

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the duration of the contract period include (i) new means of synthesizing AlGaN and InN quantum dots by droplet heteroepitaxy, (ii) synthesis of AlGaInN nanowires as building blocks for GaN-based microcavity devices, (iii) progress towards direct epitaxial alignment of the dense arrays of nanowires, (iv) observation and measurements of stimulated emission in dense InGaN nanopost arrays, (v) design and fabrication of InGaN photonic crystal emitters, and (vi) observation and measurements of enhanced fluorescence from coupled quantum dot and plasmonic nanostructures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  7. Polarized Light-Emitting Diodes Based on Patterned MoS2 Nanosheet Hole Transport Layer.

    Science.gov (United States)

    Choi, Gyu Jin; Van Le, Quyet; Choi, Kyoung Soon; Kwon, Ki Chang; Jang, Ho Won; Gwag, Jin Seog; Kim, Soo Young

    2017-09-01

    Here, this study successfully fabricates few-layer MoS2 nanosheets from (NH4 )2 MoS4 and applies them as the hole transport layer as well as the template for highly polarized organic light-emitting diodes (OLEDs). The obtained material consists of polycrystalline MoS2 nanosheets with thicknesses of 2 nm. The MoS2 nanosheets are patterned by rubbing/ion-beam treatment. The Raman spectra shows that {poly(9,9-dioctylfluorene-alt-benzothiadiazole), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)]} (F8BT) on patterned MoS2 exhibits distinctive polarization behavior. It is discovered that patterned MoS2 not only improves the device efficiency but also changes the polarization behavior of the devices owing to the alignment of F8BT. This work demonstrates a highly efficient polarized OLED with a polarization ratio of 62.5:1 in the emission spectrum (166.7:1 at the peak intensity of 540 nm), which meets the manufacturing requirement. In addition, the use of patterned MoS2 nanosheets not only tunes the polarization of the OLEDs but also dramatically improves the device performance as compared with that of devices using untreated MoS2 . © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zi-Hui, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn; Zhang, Yonghui; Bi, Wengang, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn; Geng, Chong; Xu, Shu [Key Laboratory of Electronic Materials and Devices of Tianjin, School of Electronics and Information Engineering, Hebei University of Technology, 5340 Xiping Road, Beichen District, Tianjin 300401 (China); Demir, Hilmi Volkan, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore (Singapore); Department of Electrical and Electronics, Department of Physics, and UNAM-Institute of Material Science and Nanotechnology, Bilkent University, TR-06800 Ankara (Turkey); Sun, Xiao Wei, E-mail: zh.zhang@hebut.edu.cn, E-mail: wbi@hebut.edu.cn, E-mail: volkan@stanfordalumni.org, E-mail: sunxw@sustc.edu.cn [LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore (Singapore); Department of Electrical and Electronic Engineering, College of Engineering, South University of Science and Technology, 1088 Xue-Yuan Road, Nanshan, Shenzhen, Guangdong 518055 (China)

    2016-03-28

    In this work, we propose a charge inverter that substantially increases the hole injection efficiency for InGaN/GaN light-emitting diodes (LEDs). The charge inverter consists of a metal/electrode, an insulator, and a semiconductor, making an Electrode-Insulator-Semiconductor (EIS) structure, which is formed by depositing an extremely thin SiO{sub 2} insulator layer on the p{sup +}-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{sup +}-GaN and SiO{sub 2} insulator. The weak inversion region can shorten the carrier tunnel distance. Meanwhile, the smaller dielectric constant of the thin SiO{sub 2} layer increases the local electric field within the tunnel region, and this is effective in promoting the hole transport from the p-electrode into the p{sup +}-GaN layer. Due to the improved hole injection, the external quantum efficiency is increased by 20% at 20 mA for the 350 × 350 μm{sup 2} LED chip. Thus, the proposed EIS holds great promise for high efficiency LEDs.

  9. Application of ultraviolet light-emitting diodes (UV-LEDs) for water disinfection: A review.

    Science.gov (United States)

    Song, Kai; Mohseni, Madjid; Taghipour, Fariborz

    2016-05-01

    Ultraviolet (UV) disinfection is an effective technology for the inactivation of pathogens in water and is of growing interest for industrial application. A new UV source - ultraviolet light-emitting diode (UV-LED) - has emerged in the past decade with a number of advantages compared to traditional UV mercury lamps. This promising alternative raises great interest in the research on application of UV-LEDs for water treatment. Studies on UV-LED water disinfection have increased during the past few years. This article presents a comprehensive review of recent studies on UV-LEDs with various wavelengths for the inactivation of different microorganisms. Many inconsistent and incomparable data were found from published studies, which underscores the importance of establishing a standard protocol for studying UV-LED inactivation of microorganisms. Different UV sensitivities to UV-LEDs and traditional UV lamps were observed in the literature for some microorganisms, which requires further investigation for a better understanding of microorganism response to UV-LEDs. The unique aspects of UV-LEDs improve inactivation effectiveness by applying LED special features, such as multiple wavelengths and pulsed illumination; however, more studies are needed to investigate the influencing factors and mechanisms. The special features of UV-LEDs offer the flexibility of novel reactor designs for a broad application of UV-LED reactors. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting

    Energy Technology Data Exchange (ETDEWEB)

    Arto V. Nurmikko; Jung Han

    2005-09-30

    We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the second 12 month contract period include (i) new means of synthesizing AlGaN and InN quantum dots by droplet heteroepitaxy, (ii) synthesis of AlGaInN nanowires as building blocks for GaN-based microcavity devices, (iii) progress towards direct epitaxial alignment of the dense arrays of nanowires, (iv) observation and measurements of stimulated emission in dense InGaN nanopost arrays, (v) design and fabrication of InGaN photonic crystal emitters, and (vi) observation and measurements of enhanced fluorescence from coupled quantum dot and plasmonic nanostructures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

  11. Energy down converting organic fluorophore functionalized mesoporous silica hybrids for monolith-coated light emitting diodes

    Directory of Open Access Journals (Sweden)

    Markus Börgardts

    2017-04-01

    Full Text Available The covalent attachment of organic fluorophores in mesoporous silica matrices for usage as energy down converting phosphors without employing inorganic transition or rare earth metals is reported in this article. Triethoxysilylpropyl-substituted derivatives of the blue emitting perylene, green emitting benzofurazane, and red emitting Nile red were synthesized and applied in the synthesis of mesoporous hybrid materials by postsynthetic grafting to commercially available MCM-41. These individually dye-functionalized hybrid materials are mixed in variable ratios to furnish a powder capable of emitting white light with CIE chromaticity coordinates of x = 0.33, y = 0.33 and an external quantum yield of 4.6% upon irradiation at 410 nm. Furthermore, as a proof of concept two different device setups of commercially available UV light emitting diodes, are coated with silica monoliths containing the three triethoxysilylpropyl-substituted fluorophore derivatives. These coatings are able to convert the emitted UV light into light with correlated color temperatures of very cold white (41100 K, 10700 K as well as a greenish white emission with correlated color temperatures of about 5500 K.

  12. Colour tuning in white hybrid inorganic/organic light-emitting diodes

    Science.gov (United States)

    Bruckbauer, Jochen; Brasser, Catherine; Findlay, Neil J.; Edwards, Paul R.; Wallis, David J.; Skabara, Peter J.; Martin, Robert W.

    2016-10-01

    White hybrid inorganic/organic light-emitting diodes (LEDs) were fabricated by combining a novel organic colour converter with a blue inorganic LED. An organic small molecule was specifically synthesised to act as down-converter. The characteristics of the white colour were controlled by changing the concentration of the organic molecule based on the BODIPY unit, which was embedded in a transparent matrix, and volume of the molecule and encapsulant mixture. The concentration has a critical effect on the conversion efficiency, i.e. how much of the absorbed blue light is converted into yellow light. With increasing concentration the conversion efficiency decreases. This quenching effect is due to aggregation of the organic molecule at higher concentrations. Increasing the deposited amount of the converter does not increase the yellow emission despite more blue light being absorbed. Degradation of the organic converter was also observed during a period of 15 months from LED fabrication. Angular-dependent measurements revealed slight deviation from a Lambertian profile for the blue and yellow emission peaks leading to a small change in ‘whiteness’ with emission angle. Warm white and cool white light with correlated colour temperatures of 2770 K and 7680 K, respectively, were achieved using different concentrations of the converter molecule. Although further work is needed to improve the lifetime and poor colour rendering, these hybrid LEDs show promising results as an alternative approach for generating white LEDs compared with phosphor-based white LEDs.

  13. The effect of rubidium chloride on properties of organic light-emitting diodes

    Science.gov (United States)

    Lü, Zhaoyue; Deng, Zhenbo; Du, Hailiang; Li, Degang; Zou, Ye; Xu, Denghui; Chen, Zheng; Wang, Yongsheng

    2009-11-01

    A multilayer organic light-emitting diode (OLED) was fabricated with a thin rubidium chloride (RbCl) layer inserted inside an electron transport layer (ETL), tris (8-hydroxyquinoline) aluminum (Alq 3). Here, we set d is the distance of the RbCl layer away from the Alq 3/Al interface. The rubidium chloride layer was inserted inside 60 nm Alq 3 at d = 0.0, 2.5, 5.0, 7.5, 10, 20 and 30 nm positions. When the RbCl layer is positioned closer to the Al cathode, both the current density and EL efficiency are enhanced due to the enhanced electron injection. The devices show the electroluminescent (EL) efficiency improvement without an enhanced injection if the value of d is lager than 5.0 nm. The suggested mechanism of RbCl EL efficiency enhancer is carrier trap sites induced by the thin RbCl layer. The trapped charges alter the distribution of the field inside the OLED and, consequently, give better recombination in the device.

  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. Light-emitting-diode induced retinal damage and its wavelength dependency in vivo.

    Science.gov (United States)

    Shang, Yu-Man; Wang, Gen-Shuh; Sliney, David H; Yang, Chang-Hao; Lee, Li-Ling

    2017-01-01

    To examine light-emitting-diode (LED)-induced retinal neuronal cell damage and its wavelength-driven pathogenic mechanisms. Sprague-Dawley rats were exposed to blue LEDs (460 nm), green LEDs (530 nm), and red LEDs (620 nm). Electroretinography (ERG), Hematoxylin and eosin (H&E) staining, transmission electron microscopy (TEM), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and immunohistochemical (IHC) staining, Western blotting (WB) and the detection of superoxide anion (O2(-)·), hydrogen peroxide (H2O2), total iron, and ferric (Fe(3+)) levels were applied. ERG results showed the blue LED group induced more functional damage than that of green or red LED groups. H&E staining, TUNEL, IHC, and TEM revealed apoptosis and necrosis of photoreceptors and RPE, which indicated blue LED also induced more photochemical injury. Free radical production and iron-related molecular marker expressions demonstrated that oxidative stress and iron-overload were associated with retinal injury. WB assays correspondingly showed that defense gene expression was up-regulated after the LED light exposure with a wavelength dependency. The study results indicate that LED blue-light exposure poses a great risk of retinal injury in awake, task-oriented rod-dominant animals. The wavelength-dependent effect should be considered carefully when switching to LED lighting applications.

  16. High fluence light emitting diode-generated red light modulates characteristics associated with skin fibrosis.

    Science.gov (United States)

    Mamalis, Andrew; Koo, Eugene; Garcha, Manveer; Murphy, William J; Isseroff, R Rivkah; Jagdeo, Jared

    2016-12-01

    Skin fibrosis, often referred to as skin scarring, is a significant international health problem with limited treatment options. The hallmarks of skin fibrosis are increased fibroblast proliferation, collagen production, and migration speed. Recently published clinical observations indicate that visible red light may improve skin fibrosis. In this study we hypothesize that high-fluence light-emitting diode-generated red light (HF-LED-RL) modulates the key cellular features of skin fibrosis by decreasing cellular proliferation, collagen production, and migration speed of human skin fibroblasts. Herein, we demonstrate that HF-LED-RL increases reactive oxygen species (ROS) generation for up to 4 hours, inhibits fibroblast proliferation without increasing apoptosis, inhibits collagen production, and inhibits migration speed through modulation of the phosphoinositide 3-kinase (PI3K)/Akt pathway. We demonstrate that HF-LED-RL is capable of inhibiting the unifying cellular processes involved in skin fibrosis including fibroblast proliferation, collagen production, and migration speed. These findings suggest that HF-LED-RL may represent a new approach to treat skin fibrosis. LED advantages include low cost, portability, and ease of use. Further characterizing the photobiomodulatory effects of HF-LED-RL on fibroblasts and investigating the anti-fibrotic effects of HF-LED-RL in human subjects may provide new insight into the utility of this therapeutic approach for skin fibrosis. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. An Optically Stabilized Fast-Switching Light Emitting Diode as a Light Source for Functional Neuroimaging

    Science.gov (United States)

    Wagenaar, Daniel A.

    2012-01-01

    Neuroscience research increasingly relies on optical methods for evoking neuronal activity as well as for measuring it, making bright and stable light sources critical building blocks of modern experimental setups. This paper presents a method to control the brightness of a high-power light emitting diode (LED) light source to an unprecedented level of stability. By continuously monitoring the actual light output of the LED with a photodiode and feeding the result back to the LED's driver by way of a proportional-integral controller, drift was reduced to as little as 0.007% per hour over a 12-h period, and short-term fluctuations to 0.005% root-mean-square over 10 seconds. The LED can be switched on and off completely within 100 s, a feature that is crucial when visual stimuli and light for optical recording need to be interleaved to obtain artifact-free recordings. The utility of the system is demonstrated by recording visual responses in the central nervous system of the medicinal leech Hirudo verbana using voltage-sensitive dyes. PMID:22238663

  18. New photic stimulating system with white light-emitting diodes to elicit electroretinograms from zebrafish larvae.

    Science.gov (United States)

    Matsubara, Hisashi; Matsui, Yoshitsugu; Miyata, Ryohei; Nishimura, Yuhei; Yamamoto, Tetsuro; Tanaka, Toshio; Kondo, Mineo

    2017-10-01

    The zebrafish is an established animal model commonly used in biological, neuroscience, and genetic research. We have developed a new light stimulating system using white light-emitting diodes (LEDs) to elicit ERGs from zebrafish larvae. The purpose of this study was to record full-field ERGs and to evaluate the inter-trial reliability of the ERGs recorded with our system from zebrafish larvae. The stimulating device used white LEDs that were attached to a stereomicroscope, and the location of the recording electrode on the cornea could be monitored while the eye was being stimulated. Full-field scotopic and photopic ERGs were recorded from larvae at the age of 5-7 days post-fertilization (dpf). Intensity-response curves were constructed from the ERGs. Inter-trial reliability of the ERGs recorded by our system was evaluated. This stimulating system could be used for efficient and reliable ERG recordings from 5-7 dpf larvae. The amplitudes, implicit times, and the waveforms of the scotopic and photopic ERGs were similar to those reported in earlier studies. Inter-trial reliability of the amplitudes of the photopic ERG b-waves was excellent with an intra-class correlation coefficient of 0.98. We conclude that this new light stimulation system using white LEDs attached to a stereomicroscope will be helpful in recording reliable ERGs from zebrafish larvae.

  19. 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.

  20. Multiple night-time light-emitting diode lighting strategies impact grassland invertebrate assemblages.

    Science.gov (United States)

    Davies, Thomas W; Bennie, Jonathan; Cruse, Dave; Blumgart, Dan; Inger, Richard; Gaston, Kevin J

    2017-07-01

    White light-emitting diodes (LEDs) are rapidly replacing conventional outdoor lighting technologies around the world. Despite rising concerns over their impact on the environment and human health, the flexibility of LEDs has been advocated as a means of mitigating the ecological impacts of globally widespread outdoor night-time lighting through spectral manipulation, dimming and switching lights off during periods of low demand. We conducted a three-year field experiment in which each of these lighting strategies was simulated in a previously artificial light naïve grassland ecosystem. White LEDs both increased the total abundance and changed the assemblage composition of adult spiders and beetles. Dimming LEDs by 50% or manipulating their spectra to reduce ecologically damaging wavelengths partially reduced the number of commoner species affected from seven to four. A combination of dimming by 50% and switching lights off between midnight and 04:00 am showed the most promise for reducing the ecological costs of LEDs, but the abundances of two otherwise common species were still affected. The environmental consequences of using alternative lighting technologies are increasingly well established. These results suggest that while management strategies using LEDs can be an effective means of reducing the number of taxa affected, averting the ecological impacts of night-time lighting may ultimately require avoiding its use altogether. © 2017 John Wiley & Sons Ltd.

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

    Science.gov (United States)

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

    2011-10-01

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

  2. Efficient organic light-emitting diodes fabricated on cellulose nanocrystal substrates

    Science.gov (United States)

    Najafabadi, E.; Zhou, Y. H.; Knauer, K. A.; Fuentes-Hernandez, C.; Kippelen, B.

    2014-08-01

    Organic light-emitting diodes (OLEDs) fabricated on recyclable and biodegradable substrates are a step towards the realization of a sustainable OLED technology. We report on efficient OLEDs with an inverted top-emitting architecture on recyclable cellulose nanocrystal (CNC) substrates. The OLEDs have a bottom cathode of Al/LiF deposited on a 400 nm thick N,N'-Di-[(1-naphthyl)-N,N'-diphenyl]-(1,1'-biphenyl)-4,4'-diamine (α-NPD) layer and a top anode of Au/MoO3. They achieve a maximum luminance of 74 591 cd/m2 with a current efficacy of 53.7 cd/A at a luminance of 100 cd/m2 and 41.7 cd/A at 1000 cd/m2. It is shown that the α-NPD layer on the CNC substrate is necessary for achieving high performance OLEDs. The electroluminescent spectra of the OLEDs as a function of viewing angle are presented and show that the OLED spectra are subject to microcavity effects.

  3. Efficient light emitting diodes by photon recycling and their application in pixelless infrared imaging devices

    Science.gov (United States)

    Dupont, E.; Chiu, S.

    2000-02-01

    The success of the pixelless imaging concept using a quantum well infrared photodetector integrated with a light emitting diode (QWIP-LED) depends critically on the extent of spatial lateral spreading of both photocurrent generated in the QWIP and near infrared (NIR) photons emitted by the LED as they escape from the device layers. According to the photon recycling model proposed by Schnitzer et al. [Appl. Phys. Lett. 62, 131 (1993)] there appears to be a trade-off between a high LED external quantum efficiency and a small photon lateral spread, the former being a necessary condition for achieving high detector sensitivity. This lateral spreading due to multireflections and reincarnations of the NIR photons could potentially degrade the image quality or resolution of the device. By adapting Schnitzer's model to the QWIP-LED structure, we have identified device parameters that could potentially influence the NIR photon lateral spread and the LED external efficiency. In addition, we have developed a simple sequential model to estimate the crosstalk between the incoming far infrared image and the up-converted NIR image. We have found that the thickness of the LED is an important parameter that needs to be optimized in order to maximize the external efficiency and to minimize the crosstalk. A 6000-Å-thick LED active layer should give a resolution of ˜30 μm and an external efficiency of ˜10%.

  4. Light extraction mechanisms in surface-textured light-emitting diodes

    Science.gov (United States)

    Windisch, Reiner; Meilnschmidt, Stefan; Rooman, Cathleen; Zimmermann, Lars; Dutta, Barundeb; Kuijk, Maarten; Kiesel, Peter; Doehler, Gottfried H.; Borghs, Gustaaf; Heremans, Paul L.

    2001-05-01

    Light-emitting diodes (LEDs) with high efficiencies can be fabricated by a combination of surface texturing and the application of a rear reflector. We demonstrate an external quantum efficiency of 43% for unencapsulated surface-textured thin-film LEDs, which increases to 54% after encapsulation. At low temperatures, the efficiency of unencapsulated devices increases up to 68%. We investigate the light extraction mechanism from such LEDs employing a Monte Carlo simulation of the light propagation inside the LED structure. One essential input parameter for the simulation are the light scattering properties of the textured surface, which have been investigated experimentally. For light incidence below the critical angle of total internal reflection, the transmission through a textured surface is reduced compared to a flat surface. However, due to surface texturing, transmission becomes possible for incident angles above the critical angle. As a result, the internal scattering during internal reflection at the textured surface is not necessary for an efficient extraction of the light generated inside the LED structure. In addition, the Monte Carlo simulation also explains the strong increase of the LED efficiency at low temperatures quantitatively by photon recycling effects. Photon recycling is also demonstrated to be partially responsible for the shift of the emission wavelength in thin- film LEDs, as compared to conventional LEDs.

  5. Characterization of photon recycling in thin crystalline GaAs light emitting diodes

    Science.gov (United States)

    Patkar, M. P.; Lundstrom, M. S.; Melloch, M. R.

    1995-08-01

    Gallium arsenide light emitting diodes (LEDs) were fabricated using molecular beam epitaxial films on GaAs substrates and removed by epitaxial lift-off (ELO). Lifted off devices were then mounted on a Si wafer using a Pd/Au/Cr contact layer, which also served as a back surface reflector. Devices were characterized by electrical and optical measurements, and the results for devices on the GaAs substrate were compared to those for ELO devices. ELO LEDs coated with a ZnS/MgF2 antireflection coating exhibited an optical output that was up to six times that of LEDs on GaAs substrates. At the same time, the measured current-voltage characteristics of the ELO devices displayed a lower n=1 current component. ELO LEDs with efficiencies up to 12.5% were realized. We attribute these results to photon recycling enhanced by the back-surface reflector in the ELO LEDs. The luminescence versus current and current versus voltage characteristics of the LEDs were analyzed to obtain the nonradiative minority carrier lifetimes and the photon recycling factors. The results demonstrate that the measured characteristics are well described by photon recycling theory. ELO LEDs may prove useful for characterizing recombination processes in LEDs, and thin-crystalline structures could provide substantial efficiency enhancements for LEDs and solar cells.

  6. High optical bandwidth GaN based photonic-crystal light-emitting diodes

    Science.gov (United States)

    Lin, Tung-Ching; Yin, Yu-Feng; Lan, Wen-Yi; Huang, JianJang

    2016-09-01

    Light emitting diodes (LEDs) for visible light communication (VLC) as radio sources is a solution to channel crowding of radio frequency (RF) signal. However, for the application on high-speed communication, getting higher bandwidth of LEDs is always the problem which is limited by the spontaneous carrier lifetime in the multiple quantum wells. In this paper, we proposed GaN-based LEDs accompanied with photonic crystal (PhC) nanostructure for high speed communication. Using the characteristic of photonic band selection in photonic crystal structure, the guided modes are modulated by RF signal. The PhC can also provide faster mode extraction. From time resolved photoluminescence (TRPL) at room temperature, carrier lifetime of both lower- and higher-order modes is shortened. By observing f-3dB -J curve, it reveals that the bandwidth of PhC LEDs is higher than that of typical LED. The optical - 3-dB bandwidth (f-3dB) can be achieved up to 240 MHz in the PhC LED (PhCLED). We conclude that the higher operation speed can be obtained due to faster radiative carrier recombination of extracted guided modes from the PhC nanostructure.

  7. Efficiency Control in Iridium Complex-Based Phosphorescent Light-Emitting Diodes

    Directory of Open Access Journals (Sweden)

    Boucar Diouf

    2012-01-01

    Full Text Available Key factors to control the efficiency in iridium doped red and green phosphorescent light emitting diodes (PhOLEDs are discussed in this review: exciton confinement, charge trapping, dopant concentration and dopant molecular structure. They are not independent from each other but we attempt to present each of them in a situation where its specific effects are predominant. A good efficiency in PhOLEDs requires the triplet energy of host molecules to be sufficiently high to confine the triplet excitons within the emitting layer (EML. Furthermore, triplet excitons must be retained within the EML and should not drift into the nonradiative levels of the electron or hole transport layer (resp., ETL or HTL; this is achieved by carefully choosing the EML’s adjacent layers. We prove how reducing charge trapping results in higher efficiency in PhOLEDs. We show that there is an ideal concentration for a maximum efficiency of PhOLEDs. Finally, we present the effects of molecular structure on the efficiency of PhOLEDs using red iridium complex dopant with different modifications on the ligand to tune its highest occupied molecular orbital (HOMO and lowest unoccupied molecular orbital (LUMO energies.

  8. Development and evaluation of a light-emitting diode endoscopic light source

    Science.gov (United States)

    Clancy, Neil T.; Li, Rui; Rogers, Kevin; Driscoll, Paul; Excel, Peter; Yandle, Ron; Hanna, George; Copner, Nigel; Elson, Daniel S.

    2012-03-01

    Light-emitting diode (LED) based endoscopic illumination devices have been shown to have several benefits over arclamp systems. LEDs are energy-efficient, small, durable, and inexpensive, however their use in endoscopy has been limited by the difficulty in efficiently coupling enough light into the endoscopic light cable. We have demonstrated a highly homogenised lightpipe LED light source that combines the light from four Luminus LEDs emitting in the red, green, blue and violet using innovative dichroics that maximise light throughput. The light source spectrally combines light from highly divergent incoherent sources that have a Lambertian intensity profile to provide illumination matched to the acceptance numerical aperture of a liquid light guide or fibre bundle. The LED light source was coupled to a standard laparoscope and performance parameters (power, luminance, colour temperature) compared to a xenon lamp. Although the total illuminance from the endoscope was lower, adjustment of the LEDs' relative intensities enabled contrast enhancement in biological tissue imaging. The LED light engine was also evaluated in a minimally invasive surgery (MIS) box trainer and in vivo during a porcine MIS procedure where it was used to generate 'narrowband' images. Future work using the violet LED could enable photodynamic diagnosis of bladder cancer.

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

    Science.gov (United States)

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

    2014-11-01

    We report on the use of nucleic acid bases (NBs) in organic light emitting diodes (OLEDs). NBs are small molecules that are the basic building blocks of the larger DNA polymer. NBs readily thermally evaporate and integrate well into the vacuum deposited OLED fabrication. Adenine (A) and thymine (T) were deposited as electron-blocking/hole-transport layers (EBL/HTL) that resulted in increases in performance over the reference OLED containing the standard EBL material NPB. A-based OLEDs reached a peak current efficiency and luminance performance of 48 cd/A and 93,000 cd/m2, respectively, while T-based OLEDs had a maximum of 76 cd/A and 132,000 cd/m2. By comparison, the reference OLED yielded 37 cd/A and 113,000 cd/m2. The enhanced performance of T-based devices is attributed to a combination of energy levels and structured surface morphology that causes more efficient and controlled hole current transport to the emitting layer.

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

    Science.gov (United States)

    Olusanya, Bolajoko O; Osibanjo, Folashade B; Emokpae, Abieyuwa A; Slusher, Tina M

    2016-10-01

    We set out to determine the rate of decline of irradiance for fluorescent tube (FT) and light-emitting diode (LED) phototherapy devices in resource-limited settings where routine irradiance monitoring is uncommon. Irradiance levels (μW/cm(2)/nm) were measured weekly using BiliBlanket(®) II Meter on three FT-based and two LED-based phototherapy devices over a 19 week period. The two LED devices showed stable irradiance levels and did not require any lamp changes. The three FT-based devices showed rapid decline in irradiance, and all required three complete lamp exchanges approximately every 5-6 weeks. FT-based devices are associated with more rapid decline in irradiance to sub-therapeutic levels and require more frequent lamp changes than LED devices. Clinicians should be alert to the maintenance requirements of the phototherapy devices available in their settings to ensure efficacy of treatment. © The Author [2016]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  11. Review paper: Recent developments in light extraction technologies of organic light emitting diodes

    Science.gov (United States)

    Hong, Kihyon; Lee, Jong-Lam

    2011-06-01

    Organic light emitting diodes (OLEDs) have rapidly progressed in recent years due to their potential applications in flat panel displays and solid-state lighting. In spite of the commercialization of OLEDs, they still have a low out-coupling efficiency of about 20% due to factors such as the total internal reflection, absorption, and surface plasmon coupling. This light out-coupling efficiency is a major limitation on the high efficiency levels of OLEDs. Hence, enhancing the light out-coupling efficiency of OLEDs offers the greatest potential for achieving a substantial increase in the external quantum efficiency and power efficiency of OLEDs. Accordingly, significant advancements in OLEDs have driven the development of light extraction technologies as well as highly transparent conducting electrode materials. Recent efforts to combine light extraction structures with the improved out-coupling efficiency of OLEDs have produced OLEDs with an efficiency level that matches the efficiency of a fluorescent tube (>100 lm/W). This paper reviews the technical issues and recent progress in light extraction technologies and discusses ways of enhancing the out-coupling efficiency of OLEDs.

  12. 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

    2015-12-09

    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 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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Light-emitting-diode induced retinal damage and its wavelength dependency in vivo

    Science.gov (United States)

    Shang, Yu-Man; Wang, Gen-Shuh; Sliney, David H.; Yang, Chang-Hao; Lee, Li-Ling

    2017-01-01

    AIM To examine light-emitting-diode (LED)-induced retinal neuronal cell damage and its wavelength-driven pathogenic mechanisms. METHODS Sprague-Dawley rats were exposed to blue LEDs (460 nm), green LEDs (530 nm), and red LEDs (620 nm). Electroretinography (ERG), Hematoxylin and eosin (H&E) staining, transmission electron microscopy (TEM), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and immunohistochemical (IHC) staining, Western blotting (WB) and the detection of superoxide anion (O2−·), hydrogen peroxide (H2O2), total iron, and ferric (Fe3+) levels were applied. RESULTS ERG results showed the blue LED group induced more functional damage than that of green or red LED groups. H&E staining, TUNEL, IHC, and TEM revealed apoptosis and necrosis of photoreceptors and RPE, which indicated blue LED also induced more photochemical injury. Free radical production and iron-related molecular marker expressions demonstrated that oxidative stress and iron-overload were associated with retinal injury. WB assays correspondingly showed that defense gene expression was up-regulated after the LED light exposure with a wavelength dependency. CONCLUSION The study results indicate that LED blue-light exposure poses a great risk of retinal injury in awake, task-oriented rod-dominant animals. The wavelength-dependent effect should be considered carefully when switching to LED lighting applications. PMID:28251076

  14. Comparative effectiveness of light emitting diodes (LEDs) and Lasers in near infrared photoimmunotherapy

    Science.gov (United States)

    Sato, Kazuhide; Watanabe, Rira; Hanaoka, Hirofumi; Nakajima, Takahito; Choyke, Peter L.; Kobayashi, Hisataka

    2016-01-01

    Near infrared photoimmunotherapy (NIR-PIT) is a new cancer treatment that combines the specificity of antibodies for targeting tumors with the toxicity induced by photosensitizers after exposure to near infrared (NIR) light. Herein we compare two NIR-light sources; light emitting diodes (LEDs) and Lasers, for their effectiveness in NIR-PIT. A photosensitizer, IRDye-700DX, conjugated to panitumumab (pan-IR700), was incubated with EGFR-expressing A431 and MDA-MB-468-luc cells. NIR-light was provided by LEDs or Lasers at the same light dose. Laser-light produced more cytotoxicity and greater reductions in IR700-fluorescence intensity than LED-light. Laser-light also produced more cytotoxicity in vivo in both cell lines. Assessment of super-enhanced permeability and retention (SUPR) effects were stronger with Laser than LED. These results suggest that Laser-light produced significantly more cytotoxic effects compared to LEDs. Although LED is less expensive, Laser-light produces superior results in NIR-PIT. PMID:26885688

  15. Image quality of a novel light-emitting diode (LED)-illuminated colonoscope.

    Science.gov (United States)

    Sasaki, Sho; Nishikawa, Jun; Yanai, Hideo; Nakamura, Munetaka; Nishimura, Junichi; Goto, Atsushi; Kiyotoki, Shu; Saito, Mari; Hamabe, Kouichi; Tanabe, Ryo; Nakamura, Yohei; Tokiyama, Hiroshi; Hashimoto, Shinichi; Okamoto, Takeshi; Higaki, Shingo; Kurai, Satoshi; Ogihara, Hiroyuki; Hamamoto, Yoshihiko; Sakaida, Isao

    2016-10-01

    Light-emitting diodes (LEDs) are used widely for their high luminous efficiency and durability. We developed a novel prototype high definition endoscope with white LEDs and evaluated the image quality it produced against a commercial endoscope with conventional light source. The specifications of both colonoscopes were identical, except for the LED light source at the tip of the prototype. We examined 20 patients with rectal or sigmoid colon lesions and the image quality was evaluated in 40 images (one image from the LED colonoscope and one from the conventional colonoscope for each lesion) by three endoscopists. We additionally evaluated the 17 videos recorded with the LED colonoscope that were available. Image quality, mucosal and vascular color, and luminous distribution and intensity were scored on a 5-point scale. The mean score for vascular color given by one evaluator was significantly higher using the LED colonoscope than using the conventional colonoscope. The mean scores for mucosal color and luminous intensity from another evaluator were significantly lower with the LED colonoscope than with the conventional colonoscope. There were no significant differences in the luminous distribution scores for any of the evaluators. The image quality of the videos was evaluated as being similar with both colonoscopes. Image quality from the LED and conventional colonoscopes were similar, although the luminous intensity of the LEDs is inferior to that of the conventional light source at the present time. © Georg Thieme Verlag KG Stuttgart · New York.

  16. Extremely Vivid, Highly Transparent, and Ultrathin Quantum Dot Light-Emitting Diodes.

    Science.gov (United States)

    Choi, Moon Kee; Yang, Jiwoong; Kim, Dong Chan; Dai, Zhaohe; Kim, Junhee; Seung, Hyojin; Kale, Vinayak S; Sung, Sae Jin; Park, Chong Rae; Lu, Nanshu; Hyeon, Taeghwan; Kim, Dae-Hyeong

    2018-01-01

    Displaying information on transparent screens offers new opportunities in next-generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such "see-through" displays to show vivid images over clear background view. Here transparent quantum dot light-emitting diodes (Tr-QLEDs) are reported with high brightness (bottom: ≈43 000 cd m-2 , top: ≈30 000 cd m-2 , total: ≈73 000 cd m-2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplished by novel electron transport layers (ETLs) and engineered quantum dots (QDs). The ETLs, ZnO nanoparticle assemblies with ultrathin alumina overlayers, dramatically enhance durability of active layers, and balance electron/hole injection into QDs, which prevents nonradiative recombination processes. In addition, the QD structure is further optimized to fully exploit the device architecture. The ultrathin nature of Tr-QLEDs allows their conformal integration on various shaped objects. Finally, the high resolution patterning of red, green, and blue Tr-QLEDs (513 pixels in.-1 ) shows the potential of the full-color transparent display. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Science.gov (United States)

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

    2015-02-04

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

  18. Improving lumen maintenance by nanopore array dispersed quantum dots for on-chip light emitting diodes

    Science.gov (United States)

    Chen, Quan; Yang, Fan; Wan, Renzhuo; Fang, Dong

    2017-12-01

    The temperature stability of quantum dots (QDs), which is crucial for integrating into high power light-emitting diodes (LEDs) in the on-chip configuration, needs to be further improved. In this letter, we report warm white LEDs, where CdSe/ZnS nanoparticles were incorporated into a porous anodic alumina (PAA) matrix with a chain structure by the self-assembly method. Experiments demonstrate that the QD concentration range in toluene solvent from 1% mg/μl to 1.2% mg/μl in combination with the PAA matrix shows the best luminous property. To verify the reliability of the as-prepared device, a comparison experiment was conducted. It indicates excellent lumen maintenance of the light source and less chromaticity coordinate shift under accelerated life testing conditions. Experiments also prove that optical depreciation was only up to 4.6% of its initial value after the 1500 h aging test at the junction temperature of 76 °C.

  19. Controlling ion motion in polymer light-emitting diodes containing conjugated polyelectrolyte electron injection layers.

    Science.gov (United States)

    Garcia, Andres; Bakus, Ronald C; Zalar, Peter; Hoven, Corey V; Brzezinski, Jacek Z; Nguyen, Thuc-Quyen

    2011-03-02

    The properties and function of an anionic conjugated polyelectrolyte (CPE)-containing ion-conducting polyethylene oxide pendant (PF(PEO)CO(2)Na) as electron injection layers (EILs) in polymer light-emitting diodes (PLEDs) are investigated. A primary goal was to design a CPE structure that would enable acceleration of the device temporal response through facilitation of ion motion. Pristine PLEDs containing PF(PEO)CO(2)Na exhibit luminance response times on the order of tenths of seconds. This delay is attributed to the formation of ordered structures within the CPE film, as observed by atomic force microscopy. Complementary evidence is provided by electron transport measurements. The ordered structures are believed to slow ion migration within the CPE EIL and hence result in a longer temporal response time. It is possible to accelerate the response by a combination of thermal and voltage treatments that "lock" ions within the interfaces adjacent to PF(PEO)CO(2)Na. PLED devices with luminance response times of microseconds, a 10(5) fold enhancement, can therefore be achieved. Faster luminance response time opens up the application of PLEDs with CPE layers in display technologies.

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

    Science.gov (United States)

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

    2016-06-02

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

  1. Effects of white light-emitting diode (LED) exposure on retinal pigment epithelium in vivo.

    Science.gov (United States)

    Jaadane, Imene; Villalpando Rodriguez, Gloria Elisa; Boulenguez, Pierre; Chahory, Sabine; Carré, Samuel; Savoldelli, Michèle; Jonet, Laurent; Behar-Cohen, Francine; Martinsons, Christophe; Torriglia, Alicia

    2017-12-01

    Ageing and alteration of the functions of the retinal pigment epithelium (RPE) are at the origin of lost of vision seen in age-related macular degeneration (AMD). The RPE is known to be vulnerable to high-energy blue light. The white light-emitting diodes (LED) commercially available have relatively high content of blue light, a feature that suggest that they could be deleterious for this retinal cell layer. The aim of our study was to investigate the effects of "white LED" exposure on RPE. For this, commercially available white LEDs were used for exposure experiments on Wistar rats. Immunohistochemical stain on RPE flat mount, transmission electron microscopy and Western blot were used to exam the RPE. LED-induced RPE damage was evaluated by studying oxidative stress, stress response pathways and cell death pathways as well as the integrity of the outer blood-retinal barrier (BRB). We show that white LED light caused structural alterations leading to the disruption of the outer blood-retinal barrier. We observed an increase in oxidized molecules, disturbance of basal autophagy and cell death by necrosis. We conclude that white LEDs induced strong damages in rat RPE characterized by the breakdown of the BRB and the induction of necrotic cell death. © 2017 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.

  2. A facile and high sensitive micro fluorimeter based on light emitting diode and photodiode.

    Science.gov (United States)

    Geng, Xuhui; Gao, Yan; Feng, Chunbo; Guan, Yafeng

    2017-12-01

    A facile and high sensitive micro fluorimeter was developed and evaluated. It employed light emitting diode (LED) as light source, cuvette as detection cell, and photodiode (PD) as optoelectronic detector. Optical and electronic parameters were optimized and demonstrated. A high power LED was chosen, which could irradiate the inner area of the cuvette completely at the same time with divergence angle as small as possible. The optimum LED brought 2.5 times signal-to-noise ratio (SNR) enhancement. Using reflector at the opposite direction of excitation light path doubled SNR. The amplifier circuit of PD was deeply investigated to achieve high sensitivity, low noise, and good stability. The limit of detection (LOD) of fluorescein isothiocyanate (FITC) and chlorophyll at SNR = 3 were 10pM ~ 0.004 ppb and 0.05 ppb, respectively. Basing on the principle structure, a portable fluorimeter for fungimycin detection was developed using a low power UV LED as light source. The LOD for aflatoxin B1 was 0.1 ppb. Copyright © 2017 Elsevier B.V. All rights reserved.

  3. Inhibitory effect of blue light emitting diode on migration and invasion of cancer cells.

    Science.gov (United States)

    Oh, Phil-Sun; Kim, Hyun-Soo; Kim, Eun-Mi; Hwang, Hyosook; Ryu, Hyang Hwa; Lim, SeokTae; Sohn, Myung-Hee; Jeong, Hwan-Jeong

    2017-12-01

    The aim of this study was to determine the effects and molecular mechanism of blue light emitting diode (LED) in tumor cells. A migration and invasion assay for the metastatic behavior of mouse colon cancer CT-26 and human fibrosarcoma HT-1080 cells was performed. Cancer cell migration-related proteins were identified by obtaining a 2-dimensional gel electrophoresis (2-DE) in total cellular protein profile of blue LED-irradiated cancer cells, followed by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis of proteins. Protein levels were examined by immunoblotting. Irradiation with blue LED inhibited CT-26 and HT-1080 cell migration and invasion. The anti-metastatic effects of blue LED irradiation were associated with inhibition of matrix metalloproteinase (MMP)-2 and MMP-9 expression. P38 MAPK phosphorylation was increased in blue LED-irradiated CT-26 and HT-1080 cells, but was inhibited after pretreatment with SB203580, a specific inhibitor of p38 MAPK. Inhibition of p38 MAPK phosphorylation by SB203580 treatment increased number of migratory cancer cells in CT-26 and HT-1080 cells, indicating that blue LED irradiation inhibited cancer cell migration via phosphorylation of p38 MAPK. Additionally blue LED irradiation of mice injected with CT-26 cells expressing luciferase decreased early stage lung metastasis compared to untreated control mice. These results indicate that blue LED irradiation inhibits cancer cell migration and invasion in vitro and in vivo. © 2017 Wiley Periodicals, Inc.

  4. Tuning the white light spectrum of light emitting diode lamps to reduce attraction of nocturnal arthropods.

    Science.gov (United States)

    Longcore, Travis; Aldern, Hannah L; Eggers, John F; Flores, Steve; Franco, Lesly; Hirshfield-Yamanishi, Eric; Petrinec, Laina N; Yan, Wilson A; Barroso, André M

    2015-05-05

    Artificial lighting allows humans to be active at night, but has many unintended consequences, including interference with ecological processes, disruption of circadian rhythms and increased exposure to insect vectors of diseases. Although ultraviolet and blue light are usually most attractive to arthropods, degree of attraction varies among orders. With a focus on future indoor lighting applications, we manipulated the spectrum of white lamps to investigate the influence of spectral composition on number of arthropods attracted. We compared numbers of arthropods captured at three customizable light-emitting diode (LED) lamps (3510, 2704 and 2728 K), two commercial LED lamps (2700 K), two commercial compact fluorescent lamps (CFLs; 2700 K) and a control. We configured the three custom LEDs to minimize invertebrate attraction based on published attraction curves for honeybees and moths. Lamps were placed with pan traps at an urban and two rural study sites in Los Angeles, California. For all invertebrate orders combined, our custom LED configurations were less attractive than the commercial LED lamps or CFLs of similar colour temperatures. Thus, adjusting spectral composition of white light to minimize attracting nocturnal arthropods is feasible; not all lights with the same colour temperature are equally attractive to arthropods. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

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

    Science.gov (United States)

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

    2018-01-01

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

  6. High Performance Metal Halide Perovskite Light-Emitting Diode: From Material Design to Device Optimization.

    Science.gov (United States)

    Shan, Qingsong; Song, Jizhong; Zou, Yousheng; Li, Jianhai; Xu, Leimeng; Xue, Jie; Dong, Yuhui; Han, Boning; Chen, Jiawei; Zeng, Haibo

    2017-12-01

    Metal halide perovskites have drawn significant interest in the past decade. Superior optoelectronic properties, such as a narrow bandwidth, precise and facile tunable luminance over the entire visible spectrum, and high photoluminescence quantum yield of up to ≈100%, render metal halide perovskites suitable for next-generation high-definition displays and healthy lighting systems. The external quantum efficiency of perovskite light-emitting diodes (LEDs) increases from 0.1 to 11.7% in three years; however, the energy conversion efficiency and the long-term stability of perovskite LEDs are inadequate for practical application. Strategies to optimize the emitting layer and the device structure, with respect to material design, synthesis, surface passivation, and device optimization, are reviewed and highlighted. The long-term stability of perovskite LEDs is evaluated as well. Meanwhile, several challenges and prospects for future development of perovskite materials and LEDs are identified. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Optoelectronic properties of a novel fluorene derivative for organic light-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Junsheng; Lou, Shuangling; Qian, Jincheng; Jiang, Yadong [University of Electronic Science and Technology of China (UESTC), State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, Chengdu (China); Zhang, Qing [Shanghai Jiaotong University, Department of Polymer Science, School of Chemistry and Chemical Technology, Shanghai (China)

    2009-03-15

    We report the optoelectronic properties of a novel fluorene derivative of 6,6'-(9H-fluoren-9,9-diyl)bis(2,3-bis (9,9-dihexyl-9H-fluoren-2-yl)quinoxaline) (BFLBBFLYQ) used for organic light-emitting diode. UV-Vis absorption, photoluminescence (PL) and electroluminescence (EL) spectra of BFLBBFLYQ and the blend doped with N,N'-biphenyl-N,N'-bis-(3-methylphenyl)-1,1'-biphenyl-4,4'-di- amine (TPD) in solid state and in solution were investigated. The results showed that BFLBBFLYQ had a PL peak at 451 nm in solid and solution states and an EL peak at 483 nm with a broad emission band, resulting from fluorenone defects. Exciplex emission was observed in BFLBBFLYQ-TPD blend solid state with a green emission peaking at 530 nm. Also the blend in solution showed solvatochromism in polarity solvent upon UV irradiation. A new absorption band appeared at around 470 nm of BFLBBFLYQ-TPD blend in chloroform solution, and disappeared when diluted in absorption spectrum. Meanwhile, a low energy emission band from 530 to 580 nm appeared and increased with material concentration and UV irradiation time. (orig.)

  8. Deep blue phosphorescent organic light-emitting diodes with very high brightness and efficiency.

    Science.gov (United States)

    Lee, Jaesang; Chen, Hsiao-Fan; Batagoda, Thilini; Coburn, Caleb; Djurovich, Peter I; Thompson, Mark E; Forrest, Stephen R

    2016-01-01

    The combination of both very high brightness and deep blue emission from phosphorescent organic light-emitting diodes (PHOLED) is required for both display and lighting applications, yet so far has not been reported. A source of this difficulty is the absence of electron/exciton blocking layers (EBL) that are compatible with the high triplet energy of the deep blue dopant and the high frontier orbital energies of hosts needed to transport charge. Here, we show that N-heterocyclic carbene (NHC) Ir(III) complexes can serve as both deep blue emitters and efficient hole-conducting EBLs. The NHC EBLs enable very high brightness (>7,800 cd m(-2)) operation, while achieving deep blue emission with colour coordinates of [0.16, 0.09], suitable for most demanding display applications. We find that both the facial and the meridional isomers of the dopant have high efficiencies that arise from the unusual properties of the NHC ligand-that is, the complexes possess a strong metal-ligand bond that destabilizes the non-radiative metal-centred ligand-field states. Our results represent an advance in blue-emitting PHOLED architectures and materials combinations that meet the requirements of many critical illumination applications.

  9. Solid State pH Sensor Based on Light Emitting Diodes (LED As Detector Platform

    Directory of Open Access Journals (Sweden)

    Dermot Diamond

    2006-08-01

    Full Text Available A low-power, high sensitivity, very low-cost light emitting diode (LED-baseddevice developed for low-cost sensor networks was modified with bromocresol greenmembrane to work as a solid-state pH sensor. In this approach, a reverse-biased LEDfunctioning as a photodiode is coupled with a second LED configured in conventionalemission mode. A simple timer circuit measures how long (in microsecond it takes for thephotocurrent generated on the detector LED to discharge its capacitance from logic 1 ( 5 Vto logic 0 ( 1.7 V. The entire instrument provides an inherently digital output of lightintensity measurements for a few cents. A light dependent resistor (LDR modified withsimilar sensor membrane was also used as a comparison method. Both the LED sensor andthe LDR sensor responded to various pH buffer solutions in a similar way to obtainsigmoidal curves expected of the dye. The pKa value obtained for the sensors was found toagree with the literature value.

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

    Science.gov (United States)

    Li, Ying-Chang; Chang, Liann-Be; Chen, Hou-Jen; Yen, Chia-Yi; Pan, Ke-Wei; Huang, Bohr-Ran; Kuo, Wen-Yu; Chow, Lee; Zhou, Dan; Popko, Ewa

    2017-01-01

    Monolithic phosphor-free two-color gallium nitride (GaN)-based white light emitting diodes (LED) have the potential to replace current phosphor-based GaN white LEDs due to their low cost and long life cycle. Unfortunately, the growth of high indium content indium gallium nitride (InGaN)/GaN quantum dot and reported LED’s color rendering index (CRI) are still problematic. Here, we use flip-chip technology to fabricate an upside down monolithic two-color phosphor-free LED with four grown layers of high indium quantum dots on top of the three grown layers of lower indium quantum wells separated by a GaN tunneling barrier layer. The photoluminescence (PL) and electroluminescence (EL) spectra of this white LED reveal a broad spectrum ranging from 475 to 675 nm which is close to an ideal white-light source. The corresponding color temperature and color rendering index (CRI) of the fabricated white LED, operated at 350, 500, and 750 mA, are comparable to that of the conventional phosphor-based LEDs. Insights of the epitaxial structure and the transport mechanism were revealed through the TEM and temperature dependent PL and EL measurements. Our results show true potential in the Epi-ready GaN white LEDs for future solid state lighting applications. PMID:28772792

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

    Directory of Open Access Journals (Sweden)

    Ying-Chang Li

    2017-04-01

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

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

    Science.gov (United States)

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

    2018-02-01

    Four configurations of buffer layers were inserted into the structure of a white organic light emitting diode, and their impacts on the hole tunneling-injection and exciton diffusion processes were investigated. The insertion of a single buffer layer of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) resulted in a balanced carrier concentration and excellent color stability with insignificant chromaticity coordinate variations of Δ x < 0.023 and Δ y < 0.023. A device with a 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) buffer layer was beneficial for hole tunneling to the emission layer, resulting in a 1.45-fold increase in current density. The tunneling of holes and the diffusion of excitons were confirmed by the preparation of a dual buffer layer of CBP:tris-(phenylpyridine)-iridine (Ir(ppy)3)/BCP. A maximum current efficiency of 12.61 cd/A with a luminance of 13,850 cd/m2 was obtained at 8 V when a device with a dual-buffer layer of CBP:6 wt.% Ir(ppy)3/BCP was prepared.

  13. High performance near-ultraviolet flip-chip light-emitting diodes with distributed Bragg reflector

    Science.gov (United States)

    Choi, Il-Gyun; Jin, Geun-Mo; Park, Jun-Cheon; Jeon, Soo-Kun; Park, Eun-Hyun

    2015-09-01

    We have fabricated the near-ultraviolet (NUV) flip-chip (FC) light-emitting diodes (LEDs) with the high external quantum efficiency (EQE) using distributed Bragg reflectors (DBRs) and compared with conventional FC-LED using silver (Ag) reflector. Reflectance of Ag is very high (90 ~ 95 %) at visible spectrum region, but sharply decrease at NUV region. Therefore we used DBR composed of two different materials which have high-index contrast, such as TiO2 and SiO2. However, to achieve high-performance NUV flip-chip LEDs, we used Ta2O5 instead of TiO2 that absorbs lights of NUV region. Thus, we have designed a DBR composed of twenty pairs of Ta2O5 and SiO2 using optical coating design software. The DBR designed by our group achieves a reflectance of ~99 % in the NUV region (350 ~ 500 nm), which is much better than Ag reflector. Optical power is higher than the Ag-LED up to 22 % @ 390 nm.

  14. Exciplex-Forming Cohost for High Efficiency and High Stability Phosphorescent Organic Light-Emitting Diodes.

    Science.gov (United States)

    Shih, Chun-Jen; Lee, Chih-Chien; Chen, Ying-Hao; Biring, Sajal; Kumar, Gautham; Yeh, Tzu-Hung; Sen, Somaditya; Liu, Shun-Wei; Wong, Ken-Tsung

    2018-01-17

    An exciplex forming cohost system is employed to achieve a highly efficient organic light-emitting diode (OLED) with good electroluminescent lifetime. The exciplex is formed at the interfacial contact of a conventional star-shaped carbazole hole-transporting material, 4,4',4″-tris(N-carbazolyl)-triphenylamine (TCTA), and a triazine electron-transporting material, 2,4,6-tris[3-(1H-pyrazol-1-yl)phenyl]-1,3,5-triazine (3P-T2T). The excellent combination of TCTA and 3P-T2T is applied as the cohost of a common green phosphorescent emitter with almost zero energy loss. When Ir(ppy)2(acac) is dispersed in such exciplex cohost system, OLED device with maximum external quantum efficiency of 29.6%, the ultrahigh power efficiency of 147.3 lm/W, and current efficiency of 107 cd/A were successfully achieved. More importantly, the OLED device showed a low-efficiency roll-off and an operational lifetime (τ80) of ∼1020 min with the initial brightness of 2000 cd/m2, which is 56 times longer than the reference device. The significant difference of device stability was attributed to the degradation of exciplex system for energy transfer process, which was investigated by the photoluminescence aging measurement at room temperature and 100 K, respectively.

  15. Recent advances in the science and engineering of organic light-emitting diodes (Conference Presentation)

    Science.gov (United States)

    Kippelen, Bernard; Gaj, Michael P.; Zhang, Xiaoqing; Choi, Sangmoo; Fuentes-Hernandez, Canek; Zhang, Yadong; Barlow, Stephen; Marder, Seth R.; Voit, Walter E.; Wei, Andrew

    2016-09-01

    In this talk, we will discuss recent advances in the science and engineering of organic light-emitting diodes (OLEDs). First, we will focus on materials in which light emission involves the process of thermally activated delayed fluorescence (TADF). In these materials, triplet excited states can convert into optically emissive singlet excited states by reverse intersystem crossing, allowing for nearly 100% internal quantum efficiency. This process can be used to design a new class of materials that are all organic, offering a lower cost alternative to conventional electrophosphorescent materials that contain heavy and expensive elements such as Pt and Ir. We will discuss molecular design strategies and present examples of materials that can be used as emitters or hosts in the emissive layer. In a second part of this talk, we will review recent progress in fabricating OLEDs on shape memory polymer substrates (SMPs). SMPs are mechanically active, smart materials that can exhibit a significant drop in modulus once an external stimulus such as temperature is applied. In their rubbery state upon heating, the SMP can be easily deformed by external stresses into a temporary geometric configuration that can be retained even after the stress is removed by cooling the SMP to below the glass transition temperature. Reheating the SMP causes strain relaxation within the polymer network and induces recovery of its original shape. We will discuss how these unique mechanical properties can also be extended to a new class of OLEDs.

  16. Sliding Mode Pulsed Averaging IC Drivers for High Brightness Light Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Dr. Anatoly Shteynberg, PhD

    2006-08-17

    This project developed new Light Emitting Diode (LED) driver ICs associated with specific (uniquely operated) switching power supplies that optimize performance for High Brightness LEDs (HB-LEDs). The drivers utilize a digital control core with a newly developed nonlinear, hysteretic/sliding mode controller with mixed-signal processing. The drivers are flexible enough to allow both traditional microprocessor interface as well as other options such as “on the fly” adjustment of color and brightness. Some other unique features of the newly developed drivers include • AC Power Factor Correction; • High power efficiency; • Substantially fewer external components should be required, leading to substantial reduction of Bill of Materials (BOM). Thus, the LED drivers developed in this research : optimize LED performance by increasing power efficiency and power factor. Perhaps more remarkably, the LED drivers provide this improved performance at substantially reduced costs compared to the present LED power electronic driver circuits. Since one of the barriers to market penetration for HB-LEDs (in particular “white” light LEDs) is cost/lumen, this research makes important contributions in helping the advancement of SSL consumer acceptance and usage.

  17. Modeling of light-emitting diode wavefronts for the optimization of transmission holograms.

    Science.gov (United States)

    Karthaus, Daniela; Giehl, Markus; Sandfuchs, Oliver; Sinzinger, Stefan

    2017-06-20

    The objective of applying transmission holograms in automotive headlamp systems requires the adaptation of holograms to divergent and polychromatic light sources like light-emitting diodes (LEDs). In this paper, four different options to describe the scalar light waves emitted by a typical automotive LED are regarded. This includes a new approach to determine the LED's wavefront from interferometric measurements. Computer-generated holograms are designed considering the different LED approximations and recorded into a photopolymer. The holograms are reconstructed with the LED and the resulting images are analyzed to evaluate the quality of the wave descriptions. In this paper, we show that our presented new approach leads to better results in comparison to other wave descriptions. The enhancement is evaluated by the correlation between reconstructed and ideal images. In contrast to the next best approximation, a spherical wave, the correlation coefficient increased by 0.18% at 532 nm, 1.69% at 590 nm, and 0.75% at 620 nm.

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

    Science.gov (United States)

    Gan, Ruting; Guo, Zhenning; Lin, Jieben

    2015-09-01

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

  19. Susceptibility of planktonic cultures of Streptococcus mutans to photodynamic therapy with a light-emitting diode

    Directory of Open Access Journals (Sweden)

    Anna Carolina Borges Pereira a Costa

    2010-12-01

    Full Text Available The objective of this study was to evaluate the effect of photodynamic therapy with erythrosine and rose bengal using a light-emitting diode (LED on planktonic cultures of S. mutans. Ten S. mutans strains, including nine clinical strains and one reference strain (ATCC 35688, were used. Suspensions containing 10(6 cells/mL were prepared for each strain and were tested under different experimental conditions: a LED irradiation in the presence of rose bengal as a photosensitizer (RB+L+; b LED irradiation in the presence of erythrosine as a photosensitizer (E+L+; c LED irradiation only (P-L+; d treatment with rose bengal only (RB+L-; e treatment with erythrosine only (E+L-; and f no LED irradiation or photosensitizer treatment, which served as a control group (P-L-. After treatment, the strains were seeded onto BHI agar for determination of the number of colony-forming units (CFU/mL. The results were submitted to analysis of variance and the Tukey test (p < 0.05. The number of CFU/mL was significantly lower in the groups submitted to photodynamic therapy (RB+L+ and E+L+ compared to control (P-L-, with a reduction of 6.86 log10 in the RB+L+ group and of 5.16 log10 in the E+L+ group. Photodynamic therapy with rose bengal and erythrosine exerted an antimicrobial effect on all S. mutans strains studied.

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

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Peng [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 (China); Bai, Xue, E-mail: baix@jlu.edu.cn, E-mail: yuzhang@jlu.edu.cn; Sun, Chun; Zhang, Xiaoyu; Zhang, Yu, E-mail: baix@jlu.edu.cn, E-mail: yuzhang@jlu.edu.cn [State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Zhang, Tieqiang [State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 (China)

    2016-08-08

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

  1. Structural design and optimization of near-ultraviolet light-emitting diodes with wide wells

    Energy Technology Data Exchange (ETDEWEB)

    Kuo, Yen-Kuang, E-mail: ykuo@cc.ncue.edu.tw [Department of Physics, National Changhua University of Education, Changhua 500, Taiwan (China); Chen, Fang-Ming [Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan (China); Chang, Jih-Yuan [Center for Teacher Education, National Changhua University of Education, Changhua 500, Taiwan (China); Shih, Ya-Hsuan [Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan (China)

    2016-03-07

    The characteristics of the near-ultraviolet (NUV) light-emitting diodes (LEDs) with wide (14-nm-thick) and narrow (2-nm-thick) wells under the situations of different numbers of wells and degree of polarization are systematically investigated. The simulation results show that the Auger recombination can be efficiently suppressed with the increase of number of wells in NUV LEDs. For the LEDs with wide wells, the quantum-confined Stark effect and Shockley–Read–Hall recombination play an important role when the number of wells increases, especially when the LED is under low current injection or high degree of polarization. In order to take the advantage of using wide wells, it is proposed that the quaternary Al{sub 0.1}In{sub 0.05}Ga{sub 0.85}N barriers be used in wide-well NUV LEDs along with the use of Al{sub 0.3}Ga{sub 0.7}N/Al{sub 0.1}Ga{sub 0.9}N superlattice electron-blocking layer to mitigate the polarization effect and electron overflow. With this band-engineering structural design, the optical performance of the wide-well NUV LEDs is much better than its thin-well counterpart even under the situation of high degree of polarization.

  2. Perovskite Quantum Dots and Their Application in Light-Emitting Diodes.

    Science.gov (United States)

    Wang, Hung-Chia; Bao, Zhen; Tsai, Hsin-Yu; Tang, An-Cih; Liu, Ru-Shi

    2018-01-01

    Perovskite quantum dots (PQDs) attract significant interest in recent years because of their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence quantum efficiency (PLQY). Recent studies report new types of formamidinium (FA) PbBr3 PQDs, PQDs with organic-inorganic mixed cations, divalent cation doped colloidal CsPb1-x Mx Br3 PQDs (M = Sn2+ , Cd2+ , Zn2+ , Mn2+ ) featuring partial cation exchange, and heterovalent cation doped into PQDs (Bi3+ ). These PQD analogs open new possibilities for optoelectronic devices. For commercial applications in lighting and backlight displays, stability of PQDs requires further improvement to prevent their degradation by temperature, oxygen, moisture, and light. Oxygen and moisture-facilitated ion migration may easily etch unstable PQDs. Easy ion migration may result in crystal growth, which lowers PLQY of PQDs. Surface coating and treatment are important procedures for overcoming such factors. In this study, new types of PQDs and a strategy of improving their stabilities are introduced. Finally, this paper discusses future applications of PQDs in light-emitting diodes. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Sugarcane micropropagation using light emitting diodes and adjustment in growth-medium sucrose concentration

    Directory of Open Access Journals (Sweden)

    Paulo Sérgio Gomes da Rocha

    2013-07-01

    Full Text Available The aim of this research was to evaluate the use of light emitting diodes (LEDs instead of white fluorescent lamps as light source and adequate growth-medium sucrose concentration for sugarcane micropropagation (Saccharum officinarum L.. Sugarcane (RB 872552 variety bud explants were evaluated during the multiplication and rooting phases under controlled growth-room conditions. Different light sources (blue, red and green LEDs; Growlux and white fluorescent lamps and different medium sucrose concentrations (0; 15; 30 and 45g L-1 were used, maintaining constant light intensity (20µmol m-2 s-1, photoperiod (16h and temperature (25+2°C. The experiment was a completely randomized design, and treatments were arranged in a 5x4 factorial (five light sources and four medium sucrose concentrations with six replications. Sugarcane bud growth was satisfactory under the three LED types studied. The presence of sucrose in growth media was essential for bud multiplication and rooting. Nevertheless, each light source requires the respective medium sucrose concentration adjustment for best results. Red LEDs provided a significantly high multiplication rate (although not the highest with 8.5 buds per sub-culture and 34.9g L-1 of sucrose; also, the highest bud length (33.3mm and the best plantlet acclimatization. Therefore, LED sources can advantageously substitute fluorescent lamps in laboratories of sugarcane micropropagation.

  4. Light-emitting diodes: whether an efficient source of light for indoor plants?

    Science.gov (United States)

    Rehman, Muzammal; Ullah, Sana; Bao, Yaning; Wang, Bo; Peng, Dingxiang; Liu, Lijun

    2017-11-01

    Availability of sufficient light for growth optimization of plants in greenhouse environment during winter is a major challenge, as light during winter is significantly lower than that in the summer. The most commonly used artificial light sources (e.g., metal halide lamps, high pressure sodium lamps, and high fluorescent lamps) are of low quality and inefficient. Therefore, better options should be developed for sustaining agricultural food production during low levels of solar radiation. In recent advances, light-emitting diodes (LEDs) have remarkable potential as supplemental source of light for promoting plant growth. LEDs are novel and versatile source of light with cool emitting surface, wavelength specificity, and low electric power requirement. In the present study, we provided a contemporary synthesis of existing evidence along with our hypothetical concepts to clarify how LED approach could be an efficient and cost-effective source of light for plant growth and development especially in closed production system. In comparative analysis of common artificial vs. LED lighting, we revealed that spectral quality of LEDs can have vivid effects on plant morphogenesis and anatomy. We also discussed the influence of different colors of LEDs on growth performance of plants and provided the cost benefit analysis of using LEDs compared with other traditional sources. Overall, we hope that this article will be of great worth in future due to its practical implications as well as research directions.

  5. Methylene blue is a good background stain for tuberculosis light-emitting diode fluorescence microscopy.

    Science.gov (United States)

    Van Deun, A; Aung, K J M; Hamid Salim, A; Gumusboga, M; Nandi, P; Hossain, Md A

    2010-12-01

    Damien Foundation Bangladesh tuberculosis (TB) control projects. To compare blue ink, potassium permanganate and methylene blue background staining for transmitted light-emitting diode (LED) TB fluorescence microscopy (FM). Auramine smears made in triplicate from Ziehl-Neelsen (ZN) acid-fast bacilli (AFB) positive or negative sputum and stained with one of the background variations were read blind by LED FM. Reference laboratory rechecking of discordant series was used before and after auramine restaining as the gold standard. Of 1977 series evaluated, 991 (50.1%) were made from ZN-positive specimens. There were 919, 942 and 958 FM true-positives with blue ink, permanganate and methylene blue counterstaining, against respectively 12, 12 and 16 false-positives. Methylene blue counterstaining was more sensitive (95.6%, 95%CI 94.2-96.8) than blue ink or permanganate (92.7%, 95%CI 90.9-94.3 and 93.6%, 95%CI 91.9-95.0; respectively P < 0.01 and < 0.05). No AFB could be found in 85% and 18% of 180 discordant series without and with restaining. Methylene blue is at least equivalent to potassium permanganate counterstaining for FM using blue LED transmitted excitation and is cheaper than blue ink. Restaining of all smears prior to first re-reading may be unavoidable for blinded rechecking of auramine-stained smears for external quality assessment.

  6. Fully transparent quantum dot light-emitting diode integrated with graphene anode and cathode.

    Science.gov (United States)

    Seo, Jung-Tak; Han, Junebeom; Lim, Taekyung; Lee, Ki-Heon; Hwang, Jungseek; Yang, Heesun; Ju, Sanghyun

    2014-12-23

    A fully transparent quantum dot light-emitting diode (QD-LED) was fabricated by incorporating two types (anode and cathode) of graphene-based electrodes, which were controlled in their work functions and sheet resistances. Either gold nanoparticles or silver nanowires were inserted between layers of graphene to control the work function, whereas the sheet resistance was determined by the number of graphene layers. The inserted gold nanoparticles or silver nanowires in graphene films caused a charge transfer and changed the work function to 4.9 and 4.3 eV, respectively, from the original work function (4.5 eV) of pristine graphene. Moreover the sheet resistance values for the anode and cathode electrodes were improved from ∼63,000 to ∼110 Ω/sq and from ∼100,000 to ∼741 Ω/sq as the number of graphene layers increased from 1 to 12 and from 1 to 8, respectively. The main peak wavelength, luminance, current efficiency, and optical transmittance of the fully transparent QD-LED integrated with graphene anode and cathode were 535 nm, ∼358 cd/m2, ∼0.45 cd/A, and 70-80%, respectively. The findings of the study are expected to lay a foundation for the production of high-efficiency, fully transparent, and flexible displays using graphene-based electrodes.

  7. Blinded rechecking of acid-fast bacilli smears by light-emitting diode microscopy.

    Science.gov (United States)

    Radhakrishnan, R; Prabuseenivasan, S; Balaji, S; Sankar, U; Thomas, A; Kumar, V; Selvakumar, N

    2013-09-01

    Blinded rechecking of auramine-stained acid-fast bacilli (AFB) sputum smears using fluorescence microscopy (FM), especially FM using light-emitting diode (LED), is not well understood. To examine the rechecking of auramine-stained sputum smears without restaining within a month using LED FM. A total of 4799 centrifuged smears of sputum samples were stained by the auramine phenol method and examined using LED FM; 564 systematically selected smears were subjected to blinded rechecking without restaining by controllers. The initial results of the readers were compared to those of the controllers. Discrepancies were resolved by a referee. The quality of LED FM was assessed by the referee using the culture result as gold standard. Among the rechecked smears, one high false-negative error was made by a reader, while one high false-positive error and 19 high false-negative errors were made by the controllers. The errors were resolved by culture. Smear results for 18 slides were not available due to AFB fading. AFB colour fading using LED FM, which affected the accurate evaluation of blinded rechecking of AFB smears without restaining within a month, is confirmed in this large study.

  8. Hybrid metal grid-polymer-carbon nanotube electrodes for high luminance organic light emitting diodes

    Science.gov (United States)

    Sam, F. Laurent M.; Dabera, G. Dinesha M. R.; Lai, Khue T.; Mills, Christopher A.; Rozanski, Lynn J.; Silva, S. Ravi P.

    2014-08-01

    Organic light emitting diodes (OLEDs) incorporating grid transparent conducting electrodes (TCEs) with wide grid line spacing suffer from an inability to transfer charge carriers across the gaps in the grids to promote light emission in these areas. High luminance OLEDs fabricated using a hybrid TCE composed of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS PH1000) or regioregular poly(3-hexylthiophene)-wrapped semiconducting single-walled carbon nanotubes (rrP3HT-SWCNT) in combination with a nanometre thin gold grid are reported here. OLEDs fabricated using the hybrid gold grid/PH1000 TCE have a luminance of 18 000 cd m-2 at 9 V; the same as the reference indium tin oxide (ITO) OLED. The gold grid/rrP3HT-SWCNT OLEDs have a lower luminance of 8260 cd m-2 at 9 V, which is likely due to a rougher rrP3HT-SWCNT surface. These results demonstrate that the hybrid gold grid/PH1000 TCE is a promising replacement for ITO in future plastic electronics applications including OLEDs and organic photovoltaics. For applications where surface roughness is not critical, e.g. electrochromic devices or discharge of static electricity, the gold grid/rrP3HT-SWCNT hybrid TCE can be employed.

  9. Surface-Passivated AlGaN Nanowires for Enhanced Luminescence of Ultraviolet Light Emitting Diodes

    KAUST Repository

    Sun, Haiding

    2017-12-19

    Spontaneously-grown, self-aligned AlGaN nanowire ultraviolet light emitting diodes still suffer from low efficiency partially because of the strong surface recombination caused by surface states, i.e., oxidized surface and high density surface states. Several surface passivation methods have been introduced to reduce surface non-radiative recombination by using complex and toxic chemicals. Here, we present an effective method to suppress such undesirable surface recombination of the AlGaN nanowires via diluted potassium hydroxide (KOH) solution; a commonly used chemical process in semiconductor fabrication which is barely used as surface passivation solution in self-assembled nitride-based nanowires. The transmission electron microscopy investigation on the samples reveals almost intact nanowire structures after the passivation process. We demonstrated an approximately 49.7% enhancement in the ultraviolet light output power after 30-s KOH treatment on AlGaN nanowires grown on titanium-coated silicon substrates. We attribute such a remarkable enhancement to the removal of the surface dangling bonds and oxidized nitrides (Ga-O or Al-O bonds) at the surface as we observe the change of the carrier lifetime before and after the passivation. Thus, our results highlight the possibility of employing this process for the realization of high performance nanowire UV emitters.

  10. Reflectance bandwidth and efficiency improvement of light-emitting diodes with double-distributed Bragg reflector.

    Science.gov (United States)

    Ding, Xinghuo; Gui, Chengqun; Hu, Hongpo; Liu, Mengling; Liu, Xingtong; Lv, Jiajiang; Zhou, Shengjun

    2017-05-20

    Distributed Bragg reflectors (DBR) with metal film on the bottom have been demonstrated to further improve the light output power of GaN-based light-emitting diodes (LEDs). Periods of TiO2/SiO2 stacks, thickness of metal film, and material of metallic reflector were designed and optimized in simulation software. The maximal bandwidth of double-DBR stacks have reached up to 272 nm, which was 102 nm higher than a single-DBR stack. The average reflectance of LEDs with wavelength from 380 nm to 780 nm in double-DBR stacks is 95.09% at normal incident, which was much higher than that of a single-DBR stack whose average reflectance was 91.38%. Meanwhile, maximal average reflectance of LEDs for double-DBR stacks with an incident angle from 0 to 90° was 97.41%, which was 3.2% higher than that of a single-DBR stack with maximal average reflectance of 94.21%. The light output power of an LED with double-DBR stacks is 3% higher than that of an LED with a single-DBR stack, which was attributed to high reflectance of double-DBR stacks.

  11. Comparison of light emitting diodes and semiconductor laser inducing photodynamic therapy of cancer cells in vitro

    Science.gov (United States)

    Macecek, Jaroslav; Kolarova, Hana; Bajgar, Robert; Strnad, Miroslav

    2007-03-01

    The goal of anticancer therapy is achievement of balance between destruction of tumour cells and tissues and conservation of physiological functions of noncancer cells. Photodynamic therapy (PDT) is one of novel alternative treatment modality of malignant neoplasms. This method is based on cytotoxic action of excited sensitizers in the oxygen-rich environment. Sensitizers bound to cells and are excited by light source identical to absorption maximum of sensitizer. Photodynamic reactions lead to production of reactive oxygen species (ROS), which cause necrosis or apoptosis of cancer cells. The objective of our work was to analyse of phototoxicity in the sense of DNA damage in cancer cells after PDT by single cell gell electrophoresis (SCGE, comet assay) using ZnTPPS4 (zinc(II)-5,10,15,20-tetrakis(4-sulphonatophenyl) porphyrine and disulfonated chloraluminium phthalocyanine ClAlPcS II as sensitizers. Violet light emitting diodes (LEDs; 1.5 mJ.cm -2.s -1; 418 nm) and semiconductor laser (50mW; 675 nm) were used as sources of radiation. Level of DNA fragmentation was detected after application of different light doses.

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

    Directory of Open Access Journals (Sweden)

    Dai Geon Yoon

    2018-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Shun-Wei Liu

    2014-01-01

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

  14. 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.

  15. Direct measurement of internal quantum efficiency in light emitting diodes under electrical injection

    Science.gov (United States)

    Matioli, Elison; Weisbuch, Claude

    2011-04-01

    A method is presented for the direct measurement of the internal quantum efficiency in light emitting diodes (LEDs), based on the ratio of the measured external quantum efficiency and the calculated light extraction efficiency. The external quantum efficiency is measured from a single facet of the device in a simple, well-defined geometry, for which the light extraction efficiency can be calculated with good accuracy. In the proposed method, all LED facets are coated with highly absorbing material which suppresses any light that is not directly emitted into a small aperture on the top facet of the LED. We present a full wave optical model for a multilayer LED structure, from which we derive and validate an approximate model to easily calculate the extraction efficiency through the top facet of the LED. Because a current spreading electrode, often metallic, is required for uniform injection, we show that its impact on the extraction efficiency can be simply modeled through a separate transmission function calculated from the complex index of refraction of the electrode material. The various assumptions made to justify the direct emission model through a single facet (absence of photon backscatter, no photon recycling, simplified device layer model) are discussed and evaluated. The model is applied to a specific GaN LED structure.

  16. Accurate measurement and influence on device reliability of defect density of a light-emitting diode

    Science.gov (United States)

    Guo, Zu-Qiang; Qian, Ke-Yuan

    2013-10-01

    A method of accurately measuring the defect density of a high-power light-emitting diode (LED) is proposed. The method is based on measuring the number of emitting photons in the magnitude of 105 under the injection current as weak as nA and calculating the non-radiative recombination coefficient which is related to defect density. Defect density is obtained with the self-developed measurement system, and it is demonstrated that defect density has an important influence on LED optical properties like luminous flux and internal quantum efficiency (IQE). At the same time, a batch of GaN-based LEDs with the chip size of 1 mm × 1 mm are selected to conduct the accelerated aging tests lasting for 1000 hours. The results show that defect density exhibits a greater variation and is more sensitive to LED reliability than luminous flux during aging tests. Based on these results, it is concluded that for the GaN-based LED with a chip size of 1mm × 1mm, if its defect density is over 1017/cm3, the LED device performance suffers a serious deterioration, and finally fails.

  17. Flexible Blade-Coated Multicolor Polymer Light-Emitting Diodes for Optoelectronic Sensors.

    Science.gov (United States)

    Han, Donggeon; Khan, Yasser; Ting, Jonathan; King, Simon M; Yaacobi-Gross, Nir; Humphries, Martin J; Newsome, Christopher J; Arias, Ana C

    2017-06-01

    A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light-emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface-energy-patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near-infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Hybrid Perovskite Light-Emitting Diodes Based on Perovskite Nanocrystals with Organic-Inorganic Mixed Cations.

    Science.gov (United States)

    Zhang, Xiaoli; Liu, He; Wang, Weigao; Zhang, Jinbao; Xu, Bing; Karen, Ke Lin; Zheng, Yuanjin; Liu, Sheng; Chen, Shuming; Wang, Kai; Sun, Xiao Wei

    2017-05-01

    Organic-inorganic hybrid perovskite materials with mixed cations have demonstrated tremendous advances in photovoltaics recently, by showing a significant enhancement of power conversion efficiency and improved perovskite stability. Inspired by this development, this study presents the facile synthesis of mixed-cation perovskite nanocrystals based on FA(1-x) 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. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qingyang, E-mail: wqy1527@163.com [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Zhang, Shiming [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Département of Chemical Engineering, École Polytechnique de Montréal, Montréal, Québec, Canada H3C3J7 (Canada); Yue, Shouzhen; Zhang, Zhensong [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Xie, Guohua [Institut für Angewandte Photophysik, Technische Universtität Dresden, Dresden 01062 (Germany); Zhao, Yi; Liu, Shiyong [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China)

    2013-11-15

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

  20. Fiber-coupled light-emitting diode for localized photostimulation of neurons expressing channelrhodopsin-2.

    Science.gov (United States)

    Campagnola, Luke; Wang, Hong; Zylka, Mark J

    2008-03-30

    Channelrhodopsin-2 (ChR2) is a blue-light-gated ion channel that can be used to stimulate genetically defined neurons reproducibly, rapidly and non-invasively. Existing approaches for delivering light to cells expressing ChR2 rely upon microscopes, lasers, arc lamps and shutters, all of which are relatively expensive and are not readily scalable for use on more than one brain region or animal at a time. In this paper, we describe an inexpensive method for delivering blue light locally and with millisecond precision to cells expressing ChR2. We accomplished this by coupling the light from a high-intensity blue light-emitting diode (LED; XLamp XR-E from CREE) into an optical fiber. When positioned in proximity to ChR2-expressing HEK293 cells, this fiber-coupled LED provided localized illumination of up to 32mW/mm2 and generated ChR2 photocurrents as efficiently as wide-field mercury arc lamp illumination. This fiber-coupled LED was also used to photostimulate action potentials in ChR2-expressing dorsal root ganglia (DRG) sensory neurons. LED light power and pulse frequency were controlled with an inexpensive, custom-built amplifier circuit. This scalable fiber-coupled LED system can be used to deliver light independent of the microscope objective and could, in principle, deliver light in parallel to multiple brain regions or to multiple genetically engineered animals.

  1. Role of wide bandgap host in the degradation of blue phosphorescent organic light-emitting diodes

    Science.gov (United States)

    Yang, R. Y.; Li, X. M.; Cao, X. A.

    2017-08-01

    Accelerated reliability tests of blue phosphorescent organic light-emitting diodes (OLEDs) comprising bis[(4,6-difluorophenyl)pyridinato-N,C2](picolinato)-iridium(III) (FIrpic) doped in four different wide bandgap hosts were conducted. The half-life of the OLEDs stressed under a high current density of 100 mA/cm2 varied in a wide range, revealing an important role of the host. Pulsed current stressing with a 1% duty cycle was performed to suppress self-heating, but only extended the lifetime by 2-3.2×. For blue OLEDs with a host favoring hole transport, current stressing caused a shift of the recombination zone toward the anode, turning the emission color to greenish blue. These results suggest that device degradation was mainly caused by charge-trapping defects generated within a narrow zone close to the electron-transport layer. It is expected that the lifetime of blue phosphorescent OLEDs can be effectively extended by selecting an appropriate host which has good stability, enables efficient charge injection and balanced charge transport in the emissive layer.

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

    Directory of Open Access Journals (Sweden)

    Kai Ding

    2017-10-01

    Full Text Available We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV light-emitting diodes (LEDs, with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances in the methods for the growth of bulk single crystal AlN intended as a native substrate together with a discussion of its UV transparency. It should be stated, however, that due to the high-cost of bulk AlN substrates at the time of writing, the growth of DUV LEDs on foreign substrates such as sapphire still dominates the field. On the deposition front, the heteroepitaxial growth approaches incorporate high-temperature metal organic chemical vapor deposition (MOCVD and pulsed-flow growth, a variant of MOCVD, with the overarching goal of enhancing adatom surface mobility, and thus epitaxial lateral overgrowth which culminates in minimization the effect of lattice- and thermal-mismatches. This is followed by addressing the benefits of pseudomorphic growth of strained high Al-molar fraction AlGaN on AlN. Finally, methods utilized to enhance both p- and n-type conductivity of high Al-molar fraction AlGaN are reviewed.

  3. Origin of White Electroluminescence in Graphene Quantum Dots Embedded Host/Guest Polymer Light Emitting Diodes

    Science.gov (United States)

    Kyu Kim, Jung; Bae, Sukang; Yi, Yeonjin; Jin Park, Myung; Jin Kim, Sang; Myoung, NoSoung; Lee, Chang-Lyoul; Hee Hong, Byung; Hyeok Park, Jong

    2015-01-01

    Polymer light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nano-material without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions. PMID:26067060

  4. Efficient phosphorescent polymer light-emitting diodes by suppressing triplet energy back transfer.

    Science.gov (United States)

    Gong, Shaolong; Yang, Chuluo; Qin, Jingui

    2012-07-21

    Phosphorescent polymer light-emitting diodes (PhPLEDs) are promising devices in flat panel displays and solid state lighting sources since they can combine the advantages of the high efficiency of electrophosphorescence and low-cost, large-scale manufacture by using a solution process. However, their efficiencies are generally much lower than those of small-molecule-based devices fabricated by using a thermal deposition approach. One of the major reasons for their low efficiency is that energy is lost by back transfer to a polymer host. This tutorial review gives a brief introduction to the fundamentals of PhPLEDs, and then highlights recent progress in the main approaches to suppress triplet energy back transfer from the phosphor to the polymer host towards realizing highly efficient PhPLEDs. The suppressing mechanisms are discussed, and the achievement of high device efficiencies are demonstrated. Emphasis is placed on the relationships between molecular structure, the extent of suppressing triplet energy back transfer, and device performance.

  5. Efficient green phosphorescent tandem organic light emitting diodes with solution processable mixed hosts charge generating layer

    Energy Technology Data Exchange (ETDEWEB)

    Talik, N.A.; Yeoh, K.H.; Ng, C.Y.B [Low Dimensional Research Center, Department of Physics, University Malaya, 50603 Kuala Lumpur (Malaysia); ItraMAS Corporation. Sdn. Bhd., 542A-B Mukim 1, Lorong Perusahaan Baru 2, Kawasan Perindustrian, Perai 13600, Penang (Malaysia); Yap, B.K. [Center of Microelectronic and Nanotechnology Engineering (CeMNE), College of Engineering, Universiti Tenaga Nasional, Jln. Uniten-Ikram, 4300 Kajang, Selangor (Malaysia); Woon, K.L., E-mail: ph7klw76@um.edu.my [Low Dimensional Research Center, Department of Physics, University Malaya, 50603 Kuala Lumpur (Malaysia)

    2014-10-15

    A novel solution processable charge generating layer (CGL) that consists of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN{sub 6})/Poly(N-vinylcarbazole) (PVK): 1,1-bis-(4-bis(4-tolyl)-aminophenyl) cyclohexene (TAPC) for a tandem green phosphorescent organic light emitting diode (PHOLED) is demonstrated. The use of orthogonal solvent to dissolve HATCN{sub 6} and PVK:TAPC is the key to overcome the interface erosion problem for the solution processed CGL. The current efficiency of the 2 wt% TAPC mixed with PVK is the highest at 24.2 cd/A, which is more than three-folds higher than that of the single device at 1000 cd/m{sup 2}. - Highlights: • A solution processable tandem OLED is built using a novel charge generating layer. • HATCN{sub 6} and PVK:TAPC are shown to be effective charge generating layers. • The turn on voltages for tandem devices are almost similar to single unit. • 2 wt% TAPC blended with PVK exhibits three-folds increase in efficiency.

  6. Dislocation-related trap levels in nitride-based light emitting diodes

    Energy Technology Data Exchange (ETDEWEB)

    Venturi, Giulia; Castaldini, Antonio; Cavallini, Anna [Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Bologna 40127 (Italy); Meneghini, Matteo; Zanoni, Enrico [Department of Information Engineering, University of Padova, via Gradenigo 6/B, Padova 35131 (Italy); Zhu, Dandan; Humphreys, Colin [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2014-05-26

    Deep level transient spectroscopy was performed on InGaN/GaN multiple quantum well light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by metalorganic vapor phase epitaxy on GaN templates with a high dislocation density of 8 × 10{sup 9} cm{sup −2} and a low dislocation density of 3 × 10{sup 8} cm{sup −2}. Three trapping levels for electrons were revealed, named A, A1, and B, with energies E{sub A} ≈ 0.04 eV, E{sub A1} ≈ 0.13 eV, and E{sub B} ≈ 0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels.

  7. Blue Quantum Dot Light-Emitting Diodes with High Electroluminescent Efficiency.

    Science.gov (United States)

    Wang, Lishuang; Lin, Jie; Hu, Yongsheng; Guo, Xiaoyang; Lv, Ying; Tang, Zhaobing; Zhao, Jialong; Fan, Yi; Zhang, Nan; Wang, Yunjun; Liu, Xingyuan

    2017-11-08

    High-efficiency blue CdSe/ZnS quantum dots (QDs) have been synthesized for display application with emission peak over 460 nm with the purpose of reducing the harmful effect of short-wavelength light to human eyes. To reach a better charge balance, different size ZnO nanoparticles (NPs) were synthesized and electrical properties of ZnO NPs were analyzed. Quantum dot light-emitting diodes (QLEDs) based on as-prepared blue QDs and optimized ZnO NPs have been successfully fabricated. Using small-size ZnO NPs, we have obtained a maximum current efficiency (CE) of 14.1 cd A(-1) and a maximum external quantum efficiency (EQE) of 19.8% for QLEDs with an electroluminescence (EL) peak at 468 nm. To the best of our knowledge, this EQE is the highest value in comparison to the previous reports. The CIE 1931 color coordinates (0.136, 0.078) of this device are quite close to the standard (0.14, 0.08) of National Television System Committee (NTSC) 1953. The color saturation blue QLEDs show great promise for use in next-generation full-color displays.

  8. Performance enhancement of organic light-emitting diodes by chlorine plasma treatment of indium tin oxide

    Science.gov (United States)

    Cao, X. A.; Zhang, Y. Q.

    2012-04-01

    The characteristics of green phosphorescent organic light-emitting diodes (OLEDs) fabricated on ITO/glass substrates pretreated with low-energy O2 and Cl2 plasma were compared. At 20 mA/cm2, the OLEDs with O2 and Cl2 plasma-treated indium tin oxide (ITO) had voltages of 9.6 and 7.6 eV, and brightness of 9580 and 12380 cd/m2, respectively. At ˜104 cd/m2, the latter had a 30% higher external quantum efficiency and a 74% higher power efficiency. Photoelectron spectroscopies revealed that Cl2 plasma treatment created stable In-Cl bonds and raised the work function of ITO by up to 0.9 eV. These results suggest that the better energy level alignment at the chlorinated ITO/organic interface enhances hole injection, leading to more efficient and more reliable operation of the OLEDs. The developed plasma chlorination process is very effective for surface modification of ITO and compatible with the fabrication of various organic electronics.

  9. Red/near-infrared light-emitting diode therapy for traumatic brain injury

    Science.gov (United States)

    Naeser, Margaret A.; Martin, Paula I.; Ho, Michael D.; Krengel, Maxine H.; Bogdanova, Yelena; Knight, Jeffrey A.; Yee, Megan K.; Zafonte, Ross; Frazier, Judith; Hamblin, Michael R.; Koo, Bang-Bon

    2015-05-01

    This invited paper reviews our research with scalp application of red/near-infrared (NIR) light-emitting diodes (LED) to improve cognition in chronic, traumatic brain injury 1. Application of red/NIR light improves mitochondrial function (especially hypoxic/compromised cells) promoting increased ATP, important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. Eleven chronic, mTBI participants with closed-head injury and cognitive dysfunction received 18 outpatient treatments (MWF, 6 Wks) starting at 10 Mo. to 8 Yr. post-mTBI (MVA, sports-related, IED blast injury). LED therapy is non-invasive, painless, non-thermal (FDA-cleared, non-significant risk device). Each LED cluster head (2.1" diameter, 500mW, 22.2mW/cm2) was applied 10 min (13J/cm2) to 11 scalp placements: midline, from front-to-back hairline; and bilaterally on dorsolateral prefrontal cortex, temporal, and parietal areas. Testing performed pre- and post-LED (+1 Wk, 1 and 2 Mo post- 18th treatment) showed significant linear trend for LED effect over time, on improved executive function and verbal memory. Fewer PTSD symptoms were reported. New studies at VA Boston include TBI patients treated with transcranial LED (26J/cm2); or treated with only intranasal red, 633nm and NIR, 810nm diodes placed into the nostrils (25 min, 6.5mW, 11.4J/cm2). Intranasal LEDs are hypothesized to deliver photons to hippocampus. Results are similar to Naeser et al. (2014). Actigraphy sleep data show increased sleep time (average, +1 Hr/night) post-18th transcranial or intranasal LED treatment. LED treatments may be self-administered at home (Naeser et al., 2011). A shamcontrolled study with Gulf War Illness Veterans is underway.

  10. Processes for design, construction and utilisation of arrays of light-emitting diodes and light-emitting diode-coupled optical fibres for multi-site brain light delivery

    OpenAIRE

    Jacob Gold Bernstein; Brian Douglas Allen; Guerra, Alexander A.; Edward Stuart Boyden

    2014-01-01

    Optogenetics enables light to be used to control the activity of genetically targeted cells in the living brain. Optical fibres can be used to deliver light to deep targets, and light-emitting diodes (LEDs) can be spatially arranged to enable patterned light delivery. In combination, arrays of LED-coupled optical fibres can enable patterned light delivery to deep targets in the brain. Here the authors describe the process flow for making LED arrays and LED-coupled optical fibre arrays, explai...

  11. Resonant cavity light-emitting diodes based on dielectric passive cavity structures

    Science.gov (United States)

    Ledentsov, N.; Shchukin, V. A.; Kropp, J.-R.; Zschiedrich, L.; Schmidt, F.; Ledentsov, N. N.

    2017-02-01

    A novel design for high brightness planar technology light-emitting diodes (LEDs) and LED on-wafer arrays on absorbing substrates is proposed. The design integrates features of passive dielectric cavity deposited on top of an oxide- semiconductor distributed Bragg reflector (DBR), the p-n junction with a light emitting region is introduced into the top semiconductor λ/4 DBR period. A multilayer dielectric structure containing a cavity layer and dielectric DBRs is further processed by etching into a micrometer-scale pattern. An oxide-confined aperture is further amended for current and light confinement. We study the impact of the placement of the active region into the maximum or minimum of the optical field intensity and study an impact of the active region positioning on light extraction efficiency. We also study an etching profile composed of symmetric rings in the etched passive cavity over the light emitting area. The bottom semiconductor is an AlGaAs-AlAs multilayer DBR selectively oxidized with the conversion of the AlAs layers into AlOx to increase the stopband width preventing the light from entering the semiconductor substrate. The approach allows to achieve very high light extraction efficiency in a narrow vertical angle keeping the reasonable thermal and current conductivity properties. As an example, a micro-LED structure has been modeled with AlGaAs-AlAs or AlGaAs-AlOx DBRs and an active region based on InGaAlP quantum well(s) emitting in the orange spectral range at 610 nm. A passive dielectric SiO2 cavity is confined by dielectric Ta2O5/SiO2 and AlGaAs-AlOx DBRs. Cylindrically-symmetric structures with multiple ring patterns are modeled. It is demonstrated that the extraction coefficient of light to the air can be increased from 1.3% up to above 90% in a narrow vertical angle (full width at half maximum (FWHM) below 20°). For very small oxide-confined apertures 100nm the narrowing of the FWHM for light extraction can be reduced down to 5

  12. Mobility balance in the light-emitting layer governs the polaron accumulation and operational stability of organic light-emitting diodes

    Science.gov (United States)

    Kim, Jae-Min; Lee, Chang-Heon; Kim, Jang-Joo

    2017-11-01

    Organic light-emitting diode (OLED) displays are lighter and more flexible, have a wider color gamut, and consume less power than conventional displays. Stable materials and the structural design of the device are important for OLED longevity. Control of charge transport and accumulation in the device is particularly important because the interaction of excitons and polarons results in material degradation. This research investigated the charge dynamics of OLEDs experimentally and by drift-diffusion modeling. Parallel capacitance-voltage measurements of devices provided knowledge of charge behavior at different driving voltages. A comparison of exciplex-forming co-host and single host structures established that the mobility balance in the emitting layers determined the amount of accumulated polarons in those layers. Consequently, an exciplex-forming co-host provides a superior structure in terms of device lifetime and efficiency because of its well-balanced mobility. Minimizing polaron accumulation is key to achieving long OLED device lifetimes. This is a crucial aspect of device physics that must be considered in the device design structure.

  13. Light-emitting diode effects on combined decellularization of tracheae. A novel approach to obtain biological scaffolds.

    Science.gov (United States)

    Evaristo, Thaiane Cristine; CruzAlves, Flávia Cilene Maciel da; Moroz, Andrei; Mion, Woner; Acorci-Valério, Michele Janegitz; Felisbino, Sérgio Luis; Rossi-Ferreira, Rosana; Ruiz Júnior, Raul Lopes; Deffune, Elenice

    2014-08-01

    To obtain a decellularized tracheal scaffold associating traditional approaches with the novel light-emitting diode (LED) proposal. This study was performed with New Zealand adult rabbits weighing 3.0 - 4.0 kg. Different protocols (22) were used combining physical (agitation and LED irradiation), chemical (SDS and Triton X-100 detergents), and enzymatic methods (DNase and RNase). Generally, the cells surrounding soft tissues were successfully removed, but none protocol removed cells from the tracheal cartilage. However, longer protocols were more effective. The cost-benefits relation of the enzymatic processes was not favorable. It was possible to find out that the cartilaginous tissue submitted to the irradiation with LED 630nm and 475 nm showed an increased number of gaps without cells, but several cells were observed to be still present. The light-emitting diode is a promising tool for decellularization of soft tissues.

  14. Ordered and ultrathin reduced graphene oxide LB films as hole injection layers for organic light-emitting diode.

    Science.gov (United States)

    Yang, Yajie; Yang, Xiaojie; Yang, Wenyao; Li, Shibin; Xu, Jianhua; Jiang, Yadong

    2014-01-01

    In this paper, we demonstrated the utilization of reduced graphene oxide (RGO) Langmuir-Blodgett (LB) films as high performance hole injection layer in organic light-emitting diode (OLED). By using LB technique, the well-ordered and thickness-controlled RGO sheets are incorporated between the organic active layer and the transparent conducting indium tin oxide (ITO), leading to an increase of recombination between electrons and holes. Due to the dramatic increase of hole carrier injection efficiency in RGO LB layer, the device luminance performance is greatly enhanced comparable to devices fabricated with spin-coating RGO and a commercial conducting polymer PEDOT:PSS as the hole transport layer. Furthermore, our results indicate that RGO LB films could be an excellent alternative to commercial PEDOT:PSS as the effective hole transport and electron blocking layer in light-emitting diode devices.

  15. Low-threshold voltage ultraviolet light-emitting diodes based on (Al,Ga)N metal–insulator–semiconductor structures

    Science.gov (United States)

    Liang, Yu-Han; Towe, Elias

    2017-12-01

    Al-rich III–nitride-based deep-ultraviolet (UV) (275–320 nm) light-emitting diodes are plagued with a low emission efficiency and high turn-on voltages. We report Al-rich (Al,Ga)N metal–insulator–semiconductor UV light-emitting Schottky diodes with low turn-on voltages of insulator and an n-type Al0.58Ga0.42N film as the semiconductor. To improve the efficiency, we inserted a GaN quantum-well structure between the AlN insulator and the n-type Al x Ga1‑ x N semiconductor. The benefits of the quantum-well structure include the potential to tune the emission wavelength and the capability to confine carriers for more efficient radiative recombination.

  16. Genetic Algorithm for Innovative Device Designs in High-Efficiency III–V Nitride Light-Emitting Diodes

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Di [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Electrical, Computer and Systems Engineering; Schubert, Martin F. [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Electrical, Computer and Systems Engineering; Cho, Jaehee [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Electrical, Computer and Systems Engineering; Schubert, E. Fred [Rensselaer Polytechnic Inst., Troy, NY (United States). Dept. of Electrical, Computer and Systems Engineering; Crawford, Mary H. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Koleske, Daniel D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Shim, Hyunwook [Samsung LED, R& D Inst., Suwon (Republic of Korea); Sone, Cheolsoo [Samsung LED, R& D Inst., Suwon (Republic of Korea)

    2012-01-01

    Light-emitting diodes are becoming the next-generation light source because of their prominent benefits in energy efficiency, versatility, and benign environmental impact. However, because of the unique polarization effects in III–V nitrides and the high complexity of light-emitting diodes, further breakthroughs towards truly optimized devices are required. Here we introduce the concept of artificial evolution into the device optimization process. Reproduction and selection are accomplished by means of an advanced genetic algorithm and device simulator, respectively. We demonstrate that this approach can lead to new device structures that go beyond conventional approaches. The innovative designs originating from the genetic algorithm and the demonstration of the predicted results by implementing structures suggested by the algorithm establish a new avenue for complex semiconductor device design and optimization.

  17. Envelope-function analysis of wurtzite InGaN/GaN quantum well light emitting diodes

    Science.gov (United States)

    Xiao, D.; Kim, K. W.; Zavada, J. M.

    2004-07-01

    Fundamental electrical and optical properties of strained wurtzite InGaN/GaN-based quantum-well light-emitting diodes are calculated based on the Rashba-Sheka-Pikus Hamiltonian in the vicinity of the Γ point. It is found that the strain and the strain-induced piezoelectric field significantly alter the subband structure and determines the output intensity of the nitride quantum well light emitting diodes. For the case with high In composition (≳0.2), the calculation also supports the possibility of strain relaxation in the quantum well. Coupled with an optimized set of parameters, our theoretical model provides an excellent agreement with the available experimental data over a wide range of In composition (0-0.5).

  18. Design of white light-emitting diodes using InGaN/AlInGaN quantum-well structures

    Science.gov (United States)

    Xiao, D.; Kim, K. W.; Bedair, S. M.; Zavada, J. M.

    2004-02-01

    Based on the Rashba-Sheka-Pikus Hamiltonian in the vicinity of the Γ point, and taking into consideration spontaneous and piezoelectric polarization, the optical intensity of nitride-based quantum-well light-emitting diodes has been calculated. It is found that strain substantially alters the subband structure and thus the output intensity of these nitride-biased quantum-well light-emitting diodes. A design that uses AlInGaN as the quantum barrier is proposed to realize efficient red emission, which is hard to achieve if GaN is used as the barrier. In the proposed design, three different InGaN/AlInGaN quantum-well structures emit red, green, and blue light of similar intensity. Also, to achieve high efficiency, important factors related to the oscillator strength are discussed in detail.

  19. High-efficiency pyrene-based blue light emitting diodes: Aggregation suppression using a calixarene 3D-scaffold

    KAUST Repository

    Chan, Khaileok

    2012-01-01

    An efficient blue light emitting diode based on solution processable pyrene-1,3-alt-calix[4]arene is demonstrated, providing a record current efficiency of 10.5 cd A -1 in a simple non-doped OLED configuration. Complete suppression of pyrene aggregation in the solid state is achieved by controlling chromophore dispersion using the 1,3-alt-calix[4]arene scaffold. © 2012 The Royal Society of Chemistry.

  20. A Single-Stage High-Power-Factor Light-Emitting Diode (LED) Driver with Coupled Inductors for Streetlight Applications

    OpenAIRE

    Chun-An Cheng; Chien-Hsuan Chang; Hung-Liang Cheng; Ching-Hsien Tseng; Tsung-Yuan Chung

    2017-01-01

    This paper presents and implements a single-stage high-power-factor light-emitting diode (LED) driver with coupled inductors, suitable for streetlight applications. The presented LED driver integrates an interleaved buck-boost power factor correction (PFC) converter with coupled inductors and a half-bridge-type series-resonant converter cascaded with a full-bridge rectifier into a single-stage power conversion circuit. Coupled inductors inside the interleaved buck-boost PFC converter sub-circ...