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Sample records for light-emitting diode treatment

  1. Light-emitting Diodes

    PubMed Central

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

    2015-01-01

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

  2. Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Schubert, E. Fred

    2003-06-01

    Light emitting diodes (LEDs) are devices that are used in a myriad of applications, such as indicator lights in instruments, signage, illuminations, and communication. This graduate textbook covers all aspects of the technology and physics of infrared, visible-spectrum, and white light-emitting diodes (LEDs) made from III-V semiconductors. It reviews elementary properties of LEDs such as the electrical and optical characteristics. Exercises and illustrative examples reinforce the topics discussed.

  3. Light Emitting Diode (LED)

    NASA Technical Reports Server (NTRS)

    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.

  4. Light Emitting Diodes (LEDs)

    NASA Technical Reports Server (NTRS)

    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.

  5. White light emitting diodes

    NASA Astrophysics Data System (ADS)

    Baur, J.; Schlotter, P.; Schneider, J.

    Using blue-emitting GaN LEDs on SiC substrate chips as primary light sources, we have fabricated green, yellow, red and white light emitting diodes (LUCOLEDs). The generation of mixed colors, as turquoise and magenta, is also demonstrated. The underlying physical principle is that of luminescence downconversion (Stokes shift), as typical for organic dye molecules and many inorganic phosphors. For white light generation via the LUCOLED principle, the phosphor Y3Al5O12:Ce3+(4f1) is ideally suited. The optical characteristics of Ce3+(4f1) in Y3Al5O12(YAG) are discussed in detail. Possibilities to "tune" the white color by various substitutions in the garnet lattice are shortly outlined.

  6. Photodynamic therapy using light-emitting diodes for the treatment of viral warts.

    PubMed

    Ohtsuki, Akiko; Hasegawa, Toshio; Hirasawa, Yusuke; Tsuchihashi, Hitoshi; Ikeda, Shigaku

    2009-10-01

    Photodynamic therapy with topical 5-aminolevulinic acid is an effective and safe treatment for actinic keratosis and superficial non-melanoma skin cancer. Further, some studies have reported good efficacy when using photodynamic therapy to treat viral warts. The light-emitting diode is an incoherent, narrow-spectrum light source. The purpose of this study is to evaluate the efficacy of photodynamic therapy using a light-emitting diode for viral warts. Six patients with a total of 41 foot and hand warts were recruited in this study. They were treated with 20% 5-aminolevulinic acid cream under occlusion for 5 h. Thereafter, the treated area was irradiated with the light from a red light-emitting diode (633 +/- 6 nm) with a dose of 126 J/cm(2). This treatment was repeated at 2- or 3-week intervals. The rate of improvement observed in patients was 68.3%. The adverse effects included mild to moderate pain and erythema, which was well-tolerated by all six patients. No patients withdrew from the study due to the adverse effects. Photodynamic therapy with topical 5-aminolevulinic acid using the light from a red light-emitting diode has the advantage of non-invasiveness, minimal associated adverse reactions, and production of good results in a significant proportion of cases: therefore, it is an alternative treatment for recalcitrant viral warts.

  7. Light-Emitting Diode Versus Sham in the Treatment of Plantar Fasciitis: A Randomized Trial

    PubMed Central

    Higgins, Paul E.; Hews, Katherine; Windon, Lowell; Chasse, Patrick

    2015-01-01

    Objective The purpose of this preliminary study was to compare the application of the light emitting diode (LED) to sham LED in the treatment of plantar fasciitis. Methods Eighteen subjects met the inclusion criteria and were randomly assigned into 2 groups: light emitting diode or sham LED. The subjects received either the LED at 12 J/cm2 or sham LED along 2 points of the plantar fascia. Subjects in both groups received a 10 minute transverse friction massage and participated in 4 plantar fascia stretching exercises. All subjects received a total of 6 treatments over 3 weeks. Progress was assessed using the lower extremity functional and analog pain scale. Results No significant difference was found between treatment groups (P = .845). There was a significant difference in pain and outcome scores over time within both groups (P < .35). Conclusion Among patients with plantar fasciitis, the use of LED did not result in greater improvement in function or pain compared with sham treatment. The findings suggest that manual intervention and passive stretching activities may have provided significant pain relief and improvement in functional outcome scores. PMID:26644784

  8. Light-Emitting Diodes: Solving Complex Problems

    ERIC Educational Resources Information Center

    Planinšic, Gorazd; Etkina, Eugenia

    2015-01-01

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

  9. Light-Emitting Diodes: Learning New Physics

    ERIC Educational Resources Information Center

    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…

  10. Broadband light-emitting diode

    DOEpatents

    Fritz, I.J.; Klem, J.F.; Hafich, M.J.

    1998-07-14

    A broadband light-emitting diode is disclosed. 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 {micro}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-divisionmultiplexed (WDM) fiber-optic data links, and WDM fiber-optic sensor networks for automobiles and aircraft. 10 figs.

  11. Broadband light-emitting diode

    DOEpatents

    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.

  12. Quantum Dot Light Emitting Diode

    SciTech Connect

    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.

  13. Quantum Dot Light Emitting Diode

    SciTech Connect

    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.

  14. Optical fluence modelling for ultraviolet light emitting diode-based water treatment systems.

    PubMed

    Simons, R; Gabbai, U E; Moram, M A

    2014-12-01

    This work presents a validated optical fluence rate model optimised for ultraviolet light-emitting diodes (UV-LEDs), which allow a very wide range of emission wavelengths and source geometries to be used in water treatment units. The model is based on a Monte Carlo approach, in which an incremental ray-tracing algorithm is used to calculate the local volumetric rate of energy absorption and subsequently convert it to the local fluence rate distribution for an UV-LED water treatment chamber of arbitrary design. The model includes contributions from optical reflections and scattering by treatment chamber walls and from scattering due to particulates and/or microorganisms. The model successfully predicts optical fluence rates in point-of-use water treatment units, as verified using biodosimetry with MS-2 bacteriophage at a UV-LED emission wavelength of 254 nm. The effects of chamber geometry are also modelled effectively and are consistent with the inactivation data for E. coli at 254 nm. The data indicate that this model is suitable for application in the design and optimisation of UV-LED-based water treatment systems.

  15. Electroluminescence dependence of the simplified green light organic light emitting diodes on in situ thermal treatment

    NASA Astrophysics Data System (ADS)

    Mu, Haichuan; Rao, Lu; Li, Weiling; Wei, Bin; Wang, Keke; Xie, Haifen

    2015-12-01

    Simplified multilayer green light phosphorescent organic light emitting diodes (PHOLED) with the structure of ITO/MoO3(1 nm)/CBP(20 nm)/CBP:Ir(ppy)3 (1 wt%) (15 nm)/TPBi(60 nm)/LiF(0.5 nm)/Al were fabricated via thermal evaporation and in situ thermal treatment (heating the OLED substrates to certain temperatures during the thermal evaporation of the organic materials) was performed. The effect of the in situ thermal treatment on the electroluminescence (EL) performance of the PHOLED was investigated. It was found that the OLED exhibited strong EL dependence on the thermal treatment temperatures, and their current efficiency was improved with the increasing temperature from room temperature (RT) to 69 °C and deteriorated with the further increasing temperature to 105 °C. At the brightness of 1000 cd/m2, over 80% improvement of the current efficiency at the optimal thermal treatment temperature of 69 °C (64 cd/A) was demonstrated compared to that at RT (35 cd/A). Meanwhile, the tremendous influences of the in situ thermal treatment on the morphology of the multilayer CBP/CBP:Ir(ppy)3/TPBi were also observed. At the optimal thermal treatment temperature of 69 °C, the improvement of the EL performance could be ascribed to the enhancement of the electron and hole transporting in the CBP:Ir(ppy)3 emitting layer, which suppressed the triplets self-quenching interactions and promoted the charge balance and excitons formation. The working mechanism responsible for such EL dependence was discussed in detail.

  16. Polymer light-emitting devices: Light-emitting diodes and light-emitting electrochemical cells

    SciTech Connect

    Heeger, A.J.; Cao, Y.; Pei, Q.; Yu, G.

    1996-10-01

    We will summarize recent progress using two different device configurations: tunneling injection light-emitting diodes (LEDs) and light-emitting electrochemical cells (LECs). In the LEC, a p-n junction diode is created in-situ through simultaneous p-type and n-type electrochemical doping on opposite sides, respectively, of a film of conjugated polymer which contains added electrolyte to provide the necessary counterions for doping. Blue, green and orange emitting LECs have been fabricated. The LEC has been used to directly measure the charge injection energy gap in semiconducting polymers. Simultaneous measurements of the onset of electrochemical doping, electrical injection, and electroluminescence from light-emitting electrochemical cells eliminates the uncertainty in the magnitude of the exciton binding energy; the LEC data are consistent with the semiconductor model in which the exciton binding energy is at most a few times k{sub B}T (at room temperature).

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

    NASA Technical Reports Server (NTRS)

    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. Demonstrating the Light-Emitting Diode.

    ERIC Educational Resources Information Center

    Johnson, David A.

    1995-01-01

    Describes a simple inexpensive circuit which can be used to quickly demonstrate the basic function and versatility of the solid state diode. Can be used to demonstrate the light-emitting diode (LED) as a light emitter, temperature sensor, light detector with both a linear and logarithmic response, and charge storage device. (JRH)

  19. Anode modification of polymer light-emitting diode using graphene oxide interfacial layer: The role of ultraviolet-ozone treatment

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao-Chen; Li, Yan-Qing; Deng, Yan-Hong; Zhuo, Qi-Qi; Lee, Shuit-Tong; Tang, Jian-Xin

    2013-08-01

    A simple and efficient method has been developed to modify the anode interface of polymer light-emitting diode by incorporating solution-processable graphene oxide as hole transport layer. Interface engineering of ultraviolet-ozone treatment on graphene oxide is demonstrated to dramatically enhance the electrical properties, leading to 15% increase in efficiency compared to that with a traditionally used poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) layer. As determined by photoelectron spectroscopy and impedance spectroscopy, an optimized ultraviolet-ozone treatment results in a more favorable energy level alignment and a decrease in series resistance, which can subsequently facilitate charge injection at the anodic interface.

  20. Light-Emitting Diodes: A Hidden Treasure

    ERIC Educational Resources Information Center

    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…

  1. Phosphorescent Nanocluster Light-Emitting Diodes.

    PubMed

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

    2016-01-13

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

  2. Phosphorescent Nanocluster Light-Emitting Diodes.

    PubMed

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

    2016-01-13

    Devices utilizing an entirely new class of earth abundant, inexpensive phosphorescent emitters based on metal-halide nanoclusters are reported. Light-emitting diodes with tunable performance are demonstrated by varying cation substitution to these nanoclusters. Theoretical calculations provide insight about the nature of the phosphorescent emitting states, which involves a strong pseudo-Jahn-Teller distortion. PMID:26568044

  3. Bioinspired Hybrid White Light-Emitting Diodes.

    PubMed

    Weber, Michael D; Niklaus, Lukas; Pröschel, Marlene; Coto, Pedro B; Sonnewald, Uwe; Costa, Rubén D

    2015-10-01

    The first bioinspired hybrid white-light-emitting diodes (bio-HLEDs) featuring protein cascade coatings are presented. For easy fabrication a new strategy to stabilize proteins in rubber-like material was developed. The synergy between the excellent features of fluorescent proteins and the easily processed rubber produces bio-HLEDs with less than 10% loss in luminous efficiency over 100 hours.

  4. Long Persistent Light Emitting Diode Indicators

    ERIC Educational Resources Information Center

    Jia, Dongdong; Ma, Yiwei; Hunter, D. N.

    2007-01-01

    An undergraduate laboratory was designed for undergraduate students to make long persistent light emitting diode (LED) indicators using phosphors. Blue LEDs, which emit at 465 nm, were characterized and used as an excitation source. Long persistent phosphors, SrAl[subscript 2]O[subscript 4]:Eu[superscript 2+],Dy[superscript 3+] (green) and…

  5. Plasma treatment and its prospective application to polymer light-emitting diodes fabricated by ink-jet printing method

    SciTech Connect

    Jo, Sung Jin; Jeong, Soon Moon; Kim, Woo Jin; Koo, Won Hoi; Choi, Sang Hun; Kim, Chang Su; Baik, Hong Koo; Lee, Se-Jong

    2005-09-15

    The influence of CF{sub 4} plasma treatment of indium-tin-oxide (ITO) and polyimide (PI) on the patterning of ink-jet printed polymer is presented. Not much difference between the as-received ITO and PI surface energies was found, but a significant difference in surface energies between ITO and PI after CF{sub 4} plasma treatment was noted. It is expected that precise patterning can be achieved by using the difference in surface energies between the inside of the pixel and its surroundings. Also the effects of CF{sub 4} plasma treatment of ITO have been studied on the performance of polymer light-emitting diodes (PLEDs). X-ray photoelectron spectroscopy revealed that CF{sub 4} plasma treatment led to a decrease in the surface content of carbon contaminants and an increase in the surface content of fluorine, which in turn enhance the performance of PLEDs.

  6. Light-Emitting Diodes: Learning New Physics

    NASA Astrophysics Data System (ADS)

    Planinšič, Gorazd; Etkina, Eugenia

    2015-04-01

    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 in the February 2014 issue of TPT,1 provided an overview of possible uses of LEDs in a physics course. The second paper2 discussed how one could help students learn the foundational aspects of LED physics through a scaffolded inquiry approach, specifically the ISLE cycle. The goals of this paper are to show how the activities described in our second paper help to deepen student understanding of physics and to broaden student knowledge by exploring new phenomena such as fluorescence. Activities described in this paper are suitable for advanced high school courses, introductory courses for physics and engineering majors, courses for prospective physics teachers, and professional development programs.

  7. Nanoscale organic light-emitting diodes.

    PubMed

    Yamamoto, Hiromichi; Wilkinson, John; Long, James P; Bussman, Konrad; Christodoulides, Joseph A; Kafafi, Zakya H

    2005-12-01

    This study reports the fabrication and characterization of nanoscale organic light-emitting diodes (nano-OLEDs) based on poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV). The nano-OLEDs were fabricated by spin casting MEH-PPV into cylindrical nanoholes lithographically patterned into silicon nitride. The electroluminescence (EL) spectrum of MEH-PPV was similar to its photoluminescence spectrum, confirming radiative decay from the same excited state. Device characteristics in the form of current density and EL versus applied electric field are presented and compared with those of a large-scale OLED.

  8. Atomically thin quantum light-emitting diodes

    PubMed Central

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

    2016-01-01

    Transition metal dichalcogenides are optically active, layered materials promising for fast optoelectronics and on-chip photonics. We demonstrate electrically driven single-photon emission from localized sites in tungsten diselenide and tungsten disulphide. To achieve this, we fabricate a light-emitting diode structure comprising single-layer graphene, thin hexagonal boron nitride and transition metal dichalcogenide mono- and bi-layers. Photon correlation measurements are used to confirm the single-photon nature of the spectrally sharp emission. These results present the transition metal dichalcogenide family as a platform for hybrid, broadband, atomically precise quantum photonics devices. PMID:27667022

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Effect of light-emitting diode (ʎ 627 nm and 945 nm ʎ) treatment on first intention healing: immunohistochemical analysis.

    PubMed

    Kerppers, Ivo Ilvan; de Lima, Carlos José; Fernandes, Adriana Barrinha; Villaverde, Antonio Balbin

    2015-01-01

    Collagen I is not only responsible for maintaining the integrity of most tissues due to its mechanical properties, but also for its active participation in the functionality of tissues because of its interaction with cells present in the extracellular matrix. The synthesis of collagen begins with tissue injury and remains until the end of the healing process. The use of non-coherent light for healing processes is still understudied. This procedure stands out as a biostimulation method for tissue repair, which increases local circulation, cell proliferation, and collagen synthesis. This study sought to quantify collagen I in the healing process after the treatment of wounds with the light-emitting diode (LED) treatment. The histologic analysis with tissue samples stained with picrosirius red showed a statistical difference between the positive controls, LED 627 and LED 945 nm groups; the group treated with LED 627 nm showed a predominance of mature collagen. The immunohistochemical analysis showed a statistically significant high concentration of collagen I in the LED 945 nm group. The irradiation of wounds with the higher wavelength (945 nm) used in the study produced the best activity of collagen I formation in experimental model.

  11. Improved Cognitive Function After Transcranial, Light-Emitting Diode Treatments in Chronic, Traumatic Brain Injury: Two Case Reports

    PubMed Central

    Saltmarche, Anita; Krengel, Maxine H.; Hamblin, Michael R.; Knight, Jeffrey A.

    2011-01-01

    Abstract Objective: Two chronic, traumatic brain injury (TBI) cases, where cognition improved following treatment with red and near-infrared light-emitting diodes (LEDs), applied transcranially to forehead and scalp areas, are presented. Background: Significant benefits have been reported following application of transcranial, low-level laser therapy (LLLT) to humans with acute stroke and mice with acute TBI. These are the first case reports documenting improved cognitive function in chronic, TBI patients treated with transcranial LED. Methods: Treatments were applied bilaterally and to midline sagittal areas using LED cluster heads [2.1″ diameter, 61 diodes (9 × 633 nm, 52 × 870 nm); 12–15 mW per diode; total power: 500 mW; 22.2 mW/cm2; 13.3 J/cm2 at scalp (estimated 0.4 J/cm2 to cortex)]. Results: Seven years after closed-head TBI from a motor vehicle accident, Patient 1 began transcranial LED treatments. Pre-LED, her ability for sustained attention (computer work) lasted 20 min. After eight weekly LED treatments, her sustained attention time increased to 3 h. The patient performs nightly home treatments (5 years); if she stops treating for more than 2 weeks, she regresses. Patient 2 had a history of closed-head trauma (sports/military, and recent fall), and magnetic resonance imaging showed frontoparietal atrophy. Pre-LED, she was on medical disability for 5 months. After 4 months of nightly LED treatments at home, medical disability discontinued; she returned to working full-time as an executive consultant with an international technology consulting firm. Neuropsychological testing after 9 months of transcranial LED indicated significant improvement (+1, +2SD) in executive function (inhibition, inhibition accuracy) and memory, as well as reduction in post-traumatic stress disorder. If she stops treating for more than 1 week, she regresses. At the time of this report, both patients are continuing treatment. Conclusions: Transcranial

  12. Optical design of organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Wang, Z. B.; Helander, M. G.; Xu, X. F.; Puzzo, D. P.; Qiu, J.; Greiner, M. T.; Lu, Z. H.

    2011-03-01

    Out-coupling of light from organic light emitting diodes (OLEDs) is a significant challenge for the application of OLEDs in solid state lighting. Most of the light is trapped in the stratified thin film structure and the glass substrate. In this study, an optical model is developed to simulate the optical electrical field for OLEDs with a stratified structure based on the dipole source term and transfer matrix approach. The exciton distribution is also considered in the proposed model. OLEDs with weak microcavity are selected to evaluate the model. Calculation of the electroluminescence spectrum, device efficiency as well as the angular dependence is shown to have a good agreement with the experimental data. Moreover, by using the weak microcavity design, an OLED of more than 70% improved efficiency is achieved.

  13. A single blue nanorod light emitting diode

    NASA Astrophysics Data System (ADS)

    Hou, Y.; Bai, J.; Smith, R.; Wang, T.

    2016-05-01

    We report a light emitting diode (LED) consisting of a single InGaN/GaN nanorod fabricated by a cost-effective top-down approach from a standard LED wafer. The device demonstrates high performance with a reduced quantum confined Stark effect compared with a standard planar counterpart fabricated from the same wafer, confirmed by optical and electrical characterization. Current density as high as 5414 A cm‑2 is achieved without significant damage to the device due to the high internal quantum efficiency. The efficiency droop is mainly ascribed to Auger recombination, which was studied by an ABC model. Our work provides a potential method for fabricating compact light sources for advanced photonic integrated circuits without involving expensive or time-consuming fabrication facilities.

  14. Light-emitting diodes for analytical chemistry.

    PubMed

    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. Proton Degradation of Light-Emitting Diodes

    NASA Technical Reports Server (NTRS)

    Johnston, A. H.; Rax, B. G.; Selva, L. E.

    1997-01-01

    The severe degradation of optocouplers in space has been shown to be mainly due to proton displacement damage in the light-emitting diodes that are used within the optocouplers. However, a variety of LED technologies can be used in optocouplers and their sensitivity to proton displacement damage varies by about two orders of magnitude. Optocouplers are very simple hybrid devices, and the type of LED can be readily changed by the manufacturers with little cost impact. many optocoupler manufacturers purchase LEDs from outside sources with little knowledge or control of the manufacturing process used for the LED, leading to the possibility of very dramatic differences in radiation response (JPL has observed such differences for one type of optocoupler that is used in a hybrid power converter).

  16. High Intensity Organic Light-emitting Diodes

    NASA Astrophysics Data System (ADS)

    Qi, Xiangfei

    This thesis is dedicated to the fabrication, modeling, and characterization to achieve high efficiency organic light-emitting diodes (OLEDs) for illumination applications. Compared to conventional lighting sources, OLEDs enabled the direct conversion of electrical energy into light emission and have intrigued the world's lighting designers with the long-lasting, highly efficient illumination. We begin with a brief overview of organic technology, from basic organic semiconductor physics, to its application in optoelectronics, i.e. light-emitting diodes, photovoltaics, photodetectors and thin-film transistors. Due to the importance of phosphorescent materials, we will focus on the photophysics of metal complexes that is central to high efficiency OLED technology, followed by a transient study to examine the radiative decay dynamics in a series of phosphorescent platinum binuclear complexes. The major theme of this thesis is the design and optimization of a novel architecture where individual red, green and blue phosphorescent OLEDs are vertically stacked and electrically interconnected by the compound charge generation layers. We modeled carrier generation from the metal-oxide/doped organic interface based on a thermally assisted tunneling mechanism. The model provides insights to the optimization of a stacked OLED from both electrical and optical point of view. To realize the high intensity white lighting source, the efficient removal of heat is of a particular concern, especially in large-area devices. A fundamental transfer matrix analysis is introduced to predict the thermal properties in the devices. The analysis employs Laplace transforms to determine the response of the system to the combined effects of conduction, convection, and radiation. This perspective of constructing transmission matrices greatly facilitates the calculation of transient coupled heat transfer in a general multi-layer composite. It converts differential equations to algebraic forms, and

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

    PubMed

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

    2016-01-13

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

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

    PubMed

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

    2016-01-13

    On page 320, R. R. Lunt and co-workers demonstrate electroluminescence from earth-abundant phosphorescent metal halide nanoclusters. These inorganic emitters, which exhibit rich photophysics combined with a high phosphorescence quantum yield, are employed in red and near-infrared light-emitting diodes, providing a new platform of phosphorescent emitters for low-cost and high-performance light-emission applications. PMID:26749470

  19. Laterally injected light-emitting diode and laser diode

    SciTech Connect

    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.

  20. Thermally enhanced blue light-emitting diode

    NASA Astrophysics Data System (ADS)

    Xue, Jin; Zhao, Yuji; Oh, Sang-Ho; Herrington, William F.; Speck, James S.; DenBaars, Steven P.; Nakamura, Shuji; Ram, Rajeev J.

    2015-09-01

    We investigate thermoelectric pumping in wide-bandgap GaN based light-emitting diodes (LEDs) to take advantage of high junction temperature rather than avoiding the problem of temperature-induced efficiency droop through external cooling. We experimentally demonstrate a thermally enhanced 450 nm GaN LED, in which nearly fourfold light output power is achieved at 615 K (compared to 295 K room temperature operation), with nearly no reduction in the wall-plug efficiency (i.e., electrical-optical energy conversion efficiency) at bias V <ℏω/q . The LED is shown to work in a mode similar to a thermodynamic heat engine operating with charged carriers pumped into the active region by a combination of electrical work and Peltier heat (phonons) drawn from the lattice. In this optimal operating regime at 615 K, the LED injection current (3.26 A/cm2) is of similar magnitude to the operating point of common high power GaN based LEDs (5-35 A/cm2). This result suggests the possibility of removing bulky heat sinks in current high power LED products thus realizing a significant cost reduction for solid-state lighting.

  1. Aggregation in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Meyer, Abigail

    Organic light emitting diode (OLED) technology has great potential for becoming a solid state lighting source. However, there are inefficiencies in OLED devices that need to be understood. Since these inefficiencies occur on a nanometer scale there is a need for structural data on this length scale in three dimensions which has been unattainable until now. Local Electron Atom Probe (LEAP), a specific implementation of Atom Probe Tomography (APT), is used in this work to acquire morphology data in three dimensions on a nanometer scale with much better chemical resolution than is previously seen. Before analyzing LEAP data, simulations were used to investigate how detector efficiency, sample size and cluster size affect data analysis which is done using radial distribution functions (RDFs). Data is reconstructed using the LEAP software which provides mass and position data. Two samples were then analyzed, 3% DCM2 in C60 and 2% DCM2 in Alq3. Analysis of both samples indicated little to no clustering was present in this system.

  2. Sensitized fluorescence in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Nguyen, C.; Ingram, G.; Lu, Z. H.

    2014-10-01

    We have studied the effects of incorporating phosphorescent sensitizers into fluorescent organic-light emitting diode (OLED) devices. In the emissive layer of this system, the host material is co-doped at low concentrations with both a phosphorescent and a fluorescent dye. The purpose of the phosphorescent dopant is to capture both singlet and triplet excitons from the host material and to transfer them into the singlet state of the fluorescent dye. Ideally, recombination of excitons and the emission of light would occur solely on the fluorescent dye. This sensitized fluorescent system can potentially achieve 100% internal quantum efficiency as both triplet and singlet states are being harvested. We have observed an almost two-fold improvement in the quantum efficiency of a sensitized fluorescent system, utilizing rubrene as the fluorescent dye and Ir(ppy)2(acac) as the sensitizer, versus a standard rubrene-based host-guest system. By testing various dopant concentrations, the optimal emissive layer composition for this system was determine to be ~2 wt.% rubrene and ~7 wt.% Ir(ppy)2(acac) in a CBP host.

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

    PubMed

    Yook, Kyoung Soo; Lee, Jun Yeob

    2016-02-01

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

  4. A micrometer-size movable light emitting area in a resonant tunneling light emitting diode

    SciTech Connect

    Pettinari, G.; Balakrishnan, N.; Makarovsky, O.; Campion, R. P.; Patanè, A.; Polimeni, A.; Capizzi, M.

    2013-12-09

    We report on the fabrication of a micrometer-size movable light emitting area in a GaAs/AlAs quantum well resonant tunneling p-i-n diode. The spatial position of the micrometer-size light emitting area shifts linearly with increasing applied bias, up to 30 μm for a bias increment of 0.2 V. Also, the simultaneous resonant tunneling injection of both electrons and holes into the quantum well states is achieved at specific positions of the diode, thus resulting in a tenfold increase of the electroluminescence intensity.

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

    NASA Astrophysics Data System (ADS)

    Hirata, Shuzo; Shizu, Katsuyuki

    2016-10-01

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

  6. Determining Planck's Constant Using a Light-emitting Diode.

    ERIC Educational Resources Information Center

    Sievers, Dennis; Wilson, Alan

    1989-01-01

    Describes a method for making a simple, inexpensive apparatus which can be used to determine Planck's constant. Provides illustrations of a circuit diagram using one or more light-emitting diodes and a BASIC computer program for simplifying calculations. (RT)

  7. Plant Growth Under Light Emitting Diode Irradiation.

    NASA Astrophysics Data System (ADS)

    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,<=af photosynthesis and ATP status were the same in LED as in white xenon arc light. In 35 Pa CO_2, photosynthesis was 10% lower in LED than in xenon arc light due to lowered stomatal conductance. The quantum efficiency of photosynthesis in pulsed light was equal to continuous light, even when pulses were twice as bright as sunlight. Xanthophyll pigments were not affected by these bright pulses. Photomorphogenesis of tobacco (Nicotiana tabacum L.), 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

  8. Film Properties and Polycrystallization of Organic Dyes on ITOs with Surface Treatment for Organic Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Iwama, Yuki; Mori, Tatsuo; Mizutani, Teruyoshi

    ITO(Indium-Tin-Oxide) has been now widely used as the transparent anode for organic light-emitting devices(OLEDs). We used various methods of ITO surface treatment and examined the effects of them by measuring contact angle and calculating surface energy. We also prepared OLEDs with ITO treated by each method, and estimated their characteristics. The surface of ITO treated by UV-O3 or O2-plasma was more hydrophilic than that treated by only organic rinse or no treatment, and consequently the characteristic of the OLED was improved. We suppose these treatments affect the hole injection from ITO into organic layer, due to ionization potential or surface cleanness. We also investigated time degradation of NPD films on the ITO substrates. The films deposited with high deposition rate porycrystallized faster.

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

    PubMed

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

    2016-08-01

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

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

    PubMed

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

    2016-08-01

    Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices. PMID:27214091

  11. Reshaping Light-Emitting Diodes To Increase External Efficiency

    NASA Technical Reports Server (NTRS)

    Rogowski, Robert; Egalon, Claudio

    1995-01-01

    Light-emitting diodes (LEDs) reshaped, according to proposal, increasing amount of light emitted by decreasing fraction of light trapped via total internal reflection. Results in greater luminous output power for same electrical input power; greater external efficiency. Furthermore, light emitted by reshaped LEDs more nearly collimated (less diffuse). Concept potentially advantageous for conventional red-emitting LEDs. More advantageous for new "blue" LEDs, because luminous outputs and efficiencies of these devices very low. Another advantage, proposed conical shapes achieved relatively easily by chemical etching of semiconductor surfaces.

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

    ERIC Educational Resources Information Center

    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…

  13. Adjunctive dental therapy via tooth plaque reduction and gingivitis treatment by blue light-emitting diodes tooth brushing.

    PubMed

    Genina, Elina A; Titorenko, Vladimir A; Belikov, Andrey V; Bashkatov, Alexey N; Tuchin, Valery V

    2015-01-01

    The efficacy of blue light-emitting toothbrushes (B-LETBs) (405 to 420 nm, power density 2  mW/cm(2)) for reduction of dental plaques and gingival inflammation has been evaluated. Microbiological study has shown the multifactor therapeutic action of the B-LETBs on oral pathological microflora: in addition to partial mechanical removal of bacteria, photodynamic action suppresses them up to 97.5%. In the pilot clinical studies, subjects with mild to moderate gingivitis have been randomly divided into two groups: a treatment group that used the B-LETBs and a control group that used standard toothbrushes. Indices of plaque, gingival bleeding, and inflammation have been evaluated. A significant improvement of all dental indices in comparison with the baseline (by 59%, 66%, and 82% for plaque, gingival bleeding, and inflammation, respectively) has been found. The treatment group has demonstrated up to 50% improvement relative to the control group. We have proposed the B-LETBs to serve for prevention of gingivitis or as an alternative to conventional antibiotic treatment of this disease due to their effectiveness and the absence of drug side effects and bacterial resistance.

  14. Adjunctive dental therapy via tooth plaque reduction and gingivitis treatment by blue light-emitting diodes tooth brushing

    NASA Astrophysics Data System (ADS)

    Genina, Elina A.; Titorenko, Vladimir A.; Belikov, Andrey V.; Bashkatov, Alexey N.; Tuchin, Valery V.

    2015-12-01

    The efficacy of blue light-emitting toothbrushes (B-LETBs) (405 to 420 nm, power density 2 mW/cm2) for reduction of dental plaques and gingival inflammation has been evaluated. Microbiological study has shown the multifactor therapeutic action of the B-LETBs on oral pathological microflora: in addition to partial mechanical removal of bacteria, photodynamic action suppresses them up to 97.5%. In the pilot clinical studies, subjects with mild to moderate gingivitis have been randomly divided into two groups: a treatment group that used the B-LETBs and a control group that used standard toothbrushes. Indices of plaque, gingival bleeding, and inflammation have been evaluated. A significant improvement of all dental indices in comparison with the baseline (by 59%, 66%, and 82% for plaque, gingival bleeding, and inflammation, respectively) has been found. The treatment group has demonstrated up to 50% improvement relative to the control group. We have proposed the B-LETBs to serve for prevention of gingivitis or as an alternative to conventional antibiotic treatment of this disease due to their effectiveness and the absence of drug side effects and bacterial resistance.

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

    PubMed

    Zhang, Yan; Wang, Zhong Lin

    2012-09-01

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

  16. Effects on the spectrum of the blue organic light-emitting diodes by the indium tin oxide surface treatment

    NASA Astrophysics Data System (ADS)

    Ji, Xing-qiao; Li, Wei-zhi; Zhong, Zhi-you; Wang, Tao; Jiang, Ya-dong

    2006-01-01

    Deionized water, sulfur acid (98%) (H2SO4), sodium hydroxide (NaOH) solution and oxygen plasma are used to treat ITO substrates, then blue organic light emitting devices (OLEDs) with the structure of ITO/NPB(50 nm)/BAlq 3(40 nm)/Alq 3(25 nm)/Mg:Ag are fabricated in the vacuum. The experiment results show that ITO treatments influence the electroluminescence (EL) spectrum of the blue OLEDs, the OLEDs which are treated by four methods the EL spectrums change from 496 to 455 nm. According to atom force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) analysis, the surface morphology and surface composition are greatly changed, so the surface work function is changed, then recombination zone of the carrier is moved, which leading to the emission spectrums alter. The ITO substrate is treated by oxygen plasma, which has the highest oxygen concentration, so the surface work function is the greatest, the hole can jump the barrier and recombine in BAlq 3-Alq 3 interface, the spectral peak is at 496 nm. The ITO treated by acid solution, the oxygen concentration is less than that of plasma treatment, so the surface work function is also less than it, thus the hole can inject into the BAlq 3 layer, the spectral peak is at 480 nm. Roughness of deionized water treated ITO is the largest, which can became local high electric field, so some hole are excitated into the BAlq 3-Alq 3 interface, most of the hole are blocked by BAlq 3 barrier, the light from BAlq 3-Alq 3 interface and NPB layer, the spectral peak is at 474 nm. The ITO treated by NaOH solution, the oxygen concentration is the lowest, so the surface work function is also the lowest, all of the hole are blocked by BAlq 3 layer, they can only recombine in the NPB layer, the spectral peak is at 455 nm.

  17. A multi-source portable light emitting diode spectrofluorometer

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A portable luminescence spectrofluorometer weighing only 1.5 kg that uses multiple light emitting diodes (LEDs) as excitation sources was developed and evaluated. Excitation using a sequence of seven individual broad-band LED emission sources enabled the generation of excitation-emission spectra usi...

  18. Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes.

    PubMed

    Byun, Jinwoo; Cho, Himchan; Wolf, Christoph; Jang, Mi; Sadhanala, Aditya; Friend, Richard H; Yang, Hoichang; Lee, Tae-Woo

    2016-09-01

    Efficient quasi-2D-structure perovskite light-emitting diodes (4.90 cd A(-1) ) are demonstrated by mixing a 3D-structured perovskite material (methyl ammonium lead bromide) and a 2D-structured perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density. PMID:27334788

  19. Atom probe tomography of a commercial light emitting diode

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

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

  20. Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes.

    PubMed

    Byun, Jinwoo; Cho, Himchan; Wolf, Christoph; Jang, Mi; Sadhanala, Aditya; Friend, Richard H; Yang, Hoichang; Lee, Tae-Woo

    2016-09-01

    Efficient quasi-2D-structure perovskite light-emitting diodes (4.90 cd A(-1) ) are demonstrated by mixing a 3D-structured perovskite material (methyl ammonium lead bromide) and a 2D-structured perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density.

  1. The Light-Emitting Diode as a Light Detector

    ERIC Educational Resources Information Center

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

    2011-01-01

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

  2. Singlet oxygen and organic light-emitting diodes

    SciTech Connect

    Jacobs, S.J.; Sinclair, M.B.; Valencia, V.S.; Kepler, R.G.; Clough, R.L.; Scurlock, R.D.; Ogilby, P.R.

    1995-07-01

    The preparation of light emitting diodes employing a new class of materials, 5,10-dihetera 5,10-dihydro-indeno[3,2b]indenes, as hole transport agents is described. These materials have been found to be more resistant to degradation by singlet oxygen than a poly(p-phenylene vinylene) (PPV) derivative.

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

    PubMed

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

    2009-06-01

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

  4. Vegetable surface sterilization system using UVA light-emitting diodes.

    PubMed

    Aihara, Mutsumi; Lian, Xin; Shimohata, Takaaki; Uebanso, Takashi; Mawatari, Kazuaki; Harada, Yumi; Akutagawa, Masatake; Kinouchi, Yohsuke; Takahashi, Akira

    2014-01-01

    Surface sterilization of fresh produce has been needed in the food manufacturing/processing industry. Here we report a UVA-LED (Ultra Violet A-Light Emitting Diode) system for surface sterilization that is safe, efficacious, low cost, and apparently harmless to fresh produce. To test the system, Escherichia coli strain DH5α was spot-inoculated onto vegetable tissues, and treated under UVA-LED. Tissues were homogenized and bacteria quantified by colony-forming assay. Possible effects of UVA-LED on vegetable quality were evaluated by HPLC. Tissue weight changes were checked after treatment at 4℃, 15℃, and 30℃. Bacterial inactivation by UVA-LED radiation was observed after a 10 min treatment and increased with increasing time of irradiation. The log survival ratio reached -3.23 after a 90 min treatment. Bacterial cells surviving treatment grew slowly compared to non-irradiated control cells. Cabbage tissue lost weight over time after treatment, and weight loss increased with increasing incubation temperature, but there was no difference between losses by UVA-LED treated and control tissues at any temperature tested. In addition, no differences of Vitamin C content in cabbage tissue were detected by HPLC after UVA-LED treatment. These results suggest that UVA-LED treatment has great potential for vegetable surface sterilization in the food manufacturing/processing industry.

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

    DOEpatents

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

    2005-11-29

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

  6. Vacuum Nanohole Array Embedded Phosphorescent Organic Light Emitting Diodes

    PubMed Central

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

    2015-01-01

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

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

    DOEpatents

    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").

  8. High extraction efficiency ultraviolet light-emitting diode

    DOEpatents

    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.

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

    PubMed

    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

    Organic light-emitting diodes have been recently focused for flexible display and solid-state lighting applications and so much effort has been devoted to achieve highly efficient organic light-emitting diodes. 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 to the nanostructure of ZnO. The nanostructure of the ZnO layer improves the extraction of the waveguide modes inside the device structure, and a 2-ME+EA interlayer enhances the electron injection and hole blocking in addition to reducing exciton quenching between the polar-solvent-treated ZnO and the emissive layer. Therefore, our optimized inverted polymer light-emitting diodes have a luminous efficiency of 61.6 cd A(-1) and an external quantum efficiency of 17.8%, which are the highest efficiency values among polymer-based fluorescent light-emitting diodes that contain a single emissive layer.

  10. Versatile multispectral microscope based on light emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  11. High efficiency solution processed fluorescent yellow organic light-emitting diode through fluorinated alcohol treatment at the emissive layer/cathode interface

    NASA Astrophysics Data System (ADS)

    Ng, Calvin Yi Bin; Yeoh, Keat Hoe; Whitcher, Thomas J.; Azrina Talik, Noor; Woon, Kai Lin; Saisopa, Thanit; Nakajima, Hideki; Supruangnet, Ratchadaporn; Songsiriritthigul, Prayoon

    2014-01-01

    We compare solvent treatments using fluorinated alcohol (2,2,3,3,4,4,5,5-octafluoro- 1-pentanol) and ethanol in improving the efficiency of a polymer organic light-emitting diode (OLED) by spin coating the solvent on top of the emissive layer. The presence of fluorinated alcohol is confirmed using x-ray photoelectron spectroscopy. The electron current is found to be significantly enhanced following solvent treatment while the hole current remains the same. The solvent treatment by fluorinated alcohol on top of a ‘super-yellow’ poly-(p-phenylenevinylene) (SY-PPV) based OLED results in efficiency as high as 19.2 lm W-1 (20.9 cd A-1) at a brightness of 1000 cd m-2. The improvement of device efficiency through the use of fluorinated alcohol treatment can be attributed to its large dipole, which lowers the electron injection barrier. This work also suggests that fluorinated alcohol might be a better trap passivator for electrons than ethanol.

  12. Fabrication of poly(p-phenyleneacetylene) light-emitting diodes

    DOEpatents

    Shinar, Joseph; Swanson, Leland S.; Lu, Feng; Ding, Yiwei

    1994-08-02

    Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as A1 or A1/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes.

  13. Fabrication of poly(p-phenyleneacetylene) light-emitting diodes

    DOEpatents

    Shinar, J.; Swanson, L.S.; Lu, F.; Ding, Y.

    1994-08-02

    Acetylene-containing poly(p-phenyleneacetylene) (PPA)-based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes. 8 figs.

  14. Poly (p-phenyleneacetylene) light-emitting diodes

    DOEpatents

    Shinar, J.; Swanson, L.S.; Lu, F.; Ding, Y.; Barton, T.J.; Vardeny, Z.V.

    1994-10-04

    Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes. 8 figs.

  15. Poly (p-phenyleneneacetylene) light-emitting diodes

    DOEpatents

    Shinar, Joseph; Swanson, Leland S.; Lu, Feng; Ding, Yiwei; Barton, Thomas J.; Vardeny, Zeev V.

    1994-10-04

    Acetylene containing poly(p-phenyleneacetylene) (PPA) - based light-emitting diodes (LEDs) are provided. The LEDs are fabricated by coating a hole-injecting electrode, preferably an indium tin oxide (ITO) coated glass substrate, with a PPA polymer, such as a 2,5-dibutoxy or a 2,5-dihexoxy derivative of PPA, dissolved in an organic solvent. This is then followed by evaporating a layer of material capable of injecting electrons, such as Al or Al/Ca, onto the polymer to form a base electrode. This composition is then annealed to form efficient EL diodes.

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

    PubMed

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

    2015-12-22

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

  17. All-solution processed transparent organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Höfle, Stefan; Czolk, Jens; Mertens, Adrian; Colsmann, Alexander

    2015-11-01

    In this work, we report on indium tin oxide-free, all-solution processed transparent organic light emitting diodes (OLEDs) with inverted device architecture. Conductive polymer layers are employed as both transparent cathodes and transparent anodes, with the top anodes having enhanced conductivities from a supporting stochastic silver nanowire mesh. Both electrodes exhibit transmittances of 80-90% in the visible spectral regime. Upon the incorporation of either yellow- or blue-light emitting fluorescent polymers, the OLEDs show low onset voltages, demonstrating excellent charge carrier injection from the polymer electrodes into the emission layers. Overall luminances and current efficiencies equal the performance of opaque reference OLEDs with indium tin oxide and aluminium electrodes, proving excellent charge carrier-to-light conversion within the device.

  18. Effects of multiple interruptions with trimethylindium-treatment in the InGaN/GaN quantum well on green light emitting diodes

    NASA Astrophysics Data System (ADS)

    Qiao, Liang; Ma, Zi-Guang; Chen, Hong; Wu, Hai-Yan; Chen, Xue-Fang; Yang, Hao-Jun; Zhao, Bin; He, Miao; Zheng, Shu-Wen; Li, Shu-Ti

    2016-10-01

    In this study, the influence of multiple interruptions with trimethylindium (TMIn)-treatment in InGaN/GaN multiple quantum wells (MQWs) on green light-emitting diode (LED) is investigated. A comparison of conventional LEDs with the one fabricated with our method shows that the latter has better optical properties. Photoluminescence (PL) full-width at half maximum (FWHM) is reduced, light output power is much higher and the blue shift of electroluminescence (EL) dominant wavelength becomes smaller with current increasing. These improvements should be attributed to the reduced interface roughness of MQW and more uniformity of indium distribution in MQWs by the interruptions with TMIn-treatment. Project supported by the National Natural Science Foundation of China (Grant Nos. 11204360 and 61210014), the Science and Technology Planning Projects of Guangdong Province, China (Grant Nos. 2014B050505020, 2015B010114007, and 2014B090904045), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20134407110008), the Guangzhou Municipal Science and Technology Project of Guangdong Province, China (Grant No. 2016201604030027), and the Zhongshan Science and Technology Project of Guangdong Province, China (Grant No. 2013B3FC0003).

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

    SciTech Connect

    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.

  20. Theory of Microcavity Organic Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Rothberg, L. J.; Dodabalapur, A.; Jordan, R. H.; Slusher, R. E.

    1996-03-01

    We adapt the theory of Schubert and coworkers footnote N. E. J. Hunt, E. F. Schubert and G. J. Zydzik, Appl. Phys. Lett. 63, 391 (1993). for resonant cavity inorganic light-emitting diodes (LEDs) to evaluate analogous organic devices for various display applications. The theory is used to calculate angular distribution of intensity and color, as well as to investigate optimizing light output from organic LEDs. Our results agree well with experimental measurements on microcavity devices we have fabricated from hydroxyquinolinealuminum (Alq) and doped Alq emitters.

  1. Optimization of freeform lightpipes for light-emitting-diode projectors.

    PubMed

    Fournier, Florian; Rolland, Jannick

    2008-03-01

    Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

  2. Optimization of freeform lightpipes for light-emitting-diode projectors

    NASA Astrophysics Data System (ADS)

    Fournier, Florian; Rolland, Jannick

    2008-03-01

    Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

  3. Performance and trends of high power light emitting diodes

    NASA Astrophysics Data System (ADS)

    Bierhuizen, Serge; Krames, Michael; Harbers, Gerard; Weijers, Gon

    2007-09-01

    We will discuss the performance, progress and trend of High Power Light Emitting Diodes (HP-LEDs), suitable for high luminance applications like micro-display projection, car headlamps, spot lamps, theatre lamps, etc. Key drivers for the high luminance applications are LED parameters such as internal quantum efficiency, extraction efficiency, drive current, operating temperature and optical coupling efficiency, which are important for most applications as they also enable higher lumen/$ ratios. Historical progress, prospects for improving these parameters and potential optical luminance enhancement methods to meet the demands for the various illumination applications are presented.

  4. Nanosecond transient electroluminescence from polymer light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Braun, D.; Moses, D.; Zhang, C.; Heeger, A. J.

    1992-12-01

    The transient electroluminescence from polymer light-emitting diodes is reported. When the devices are mounted on a microstrip transmission line, the temporal response is limited by the electrode geometry, with rise and fall times below 50 ns. With low duty-cycle pulses (0.5%) the electroluminescence intensity remains proportional to the current at values up to 10 A/cm2, two orders of magnitude greater than possible under direct current operation. Since the spectral blue-shift observed at high current levels (with power dissipation above 1 W/cm2) indicates significant sample heating, still higher levels should be possible with proper thermal management.

  5. High efficiency III-nitride light-emitting diodes

    DOEpatents

    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.

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

    PubMed Central

    O'Toole, Martina; Diamond, Dermot

    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 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.

  7. Optimization of freeform lightpipes for light-emitting-diode projectors.

    PubMed

    Fournier, Florian; Rolland, Jannick

    2008-03-01

    Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe. PMID:18311267

  8. Thermoelectrically pumped light-emitting diodes operating above unity efficiency.

    PubMed

    Santhanam, Parthiban; Gray, Dodd Joseph; Ram, Rajeev J

    2012-03-01

    A heated semiconductor light-emitting diode at low forward bias voltage V

  9. New materials for organic light-emitting diodes

    SciTech Connect

    Jacobs, S.J.; Pollagi, T.P.; Sinclair, M.B.; Scurlock, R.D.; Ogilby, P.R.

    1995-12-01

    We have investigated the performance of a class of heterocycles, 5, 10-dihetera-5,10-dihydroindeno[3,2b]indenes, as hole transport agents in simple double heterostructure organic light-emitting diodes with tris(8-hydroxyquinoline)aluminum (Alq). The best of these materials, 5,10-dihydroindolo[3,2b]indole, yields devices with luminance and lifetimes comparable to those obtained using N,N{prime}-di-(3-methylphenyl)-N,N{prime}diphenyl-4,4{prime}-diaminobiphenyl (TPD) as a hole transporting material.

  10. Topical and Intradermal Efficacy of Photodynamic Therapy with Methylene Blue and Light-Emitting Diode in the Treatment of Cutaneous Leishmaniasis Caused by Leishmania braziliensis

    PubMed Central

    Sbeghen, Mônica Raquel; Voltarelli, Evandra Maria; Campois, Tácito Graminha; Kimura, Elza; Aristides, Sandra Mara Alessi; Hernandes, Luzmarina; Caetano, Wilker; Hioka, Noboru; Lonardoni, Maria Valdrinez Campana; Silveira, Thaís Gomes Verzignassi

    2015-01-01

    Introduction: The topical and intradermal photodynamic therapy (PDT) effect of methylene blue (MB) using light-emitting diode (LED) as light source (MB/LED-PDT) in the treatment of lesions of American cutaneous leishmaniasis (ACL) caused by Leishmania braziliensis in hamsters were investigated. Methods: Hamsters were infected in the footpad with 4×107 promastigotes of L. braziliensis and divided in 4 groups: Control group was not treated, AmB group was treated with amphotericin B, MB-Id group received intradermal MB at the edge of the lesion and MB-Tp group received MB topic. After treatment with MB, the animals were illuminated using red LEDs at the 655 nm wavelength for 1 hour. The MB/LED-PDT was carried out three times a week for 12 weeks. Results: Animals of MB-Tp group presented lesion healing with significant diminution in extent of the lesion, and reduced parasite burden compared to control group; however, no significant difference was seen compared to the AmB group. MB-Tp group also showed reconstitution of the epithelium, the formation of collagen fibers, organization in the epidermis, a little disorganization and inflammation in the dermis. MB-Id was ineffective in all parameters evaluated, and it was comparable to the control group results. Conclusion: These data show that PDT with the use of MB-Tp and LED may be an alternative for the treatment of ACL. However, additional studies are being conducted to assess the potential of MB/LED-PDT, alone or in combination with conventional therapy, for the treatment of ACL. PMID:26464777

  11. All-solution processed polymer light-emitting diode displays

    NASA Astrophysics Data System (ADS)

    Zheng, Hua; Zheng, Yina; Liu, Nanliu; Ai, Na; Wang, Qing; Wu, Sha; Zhou, Junhong; Hu, Diangang; Yu, Shufu; Han, Shaohu; Xu, Wei; Luo, Chan; Meng, Yanhong; Jiang, Zhixiong; Chen, Yawen; Li, Dongyun; Huang, Fei; Wang, Jian; Peng, Junbiao; Cao, Yong

    2013-06-01

    Adopting the emerging technology of printed electronics in manufacturing novel ultrathin flat panel displays attracts both academic and industrial interests because of the challenge in the device physics and the potential of reducing production costs. Here we produce all-solution processed polymer light-emitting diode displays by solution-depositing the cathode and utilizing a multifunctional buffer layer between the cathode and the organic layers. The use of ink-jetted conducting nanoparticles as the cathode yields high-resolution cathode patterns without any mechanical stress on the organic layers. The buffer layer, which offers the functions of solvent-proof electron injection and proper affinity, is fabricated by mixing the water/alcohol-soluble polymer and a curable epoxy adhesive. Our 1.5-inch polymer light-emitting diode displays are fabricated without any dead pixels or dead lines. The all-solution process eliminates the need for high vacuum for thermal evaporation of the cathode, which paves the way to industrial roll-to-roll manufacturing of flat panel displays.

  12. A novel yellow phosphor for white light emitting diodes

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Jun; Li, Pan-Lai; Yang, Zhi-Ping; Guo, Qing-Lin; Li, Xu

    2010-01-01

    This paper reports that a novel yellow phosphor, LiSrBO3:Eu2+, was synthesized by the solid-state reaction. The excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet (360 and 400 nm) and blue (425 and 460 nm) light, and exhibits a satisfactory yellow performance (565 nm). The role of concentration of Eu2+ on the emission intensity in LiSrBO3 is studied, and it is found that the critical concentration is 3 mol%, and the concentration self-quenching mechanism is the dipole-dipole interaction according to the Dexter theory. White light emitting diodes were generated by using an InGaN chip (460 nm or 400 nm) with LiSrBO3:Eu2+ phosphor, the CIE chromaticity is (x = 0.341, y = 0.321) and (x = 0.324, y = 0.318), respectively. Therefore, LiSrBO3:Eu2+ is a promising yellow phosphor for white light emitting diodes.

  13. Deep ultraviolet light-emitting and laser diodes

    NASA Astrophysics Data System (ADS)

    Khan, Asif; Asif, Fatima; Muhtadi, Sakib

    2016-02-01

    Nearly all the air-water purification/polymer curing systems and bio-medical instruments require 250-300 nm wavelength ultraviolet light for which mercury lamps are primarily used. As a potential replacement for these hazardous mercury lamps, several global research teams are developing AlGaN based Deep Ultraviolet (DUV) light emitting diodes (LEDs) and DUV LED Lamps and Laser Diodes over Sapphire and AlN substrates. In this paper, we review the current research focus and the latest device results. In addition to the current results we also discuss a new quasipseudomorphic device design approach. This approach which is much easier to integrate in a commercial production setting was successfully used to demonstrate UVC devices on Sapphire substrates with performance levels equal to or better than the conventional relaxed device designs.

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

    SciTech Connect

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

    1998-01-15

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

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

    SciTech Connect

    Römer, Friedhard Witzigmann, Bernd

    2015-01-12

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

  16. Vacuum nano-hole array embedded organic light emitting diodes.

    PubMed

    Jeon, Sohee; Jeong, Jun-ho; Song, Young Seok; Jeong, Won-Ik; Kim, Jang-Joo; Youn, Jae Ryoun

    2014-03-01

    We demonstrated a nano-hole array (NHA) embedded structure that was fabricated for organic light emitting diodes (OLEDs) using a robust reverse transfer process. The NHA structure is proposed in this study as a strategy for maximizing the diffraction strength of two dimensional photonic crystals (PCs) by engineering vacuum nano-holes inside a dielectric slab. The electroluminescence (EL) intensity of the OLED was improved by more than twice. Such an optical enhancement was evaluated by using the angular dependence of photoluminescence (PL). The FDTD simulation was carried out to optimize the NHA structure for extraction of the emission induced from both vertical and horizontal dipoles. We explored the effect of the NHA structure on the extraction improvement converted from waveguide mode by measuring EL intensities of the devices with a hemisphere lens. In addition, the transfer process employed in this study yielded extremely low surface roughness, and thus outstanding electrical characteristics.

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

    PubMed

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

    2016-04-18

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

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

    SciTech Connect

    Özdemir, Orhan; Kavak, Pelin; Saatci, A. Evrim; Gökdemir, F. Pınar; Menda, U. Deneb; Can, Nursel; Kutlu, Kubilay; Tekin, Emine; Pravadalı, Selin

    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.

  19. Light manipulation for organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Ou, Qing-Dong; Zhou, Lei; Li, Yan-Qing; Tang, Jian-Xin

    2014-10-01

    To realize high-efficiency organic light-emitting diodes (OLEDs), it is essential to boost out-coupling efficiency. Here we review our latest reports upon light manipulation for OLEDs by integrating a dual-side bio-inspired deterministic quasi-periodic moth's eye nanostructure with broadband anti-reflective and quasi-omnidirectional properties. Light out-coupling efficiency of OLEDs with stacked triple emission units is over 2 times that of a conventional device, resulting in drastic increase in external quantum efficiency and current efficiency to 119.7% and 366 cd A-1 without introducing spectral distortion and directionality. Theoretical calculations furthermore clarify that the improved device performance is primarily attributed to the effective extraction of the waveguide and surface plasmonic modes of the confined light over all the emission wavelengths and viewing-angles.

  20. Exciton dynamics in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Kim, Kwangsik; Won, Taeyoung

    2012-11-01

    In this paper, we present a numerical simulation for the optoelectronic material and device characterization in organic light-emitting diodes (OLEDs). Our model includes a Gaussian density of states to account for the energetic disorder in the organic semiconductors and the Fermi-Dirac statistics to account for the charge-hopping process between uncorrelated sites. The motivation for this work is the extraction of the emission profile and the source spectrum of a given OLED structure. The physical model covers all the key physical processes in OLEDs: namely, charge injection, transport and recombination, exciton diffusion, transfer, and decay. The exciton model includes generation, diffusion, energy transfer, and annihilation. We assume that the light emission originates from an oscillation and is thus embodied as excitons and is embedded in a stack of multilayers. The outcoupled emission spectrum is numerically calculated as a function of viewing angle, polarization, and dipole orientation. We also present simulated current-voltage and transient results.

  1. Quantum teleportation using a light-emitting diode

    NASA Astrophysics Data System (ADS)

    Nilsson, J.; Stevenson, R. M.; Chan, K. H. A.; Skiba-Szymanska, J.; Lucamarini, M.; Ward, M. B.; Bennett, A. J.; Salter, C. L.; Farrer, I.; Ritchie, D. A.; Shields, A. J.

    2013-04-01

    Teleportation of optical qubits can enable reliable logic operations in massively parallel quantum computers, as well as the formation of secure quantum networks. Photon teleportation has previously used laser-generated entangled photons created in random quantities. However, the practical complexities of the generating scheme coupled with errors caused by multipair emission have complicated its deployment in useful quantum information technology. Here, we demonstrate teleportation of single photonic qubits, mediated by individual pairs of entangled photons generated by an electrically driven entangled light source realized by embedding a single semiconductor quantum dot within a light-emitting diode. Teleportation is achieved with six general input states, with asymmetrically distributed fidelities, and an average fidelity above the limit possible with classical light. A theoretical framework is created that reproduces our experiments with close agreement. The unique sub-Poissonian nature of our photonic teleporter together with its electrical operation will help lift the complexity restriction of future quantum information applications.

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

    NASA Technical Reports Server (NTRS)

    1999-01-01

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

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

    PubMed

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

    2010-08-01

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

  4. Semiconductor Nanocrystals-Based White Light Emitting Diodes

    SciTech Connect

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

    2010-01-01

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

  5. Tunnel junction enhanced nanowire ultraviolet light emitting diodes

    SciTech Connect

    Sarwar, A. T. M. Golam; May, Brelon J.; Deitz, Julia I.; Grassman, Tyler J.; McComb, David W.; Myers, Roberto C.

    2015-09-07

    Polarization engineered interband tunnel junctions (TJs) are integrated in nanowire ultraviolet (UV) light emitting diodes (LEDs). A ∼6 V reduction in turn-on voltage is achieved by the integration of tunnel junction at the base of polarization doped nanowire UV LEDs. Moreover, efficient hole injection into the nanowire LEDs leads to suppressed efficiency droop in TJ integrated nanowire LEDs. The combination of both reduced bias voltage and increased hole injection increases the wall plug efficiency in these devices. More than 100 μW of UV emission at ∼310 nm is measured with external quantum efficiency in the range of 4–6 m%. The realization of tunnel junction within the nanowire LEDs opens a pathway towards the monolithic integration of cascaded multi-junction nanowire LEDs on silicon.

  6. Light-emitting diode technology improves insect trapping.

    PubMed

    Cohnstaedt, Lee W; Gillen, Jonathon I; Munstermann, Leonard E

    2008-06-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Hlobil, Patrik; Orth, Peter P.

    2015-05-01

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

  8. Mid-ultraviolet light-emitting diode detects dipicolinic acid.

    SciTech Connect

    Bogart, Katherine Huderle Andersen; Lee, Stephen Roger; Temkin, Henryk; Crawford, Mary Hagerott; Dasgupta, Purnendu K.; Li, Qingyang; Allerman, Andrew Alan; Fischer, Arthur Joseph

    2005-06-01

    Dipicolinic acid (DPA, 2,6-pyridinedicarboxylic acid) is a substance uniquely present in bacterial spores such as that from anthrax (B. anthracis). It is known that DPA can be detected by the long-lived fluorescence of its terbium chelate; the best limit of detection (LOD) reported thus far using a large benchtop gated fluorescence instrument using a pulsed Xe lamp is 2 nM. We use a novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm. Although the overlap of the emission band of this LED with the absorption band of Tb-DPA ({lambda}{sub max} doublet: 273, 279 nm) is not ideal, we demonstrate that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.

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

    PubMed Central

    2011-01-01

    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. PMID:21711711

  10. Quantum key distribution with an entangled light emitting diode

    SciTech Connect

    Dzurnak, B.; Stevenson, R. M.; Nilsson, J.; Dynes, J. F.; Yuan, Z. L.; Skiba-Szymanska, J.; Shields, A. J.; Farrer, I.; Ritchie, D. A.

    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. New TIR lens applications for light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Parkyn, William A.; Pelka, David G.

    1997-10-01

    We present two new applications for light emitting diodes of the Total Internal Reflection (TIR) lens, a non-imaging optical device presented at previous SPIE conferences on nonimaging optics. The first is a flat circularly symmetric lens that efficiently forms a highly collimated beam from the light output of Hewlett-Packard's Super Flux LEDs. The second is a linear TIR lens with die-on-board LEDs of several wavelengths positioned along its focal line. HP's Super-Flux LED package has an output half angle of 55 degree(s). Only the TIR lens can accept such a wide range for beamforming, and do it with high efficiency. We have designed and prototyped 1' models with half-power half angles of only 1.5 degree(s), utilizing a hyperbolic central section in place of the usual Fresnel lens. There are numerous applications for arrays of these lenses, since they emit more lumens per electrical watt than filtered incandescent lamps with parabolic mirrors. Moreover, they are more compact than conventional lamps, and LED lifetimes are much longer. The TIR lens in its linear form has been applied successfully to fluorescent downlighting products with much narrower transverse illumination angles than previously available with trough mirrors. More recently, light emitting diodes (LEDs) have been placed on the focal line of a linear lens. In this paper, we describe the optical properties and biomedical applications of the linear TIR lens when the LEDs have several different emission wavelengths. This single device can uniformly illuminate an extended target with several wavelengths either simultaneously, sequentially, or in complex programmed combinations. It can replace the complex systems of dichroic mirrors used with conventional white-light sources.

  12. Significant Improvements in Cognitive Performance Post-Transcranial, Red/Near-Infrared Light-Emitting Diode Treatments in Chronic, Mild Traumatic Brain Injury: Open-Protocol Study

    PubMed Central

    Zafonte, Ross; Krengel, Maxine H.; Martin, Paula I.; Frazier, Judith; Hamblin, Michael R.; Knight, Jeffrey A.; Meehan, William P.; Baker, Errol H.

    2014-01-01

    Abstract This pilot, open-protocol study examined whether scalp application of red and near-infrared (NIR) light-emitting diodes (LED) could improve cognition in patients with chronic, mild traumatic brain injury (mTBI). Application of red/NIR light improves mitochondrial function (especially in hypoxic/compromised cells) promoting increased adenosine triphosphate (ATP) important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. LED therapy is noninvasive, painless, and non-thermal (cleared by the United States Food and Drug Administration [FDA], an insignificant risk device). Eleven chronic, mTBI participants (26–62 years of age, 6 males) with nonpenetrating brain injury and persistent cognitive dysfunction were treated for 18 outpatient sessions (Monday, Wednesday, Friday, for 6 weeks), starting at 10 months to 8 years post- mTBI (motor vehicle accident [MVA] or sports-related; and one participant, improvised explosive device [IED] blast injury). Four had a history of multiple concussions. Each LED cluster head (5.35 cm diameter, 500 mW, 22.2 mW/cm2) was applied for 10 min to each of 11 scalp placements (13 J/cm2). LEDs were placed on the midline from front-to-back hairline; and bilaterally on frontal, parietal, and temporal areas. Neuropsychological testing was performed pre-LED, and at 1 week, and 1 and 2 months after the 18th treatment. A significant linear trend was observed for the effect of LED treatment over time for the Stroop test for Executive Function, Trial 3 inhibition (p=0.004); Stroop, Trial 4 inhibition switching (p=0.003); California Verbal Learning Test (CVLT)-II, Total Trials 1–5 (p=0.003); and CVLT-II, Long Delay Free Recall (p=0.006). Participants reported improved sleep, and fewer post-traumatic stress disorder (PTSD) symptoms, if present. Participants and family reported better ability to perform social, interpersonal, and occupational functions. These open-protocol data suggest

  13. Significant improvements in cognitive performance post-transcranial, red/near-infrared light-emitting diode treatments in chronic, mild traumatic brain injury: open-protocol study.

    PubMed

    Naeser, Margaret A; Zafonte, Ross; Krengel, Maxine H; Martin, Paula I; Frazier, Judith; Hamblin, Michael R; Knight, Jeffrey A; Meehan, William P; Baker, Errol H

    2014-06-01

    This pilot, open-protocol study examined whether scalp application of red and near-infrared (NIR) light-emitting diodes (LED) could improve cognition in patients with chronic, mild traumatic brain injury (mTBI). Application of red/NIR light improves mitochondrial function (especially in hypoxic/compromised cells) promoting increased adenosine triphosphate (ATP) important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. LED therapy is noninvasive, painless, and non-thermal (cleared by the United States Food and Drug Administration [FDA], an insignificant risk device). Eleven chronic, mTBI participants (26-62 years of age, 6 males) with nonpenetrating brain injury and persistent cognitive dysfunction were treated for 18 outpatient sessions (Monday, Wednesday, Friday, for 6 weeks), starting at 10 months to 8 years post- mTBI (motor vehicle accident [MVA] or sports-related; and one participant, improvised explosive device [IED] blast injury). Four had a history of multiple concussions. Each LED cluster head (5.35 cm diameter, 500 mW, 22.2 mW/cm(2)) was applied for 10 min to each of 11 scalp placements (13 J/cm(2)). LEDs were placed on the midline from front-to-back hairline; and bilaterally on frontal, parietal, and temporal areas. Neuropsychological testing was performed pre-LED, and at 1 week, and 1 and 2 months after the 18th treatment. A significant linear trend was observed for the effect of LED treatment over time for the Stroop test for Executive Function, Trial 3 inhibition (p=0.004); Stroop, Trial 4 inhibition switching (p=0.003); California Verbal Learning Test (CVLT)-II, Total Trials 1-5 (p=0.003); and CVLT-II, Long Delay Free Recall (p=0.006). Participants reported improved sleep, and fewer post-traumatic stress disorder (PTSD) symptoms, if present. Participants and family reported better ability to perform social, interpersonal, and occupational functions. These open-protocol data suggest that placebo

  14. Significant improvements in cognitive performance post-transcranial, red/near-infrared light-emitting diode treatments in chronic, mild traumatic brain injury: open-protocol study.

    PubMed

    Naeser, Margaret A; Zafonte, Ross; Krengel, Maxine H; Martin, Paula I; Frazier, Judith; Hamblin, Michael R; Knight, Jeffrey A; Meehan, William P; Baker, Errol H

    2014-06-01

    This pilot, open-protocol study examined whether scalp application of red and near-infrared (NIR) light-emitting diodes (LED) could improve cognition in patients with chronic, mild traumatic brain injury (mTBI). Application of red/NIR light improves mitochondrial function (especially in hypoxic/compromised cells) promoting increased adenosine triphosphate (ATP) important for cellular metabolism. Nitric oxide is released locally, increasing regional cerebral blood flow. LED therapy is noninvasive, painless, and non-thermal (cleared by the United States Food and Drug Administration [FDA], an insignificant risk device). Eleven chronic, mTBI participants (26-62 years of age, 6 males) with nonpenetrating brain injury and persistent cognitive dysfunction were treated for 18 outpatient sessions (Monday, Wednesday, Friday, for 6 weeks), starting at 10 months to 8 years post- mTBI (motor vehicle accident [MVA] or sports-related; and one participant, improvised explosive device [IED] blast injury). Four had a history of multiple concussions. Each LED cluster head (5.35 cm diameter, 500 mW, 22.2 mW/cm(2)) was applied for 10 min to each of 11 scalp placements (13 J/cm(2)). LEDs were placed on the midline from front-to-back hairline; and bilaterally on frontal, parietal, and temporal areas. Neuropsychological testing was performed pre-LED, and at 1 week, and 1 and 2 months after the 18th treatment. A significant linear trend was observed for the effect of LED treatment over time for the Stroop test for Executive Function, Trial 3 inhibition (p=0.004); Stroop, Trial 4 inhibition switching (p=0.003); California Verbal Learning Test (CVLT)-II, Total Trials 1-5 (p=0.003); and CVLT-II, Long Delay Free Recall (p=0.006). Participants reported improved sleep, and fewer post-traumatic stress disorder (PTSD) symptoms, if present. Participants and family reported better ability to perform social, interpersonal, and occupational functions. These open-protocol data suggest that placebo

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Dye concentration study in PVK based light emitting diodes

    NASA Astrophysics Data System (ADS)

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

    1998-06-01

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

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

    NASA Technical Reports Server (NTRS)

    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

  18. Phosphorescent Organic Light Emitting Diodes Implementing Platinum Complexes

    NASA Astrophysics Data System (ADS)

    Ecton, Jeremy Exton

    Organic light emitting diodes (OLEDs) are a promising approach for display and solid state lighting applications. However, further work is needed in establishing the availability of efficient and stable materials for OLEDs with high external quantum efficiency's (EQE) and high operational lifetimes. Recently, significant improvements in the internal quantum efficiency or ratio of generated photons to injected electrons have been achieved with the advent of phosphorescent complexes with the ability to harvest both singlet and triplet excitons. Since then, a variety of phosphorescent complexes containing heavy metal centers including Os, Ni, Ir, Pd, and Pt have been developed. Thus far, the majority of the work in the field has focused on iridium based complexes. Platinum based complexes, however, have received considerably less attention despite demonstrating efficiency's equal to or better than their iridium analogs. In this study, a series of OLEDs implementing newly developed platinum based complexes were demonstrated with efficiency's or operational lifetimes equal to or better than their iridium analogs for select cases. In addition to demonstrating excellent device performance in OLEDs, platinum based complexes exhibit unique photophysical properties including the ability to form excimer emission capable of generating broad white light emission from a single emitter and the ability to form narrow band emission from a rigid, tetradentate molecular structure for select cases. These unique photophysical properties were exploited and their optical and electrical properties in a device setting were elucidated. Utilizing the unique properties of a tridentate Pt complex, Pt-16, a highly efficient white device employing a single emissive layer exhibited a peak EQE of over 20% and high color quality with a CRI of 80 and color coordinates CIE(x=0.33, y=0.33). Furthermore, by employing a rigid, tetradentate platinum complex, PtN1N, with a narrow band emission into a

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

    SciTech Connect

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

    2012-10-15

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

  20. Curing Efficacy of Light Emitting Diodes of Dental Curing Units

    PubMed Central

    Mousavinasab, Seyed Mostafa; Meyers, Ian

    2009-01-01

    Background and aims The aim of the present study was to compare the efficacy of quartz tungsten halogen (QTH) and light emitting diode (LED) curing lights on polymerization of resin composite. Materials and methods A hybrid resin composite was used to prepare samples which were cured using two QTH and ten LED light curing sources. Twelve groups, each containing ten samples, were prepared using each light source. The cured depth of the resin was determined using ISO 4049 method and Vickers hardness values were determined at 1.0 mm intervals. Data was analyzed by ANOVA and Tukey test. Results Data analysis demonstrated a significant difference between light sources for depth of cure. At 1.0 mm below the surface all the tested light sources and at 2.0-mm intervals all light sources except two (Optilux 501 and LEDemetron I) and at 3.0-mm intervals only two light sources (PenCure and LEDemetron II) could produce hardness values higher than 80% of superficial layer values. Conclusion This study showed that a variety of LED light sources used in the present study are as effective as the high-intensity QTH lights in polymerization of resin composite. PMID:23230474

  1. Perovskite energy funnels for efficient light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Yuan, Mingjian; Quan, Li Na; Comin, Riccardo; Walters, Grant; Sabatini, Randy; Voznyy, Oleksandr; Hoogland, Sjoerd; Zhao, Yongbiao; Beauregard, Eric M.; Kanjanaboos, Pongsakorn; Lu, Zhenghong; Kim, Dong Ha; Sargent, Edward H.

    2016-10-01

    Organometal halide perovskites exhibit large bulk crystal domain sizes, rare traps, excellent mobilities and carriers that are free at room temperature—properties that support their excellent performance in charge-separating devices. In devices that rely on the forward injection of electrons and holes, such as light-emitting diodes (LEDs), excellent mobilities contribute to the efficient capture of non-equilibrium charge carriers by rare non-radiative centres. Moreover, the lack of bound excitons weakens the competition of desired radiative (over undesired non-radiative) recombination. Here we report a perovskite mixed material comprising a series of differently quantum-size-tuned grains that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture. The materials function as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence non-radiative recombination. We use the new material to build devices that exhibit an external quantum efficiency (EQE) of 8.8% and a radiance of 80 W sr‑1 m‑2. These represent the brightest and most efficient solution-processed near-infrared LEDs to date.

  2. Organic light-emitting diodes formed by soft contact lamination.

    PubMed

    Lee, Tae-Woo; Zaumseil, Jana; Bao, Zhenan; Hsu, Julia W P; Rogers, John A

    2004-01-13

    Although tremendous progress has been made in organic light-emitting diodes (OLEDs), with few exceptions they are fabricated in the standard way by sequentially depositing active layers and electrodes onto a substrate. Here we describe a different approach for building OLEDs, which is based on physical lamination of thin metal electrodes supported by an elastomeric layer against an electroluminescent organic. This method relies only on van der Waals interactions to establish spatially homogeneous, intimate contacts between the electrodes and the organic. We find that devices fabricated in this manner have better performance than those constructed with standard processing techniques. The lamination approach avoids forms of disruption that can be introduced at the electrode/organic interface by metal evaporation and has a reduced sensitivity to pinhole or partial pinhole defects. In addition, because this form of "soft" contact lamination is intrinsically compatible with the techniques of soft lithography, it is easy to build patterned OLEDs with feature sizes into the nanometer regime. This method provides a new route to OLEDs for applications ranging from high performance displays to storage and lithography systems that rely on subwavelength light sources.

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

    PubMed

    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. PMID:26855251

  4. Simulated evolution of fluorophores for light emitting diodes

    SciTech Connect

    Shu, Yinan; Levine, Benjamin G.

    2015-03-14

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

  5. Simulated evolution of fluorophores for light emitting diodes.

    PubMed

    Shu, Yinan; Levine, Benjamin G

    2015-03-14

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

  6. High efficiency white organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhang, Gang; Dong, Weili; Gao, Hongyan; Tian, Xiaocui; Zhao, Lina; Jiang, Wenlong; Zhang, Xiyan

    2015-06-01

    The light emitting diodes with the structure of ITO/ m-MTDATA(20 nm)/NPB(10 nm)/CBP BCzVBi ( x, nm, 10%)/CBP(3 nm)/CBP: Ir(ppy)3: DCJTB(10 nm, 8 and 1%)/Bphen(30 nm)/Cs2CO3: Ag2O (2 nm, 20%)/Al (100 nm) employing phosphorescence sensitization and fluorescence doping, were manufactured. The performance of the devices was studied by adjusting the thickness of fluorescence dopant layer ( x = 15, 20, 25, and 30). The best performance was achieved when its thickness was 25 nm. The device has the maximum luminance of 20260 cd/m2 at applied voltage of 14 V and the maximum current efficiency of 11.70 cd/A at 7 V. The device displays a continuous change of color from yellow to white. The CIE coordinates change from (0.49, 0.48) to (0.32, 0.39) when the driving voltage is varied from 5 to 15 V.

  7. City of Phildelphia: Light emitting diodes for traffic signal displays

    SciTech Connect

    1995-12-01

    This project investigated the feasibility of using light emitting diodes (LEDs) for red traffic signals in a demonstration program at 27 signalized intersections in the City of Philadelphia. LED traffic signals have the potential to achieve significant savings over standard incandescent signals in terms of energy usage and costs, signal relamping costs, signal system maintenance costs, tort liability, and environmental impact. Based on successful experience with the demonstration program, the City of Philadelphia is currently developing funding for the conversion of all existing red incandescent traffic signals at approximately 2,700 intersections to LED signals. This program is expected to cost approximately $4.0 million and save about $850,000 annually in energy costs. During late 1993 and early 1994, 212 red LED traffic signals (134 8-inch signals and 78 12-inch signals) were installed at 27 intersections in Philadelphia. The first group of 93 signals were installed at 13 prototypical intersections throughout the City. The remaining group of signals were installed on a contiguous route in West Philadelphia consisting of standard incandescent signals and LED signals interspersed in a random pattern.

  8. White Light Emitting Diode Development for General Illumination Applications

    SciTech Connect

    James Ibbetson

    2006-05-01

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

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Magnetoresistance detected spin collectivity in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Malissa, Hans; Waters, David P.; Joshi, Gajadhar; Kavand, Marzieh; Limes, Mark E.; Burn, Paul L.; Lupton, John M.; Boehme, Christoph

    Organic magnetoresistance (OMAR) typically refers to the significant change in the conductivity of thin layers of organic semiconductors at low static magnetic fields (< 10 mT). When radio frequency (rf) radiation is applied to an organic semiconductor under bipolar injection, and in the presence of small magnetic fields B, magnetic resonance can occur, which is observed as a change of the OMAR effect [Baker et al., Nat. Commun. 3, 898 (2012)]. When B and the resonant driving field are stronger than local hyperfine fields, an ultrastrong coupling regime emerges, which is marked by collective spin effects analogous to the optical Dicke effect [Roundy and Raikh, Phys. Rev. B 88, 125206 (2013)]. Experimentally, this collective behavior of spins can be probed in the steady state OMAR of organic light-emitting diodes (OLEDs) at room temperature by observation of a sign reversal of the OMAR change under rf irradiation. Furthermore, in the presence of strong driving fields, an ac Zeeman effect can be observed through OMAR [Waters et al., Nat. Phys. 11, 910 (2015)], a unique window to observe room temperature macroscopic spin quantum coherence.

  11. White organic light-emitting diodes based on tandem structures

    NASA Astrophysics Data System (ADS)

    Guo, Fawen; Ma, Dongge

    2005-10-01

    White organic light-emitting diodes made of two electroluminescent (EL) units connected by a charge generation layer were fabricated. Thus, with a tandem structure of indium tin oxide/N ,N'-di(naphthalene-1-yl)-N ,N'-diphenyl-benzidine (NPB)/9,10-bis-(β-naphthyl)-anthrene (ADN)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(8-hydroxyquinoline) aluminum (Alq3)/BCP:Li/V2O5/NPB/Alq3:4-(dicyanomethylene)-2-t-butyle-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB)/Alq3/LiF/Al, a stable white light with Commission Internationale De L'Eclairage chromaticity coordinates from (0.35, 0.32) at 18V to (0.36, 0.36) at 50V was generated. It was clearly seen that the EL spectra consist of red band at 600nm due to DCJTB, green band at 505nm due to Alq3, and blue band at 435nm due to ADN, and the current efficiency and brightness equal basically to the sum of the two EL units. As a result, the tandem devices showed white light emission with a maximum brightness of 10200cd /m2 at a bias of 40V and a maximum current efficiency of 10.7cd/A at a current density of 3.5mA/cm2.

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

    PubMed

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

    1991-02-01

    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.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  15. 3D printed quantum dot light-emitting diodes.

    PubMed

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

    2014-12-10

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

  16. 3D printed quantum dot light-emitting diodes.

    PubMed

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

    2014-12-10

    Developing the ability to 3D print various classes of materials possessing distinct properties could enable the freeform generation of active electronics in unique functional, interwoven architectures. Achieving seamless integration of diverse materials with 3D printing is a significant challenge that requires overcoming discrepancies in material properties in addition to ensuring that all the materials are compatible with the 3D printing process. To date, 3D printing has been limited to specific plastics, passive conductors, and a few biological materials. Here, we show that diverse classes of materials can be 3D printed and fully integrated into device components with active properties. Specifically, we demonstrate the seamless interweaving of five different materials, including (1) emissive semiconducting inorganic nanoparticles, (2) an elastomeric matrix, (3) organic polymers as charge transport layers, (4) solid and liquid metal leads, and (5) a UV-adhesive transparent substrate layer. As a proof of concept for demonstrating the integrated functionality of these materials, we 3D printed quantum dot-based light-emitting diodes (QD-LEDs) that exhibit pure and tunable color emission properties. By further incorporating the 3D scanning of surface topologies, we demonstrate the ability to conformally print devices onto curvilinear surfaces, such as contact lenses. Finally, we show that novel architectures that are not easily accessed using standard microfabrication techniques can be constructed, by 3D printing a 2 × 2 × 2 cube of encapsulated LEDs, in which every component of the cube and electronics are 3D printed. Overall, these results suggest that 3D printing is more versatile than has been demonstrated to date and is capable of integrating many distinct classes of materials. PMID:25360485

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

    PubMed

    List, Emil J W; Koch, Norbert

    2011-11-01

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

  18. Comparative efficiency analysis of GaN-based light-emitting diodes and laser diodes

    NASA Astrophysics Data System (ADS)

    Piprek, Joachim

    2016-07-01

    Nobel laureate Shuji Nakamura predicted in 2014 that GaN-based laser diodes are the future of solid state lighting. However, blue GaN-lasers still exhibit less than 40% wall-plug efficiency, while some GaN-based blue light-emitting diodes exceed 80%. This paper investigates non-thermal reasons behind this difference. The inherently poor hole conductivity of the Mg-doped waveguide cladding layer of laser diodes is identified as main reason for their low electrical-to-optical energy conversion efficiency.

  19. Surface Plasmon Enhanced Phosphorescent Organic Light Emitting Diodes

    SciTech Connect

    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 especially

  20. Evaluation of light-emitting diodes for signage applications

    NASA Astrophysics Data System (ADS)

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

    2004-01-01

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

  1. Monolithic integration of OFETs driving organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Kröger, Michael; Becker, Eike; Schildknecht, Christian; Hartmann, Sören; Johannes, Hans-Hermann; Kowalsky, Wolfgang

    2005-08-01

    Organic field effect transistors are expected to be applicable for low-cost, large-area electronic applications, e.g. the incorporation as active-matrix into displays based on organic light emitting diodes (OLED). There are two major challenges which have to be tackled. As the low charge carrier mobility allows only for comparatively low saturation currents, the ratio of channel width and length has to increase by several orders of magnitude, compared to poly-Si-technology. Furthermore, as organic semiconductor devices usually degrade upon exposure to solvents, standard photolithography cannot be applied once the organic materials have been deposited. Therefore, the definition of single pixels has to occur before the deposition of organic materials. We prepared OFETs employing a bottom-Al-gate, an 50 nm thick anodized Al-oxide gate dielectric and a inter-digital drain-source-structure (Au), topped with 30 nm of pentacene as active layer. By applying an inter-digital structure we increased the W/L-ratio to 4340. For the given configuration, a saturation current of 4 mA could be observed at -20 V drain-source- and -20 V gate-source-voltage. The drain-source-contacts enclosed a predefined ITO-anode shorted to drain and acting as OLED-anode. For preventing shortcuts between the OLED-cathode and the OFET, poly-vinyl-alcohol (PVOH) was spin-coated from an aqueous solution and structurized by photolithography. When the OFET characteristics were measured afterwards the field-effect- mobility dropped by two orders of magnitude but recovered due to desorption of residual water. Afterwards, the organic layers and a Al/LiF-cathode were deposited. The area covered by the OLED was 1.33mm2. Applying an operating bias of 11 V between cathode and source, allows for switching of the OLED by changing the gate-source-voltage from +2.5 V to -5 V. The on-state-brightness is 850 cd/m2 and the on-off-ratio 950. Considering a realistic filling factor of 40% the values observed may be

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

    ERIC Educational Resources Information Center

    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…

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

    DOEpatents

    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.

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

    DOEpatents

    Forrest, Stephen R; Zhang, Yifan

    2015-11-12

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

  5. Diffusion injected multi-quantum well light-emitting diode structure

    SciTech Connect

    Riuttanen, L. Nykänen, H.; Svensk, O.; Suihkonen, S.; Sopanen, M.; Kivisaari, P.; Oksanen, J.; Tulkki, J.

    2014-02-24

    The attention towards light-emitting diode (LED) structures based on nanowires, surface plasmon coupled LEDs, and large-area high-power LEDs has been increasing for their potential in increasing the optical output power and efficiency of LEDs. In this work we demonstrate an alternative way to inject charge carriers into the active region of an LED, which is based on completely different current transport mechanism compared to conventional current injection approaches. The demonstrated structure is expected to help overcoming some of the challenges related to current injection with conventional structures. A functioning III-nitride diffusion injected light-emitting diode structure, in which the light-emitting active region is located outside the pn-junction, is realized and characterized. In this device design, the charge carriers are injected into the active region by bipolar diffusion, which could also be utilized to excite otherwise challenging to realize light-emitting structures.

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

    PubMed

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

    2015-12-15

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

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

    PubMed

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

    2015-12-15

    This work develops a novel process of recycling rare metals (Ga, In) from waste light-emitting diodes using the combination of pyrolysis, physical disaggregation methods and vacuum metallurgy separation. Firstly, the pure chips containing InGaN/GaN are adopted to study the vacuum separation behavior of rare metals, which aims to provide the theoretical foundation for recycling gallium and indium from waste light-emitting diodes. In order to extract the rare-metal-rich particles from waste light-emitting diodes, pyrolysis and physical disaggregation methods (crushing, screening, grinding and secondly screening) are studied respectively, and the operating parameters are optimized. With low boiling points and high saturation vapor pressures under vacuum, gallium and indium are separated from rare-metal-rich particles by the process of evaporation and condensation. By reference to the separating parameters of pure chips, gallium and indium in waste light-emitting diodes are recycled with the recovery efficiencies of 93.48% and 95.67% under the conditions as follows: heating temperature of 1373 K, vacuum pressure of 0.01-0.1 Pa, and holding time of 60 min. There are no secondary hazardous materials generated in the whole processes. This work provides an efficient and environmentally friendly process for recycling rare metals from waste light-emitting diodes. PMID:26150281

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

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

    PubMed

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

    2016-07-26

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

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

    PubMed

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

    2016-07-26

    Organometal halide perovskite has recently emerged as a very promising family of materials with augmented performance in electronic and optoelectronic applications including photovoltaic devices, photodetectors, and light-emitting diodes. Herein, we propose and demonstrate facile solution synthesis of a series of colloidal organometal halide perovskite CH3NH3PbX3 (X = halides) nanoparticles with amorphous structure, which exhibit high quantum yield and tunable emission from ultraviolet to near-infrared. The growth mechanism and photoluminescence properties of the perovskite amorphous nanoparticles were studied in detail. A high-efficiency green-light-emitting diode based on amorphous CH3NH3PbBr3 nanoparticles was demonstrated. The perovskite amorphous nanoparticle-based light-emitting diode shows a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W, and an external quantum efficiency of 3.8%, which is 3.5 times higher than that of the best colloidal perovskite quantum-dot-based light-emitting diodes previously reported. Our findings indicate the great potential of colloidal perovskite amorphous nanoparticles in light-emitting devices. PMID:27284993

  11. High-efficiency organic light-emitting diodes with fluorescent emitters

    NASA Astrophysics Data System (ADS)

    Nakanotani, Hajime; Higuchi, Takahiro; Furukawa, Taro; Masui, Kensuke; Morimoto, Kei; Numata, Masaki; Tanaka, Hiroyuki; Sagara, Yuta; Yasuda, Takuma; Adachi, Chihaya

    2014-05-01

    Fluorescence-based organic light-emitting diodes have continued to attract interest because of their long operational lifetimes, high colour purity of electroluminescence and potential to be manufactured at low cost in next-generation full-colour display and lighting applications. In fluorescent molecules, however, the exciton production efficiency is limited to 25% due to the deactivation of triplet excitons. Here we report fluorescence-based organic light-emitting diodes that realize external quantum efficiencies as high as 13.4-18% for blue, green, yellow and red emission, indicating that the exciton production efficiency reached nearly 100%. The high performance is enabled by utilization of thermally activated delayed fluorescence molecules as assistant dopants that permit efficient transfer of all electrically generated singlet and triplet excitons from the assistant dopants to the fluorescent emitters. Organic light-emitting diodes employing this exciton harvesting process provide freedom for the selection of emitters from a wide variety of conventional fluorescent molecules.

  12. Voltage reduction in organic light-emitting diodes

    SciTech Connect

    Hung, L. S.; Mason, M. G.

    2001-06-04

    For practical applications, it is important to operate organic light-emitting devices at low voltages and low power consumption. When both the cathode and anode are perfectly injecting, low electron mobility in electron-transport materials, such as tris-(8-hydroxyquinoline)aluminum (Alq), becomes a limiting factor on voltage reduction. In this letter copper phthalocyanine (CuPc) is replaced for Alq as an electron-transport layer, and interfacial modification is utilized to enhance electron injection from the CuPc electron-transport layer into the Alq emissive layer. The outcome of this structure significantly facilitates electron transport through the organic materials, thus resulting in substantial reduction in operating voltages and power consumption. {copyright} 2001 American Institute of Physics.

  13. Effect of Color of Light Emitting Diode on Development of Fruit Body in Hypsizygus marmoreus

    PubMed Central

    Lee, Yun-Hae; Ju, Young-Cheol; Kim, Seong-Min; Koo, Han-Mo

    2013-01-01

    This study was conducted to identify a suitable color of light for development of the fruit body in Hypsizygus marmoreus. To accomplish this, samples were irradiated with blue (475 nm), green (525 nm), yellow (590 nm), or red (660 nm) light emitting diodes (LEDs) to induce the formation of fruiting bodies after mycelia growth. The diameter and thickness of the pileus and length of stipes in samples subjected to blue LED treatment were similar to those of subjected to fluorescent light (control), and the lengths of the stipes were highest in response to treatment with the red LED and darkness. The commercial yields of plants subjected to blue and green LED treatment were similar to those of the control. In conclusion, cultivation of H. marmoreus coupled with exposure to blue LED is useful for inducing high quality fruit bodies as well as higher levels of ergosterol, DPPH radical scavenging activity, total polyphenol content and reducing power. PMID:23610542

  14. New red phosphor for near-ultraviolet light-emitting diodes with high color-purity

    SciTech Connect

    Wang, Zhengliang; He, Pei; Wang, Rui; Zhao, Jishou; Gong, Menglian

    2010-02-15

    New red phosphors, Na{sub 5}Eu(MoO{sub 4}){sub 4} doped with boron oxide were prepared by the solid-state reaction. Their structure and photo-luminescent properties were investigated. With the introduction of boron oxide, the red emission intensity of the phosphors under 395 nm excitation is strengthened, with high color-purity (x = 0.673, y = 0.327). The single red light-emitting diode was obtained by combining InGaN chip with the red phosphor, bright red light can be observed by naked eyes from the red light-emitting diodes under a forward bias of 20 mA.

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

    SciTech Connect

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

    2014-10-21

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    Solution processed multilayer organic light-emitting diodes (OLEDs) present challenges, especially regarding dissolution of the first layer during deposition of a second layer. In this work, we first demonstrated a plasma cross-linking technology to produce a solution processed OLED. The surfaces of organic films can be cross-linked after mixed acetylene and Ar plasma treatment for several tens of seconds and resist corrosion of organic solvent. The film thickness and surface morphology of emissive layers (EMLs) with plasma treatment and subsequently spin-rinsed with chlorobenzene are nearly unchanged. The solution processed triple-layer OLED is successfully fabricated and the current efficiency increases 50% than that of the double-layer OLED. Fluorescent characteristics of EMLs are also observed to investigate factors influencing the efficiency of the triple-layer OLED. Plasma cross-linking technology may open up a new pathway towards fabrication of all-solution processed multilayer OLEDs and other soft electronic devices.

  18. Sidewall passivation for InGaN/GaN nanopillar light emitting diodes

    SciTech Connect

    Choi, Won Hyuck; Abraham, Michael; Yu, Shih-Ying; You, Guanjun; Liu, Jie; Wang, Li; Xu, Jian; Mohney, Suzanne E.

    2014-07-07

    We studied the effect of sidewall passivation on InGaN/GaN multiquantum well-based nanopillar light emitting diode (LED) performance. In this research, the effects of varying etch rate, KOH treatment, and sulfur passivation were studied for reducing nanopillar sidewall damage and improving device efficiency. Nanopillars prepared under optimal etching conditions showed higher photoluminescence intensity compared with starting planar epilayers. Furthermore, nanopillar LEDs with and without sulfur passivation were compared through electrical and optical characterization. Suppressed leakage current under reverse bias and four times higher electroluminescence (EL) intensity were observed for passivated nanopillar LEDs compared with unpassivated nanopillar LEDs. The suppressed leakage current and EL intensity enhancement reflect the reduction of non-radiative recombination at the nanopillar sidewalls. In addition, the effect of sulfur passivation was found to be very stable, and further insight into its mechanism was gained through transmission electron microscopy.

  19. Room-temperature spin-polarized organic light-emitting diodes with a single ferromagnetic electrode

    SciTech Connect

    Ding, Baofu Alameh, Kamal; Song, Qunliang

    2014-05-19

    In this paper, we demonstrate the concept of a room-temperature spin-polarized organic light-emitting diode (Spin-OLED) structure based on (i) the deposition of an ultra-thin p-type organic buffer layer on the surface of the ferromagnetic electrode of the Spin-OLED and (ii) the use of oxygen plasma treatment to modify the surface of that electrode. Experimental results demonstrate that the brightness of the developed Spin-OLED can be increased by 110% and that a magneto-electroluminescence of 12% can be attained for a 150 mT in-plane magnetic field, at room temperature. This is attributed to enhanced hole and room-temperature spin-polarized injection from the ferromagnetic electrode, respectively.

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

    PubMed

    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.

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

    PubMed

    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. PMID:27118821

  2. Light emitting diodes as a plant lighting source

    NASA Technical Reports Server (NTRS)

    Bula, R. J.; Tennessen, D. J.; Morrow, R. C.; Tibbitts, T. W.

    1994-01-01

    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 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). 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. A number of LED characteristics are of considerable importance in selecting a light source for plant lighting in a controlled environment facility. Of particular importance is the characteristic that light is generated by an LED at a rate far greater than the corresponding thermal radiation predicted by the bulk temperature of the device as defined by Plank's radiation law. This is in sharp contrast to other light sources, such as an incandescent or high intensity discharge lamp. A plant lighting system for controlled environments must provide plants with an adequate flux of photosynthetically active radiation, plus providing photons in the spectral regions that are involved in the photomorphogenic and phototropic responses that result in normal plant growth and development. Use of light sources that emit photons over a broad spectral range generally meet these two lighting requirements. Since the LED's emit over specific spectral regions, they must be carefully selected so that the levels of photsynthetically active and photomorphogenic and phototropic radiation meet these plant requirements.

  3. Tunnel junction multiple wavelength light-emitting diodes

    DOEpatents

    Olson, J.M.; Kurtz, S.R.

    1992-11-24

    A multiple wavelength LED having a monolithic cascade cell structure comprising at least two p-n junctions, wherein each of said at least two p-n junctions have substantially different band gaps, and electrical connector means by which said at least two p-n junctions may be collectively energized; and wherein said diode comprises a tunnel junction or interconnect. 5 figs.

  4. Tunnel junction multiple wavelength light-emitting diodes

    DOEpatents

    Olson, Jerry M.; Kurtz, Sarah R.

    1992-01-01

    A multiple wavelength LED having a monolithic cascade cell structure comprising at least two p-n junctions, wherein each of said at least two p-n junctions have substantially different band gaps, and electrical connector means by which said at least two p-n junctions may be collectively energized; and wherein said diode comprises a tunnel junction or interconnect.

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

    ERIC Educational Resources Information Center

    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…

  6. Active-matrix organic light-emitting diode displays on flexible metal foil substrates

    NASA Astrophysics Data System (ADS)

    Chuang, Ta-Ko

    This dissertation presents the research efforts that deal with the development of polysilicon thin film transistors (TFTs) on stainless-steel-foil substrates, the implementation of high-resolution flexible active-matrix backplanes, and the integration of the flexible polysilicon TFT backplanes with polymer light-emitting diodes. This research investigated the preparation of the steel foil substrates, the fabrication of flexible polysilicon TFT backplanes and polymer light emitting diodes (PLEDs), and the encapsulation of the flexible Active Matrix Polymer Light Emitting Diode displays. The first successful integration of polysilicon TFT backplane with PLEDs onto light-weight, robust, and flexible stainless-steel-foil substrates is presented. A top-emitting, monochrome active-matrix polymer light-emitting diode (AM-PLED) display, having the VGA (640x480) format and a 230 dpi resolution, is demonstrated for the first time on flexible stainless-steel-foil substrates. This work validates the compatibility of the polysilicon technology for high-resolution flexible AM-PLED displays. Furthermore, this work shows that a variety of other large-area microelectronics could also be implemented onto flexible metal foils, benefiting by the metal oil dimensional stability and ability to withstand high process temperature. In conclusion, the polysilicon TFT technology combining with metal-foil substrates opens up a new road for flexible displays as well as large-area flexible electronic applications.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  8. 77 FR 55499 - Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-10

    ... COMMISSION Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To Review... . Hearing-impaired persons are advised that information on this matter can be obtained by contacting the... Samsung LED America, Inc. of Atlanta, Georgia (collectively, ``SLED''). 76 FR 51396-97 (Aug. 18,...

  9. All-fibre sensing loop using pulse-modulated light-emitting diode

    NASA Technical Reports Server (NTRS)

    Adamovsky, G.

    1985-01-01

    A sensing system is presented which includes a pulse-modulated light-emitting diode (LED) and an all-fibre-optic loop generating a reference signal in the time domain. The basic principle of operation and parameters are introduced, and some properties of such a system are experimentally examined using a microbend sensor.

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

    ERIC Educational Resources Information Center

    Kamata, Masahiro; Matsunaga, Ai

    2007-01-01

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

  11. 76 FR 67761 - Certain Light-Emitting Diodes and Products Containing Same Determination Not To Review an Initial...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-02

    ... (collectively, ``LG''). 76 FR 54254 (August 31, 2011). The complaint alleged violations of section 337 based... COMMISSION Certain Light-Emitting Diodes and Products Containing Same Determination Not To Review an Initial... States after importation of certain light emitting diodes and products containing same by reason...

  12. 76 FR 51396 - Certain Light-Emitting Diodes and Products Containing Same; Notice of Institution of Investigation

    Federal Register 2010, 2011, 2012, 2013, 2014

    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... States, the sale for importation, or the sale within the United States after importation of certain...

  13. 77 FR 45377 - Certain Light-Emitting Diodes and Products Containing the Same; Notice of Request for Statements...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-31

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

  14. 77 FR 56672 - Certain Light-Emitting Diodes and Products Containing the Same; Determination To Review a Final...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-13

    ... (``the `090 patent''); 7,151,283 (``the `283 patent''); and 7,271,425 (``the `425 patent''). 76 FR 40746... COMMISSION Certain Light-Emitting Diodes and Products Containing the Same; Determination To Review a Final... importation of certain light-emitting diodes and products containing same by reason of infringement of...

  15. An evaluation of organic light emitting diode monitors for medical applications: Great timing, but luminance artifacts

    PubMed Central

    Elze, Tobias; Taylor, Christopher; Bex, Peter J.

    2013-01-01

    Purpose: In contrast to the dominant medical liquid crystal display (LCD) technology, organic light-emitting diode (OLED) monitors control the display luminance via separate light-emitting diodes for each pixel and are therefore supposed to overcome many previously documented temporal artifacts of medical LCDs. We assessed the temporal and luminance characteristics of the only currently available OLED monitor designed for use in the medical treatment field (SONY PVM2551MD) and checked the authors’ main findings with another SONY OLED device (PVM2541). Methods: Temporal properties of the photometric output were measured with an optical transient recorder. Luminances of the three color primaries and white for all 256 digital driving levels (DDLs) were measured with a spectroradiometer. Between the luminances of neighboring DDLs, just noticeable differences were calculated according to a perceptual model developed for medical displays. Luminances of full screen (FS) stimuli were compared to luminances of smaller stimuli with identical DDLs. Results: All measured luminance transition times were below 300 μs. Luminances were independent of the luminance in the preceding frame. However, for the single color primaries, up to 50.5% of the luminances of neighboring DDLs were not perceptually distinguishable. If two color primaries were active simultaneously, between 36.7% and 55.1% of neighboring luminances for increasing DDLs of the third primary were even decreasing. Moreover, luminance saturation effects were observed when too many pixels were active simultaneously. This effect was strongest for white; a small white patch was close to 400 cd/m2, but in FS the luminance of white saturated at 162 cd/m2. Due to different saturation levels, the luminance of FS green and FS yellow could exceed the luminance of FS white for identical DDLs. Conclusions: The OLED temporal characteristics are excellent and superior to those of LCDs. However, the OLEDs revealed severe

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

    SciTech Connect

    Xu, Xianmei; Wang, Yilin; Gule, Teri; Luo, Qiang; Zhou, Liya; Gong, Fuzhong

    2013-03-15

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

  17. Semiconductor-Nanocrystals-Based White Light-Emitting Diodes

    SciTech Connect

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

    2010-01-01

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

  18. The effect of interfacial layer on the performance of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Choulis, Stelios A.; Choong-En, Vi; Mathai, Mathew K.; So, Franky

    2005-09-01

    We demonstrate high efficiency organic light-emitting devices by incorporation of a nanoscale interfacial layer between a hole-conducting layer (PEDOT:PSS) and a light-emitting polymer layer (LEP) to improve hole injection. The interfacial layer has appropriate highest occupied molecular orbital level in order to act as a bridge for efficient hole injection from the PEDOT:PSS into the LEP. As an example we have incorporated a suitable interfacial layer into a green-emitting single-layer electrophosphorescent light-emitting diode. Devices with the interfacial layer show a peak efficiency of 41lm/W, an improvement of more than 25% in their performance over comparable devices without the interfacial layer. The results presented here introduce a novel method to improve hole injection and thus efficiency in organic electroluminescent devices.

  19. Quantification of energy loss mechanisms in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Meerheim, Rico; Furno, Mauro; Hofmann, Simone; Lüssem, Björn; Leo, Karl

    2010-12-01

    The external quantum efficiency of organic light-emitting diodes (OLEDs) is limited by several loss mechanisms. By applying a numerical model for the efficiency analysis of OLED devices, we analyze the distribution of the different energy loss mechanisms in bottom and top emission organic light-emitting diodes. We validate the findings by the comparison with experimental data measured on red state-of-the-art p-i-n devices containing the red phosphorescent emitting dye iridium(III)bis[2-methyldibenzo-(f, h)quinoxaline](acetylacetonate) [Ir(MDQ)2(acac)]. The model is used to design extremely efficient bottom and top emission diodes with 21% and 27% external quantum efficiencies, respectively.

  20. Effect of alcohol vapor treatment on electrical and optical properties of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) films for indium tin oxide-free organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Fallahzadeh, Ali; Saghaei, Jaber; Yousefi, Mohammad Hassan

    2014-11-01

    A simple alcohol vapor treatment (AVT) technique was proposed to improve the conductivity of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. In this technique, various alcohols, i.e. methanol, ethanol, 2-propanol and ethylene glycol, were applied to treat the surface of the films formed and then they were annealed. The sheet resistance of PEDOT:PSS films was significantly reduced from 130 kΩ/sq to 60 Ω/sq when treated with methanol vapor. The investigation of the vertical resistance of the films showed that the sample treated with methanol vapor displayed the lowest resistance as well. The mechanism of conductivity enhancement of PEDOT:PSS films through AVT method was explained by surface phase images, UV and IR spectra of PEDOT:PSS films. Optical transmittance spectrum of treated films exhibited that AVT has even enhanced the optical transmittance slightly. Improvement in the morphology, electrical and optical properties of PEDOT:PSS films prompted their applications as a transparent anode in the fabrication of ITO-free organic light-emitting diodes (OLEDs). The OLED manufactured based on methanol-treated PEDOT:PSS films demonstrated the highest luminance.

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

    SciTech Connect

    Zdoroveyshchev, A. V. Dorokhin, M. V.; Demina, P. B.; Kudrin, A. V.; Vikhrova, O. V.; Ved’, M. V.; Danilov, Yu. A.; Erofeeva, I. V.; Krjukov, R. N.; Nikolichev, D. E.

    2015-12-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    PubMed

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

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  5. Broadband visible light source based on AllnGaN light emitting diodes

    DOEpatents

    Crawford, Mary H.; Nelson, Jeffrey S.

    2003-12-16

    A visible light source device is described based on a light emitting diode and a nanocluster-based film. The light emitting diode utilizes a semiconductor quantum well structure between n-type and p-type semiconductor materials on the top surface a substrate such as sapphire. The nanocluster-based film is deposited on the bottom surface of the substrate and can be derived from a solution of MoS.sub.2, MoSe.sub.2, WS.sub.2, and WSe.sub.2 particles of size greater than approximately 2 nm in diameter and less than approximately 15 nm in diameter, having an absorption wavelength greater than approximately 300 nm and less than approximately 650 nm.

  6. Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Cho, Himchan; Jeong, Su-Hun; Park, Min-Ho; Kim, Young-Hoon; Wolf, Christoph; Lee, Chang-Lyoul; Heo, Jin Hyuck; Sadhanala, Aditya; Myoung, NoSoung; Yoo, Seunghyup; Im, Sang Hyuk; Friend, Richard H.; Lee, Tae-Woo

    2015-12-01

    Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.

  7. Active differential optical absorption spectroscopy for NO2 gas pollution using blue light emitting diodes

    NASA Astrophysics Data System (ADS)

    Aljalal, Abdulaziz; Gasmi, Khaled; Al-Basheer, Watheq

    2015-05-01

    Availability of high intensity light emitting diodes in the blue region offer excellent opportunity for using them in active Differential Optical Absorption Spectroscopy (DOAS) to detect air pollution. Their smooth and relatively broad spectral emissions as well as their long life make them almost ideal light sources for active DOAS. In this study, we report the usage of a blue light emitting diode in an active DOAS setup to measure traces of NO2 gas and achieving few parts per billion detection limit for a path length of 300 m. Details of the setup will be presented along with the effects on measurement accuracy due to shifts in the measured spectra calibration and due to using theoretical instrument Gaussian function instead of the measured instrument function.

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

    PubMed

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

    2013-07-23

    Graphene nanosheets with uniform shape are successfully incorporated into a silicone encapsulant of a light-emitting diode (LED) using a solvent-exchange approach which is a facile and straightforward method. The graphene nanosheets embedded in the silicone encapsulant have a multifunctional role which improves the performance of light-emitting diodes. The presence of graphene gives rise to effective heat dissipation, improvement of protection ability from external stimuli, such as moisture and hazardous gas, and enhancement of mechanical properties such as elastic modulus and fracture toughness. Consequently, the LEDs composed of a graphene-embedded silicone encapsulant exhibit long-term stability without loss of luminous efficiency by addition of relatively small amounts of graphene. This novel strategy offers a feasible candidate for their practical or industrial applications. PMID:23758228

  9. Finger-shaped Red Light Emitting Diode to Ascertain the Depth of Periungual Wart

    PubMed Central

    Nirmal, Balakrishnan

    2016-01-01

    Management of periungual wart is a great challenge, especially when there is subungual extension. The major cause of recurrence of wart is improper clinical assessment of its extent and not directing therapy against the entire wart. This difficulty of ascertaining its extent could be overcome with this finger-shaped red light emitting diode device. Red light in the device penetrates the thick palmar skin and dark constitutive skin colour due to its longer wavelength. PMID:27761093

  10. White light-emitting diode with quasisolar spectrum based on organic fluorescent dyes

    NASA Astrophysics Data System (ADS)

    Chung, Shuang-Chao; Li, Ming-Chia; Sun, Ching-Cherng

    2015-07-01

    We present a study of light-emitting diodes (LEDs) using organic fluorescent dyes to replace the general phosphor. The blue die with a specific organic fluorescent dye gives the LED a single color appearance. Through a color-mixing cavity, multiple LEDs are used to produce a quasisolar spectrum at a certain band and white light with a color rendering index as high as 97 at around 2800 K.

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

    PubMed

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

    2016-01-27

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

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

    PubMed

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

    2016-01-13

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

  13. Photoionization of optically trapped ultracold atoms with a high-power light-emitting diode

    SciTech Connect

    Goetz, Simone; Hoeltkemeier, Bastian; Amthor, Thomas; Weidemueller, Matthias

    2013-04-15

    Photoionization of laser-cooled atoms using short pulses of a high-power light-emitting diode (LED) is demonstrated. Light pulses as short as 30 ns have been realized with the simple LED driver circuit. We measure the ionization cross section of {sup 85}Rb atoms in the first excited state, and show how this technique can be used for calibrating efficiencies of ion detector assemblies.

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

    PubMed

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

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Extracting the emitter orientation in organic light-emitting diodes from external quantum efficiency measurements

    SciTech Connect

    Schmidt, Tobias D. Reichardt, Lukas J.; Wehrmeister, Sebastian; Scholz, Bert J.; Mayr, Christian; Brütting, Wolfgang; Rausch, Andreas F.; Wehlus, Thomas; Reusch, Thilo C. G.; Ciarnáin, Rossá Mac; Danz, Norbert

    2014-07-28

    Emitter orientation will play a major role in future applications of organic light-emitting diodes due to its strong impact on the efficiency of the devices. Up to now, determining the orientation of transition dipole moments required elaborate angular-dependent measurements of the light emission pattern. In this paper, we present a simplified and straightforward method to extract the emitter orientation from external quantum efficiency measurements. We demonstrate the validity of the method on three different dye-doped emitting systems.

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

    PubMed

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

    2016-05-01

    The preparation of highly efficient perovskite nanocrystal light-emitting diodes is shown. A new trimethylaluminum vapor-based crosslinking method to render the nanocrystal films insoluble is applied. The resulting near-complete nanocrystal film coverage, coupled with the natural confinement of injected charges within the perovskite crystals, facilitates electron-hole capture and give rise to a remarkable electroluminescence yield of 5.7%. PMID:26990965

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

    PubMed

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

    2016-09-26

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

  19. Cooling of organic light-emitting diode display panels with heat pipes

    NASA Astrophysics Data System (ADS)

    Sure, Anita; Vankayala, Gowtham Kumar; Baranwal, Vaibhav; Paramanandam, Karthikeyan; Sarma, Kalluri R.; Asokan, S.

    2016-05-01

    Organic light-emitting diode half life is a function of temperature and it decreases with increase in operating temperature. Hence thermal management is important for the efficient operation of OLED based displays. High luminance applications like aerospace cockpits require high power densities which lead to increase in their operating temperatures. Passive cooling is the preferred choice in aerospace applications. In this work passive cooling option with heat pipes is studied and implemented to reduce the display temperature rise.

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

    DOEpatents

    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. Simultaneous color and luminance control of organic light-emitting diodes for mood-lighting applications

    NASA Astrophysics Data System (ADS)

    Köhnen, Anne; Meerholz, Klaus; Hagemann, Malte; Brinkmann, Matthias; Sinzinger, Stefan

    2008-01-01

    Organic light-emitting diodes (OLEDs) using polymer blends as a single emissive layer often suffer from large color shifts with changing operational voltage. Until now, such devices cannot stand the critical demands of lighting industry. In this contribution, we introduce a pulse-width-modulation-based driver concept, enabling the user to simultaneously and independently adjust color and luminance of a single device with two contacts. This concept makes color-shifting OLEDs highly interesting for "mood-light" applications.

  2. Enhancement of Light Extracting from GaN-BASED Blue Light Emitting Diodes Using Photonic Crystal

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Wu, Fugen; Zhang, Xin; Yao, Yuanwei; Zhong, Huilin; Yan, Shuya; He, Yun

    Photonic crystal (PC) structures on LED have been known to enhance the light extraction significantly. In this paper, we report the light energy of GaN-based blue lighting emitting diode (LED) with perfect area photonic crystal (PPC) structure and defect area photonic crystal (DPC) structure. As a result, the light extracting energy of LEDs with PPC structure enhanced little compared to that of without PC structure. In addition, the light extracting energy of blue LED with DPC structure was remarkably improved.

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

    PubMed

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

    2016-09-26

    The first application of light-emitting diodes (LEDs) for ultraviolet photodissociation (UVPD) mass spectrometry is reported. LEDs provide a compact, low cost light source and have been incorporated directly into the trapping cell of an Orbitrap mass spectrometer. MS/MS efficiencies of over 50 % were obtained using an extended irradiation period, and UVPD was optimized by modulating the ion trapping parameters to maximize the overlap between the ion cloud and the irradiation volume. PMID:27605434

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

    PubMed

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

    2004-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  6. Red/near-infrared light-emitting diode therapy for traumatic brain injury

    NASA Astrophysics Data System (ADS)

    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.

  7. On the ideality factor of the radiative recombination current in semiconductor light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Lee, Gyeong Won; Shim, Jong-In; Shin, Dong-Soo

    2016-07-01

    While there have been many discussions on the standard Si pn-diodes, little attention has been paid and confusion still arises on the ideality factor of the radiative recombination current in semiconductor light-emitting diodes (LEDs). In this letter, we theoretically demonstrate and experimentally confirm by using blue and infrared semiconductor LEDs that the ideality factor of the radiative recombination current is unity especially for low-current-density ranges. We utilize the data of internal quantum efficiency measured by the temperature-dependent electroluminescence to separate the radiative current component from the total current.

  8. Phosphorus doped ZnO light emitting diodes fabricated via pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Kim, H. S.; Lugo, F.; Pearton, S. J.; Norton, D. P.; Wang, Yu-Lin; Ren, F.

    2008-03-01

    ZnO-based light emitting diodes were fabricated on c-plane sapphire using ZnO :P/Zn0.9Mg0.1O/ZnO/Zn0.9Mg0.1O/ZnO:Ga p-i-n heterostructures. The p-i-n heterojunction diodes are rectifying and show light emission under forward bias. The electroluminescence spectra shows deep level emission at low bias, but near band edge ultraviolet emission at high voltage bias. A decrease in leakage currents in as-fabricated structures was achieved via low temperature oxygen annealing.

  9. Photoresponse of poly([ital para]-phenylenevinylene) light-emitting diodes

    SciTech Connect

    Wei, X.; Raikh, M.; Vardeny, Z.V. ); Yang, Y. ); Moses, D. )

    1994-06-15

    We have studied the photoresponses of poly([ital para]-phenylene vinylene) (PPV) light-emitting diodes (LED's) with PPV derivatives sandwiched between tin oxide (ITO) and metals including calcium, aluminum, and copper. Under illumination all diodes exhibit relatively large photoconductive I(V) responses which cross the dark I(V) curve at a forward-bias voltage V[sub 0] that scales with the difference in work functions between the ITO and metal electrodes, the open-circuit voltage saturates at V[sub 0] and is temperature independent, and the enhanced electroluminescence intensity of the illuminated LED's correlates with the photocurrent. (AIP)

  10. Light-emitting diode therapy increases collagen deposition during the repair process of skeletal muscle.

    PubMed

    de Melo, Claudia Aparecida Viana; Alves, Agnelo Neves; Terena, Stella Maris Lins; Fernandes, Kristianne Porta Santos; Nunes, Fábio Daumas; da Silva, Daniela de Fátima Teixeira; Bussadori, Sandra Kalil; Deana, Alessandro Melo; Mesquita-Ferrari, Raquel Agnelli

    2016-04-01

    This study analyzed the effects of light-emitting diode (LED) therapy on the morphology of muscle tissue as well as collagen remodeling and matrix metalloproteinase 2 (MMP-2) activity in the skeletal muscle of rats following acute injury. Wistar rats were divided into four groups: (1) control, (2) sham, (3) untreated cryoinjury, and (4) cryoinjury treated with LED. Cryoinjury was induced by two applications of a metal probe cooled in liquid nitrogen directly onto the belly of the tibialis anterior muscle. For treatment, the LED equipment (wavelength 850 nm, output power 30 mW, and total energy 3.2 J) was used daily. The study periods were 1, 3, and 7 days after cryoinjury. Morphological aspects were evaluated through hematoxylin-eosin staining. The amount of collagen fibers was evaluated using Picro Sirius Red staining under polarized light. The gelatinase activity of MMP-2 was evaluated using zymography. The results showed significant reductions in inflammatory infiltrate after 3 days and an increased number of immature muscle fibers after 7 days. Furthermore, treatment induced a reduction in the gelatinolytic activity of MMP-2 after 1, 3, and 7 days in comparison to the untreated injury groups and increased the collagen deposition after 3 and 7 days in the treated groups. LED therapy at 850 nm induced a significant reduction in inflammation, decreased MMP-2 activity, and increased the amount of immature muscle and collagen fibers during the muscle repair process following acute injury.

  11. Enhancement of electrical property by oxygen doping to copper phthalocyanine in inverted top emitting organic light emitting diodes

    SciTech Connect

    Hong, Kihyon; Kim, Kisoo; Lee, Jong-Lam

    2009-11-23

    We reported the evidence of oxygen doping to copper-phthalocyanine (CuPc) by O{sub 2}-plasma treatment to inverted top-emitting organic light-emitting diodes (ITOLEDs). In situ synchrotron-radiation photoelectron spectroscopy results showed that a new Cu-O bond appeared and the energy difference between the highest-occupied molecular orbital and E{sub F} is lowered by 0.15 eV after plasma treatment. The oxygen ions chemically interacted with Cu atoms and transferred charges to the CuPc. Thus the hole injection barrier was lowered, enhancing the electroluminescent property of ITOLEDs.

  12. Optical sensors based on monolithic integrated organic light-emitting diodes (OLEDs)

    NASA Astrophysics Data System (ADS)

    Reckziegel, S.; Kreye, D.; Puegner, T.; Grillberger, C.; Toerker, M.; Vogel, U.; Amelung, J.

    2008-04-01

    Organic light-emitting diodes (OLEDs) permit the monolithic integration of microelectronic circuits and light-emitting devices on the same silicon chip. By the use of integrated photodetectors, low-cost CMOS processes and simple packaging; economically produced optoelectronic integrated circuits (OEICs) with combined sensors and actuating elements can be realized. The OLEDs are deposited directly on the top metal layer. The metal layer serves as electrode and defines the bright area. Furthermore, the area below the electrodes can be used for integrated circuits. Due to efficient emitter with low operating voltage it is possible to renounce high-voltage devices depending on selected CMOS process. Thus manufacturing cost can be further reduced. Different CMOS metallizations were examined and their effects on organic light-emitting diodes were analyzed. Red (628nm) and orange (597nm) emitting p-i-n OLEDs with a radiance of 5W/m2sr at 2.8V and 3.0V and a half angle of +/-45° were realized on metal layer with low roughness. Near infra-red emitters are in development. We will present an optical microsystem. The functionality of combined sensors and actuating elements as well as advantages and difficulties of the monolithic integration of OLEDs and CMOS will be discussed. The chip was manufactured in a commercial 1μm CMOS technology. The fabricated microsystem combines three different types of sensors: a reflective sensor, a colour sensor and a particle flow sensor.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  14. Graphene oxide/graphene vertical heterostructure electrodes for highly efficient and flexible organic light emitting diodes.

    PubMed

    Jia, S; Sun, H D; Du, J H; Zhang, Z K; Zhang, D D; Ma, L P; Chen, J S; Ma, D G; Cheng, H M; Ren, W C

    2016-05-19

    The relatively high sheet resistance, low work function and poor compatibility with hole injection layers (HILs) seriously limit the applications of graphene as transparent conductive electrodes (TCEs) for organic light emitting diodes (OLEDs). Here, a graphene oxide/graphene (GO/G) vertical heterostructure is developed as TCEs for high-performance OLEDs, by directly oxidizing the top layer of three-layer graphene films with ozone treatment. Such GO/G heterostructure electrodes show greatly improved optical transmittance, a large work function, high stability, and good compatibility with HIL materials (MoO3 in this work). Moreover, the conductivity of the heterostructure is not sacrificed compared to the pristine three-layer graphene electrodes, but is significantly higher than that of pristine two-layer graphene films. In addition to high flexibility, OLEDs with different emission colors based on the GO/G heterostructure TCEs show much better performance than those based on indium tin oxide (ITO) anodes. Green OLEDs with GO/G heterostructure electrodes have the maximum current efficiency and power efficiency, as high as 82.0 cd A(-1) and 98.2 lm W(-1), respectively, which are 36.7% (14.8%) and 59.2% (15.0%) higher than those with pristine graphene (ITO) anodes. These findings open up the possibility of using graphene for next generation high-performance flexible and wearable optoelectronics with high stability. PMID:27153523

  15. Light-emitting diodes at 940nm attenuate colitis-induced inflammatory process in mice.

    PubMed

    Belém, Mônica O; de Andrade, Giovana M M; Carlos, Thalita M; Guazelli, Carla F S; Fattori, Victor; Toginho Filho, Dari O; Dias, Ivan F L; Verri, Waldiceu A; Araújo, Eduardo J A

    2016-09-01

    Inflammatory bowel disease (IBD) presents intense inflammatory infiltrate, crypt abscesses, ulceration and even loss of function. Despite the clinical relevance of IBD, its current therapy remains poorly effective. Infrared wavelength phototherapy shows therapeutic potential on inflammation. Our goal was to evaluate whether light-emitting diodes (LED) at 940nm are capable of mitigating the colitis-induced inflammatory process in mice. Forty male Swiss mice were assigned into five groups: control; control treated with LED therapy; colitis without treatment; colitis treated with LED therapy; colitis treated with Prednisolone. Experimental colitis was induced by acetic acid 7.5% (pH2.5) rectal administration. LED therapy was performed with light characterized by wavelength of 940nm, 45nm bandwidth, intensity of 4.05J/cm(2), total power of 270mW and total dose of 64.8J for 4min in a single application. Colitis-induced intestinal transit delay was inhibited by LED therapy. Colitis caused an increase of colon dimensions (length, diameter, total area) and colon weight (edema), which were inhibited by LED therapy. LED therapy also decreased colitis-induced tissue gross lesion, myeloperoxidase activity, microscopic tissue damage score and the presence of inflammatory infiltrate in all intestinal layers. Furthermore, LED therapy inhibited colitis-induced IL-1β, TNF-α, and IL-6 production. We conclude LED therapy at 940nm inhibited experimental colitis-induced colon inflammation in mice, therefore, rendering it a promising therapeutic approach that deserves further investigation.

  16. Short-circuit prevention strategies in organic light-emitting diodes and solar cells

    NASA Astrophysics Data System (ADS)

    Michels, Jasper J.; Jolt Oostra, A.; Blom, Paul W. M.

    2016-08-01

    Short-circuit prevention and repair strategies are essential to allow for upscaled production of organic electronic devices based on thin-film production technology. Occurrence of short circuits is a consequence of manufacturing imperfections and particle contamination. After giving a concise review of short-circuit prevention methods for organic thin-film devices in the open literature of the past decade, this overview article summarizes our recent work on short-circuit prevention in organic light-emitting diodes and organic solar cells by chemical oxidation methods. Our main strategy is based on self-aligned disruption of the conductivity of exposed areas of the typically applied hole transport material poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) by aqueous sodium hypochlorite, prior to cathode deposition. The ten orders of magnitude decrease in local conductivity obtained proves sufficient to let deliberately flawed devices operate at pristine performance levels. We next show that in the case of organic solar cells based on a lithium fluoride/aluminium cathode the shunting junctions can be made sufficiently resistive to allow for near unflawed operation, without applying wet treatment.

  17. Comparison of light emitting diodes and semiconductor laser inducing photodynamic therapy of cancer cells in vitro

    NASA Astrophysics Data System (ADS)

    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.

  18. Graphene oxide/graphene vertical heterostructure electrodes for highly efficient and flexible organic light emitting diodes.

    PubMed

    Jia, S; Sun, H D; Du, J H; Zhang, Z K; Zhang, D D; Ma, L P; Chen, J S; Ma, D G; Cheng, H M; Ren, W C

    2016-05-19

    The relatively high sheet resistance, low work function and poor compatibility with hole injection layers (HILs) seriously limit the applications of graphene as transparent conductive electrodes (TCEs) for organic light emitting diodes (OLEDs). Here, a graphene oxide/graphene (GO/G) vertical heterostructure is developed as TCEs for high-performance OLEDs, by directly oxidizing the top layer of three-layer graphene films with ozone treatment. Such GO/G heterostructure electrodes show greatly improved optical transmittance, a large work function, high stability, and good compatibility with HIL materials (MoO3 in this work). Moreover, the conductivity of the heterostructure is not sacrificed compared to the pristine three-layer graphene electrodes, but is significantly higher than that of pristine two-layer graphene films. In addition to high flexibility, OLEDs with different emission colors based on the GO/G heterostructure TCEs show much better performance than those based on indium tin oxide (ITO) anodes. Green OLEDs with GO/G heterostructure electrodes have the maximum current efficiency and power efficiency, as high as 82.0 cd A(-1) and 98.2 lm W(-1), respectively, which are 36.7% (14.8%) and 59.2% (15.0%) higher than those with pristine graphene (ITO) anodes. These findings open up the possibility of using graphene for next generation high-performance flexible and wearable optoelectronics with high stability.

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

    PubMed

    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.

  20. Improved photoluminescence efficiency in UV nanopillar light emitting diode structures by recovery of dry etching damage.

    PubMed

    Jeon, Dae-Woo; Jang, Lee-Woon; Jeon, Ju-Won; Park, Jae-Woo; Song, Young Ho; Jeon, Seong-Ran; Ju, Jin-Woo; Baek, Jong Hyeob; Lee, In-Hwan

    2013-05-01

    In this study, we have fabricated 375-nm-wavelength InGaN/AlInGaN nanopillar light emitting diodes (LED) structures on c-plane sapphire. A uniform and highly vertical nanopillar structure was fabricated using self-organized Ni/SiO2 nano-size mask by dry etching method. To minimize the dry etching damage, the samples were subjected to high temperature annealing with subsequent chemical passivation in KOH solution. Prior to annealing and passivation the UV nanopillar LEDs showed the photoluminescence (PL) efficiency about 2.5 times higher than conventional UV LED structures which is attributed to better light extraction efficiency and possibly some improvement of internal quantum efficiency due to partially relieved strain. Annealing alone further increased the PL efficiency by about 4.5 times compared to the conventional UV LEDs, while KOH passivation led to the overall PL efficiency improvement by more than 7 times. Combined results of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) suggest that annealing decreases the number of lattice defects and relieves the strain in the surface region of the nanopillars whereas KOH treatment removes the surface oxide from nanopillar surface. PMID:23858920

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

    NASA Astrophysics Data System (ADS)

    Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin; Eun Lee, Song; Kwan Kim, Young; Hwa Yu, Hyeong; Turak, Ayse; Young Kim, Woo

    2015-06-01

    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/m2. Additionally, we observed a reduction of energy loss in the white PHOLED via Ir(piq)3 as phosphorescent red dopant in electron transport layer.

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

    SciTech Connect

    Abbaszadeh, D.; Wetzelaer, G. A. H.; Nicolai, H. T.

    2014-12-14

    The quenching of excitons at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) anode in blue polyalkoxyspirobifluorene-arylamine polymer light-emitting diodes is investigated. Due to the combination of a higher electron mobility and the presence of electron traps, the recombination zone shifts from the cathode to the anode with increasing voltage. The exciton quenching at the anode at higher voltages leads to an efficiency roll-off. The voltage dependence of the luminous efficiency is reproduced by a drift-diffusion model under the condition that quenching of excitons at the PEDOT:PSS anode and metallic cathode is of equal strength. Experimentally, the efficiency roll-off at high voltages due to anode quenching is eliminated by the use of an electron-blocking layer between the anode and the light-emitting polymer.

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

    SciTech Connect

    Wook Kim, Jin; Yoo, Seung Il; Sung Kang, Jin; Eun Lee, Song; Kwan Kim, Young; Hwa Yu, Hyeong; Turak, Ayse; Young Kim, Woo

    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.

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

    SciTech Connect

    Smirnova, I. P. Markov, L. K.; Pavlyuchenko, A. S.; Kukushkin, M. V.

    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.

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

    SciTech Connect

    Wierer, Jonathan J.; Tsao, Jeffrey Y.; Sizov, Dmitry S.

    2013-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    PubMed

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

    2015-04-01

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

  8. High-efficient and brightness white organic light-emitting diodes operated at low bias voltage

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Yu, Junsheng; Yuan, Kai; Jian, Yadong

    2010-10-01

    White organic light-emitting diodes (OLEDs) used for display application and lighting need to possess high efficiency, high brightness, and low driving voltage. In this work, white OLEDs consisted of ambipolar 9,10-bis 2-naphthyl anthracene (ADN) as a host of blue light-emitting layer (EML) doped with tetrabutyleperlene (TBPe) and a thin codoped layer consisted of N, N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB) as a host of yellow light-emitting layer doped with 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) were investigated. With appropriate tuning in the film thickness, position, and dopant concentration of the co-doped layer, a white OLED with a luminance yield of 10.02 cd/A with the CIE coordinates of (0.29, 0.33) has been achieved at a bias voltage of 9 V and a luminance level of over 10,000 cd/m2. By introducing the PIN structure with both HIL and bis(10- hydroxybenzo-quinolinato)-beryllium (BeBq2) ETL, the power efficiency of white OLED was improved.

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

    SciTech Connect

    Li, Baikui; Tang, Xi; Chen, Kevin J.; Wang, Jiannong

    2014-07-21

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

  10. An aluminium nitride light-emitting diode with a wavelength of 210 nanometres.

    PubMed

    Taniyasu, Yoshitaka; Kasu, Makoto; Makimoto, Toshiki

    2006-05-18

    Compact high-efficiency ultraviolet solid-state light sources--such as light-emitting diodes (LEDs) and laser diodes--are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond and III-V nitride semiconductors (GaN, AlGaN and AlN; refs 3-10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride (AlN), which has a very wide direct bandgap of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.

  11. White-blue electroluminescence from a Si quantum dot hybrid light-emitting diode

    SciTech Connect

    Xin, Yunzi; Nishio, Kazuyuki; Saitow, Ken-ichi

    2015-05-18

    A silicon (Si) quantum dot (QD)-based hybrid inorganic/organic light-emitting diode (LED) was fabricated via solution processing. This device exhibited white-blue electroluminescence at a low applied voltage of 6 V, with 78% of the effective emission obtained from the Si QDs. This hybrid LED produced current and optical power densities 280 and 350 times greater than those previously reported for such device. The superior performance of this hybrid device was obtained by both the prepared Si QDs and the optimized layer structure and thereby improving carrier migration through the hybrid LED and carrier recombination in the homogeneous Si QD layer.

  12. High efficiency white organic light emitting diodes employing blue and red platinum emitters

    NASA Astrophysics Data System (ADS)

    O'Brien, Barry; Norby, Gregory; Li, Guijie; Li, Jian

    2014-01-01

    Platinum-based blue and red emitters were used to make stacked organic light-emitting diodes devices for potential use in solid-state lighting. The electroluminescence (EL) spectra were strongly dependent on the red layer thickness and relative position of the red and blue emissive layers. Although all devices had very little EL in the green region, a color rendering index (CRI) as high as 65 was achieved. Addition of a suitable phosphorescent green emissive layer should produce higher CRI values. All devices tested exhibited external quantum efficiencies greater than 20%, indicating that the Pt-based emitters reported here are potentially useful for solid-state lighting applications.

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

    PubMed Central

    Juhasz, Peter; Nevrela, Juraj; Micjan, Michal; Novota, Miroslav; Uhrik, Jan; Stuchlikova, Lubica; Jakabovic, Jan; Harmatha, Ladislav

    2016-01-01

    Summary 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. PMID:26925351

  14. Compact light-emitting diode lighting ring for video-assisted thoracic surgery.

    PubMed

    Lu, Ming-Kuan; Chang, Feng-Chen; Wang, Wen-Zhe; Hsieh, Chih-Cheng; Kao, Fu-Jen

    2014-01-01

    In this work, a foldable ring-shaped light-emitting diode (LED) lighting assembly, designed to attach to a rubber wound retractor, is realized and tested through porcine animal experiments. Enabled by the small size and the high efficiency of LED chips, the lighting assembly is compact, flexible, and disposable while providing direct and high brightness lighting for more uniform background illumination in video-assisted thoracic surgery (VATS). When compared with a conventional fiber bundle coupled light source that is usually used in laparoscopy and endoscopy, the much broader solid angle of illumination enabled by the LED assembly allows greatly improved background lighting and imaging quality in VATS.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  17. Multilayer structured polymer light emitting diodes with cross-linked polymer matrices

    NASA Astrophysics Data System (ADS)

    Zhou, Zhang-Lin; Sheng, Xia; Nauka, K.; Zhao, Lihua; Gibson, Gary; Lam, Sity; Yang, Chung Ching; Brug, James; Elder, Rich

    2010-01-01

    Currently, there is great interest in manufacturing multilayer polymer light emitting diode (PLED) structures via low-cost solution-based spin-casting or printing methods. The difficulty with this approach is that solvent from freshly deposited films often dissolves the underlying layers. This letter demonstrates that fully operational multilayer PLED structures can be fabricated via a solution process by embedding the hole transport material in cross-linked inert polymer matrices that protect the functional material while subsequent layers are deposited using the same solvent. The resulting devices exhibited greatly improved quantum efficiency compared with devices that did not employ cross-linked polymer matrices.

  18. Active display and encoding by integrated plasmonic polarizer on light-emitting-diode

    PubMed Central

    Wang, L.; Li, T.; Guo, R. Y.; Xia, W.; Xu, X. G.; Zhu, S. N.

    2013-01-01

    An electrical pumped microscopic active display with integration of plasmonic polarizer and light-emitting-diode is proposed. Thanks to the strong polarized emission through the rectangular nanoholes, well designed pixels with respect to different polarizations are engineered, which give rise to flexible and controllable active display. As results, polarization multiplexed letter encoding, single and double gray-scale images and animation movies are successfully realized. Our results demonstrate a new strategy in electro-optical integration and indicate potential applications in designing new type of microscopic electro-optical devices. PMID:24008314

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

    PubMed Central

    Ohtani, Bunsho; Kikushima, Kotaro

    2013-01-01

    Summary The bromination of hydrocarbons with CBr4 as a bromine source, induced by light-emitting diode (LED) irradiation, has been developed. Monobromides were synthesized with high efficiency without the need for any additives, catalysts, heating, or inert conditions. Action and absorption spectra suggest that CBr4 absorbs light to give active species for the bromination. The generation of CHBr3 was confirmed by NMR spectroscopy and GC–MS spectrometry analysis, indicating that the present bromination involves the homolytic cleavage of a C–Br bond in CBr4 followed by radical abstraction of a hydrogen atom from a hydrocarbon. PMID:24062826

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

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

    PubMed

    Calderhead, R Glen; Vasily, David B

    2016-07-01

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

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

    NASA Astrophysics Data System (ADS)

    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.

  3. Light-emitting diode technology status and directions: Opportunities for horticultural lighting

    DOE PAGESBeta

    Tsao, Jeffrey Y.; Pattison, P. Morgan; Krames, Michael R.

    2016-01-01

    Here, light-emitting diode (LED) technology has advanced rapidly over the last decade, primarily driven by display and general illumination applications ("solid-state lighting (SSL) for humans"). These advancements have made LED lighting technically and economically advantageous not only for these applications, but also, as an indirect benefit, for adjacent applications such as horticultural lighting ("SSL for plants"). Moreover, LED technology has much room for continued improvement. In the near-term, these improvements will continue to be driven by SSL for humans (with indirect benefit to SSL for plants), the most important of which can be anticipated.

  4. Organic Light Emitting Diodes Using a Ga:ZnO Anode

    SciTech Connect

    Berry, J. J.; Ginley, D. S.; Burrows, Paul E.

    2008-05-12

    We report the application of gallium doped zinc oxide (GZO) films as anodes in organic light emitting diodes (OLEDs). Pulsed laser deposited GZO films of differing Ga composition are examined. Bilayer OLEDs using GZO and indium tin oxide (ITO) anodes are then compared. Relative to ITO, the GZO anodes have slightly better sheet resistance and transparency in the visible spectral region. Device data suggest GZO results in more effective hole injection into an aromatic triamine hole transporting layer. Indium free anodes are expected toimprove OLED stability while lowering the cost per unit area, crucial for OLED based lighting applications.

  5. High-resolution electrohydrodynamic jet printing of small-molecule organic light-emitting diodes.

    PubMed

    Kim, Kukjoo; Kim, Gyeomuk; Lee, Bo Ram; Ji, Sangyoon; Kim, So-Yun; An, Byeong Wan; Song, Myoung Hoon; Park, Jang-Ung

    2015-08-28

    The development of alternative organic light-emitting diode (OLED) fabrication technologies for high-definition and low-cost displays is an important research topic as conventional fine metal mask-assisted vacuum evaporation has reached its limit to reduce pixel sizes and manufacturing costs. Here, we report an electrohydrodynamic jet (e-jet) printing method to fabricate small-molecule OLED pixels with high resolution (pixel width of 5 μm), which significantly exceeds the resolutions of conventional inkjet or commercial OLED display pixels. In addition, we print small-molecule emitting materials which provide a significant advantage in terms of device efficiency and lifetime compared to those with polymers.

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

    PubMed

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

    2003-06-01

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

  7. A high quality liquid-type quantum dot white light-emitting diode

    NASA Astrophysics Data System (ADS)

    Sher, Chin-Wei; Lin, Chin-Hao; Lin, Huang-Yu; Lin, Chien-Chung; Huang, Che-Hsuan; Chen, Kuo-Ju; Li, Jie-Ru; Wang, Kuan-Yu; Tu, Hsien-Hao; Fu, Chien-Chung; Kuo, Hao-Chung

    2015-12-01

    This study demonstrates a novel package design to store colloidal quantum dots in liquid format and integrate them with a standard LED. The high efficiency and high quality color performance at a neutral white correlated color temperature is demonstrated. The experimental results indicate that the liquid-type quantum dot white light-emitting diode (LQD WLED) is highly efficient and reliable. The luminous efficiency and color rendering index (CRI) of the LQD WLED can reach 271 lm Wop-1 and 95, respectively. Moreover, a glass box is employed to prevent humidity and oxygen erosion. With this encapsulation design, our quantum dot box can survive over 1000 hours of storage time.

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

    SciTech Connect

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

    2014-12-08

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

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

    NASA Astrophysics Data System (ADS)

    Karpov, Sergey Y.

    2016-03-01

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

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

    PubMed

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

    2010-04-12

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

  11. Effects of hole carrier injection and transport in organic light-emitting diodes

    SciTech Connect

    Antoniadis, H.; Miller, J.N.; Roitman, D.B.; Campbell, I.H.

    1997-08-01

    In this paper, the authors examine the effects of hole carrier injection and mobility on both the electroluminescence (EL) quantum efficiency and the operating voltage of bilayer organic light-emitting diodes (OLED`s). They find that hole-injection is limited by the nature of the hole injecting interface and significantly affects the operating voltage, but not the quantum efficiency of the OLED. Hole mobility is found not to affect the device quantum efficiency. They demonstrate the characteristics of an ideal ohmic contact by measuring space-charge-limited currents in a trap-free hole transporting polymer layer.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  13. Measuring the profile of the emission zone in polymeric organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Gather, Malte C.; Flämmich, Michael; Danz, Norbert; Michaelis, Dirk; Meerholz, Klaus

    2009-06-01

    The profile of the emission zone (PEZ) in the emissive layer (EML) of polymeric organic light-emitting diodes (OLEDs) is determined by fitting the measured electroluminescence spectrum of the device with a series of simulated spectra that correspond to different emitter locations. The studied OLEDs are based on two different blue-emitting conjugated polymers. In one case, the PEZ is confined to a 10 nm thin sheet at the anode indicating electron dominated current in the EML. In OLEDs based on the other emitter, the PEZ spreads over the entire EML.

  14. Enhancing the emission directionality of organic light-emitting diodes by using photonic microstructures

    SciTech Connect

    Zhang, Shuyu; Turnbull, Graham A. E-mail: idws@st-andrews.ac.uk; Samuel, Ifor D. W. E-mail: idws@st-andrews.ac.uk

    2013-11-18

    We report microstructured organic light-emitting diodes (OLEDs) with directional emission based on efficient solution-processable europium-OLEDs patterned by solvent assisted microcontact molding. The angle dependence of the light emission is characterized for OLEDs with square-array photonic crystals with periods between 275 nm and 335 nm. The microstructured devices have emission patterns strongly modified from the Lambertian emission of planar OLEDs and can approximately double the emitted power in a desired angle range in both s- and p-polarizations. The modified emission is attributed to light diffracted out of the waveguide modes of the OLEDs.

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

    NASA Astrophysics Data System (ADS)

    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.

  16. Temperature-dependent efficiency droop of blue InGaN micro-light emitting diodes

    SciTech Connect

    Tian, Pengfei; McKendry, Jonathan J. D.; Herrnsdorf, Johannes; Ferreira, Ricardo; Watson, Ian M.; Gu, Erdan Dawson, Martin D.; Watson, Scott; Kelly, Anthony E.

    2014-10-27

    Temperature-dependent trends in radiative and Auger recombination coefficients have been determined at different injection carrier concentrations using InGaN micro-light emitting diodes 40 μm in diameter. The differential lifetime was obtained first from the measured modulation bandwidth and was then employed to calculate the carrier concentration in the quantum well active region. When the temperature increases, the carrier concentration increases, but both the radiative and Auger recombination coefficients decrease. In addition, the temperature dependence of radiative and Auger recombination coefficients is weaker at a higher injection carrier concentration, which is strongly related to phase space filling.

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

    NASA Astrophysics Data System (ADS)

    Guan, Yunxia; Niu, Lianbin

    2009-03-01

    White organic light-emitting diodes were fabricated by 9, 10-bis (2-naphthyl) anthracene (ADN) doped with Rubrene with a structure of ITO/copper phthalocyanine (CuPc) / NPB /ADN: Rubrene /Alq3 /CsF/Mg:Ag/Ag. Multilayer organic devices using AND and Rubrene as an emitting layer produced white emissions with good chromaticity and luminous efficiency as high as 5.93 cd/A. This performance can be explained by Förster energy transfer from the blue-emitting host to the orange-emitting dopant.

  18. Effect of current waveform on the performance of phosphor converted nitride light emitting diodes

    SciTech Connect

    Ludwiczak, Bogna; Jantsch, Wolfgang

    2014-01-21

    We investigate the influence of the current waveform on the efficiency and the emission spectra of white, high power InGaN light emitting diodes. We consider rectangular and trapezoidal current pulses, adjusted to provide the same number of charge carriers in the space charge region. Our measurements confirm the theoretical expectation that flattening of the pulse flank increases the power efficiency. This effect is stronger according to the current amplitude. The emission blue peak at trapezoidal pulses is slightly red-shifted compared to that one at rectangular pulses. This indicates a stronger effect of the quantum confined Stark effect for trapezoidal pulse driving.

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

    PubMed Central

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

    2015-01-01

    Hoover Pugedo light traps were modified for use with green and blue-light-emitting diodes to trap phlebotomine sandflies in northeastern Brazil. A total of 2,267 specimens belonging to eight genera and 15 species were sampled. The predominant species were Nyssomyia whitmani(34.41%) and Micropygomyia echinatopharynx(17.25%).The green LED trap prevailed over the blue and control lights; however, no statistically significant difference could be detected among the three light sources. Even 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. PMID:26517661

  20. Light-emitting diodes from molecularly thin porphyrin derivative: Effect of molecular packing

    NASA Astrophysics Data System (ADS)

    Chowdhury, A.; Chowdhury, J.; Pal, P.; Pal, A. J.

    1998-08-01

    Light-emitting diodes based on the molecularly thin film of a porphyrin derivative have been fabricated. Langmuir-Blodgett (LB) films at two different surface pressures have been used as active materials of the device and their characteristics have been studied and compared. Devices with LB films deposited at a higher pressure show rectifying behaviour and electroluminescence (EL) was observed only in the forward bias. The other type of devices with LB films deposited at a lower pressure, yields EL in both bias directions. The effect of thickness of the active layers has been investigated. The turn-on currents for both the cases have also been compared.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  2. Orthogonally Substituted Benzimidazole-Carbazole Benzene As Universal Hosts for Phosphorescent Organic Light-Emitting Diodes.

    PubMed

    Huang, Jau-Jiun; Hung, Yu-Hsiang; Ting, Pei-Ling; Tsai, Yu-Ning; Gao, Huan-Jie; Chiu, Tien-Lung; Lee, Jiun-Haw; Chen, Chi-Lin; Chou, Pi-Tai; Leung, Man-kit

    2016-02-19

    The novel ambipolar hosts of o-CbzBz and o-DiCbzBz contain carbazole and benzimidazole through an ortho-connection. The orthogonal conformations cause the triplet state to be confined at the carbazole units to secure efficient energy transfer. The phosphorescent organic light-emitting diodes (PhOLEDs) show a high current efficiency, power efficiency, and low efficiency roll-off. o-DiCbzBz can be used as a host for sky-blue, green, and orange-red PhOLEDs, giving 57.5, 78.4, and 60.3 cd/A, respectively. PMID:26829339

  3. Origin of Sub-Bandgap Electroluminescence in Organic Light-Emitting Diodes.

    PubMed

    Xiang, Chaoyu; Peng, Cheng; Chen, Ying; So, Franky

    2015-10-28

    Sub-bandgap electroluminescence in organic light emitting diodes is a phenomenon in which the electroluminescence turn-on voltage is lower than the bandgap voltage of the emitter. Based on the results of transient electroluminescence (EL) and photoluminescence and electroabsorption spectroscopy measurements, it is concluded that in rubrene/C60 devices, charge transfer excitons are generated at the rubrene/C60 interface under sub-bandgap driving conditions, leading to the formation of triplet excitons, and sub-bandgap EL is the result of the subsequent triplet-triplet annihilation process. PMID:26312783

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

    PubMed

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

    2011-10-01

    Chaotically spiking attractors in semiconductor lasers with optoelectronic feedback have been recently observed to be the result of canard phenomena in three-dimensional phase space (incomplete homoclinic scenarios). Since light-emitting diodes display the same dynamics and are much more easily controllable, we use one of these systems to complete the attractor analysis demonstrating experimentally and theoretically the occurrence of complex sequences of periodic mixed-mode oscillations. In particular, we investigate the transition between periodic and chaotic mixed-mode states and analyze the effects of the unavoidable experimental noise on these transitions. PMID:22181318

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  6. Sensing atmospheric reactive species using light emitting diode by incoherent broadband cavity enhanced absorption spectroscopy.

    PubMed

    Yi, Hongming; Wu, Tao; Wang, Guishi; Zhao, Weixiong; Fertein, Eric; Coeur, Cécile; Gao, Xiaoming; Zhang, Weijun; Chen, Weidong

    2016-05-16

    We overview our recent progress in the developments and applications of light emitting diode-based incoherent broadband cavity enhanced absorption spectroscopy (LED-IBBCEAS) techniques for real-time optical sensing chemically reactive atmospheric species (HONO, NO3, NO2) in intensive campaigns and in atmospheric simulation chamber. New application of optical monitoring of NO3 concentration-time profile for study of the NO3-initiated oxidation process of isoprene in a smog chamber is reported. PMID:27409951

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

    PubMed

    Calderhead, R Glen; Vasily, David B

    2016-07-01

    Low level light therapy (LLLT) with light-emitting diodes (LEDs) is emerging from the mists of black magic as a solid medico-scientific modality, with a substantial buildup of corroborative bodies of evidence for its efficacy and elucidation of the modes of action. Reports are appearing from many different specialties; however, of particular interest to plastic surgeons treating the aging face is the proven action of LED-LLLT on skin cells in both the epidermis and dermis and enhanced blood flow. Thus, LED-LLLT is a safe and effective stand-alone therapy for patients who are prepared to wait until the final effect is perceived. PMID:27363768

  8. Liquid-crystal-modulated correlated color temperature tunable light-emitting diode with highly accurate regulation.

    PubMed

    Huang, Chiu-Chang; Kuo, Yu-Yi; Chen, Szu-Hua; Chen, Wei-Ting; Chao, Chih-Yu

    2015-02-01

    A precise correlated color temperature (CCT) tuning method for light-emitting diodes (LEDs) has been developed and is demonstrated in this article. By combining LEDs and a liquid crystal (LC) cell, a light source with continuous CCT variation along a straight track on the chromaticity diagram is achieved. Moreover, the manner of CCT variation can be modulated by choosing appropriate LEDs and phosphors to yield a variation going from 3800 K to 6100 K with the track near the black-body locus. By adapting various developed LC technologies for diverse demands, the performance and applications of LEDs can be greatly improved.

  9. Compact light-emitting diode lighting ring for video-assisted thoracic surgery.

    PubMed

    Lu, Ming-Kuan; Chang, Feng-Chen; Wang, Wen-Zhe; Hsieh, Chih-Cheng; Kao, Fu-Jen

    2014-01-01

    In this work, a foldable ring-shaped light-emitting diode (LED) lighting assembly, designed to attach to a rubber wound retractor, is realized and tested through porcine animal experiments. Enabled by the small size and the high efficiency of LED chips, the lighting assembly is compact, flexible, and disposable while providing direct and high brightness lighting for more uniform background illumination in video-assisted thoracic surgery (VATS). When compared with a conventional fiber bundle coupled light source that is usually used in laparoscopy and endoscopy, the much broader solid angle of illumination enabled by the LED assembly allows greatly improved background lighting and imaging quality in VATS. PMID:25291209

  10. Compact light-emitting diode lighting ring for video-assisted thoracic surgery

    NASA Astrophysics Data System (ADS)

    Lu, Ming-Kuan; Chang, Feng-Chen; Wang, Wen-Zhe; Hsieh, Chih-Cheng; Kao, Fu-Jen

    2014-10-01

    In this work, a foldable ring-shaped light-emitting diode (LED) lighting assembly, designed to attach to a rubber wound retractor, is realized and tested through porcine animal experiments. Enabled by the small size and the high efficiency of LED chips, the lighting assembly is compact, flexible, and disposable while providing direct and high brightness lighting for more uniform background illumination in video-assisted thoracic surgery (VATS). When compared with a conventional fiber bundle coupled light source that is usually used in laparoscopy and endoscopy, the much broader solid angle of illumination enabled by the LED assembly allows greatly improved background lighting and imaging quality in VATS.

  11. Organic light emitting diode improves diabetic cutaneous wound healing in rats.

    PubMed

    Wu, Xingjia; Alberico, Stephanie; Saidu, Edward; Rahman Khan, Sazzadur; Zheng, Shijun; Romero, Rebecca; Sik Chae, Hyun; Li, Sheng; Mochizuki, Amane; Anders, Juanita

    2015-01-01

    A major complication for diabetic patients is chronic wounds due to impaired wound healing. It is well documented that visible red wavelengths can accelerate wound healing in diabetic animal models and patients. In vitro and in vivo diabetic models were used to investigate the effects of organic light emitting diode (OLED) irradiation on cellular function and cutaneous wound healing. Human dermal fibroblasts were cultured in hyperglycemic medium (glucose concentration 180 mM) and irradiated with an OLED (623 nm wavelength peak, range from 560 to 770 nm, power density 7 or 10 mW/cm2 at 0.2, 1, or 5 J/cm2). The OLED significantly increased total adenosine triphosphate concentration, metabolic activity, and cell proliferation compared with untreated controls in most parameters tested. For the in vivo experiment, OLED and laser (635 ± 5 nm wavelength) treatments (10 mW/cm2 , 5 J/cm2 daily for a total of seven consecutive days) for cutaneous wound healing were compared using a genetic, diabetic rat model. Both treatments had significantly higher percentage of wound closure on day 6 postinjury and higher total histological scores on day 13 postinjury compared with control. No statistical difference was found between the two treatments. OLED irradiation significantly increased fibroblast growth factor-2 expression at 36-hour postinjury and enhanced macrophage activation during initial stages of wound healing. In conclusion, the OLED and laser had comparative effects on enhancing diabetic wound healing.

  12. Efficiency and Color Coordinate Improvement Using Codopants in Blue Organic Light-Emitting Diode

    NASA Astrophysics Data System (ADS)

    Wang, Xiu Ru; Chen, Jiang Shan; You, Han; Ma, Dong Ge; Sun, Run Guang

    2005-12-01

    The codoping method is applied to fabricate efficient blue organic light-emitting diodes (OLEDs). With the same structure of indium-tin oxide (ITO)/N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'diamine (NPB)(80 nm)/light-emitting layer (30 nm)/tris-(8-hydroxy-quinoline)aluminum (Alq3) (20 nm)/LiF (1 nm)/Al (120 nm), a set of three devices was manufactured for comparison. For Devices 1, 2, and 3, the light-emitting layers are 9,10-di(2-naphthyl)anthracene (ADN):4,4'-(1,4-phenylenedi-2,1-ethene diyl)bis[N,N-bis(4-methylphenyl)-benzenamine] (DPAVB) (1 wt %), ADN:2,5,8,11-tetra-(t-butyl)-perylene (TBPE) (1 wt %), and ADN:DPAVB (0.3 wt %):TBPE (0.7 wt %), respectively. It is found that the codoped Device 3 has the highest maximum luminance, Electroluminescence (EL) quantum efficiency and color saturation. Further study on the effect of the codopants was through a relative photoluminescence (PL) quantum efficiency measurement. The result shows that the relative PL efficiencies of Devices 1, 2, and 3 are 15.6, 19.3, and 24%, respectively, as determined using an integrating sphere system excited at 375 nm. The codoping method improves the EL efficiency intrinsically. Codopants of the heterogeneous light-emitting molecules may decrease the possibility of self-quenching from the interaction of the homogenous molecules at the same total doping concentration. Furthermore, the decrease in the interaction of homogenous molecules suppresses the light emission from the aggregations thus narrowing the emission spectrum, and results in saturated blue light emission.

  13. Disinfection of Spacecraft Potable Water Systems by Photocatalytic Oxidation Using UV-A Light Emitting Diodes

    NASA Technical Reports Server (NTRS)

    Birmele, Michele N.; O'Neal, Jeremy A.; Roberts, Michael S.

    2011-01-01

    Ultraviolet (UV) light has long been used in terrestrial water treatment systems for photodisinfection and the removal of organic compounds by several processes including photoadsorption, photolysis, and photocatalytic oxidation/reduction. Despite its effectiveness for water treatment, UV has not been explored for spacecraft applications because of concerns about the safety and reliability of mercury-containing UV lamps. However, recent advances in ultraviolet light emitting diodes (UV LEDs) have enabled the utilization of nanomaterials that possess the appropriate optical properties for the manufacture of LEDs capable of producing monochromatic light at germicidal wavelengths. This report describes the testing of a commercial-off-the-shelf, high power Nichia UV-A LED (250mW A365nnJ for the excitation of titanium dioxide as a point-of-use (POD) disinfection device in a potable water system. The combination of an immobilized, high surface area photocatalyst with a UV-A LED is promising for potable water system disinfection since toxic chemicals and resupply requirements are reduced. No additional consumables like chemical biocides, absorption columns, or filters are required to disinfect and/or remove potentially toxic disinfectants from the potable water prior to use. Experiments were conducted in a static test stand consisting of a polypropylene microtiter plate containing 3mm glass balls coated with titanium dioxide. Wells filled with water were exposed to ultraviolet light from an actively-cooled UV-A LED positioned above each well and inoculated with six individual challenge microorganisms recovered from the International Space Station (ISS): Burkholderia cepacia, Cupriavidus metallidurans, Methylobacterium fujisawaense, Pseudomonas aeruginosa, Sphingomonas paucimobilis and Wautersia basilensis. Exposure to the Nichia UV-A LED with photocatalytic oxidation resulted in a complete (>7-log) reduction of each challenge bacteria population in <180 minutes of contact

  14. Graphene oxide/graphene vertical heterostructure electrodes for highly efficient and flexible organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Jia, S.; Sun, H. D.; Du, J. H.; Zhang, Z. K.; Zhang, D. D.; Ma, L. P.; Chen, J. S.; Ma, D. G.; Cheng, H. M.; Ren, W. C.

    2016-05-01

    The relatively high sheet resistance, low work function and poor compatibility with hole injection layers (HILs) seriously limit the applications of graphene as transparent conductive electrodes (TCEs) for organic light emitting diodes (OLEDs). Here, a graphene oxide/graphene (GO/G) vertical heterostructure is developed as TCEs for high-performance OLEDs, by directly oxidizing the top layer of three-layer graphene films with ozone treatment. Such GO/G heterostructure electrodes show greatly improved optical transmittance, a large work function, high stability, and good compatibility with HIL materials (MoO3 in this work). Moreover, the conductivity of the heterostructure is not sacrificed compared to the pristine three-layer graphene electrodes, but is significantly higher than that of pristine two-layer graphene films. In addition to high flexibility, OLEDs with different emission colors based on the GO/G heterostructure TCEs show much better performance than those based on indium tin oxide (ITO) anodes. Green OLEDs with GO/G heterostructure electrodes have the maximum current efficiency and power efficiency, as high as 82.0 cd A-1 and 98.2 lm W-1, respectively, which are 36.7% (14.8%) and 59.2% (15.0%) higher than those with pristine graphene (ITO) anodes. These findings open up the possibility of using graphene for next generation high-performance flexible and wearable optoelectronics with high stability.The relatively high sheet resistance, low work function and poor compatibility with hole injection layers (HILs) seriously limit the applications of graphene as transparent conductive electrodes (TCEs) for organic light emitting diodes (OLEDs). Here, a graphene oxide/graphene (GO/G) vertical heterostructure is developed as TCEs for high-performance OLEDs, by directly oxidizing the top layer of three-layer graphene films with ozone treatment. Such GO/G heterostructure electrodes show greatly improved optical transmittance, a large work function, high stability

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

    NASA Astrophysics Data System (ADS)

    Ma, Xin

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

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

    PubMed

    Bak, Jimmy; Ladefoged, Søren D; Tvede, Michael; Begovic, Tanja; Gregersen, Annette

    2010-01-01

    Bacterial biofilms on long-term catheters are a major source of infection. Exposure to ultraviolet C (UVC - 265 nm) light was shown in an earlier study to reduce the number of bacteria substantially on ex vivo treated urinary patient catheters. Very large doses (long treatment times) should, however, be applied to obtain 99.9% disinfection rates. The major reason was that besides cells the mature biofilm contained absorbing and scattering particulates, which made the biofilm opaque. The potential of UVC light emitting diodes (LED) for disinfection purposes in catheter-like tubes contaminated with biofilm was investigated. It was shown that UVC light propagation was possible through both Teflon and catheter tubes (silicone). The disinfection efficiency of the diodes was demonstrated on tubes contaminated artificially with a Pseudomonas aeruginosa biofilm. The tubes were connected to a flow system and biofilms were produced during a 3 day period. Tubes in lengths of 10 (Teflon, silicone) and 20 cm (Teflon) were contaminated. Tubes for control and for UVC treatment were contaminated in parallel. Biofilms were sampled from the total inner surface of the tubes. Colony counts on the control samples were in the range of 5 x 10(5)-1.3 x 10(9) CFU ml(-1), with disinfection rates in the range 96-100%. The applied UVC doses corresponded to treatment times between 15 and 300 min. Disinfection (100%) was obtained in 10 cm Teflon tubes exposed for 30 min (detection limit <5 CFU ml(-1)). The same result was obtained for a 20 cm Teflon tube exposed for 300 min. The disinfection rate was 96% for the 20 cm tube if the dose was reduced to 30 min. A disinfection rate of 99.99% was observed for a 10 cm peritoneal dialysis catheter tube (silicone) exposed for 300 min. Differences between the tubes were dependent on the differences in length and the type of the material. The UVC light was transmitted six times more efficiently in Teflon than in silicone tubes of equal length (10 cm). The

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

    PubMed

    Bak, Jimmy; Ladefoged, Søren D; Tvede, Michael; Begovic, Tanja; Gregersen, Annette

    2010-01-01

    Bacterial biofilms on long-term catheters are a major source of infection. Exposure to ultraviolet C (UVC - 265 nm) light was shown in an earlier study to reduce the number of bacteria substantially on ex vivo treated urinary patient catheters. Very large doses (long treatment times) should, however, be applied to obtain 99.9% disinfection rates. The major reason was that besides cells the mature biofilm contained absorbing and scattering particulates, which made the biofilm opaque. The potential of UVC light emitting diodes (LED) for disinfection purposes in catheter-like tubes contaminated with biofilm was investigated. It was shown that UVC light propagation was possible through both Teflon and catheter tubes (silicone). The disinfection efficiency of the diodes was demonstrated on tubes contaminated artificially with a Pseudomonas aeruginosa biofilm. The tubes were connected to a flow system and biofilms were produced during a 3 day period. Tubes in lengths of 10 (Teflon, silicone) and 20 cm (Teflon) were contaminated. Tubes for control and for UVC treatment were contaminated in parallel. Biofilms were sampled from the total inner surface of the tubes. Colony counts on the control samples were in the range of 5 x 10(5)-1.3 x 10(9) CFU ml(-1), with disinfection rates in the range 96-100%. The applied UVC doses corresponded to treatment times between 15 and 300 min. Disinfection (100%) was obtained in 10 cm Teflon tubes exposed for 30 min (detection limit <5 CFU ml(-1)). The same result was obtained for a 20 cm Teflon tube exposed for 300 min. The disinfection rate was 96% for the 20 cm tube if the dose was reduced to 30 min. A disinfection rate of 99.99% was observed for a 10 cm peritoneal dialysis catheter tube (silicone) exposed for 300 min. Differences between the tubes were dependent on the differences in length and the type of the material. The UVC light was transmitted six times more efficiently in Teflon than in silicone tubes of equal length (10 cm). The

  18. Light-emitting diodes at 940nm attenuate colitis-induced inflammatory process in mice.

    PubMed

    Belém, Mônica O; de Andrade, Giovana M M; Carlos, Thalita M; Guazelli, Carla F S; Fattori, Victor; Toginho Filho, Dari O; Dias, Ivan F L; Verri, Waldiceu A; Araújo, Eduardo J A

    2016-09-01

    Inflammatory bowel disease (IBD) presents intense inflammatory infiltrate, crypt abscesses, ulceration and even loss of function. Despite the clinical relevance of IBD, its current therapy remains poorly effective. Infrared wavelength phototherapy shows therapeutic potential on inflammation. Our goal was to evaluate whether light-emitting diodes (LED) at 940nm are capable of mitigating the colitis-induced inflammatory process in mice. Forty male Swiss mice were assigned into five groups: control; control treated with LED therapy; colitis without treatment; colitis treated with LED therapy; colitis treated with Prednisolone. Experimental colitis was induced by acetic acid 7.5% (pH2.5) rectal administration. LED therapy was performed with light characterized by wavelength of 940nm, 45nm bandwidth, intensity of 4.05J/cm(2), total power of 270mW and total dose of 64.8J for 4min in a single application. Colitis-induced intestinal transit delay was inhibited by LED therapy. Colitis caused an increase of colon dimensions (length, diameter, total area) and colon weight (edema), which were inhibited by LED therapy. LED therapy also decreased colitis-induced tissue gross lesion, myeloperoxidase activity, microscopic tissue damage score and the presence of inflammatory infiltrate in all intestinal layers. Furthermore, LED therapy inhibited colitis-induced IL-1β, TNF-α, and IL-6 production. We conclude LED therapy at 940nm inhibited experimental colitis-induced colon inflammation in mice, therefore, rendering it a promising therapeutic approach that deserves further investigation. PMID:27424097

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

    DOEpatents

    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.

  20. Hierarchical growth of GaN nanowires for light emitting diode applications

    NASA Astrophysics Data System (ADS)

    Raj, Rishabh; Ra, Yong-Ho; Lee, Cheul-Ro; Obheroi, Sonika; Navamathavan, R.

    2016-02-01

    Gallium nitride nanostructures have been receiving considerable attention as building blocks for nanophotonic technologies due to their unique high aspect ratios, promising the realization of photonic and biological nanodevices such as blue light emitting diodes (LEDs), short-wavelength ultraviolet nanolasers and nanofluidic biochemical sensors. In this study, we report on the hierarchical growth of GaN nanowires (NWs) by dynamically adjusting the growth parameters using pulsed flow metalorganic chemical vapor deposition (MOCVD) technique. We carried out two step growth processes to grow hierarchical GaN NWs. At the first step the GaN NWs were grown at 950°C and in the second stage, we suitably decreased the growth temperature to 710°C to grow the hierarchical structures. The surface morphology, structural and optical characterization of the grown hierarchical GaN NWs were studied by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and photoluminescence (PL) measurements, respectively. These kind of hierarchical NWs are promising to allow flat band quantum structures that are shown to improve the efficiency of light-emitting diodes.

  1. Toward fully flexible multilayer moisture-barriers for organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Seo, Seung-Woo; Jung, Eun; Joon Seo, Sang; Chae, Heeyeop; Kyoon Chung, Ho; Min Cho, Sung

    2013-10-01

    Flexible organic light-emitting diodes require flexible thin-film encapsulation to ensure both a long lifetime and flexibility of the device. Although an aluminum oxide layer grown by atomic layer deposition can protect the device from oxidative species, such as moisture, it does not provide sufficient flexibility for a flexible device. Thus, organic-inorganic multilayer structures were prepared and tested for both the moisture-barrier property and flexibility to achieve fully flexible thin-film encapsulation for organic light-emitting diodes. The flexible thin-film encapsulation developed in this study resulted in an initial water vapor transmission rate of 3 × 10-4 g/m2/day that decreased by only 10% even after a 10 000 severe bending cycles at a bending radius of 0.3 cm. This result was possible by reducing the thickness of the aluminum-oxide sub-layer as low as possible down to only 1 cycle of atomic layer deposition and placing it in a neutral stress plane. Theoretical estimations of tensile strain supported the experimental results.

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

    PubMed

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

    2016-08-10

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

  3. New technical approach using light-emitting diodes (LED) in neonatal vascular transillumination

    NASA Astrophysics Data System (ADS)

    de Riese, Johannes; Perez-Benavides, Fortunato

    2005-04-01

    A challenging and frequent problem in premature neonates is vascular access because of their very small blood vessels. The use of small tourniquets and direct light has been the traditional technique, but its limitations are most apparent in the extremely small child. In the last three years we have been using Light Emitting Diodes (Red light) to transiluminate the vascular structures in arms and legs in these small patients, this has improved significantly the visualization and access of the vascular structures in our smallest patients. Light Emitting Diodes (LED) are small and inexpensive devices that emit powerful "Cold light" capable to transiluminate a portion of an infant's extremity without burning the area of contact. The individual working on the IV access virtually sees through the tissues to place a catheter at the precise location of the extremity. According to an extensive search of the available literature, this LED application for vascular access in small newborns has not been described. In our physician's and neonatal nurse's hands, it is a simple and very efficient procedure for vascular access in the smallest patients. This paper presents an overview of vascular access technique using LED in the premature infant.

  4. High-resolution electrohydrodynamic jet printing of small-molecule organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Kim, Kukjoo; Kim, Gyeomuk; Lee, Bo Ram; Ji, Sangyoon; Kim, So-Yun; An, Byeong Wan; Song, Myoung Hoon; Park, Jang-Ung

    2015-08-01

    The development of alternative organic light-emitting diode (OLED) fabrication technologies for high-definition and low-cost displays is an important research topic as conventional fine metal mask-assisted vacuum evaporation has reached its limit to reduce pixel sizes and manufacturing costs. Here, we report an electrohydrodynamic jet (e-jet) printing method to fabricate small-molecule OLED pixels with high resolution (pixel width of 5 μm), which significantly exceeds the resolutions of conventional inkjet or commercial OLED display pixels. In addition, we print small-molecule emitting materials which provide a significant advantage in terms of device efficiency and lifetime compared to those with polymers.The development of alternative organic light-emitting diode (OLED) fabrication technologies for high-definition and low-cost displays is an important research topic as conventional fine metal mask-assisted vacuum evaporation has reached its limit to reduce pixel sizes and manufacturing costs. Here, we report an electrohydrodynamic jet (e-jet) printing method to fabricate small-molecule OLED pixels with high resolution (pixel width of 5 μm), which significantly exceeds the resolutions of conventional inkjet or commercial OLED display pixels. In addition, we print small-molecule emitting materials which provide a significant advantage in terms of device efficiency and lifetime compared to those with polymers. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03034j

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  6. Visible-light emission at room temperature in Mn-doped Si light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Hai, Pham Nam; Maruo, Daiki; Anh, Le Duc; Tanaka, Masaaki

    2016-03-01

    We demonstrate Si-based light-emitting diodes that continuously emit reddish-yellow visible light at room temperature by utilizing optical transitions between the p-d hybrid orbitals of Mn atoms doped in Si. Our light-emitting diodes show clear visible-light electroluminescence with two peaks at E1=1.75 and E2=2.30 eV , corresponding to optical transitions between p-d hybrid orbitals of Mn atoms. The electrons at the p-d hybrid orbitals of Mn in Si are excited by hot holes that are accelerated by an intensive electric field in the depletion layer of reverse biased Si p -n junctions containing a Mn-doped Si (Si:Mn) layer. The observed two peaks at E1=1.75 and E2=2.30 eV are redshifted and blueshifted by 0.14 eV, respectively, from those of GaAs:Mn or ZnS:Mn. Our observations are consistent with the p -d hybridized electronic structure of Mn atoms doped in Si as predicted by first-principles calculations.

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

    PubMed

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

    2016-08-10

    Polymer light-emitting diodes (PLEDs) have attracted broad interest due to their solution-processable properties. It is well-known that to achieve better performance, organic light-emitting diodes require multilayer device structures. However, it is difficult to realize multilayer device structures by solution processing for PLEDs. Because most semiconducting polymers have similar solubility in common organic solvents, such as toluene, xylene, chloroform, and chlorobenzene, the deposition of multilayers can cause layers to mix together and damage each layer. Herein, a novel semiorthogonal solubility relationship was developed and demonstrated. For the first time, an alkane-soluble dendrimer is utilized as the electron-transport layer (ETL) in PLEDs via a solution-based process. With the dendrimer ETL, the external quantum efficiency increases more than threefold. This improvement in the device performance is attributed to better exciton confinement, improved exciton energy transfer, and better charge carrier balance. The semiorthogonal solubility provided by alkane offers another process dimension in PLEDs. By combining them with water/alcohol-soluble polyelectrolytes, more exquisite multilayer devices can be fabricated to achieve high device performance, and new device structures can be designed and realized. PMID:27435357

  8. Organic light-emitting diode microcavities from transparent conducting metal oxide photonic crystals.

    PubMed

    Puzzo, Daniel P; Helander, Michael G; O'Brien, Paul G; Wang, Zhibin; Soheilnia, Navid; Kherani, Nazir; Lu, Zhenghong; Ozin, Geoffrey A

    2011-04-13

    We report herein on the integration of novel transparent and conducting one-dimensional photonic crystals that consist of periodically alternating layers of spin-coated antimony-doped tin oxide nanoparticles and sputtered tin-doped indium oxide into organic light emitting diode (OLED) microcavities. The large refractive index contrast between the layers due the porosity of the nanoparticle layer led to facile fabrication of dielectric mirrors with intense and broadband reflectivity from structures consisting of only five bilayers. Because our photonic crystals are easily amenable to large scale OLED fabrication and simultaneously selectively reflective as well as electronically conductive, such materials are ideally suited for integration into OLED microcavities. In such a device, the photonic crystal, which represents a direct drop-in replacement for typical ITO anodes, is capable of serving two necessary functions: (i) as one partially reflecting mirror of the optical microcavity; and (ii) as the anode of the diode.

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

    PubMed

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

    2015-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Ziebarth, Jonathan M.

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

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

    PubMed

    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.

  13. Energetics of conjugated polymer and electrode interfaces in light emitting diode

    NASA Astrophysics Data System (ADS)

    Hwang, Jaehyung

    Recently, polymers have emerged as strong candidates for various semiconductor device applications. The physical and electrical properties of these polymer semiconductors are drastically different from those of inorganic semiconductors, and a solid understanding of these properties is necessary in order to further develop polymer electronics. This work concentrates on polymers for light emitting diode (LED) devices, which is the most promising application in polymer electronics. Understanding and control of charge injection from anode/cathode to active (light emitting) layer are crucial for high efficiency LED. To understand the charge injection efficiency, the energy band alignment and their impact on charge injection at polymer-electrode interfaces are investigated with a range of electron spectroscopies and electrical measurements. First, electronic structure of the best known hole injecting polymer (i.e., anode), poly(3,4-ethylene-dioxythiophene) -- poly(styrene-sulfonate) (PEDOT-PSS) is studied. We investigate the unique shell -- like structure of the PEDOT-PSS and its impact on the electrical properties. The role of PSS surface layer in enhancing the hole injection efficiency into the active layer is discussed. The electronic structures of two light emitting conjugated polymers, poly(9,9'-dioctylfluorene) (F8, also known as PFO) and poly(9,9'-dioctylfluorene- co-bis-N,N'-(4-butylphenyl) diphenylamine) (TFB), are also studied by various methods. The alignment of the energy levels at the anode and the cathode interfaces is investigated in detail. Different mechanisms seem to apply for the energy level alignment at the anode and the cathode. We discuss the difference in the light of different degrees of contamination at the interface which results from different processing conditions. Finally, a modification of energetics of polymer-anode interface by doping is discussed. We propose a co-solution doping method suitable for solution processed polymer material

  14. Blue/white organic light-emitting diodes and passive matrix display

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi-Lin; Jiang, Xue-Yin; Zhu, Wen-Qing; Xu, Shao-Hong

    2005-01-01

    The blue organic light emitting diodes (OLED) based on anthracene derivatives (ADN) doped with distryrylarylene derivatives (BCzVB and DSA-ph) were presented. The device of ADN doped with BCzVb shows high color purity (x=0.146, y=0.162) with maximum luminance 11600 cd/m2 (15V), current efficiency 2.8 cd/A, while the device of ADN doped with DSA-ph exhibits a sky blue with as high as efficiency 8.29 cd/A, both have a flat efficiency vs current density responses. A typical blue device of ADN doped with TBPe is used for comparison, which gives greenish blue and a stronger current-induced flyorescence quenching. Three kinds of White organic light emitting devices (WOLED) with different dopants and doping sites were constructed. The cell with a single-doped red dye in the light emitting layer (EML)(single-doped) and the cell with both red and blue dyes doped in a single EML (double-doped as well as the cell with red and blue dyes doped in EML and a green dye in another layer (triple-doped). The triple-doped cell shows much higher performance than other two cells: maximum luminance 21200cd/m2, 1026 cd/m2 at driving current 20mA/cm2, efficiency 6cd/A and a half lifetime over 22245h were reached. A passive display features 102x64 pixels with pixel size of 0.25x0.25mm2 pixel pitch 0.08mm, luminance 100 cd/m2 at driving duty 1/64, and power consumption of 0.6W was constructed.

  15. Comparative Study of Lettuce and Radish Grown Under Red and Blue Light-Emitting Diodes (LEDs) and White Fluorescent Lamps

    NASA Technical Reports Server (NTRS)

    Mickens, Matthew A.

    2012-01-01

    Growing vegetable crops in space will be an essential part of sustaining astronauts during long-term missions. To drive photosynthesis, red and blue light-emitting diodes (LEDs) have attracted attention because of their efficiency, longevity, small size, and safety. In efforts to optimize crop production, there have also been recent interests in analyzing the subtle effects of green light on plant growth, and to determine if it serves as a source of growth enhancement or suppression. A comparative study was performed on two short cycle crops of lettuce (Outredgeous) and radish (Cherry Bomb) grown under two light treatments. The first treatment being red and blue LEDs, and the second treatment consisting of white fluorescent lamps which contain a portion of green light. In addition to comparing biomass production, physiological characterizations were conducted on how the light treatments influence morphology, water use, chlorophyll content, and the production of A TP within plant tissues.

  16. An aluminium nitride light-emitting diode with a wavelength of 210 nanometres.

    PubMed

    Taniyasu, Yoshitaka; Kasu, Makoto; Makimoto, Toshiki

    2006-05-18

    Compact high-efficiency ultraviolet solid-state light sources--such as light-emitting diodes (LEDs) and laser diodes--are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond and III-V nitride semiconductors (GaN, AlGaN and AlN; refs 3-10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride (AlN), which has a very wide direct bandgap of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources. PMID:16710416

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

    PubMed

    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.

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

    SciTech Connect

    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

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

    NASA Astrophysics Data System (ADS)

    Sharma, Pratibha; Kwok, Harry

    2006-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  1. Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

    SciTech Connect

    Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep

    2013-01-28

    We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

  2. Emission properties of organic light-emitting diodes directly patterned using optically controlled nanostructuration means

    NASA Astrophysics Data System (ADS)

    Hubert, Christophe; Fiorini-Debuisschert, Celine; Rocha, Licinio; Raimond, Paul; Nunzi, Jean-Michel

    2004-09-01

    In a classical multilayer organic light emitting diode (OLED) structure, almost 80% of the light emitted happens to be lost following guiding through the different layers. Patterning of the OLEDs structure was already proposed and reported as an interesting solution towards the optimization of an OLED external efficiency. As an alternative to classical lithographic patterning methods which appear to be quite complex, we propose here the implementation of a quite direct and easy-to-set light-induced patterning method using azo-dye polymers. When a polymer film containing azobenzene dyes is irradiated by an interference pattern between polarized laser beams at a wavelength near the chromophore absorption band, the film surface undergoes a direct, reversible and controlled topographic modification. More surprisingly, we have recently experimentally evidenced that uniform irradiation of an azo-dye polymer using a single laser beam with normal incidence onto the polymer film surface could lead to a self structuration process resulting in the formation of a quasi hexagonal surface-relief grating. After a description of the main features related to light-induced surface relief gratings, we show here that this original patterning process offers an interesting solution for control and optimisation of optoelectronic devices such as OLEDs. The guiding properties of both 1D and 2D structures have been studied and their effects on the light emission properties of a patterned electroluminescent polymer have been characterized and compared after angle dependent measurement of the photoluminescence spectrum. Quite efficient decoupling is evidenced.

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

    PubMed Central

    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

  4. Unusual Optoelectronic Properties of Hydrogenated Bilayer Silicene: From Solar Absorber to Light-emitting Diode Applications

    NASA Astrophysics Data System (ADS)

    Huang, Bing; Deng, Hui-Xiong; Lee, Hoonkyung; Park, Changwon; Yoon, Mina; Sumpter, Bobby; Liu, Feng; Smith, Sean; Wei, Su-Huai

    2014-03-01

    Silicon is arguably the greatest electronic material, but not so good an optoelectronic material. By employing first-principles calculations and cluster-expansion approach, we discover that hydrogenated bilayer silicene (BS) shows promising potential as new optoelectronic materials. Most significantly, hydrogenation will covert the intrinsic BS, a strongly indirect semiconductor, into a direct-gap semiconductor with a widely tunable band gap. At low hydrogen concentrations, four ground states of single- and double-side hydrogenated BS are characterized with dipole-allowed direct (or quasidirect) band gaps in the desirable range from 1 to 1.5 eV, suitable for solar applications. At high hydrogen concentrations, three well-ordered double-side hydrogenated BS structures exhibit direct (or quasidirect) band gaps in the range of red, green, and blue colors, respectively, affording white light emitting diodes. Our findings open a door to the search of new silicon-based light-absorption and light-emitting materials for earth-abundant high-efficiency optoelectronic applications. This research is sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy.

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

    SciTech Connect

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

    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.

  6. Colloidal electroluminescence: Novel routes to controlled emission of organic light emitting diode devices

    NASA Astrophysics Data System (ADS)

    Huebner, Christopher Fletcher

    In recent years the importance of the organic light emitting diode (OLED) has grown immensely, and the past two decades have seen ongoing and exhaustive research in organic routes to solid state lighting, wherein electricity is directly converted into emitted light through an excited state relaxation mechanism. The benefits of incorporating polymeric and small molecule materials into solid state lighting devices include high efficiences, low production costs, amenability to large-scale production and devices, reduced environmental impact and low energy consumption. Herein are presented novel routes to materials engineering and preparation, device fabrication and emission tailoring through the abilility to form a variety of polymeric and small molecule materials into aqueously dispersed semiconductive electroluminescent (EL) colloids. Compartmentalization of the emissive and semiconductive species into colloidal particles affords the ability to systematically control energy transfer processes that occur in light emitting devices. Energy transfer can occur through a Coulombic (Forster) or an electronic (Dexter) process, each needing several conditions to be met for the transfer to occur, however common to both are spectral and proximal characteristics. In this work, energy transfer will be simultaneously exploited and inhibited through the creation of EL colloidal particles which can be combined in a dispersion or thin layer in order to tailor the light emission for a variety of applications.

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

    SciTech Connect

    Chang, Y. L. Gong, S. White, R.; Lu, Z. H.; Wang, X.; Wang, S.; Yang, C.

    2014-04-28

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

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

    NASA Astrophysics Data System (ADS)

    Chang, Y. L.; Gong, S.; Wang, X.; White, R.; Yang, C.; Wang, S.; Lu, Z. H.

    2014-04-01

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

  9. Crystalline/amorphous Raman markers of hole-transport material NPD in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Sugiyama, Takuro; Furukawa, Yukio; Fujimura, Hidetoshi

    2005-04-01

    Raman marker bands characteristic of solid-state structure have been found for N, N'-di-1-naphthaleyl- N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD), which is used as a hole-transport material in organic light-emitting diodes. The widths of the marker bands observed for an amorphous state at 1607, 1290, and 1192 cm -1 are broader than those for the crystalline state observed at 1609, 1288, and 1198 cm -1. These Raman bands are found to be useful for detecting the crystallization, which may cause degradation of organic light emitting diodes, of amorphous NPD films.

  10. Design method of a light emitting diode front fog lamp based on a freeform reflector

    NASA Astrophysics Data System (ADS)

    Wu, Heng; Zhang, Xianmin; Ge, Peng

    2015-09-01

    We propose a method for the design of a light emitting diode front fog lamp based on a freeform reflector. The source-target mapping is used to establish the relationship between the solid angle of the source and the target plane. The reflector is then constructed based on the non-imaging optics theory and Snell's law. A feedback function is deduced from the deviation in the simulated light pattern based on the sampling method. The reflector is then regenerated with feedback modifications and the variance is minimized after several feedbacks. A reflector for the automobile front fog lamp is designed for the OSTAR Headlamp LED source whose emitting surface is 2.8 mm×2.5 mm. Simulation results indicate that the light performance can well meet the standard of the front fog lamps in ECE R19 Revision 7.

  11. Design method of a light-emitting diode front fog lamp based on a freeform reflector

    NASA Astrophysics Data System (ADS)

    Wu, Heng; Zhang, Xianmin; Ge, Peng

    2015-06-01

    We propose a method for the design of a light-emitting diode front fog lamp based on a freeform reflector. The source-target mapping is used to establish the relationship between the solid angle of the source and the target plane. The reflector is then constructed based on the non-imaging optics theory and Snell's Law. A feedback function is deduced from the deviation in the simulated light pattern based on the sampling method. The reflector is then regenerated with feedback modifications and the variance is minimized after several feedbacks. A reflector for the automobile front fog lamp is designed for the OSTAR Headlamp LED source whose emitting surface is 2.8 mm×2.5 mm. Simulation results indicate that the light performance can well meet the standard of the front fog lamps in ECE R19 Revision 7.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Hong, Seokhwan; Kim, Ji Whan; Lee, Sangyeob

    2015-07-27

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

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

    SciTech Connect

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

    2015-04-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  16. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Nam Hai, Pham; Maruo, Daiki; Tanaka, Masaaki

    2014-03-01

    We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4A2(4F) → 4T1(4G) and 4T1(4G) → 6A1(6S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs.

  17. Quantum cascade light emitting diodes based on type-2 quantum wells

    NASA Technical Reports Server (NTRS)

    Lin, C. H.; Yang, R. Q.; Zhang, D.; Murry, S. J.; Pei, S. S.; Allerman, A. A.; Kurtz, S. R.

    1997-01-01

    The authors have demonstrated room-temperature CW operation of type-2 quantum cascade (QC) light emitting diodes at 4.2 (micro)m using InAs/InGaSb/InAlSb type-2 quantum wells. The type-2 QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-2 quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was compared of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 (micro)W at 80 K, and 140 (micro)W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

  18. Fabrication of suspended light-emitting diode and waveguide on a single chip

    NASA Astrophysics Data System (ADS)

    Bai, Dan; Gao, Xumin; Cai, Wei; Yuan, Wei; Shi, Zheng; Li, Xin; Xu, Yin; Yuan, Jialei; Zhu, Guixia; Yang, Yongchao; Yang, Cheng; Cao, Xun; Zhu, Hongbo; Wang, Yongjin

    2016-05-01

    We attempt to integrate light-emitting diode (LED) and waveguide on the same GaN-on-silicon platform, which is fashioned with suspended p-n junction InGaN/GaN multiple quantum wells. Silicon substrate is removed to form highly confined waveguide structures and suspended LED. The light emission measurements experimentally demonstrate that part of the LED emission is coupled into suspended waveguide. The light is then guided in the waveguide and propagates along the waveguide structure, and is finally diffracted into the air at the waveguide output facet. The light spectra captured by a micro-transmittance setup confirm that the lateral light propagation inside the waveguide is electrically driven and power-dependent. These results indicate that the proposed integrated device is promising for the monolithic integration of LED with waveguide and photodetector toward next-generation photonic chips based on the GaN-on-silicon platform.

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

    NASA Astrophysics Data System (ADS)

    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. Numerical study of light-emitting diode with injected current modulated by designed electrode

    NASA Astrophysics Data System (ADS)

    Nishidate, Yohei; Khmyrova, Irina; Kholopova, Julia; Polushkin, Evgeny; Shevchenko, Bogdan; Shapoval, Sergei

    2016-10-01

    Numerical model and procedure are developed to study the output optical performance of light-emitting diode (LED) in which injected current is spatially modulated by mesh-like top metal electrode. The mesh strips have rectangular crossection as in realistic LEDs. The finite element method is applied to obtain three-dimensional distributions of electric potential which are incorporated in the equations for total output power. The numerical procedure is applied to evaluate LED's total output optical power at different geometric parameters of the electrode: the mesh pitch, the width, and the height of the top mesh-like electrodes. Modeling results demonstrate the effect of mesh pitch variation on the output optical power. In particular, at a certain value of the mesh pitch maximum total output optical power is revealed. The presented approach can be used in the optimization of the LEDs with designed metal electrodes.

  1. 3D thermal analysis of rectangular microscale inorganic light-emitting diodes in a pulsed operation

    NASA Astrophysics Data System (ADS)

    Cui, Y.; Bian, Z.; Li, Y.; Xing, Y.; Song, J.

    2016-10-01

    Microscale inorganic light-emitting diodes (µ-ILEDs) have attracted much attention due to their excellent performance in biointegrated applications such as optogenetics. The thermal behaviors of µ-ILEDs are critically important since a certain temperature increase may degrade the LED performance and cause tissue lesion. The µ-ILEDs in a pulsed operation offer an advantage in thermal management. In this paper, a 3D analytic model, as validated by finite element analysis, is developed to study the thermal response of rectangular µ-ILEDs in a pulsed operation. A scaling law for the maximum normalized temperature increase of rectangular µ-ILEDs in terms of non-dimensional parameters is established. The influences of geometric (i.e. shape factor) and loading parameters (e.g. duty cycle and period) on the temperature increase are systematically investigated. These results are very helpful in designing µ-ILEDs by providing guidelines to avoid adverse thermal effects.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  3. Light extraction from organic light-emitting diodes for lighting applications by sand-blasting substrates.

    PubMed

    Chen, Shuming; Kwok, Hoi Sing

    2010-01-01

    Light extraction from organic light-emitting diodes (OLEDs) by scattering the light is one of the effective methods for large-area lighting applications. In this paper, we present a very simple and cost-effective method to rough the substrates and hence to scatter the light. By simply sand-blasting the edges and back-side surface of the glass substrates, a 20% improvement of forward efficiency has been demonstrated. Moreover, due to scattering effect, a constant color over all viewing angles and uniform light pattern with Lambertian distribution has been obtained. This simple and cost-effective method may be suitable for mass production of large-area OLEDs for lighting applications.

  4. Hybrid daylight/light-emitting diode illumination system for indoor lighting.

    PubMed

    Ge, Aiming; Qiu, Peng; Cai, Jinlin; Wang, Wei; Wang, Junwei

    2014-03-20

    A hybrid illumination method using both daylight and light-emitting diodes (LEDs) for indoor lighting is presented in this study. The daylight can be introduced into the indoor space by a panel-integration system. The daylight part and LEDs are combined within a specific luminaire that can provide uniform illumination. The LEDs can be turned on and dimmed through closed-loop control when the daylight illuminance is inadequate. We simulated the illumination and calculated the indoor lighting efficiency of our hybrid daylight and LED lighting system, and compared this with that of LED and fluorescent lighting systems. Simulation results show that the efficiency of the hybrid daylight/LED illumination method is better than that of LED and traditional lighting systems, under the same lighting conditions and lighting time; the method has hybrid lighting average energy savings of T5 66.28%, and that of the LEDs is 41.62%.

  5. Low Temperature Polycrystalline Silicon Thin Film Transistor Pixel Circuits for Active Matrix Organic Light Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Fan, Ching-Lin; Lin, Yu-Sheng; Liu, Yan-Wei

    A new pixel design and driving method for active matrix organic light emitting diode (AMOLED) displays that use low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with a voltage programming method are proposed and verified using the SPICE simulator. We had employed an appropriate TFT model in SPICE simulation to demonstrate the performance of the pixel circuit. The OLED anode voltage variation error rates are below 0.35% under driving TFT threshold voltage deviation (Δ Vth =± 0.33V). The OLED current non-uniformity caused by the OLED threshold voltage degradation (Δ VTO =+0.33V) is significantly reduced (below 6%). The simulation results show that the pixel design can improve the display image non-uniformity by compensating for the threshold voltage deviation in the driving TFT and the OLED threshold voltage degradation at the same time.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Qi, Xiangfei; Forrest, Stephen R.

    2011-12-01

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

  10. Silicon carbide light-emitting diode as a prospective room temperature source for single photons

    PubMed Central

    Fuchs, F.; Soltamov, V. A.; Väth, S.; Baranov, P. G.; Mokhov, E. N.; Astakhov, G. V.; Dyakonov, V.

    2013-01-01

    Generation of single photons has been demonstrated in several systems. However, none of them satisfies all the conditions, e.g. room temperature functionality, telecom wavelength operation, high efficiency, as required for practical applications. Here, we report the fabrication of light-emitting diodes (LEDs) based on intrinsic defects in silicon carbide (SiC). To fabricate our devices we used a standard semiconductor manufacturing technology in combination with high-energy electron irradiation. The room temperature electroluminescence (EL) of our LEDs reveals two strong emission bands in the visible and near infrared (NIR) spectral ranges, associated with two different intrinsic defects. As these defects can potentially be generated at a low or even single defect level, our approach can be used to realize electrically driven single photon source for quantum telecommunication and information processing. PMID:23572127

  11. External modes in quantum dot light emitting diode with filtered optical feedback

    NASA Astrophysics Data System (ADS)

    Al Husseini, Hussein B.; Al Naimee, Kais A.; Al-Khursan, Amin H.; Khedir, Ali. H.

    2016-06-01

    This research reports a theoretical investigation on the role of filtered optical feedback (FOF) in the quantum dot light emitting diode (QD-LED). The underlying dynamics is affected by a sidle node, which returns to an elliptical shape when the wetting layer (WL) is neglected. Both filter width and time delay change the appearance of different dynamics (chaotic and mixed mode oscillations, MMOs). The results agree with the experimental observations. Here, the fixed point analysis for QDs was done for the first time. For QD-LED with FOF, the system transits from the coherence collapse case in conventional optical feedback to a coherent case with a filtered mode in FOF. It was found that the WL washes out the modes which is an unexpected result. This may attributed to the longer capture time of WL compared with that between QD states. Thus, WL reduces the chaotic behavior.

  12. Highly efficient white top-emitting organic light-emitting diodes comprising laminated microlens films.

    PubMed

    Thomschke, Michael; Reineke, Sebastian; Lüssem, Björn; Leo, Karl

    2012-01-11

    White top-emitting organic light-emitting diodes (OLEDs) attract much attention, as they are optically independent from the substrate used. While monochrome top-emitting OLEDs can be designed easily to have high-emission efficiency, white light emission faces obstacles. The commonly used thin metal layers as top electrodes turn the device into a microresonator having detrimental narrow and angular dependent emission characteristics. Here we report on a novel concept to improve the color quality and efficiency of white top-emitting OLEDs. We laminate a refractive index-matched microlens film on the top-emitting device. The microlens film acts both as outcoupling-enhancing film and an integrating element, mixing the optical modes to a broadband spectrum. PMID:22132876

  13. Extremely bendable thin-film encapsulation of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Seo, Seung-Woo; Chae, Heeyeop; Joon Seo, Sang; Kyoon Chung, Ho; Min Cho, Sung

    2013-04-01

    We report on an extremely bendable moisture barrier for the thin-film encapsulation of organic light-emitting diodes (OLEDs). Hybrid barriers with various dyads of alternating aluminum oxide (Al2O3) and plasma-polymerized layers, which are utilizable for the thin-film encapsulation of flexible OLEDs, were prepared by atomic layer deposition and plasma chemical vapor deposition, respectively. When the total thickness of Al2O3 was fixed at 20 nm, an ultimate 200-dyad multilayer barrier showed change of less than 20% in water vapor transmission rate from its initial value of the order of 10-4 g/m2/day, even after 10 000 times of bending with a bending radius of 5 mm.

  14. Glare-Tunable Transparent Electrochemical Smart Window Coupled with Transparent Organic Light-Emitting Diode

    NASA Astrophysics Data System (ADS)

    Uchida, Takayuki; Shibasaki, Masaaki; Matsuzaki, Tatsuya; Nagata, Yujiro

    2013-04-01

    We fabricated a novel device assembled by coupling a transparent organic light-emitting diode (TOLED) and a glare-tunable transparent electrochemical device. This device could be operated in six different states, namely, (1) transparent, (2) mirror, (3) black, (4) dual emission, (5) single-side emission with mirror, and (6) single-side emission with black. Switching between each of these states could be tuned by varying/selecting the applied DC bias voltage. The device showed 63.8% transmittance in the transparent state, and 42.1% reflectance in the mirror state at 700 nm. Transmittance in both the mirror and black states was less than 0.1% in the visible range.

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

    PubMed

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

    2015-12-01

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

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

    PubMed

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

    2016-02-01

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

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

    PubMed

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

    2016-07-01

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

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

    PubMed

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

    2016-02-23

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

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

    PubMed

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

    2016-03-01

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

  20. Quantum cascade light emitting diodes based on type-II quantum wells

    SciTech Connect

    Lin, C.H.; Yang, R.Q.; Zhang, D.; Murry, S.J.; Pei, S.S.; Allerman, A.A.; Kurtz, S.R.

    1997-01-21

    The authors have demonstrated room-temperature CW operation of type-II quantum cascade (QC) light emitting diodes at 4.2 {micro}m using InAs/InGaSb/InAlSb type-II quantum wells. The type-II QC configuration utilizes sequential multiple photon emissions in a staircase of coupled type-II quantum wells. The device was grown by molecular beam epitaxy on a p-type GaSb substrate and was compared of 20 periods of active regions separated by digitally graded quantum well injection regions. The maximum average output power is about 250 {micro}W at 80 K, and 140 {micro}W at 300 K at a repetition rate of 1 kHz with a duty cycle of 50%.

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

    PubMed

    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. PMID:25967311

  2. A new switched-capacitor frequency modulated driver for light emitting diodes.

    PubMed

    Feng, Weifeng; Shi, Frank G

    2007-11-01

    A new type of drivers for light emitting diodes (LEDs) is introduced based on the switched-capacitor frequency modulation. In contrast to conventional constant dc current drivers, the current pulse is provided by this new switched-capacitor LED driver. In the present driver, the charging capacitor is charged and discharged through a LED and the current flow direction is controlled by a metal oxide semiconductor switch. The input current (and thus the LED brightness) is proportional to the switch clock frequency at relatively low frequencies and becomes saturated at relatively high frequencies. This new driver circuit is simple and robust and maintains high efficiency for a wide range of input powers. In addition, the dimming control is easily realized by modulating clock frequency. Finally, this LED driver consumes no dc current and thus provides inherent protection to LED in standby mode. PMID:18052494

  3. Portable and visual electrochemical sensor based on the bipolar light emitting diode electrode.

    PubMed

    Zhang, Xiaowei; Chen, Chaogui; Yin, Jianyuan; Han, Yanchao; Li, Jing; Wang, Erkang

    2015-01-01

    Here we report a novel sensing strategy based on the closed bipolar system, in which we utilize a light emitting diode (LED) to connect a split bipolar electrode (BPE) and generate the luminescent signal in the presence of the target. With this design, we have constructed a BPE array for the quick and high-throughput determination of various electroactive substances with naked eyes. Due to the ultrahigh current efficiency of the closed bipolar system, the sample concentration can be reported by the luminous intensity of the inserted LED without the expensive luminescent agent and instruments. Besides, the stability of the signal is improved because of the electroluminescent property of the LED. To demonstrate the promising applications of the bipolar LED electrode (BP-LED-E), the rapid quantification of four model targets (H2O2, ascorbic acid (AA), glucose, and blood sugar) has been achieved based on different principles. PMID:25873190

  4. Real-time monitoring and diagnosis of scintillation dosimeters using an ultraviolet light emitting diode

    NASA Astrophysics Data System (ADS)

    Yin, Y.; Lambert, J.; McKenzie, D. R.; Suchowerska, N.

    2008-05-01

    Plastic scintillator fibre optic dosimeters (FODs) have advantages for both brachytherapy and external beam radiotherapy applications. Convenient real-time monitoring and diagnosis of such dosimeters are desirable because of changes in the optical circuit that may arise in use. In this paper, we propose and demonstrate a real-time method using ultraviolet light emitting diodes (LED) to stimulate the scintillator and to diagnose failures of FODs. Key aspects of the LED FOD dosimetry design are investigated, enabling the design of a stable and accurate real-time monitoring dosimetry system. We demonstrate experimentally that the real-time monitoring FOD system is convenient to be used to monitor FOD dosimeters and to diagnose their failures resulted from different mechanisms.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed Central

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

    2016-01-01

    Exposure to X-rays, high-intensity visible light or ultraviolet radiation results in alterations to protein structure such as the breakage of disulfide bonds, the loss of electron density at electron-rich centres and the movement of side chains. These specific changes can be exploited in order to obtain phase information. Here, a case study using insulin to illustrate each step of the radiation-damage-induced phasing (RIP) method is presented. Unlike a traditional X-ray-induced damage step, specific damage is introduced via ultraviolet light-emitting diodes (UV-LEDs). In contrast to UV lasers, UV-LEDs have the advantages of small size, low cost and relative ease of use. PMID:26960126

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Investigation of Remote-Phosphor White Light-Emitting Diodes with Multi-Phosphor Layers

    NASA Astrophysics Data System (ADS)

    Zhu, Yiting; Narendran, Nadarajah

    2010-10-01

    To understand how multiple phosphors in a mixture or stacked layers affect the performance of the remote-phosphor “scattered photon extraction (SPE)” white light-emitting diode (LED), a laboratory study was conducted with commercial yellow [quantum efficiency (QE)=0.91] and red (QE=0.59) phosphors in equal amounts. The highest light output was obtained when the longer-wavelength red phosphor was placed as the second layer. Experiments showed that when using two phosphors in an SPE package, several factors influence the performance: mixture or stacked layers; specific layer order; phosphor densities; phosphor external QE; overall spectral power distribution (SPD); phosphor excitation and emission spectra and efficiencies.

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

    NASA Technical Reports Server (NTRS)

    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.

  10. Admittance spectroscopy of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) based organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Petrosino, Mario; Rubino, Alfredo

    2011-06-01

    Admittance spectroscopy of Indium Tin Oxide (ITO)-poly(3,4-ethylenedioxythiophene) (PEDOT)-polyfluorene-Al organic light emitting diodes is analyzed by varying PEDOT dispersion. Loss-frequency diagrams show one or two peaks. The results have been interpreted by using the Nicollian and Brews admittance model. Single level and multi level interface state distributions are found for each kind of PEDOT. Surface state density is about 1011 eV-1cm-2 for all distributions while the interface time constant varies between 471 μs and 220 ns. Good agreement is found between experimental data and analytical model. The combined effect of PEDOT conductivity and the inferred interface state density is analyzed and discussed.

  11. Horizontal molecular orientation in solution-processed organic light-emitting diodes

    SciTech Connect

    Zhao, L.; Inoue, M.; Komino, T.; Kim, J.-H.; Ribierre, J. C. E-mail: adachi@cstf.kyushu-u.ac.jp [Center for Organic Photonics and Electronics Research , Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395; Japan Science and Technology Agency , ERATO, Adachi Molecular Exciton Engineering Project, c and others

    2015-02-09

    Horizontal orientation of the emission transition dipole moments achieved in glassy vapor-deposited organic thin films leads to an enhancement of the light out-coupling efficiency in organic light-emitting diodes (OLEDs). Here, our combined study of variable angle spectroscopic ellipsometry and angle dependent photoluminescence demonstrates that such a horizontal orientation can be achieved in glassy spin-coated organic films based on a composite blend of a heptafluorene derivative as a dopant and a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl as a host. Solution-processed fluorescent OLEDs with horizontally oriented heptafluorene emitters were then fabricated and emitted deep blue electroluminescence with an external quantum efficiency as high as 5.3%.

  12. Is it viable to improve light output efficiency by nano-light-emitting diodes?

    SciTech Connect

    Wang, Chao-Hung; Huang, Yu-Wen; Wu, Shang-En; Liu, Chuan-Pu

    2013-12-02

    Nanopillar arrays with InGaN/GaN multiple-quantum-disks (MQDs) are fabricated by focused-ion-beam milling with surface damage layer removed by KOH wet etching. Nano-light-emitting diodes (Nano-LEDs) made of the InGaN/GaN MQD nanopillars are found to have 19.49% less output power than that of a conventional LED. The reasons are analyzed in detail and considering their current-voltage and electroluminescence characteristics, internal quantum efficiency, external quantum efficiency, light extraction, and wall-plug efficiency. Our results suggest that nanopillar-LED can outperform if the density can be increased to 2.81 × 10{sup 9} cm{sup −2} with the size unchanged or the size can be increased to 854.4 nm with the density unchanged.

  13. Regulation of lipid production by light-emitting diodes in human sebocytes.

    PubMed

    Jung, Yu Ra; Kim, Sue Jeong; Sohn, Kyung Cheol; Lee, Young; Seo, Young Joon; Lee, Young Ho; Whang, Kyu Uang; Kim, Chang Deok; Lee, Jeung Hoon; Im, Myung

    2015-04-01

    Light-emitting diodes (LED) have been used to treat acne vulgaris. However, the efficacy of LED on sebaceous lipid production in vitro has not been examined. This study investigated the efficacy of 415 nm blue light and 630 nm red light on lipid production in human sebocytes. When applied to human primary sebocytes, 415 nm blue light suppressed cell proliferation. Based on a lipogenesis study using Oil Red O, Nile red staining, and thin-layered chromatography, 630 nm red light strongly downregulated lipid production in sebocytes. These results suggest that 415 nm blue light and 630 nm red light influence lipid production in human sebocytes and have beneficial effects on acne by suppressing sebum production.

  14. Operating organic light-emitting diodes imaged by super-resolution spectroscopy

    NASA Astrophysics Data System (ADS)

    King, John T.; Granick, Steve

    2016-06-01

    Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semiconducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packed chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. This points the way towards real-time analysis of materials design principles in devices as they actually operate.

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

    SciTech Connect

    Shi, Xiao-Bo; Qian, Min; Wang, Zhao-Kui E-mail: lsliao@suda.edu.cn; Liao, Liang-Sheng E-mail: lsliao@suda.edu.cn

    2015-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Asare, J.; Adeniji, S. A.; Oyewole, O. K.; Agyei-Tuffour, B.; Du, J.; Arthur, E.; Fashina, A. A.; Zebaze Kana, M. G.; Soboyejo, W. O.

    2016-06-01

    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.

  17. High efficiency polymer light-emitting diodes using ternary electron injection layers

    NASA Astrophysics Data System (ADS)

    Wen, Ten-Chin; Tsai, Kai-Wei; Jan, Jiun-Yun; Guo, Tzung-Fang

    2016-02-01

    The high efficiency of polymer light-emitting diodes (PLED) with ternary electron injection layers (EILs) including tetraoctylammonium bromide (TOAB), poly (vinylpyrrolidone) (PVP) and polyethylenimine (PEIE) to comprise PEIE-PVP-TOAB (E-P-T) EIL that has been achieved and well-studied via mixture design. In the unary system, TOAB can construct interfacial dipole via self-assembly crystallization atop various conjugated polymer surfaces to elevate the vacuum level of cathode. When employing three EILs as ternary system, the electrical property of PLED was further improved. The optimum luminescence efficiency respectively are 13.4 cd/A and 13.5 cd/A for T-P-D and E-P-T based PLED. In the ternary system (E-P-T), PEIE , PVP, and TOAB respectively provides electron injection, hole blocking, and polymer intersecting in the ternary based devices. The intersecting between PEIE and PVP by TOAB was evidenced by roughness change from AFM images.

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

    PubMed

    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.

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

    PubMed

    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).

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    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.

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

    PubMed

    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. PMID:27474341

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

    PubMed

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

    2016-07-21

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

  4. Indium-zinc oxide transparent electrode for nitride-based light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Mizutani, S.; Nakashima, S.; Iwaya, M.; Takeuchi, T.; Kamiyama, S.; Akasaki, I.; Kondo, T.; Teramae, F.; Suzuki, A.; Kitano, T.; Mori, M.; Matsubara, M.

    2013-03-01

    The basic properties of indium-zinc oxide (IZO) were investigated from the view point of the potential of light-emitting diodes (LEDs) for nanostructured transparent contact. The resistivity and contact resistance to p-GaN were obtained to be 2.5×10-4 Ωcm and 9.4×10-4 Ωcm2, respectively, which are comparable to those of indium-tin oxide (ITO). The light output of the LED with the moth-eye IZO was 10 % and 40 % higher than that of the LED with the moth-eye ITO and that of the LED without the moth-eye structure, respectively.

  5. Imprinted nonoxidized graphene sheets as an efficient hole transport layer in polymer light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Huang, Chun-Yuan; Peter Chen, I.-Wen; Chen, Chih-Jung; Chiang, Ray-Kuang; Vu, Hoang-Tuan

    2014-02-01

    Nonoxidized graphene sheets (NGSs) with single- and multilayered structures were generated by direct exfoliation of highly oriented pyrolytic graphite in a water-ethanol mixture with the assistances of pyridinium salt (Py+Br3-) and sonication. Raman spectrum exhibited a low intensity ratio (0.055) of D and G bands, indicating that the NGSs were nearly defect-free. Their application for the fabrication of polymer light-emitting diodes (PLEDs) was also demonstrated. The PLEDs that used an imprinted NGS film as a hole transport layer show a luminance exceeding 13000 cd/m2, which was comparable to that of devices using the typical hole transport material: poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid.

  6. Portable and visual electrochemical sensor based on the bipolar light emitting diode electrode.

    PubMed

    Zhang, Xiaowei; Chen, Chaogui; Yin, Jianyuan; Han, Yanchao; Li, Jing; Wang, Erkang

    2015-01-01

    Here we report a novel sensing strategy based on the closed bipolar system, in which we utilize a light emitting diode (LED) to connect a split bipolar electrode (BPE) and generate the luminescent signal in the presence of the target. With this design, we have constructed a BPE array for the quick and high-throughput determination of various electroactive substances with naked eyes. Due to the ultrahigh current efficiency of the closed bipolar system, the sample concentration can be reported by the luminous intensity of the inserted LED without the expensive luminescent agent and instruments. Besides, the stability of the signal is improved because of the electroluminescent property of the LED. To demonstrate the promising applications of the bipolar LED electrode (BP-LED-E), the rapid quantification of four model targets (H2O2, ascorbic acid (AA), glucose, and blood sugar) has been achieved based on different principles.

  7. Efficient red, green, blue and white organic light-emitting diodes with same exciplex host

    NASA Astrophysics Data System (ADS)

    Chang, Chih-Hao; Wu, Szu-Wei; Huang, Chih-Wei; Hsieh, Chung-Tsung; Lin, Sung-En; Chen, Nien-Po; Chang, Hsin-Hua

    2016-03-01

    Recently, exciplex had drawn attention because of its potential for efficient electroluminescence or for use as a host in organic light-emitting diodes (OLEDs). In this study, four kinds of hole transport material/electron transport material combinations were examined to verify the formation of exciplex and the corresponding energy bandgaps. We successfully demonstrated that the combination of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 3,5,3‧,5‧-tetra(m-pyrid-3-yl)phenyl[1,1‧]biphenyl (BP4mPy) could form a stable exciplex emission with an adequate energy gap. Using exciplex as a host in red, green, and blue phosphorescent OLEDs with an identical trilayer architecture enabled effective energy transfer from exciplex to emitters, achieving corresponding efficiencies of 8.8, 14.1, and 15.8%. A maximum efficiency of 11.3% and stable emission was obtained in white OLEDs.

  8. Effect of hole transport on performance of infrared type-II superlattice light emitting diodes

    SciTech Connect

    Lin, Youxi; Suchalkin, Sergey; Kipshidze, Gela; Hosoda, Takashi; Westerfeld, David; Shterengas, Leon; Belenky, Gregory; Laikhtman, Boris

    2015-04-28

    The effect of hole transport on the performance of infrared light emitting diodes (LED) was investigated. The active area of the LEDs comprised two type-II superlattices with different periods and widths connected in series. Electroluminescence spectra of the devices with different positions of long wave and mid wave superlattice sections were mostly contributed by the superlattice closest to the p-contact. The experimental results indicate that due to suppressed vertical hole transport, the recombination of electrically injected electrons and holes in a type II superlattice LED active region takes place within a few superlattice periods near p-barrier. Possible reason for the effect is reduction of hole diffusion coefficient in an active area of a superlattice LED under bias.

  9. Design and analysis of reflector for uniform light-emitting diode illuminance.

    PubMed

    Tsai, Chung-Yu

    2013-05-01

    A light-emitting diode (LED) projection system is proposed, composed of an LED chip and a variable-focus-parabolic (VFP) reflector, in which the focal length varies as a function of the vertical displacement of the incidence point relative to the horizontal centerline of the LED chip. The light-ray paths within the projection system are analyzed using an exact analytical model and a skew-ray tracing approach. The profile of the proposed VFP reflector and the position of the LED chip are then optimized in such a way as to enhance the uniformity of the illuminance distribution on the target region of the image plane. The validity of the optimized design is demonstrated by means of ZEMAX simulations. It is shown that the optimized VFP projector system yields a significant improvement in illuminance uniformity compared to conventional spherical and parabolic projectors and therefore minimizes the glare effect.

  10. Organic Light-Emitting Diodes with Heterojunction of Thiophene/Phenylene Co-Oligomer Derivatives.

    PubMed

    Dokiya, Shohei; Ono, Yasuyuki; Sasaki, Fumio; Hotta, Shu; Yanagi, Hisao

    2016-04-01

    Organic light-emitting diodes are fabricated by heterojunction of thiophene/phenylene co-oligomer films using biphenyl-capped bithiophene (BP2T) and its cyano-substituted derivative (BP2T-CN). Strong electron-withdrawing cyano-groups in BP2T-CN transform the p-type BP2T into n-type. Photoluminescence and electroluminescence from their bilayered films dominantly result from the BP2T-CN layer since the lying molecular orientation of BP2T-CN facilitates surface emission while the standing orientation of BP2T is not suitable for the device configuration. The current density and electroluminescence intensity are considerably increased by carrier doping with MoO3 and Cs2CO3 into the BP2T and BP2T-CN films, respectively. PMID:27451603

  11. Light Emitting Diodes and Astronomical Environments: Results from in situ Field Measurements

    NASA Astrophysics Data System (ADS)

    Craine, Brian L.; Craine, Eric R.

    2015-05-01

    Light emitting diode (LED) light fixtures are rapidly becoming industry standards for outdoor lighting. They are promoted on the strength of long lifetimes (hence economic efficiencies), low power requirements, directability, active brightness controls, and energy efficiency. They also tend to produce spectral shifts that are undesirable in astronomical settings, but which can be moderated by filters. LED lighting for continuous roadway and parking lot lighting is particularly popular, and many communities are in the process of retrofitting Low Pressure Sodium (LPS) and other lights by tens of thousands of new LED fixtures at a time. What is the impact of this process on astronomical observatories and on dark skies upon which amateur astronomers rely? We bypass modeling and predictions to make actual measurements of these lights in the field. We report on original ground, airborne, and satellite observations of LED lights and discuss their light budgets, zenith angle functions, and impacts on observatory environs.

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

    PubMed

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

    2009-12-01

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

  13. Single nanowire green InGaN/GaN light emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Zhou, Dong-Ying; Shi, Xiao-Bo; Gao, Chun-Hong; Cai, Shi-Duan; Jin, Yue; Liao, Liang-Sheng

    2014-09-01

    A combination of a scattering medium layer and a roughened substrate was proposed to enhance the light extraction efficiency of organic light-emitting diodes (OLEDs). Comparing with a reference OLED without any scattering layer, 65% improvement in the forward emission has been achieved with a scattering layer formed on an intentionally roughened external substrate surface of the OLED by spin-coating a sol-gel fabricated matrix containing well dispersed titania (TiO2) particles. Such a combination method not only demonstrated efficient extraction of the light trapped in the glass substrate but also achieved homogenous emission from the OLED panel. The proposed technique, convenient and inexpensive, is believed to be suitable for the large area OLED production in lighting applications.

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

    PubMed

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

    2016-07-01

    In this study, we report a contact printing technique that uses polyurethane-acrylate (PUA) polymers as the printing stamps to pattern electroluminescent layers of organic light emitting diodes (OLEDs). We demonstrate that electroluminescent thin films can be printed with high uniformity and resolution. We also show that the performance of the printed devices can be improved via postprinting thermal annealing, and that the external quantum efficiency of the printed devices is comparable with the efficiency of the vacuum-deposited OLEDs. Our results suggest that the PUA-based contact printing can be used as an alternative to the traditional shadow mask deposition, permitting manufacturing of OLED displays with the resolution up to the diffraction limit of visible-light emission. PMID:27302425

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

    SciTech Connect

    Mazzeo, M.; Genco, A.; Gambino, S.; Ballarini, D.; Mangione, F.; Sanvitto, D.; Di Stefano, O.; Patanè, S.; Savasta, S.; Gigli, G.

    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.

  18. GaN nanorod light emitting diode arrays with a nearly constant electroluminescent peak wavelength.

    PubMed

    Wang, Cheng-Yin; Chen, Liang-Yi; Chen, Cheng-Pin; Cheng, Yun-Wei; Ke, Min-Yung; Hsieh, Min-Yann; Wu, Han-Ming; Peng, Lung-Han; Huang, JianJang

    2008-07-01

    A practical process to fabricate InGaN/GaN multiple quantum well light emitting diodes (LEDs) with a self-organized nanorod structure is demonstrated. The nanorod array is realized by using nature lithography of surface patterned silica spheres followed by dry etching. A layer of spin-on-glass (SOG), which intervening the rod spacing, serves the purpose of electric isolation to each of the parallel nanorod LED units. The electroluminescence peak wavelengths of the nanorod LEDs nearly remain as constant for an injection current level between 25mA and 100mA, which indicates that the quantum confined stark effect is suppressed in the nanorod devices. Furthermore, from the Raman light scattering analysis we identify a strain relaxation mechanism for lattice mismatch layers in the nanostructure. PMID:18607469

  19. Design, calibration, and characterization of a field radiometer using light-emitting diodes as detectors.

    PubMed

    Czapla-Myers, Jeffrey S; Thome, Kurtis J; Biggar, Stuart F

    2008-12-20

    The Remote Sensing Group at the University of Arizona has developed multispectral ground-viewing radiometers that use light-emitting diodes as detectors. This work describes the optical design, electrical design, and laboratory calibration of a three-channel radiometer that operates in the visible and near-infrared region of the spectrum. The optical and electrical design of the radiometer is introduced, and then the calibration and characterization of the radiometer are described. Laboratory measurements include the spectral responsivity for each channel of the radiometer, the temperature dependence of the total responsivity for each channel, system linearity, field of view, and finally, the absolute radiometric calibration. A solar-radiation-based calibration is used to determine the absolute responsivity.

  20. GaInN-based light emitting diodes embedded with wire grid polarizers

    NASA Astrophysics Data System (ADS)

    Cho, Jaehee; Meyaard, David S.; Ma, Ming; Schubert, E. Fred

    2015-02-01

    The use of liquid crystal displays (LCDs) has become prevalent in our modern, technology driven society. We demonstrate a linearly polarized GaInN light-emitting diode (LED) embedded with a wire-grid polarizer (WGP). A derivation of rigorous coupled-wave analysis is given; starting from Maxwell’s equations and finishing by matching the boundary conditions in the grating and other regions of interest. Simulated results are shown for various grating parameters, including different metals used for the grating and the metal-line dimensions. An LED fabrication process is developed for demonstrating WGP-LEDs. A clear polarization preference for the light coming out of the WGP-LED is experimentally demonstrated with a polarization ratio over 0.90, which is in good agreement with simulation results.

  1. Effect of 670-nm Light-Emitting Diode Light On Neuronal Cultures

    NASA Technical Reports Server (NTRS)

    Wong-Riley, Margaret T. T.; Whelan, Harry T.

    2002-01-01

    Light close to and within the near infrared range has documented benefits for promoting wound healing in human and animal studies. Our preliminary results using light-emitting diodes (LEDs) in this range have also demonstrated two-to five-fold increases in growth-phase-specific DNA synthesis in normal fibroblasts, muscle cells, osteoblasts, and mucosal epithelial cells in tissue cultures. However, the mechanisms of action of such light on cells are poorly understood. We hypothesized that the therapeutic effects of such light result from the stimulation of cellular events associated with increases in cytochrome oxidase activity. As a first step in testing our hypothesis, we subjected primary neuronal cultures to impulse blockade by tetrodotoxin (TTX), a voltage-dependent sodium channel blocker, and applied LED light at 670 nm to determine if it could partially or fully reverse the reduction of cytochrome oxidase activity by TTX. The wavelength and parameters were previously tested to be beneficial for wound healing.

  2. Highly efficient white top-emitting organic light-emitting diodes comprising laminated microlens films.

    PubMed

    Thomschke, Michael; Reineke, Sebastian; Lüssem, Björn; Leo, Karl

    2012-01-11

    White top-emitting organic light-emitting diodes (OLEDs) attract much attention, as they are optically independent from the substrate used. While monochrome top-emitting OLEDs can be designed easily to have high-emission efficiency, white light emission faces obstacles. The commonly used thin metal layers as top electrodes turn the device into a microresonator having detrimental narrow and angular dependent emission characteristics. Here we report on a novel concept to improve the color quality and efficiency of white top-emitting OLEDs. We laminate a refractive index-matched microlens film on the top-emitting device. The microlens film acts both as outcoupling-enhancing film and an integrating element, mixing the optical modes to a broadband spectrum.

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

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  5. Degradation of Bilayer Organic Light-Emitting Diodes Studied by Impedance Spectroscopy.

    PubMed

    Sato, Shuri; Takata, Masashi; Takada, Makoto; Naito, Hiroyoshi

    2016-04-01

    The degradation of bilayer organic light-emitting diodes (OLEDs) with a device structure of N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD) (hole transport layer) and tris-(8-hydroxyquinolate)aluminum (Alq3) (emissive layer and electron transport layer) has been studied by impedance spectroscopy and device simulation. Two modulus peaks are found in the modulus spectra of the OLEDs below the electroluminescence threshold. After aging of the OLEDs, the intensity of electroluminescence is degraded and the modulus peak due to the Alq3 layer is shifted to lower frequency, indicating that the resistance of the Alq3 layer is increased. Device simulation reveals that the increase in the resistance of the Alq3 layer is due to the decrease in the electron mobility in the Alq3 layer. PMID:27451634

  6. Organic Light Emitting Diodes with Opal Photonic Crystal Layer and Carbon Nanotube Anode

    NASA Astrophysics Data System (ADS)

    Ovalle Robles, Raquel; Del Rocio Nava, Maria; Williams, Christopher; Zhang, Mei; Fang, Shaoli; Lee, Sergey; Baughman, Ray; Zakhidov, Anvar

    2007-03-01

    We report electroluminescence intensity and spectral changes in light emission from organic light emitting diode (OLEDs) structures, which have thin transparent films of opal photonic crystal (PC). The anode in such PC-OLED is laminated on opal layer from free standing optically transparent multiwall carbon nanotubes (T-CNT) sheets made by dry spinning from CVD grown forests. Silica and polystyrene opal films were grown on glass substrates by vertical sedimentation in colloids in thermal baths and the particle size of opal spheres ranges from 300 nm to 450 nm. The use of T-CNTs, (coated by PEDOT-PSS to avoid shorting) as hole injector, allows to eliminate the use of vacuum deposition of metals and permits to achieve tunneling hole injection regime from CNT tips into Alq^3 emission layer

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

    PubMed

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

    2016-02-23

    Printed organometal halide perovskite light-emitting diodes (LEDs) are reported that have indium tin oxide (ITO) or carbon nanotubes (CNTs) as the transparent anode, a printed composite film consisting of methylammonium lead tribromide (Br-Pero) and poly(ethylene oxide) (PEO) as the emissive layer, and printed silver nanowires as the cathode. The fabrication can be carried out in ambient air without humidity control. The devices on ITO/glass have a low turn-on voltage of 2.6 V, a maximum luminance intensity of 21014 cd m(-2), and a maximum external quantum efficiency (EQE) of 1.1%, surpassing previous reported perovskite LEDs. The devices on CNTs/polymer were able to be strained to 5 mm radius of curvature without affecting device properties. PMID:26713348

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

    SciTech Connect

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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  10. A Hybrid Micro-Pixel Based Deep Ultraviolet Light-Emitting Diode Lamp

    NASA Astrophysics Data System (ADS)

    Hwang, Seongmo; Islam, Monirul; Zhang, Bin; Lachab, Mohamed; Dion, Joe; Heidari, Ahmad; Nazir, Haseeb; Adivarahan, Vinod; Khan, Asif

    2011-01-01

    We report on the room temperature electrical and optical characterization of a multichip light-emitting diode (LED) lamp with peak emission at 281 nm. Four pairs of micro-pixel LED arrays were connected in series to fabricate the lamp, which delivered a pulsed output power of 235 mW at 1.18 A (duty cycle ˜0.5%), and attained a high external quantum efficiency of 4.63%. Under dc operation, the maximum power achieved by this lamp was ˜20 mW at a drive current of 220 mA. The peak output power improved 1.62-fold after a thermoelectric cooler was added to the device packaging assembly.

  11. Fabrication and Characterization of InP Nanowire Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Maeda, Satoshi; Tomioka, Katsuhiro; Hara, Shinjiroh; Motohisa, Junichi

    2012-02-01

    We fabricated nanowire light-emitting diodes (LEDs) using InP nanowires (NWs). Indium phosphide NWs with axial p-n junction were grown by selective-area metalorganic vapor phase epitaxy. The results of secondary-electron-microscopy (SEM) observation and photoluminescence measurement showed the formation of wurtzite InP NWs with some mixture of zincblende crystal phase, as expected from the used growth conditions. NW-LEDs were fabricated by sputtering indium tin oxide (ITO) after a planarization process for the top contact and AuZn evaporation for the backside contact. Current-voltage characterisitics showed clear rectifying characteristics with a small leakage current, and fairly linear current-light output characteristics were observed. By designing the pitch of the NW array, emission from individual NWs was confirmed, which opens the possibility for realizing a single NW-LED applicable to single-photon emitters.

  12. Thermal properties of microscale inorganic light-emitting diodes in a pulsed operation

    NASA Astrophysics Data System (ADS)

    Li, Yuhang; Shi, Yan; Song, Jizhou; Lu, Chaofeng; Kim, Tae-il; Rogers, John A.; Huang, Yonggang

    2013-04-01

    Light-emitting diodes (LEDs) in a pulsed operation offer combined characteristics in efficiency, thermal management, and communication, which make them attractive for many applications such as backlight unit, optical communication, and optogenetics. In this paper, an analytic model, validated by three dimensional finite element analysis and experiments, is developed to study the thermal properties of micro-scale inorganic LEDs (μ-ILED) in a pulsed operation. A simple scaling law for the μ-ILED temperature after saturation is established in terms of the material and geometrical parameters of μ-ILED systems, peak power, and duty cycle. It shows that the normalized maximum temperature increase only depends on two non-dimensional parameters: normalized μ-ILED area and duty cycle. This study provides design guidelines for minimizing adverse thermal effects of μ-ILEDs.

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

    SciTech Connect

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

    2015-12-21

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

  14. Fabrication of Organic Light-Emitting Diodes Using Photosynthetic Pigments Extracted from Spinach

    NASA Astrophysics Data System (ADS)

    Ohtani, Naoki; Kitagawa, Natsuko; Matsuda, Takashi

    2011-01-01

    We fabricated organic light-emitting diodes (OLEDs) containing chlorophylls in the active region, which were extracted from spinach using a chemical method. Photoluminescence (PL) cannot be observed in the thin film of the extracted chlorophylls owing to concentration quenching. To overcome the concentration quenching, a host material, poly[(m-phenylenevinylene)-alt-(2,5-dihexyloxy-p-phenylenevinylene)] (PPV) was added in the active region. This leads to the observaton of electroluminescence (EL) signals originating from chlorophyll a. We also evaluated the lifetime of the PL and EL. Consequently, the OLEDs containing carotenoids in the active region exhibit the light-emission much longer time than that without carotenoidos. This is assigned to the antioxidant activities of carotenoids. OLEDs containing a large amount of carotenoids are resistant to the oxidation damage.

  15. Green cubic GaInN/GaN light-emitting diode on microstructured silicon (100)

    SciTech Connect

    Stark, Christoph J. M.; Detchprohm, Theeradetch; Wetzel, Christian; Lee, S. C.; Brueck, S. R. J.; Jiang, Y.-B.

    2013-12-02

    GaInN/GaN light-emitting diodes free of piezoelectric polarization were prepared on standard electronic-grade Si(100) substrates. Micro-stripes of GaN and GaInN/GaN quantum wells in the cubic crystal structure were grown on intersecting (111) planes of microscale V-grooved Si in metal-organic vapor phase epitaxy, covering over 50% of the wafer surface area. Crystal phases were identified in electron back-scattering diffraction. A cross-sectional analysis reveals a cubic structure virtually free of line defects. Electroluminescence over 20 to 100 μA is found fixed at 487 nm (peak), 516 nm (dominant). Such structures therefore should allow higher efficiency, wavelength-stable light emitters throughout the visible spectrum.

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

    NASA Astrophysics Data System (ADS)

    Wang, Rulin; Zhang, Yu; Bi, Fuzhen; Frauenheim, Thomas; Chen, Guanhua; Yam, Chiyung

    2016-07-01

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

  17. Characteristics of blue organic light emitting diodes with different thick emitting layers

    NASA Astrophysics Data System (ADS)

    Li, Chong; Tsuboi, Taiju; Huang, Wei

    2014-08-01

    We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.

  18. White organic light-emitting diodes based on incomplete energy transfer from perylene to rubrene

    NASA Astrophysics Data System (ADS)

    Ding, Bangdong; Zhu, Wenqing; Jiang, Xueyin; Zhang, Zhilin

    2008-11-01

    This paper presents organic light-emitting diodes which generate white emission based on both perylene and rubrene doped in 9,10-di(2-naphthyl)anthracene (ADN). In this doping system, the blue dopant perylene not only emitted but also assisted the energy transfer from ADN to rubrene, which contributes to a lower doping concentration of rubrene. The optimal configuration of the device is ITO/TPD(50 nm)/ADN:0.5 wt% perylene:0.006 wt% rubrene(40 nm)/Bphen(25 nm)/LiF(1 nm)/Al. The maximum luminance of 11 665 cd/m 2 at 14 V according to a luminance efficiency of 2.9 cd/A was obtained. A CIE color coordinate of (0.30, 0.37) at 4 mA/cm 2 was also achieved.

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

    NASA Astrophysics Data System (ADS)

    Mazzeo, M.; Genco, A.; Gambino, S.; Ballarini, D.; Mangione, F.; Di Stefano, O.; Patanè, S.; Savasta, S.; Sanvitto, D.; Gigli, G.

    2014-06-01

    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.

  20. A trichromatic phosphor-free white light-emitting diode by using adhesive bonding scheme

    NASA Astrophysics Data System (ADS)

    Chuai, D. X.; Guo, X.; Guan, B. L.; Zhang, J. L.; Shen, G. D.

    2009-11-01

    A trichromatic phosphor-free white light-emitting diode (LED) has been implemented by using adhesive bonding scheme. The device has been operated as a three-terminal device with independent electrical control of an AlGaInPbased red LED chip and a GaN-based dual-wavelength (blue and green) LED chip. As 25mA and 60mA was injected into the red and blue-green LED chips at room temperature respectively, white light emission could be observed with CIE chromaticity coordinates (0.3330,0.3241), correlated color temperature Tc=5467K and optical power Φe=2.223mW. The electroluminescence measurements also show that the emitted white light is composed of blue, green and red lights, centered at around 452nm, 517nm and 632nm. The fabrication and the electrical and optical performances of such white LED were described.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  2. Multi-spectral imaging with infrared sensitive organic light emitting diode.

    PubMed

    Kim, Do Young; Lai, Tzung-Han; Lee, Jae Woong; Manders, Jesse R; So, Franky

    2014-01-01

    Commercially available near-infrared (IR) imagers are fabricated by integrating expensive epitaxial grown III-V compound semiconductor sensors with Si-based readout integrated circuits (ROIC) by indium bump bonding which significantly increases the fabrication costs of these image sensors. Furthermore, these typical III-V compound semiconductors are not sensitive to the visible region and thus cannot be used for multi-spectral (visible to near-IR) sensing. Here, a low cost infrared (IR) imaging camera is demonstrated with a commercially available digital single-lens reflex (DSLR) camera and an IR sensitive organic light emitting diode (IR-OLED). With an IR-OLED, IR images at a wavelength of 1.2 µm are directly converted to visible images which are then recorded in a Si-CMOS DSLR camera. This multi-spectral imaging system is capable of capturing images at wavelengths in the near-infrared as well as visible regions. PMID:25091589

  3. Multi-spectral imaging with infrared sensitive organic light emitting diode

    NASA Astrophysics Data System (ADS)

    Kim, Do Young; Lai, Tzung-Han; Lee, Jae Woong; Manders, Jesse R.; So, Franky

    2014-08-01

    Commercially available near-infrared (IR) imagers are fabricated by integrating expensive epitaxial grown III-V compound semiconductor sensors with Si-based readout integrated circuits (ROIC) by indium bump bonding which significantly increases the fabrication costs of these image sensors. Furthermore, these typical III-V compound semiconductors are not sensitive to the visible region and thus cannot be used for multi-spectral (visible to near-IR) sensing. Here, a low cost infrared (IR) imaging camera is demonstrated with a commercially available digital single-lens reflex (DSLR) camera and an IR sensitive organic light emitting diode (IR-OLED). With an IR-OLED, IR images at a wavelength of 1.2 µm are directly converted to visible images which are then recorded in a Si-CMOS DSLR camera. This multi-spectral imaging system is capable of capturing images at wavelengths in the near-infrared as well as visible regions.

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

    NASA Astrophysics Data System (ADS)

    Tamulaitis, G.; Duchovskis, P.; Bliznikas, Z.; Breive, K.; Ulinskaite, R.; Brazaityte, A.; Novickovas, A.; Zukauskas, A.

    2005-09-01

    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.

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

    PubMed

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

    2015-12-01

    Triarylboron compounds have attracted much attention, and found wide use as functional materials because of their electron-accepting properties arising from the vacant p orbitals on the boron atoms. In this study, we design and synthesize new donor-acceptor triarylboron emitters that show thermally activated delayed fluorescence. These emitters display sky-blue to green emission and high photoluminescence quantum yields of 87-100 % in host matrices. Organic light-emitting diodes using these emitting molecules as dopants exhibit high external quantum efficiencies of 14.0-22.8 %, which originate from efficient up-conversion from triplet to singlet states and subsequent efficient radiative decay from singlet to ground states. PMID:26563845

  6. Tandem white organic light-emitting diodes adopting a C60:rubrene charge generation layer

    NASA Astrophysics Data System (ADS)

    Bi, Wen-Tao; Wu, Xiao-Ming; Hua, Yu-Lin; Sun, Jin-E.; Xiao, Zhi-Hui; Wang, Li; Yin, Shou-Gen

    2014-01-01

    Organic bulk heterojunction fullerence (C60) doped 5, 6, 11, 12-tetraphenylnaphthacene (rubrene) as the high quality charge generation layer (CGL) with high transparency and superior charge generating capability for tandem organic light emitting diodes (OLEDs) is developed. This CGL shows excellent optical transparency about 90%, which can reduce the optical interference effect formed in tandem OLEDs. There is a stable white light emission including 468 nm and 500 nm peaks from the blue emitting layer and 620 nm peak from the red emitting layer in tandem white OLEDs. A high efficiency of about 17.4 cd/A and CIE coordinates of (0.40, 0.35) at 100 cd/m2 and (0.36, 0.34) at 1000 cd/m2 have been demonstrated by employing the developed CGL, respectively.

  7. White light-emitting diodes (LEDs) using (oxy)nitride phosphors

    NASA Astrophysics Data System (ADS)

    Xie, R.-J.; Hirosaki, N.; Sakuma, K.; Kimura, N.

    2008-07-01

    (Oxy)nitride phosphors have attracted great attention recently because they are promising luminescent materials for phosphor-converted white light-emitting diodes (LEDs). This paper reports the luminescent properties of (oxy)nitride phosphors in the system of M-Si-Al-O-N (M = Li, Ca or Sr), and optical properties of white LEDs using a GaN-based blue LED and (oxy)nitride phosphors. The phosphors show high conversion efficiency of blue light, suitable emission colours and small thermal quenching. The bichromatic white LEDs exhibit high luminous efficacy (~55 lm W-1) and the multi-phosphor converted white LEDs show high colour rendering index (Ra = 82-95). The results indicate that (oxy)nitride phosphors demonstrate their superior suitability to use as down-conversion luminescent materials in white LEDs.

  8. Numerical study of light-emitting diode with injected current modulated by designed electrode

    NASA Astrophysics Data System (ADS)

    Nishidate, Yohei; Khmyrova, Irina; Kholopova, Julia; Polushkin, Evgeny; Shevchenko, Bogdan; Shapoval, Sergei

    2016-07-01

    Numerical model and procedure are developed to study the output optical performance of light-emitting diode (LED) in which injected current is spatially modulated by mesh-like top metal electrode. The mesh strips have rectangular crossection as in realistic LEDs. The finite element method is applied to obtain three-dimensional distributions of electric potential which are incorporated in the equations for total output power. The numerical procedure is applied to evaluate LED's total output optical power at different geometric parameters of the electrode: the mesh pitch, the width, and the height of the top mesh-like electrodes. Modeling results demonstrate the effect of mesh pitch variation on the output optical power. In particular, at a certain value of the mesh pitch maximum total output optical power is revealed. The presented approach can be used in the optimization of the LEDs with designed metal electrodes.

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

    PubMed

    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

    2015-04-01

    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. Role of defects in the thermal droop of InGaN-based light emitting diodes

    NASA Astrophysics Data System (ADS)

    De Santi, C.; Meneghini, M.; La Grassa, M.; Galler, B.; Zeisel, R.; Goano, M.; Dominici, S.; Mandurrino, M.; Bertazzi, F.; Robidas, D.; Meneghesso, G.; Zanoni, E.

    2016-03-01

    This paper reports an investigation of the physical origin of the thermal droop (the drop of the optical power at high temperatures) in InGaN-based light-emitting diodes. We critically investigate the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon-assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, we propose a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters. The model is based on a two-step phonon-assisted tunneling over an intermediate defective state, corrected in order to take into account the pure thermionic component at zero bias and the field-assisted term.

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

    NASA Astrophysics Data System (ADS)

    Chen, Enguo; Wu, Rengmao

    2014-07-01

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

  12. Optimizing spherical light-emitting diode array for highly uniform illumination distribution by employing genetic algorithm

    NASA Astrophysics Data System (ADS)

    Shen, Yanxia; Ji, Zhicheng; Su, Zhouping

    2013-01-01

    A numerical optimization method (genetic algorithm) is employed to design the spherical light-emitting diode (LED) array for highly uniform illumination distribution. An evaluation function related to the nonuniformity is constructed for the numerical optimization. With the minimum of evaluation function, the LED array produces the best uniformity. The genetic algorithm is used to seek the minimum of evaluation function. By this method, we design two LED arrays. In one case, LEDs are positioned symmetrically on the sphere and the illuminated target surface is a plane. However, in the other case, LEDs are positioned nonsymmetrically with a spherical target surface. Both the symmetrical and nonsymmetrical spherical LED arrays generate good uniform illumination distribution with calculated nonuniformities of 6 and 8%, respectively.

  13. Design and analysis of reflector for uniform light-emitting diode illuminance.

    PubMed

    Tsai, Chung-Yu

    2013-05-01

    A light-emitting diode (LED) projection system is proposed, composed of an LED chip and a variable-focus-parabolic (VFP) reflector, in which the focal length varies as a function of the vertical displacement of the incidence point relative to the horizontal centerline of the LED chip. The light-ray paths within the projection system are analyzed using an exact analytical model and a skew-ray tracing approach. The profile of the proposed VFP reflector and the position of the LED chip are then optimized in such a way as to enhance the uniformity of the illuminance distribution on the target region of the image plane. The validity of the optimized design is demonstrated by means of ZEMAX simulations. It is shown that the optimized VFP projector system yields a significant improvement in illuminance uniformity compared to conventional spherical and parabolic projectors and therefore minimizes the glare effect. PMID:23695333

  14. Hybrid daylight/light-emitting diode illumination system for indoor lighting.

    PubMed

    Ge, Aiming; Qiu, Peng; Cai, Jinlin; Wang, Wei; Wang, Junwei

    2014-03-20

    A hybrid illumination method using both daylight and light-emitting diodes (LEDs) for indoor lighting is presented in this study. The daylight can be introduced into the indoor space by a panel-integration system. The daylight part and LEDs are combined within a specific luminaire that can provide uniform illumination. The LEDs can be turned on and dimmed through closed-loop control when the daylight illuminance is inadequate. We simulated the illumination and calculated the indoor lighting efficiency of our hybrid daylight and LED lighting system, and compared this with that of LED and fluorescent lighting systems. Simulation results show that the efficiency of the hybrid daylight/LED illumination method is better than that of LED and traditional lighting systems, under the same lighting conditions and lighting time; the method has hybrid lighting average energy savings of T5 66.28%, and that of the LEDs is 41.62%. PMID:24663465

  15. Positive and negative innate immune responses in zebrafish under light emitting diodes conditions.

    PubMed

    Zheng, Jia-Lang; Yuan, Shuang-Shuang; Li, Wei-Ye; Wu, Chang-Wen

    2016-09-01

    Certain light emitting diodes (LEDs) have become popular in fish farming beacause of a promoting effect on growth and reproduction. However, little information is available on innate immune responses in related tissues under LEDs conditions. The present study assessed the effects of a white fluorescent bulb (the control) and two different light-emitting diodes (LEDs: blue, LDB, peak at 450 nm; red, LDR, 630 nm) on growth and innate immune responses in the serum, liver and ovary of zebrafish for 8 weeks. LDB significantly enhanced specific growth rate (SGR), food intake (FI), and serum globulin levels. In contrast, LDR sharply inhibited SGR, FI, and the levels of albumin and globulin. Under LDB condition, there was an increase in protein levels of alkaline phophatase (AKP) and protein and activity levels of lysozyme (LZM) in the liver, and the levels of mRNA, protein, and activity of LZM in the ovary. Under LDR condition, LZM was dramatically down-regulated at mRNA, protein and activity levels in the ovary, suggesting that LZM was regulated at a transcriptional level. In the liver of the LDR group, though AKP mRNA levels sharply increased, its protein and activity levels significantly declined, indicating that AKP was regulated at translational level. Furthermore, a positive correlation between transcription factor NF-κB RelA mRNA levels and expression levels of AKP and LZM was observed in the liver and ovary, implying a transcriptional regulation of NF-κB RelA. In conclusion, the present study demonstrated a positive effect of LDB and negative effect of LDR on fish growth and innate immune responses, possibly associated with modifications at transcriptional, translational, and post-translational levels, and the transcriptional regulation of the NF-κB signaling molecule. PMID:27452972

  16. Optical-Fiber-Matrix Exposure Using Light-Emitting-Diode Sources

    NASA Astrophysics Data System (ADS)

    Horiuchi, Toshiyuki; Mirumachi, Naofumi; Ooshima, Yuki

    2007-09-01

    A new projection exposure method without using reticles was proposed, and the feasibility of printing arbitrary patterns was investigated. The preparation of expensive reticles is not favorable for the small-volume production of micro-electro-mechanical systems (MEMS), optomechanical systems, and their components. On the other hand, long turnaround time (TAT) becomes a fatal bottleneck preventing the rapid follow-up of various design changes. As a countermeasure, we previously proposed a new exposure method named optical-fiber-matrix exposure. In this method, patterns are delineated by superimposing light spots from an optical-fiber matrix, and expensive reticles are not necessary. Therefore, patterns are easily changeable by controlling the pattern delineation program. However, in the previous method, light rays from one intensive lamp were divided and switched using small mechanical shutters placed at each fiber entrance, and the shutters were not sufficiently reliable. For this reason, violet light-emitting diodes (LEDs) were used in this research in place of the lamp source and mechanical shutters, and the light or dark state at each optical fiber end was controlled using a microcomputer that switched each LED attached to each fiber entrance one by one. Since the illuminance of each LED was different, LEDs with approximately the same illuminance were selectively used, and each illuminance was adjusted to be uniform by inserting an individual color filter. Thus, the widths of patterns printed by scanning different fiber elements were homogenized. Since line-and-space patterns and various alphabet patterns were successfully printed, the feasibility of fabricating a large-scale optical-fiber matrix was also investigated. An optical-fiber line matrix composed of more than 330 fibers was fabricated without including any gaps between neighbor fibers. There will probably be no fatal problems to enlarge the matrix scale. Although the exposure speed should be improved

  17. Positive and negative innate immune responses in zebrafish under light emitting diodes conditions.

    PubMed

    Zheng, Jia-Lang; Yuan, Shuang-Shuang; Li, Wei-Ye; Wu, Chang-Wen

    2016-09-01

    Certain light emitting diodes (LEDs) have become popular in fish farming beacause of a promoting effect on growth and reproduction. However, little information is available on innate immune responses in related tissues under LEDs conditions. The present study assessed the effects of a white fluorescent bulb (the control) and two different light-emitting diodes (LEDs: blue, LDB, peak at 450 nm; red, LDR, 630 nm) on growth and innate immune responses in the serum, liver and ovary of zebrafish for 8 weeks. LDB significantly enhanced specific growth rate (SGR), food intake (FI), and serum globulin levels. In contrast, LDR sharply inhibited SGR, FI, and the levels of albumin and globulin. Under LDB condition, there was an increase in protein levels of alkaline phophatase (AKP) and protein and activity levels of lysozyme (LZM) in the liver, and the levels of mRNA, protein, and activity of LZM in the ovary. Under LDR condition, LZM was dramatically down-regulated at mRNA, protein and activity levels in the ovary, suggesting that LZM was regulated at a transcriptional level. In the liver of the LDR group, though AKP mRNA levels sharply increased, its protein and activity levels significantly declined, indicating that AKP was regulated at translational level. Furthermore, a positive correlation between transcription factor NF-κB RelA mRNA levels and expression levels of AKP and LZM was observed in the liver and ovary, implying a transcriptional regulation of NF-κB RelA. In conclusion, the present study demonstrated a positive effect of LDB and negative effect of LDR on fish growth and innate immune responses, possibly associated with modifications at transcriptional, translational, and post-translational levels, and the transcriptional regulation of the NF-κB signaling molecule.

  18. Enhancement of hole injection using ozone treated Ag nanodots dispersed on indium tin oxide anode for organic light emitting diodes

    SciTech Connect

    Moon, Jong-Min; Bae, Jung-Hyeok; Jeong, Jin-A; Jeong, Soon-Wook; Park, No-Jin; Kim, Han-Ki; Kang, Jae-Wook; Kim, Jang-Joo; Yi, Min-Su

    2007-04-16

    The authors report the enhancement of hole injection using an indium tin oxide (ITO) anode covered with ultraviolet (UV) ozone-treated Ag nanodots for fac tris (2-phenylpyridine) iridium Ir(ppy){sub 3}-doped phosphorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy and UV-visible spectrometer analysis exhibit that UV-ozone treatment of the Ag nanodots dispersed on the ITO anode leads to formation of Ag{sub 2}O nanodots with high work function and high transparency. Phosphorescent OLEDs fabricated on the Ag{sub 2}O nanodot-dispersed ITO anode showed a lower turn-on voltage and higher luminescence than those of OLEDs prepared with a commercial ITO anode. It was thought that, as Ag nanodots changed to Ag{sub 2}O nanodots by UV-ozone treatment, the decrease of the energy barrier height led to the enhancement of hole injection in the phosphorescent OLEDs.

  19. Light-emitting diode-based multiwavelength diffuse optical tomography system guided by ultrasound

    PubMed Central

    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

  20. Importance of indium tin oxide surface acido basicity for charge injection into organic materials based light emitting diodes

    NASA Astrophysics Data System (ADS)

    Nüesch, F.; Forsythe, E. W.; Le, Q. T.; Gao, Y.; Rothberg, L. J.

    2000-06-01

    The influence of the indium tin oxide (ITO) electrode surface acido basicity on organic electroluminescent device characteristics is studied. As measured by photoelectron spectroscopy, acid and base treatments produce large work function shifts of the oxide compared to standard ITO treated by an oxygen plasma or water. The current onsets for triphenyldiamine (TPD) single layer diodes sandwiched between ITO and a silver electrode are in qualitative agreement with the work function of the hole injecting oxide electrode. However, saturated photovoltage measurements on single layer diodes built on acid and water treated ITO disagree with the work function obtained from photoelectron experiments. This is explained by protonation of the diamine layer close to the electrode surface producing a charged double layer. It suggests that even acidic surface hydroxyl groups of the oxide electrode are able to protonate the diamine layer, explaining the importance of plasma cleaning to remove surface hydroxyls. The same ITO treatments are investigated in tris(8-hydroxyquinoline) (Alq) aluminum single layer diodes as well as hybrid TPD/Alq light emitting devices. Implications of metal-oxide surface acido basicity on electrode treatment and molecular material design are discussed.

  1. Demonstration Assessment of Light-Emitting Diode (LED) Post-Top Lighting at Central Park in New York City

    SciTech Connect

    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.

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

    PubMed Central

    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. However, there are remaining challenges in terms of polychromatic configuration, electroluminescence efficiency and/or multidirectional deformability. Here we present ultra-thin, wearable colloidal quantum dot light-emitting diode arrays utilizing the intaglio transfer printing technique, which allows the alignment of red–green–blue pixels with high resolutions up to 2,460 pixels per inch. This technique is readily scalable and adaptable for low-voltage-driven pixelated white quantum dot light-emitting diodes and electronic tattoos, showing the best electroluminescence performance (14,000 cd m−2 at 7 V) among the wearable light-emitting diodes reported up to date. The device performance is stable on flat, curved and convoluted surfaces under mechanical deformations such as bending, crumpling and wrinkling. These deformable device arrays highlight new possibilities for integrating high-definition full-colour displays in wearable electronics. PMID:25971194

  3. Light-Emitting Diodes with Hierarchical and Multifunctional Surface Structures for High Light Extraction and an Antifouling Effect.

    PubMed

    Leem, Young-Chul; Park, Jung Su; Kim, Joon Heon; Myoung, NoSoung; Yim, Sang-Youp; Jeong, Sehee; Lim, Wantae; Kim, Sung-Tae; Park, Seong-Ju

    2016-01-13

    Bioinspired hierarchical structures on the surface of vertical light-emitting diodes (VLEDs) are demonstrated by combining a self-assembled dip-coating process and nanopatterning transfer method using thermal release tape. This versatile surface structure can efficiently reduce the total internal reflection and add functions, such as superhydrophobicity and high oleophobicity, to achieve an antifouling effect for VLEDs.

  4. High-Efficiency Blue Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence from Phenoxaphosphine and Phenoxathiin Derivatives.

    PubMed

    Lee, Sae Youn; Adachi, Chihaya; Yasuda, Takuma

    2016-06-01

    High-efficiency blue thermally activated delayed fluorescence (TADF) molecules, consisting of phenoxaphosphine oxide and phenoxathiin dioxide as acceptor units and 9,9-dimethylacridan as a donor unit, are reported. Maximum external electroluminescence quantum efficiencies of up to 20.5% are achieved in blue organic light-emitting diodes (OLEDs) by employing these materials as TADF emitters.

  5. Fluorescent Organic Planar pn Heterojunction Light-Emitting Diodes with Simplified Structure, Extremely Low Driving Voltage, and High Efficiency.

    PubMed

    Chen, Dongcheng; Xie, Gaozhan; Cai, Xinyi; Liu, Ming; Cao, Yong; Su, Shi-Jian

    2016-01-13

    Fluorescent organic light-emitting diodes capable of radiative utilization of both singlet and triplet excitons are achieved via a simple double-layer planar pn hetero-junction configuration without a conventional emission layer, leading to high external quantum efficiency above 10% and extremely low driving voltages close to the theoretical minima.

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

    ERIC Educational Resources Information Center

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

    2014-01-01

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

  7. Methods and apparatus of spatially resolved electroluminescence of operating organic light-emitting diodes using conductive atomic force microscopy

    NASA Technical Reports Server (NTRS)

    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.

  8. Vertical GaN based Light Emitting Diodes on Metal Alloy Substrate for Solid State Lighting Application

    NASA Astrophysics Data System (ADS)

    Doan, T.; Chu, C.; Chen, C.; Liu, W.; Chu, J.; Yeh, J.; Chen, H.; Fan, F.; Tran, C.

    2006-02-01

    Vertical GaN based Light Emitting Diodes on metal alloy substrate were realized and characterized for solid state lighting application. An efficiency of more than 70 lumens/watt was achieved. In addition, these LEDs exhibit many advantages over those on sapphire under extreme operation conditions for general lighting application.

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

    ERIC Educational Resources Information Center

    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. Manipulating the Local Light Emission in Organic Light-Emitting Diodes by using Patterned Self-Assembled Monolayers.

    PubMed

    Mathijssen, Simon G J; van Hal, Paul A; van den Biggelaar, Ton J M; Smits, Edsger C P; de Boer, Bert; Kemerink, Martijn; Janssen, René A J; de Leeuw, Dago M

    2008-07-17

    Patterned organic light-emitting diodes are fabricated by using microcontact- printed self-assembled monolayers on a gold anode (see background figure). Molecules with dipole moments in opposite directions result in an increase or a decrease of the local work function (foreground picture), providing a direct handle on charge injection and enabling local modification of the light emission. PMID:25213893

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

    NASA Astrophysics Data System (ADS)

    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

    2015-05-01

    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. However, there are remaining challenges in terms of polychromatic configuration, electroluminescence efficiency and/or multidirectional deformability. Here we present ultra-thin, wearable colloidal quantum dot light-emitting diode arrays utilizing the intaglio transfer printing technique, which allows the alignment of red-green-blue pixels with high resolutions up to 2,460 pixels per inch. This technique is readily scalable and adaptable for low-voltage-driven pixelated white quantum dot light-emitting diodes and electronic tattoos, showing the best electroluminescence performance (14,000 cd m-2 at 7 V) among the wearable light-emitting diodes reported up to date. The device performance is stable on flat, curved and convoluted surfaces under mechanical deformations such as bending, crumpling and wrinkling. These deformable device arrays highlight new possibilities for integrating high-definition full-colour displays in wearable electronics.

  12. Light-emitting diodes by band-structure engineering in van der Waals heterostructures.

    PubMed

    Withers, F; Del Pozo-Zamudio, O; Mishchenko, A; Rooney, A P; Gholinia, A; Watanabe, K; Taniguchi, T; Haigh, S J; Geim, A K; Tartakovskii, A I; Novoselov, K S

    2015-03-01

    The advent of graphene and related 2D materials has recently led to a new technology: heterostructures based on these atomically thin crystals. The paradigm proved itself extremely versatile and led to rapid demonstration of tunnelling diodes with negative differential resistance, tunnelling transistors, photovoltaic devices and so on. Here, we take the complexity and functionality of such van der Waals heterostructures to the next level by introducing quantum wells (QWs) engineered with one atomic plane precision. We describe light-emitting diodes (LEDs) made by stacking metallic graphene, insulating hexagonal boron nitride and various semiconducting monolayers into complex but carefully designed sequences. Our first devices already exhibit an extrinsic quantum efficiency of nearly 10% and the emission can be tuned over a wide range of frequencies by appropriately choosing and combining 2D semiconductors (monolayers of transition metal dichalcogenides). By preparing the heterostructures on elastic and transparent substrates, we show that they can also provide the basis for flexible and semi-transparent electronics. The range of functionalities for the demonstrated heterostructures is expected to grow further on increasing the number of available 2D crystals and improving their electronic quality.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

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

    PubMed

    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. PMID:23893947

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

    PubMed

    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.

  16. High power visible light emitting diodes as pulsed excitation sources for biomedical photoacoustics.

    PubMed

    Allen, Thomas J; Beard, Paul C

    2016-04-01

    The use of visible light emitting diodes (LEDs) as an alternative to Q-switched lasers conventionally used as photoacoustic excitation sources has been explored. In common with laser diodes, LEDs offer the advantages of compact size, low cost and high efficiency. However, laser diodes suitable for pulsed photoacoustic generation are typically available only at wavelengths greater than 750nm. By contrast, LEDs are readily available at visible wavelengths below 650nm where haemoglobin absorption is significantly higher, offering the prospect of increased SNR for superficial vascular imaging applications. To demonstrate feasibility, a range of low cost commercially available LEDs operating in the 420-620nm spectral range were used to generate photoacoustic signals in physiologically realistic vascular phantoms. Overdriving with 200ns pulses and operating at a low duty cycle enabled pulse energies up to 10µJ to be obtained with a 620nm LED. By operating at a high pulse repetition frequency (PRF) in order to rapidly signal average over many acquisitions, this pulse energy was sufficient to generate detectable signals in a blood filled tube immersed in an Intralipid suspension (µs' = 1mm(-1)) at a depth of 15mm using widefield illumination. In addition, a compact four-wavelength LED (460nm, 530nm, 590nm, 620nm) in conjunction with a coded excitation scheme was used to illustrate rapid multiwavelength signal acquisition for spectroscopic applications. This study demonstrates that LEDs could find application as inexpensive and compact multiwavelength photoacoustic excitation sources for imaging superficial vascular anatomy. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. PMID:27446652

  17. High power visible light emitting diodes as pulsed excitation sources for biomedical photoacoustics

    PubMed Central

    Allen, Thomas J.; Beard, Paul C.

    2016-01-01

    The use of visible light emitting diodes (LEDs) as an alternative to Q-switched lasers conventionally used as photoacoustic excitation sources has been explored. In common with laser diodes, LEDs offer the advantages of compact size, low cost and high efficiency. However, laser diodes suitable for pulsed photoacoustic generation are typically available only at wavelengths greater than 750nm. By contrast, LEDs are readily available at visible wavelengths below 650nm where haemoglobin absorption is significantly higher, offering the prospect of increased SNR for superficial vascular imaging applications. To demonstrate feasibility, a range of low cost commercially available LEDs operating in the 420-620nm spectral range were used to generate photoacoustic signals in physiologically realistic vascular phantoms. Overdriving with 200ns pulses and operating at a low duty cycle enabled pulse energies up to 10µJ to be obtained with a 620nm LED. By operating at a high pulse repetition frequency (PRF) in order to rapidly signal average over many acquisitions, this pulse energy was sufficient to generate detectable signals in a blood filled tube immersed in an Intralipid suspension (µs’ = 1mm−1) at a depth of 15mm using widefield illumination. In addition, a compact four-wavelength LED (460nm, 530nm, 590nm, 620nm) in conjunction with a coded excitation scheme was used to illustrate rapid multiwavelength signal acquisition for spectroscopic applications. This study demonstrates that LEDs could find application as inexpensive and compact multiwavelength photoacoustic excitation sources for imaging superficial vascular anatomy. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. PMID:27446652

  18. High power visible light emitting diodes as pulsed excitation sources for biomedical photoacoustics.

    PubMed

    Allen, Thomas J; Beard, Paul C

    2016-04-01

    The use of visible light emitting diodes (LEDs) as an alternative to Q-switched lasers conventionally used as photoacoustic excitation sources has been explored. In common with laser diodes, LEDs offer the advantages of compact size, low cost and high efficiency. However, laser diodes suitable for pulsed photoacoustic generation are typically available only at wavelengths greater than 750nm. By contrast, LEDs are readily available at visible wavelengths below 650nm where haemoglobin absorption is significantly higher, offering the prospect of increased SNR for superficial vascular imaging applications. To demonstrate feasibility, a range of low cost commercially available LEDs operating in the 420-620nm spectral range were used to generate photoacoustic signals in physiologically realistic vascular phantoms. Overdriving with 200ns pulses and operating at a low duty cycle enabled pulse energies up to 10µJ to be obtained with a 620nm LED. By operating at a high pulse repetition frequency (PRF) in order to rapidly signal average over many acquisitions, this pulse energy was sufficient to generate detectable signals in a blood filled tube immersed in an Intralipid suspension (µs' = 1mm(-1)) at a depth of 15mm using widefield illumination. In addition, a compact four-wavelength LED (460nm, 530nm, 590nm, 620nm) in conjunction with a coded excitation scheme was used to illustrate rapid multiwavelength signal acquisition for spectroscopic applications. This study demonstrates that LEDs could find application as inexpensive and compact multiwavelength photoacoustic excitation sources for imaging superficial vascular anatomy. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

  19. Increased light extraction and directional emission control in gallium nitride photonic crystal light emitting diodes

    NASA Astrophysics Data System (ADS)

    McGroddy, Kelly C.

    GaN has become the prominent material for blue-green light emitting diodes (LEDs) and efficient white light sources. Advancements in LED efficiency for lighting has the potential to dramatically impact energy consumption world wide. A limiting factor to achieving high efficiencies in GaN LEDs is the light extraction efficiency. This work addresses many key issues pertaining to the use of PhCs to increase the extraction efficiency and emission directionality of GaN LEDs. Limitations in extraction efficiency of GaN photonic crystal light emitting diodes (LEDs) are addressed by implementing an LED design using both 2D photonic crystals (PhCs) in-plane and index guiding layers (IGLs) in the vertical direction. The effects of PhCs on light extraction and emission directionality from GaN LEDs are studied experimentally. Angular resolved electroluminescence clearly shows the combined effect of controlling the vertical mode profile with the IGLs and tailoring the emission profile with the periodicity of the PhC lattice. Various materials are used to increase the index contrast of the IGL and the effects are measured. Increases in vertical emission as high as 3.5x are achieved for PhC LEDs with an Al0.12Ga0.88N IGL over non-PhC LEDs with a ˜30% improvement attributed to the incorporation of the AlGaN IGL. This enhancement is achieved by tailoring both the directionality and guided mode control. The impact of incorporating PhCs and IGLs on LED device design and performance are addressed. Effects of etching the PhCs near the QWs have been observed and explanations for this behavior will be discussed. It will be shown that an un-doped IGL can severely limit current spreading in the n-type side of the device and have a detrimental impact on device performance. Finally, a method of patterning PhCs with periodicities as small as 230nm by laser interference lithography and imprint lithography has been developed to provide a fast, inexpensive method of pattering PhCs over large

  20. Improvements to III-nitride light-emitting diodes through characterization and material growth

    NASA Astrophysics Data System (ADS)

    Getty, Amorette Rose Klug

    A variety of experiments were conducted to improve or aid the improvement of the efficiency of III-nitride light-emitting diodes (LEDs), which are a critical area of research for multiple applications, including high-efficiency solid state lighting. To enhance the light extraction in ultraviolet LEDs grown on SiC substrates, a distributed Bragg reflector (DBR) optimized for operation in the range from 250 to 280 nm has been developed using MBE growth techniques. The best devices had a peak reflectivity of 80% with 19.5 periods, which is acceptable for the intended application. DBR surfaces were sufficiently smooth for subsequent epitaxy of the LED device. During the course of this work, pros and cons of AlGaN growth techniques, including analog versus digital alloying, were examined. This work highlighted a need for more accurate values of the refractive index of high-Al-content AlxGa1-xNin the UV wavelength range. We present refractive index results for a wide variety of materials pertinent to the fabrication of optical III-nitride devices. Characterization was done using Variable-Angle Spectroscopic Ellipsometry. The three binary nitrides, and all three ternaries, have been characterized to a greater or lesser extent depending on material compositions available. Semi-transparent p-contact materials and other thin metals for reflecting contacts have been examined to allow optimization of deposition conditions and to allow highly accurate modeling of the behavior of light within these devices. Standard substrate materials have also been characterized for completeness and as an indicator of the accuracy of our modeling technique. We have demonstrated a new technique for estimating the internal quantum efficiency (IQE) of nitride light-emitting diodes. This method is advantageous over the standard low-temperature photoluminescence-based method of estimating IQE, as the new method is conducted under the same conditions as normal device operation. We have developed

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  2. Fabrication and Characterization of New Hybrid Organic Light Emitting Diode (OLED): Europium-picrate-triethylene oxide Complex

    SciTech Connect

    Sarjidan, M. A. Mohd; Abu Zakaria, N. Z. A.; Abd. Majid, W. H.; Kusrini, Eny; Saleh, M. I.

    2009-07-07

    Thin-film light emitting devices based on organic materials have attracted vast interest in applications such as light emitting diode (LED) and flat-panel display. The organic material can be attached with inorganic material to enhance the performance of the light emitting device. A hybrid OLED based on a new complex of europium picrate (Eu-pic) with triethylene oxide (EO3) ligand is fabricated. The OLED is fabricated by using spin coating technique with acetone as the solvent and aluminum as the top electrode. The optical, photoluminescence (PL) and electrical properties of the sample are carried out by UV-Vis spectroscopy (Jasco V-750), luminescence spectroscopy (Perkin Elmer LS-500) and source measure unit (SMU)(Keithly), respectively.

  3. Effect of Hole Mobility Through Emissive Layer on Temporal Stability of Blue Organic Light-Emitting Diodes

    SciTech Connect

    Culligan, S.W.; Chen, A.C.-A.; Wallace, J.U.; Klubek, K.P.; Tang, C.W.; Chen, S.H.

    2006-07-13

    Light-emitting conjugated oligomers comprising anthracene, naphthalene, and fluorene units have been synthesized to investigate three configurations of blue organic light-emitting diodes (OLEDs) that are designed to identify the origins of device instablilty. The transient OLED technique is employed to measure hole mobilities, which are found to be 3.1 x 10^-4, 8.9 x 10^-5, and 3.6 x 10^-5 cm^2V^-1s^-1 for three different blue-light-emitting model compounds with varying fluorene content. A higher hole mobility through the emissive layer results in a wider recombination zone, which, in turn, is responsible for a longer device lifetime and a lower drive voltage at the expense of luminance yield.

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

    SciTech Connect

    Barillaro, G. Strambini, L. M.

    2014-03-03

    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.

  5. A Solution Processed Flexible Nanocomposite Electrode with Efficient Light Extraction for Organic Light Emitting Diodes

    PubMed Central

    Li, Lu; Liang, Jiajie; Chou, Shu-Yu; Zhu, Xiaodan; Niu, Xiaofan; ZhibinYu; Pei, Qibing

    2014-01-01

    Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m2 with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost. PMID:24632742

  6. Defect-Enabled Electrical Current Leakage in Ultraviolet Light-Emitting Diodes

    DOE PAGESBeta

    Moseley, Michael William; Allerman, Andrew A.; Crawford, Mary H.; Wierer, Jonathan; Smith, Michael L.; Biedermann, Laura

    2015-04-13

    The AlGaN materials system offers a tunable, ultra-wide bandgap that is exceptionally useful for high-power electronics and deep ultraviolet optoelectronics. Moseley et al. (pp. 723–726) investigate a structural defect known as an open-core threading dislocation or ''nanopipe'' that is particularly detrimental to devices that employ these materials. Furthermore, an AlGaN thin film was synthesized using metal-organic chemical-vapor deposition. Electrical current leakage is detected at a discrete point using a conductive atomic-force microscope (CAFM). However, no physical feature or abnormality at this location was visible by an optical microscope. The AlGaN thin film was then etched in hot phosphoric acid, andmore » the same location that was previously analyzed was revisited with the CAFM. The point that previously exhibited electrical current leakage had been decorated with a 1.1 μm wide hexagonal pit, which identified the site of electrical current leakage as a nanopipe and allows these defects to be easily observed by optical microscopy. Moreover, with this nanopipe identification and quantification strategy, the authors were able to correlate decreasing ultraviolet light-emitting diode optical output power with increasing nanopipe density.« less

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

    NASA Astrophysics Data System (ADS)

    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.

  8. Adjunctive 830 nm light-emitting diode therapy can improve the results following aesthetic procedures

    PubMed Central

    Kim, Won-Serk; Ohshiro, Toshio; Trelles, Mario A; Vasily, David B

    2015-01-01

    Background: Aggressive, or even minimally aggressive, aesthetic interventions are almost inevitably followed by such events as discomfort, erythema, edema and hematoma formation which could lengthen patient downtime and represent a major problem to the surgeon. Recently, low level light therapy with light-emitting diodes (LED-LLLT) at 830 nm has attracted attention in wound healing indications for its anti-inflammatory effects and control of erythema, edema and bruising. Rationale: The wavelength of 830 nm offers deep penetration into living biological tissue, including bone. A new-generation of 830 nm LEDs, based on those developed in the NASA Space Medicine Laboratory, has enabled the construction of planar array-based LED-LLLT systems with clinically useful irradiances. Irradiation with 830 nm energy has been shown in vitro and in vivo to increase the action potential of epidermal and dermal cells significantly. The response of the inflammatory stage cells is enhanced both in terms of function and trophic factor release, and fibroblasts demonstrate superior collagenesis and elastinogenesis. Conclusions: A growing body of clinical evidence is showing that applying 830 nm LED-LLLT as soon as possible post-procedure, both invasive and noninvasive, successfully hastens the resolution of sequelae associated with patient downtime in addition to significantly speeding up frank wound healing. This article reviews that evidence, and attempts to show that 830 nm LED-LLLT delivers swift resolution of postoperative sequelae, minimizes downtime and enhances patient satisfaction. PMID:26877592

  9. Tuning the white light spectrum of light emitting diode lamps to reduce attraction of nocturnal arthropods

    PubMed Central

    Longcore, Travis; Aldern, Hannah L.; Eggers, John F.; Flores, Steve; Franco, Lesly; Hirshfield-Yamanishi, Eric; Petrinec, Laina N.; Yan, Wilson A.; Barroso, André M.

    2015-01-01

    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. PMID:25780237

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

    PubMed Central

    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

    2015-01-01

    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 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. PMID:26119218

  11. High-brightness organic light-emitting diodes for optogenetic control of Drosophila locomotor behaviour

    NASA Astrophysics Data System (ADS)

    Morton, Andrew; Murawski, Caroline; Pulver, Stefan R.; Gather, Malte C.

    2016-08-01

    Organic light emitting diodes (OLEDs) are in widespread use in today’s mobile phones and are likely to drive the next generation of large area displays and solid-state lighting. Here we show steps towards their utility as a platform technology for biophotonics, by demonstrating devices capable of optically controlling behaviour in live animals. Using devices with a pin OLED architecture, sufficient illumination intensity (0.3 mW.mm‑2) to activate channelrhodopsins (ChRs) in vivo was reliably achieved at low operating voltages (5 V). In Drosophila melanogaster third instar larvae expressing ChR2(H134R) in motor neurons, we found that pulsed illumination from blue and green OLEDs triggered robust and reversible contractions in animals. This response was temporally coupled to the timing of OLED illumination. With blue OLED illumination, the initial rate and overall size of the behavioural response was strongest. Green OLEDs achieved roughly 70% of the response observed with blue OLEDs. Orange OLEDs did not produce contractions in larvae, in agreement with the spectral response of ChR2(H134R). The device configuration presented here could be modified to accommodate other small model organisms, cell cultures or tissue slices and the ability of OLEDs to provide patterned illumination and spectral tuning can further broaden their utility in optogenetics experiments.

  12. Anomalous hole injection deterioration of organic light-emitting diodes with a manganese phthalocyanine layer

    SciTech Connect

    Lee, Hyunbok; Lee, Jeihyun; Yi, Yeonjin; Cho, Sang Wan; Kim, Jeong Won

    2015-01-21

    Metal phthalocyanines (MPcs) are well known as an efficient hole injection layer (HIL) in organic devices. They possess a low ionization energy, and so the low-lying highest occupied molecular orbital (HOMO) gives a small hole injection barrier from an anode in organic light-emitting diodes. However, in this study, we show that the hole injection characteristics of MPc are not only determined by the HOMO position but also significantly affected by the wave function distribution of the HOMO. We show that even with the HOMO level of a manganese phthalocyanine (MnPc) HIL located between the Fermi level of an indium tin oxide anode and the HOMO level of a N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine hole transport layer the device performance with the MnPc HIL is rather deteriorated. This anomalous hole injection deterioration is due to the contracted HOMO wave function, which leads to small intermolecular electronic coupling. The origin of this contraction is the significant contribution of the Mn d-orbital to the MnPc HOMO.

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

    PubMed

    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.

  14. Free-form lenses for high illumination quality light-emitting diode MR16 lamps

    NASA Astrophysics Data System (ADS)

    Chen, Fei; Liu, Sheng; Wang, Kai; Liu, Zongyuan; Luo, Xiaobing

    2009-12-01

    Light-emitting diode (LED) MR16 lamps, regarded as one typical general lighting product of LEDs, are being widely used in many applications. Light efficiency into a main beam and uniformity are two key issues for high quality illumination of LED MR16 lamps. In this study, a practical and precise nonimaging optical design method is presented, and two novel 90- and 120-deg free-form lenses for high illumination quality LED MR16 lamps are designed according to this method. Based on the Monte-Carlo ray-tracing method, numerical simulation results demonstrate that the light output efficiencies of these novel lenses reach as high as 98% and are 17% higher than that of traditional total internal reflection (TIR) MR16 lens. Moreover, more than 89% of light exiting from the surfaces of these novel lenses irradiate within the desired receive target, while only 60% irradiate for traditional TIR lens. The uniformities of illuminance distribution across the target of these novel MR16 lamps also are much higher. In addition, these novel lenses are both quite compact and no more than 1/5 of that of the TIR lens. Therefore, these LED MR16 lamps integrated by novel lenses provide an effective solution to high quality illumination.

  15. A solution processed flexible nanocomposite electrode with efficient light extraction for organic light emitting diodes.

    PubMed

    Li, Lu; Liang, Jiajie; Chou, Shu-Yu; Zhu, Xiaodan; Niu, Xiaofan; ZhibinYu; Pei, Qibing

    2014-03-17

    Highly efficient organic light emitting diodes (OLEDs) based on multiple layers of vapor evaporated small molecules, indium tin oxide transparent electrode, and glass substrate have been extensively investigated and are being commercialized. The light extraction from the exciton radiative decay is limited to less than 30% due to plasmonic quenching on the metallic cathode and the waveguide in the multi-layer sandwich structure. Here we report a flexible nanocomposite electrode comprising single-walled carbon nanotubes and silver nanowires stacked and embedded in the surface of a polymer substrate. Nanoparticles of barium strontium titanate are dispersed within the substrate to enhance light extraction efficiency. Green polymer OLED (PLEDs) fabricated on the nanocomposite electrode exhibit a maximum current efficiency of 118 cd/A at 10,000 cd/m(2) with the calculated external quantum efficiency being 38.9%. The efficiencies of white PLEDs are 46.7 cd/A and 30.5%, respectively. The devices can be bent to 3 mm radius repeatedly without significant loss of electroluminescent performance. The nanocomposite electrode could pave the way to high-efficiency flexible OLEDs with simplified device structure and low fabrication cost.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  17. Organic thin-film transistor arrays for active-matrix organic light emitting diode

    NASA Astrophysics Data System (ADS)

    Lee, Sangyun; Moon, Hyunsik; Kim, Do H.; Koo, Bon-Won; Jeong, Eun-Jeong; Lee, Bang-Lin; Kim, Joo-Young; Lee, Eunkyung; Hahn, Kook-Min; Han, Jeong-Seok; Park, Jung-Il; Seon, Jong-Baek; Kim, Jung-Woo; Chun, Young-Tea; Kim, Sangyeol; Kang, Sung K.

    2007-09-01

    We developed an active matrix organic light-emitting diodes (AMOLEDs) on a glass using two organic thin-film transistors (OTFTs) and a capacitor in a pixel. OTFTs switching-arrays with 64 scan lines and 64 (RGB) data lines were designed and fabricated to drive OLED arrays. In this study, OTFT devices have bottom contact structures with an ink-jet printed polymer semiconductor and an organic insulator as a gate dielectric. The width and length of the switching OTFT is 500μm and 10μm, respectively and the driving OTFT has 900μm channel width with the same channel length. The characteristics of the OTFTs were examined using test cells around display area. On/off ratio, mobility, on-current of switching OTFT and on-current of driving OTFT were 10 6, 0.1 cm2/V-sec, order of 8μA and over 70 μA respectively. These properties were enough to drive the AMOLEDs over 60 Hz frame rate. AMOLEDs composed of the OTFT switching arrays and OLEDs made by deposition of small molecule materials were fabricated and driven to make moving images, successfully.

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

  19. Active matrix organic light emitting diode (OLED)-XL life test results

    NASA Astrophysics Data System (ADS)

    Fellowes, David A.; Wood, Michael V.; Hastings, Arthur R., Jr.; Ghosh, Amalkumar P.; Prache, Olivier

    2008-04-01

    OLED displays have been known to exhibit high levels of performance with regards to contrast, response time, uniformity, and viewing angle, but a lifetime improvement has been perceived to be essential for broadening the applications of OLED's in the military and in the commercial market. As a result of this need, the US Army and eMagin Corporation established a Cooperative Research and Development Agreement (CRADA) to improve the lifetime of OLED displays. In 2006, eMagin Corporation developed long-life OLED-XL devices for use in their AMOLED microdisplays for head-worn applications, and RDECOM CERDEC NVESD ran life tests on these displays, finding over 200% lifetime improvement for the XL devices over the standard displays. Early results were published at the 2007 SPIE Defense and Security Symposium. Further life testing of XL and standard devices at ambient conditions and at high temperatures will be presented this year along with a recap of previous data. This should result in a better understanding of the applicability of AMOLEDs in military and commercial head mounted systems: where good fits are made, and where further development might be needed. This is a continuation of the paper "Life test results of OLED-XL long-life devices for use in active matrix organic light emitting diode (AMOLED) displays for head mounted applications" presented at SPIE DSS in 2007.

  20. Separated Carbon Nanotube Macroelectronics for Active Matrix Organic Light-Emitting Diode Displays

    NASA Astrophysics Data System (ADS)

    Fu, Yue; Zhang, Jialu; Wang, Chuan; Chen, Pochiang; Zhou, Chongwu

    2012-02-01

    Active matrix organic light-emitting diode (AMOLED) display holds great potential for the next generation visual technologies due to its high light efficiency, flexibility, lightweight, and low-temperature processing. However, suitable thin-film transistors (TFTs) are required to realize the advantages of AMOLED. Pre-separated, semiconducting enriched carbon nanotubes are excellent candidates for this purpose because of their excellent mobility, high percentage of semiconducting nanotubes, and room-temperature processing compatibility. Here we report, for the first time, the demonstration of AMOLED displays driven by separated nanotube thin-film transistors (SN-TFTs) including key technology components such as large-scale high-yield fabrication of devices with superior performance, carbon nanotube film density optimization, bilayer gate dielectric for improved substrate adhesion to the deposited nanotube film, and the demonstration of monolithically integrated AMOLED display elements with 500 pixels driven by 1000 SN-TFTs. Our approach can serve as the critical foundation for future nanotube-based thin-film display electronics.

  1. Core/multishell nanowire heterostructures as multicolor, high-efficiency light-emitting diodes.

    PubMed

    Qian, Fang; Gradecak, Silvija; Li, Yat; Wen, Cheng-Yen; Lieber, Charles M

    2005-11-01

    We report the growth and characterization of core/multishell nanowire radial heterostructures, and their implementation as efficient and synthetically tunable multicolor nanophotonic sources. Core/multishell nanowires were prepared by metal-organic chemical vapor deposition with an n-GaN core and InxGa1-xN/GaN/p-AlGaN/p-GaN shells, where variation of indium mole fraction is used to tune emission wavelength. Cross-sectional transmission electron microscopy studies reveal that the core/multishell nanowires are dislocation-free single crystals with a triangular morphology. Energy-dispersive X-ray spectroscopy clearly shows shells with distinct chemical compositions, and quantitatively confirms that the thickness and composition of individual shells can be well controlled during synthesis. Electrical measurements show that the p-AlGaN/p-GaN shell structure yields reproducible hole conduction, and electroluminescence measurements demonstrate that in forward bias the core/multishell nanowires function as light-emitting diodes, with tunable emission from 365 to 600 nm and high quantum efficiencies. The ability to synthesize rationally III-nitride core/multishell nanowire heterostructures opens up significant potential for integrated nanoscale photonic systems, including multicolor lasers.

  2. Enhanced light out-coupling from surface plasmonic loss minimized transparent organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Bum; Lee, Jeong-Hwan; Moon, Chang-Ki; Kim, Sei-Yong; Kim, Jang-Joo

    2013-09-01

    We report extremely high light out-coupling efficiency from a transparent organic light-emitting diode (OLED) integrated with microstructures on both sides of the device.[1] The OLED having a metal free structure offers dramatically reduced surface plasmonic loss and absorption loss. To extract the confined light inside the device, a high refractive index light extraction pattern was directly fabricated on the top side transparent conducting oxide electrode using a simple evaporation method, and a micro lens array sheet was simultaneously attached on the bottom side of the glass substrate. As a result, the external quantum efficiency of the device increased from 18.2% to 47.3% by using the microstructures, and was additionally enhanced to 62.9% by attaching an index-matched hemisphere lens instead of the micro lens array on the glass side in order to reduce additional light guiding loss inside of the device. These values showed very good agreement with the simulation performed by a combination of the dipole model and a 3-dimensional geometrical simulation.

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

    PubMed

    Reddy, M Siva Pratap; Park, Chinho

    2016-01-01

    Recently, significant advances have occurred in the development of phosphors for bio hybrid light-emitting diodes (Bio-HLEDs), which have created brighter, metal-free, rare-earth phosphor-free, eco-friendly, and cost-competitive features for visible light emission. Here, we demonstrate an original approach using bioinspired phosphors in Bio-HLEDs based on natural deoxyribonucleic acid (DNA)-curcumin complexes with cetyltrimethylammonium (CTMA) in bio-crystalline form. The curcumin chromophore was bound to the DNA double helix structure as observed using field emission tunnelling electron microscopy (FE-TEM). Efficient luminescence occurred due to tightly bound curcumin chromophore to DNA duplex. Bio-HLED shows low luminous drop rate of 0.0551 s(-1). Moreover, the solid bio-crystals confined the activating bright luminescence with a quantum yield of 62%, thereby overcoming aggregation-induced quenching effect. The results of this study herald the development of commercially viable large-scale hybrid light applications that are environmentally benign. PMID:27572113

  4. Influence of Ambient Gas on the Performance of Quantum-Dot Light-Emitting Diodes.

    PubMed

    Lin, Qingli; Chen, Fei; Wang, Hongzhe; Shen, Huaibin; Wang, Aqiang; Wang, Lei; Zhang, Fengjuan; Guo, Fang; Li, Lin Song

    2016-05-11

    Here, we report the influence of the ambient gas on the performance of quantum dot-based light-emitting diodes (QD-LEDs). The blue QD-LED devices with the maximum external quantum efficiency of 8.1% and the turn-on voltage of 2.7 V could be obtained in air. The efficiency decreases by 12% and turn-on voltage increases by 0.3 V relative to the control devices fabricated in a N2-filled glovebox. The histogram of maximum external quantum efficiency (EQE) shows average peak EQE of 8.08% and a low standard deviation of 3.63%, suggesting high reproducibility. Correspondingly, the operational lifetime of 376 h is obtained, which is on par with 408 h of devices fabricated in N2. For the devices fabricated in air, relatively high efficiency could be maintained only at low voltages, because of the near balanced injection of carriers under low bias. The measurements of contact potential difference, chemical composition, and surface roughness are used to verify the variation of energy level and surface morphology of films influenced by different ambient gas. These results would offer reasonable guidance for the application of QD-LEDs in actual large-scale production.

  5. Application of light-emitting diodes (LEDs) in cultivation of phototrophic microalgae: current state and perspectives.

    PubMed

    Glemser, M; Heining, M; Schmidt, J; Becker, A; Garbe, D; Buchholz, R; Brück, T

    2016-02-01

    The quality and regulation of the incident light is crucial in microalgae cultivation processes. Depending on wavelength, spectrum, and intensity, growth characteristics and biochemical composition of these organisms vary. With mainly fluorescent lamps (FL) used previously for illumination, such variabilities could not be studied adequately due to their broad emission spectrum. In contrast, light-emitting diodes (LEDs) emit a very narrow wavelength band and enable flexible photobioreactor designs due to their small size. This review provides a condensed overview on the application of LEDs in microalgal cultivation processes. It summarizes the current availability and applicability of LED technologies as an illumination source for research-focused photobioreactor systems. A particular focus is the use of narrow-wavelength LEDs to address fundamental as well as applied aspects of light color on algae biomass and value-added compound formation. In this respect, the application of internal and external illumination systems is reviewed together with trends in the industrial use of LED systems to intensify algae process efficiency.

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

    PubMed

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

    2015-12-01

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

  7. Hybrid Tunnel Junction-Graphene Transparent Conductive Electrodes for Nitride Lateral Light Emitting Diodes.

    PubMed

    Wang, Liancheng; Cheng, Yan; Liu, Zhiqiang; Yi, Xiaoyan; Zhu, Hongwei; Wang, Guohong

    2016-01-20

    Graphene transparent conductive electrode (TCE) applications in nitride light emitting diodes (LEDs) are still limited by the large contact resistance and interface barrier between graphene and p-GaN. We propose a hybrid tunnel junction (TJ)-graphene TCE approach for nitride lateral LEDs theoretically and experimentally. Through simulation using commercial advanced physical models of semiconductor devices (APSYS), we found that low tunnel resistance can be achieved in the n(+)-GaN/u-InGaN/p(+)-GaN TJ, which has a lower tunneling barrier and an enhanced electric field due to the polarization effect. Graphene TCEs and hybrid graphene-TJ TCEs are then modeled. The designed hybrid TJ-graphene TCEs show sufficient current diffusion length (Ls), low introduced series resistance, and high transmittance. The assembled TJ LED with the triple-layer graphene (TLG) TCEs show comparable optoelectrical performance (3.99 V@20 mA, LOP = 10.8 mW) with the reference LED with ITO TCEs (3.36 V@20 mA, LOP = 12.6 mW). The experimental results further prove that the TJ-graphene structure can be successfully incorporated as TCEs for lateral nitride LEDs.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Numerical modeling and uncertainty analysis of light emitting diodes for photometric measurements

    NASA Astrophysics Data System (ADS)

    Khan, Mohammed Z. U.; Abbas, Mohammed; Al-Hadhrami, Luai M.

    2015-06-01

    With the rapid evolution of new, energy-efficient solid-state lighting (SSL) systems, a requirement has risen for new performance metrics and measurement methods to address their unique construction and operating conditions. In this paper, light propagation characteristics in light emitting diodes are analyzed for measurement uncertainty through numerical modeling and simulation. A general 2D EM simulator with PML boundary conditions is formulated to solve Maxwell's equations using finite-difference time domain (FDTD) numerical method to describe the light propagation in LEDs. A practical GaN LED used in SSL systems is simulated for light propagation. The optical properties of dispersive materials are modeled using multi-pole Lorentz-Drude model. The input dipole source for the LED structure is modeled explicitly through a Gaussian pulse line source at a central wavelength of 460 nm corresponding to GaN emission. Finally, the expression for combined standard uncertainty in the light extraction efficiency due to uncertainties in inputs such as emission in the active layer and EM fields is developed using the GUM law of propagation of uncertainties. The uncertainty in GaN LED emission wavelength obtained from Full Width Half Maximum (FWHM) of the emission spectrum is computed to be 16.98 nm. Therefore, the uncertainty analysis model is then used to compute the corresponding uncertainties in the LED output measurements i.e. light extraction efficiency, LED output power and EM fields.

  10. Effectiveness of light emitting diode and halogen light curing units for curing microhybrid and nanocomposites

    PubMed Central

    Choudhary, Shwetha; Suprabha, BS

    2013-01-01

    Aim: To compare the polymerization efficacy of micro-hybrid and nanocomposites cured with Quartz-tungsten halogen (QTH) and light emitting diode (LED) light curing units (LCUs). The effectiveness of pulse cure mode in LED LCU was also investigated. Materials and Methods: Both micro-hybrid and nanocomposite specimens were cured using four different curing protocols giving a total of eight experimental groups. Ten cylindrical specimens were prepared for each group, and light cured for 40 s on the top surface, thus giving a total of eighty specimens. Vicker hardness measurements were carried out on the top and bottom surfaces after 24 h and hardness ratio was calculated. Results: For both micro-hybrid and nanocomposites, highest mean VHN was observed for the group cured with QTH LCU, and the lowest was observed for the group cured with second LED LCU in standard mode but the difference was significant only in case of nanocomposite. Conclusion: Curing nanocomposites with QTH LCU results in better micro hardness. Pulse cure mode does not effectively increase polymerization efficacy than the standard mode of curing. PMID:23833457

  11. Effects of light-emitting diode radiations on human retinal pigment epithelial cells in vitro.

    PubMed

    Chamorro, Eva; Bonnin-Arias, Cristina; Pérez-Carrasco, María Jesús; Muñoz de Luna, Javier; Vázquez, Daniel; Sánchez-Ramos, Celia

    2013-01-01

    Human visual system is exposed to high levels of natural and artificial lights of different spectra and intensities along lifetime. Light-emitting diodes (LEDs) are the basic lighting components in screens of PCs, phones and TV sets; hence it is so important to know the implications of LED radiations on the human visual system. The aim of this study was to investigate the effect of LEDs radiations on human retinal pigment epithelial cells (HRPEpiC). They were exposed to three light-darkness (12 h/12 h) cycles, using blue-468 nm, green-525 nm, red-616 nm and white light. Cellular viability of HRPEpiC was evaluated by labeling all nuclei with DAPI; Production of reactive oxygen species (ROS) was determined by H2DCFDA staining; mitochondrial membrane potential was quantified by TMRM staining; DNA damage was determined by H2AX histone activation, and apoptosis was evaluated by caspases-3,-7 activation. It is shown that LED radiations decrease 75-99% cellular viability, and increase 66-89% cellular apoptosis. They also increase ROS production and DNA damage. Fluorescence intensity of apoptosis was 3.7% in nonirradiated cells and 88.8%, 86.1%, 83.9% and 65.5% in cells exposed to white, blue, green or red light, respectively. This study indicates three light-darkness (12 h/12 h) cycles of exposure to LED lighting affect in vitro HRPEpiC.

  12. Recent advances in light outcoupling from white organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Gather, Malte C.; Reineke, Sebastian

    2015-01-01

    Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ˜100% yield. However, the extraction of photons remains rather inefficient (typically <30%). Here, we provide an introduction to the underlying physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal-metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.

  13. Light emitting diode-based nanosecond ultraviolet light source for fluorescence lifetime measurements

    NASA Astrophysics Data System (ADS)

    Araki, Tsutomu; Misawa, Hiroaki

    1995-12-01

    A compact pulsed-light source is devised from an InGaN/AlGaN double heterostructure light-emitting diode (LED). The LED emits a 450-nm (blue) light under conventional dc operation below 30 mA. When a current larger than 50 mA is applied, the intensity of the 450-nm light saturates, but that of the 380-nm light due to the InGaN component continues to increase. This phenomenon is utilized to realize a nanosecond ultraviolet (UV) light source. Under repetitive, large current pulsing (frequency=10 kHz, pulse width=4 ns, peak current=2 A), the peak LED emission shifts from 450 to 380 nm. Intense light pulses (peak value=40 mW) of 4-ns duration were generated. To evaluate the potential of the pulsed LED as an excitation source, the fluorescence lifetime of a quinine-sulfate solution was measured. The observed lifetime characteristics agreed well with the generally accepted behavior.

  14. GaN-based ultraviolet light-emitting diodes with AuCl₃-doped graphene electrodes.

    PubMed

    Kim, Byung-Jae; Yang, Gwangseok; Kim, Hong-Yeol; Baik, Kwang Hyeon; Mastro, Michael A; Hite, Jennifer K; Eddy, Charles R; Ren, Fan; Pearton, Stephen J; Kim, Jihyun

    2013-11-18

    We demonstrate AuCl3-doped graphene transparent conductive electrodes integrated in GaN-based ultraviolet (UV) light-emitting diodes (LEDs) with an emission peak of 363 nm. AuCl3 doping was accomplished by dipping the graphene electrodes in 5, 10 and 20 mM concentrations of AuCl3 solutions. The effects of AuCl3 doping on graphene electrodes were investigated by current-voltage characteristics, sheet resistance, scanning electron microscope, optical transmittance, micro-Raman scattering and electroluminescence images. The optical transmittance was decreased with increasing the AuCl3 concentrations. However, the forward currents of UV LEDs with p-doped (5, 10 and 20 mM of AuCl3 solutions) graphene transparent conductive electrodes at a forward bias of 8 V were increased by ~48, 63 and 73%, respectively, which can be attributed to the reduction of sheet resistance and the increase of work function of the graphene. The performance of UV LEDs was drastically improved by AuCl3 doping of graphene transparent conductive electrodes. PMID:24514418

  15. Optical Simulation and Optimization of Light Extraction Efficiency for Organic Light Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Su, Hang

    Current organic light emitting diodes (OLEDs) suffer from the low light extraction efficiency. In this thesis, novel OLED structures including photonic crystal, Fabry-Perot resonance cavity and hyperbolic metamaterials were numerically simulated and theoretically investigated. Finite-difference time-domain (FDTD) method was employed to numerically simulate the light extraction efficiency of various 3D OLED structures. With photonic crystal structures, a maximum of 30% extraction efficiency is achieved. A higher external quantum efficiency of 35% is derived after applying Fabry-Perot resonance cavity into OLEDs. Furthermore, different factors such as material properties, layer thicknesses and dipole polarizations and locations have been studied. Moreover, an upper limit for the light extraction efficiency of 80% is reached theoretically with perfect reflector and single dipole polarization and location. To elucidate the physical mechanism, transfer matrix method is introduced to calculate the spectral-hemispherical reflectance of the multilayer OLED structures. In addition, an attempt of using hyperbolic metamaterial in OLED has been made and resulted in 27% external quantum efficiency, due to the similar mechanism of wave interference as Fabry-Perot structure. The simulation and optimization methods and findings would facilitate the design of next generation, high-efficiency OLED devices.

  16. Soft holographic interference lithography microlens for enhanced organic light emitting diode light extraction

    SciTech Connect

    Park, Joong-Mok; Gan, Zhengqing; Leung, Wai Y.; Liu, Rui; Ye, Zhuo; Constant, Kristen; Shinar, Joseph; Shinar, Ruth; Ho, Kai-Ming

    2011-06-06

    Very uniform 2 {micro}m-pitch square microlens arrays ({micro}LAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by {approx}100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the {mu}LA is {approx}15 x 15 mm{sup 2}, i.e., much larger than the {approx}3 x 3 mm{sup 2} OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by {approx}100%. Similarly, a 19 x 25 mm{sup 2} {mu}LA enhances the EL extracted from a 3 x 3 array of 2 x 2 mm{sup 2} OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a {approx}140% enhancement.

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

    NASA Astrophysics Data System (ADS)

    Gentle, A. R.; Yambem, S. D.; Burn, P. L.; Meredith, P.; Smith, G. B.

    2016-06-01

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

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

    SciTech Connect

    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.

  19. Effects of 940 nm light-emitting diode (led) on sciatic nerve regeneration in rats.

    PubMed

    Serafim, Karla Guivernau Gaudens; Ramos, Solange de Paula; de Lima, Franciele Mendes; Carandina, Marcelo; Ferrari, Osny; Dias, Ivan Frederico Lupiano; Toginho Filho, Dari de Oliveira; Siqueira, Cláudia Patrícia Cardoso Martins

    2012-01-01

    The objective of the present study was to evaluate the effect of 940 nm wavelength light emitting diode (LED) phototherapy on nerve regeneration in rats. Forty male Wistar rats weighing approximately 300 g each were divided into four groups: control (C); control submitted to LED phototherapy (CLed); Sciatic Nerve Lesion without LED phototherapy (L); Sciatic Nerve Lesion with LED phototherapy (LLed). The lesion was caused by crushing the right sciatic nerve. A dose of 4 J/cm(2) was used for ten consecutive days beginning on the first postoperative day. Groups C and L were submitted to the same procedure as the LLed group, but the equipment was turned off. The LED phototherapy with 940 nm wavelength reduced the areas of edema, the number of mononuclear cells present in the inflammatory infiltration, and increased functional recovery scores at 7, 14 and 21 days. The results suggest that the use of phototherapy at 940 nm after nerve damage improves morphofunctional recovery and nerve regeneration. PMID:21547474

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

    PubMed

    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 D(3) 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 D(3) 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes

    SciTech Connect

    Price, J. S.; Giebink, N. C.

    2015-06-29

    Various exciton annihilation processes are known to impact the efficiency roll-off of organic light emitting diodes (OLEDs); however, isolating and quantifying their contribution in the presence of other factors such as changing charge balance continue to be a challenge for routine device characterization. Here, we analyze OLED electroluminescence resulting from a sinusoidal dither superimposed on the device bias and show that nonlinearity between recombination current and light output arising from annihilation mixes the quantum efficiency measured at different dither harmonics in a manner that depends uniquely on the type and magnitude of the annihilation process. We derive a series of analytical relations involving the DC and first harmonic external quantum efficiency that enable annihilation rates to be quantified through linear regression independent of changing charge balance and evaluate them for prototypical fluorescent and phosphorescent OLEDs based on the emitters 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran and platinum octaethylporphyrin, respectively. We go on to show that, in most cases, it is sufficient to calculate the needed quantum efficiency harmonics directly from derivatives of the DC light versus current curve, thus enabling this analysis to be conducted solely from standard light-current-voltage measurement data.

  3. Effects of 940 nm light-emitting diode (led) on sciatic nerve regeneration in rats.

    PubMed

    Serafim, Karla Guivernau Gaudens; Ramos, Solange de Paula; de Lima, Franciele Mendes; Carandina, Marcelo; Ferrari, Osny; Dias, Ivan Frederico Lupiano; Toginho Filho, Dari de Oliveira; Siqueira, Cláudia Patrícia Cardoso Martins

    2012-01-01

    The objective of the present study was to evaluate the effect of 940 nm wavelength light emitting diode (LED) phototherapy on nerve regeneration in rats. Forty male Wistar rats weighing approximately 300 g each were divided into four groups: control (C); control submitted to LED phototherapy (CLed); Sciatic Nerve Lesion without LED phototherapy (L); Sciatic Nerve Lesion with LED phototherapy (LLed). The lesion was caused by crushing the right sciatic nerve. A dose of 4 J/cm(2) was used for ten consecutive days beginning on the first postoperative day. Groups C and L were submitted to the same procedure as the LLed group, but the equipment was turned off. The LED phototherapy with 940 nm wavelength reduced the areas of edema, the number of mononuclear cells present in the inflammatory infiltration, and increased functional recovery scores at 7, 14 and 21 days. The results suggest that the use of phototherapy at 940 nm after nerve damage improves morphofunctional recovery and nerve regeneration.

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

    NASA Astrophysics Data System (ADS)

    Reddy, M. Siva Pratap; Park, Chinho

    2016-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We report the self-aligned passivation of a current distribution grid for an organic light emitting diode (OLED) anode using a pulsed Joule heating method to align the passivation layer accurately on the metal grid. This method involves passing an electric current through the grid to cure a polymer dielectric. Uncured polymer is then rinsed away, leaving a patterned dielectric layer that conforms to the shape of the grid lines. To enhance the accuracy of the alignment, heat conduction into the substrate and the transparent electrode is limited by using short current pulses instead of a constant current. Excellent alignment accuracy of the dielectric layer on printed metal grid lines has been achieved, with a typical 4-μm dielectric overhang. In addition to good accuracy, pulsed Joule heating significantly cuts down process time and energy consumption compared to heating with a constant current. The feasibility of using a printed current distribution grid and Joule heating was demonstrated in an OLED device.

  6. A hole modulator for InGaN/GaN light-emitting diodes

    SciTech Connect

    Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei E-mail: VOLKAN@stanfordalumni.org; Demir, Hilmi Volkan E-mail: VOLKAN@stanfordalumni.org

    2015-02-09

    The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm{sup 2} and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.

  7. Performance Enhancement of Organic Light-Emitting Diodes Using Electron-Injection Materials of Metal Carbonates

    NASA Astrophysics Data System (ADS)

    Shin, Jong-Yeol; Kim, Tae Wan; Kim, Gwi-Yeol; Lee, Su-Min; Shrestha, Bhanu; Hong, Jin-Woong

    2016-05-01

    Performance of organic light-emitting diodes was investigated depending on the electron-injection materials of metal carbonates (Li2CO3 and Cs2CO3 ); and number of layers. In order to improve the device efficiency, two types of devices were manufactured by using the hole-injection material (Teflon-amorphous fluoropolymer -AF) and electron-injection materials; one is a two-layer reference device ( ITO/Teflon-AF/Alq3/Al ) and the other is a three-layer device (ITO/Teflon-AF/Alq3/metal carbonate/Al). From the results of the efficiency for the devices with hole-injection layer and electron-injection layer, it was found that the electron-injection layer affects the electrical properties of the device more than the hole-injection layer. The external-quantum efficiency for the three-layer device with Li2CO3 and Cs2CO3 layer is improved by approximately six and eight times, respectively, compared with that of the two-layer reference device. It is thought that a use of electron-injection layer increases recombination rate of charge carriers by the active injection of electrons and the blocking of holes.

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

    NASA Astrophysics Data System (ADS)

    Zhu, Peifen

    2016-02-01

    The light extraction efficiency of top-emitting organic light-emitting diodes (OLEDs) is numerically investigated employing the finite-difference time-domain method. The periodic nanostructures formed by embedding the sphere arrays in polystyrene (PS) are placed on top of OLED to frustrate the total internal reflection at the interface between OLED and free space. These nanostructures serve as an intermediate medium to extract the light out of OLED devices. Efficiently coupling both evanescent waves and propagation waves into spheres and subsequently extracting these light waves out of the sphere is key to achieving high extraction efficiency. By tuning the thickness of PS layer, both of the in-coupling efficiency and out-coupling efficiency are optimized for achieving high light extraction efficiency. Thicker PS layer results in higher in-coupling efficiency in sphere while the thinner PS layer leads to higher out-coupling efficiency. Thus the maximum light extraction is a trade-off between the in-coupling efficiency and out-coupling efficiency. The study shows that light extraction efficiency of 89% can be achieved by embedding 0.90 μm TiO2 sphere in 0.30 μm PS layer with optimized in-coupling efficiency, out-coupling efficiency and cavity effect.

  9. Probability characteristics of electrical noise in heterojunction light-emitting diodes

    SciTech Connect

    Sergeev, V. A. Frolov, I. V.; Shirokov, A. A.; Shcherbatyuk, Yu. N.

    2011-12-15

    A hardware-software complex for measurements of the characteristics of electrical and optical noise in light-emitting diodes (LEDs) in the frequency range from 1 to 40 kHz is described. The electrical noise of several types of heterojunction-based LEDs are studied; these types include red-emission LEDs with AlInGaP/GaAs quantum wells and the green- and blue-emission LEDs with AlInGaN/SiC quantum wells are studied by the method of discrete samples. The spectra of all studied LEDs in the frequency range from 1 to 10 kHz have the form 1/f{sup {gamma}}. It is noteworthy that, for red-emission LEDs, the exponent {gamma} is significantly smaller than unity; this index is close to unity for the green- and blue-emission LEDs. The characteristic time of correlation of the noise of red-emission LEDs by several times exceeds the correlation times for the blue- and green-emission LEDs. It is shown that reduced functions of the amplitude distribution of the noise voltage are close to Gaussian functions with almost the same dispersion for all LED types.

  10. Silver nanowires for transparent conductive electrode to GaN-based light-emitting diodes

    SciTech Connect

    Jeong, Gyu-Jae; Lee, Jae-Hwan; Han, Sang-Hyun; Lee, Sung-Nam; Jin, Won-Yong; Kang, Jae-Wook

    2015-01-19

    Transparent, conductive, and uniform Ag nanowires (NWs) were introduced to improve the optical performance of GaN-based light-emitting diodes (LEDs) by a spin-coating technique. The Ag NWs acted as a current spreading layer, exhibiting high transmittance and low sheet resistance, and ultimately leading to high performance GaN-based LEDs with an ultra large size of 5 × 5 mm{sup 2}. Compared to the transmittance of conventional LEDs without Ag NWs, the relative transmittance of LEDs with Ag NWs was approximately 90% of the overall wavelength region. However, the electroluminescence (EL) intensity of LED with Ag NWs was much higher than that of conventional LEDs without Ag NWs for injection current above 45 mA. In addition, the EL full width at half maximum of LEDs with Ag NWs was much lower than that of conventional LEDs without Ag NWs. Based on these results, we believe that the enhanced optical performance of ultra large LEDs was due to an increase in the current spreading effect.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Dislocation-related trap levels in nitride-based light emitting diodes

    SciTech Connect

    Venturi, Giulia; Castaldini, Antonio; Cavallini, Anna

    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.

  13. The activation of directional stem cell motility by green light-emitting diode irradiation.

    PubMed

    Ong, Wei-Kee; Chen, How-Foo; Tsai, Cheng-Ting; Fu, Yun-Ju; Wong, Yi-Shan; Yen, Da-Jen; Chang, Tzu-Hao; Huang, Hsien-Da; Lee, Oscar Kuang-Sheng; Chien, Shu; Ho, Jennifer Hui-Chun

    2013-03-01

    Light-emitting diode (LED) irradiation is potentially a photostimulator to manipulate cell behavior by opsin-triggered phototransduction and thermal energy supply in living cells. Directional stem cell motility is critical for the efficiency and specificity of stem cells in tissue repair. We explored that green LED (530 nm) irradiation directed the human orbital fat stem cells (OFSCs) to migrate away from the LED light source through activation of extracellular signal-regulated kinases (ERK)/MAP kinase/p38 signaling pathway. ERK inhibitor selectively abrogated light-driven OFSC migration. Phosphorylation of these kinases as well as green LED irradiation-induced cell migration was facilitated by increasing adenosine triphosphate (ATP) production in OFSCs after green LED exposure, and which was thermal stress-independent mechanism. OFSCs, which are multi-potent mesenchymal stem cells isolated from human orbital fat tissue, constitutionally express three opsins, i.e. retinal pigment epithelium-derived rhodopsin homolog (RRH), encephalopsin (OPN3) and short-wave-sensitive opsin 1 (OPN1SW). However, only two non-visual opsins, i.e. RRH and OPN3, served as photoreceptors response to green LED irradiation-induced OFSC migration. In conclusion, stem cells are sensitive to green LED irradiation-induced directional cell migration through activation of ERK signaling pathway via a wavelength-dependent phototransduction.

  14. Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes

    SciTech Connect

    Zhu, Liping; Chen, Jiangshan; Ma, Dongge

    2015-11-07

    We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency, and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m{sup 2} luminance. The critical current density is as high as 210 mA/cm{sup 2}. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.

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

    SciTech Connect

    Fritz, I.J.; Klem, J.F.; Hafich, M.J.

    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.

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

    PubMed

    Reddy, M Siva Pratap; Park, Chinho

    2016-01-01

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

  17. High-brightness organic light-emitting diodes for optogenetic control of Drosophila locomotor behaviour.

    PubMed

    Morton, Andrew; Murawski, Caroline; Pulver, Stefan R; Gather, Malte C

    2016-01-01

    Organic light emitting diodes (OLEDs) are in widespread use in today's mobile phones and are likely to drive the next generation of large area displays and solid-state lighting. Here we show steps towards their utility as a platform technology for biophotonics, by demonstrating devices capable of optically controlling behaviour in live animals. Using devices with a pin OLED architecture, sufficient illumination intensity (0.3 mW.mm(-2)) to activate channelrhodopsins (ChRs) in vivo was reliably achieved at low operating voltages (5 V). In Drosophila melanogaster third instar larvae expressing ChR2(H134R) in motor neurons, we found that pulsed illumination from blue and green OLEDs triggered robust and reversible contractions in animals. This response was temporally coupled to the timing of OLED illumination. With blue OLED illumination, the initial rate and overall size of the behavioural response was strongest. Green OLEDs achieved roughly 70% of the response observed with blue OLEDs. Orange OLEDs did not produce contractions in larvae, in agreement with the spectral response of ChR2(H134R). The device configuration presented here could be modified to accommodate other small model organisms, cell cultures or tissue slices and the ability of OLEDs to provide patterned illumination and spectral tuning can further broaden their utility in optogenetics experiments. PMID:27484401

  18. Patternless light outcoupling enhancement method for top-emission organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Kim, Doo-Hoon; Lee, Ho-Nyeon

    2016-11-01

    An increase of 65% in the luminous flux of a top-emission organic light-emitting diode (TE-OLED) was obtained by fabricating a stacked N,N‧-bis(naphthalen-1-yl)-N,N‧-bis(phenyl)benzidine (NPB) (0.2 µm)/CaF2 (2.5 µm) light outcoupling layer on the TE-OLED. The high-refractive-index NPB layer extracted the trapped light energy in the TE-OLED for input into the light outcoupling layer and protected the top cathode of the TE-OLED from damage due to the CaF2 layer. The surface morphology of the CaF2 layer had an irregular shape consisting of randomly dispersed pyramids; the irregular structure scattered the waveguide mode energy into air. By combining the effects of the NPB and CaF2 layers, the external quantum efficiency of the TE-OLED was increased significantly. The light outcoupling layer can be fabricated using a thermal evaporation process without patterning and, hence, provides a practical solution for the enhancement of TE-OLED light outcoupling using a patternless fabrication process.

  19. Hybrid Tunnel Junction-Graphene Transparent Conductive Electrodes for Nitride Lateral Light Emitting Diodes.

    PubMed

    Wang, Liancheng; Cheng, Yan; Liu, Zhiqiang; Yi, Xiaoyan; Zhu, Hongwei; Wang, Guohong

    2016-01-20

    Graphene transparent conductive electrode (TCE) applications in nitride light emitting diodes (LEDs) are still limited by the large contact resistance and interface barrier between graphene and p-GaN. We propose a hybrid tunnel junction (TJ)-graphene TCE approach for nitride lateral LEDs theoretically and experimentally. Through simulation using commercial advanced physical models of semiconductor devices (APSYS), we found that low tunnel resistance can be achieved in the n(+)-GaN/u-InGaN/p(+)-GaN TJ, which has a lower tunneling barrier and an enhanced electric field due to the polarization effect. Graphene TCEs and hybrid graphene-TJ TCEs are then modeled. The designed hybrid TJ-graphene TCEs show sufficient current diffusion length (Ls), low introduced series resistance, and high transmittance. The assembled TJ LED with the triple-layer graphene (TLG) TCEs show comparable optoelectrical performance (3.99 V@20 mA, LOP = 10.8 mW) with the reference LED with ITO TCEs (3.36 V@20 mA, LOP = 12.6 mW). The experimental results further prove that the TJ-graphene structure can be successfully incorporated as TCEs for lateral nitride LEDs. PMID:26699194

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

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, D.; Wetzelaer, G. A. H.; Doumon, N. Y.; Blom, P. W. M.

    2016-03-01

    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 (AlOx) cathode. Usually, the high work function of aluminum (4.2 eV) imposes a high barrier for injecting electrons into the lowest unoccupied molecular orbital (LUMO) of the emissive polymer (2.9 eV below the vacuum level). By partially oxidizing aluminum, its work function is decreased, but not sufficiently low for efficient electron injection. Efficient injection is obtained by inserting an electron transport layer of poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT), which has its LUMO at 3.3 eV below vacuum, between the AlOx cathode and the emissive polymer. The intermediate F8BT layer not only serves as a hole-blocking layer but also provides an energetic staircase for electron injection from AlOx into the emissive layer. PLEDs with an AlOx cathode and F8BT interlayer exhibit a doubling of the efficiency as compared to conventional Ba/Al PLEDs, and still operate even after being kept in ambient atmosphere for one month without encapsulation.