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

    PubMed

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

    2017-09-28

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

  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 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.

  5. 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.

  6. 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.

  7. 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.

  8. Double Light-Emitting Diode

    NASA Technical Reports Server (NTRS)

    Johnson, R. L.; Hall, T. C.

    1985-01-01

    Two GaAs light-emitting diodes packaged as single unit offer greater reliability than conventional single-diode package. One diode is primary light source. If it fails, backup diode switched in. Each diode has separate power lead, so either or both switched on or off at same time.

  9. 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.

  10. 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

  11. 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…

  12. 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…

  13. 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…

  14. 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…

  15. 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.

  16. 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.

  17. Nitride light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Mukai, T.; Nagahama, S.; Iwasa, N.; Senoh, M.; Yamada, T.

    2001-08-01

    We review the progress in the field of InGaN-based light-emitting diodes (LEDs) and discuss the issue of threading dislocations and the luminous efficiency. The first candela-class blue LEDs have been developed. An InGaN layer was used to produce these LEDs instead of a GaN active layer. The quantum-well structure InGaN active layer dramatically improved the external quantum efficiency. There are a number of threading dislocations in nitride-based LEDs. InGaN LEDs, however, have quite high external quantum efficiency. With regard to this, it is thought that the fluctuation of the indium mole fraction is strongly related to the high external quantum efficiency. Considering the density of threading dislocations in the nitride-based LEDs, we discuss what can improve the external quantum efficiency of nitride-based LEDs.

  18. 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. Copyright © 2014 Elsevier Ltd. All rights reserved.

  19. Temperature compensation of light-emitting diodes

    NASA Technical Reports Server (NTRS)

    Deboo, G. J.; Burrous, C. N.

    1972-01-01

    Circuit which includes a thermistor-resistor combination to compensate for temperature fluctuations by supplying input voltage to light-emitting diode, maintains constant light output. Similar circuits can be used for temperature-induced variations in photodiode applications.

  20. Effect of oxygen plasma treatment on CdSe/CdZnS quantum-dot light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Cho, Nam-Kwang; Yu, Jae-woong; Kim, Young Heon; Kang, Seong Jun

    2014-03-01

    Red-light-emitting diodes (LEDs) were fabricated using CdSe/CdZnS quantum dots (QDs). During the device fabrication process, the oxygen plasma treatment of the indium-tin oxide (ITO) surface was performed to improve the interfacial contact between the ITO anode and the hole injection layer. The device showed red emission at 622 nm, which was consistent with the dimensions of the QDs (band gap: 1.99 eV). The luminance was 108.77 cd/m2 and the current density was 230.2 mA/cm2 at an operating voltage of 7 V, when the oxygen plasma treatment was performed on the ITO surface. The luminance showed 207% improvement compared with that of LEDs fabricated without oxygen plasma treatment. These results suggested that the oxygen plasma treatment of the ITO surface improved the contact between ITO and PEDOT:PSS, and that the light emitting intensity was markedly improved.

  1. 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)

  2. 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)

  3. 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.

  4. 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.

  5. Light-emitting Diodes: A Brief Review and Clinical Experience.

    PubMed

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

    2015-06-01

    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. 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. 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. 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.

  6. 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…

  7. 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…

  8. 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…

  9. 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…

  10. Bioinspired Hybrid White Light-Emitting Diodes.

    PubMed

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

    2015-10-07

    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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Safety of light emitting diodes in toys.

    PubMed

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

    2012-03-01

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

  12. 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.

  13. Low-cost electrochemical treatment of indium tin oxide anodes for high-efficiency organic light-emitting diodes

    SciTech Connect

    Hui Cheng, Chuan Shan Liang, Ze; Gang Wang, Li; Dong Gao, Guo; Zhou, Ting; Ming Bian, Ji; Min Luo, Ying; Tong Du, Guo

    2014-01-27

    We demonstrate a simple low-cost approach as an alternative to conventional O{sub 2} plasma treatment to modify the surface of indium tin oxide (ITO) anodes for use in organic light-emitting diodes. ITO is functionalized with F{sup −} ions by electrochemical treatment in dilute hydrofluoric acid. An electrode with a work function of 5.2 eV is achieved following fluorination. Using this electrode, a maximum external quantum efficiency of 26.0% (91 cd/A, 102 lm/W) is obtained, which is 12% higher than that of a device using the O{sub 2} plasma-treated ITO. Fluorination also increases the transparency in the near-infrared region.

  14. Light-Emitting Diodes: Solving Complex Problems

    NASA Astrophysics Data System (ADS)

    Planinšič, Gorazd; Etkina, Eugenia

    2015-05-01

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

  15. Assessment of the effectiveness of light-emitting diode and diode laser hybrid light sources to intensify dental bleaching treatment.

    PubMed

    Torres, Carlos Rocha Gomes; Barcellos, Daphne Câmara; Batista, Graziela Ribeiro; Borges, Alessandra Buhler; Cassiano, Karla Viana; Pucci, César Rogério

    2011-05-01

    To evaluate the effectiveness of the color change of hybrid light-emitting diode (LED) and low-intensity infrared diode laser devices for activating dental bleaching and to verify the occurrence of a color regression with time. A total of 180 specimens obtained from human premolars were immersed in a coffee solution for 15 days for darkening and then divided into eight experimental groups (n = 20 in each) as follows: G1, bleaching without light; G2, bleaching with halogen light; G3, bleaching with a blue LED (1000 mW/470 nm) and a laser device (120 mW/795 nm) simultaneously; G4, bleaching with an LED emitting blue light (1000 mW/470 nm); G5, bleaching with a blue LED (800 mW/470 nm) and a laser device (500 mW/830 nm) simultaneously; G6, bleaching with a blue LED device (800 mW); G7, bleaching with a green LED (600 mW/530 nm) and a laser device (120 mW/795 nm) simultaneously; and G8, bleaching with a green LED (600 mW). Three measurements were performed (at baseline and 14 days and 12 months after bleaching) using a Vita Easyshade spectrophotometer. The data were submitted to two-way ANOVA and a Tukey test. All groups showed significantly higher ΔE values than Group G1, with the exception of Group G8. Variations in the ΔE values at 14 days were significant when compared with those obtained at baseline and after 12 months. Light activation of the bleaching gel provided faster and more intense bleaching than use of the bleaching gel without light activation. Combinations of low-intensity diode lasers are ineffective as a bleaching gel activator. Color regression was observed after 12 months of storage.

  16. Flexible inorganic nanowire light-emitting diode.

    PubMed

    Nadarajah, Athavan; Word, Robert C; Meiss, Jan; Könenkamp, Rolf

    2008-02-01

    We report a highly flexible light-emitting device in which inorganic nanowires are the optically active components. The single-crystalline ZnO nanowires are grown at 80 degrees C on flexible polymer-based indium-tin-oxide-coated substrates and subsequently encapsulated in a minimal-thickness, void-filling polystyrene film. A reflective top contact serving as the anode in the diode structure is provided by a strongly doped p-type polymer and an evaporated Au film. The emission through the polymer side of this arrangement covers most of the visual region. Electrical and optical properties as well as performance limitations of the device structure are discussed.

  17. Glareless light-emitting diode lighting tube

    NASA Astrophysics Data System (ADS)

    Chang, Rong-Seng; Li, Tung-Yen; Jwo, Ko-Wen; Wang, Sha-Wei; Tsai, Jang-Zern

    2012-03-01

    We develop a novel light bar waveguide design to produce a glareless light-emitting diode (LED) lighting tube. We design optimal parameters, such as the gap y between the tube and the reflective surface, the relative distance x between the lens and the LED, and so on. Using these parameters, we fabricate an illumination system consisting of LED light bulb installed at both ends of lighting tube. The lighting tube is shaped the same as a traditional fluorescent lighting tube in order to replace traditional lighting tubes without the modification of the lighting stand. The LED lighting tube is glareless to the observer from the side view.

  18. 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.

  19. Atomically thin quantum light-emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  20. Quantum dots for light emitting diodes.

    PubMed

    Qasim, Khan; Lei, Wei; Li, Qing

    2013-05-01

    In this article we discuss the development and key advantages of quantum dot based light emitting diode (QD-LED) and other applications based on their color purity, stability, and solution processibility. Analysis of quantum dot based LEDs and the main challenges faced in this field, such as the QD luminescence quenching, QD charging in thin films, and external quantum efficiency are discussed in detail. The description about how different optical down-conversion and structures enabled researchers to overcome these challenges and to commercialize the products. The recent developments about how to overcome these difficulties have also been discussed in this article.

  1. 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

  2. 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.

  3. Beneficial effects of Red Light-Emitting Diode treatment in experimental model of acute lung injury induced by sepsis.

    PubMed

    Costa, Silvia Goes; Barioni, Éric Diego; Ignácio, Aline; Albuquerque, Juliana; Câmara, Niels Olsen Saraiva; Pavani, Christiane; Vitoretti, Luana Beatriz; Damazo, Amílcar Sabino; Farsky, Sandra Helena Poliselli; Lino-Dos-Santos-Franco, Adriana

    2017-10-04

    Sepsis is a severe disease with a high mortality index and it is responsible for the development of acute lung injury (ALI). We evaluated the effects of light-emitting diode (LED) on ALI induced by sepsis. Balb-c mice were injected with lipopolysaccharide or saline and then irradiated or not with red LED on their tracheas and lungs for 150 s, 2 and 6 h after LPS injections. The parameters were investigated 24 h after the LPS injections. Red LED treatment reduced neutrophil influx and the levels of interleukins 1β, 17 A and, tumor necrosis factor-α; in addition to enhanced levels of interferon γ in the bronchoalveolar fluid. Moreover, red LED treatment enhanced the RNAm levels of IL-10 and IFN-γ. It also partially reduced the elevated oxidative burst and enhanced apoptosis, but it did not alter the translocation of nuclear factor κB, the expression of toll-like receptor 4 (TLR4), as well as, oedema or mucus production in their lung tissues. Together, our data has shown the beneficial effects of short treatment with LED on ALI that are caused by gram negative bacterial infections. It is suggested that LED applications are an inexpensive and non-invasive additional treatment for sepsis.

  4. Color control of nanowire InGaN/GaN light emitting diodes by post-growth treatment.

    PubMed

    Zhang, Hezhi; Jacopin, Gwénolé; Neplokh, Vladimir; Largeau, Ludovic; Julien, François H; Kryliouk, Olga; Tchernycheva, Maria

    2015-11-20

    Core/shell InGaN/GaN nanowire light emitting diodes (LEDs) based on vertically standing single nanowires and nanowire arrays were fabricated and extensively characterized. The emission of single wire LEDs with the same conformal contact geometry as the array device exhibits the same broadening as the array LED electroluminescence, which proves an excellent wire-to-wire homogeneity. The electroluminescence spectra present two peaks corresponding to the m-plane InGaN quantum well (blue emission) and to an In-rich region at the m-plane-semipolar plane junction (green emission), in agreement with structural characterizations. Modification of the contact layout and a post-growth plasma treatment enable strongly suppressing the unwanted green electroluminescence while increasing the intensity in the blue spectral range for the same injected electrical power. Electron beam induced current mapping proves the inhibition of the electrical activity of the top part of the nanowire after plasma treatment. Inductively coupled plasma etching of the In-rich region permits one to completely remove the green emission for all injection currents, but loss of intensity in the blue spectral range is observed. Selectively contacting the m-plane and plasma treatment of the top part of the nanowire appear as a viable solution for controlling the color of core/shell nanowire LEDs with an inhomogeneous indium composition.

  5. 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.

  6. 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.

  7. 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).

  8. 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.

  9. 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

  10. Compact light-emitting diode optical fiber immobilized TiO2 reactor for photocatalytic water treatment.

    PubMed

    O'Neal Tugaoen, Heather; Garcia-Segura, Sergi; Hristovski, Kiril; Westerhoff, Paul

    2017-09-27

    A key barrier to implementing photocatalysis is delivering light to photocatalysts that are in contact with aqueous pollutants. Slurry photocatalyst systems suffer from poor light penetration and require post-treatment to separate the catalyst. The alternative is to deposit photocatalysts on fixed films and deliver light onto the surface or the backside of the attached catalysts. In this study, TiO2-coated quartz optical fibers were coupled to light emitting diodes (OF/LED) to improve in situ light delivery. Design factors and mechanisms studied for OF/LEDs in a flow-through reactor included: (i) the influence of number of LED sources coupled to fibers and (ii) the use of multiple optical fibers bundled to a single LED. The light delivery mechanism from the optical fibers into the TiO2 coatings is thoroughly discussed. To demonstrate influence of design variables, experiments were conducted in the reactor using the chlorinated pollutant para-chlorobenzoic acid (pCBA). From the degradation kinetics of pCBA, the quantum efficiencies (Φ) of oxidation and electrical energies per order (EEO) were determined. The use of TiO2 coated optical fiber bundles reduced the energy requirements to deliver photons and increased available surface area, which improved Φ and enhanced oxidative pollutant removal performance (EEO). Copyright © 2017 Elsevier B.V. All rights reserved.

  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. Improved cognitive function after transcranial, light-emitting diode treatments in chronic, traumatic brain injury: two case reports.

    PubMed

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

    2011-05-01

    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. 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. 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/cm(2); 13.3 J/cm(2) at scalp (estimated 0.4 J/cm(2) to cortex)]. 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. Transcranial LED may improve cognition, reduce costs in TBI treatment

  13. 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. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Proton displacement damage in light-emitting and laser diodes

    NASA Technical Reports Server (NTRS)

    Johnston, A. H.

    2000-01-01

    The effects of proton displacement damage on light-emitting diodes and laser diodes are discussed, comparing the radiation sensitivity of current technology devices with older devices for which data exists in the literature.

  15. 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.

  16. Biologically Inspired Organic Light-Emitting Diodes.

    PubMed

    Kim, Jae-Jun; Lee, Jaeho; Yang, Sung-Pyo; Kim, Ha Gon; Kweon, Hee-Seok; Yoo, Seunghyup; Jeong, Ki-Hun

    2016-05-11

    Many animal species employ highly conspicuous traits as courtship signals for successful mating. Fireflies utilize their bioluminescent light as visual courtship signals. In addition to efficient bioluminescent light emission, the structural components of the firefly lantern also contribute to the enhancement of conspicuous optical signaling. Recently, these firefly lantern ultrastructures have attracted much interest and inspired highly efficient light management approaches. Here we report on the unique optical function of the hierarchical ultrastructures found in a firefly (Pyrocoelia rufa) and their biological inspiration of highly efficient organic light-emitting diode (OLED) applications. The hierarchical structures are comprised of longitudinal nanostructures and asymmetric microstructures, which were successfully replicated using geometry-guided resist reflow, replica molding, and polydimethylsiloxane (PDMS) oxidation. The external quantum efficiency (EQE) of the bioinspired OLEDs was enhanced by up to 61%. The bioinspired OLEDs clearly showed side-enhanced super-Lambertian emission with a wide-viewing angle. The highly efficient light extraction and wide-angle illumination suggest how the hierarchical structures likely improve the recognition of firefly optical courtship signals over a wide-angle range. At the same time, the biologically inspired designs provide a new paradigm for designing functional optical surfaces for lighting or display applications.

  17. 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.

  18. Long wavelength nanowire light emitting diodes

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Pallab; Jahangir, Shafat; Stark, Ethan; Mandl, Martin; Schimpke, Tilman; Strassburg, Martin

    2014-02-01

    Green (λ~540 nm) - and red-emitting (λ~610 nm) InGaN/GaN disks-in-nanowires have been grown by RF plasma-assisted molecular beam epitaxy on (001) Silicon substrates. The growth of disks-in-nanowires heterostructures has been optimized and the nanowires have been passivated to achieve radiative efficiencies of 54% and 52% in the green and red InGaN disks, respectively. Radiative efficiency increases significantly (by ~10%) when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. Light emitting diodes on silicon, incorporating InGaN/GaN quantum disks as the active medium have been fabricated and the devices have been characterized. Quantum Confined Stark Effect (QCSE) blue-shift of 7nm and 15nm have been observed in the measured electroluminescence peak of the green and red LEDs respectively, from which polarization fields have been calculated in the disks to be 605kV/cm for green and 1.26MV/cm for red. For green and red LEDs, external quantum efficiency peaks at current densities of ~25A/cm2 and 12A/cm2, respectively. To improve light extraction efficiency, LED heterostructures have been transferred to Ag mirrors from the silicon growth substrate and preliminary device results have been demonstrated.

  19. Tandem Organic Light-Emitting Diodes.

    PubMed

    Fung, Man-Keung; Li, Yan-Qing; Liao, Liang-Sheng

    2016-12-01

    A tandem organic light-emitting diode (OLED) is an organic optoelectronic device that has two or more electroluminescence (EL) units connected electrically in series with unique intermediate connectors within the device. Researchers have studied this new OLED architecture with growing interest and have found that the current efficiency of a tandem OLED containing N EL units (N > 1) should be N times that of a conventional OLED containing only a single EL unit. Therefore, this new architecture is potentially useful for constructing high-efficiency, high-luminance, and long-lifetime OLED displays and organic solid-state lighting sources. In a tandem OLED, the intermediate connector plays a crucial role in determining the effectiveness of the stacked EL units. The interfaces in the connector control the inner charge generation and charge injection into the adjacent EL units. Meanwhile, the transparency and the thickness of the connector affect the light output of the device. Therefore, the intermediate connector should be made to meet both the electrical and optical requirements for achieving optimal performance. Here, recent advances in the research of the tandem OLEDs is discussed, with the main focus on material selection and interface studies in the intermediate connectors, as well as the optical design of the tandem OLEDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  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. Topical methyl-aminolevulinate photodynamic therapy using red light-emitting diode light for treatment of multiple actinic keratoses: A randomized, double-blind, placebo-controlled study.

    PubMed

    Pariser, David; Loss, Robert; Jarratt, Michael; Abramovits, William; Spencer, James; Geronemus, Roy; Bailin, Philip; Bruce, Suzanne

    2008-10-01

    The use of light-emitting diode light offers practical advantages in photodynamic therapy (PDT) with topical methyl-aminolevulinate (MAL) for management of actinic keratoses (AK). We sought to evaluate the efficacy of MAL PDT using red light-emitting diode light. We conducted a multicenter, double-blind, randomized study. A total of 49 patients with 363 AK lesions had 16.8% MAL cream applied under occlusion for 3 hours, and 47 patients with 360 AK lesions had vehicle cream similarly applied. The lesions were then illuminated (630 nm, light dose 37 J/cm2) with repeated treatment 1 week later. Complete lesion and patient (all lesions showing complete response) response rates were evaluated 3 months after last treatment. MAL PDT was superior (P<.0001) to vehicle PDT with respect to lesion complete response (86.2% vs 52.2%, odds ratio 6.9 [95% confidence interval 4.7-10.3]) and patient complete response (59.2% vs 14.9%, odds ratio 13.2 [95% confidence interval 4.1-43.1]). The study population may not be representative of all patients with AK. MAL PDT using red light-emitting diode light is an appropriate treatment alternative for multiple AK lesions.

  2. 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.

  3. 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)

  4. 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.

  5. 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)

  6. Organic light emitting diode with light extracting electrode

    DOEpatents

    Bhandari, Abhinav; Buhay, Harry

    2017-04-18

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

  7. Organic light emitting diode with surface modification layer

    DOEpatents

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

    2017-09-12

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

  8. 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

  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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. 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.

  11. 1,2-Ethanedithiol Treatment for AgIn5S8/ZnS Quantum Dot Light-Emitting Diodes with High Brightness.

    PubMed

    Ji, Changyin; Lu, Min; Wu, Hua; Zhang, Xiaoyu; Shen, Xinyu; Wang, Xiao; Zhang, Yu; Wang, Yiding; Yu, William W

    2017-03-08

    The surface organic ligands of the quantum dots (QDs) play important roles in the performance of QD electronic devices. Here, we fabricated low toxic AgIn5S8/ZnS QDs light-emitting diodes (QD-LEDs) and greatly enhanced the device efficiency through surface ligand exchange treatments. The oleic acid-capped QDs were replaced with a shorter ligand 1,2-ethanedithiol, which was proved by the Fourier transform infrared spectrum measurement. The treated QD films became more compact with higher film mobility and shorter film photoluminescence lifetime. The more conductive QD films fabricated LEDs showed an external quantum efficiency over 1.52%.

  12. Effects of substrate bias power on the surface of ITO electrodes during O2/CF4 plasma treatment and the resulting performance of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Han, D. M.; Lee, J. H.; Jeong, K. H.; Lee, J. G.

    2010-08-01

    During surface treatment using O2/CF4 plasma chemistry, the bias power applied to the indium-tin-oxide(ITO) substrate significantly degrades the electrical and optical performance of the organic light emitting diode (OLED) formed on the ITO electrode as a result of the formation of CFx polymer, In-Sn-F compounds, and structural defects. Application of bias power to the substrate effectively increases the sheath potential over the substrate and thus the flux of CFx + ion created in the O2/CF4 plasma, which leads to the production of CFx polymers as well as structural defects.

  13. 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.

  14. 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.

  15. 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…

  16. 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…

  17. 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.

  18. 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.

  19. Degradation of light emitting diodes: a proposed methodology

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Best, S. W.

    1980-10-01

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

  1. Si-based blue light emitting diode

    NASA Astrophysics Data System (ADS)

    Namavar, Fereydoon

    1994-05-01

    Phase 1 results demonstrated for the first time a strong, stable blue-green emission from C-implanted red-emitting porous silicon. The objective of Phase 1 was to obtain blue-green emission from porous Si structure either by increasing the bandgap of the substrate by growth of Si-C random alloys prior to forming nanostructures with quantum confined properties, or by increasing the confinement energy of red-emitting Si nanostructures. Porous structures fabricated from group 4 alloys epitaxially grown by chemical vapor deposition (CVD) resulted in an enhancement in light emission of about one order of magnitude after incorporation of a very small amount of carbon in the epitaxial grown films. Strong blue-green light emission was observed by the naked eye from C-implanted and annealed porous Si. Using AlGaAs as a reference, we observed that the intensity of blue-green emission was one order of magnitude higher than that of the original red-emitting porous Si. Catholuminescence measurements of our samples performed at the University of Colorado show blue emission at 1.80 eV and 2.80 eV. Fourier transform infrared (FTIR) spectra of a blue-green emitting porous structure shows an IR absorption line identical to that of SiC and electron diffraction studies clearly show reflections corresponding to beta-SiC. Phase 1 results indicate that blue-green light is from SiC nanostructures with quantum confined properties. This material may be used to fabricate blue light-emitting Si-based devices which can be easily integrated into Si technology.

  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. Light emitting diode absorption spectroscopy for combustible gas monitoring

    NASA Astrophysics Data System (ADS)

    Fanchenko, S. S.; Baranov, A. M.; Savkin, A. V.; Samotaev, N. N.

    2016-10-01

    A new generation of the infrared light-emitting diodes (LEDs) and photodiodes (PDs) was used to construct an open path non-dispersive infrared (NDIR) methane analyzer. It was shown earlier that its characteristics are suitable for usual alarm systems, but new measurements have shown that cross sensitivity to other alkanes is rather high.

  4. 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…

  5. Polymer Light-Emitting Diode (PLED) Process Development

    DTIC Science & Technology

    2003-12-01

    conclusions and recommendations for Phase II of the Flexible Display Program. 15. SUBJECT TERMS LIGHT EMITTING DIODES LIQUID CRYSTAL DISPLAY SYSTEMS...space for Phase I and II confined by backplane complexity and substrate form...12 Figure 6. Semi automated I-V curve measurement setup consisting of Keithley power supply, computer and

  6. A multi-source portable light emitting diode spectrofluorometer

    USDA-ARS?s Scientific Manuscript database

    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...

  7. 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.

  8. 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…

  9. 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.

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

    PubMed

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

    2009-06-08

    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.

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

    PubMed Central

    Chen, Lei; Lin, Chun-Che; Yeh, Chiao-Wen; Liu, Ru-Shi

    2010-01-01

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

  12. Improvement of device performance of polymer organic light-emitting diodes on smooth transparent sheet with graphene films synthesized by plasma treatment

    NASA Astrophysics Data System (ADS)

    Okigawa, Yuki; Mizutani, Wataru; Suzuki, Kenkichi; Ishihara, Masatou; Yamada, Takatoshi; Hasegawa, Masataka

    2015-09-01

    Because graphene films have one-atom thickness, the morphology of the transparent sheets could have a greater effect on the performance of organic light-emitting diode (OLED) devices with graphene films than on that with indium tin oxide (ITO). In this study, we have evaluated the polymer OLED devices with graphene films synthesized by plasma treatment on poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) sheets having high flatness. The results imply that the surface roughness of the transparent sheets predominantly affects the luminescence of polymer OLED devices with graphene films. The suppression of leakage current and a luminescence higher than 8000 cd/m2 at 15 V were attained for the devices on the transparent sheet with higher flatness in spite of the presence of large sharp spikes.

  13. Micrometer- and Nanometer-Sized Polymeric Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Granstrom, Magnus; Berggren, Magnus; Inganas, Olle

    1995-03-01

    A method for the fabrication of micrometer- and submicrometer-sized polymeric light-emitting diodes is presented. Such diodes have a variety of applications. Light sources of dimensions around 100 nanometers are required for subwavelength, near-field optical microscopy. Another possible application is patterning on the micrometer and nanometer scale. The diodes have been made in the form of a sandwich structure, with the conductive polymer poly(3,4-ethylene-dioxythiophene) polymerized in the pores of commercially available microfiltration membranes defining the hole-injecting contacts, poly[3-(4-octylphenyl)-2,2'-bithiophene] as the light-emitting layer, and a thin film of calcium-aluminum as the electron injector.

  14. Photodynamic Therapy for Actinic Keratoses: A Randomized Prospective Non-sponsored Cost-effectiveness Study of Daylight-mediated Treatment Compared with Light-emitting Diode Treatment.

    PubMed

    Neittaanmäki-Perttu, Noora; Grönroos, Mari; Karppinen, Toni; Snellman, Erna; Rissanen, Pekka

    2016-02-01

    Daylight-mediated photodynamic therapy (DL-PDT) is considered as effective as conventional PDT using artificial light (light-emitting diode (LED)-PDT) for treatment of actinic keratoses (AK). This randomized prospective non-sponsored study assessed the cost-effectiveness of DL-PDT compared with LED-PDT. Seventy patients with 210 AKs were randomized to DL-PDT or LED-PDT groups. Effectiveness was assessed at 6 months. The costs included societal costs and private costs, including the time patients spent in treatment. Results are presented as incremental cost-effectiveness ratio (ICER). The total costs per patient were significantly lower for DL-PDT (€132) compared with LED-PDT (€170), giving a cost saving of €38 (p = 0.022). The estimated probabilities for patients' complete response were 0.429 for DL-PDT and 0.686 for LED-PDT; a difference in probability of being healed of 0.257. ICER showed a monetary gain of €147 per unit of effectiveness lost. DL-PDT is less costly and less effective than LED-PDT. In terms of cost-effectiveness analysis, DL-PDT provides lower value for money compared with LED-PDT.

  15. 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

  16. 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.

  17. 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.

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

    SciTech Connect

    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").

  19. Space-charge-limited current in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Torricelli, Fabrizio; Zappa, Dario; Colalongo, Luigi

    2010-03-01

    A physically based mathematical model for the dc current of single-carrier organic light emitting diodes is presented. The model accounts for the most important physical quantities that influence the carrier mobility and thus the device current itself: temperature, charge carrier concentration, and electric field. It is rigorously developed basing on the variable range hopping transport theory and extends the pioneering work of Mark and Helfrich [J. Appl. Phys. 33, 205 (1962)] to large electric fields typical of light emitting diodes. It was validated on experimental data collected from devices of different materials in a wide range of operating conditions. Thanks to the effective electric field approach, the mathematical expression is simple, accurate and suitable for CAD applications.

  20. 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

    2014-09-10

    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.

  1. 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.

  2. Ultraviolet Light Emitting Diode Use in Advanced Oxidation Processes

    DTIC Science & Technology

    2014-03-27

    as they are durable; compact; can be powered by low voltage, direct current from solar cells or batteries; and do not contain other hazardous...into hydroxyl radicals, is one way to potentially treat the contaminated water. Traditionally UV light sources for water disinfection have been low...or medium pressure mercury lamps, but UV light emitting diodes (LEDs) have the capacity to be used for water disinfection also. Traditional mercury

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

  4. Light-Emitting Diodes - 2nd Edition

    NASA Astrophysics Data System (ADS)

    Schubert, E. Fred

    2006-06-01

    Revised and fully up-dated, the second edition of this graduate textbook offers a comprehensive explanation of the technology and physics of LEDs such as infrared, visible-spectrum, ultraviolet, and white LEDs made from III-V semiconductors. Elementary properties such as electrical and optical characteristics are reviewed, followed by the analysis of advanced device structures. With nine additional chapters, the treatment of LEDs has been vastly expanded, including new material on device packaging, reflectors, UV LEDs, III-V nitride materials, solid-state sources for illumination applications, and junction temperature. Radiative and non-radiative recombination dynamics, methods for improving light extraction, high-efficiency and high-power device designs, white-light emitters with wavelength-converting phosphor materials, optical reflectors, and spontaneous recombination in resonant-cavity structures are discussed in detail. With exercises, solutions, and illustrative examples, this textbook will be of interest to scientists and engineers working on LEDs and graduate students in electrical engineering, applied physics, and materials science. Contains 30 exercises, over 20 of which have solutions provided in the book Many illustrative examples Contains the same broad perspective as the first edition but is significantly expanded with new material on device packaging, reflectors, UV LEDs, solid-state sources for illumination applications, junction temperature, and III-V nitride materials

  5. Characterization of an Optical Device with an Array of Blue Light Emitting Diodes LEDS for Treatment of Neonatal Jaundice.

    NASA Astrophysics Data System (ADS)

    Sebbe, Priscilla Fróes; Villaverde, Antonio G. J. Balbin; Nicolau, Renata Amadei; Barbosa, Ana Maria; Veissid, Nelson

    2008-04-01

    Phototherapy is a treatment that consists in irradiating a patient with light of high intensity, which promotes beneficial photochemical transformations in the irradiated area. The phototherapy for neonates is applied to break down the bilirubin, an organic pigment that is a sub product of the erythrocytes degradation, and to increase its excretion by the organism. Neonates should be irradiated with light of wavelength that the bilirubin can absorb, and with spectral irradiances between 4 and 16 μW/cm2/nm. The efficiency of the treatment depends on the irradiance and the area of the body that is irradiated. A convenient source of light for treatment of neonatal jaundice is the blue Light Emitter Diode (LED), emitting in the range of 400 to 500 nm, with power of the order of 10-150 mW. Some of the advantages for using LEDS are: low cost, operating long lifetime (over 100,000 hours), narrow emission linewith, low voltage power supply requirement and low heating. The aim of this work was to build and characterize a device for phototherapy treatment of neonatal jaundice. This consists of a blanket with 88 blue LEDs (emission peak at 472 nm), arranged in an 8×11 matrix, all connected in parallel and powered by a 5V-2A power supply. The device was characterized by using a spectroradiometer USB2000 (Ocean Optics Inc, USA), with a sensitivity range of 339-1019 nm. For determination of light spatial uniformity was used a calibrated photovoltaic sensor for measuring light intensity and mapping of the light intensity spatial distribution. Results indicate that our device shows a uniform spatial distribution for distances from the blanket larger than 10 cm, with a maximum of irradiance at such a distance. This device presenting a large and uniform area of irradiation, efficient wavelength emission and high irradiance seems to be promising for neonates' phototherapy treatment.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Broadband Light-Emitting Diodes with One-Dimensional Photonic Crystal Layer

    NASA Astrophysics Data System (ADS)

    Chiang, Jung-Sheng; Tseng, Chun-Lung; Chung, Ken-Lin; Lin, Yen-Sheng; Sun, Nai-Hsiang

    2016-01-01

    In this article, a broadband gallium-nitride-based light-emitting diode with a one-dimensional photonic crystal layer is investigated. The broadband light-emitting diode using the proposed backside reflector has high reflectance (>95%) over a 270-nm bandwidth in visible light at an arbitrary incidence angle. A broadband light-emitting diode of high output power due to the high reflectivity is achieved. Also reported are the results for light-emitting diodes by the transistor outline can (TO-can) package. The proposed light-emitting diodes possess broadband high reflected spectra, high output power for light extraction, and a good view angle.

  11. 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.

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

    PubMed

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

    2014-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Argyraki, Aikaterini; Markvart, Merete; Bjørndal, Lars; Bjarnsholt, Thomas; Petersen, Paul Michael

    2017-06-01

    The objective of this study was to test the inactivation efficiency of two different light-based treatments, namely ultraviolet B (UVB) and ultraviolet C (UVC) irradiation, on Pseudomonas aeruginosa biofilms at different growth stages (24, 48, and 72 h grown). In our experiments, a type of AlGaN light-emitting diodes (LEDs) was used to deliver UV irradiation on the biofilms. The effectiveness of the UVB at 296 nm and UVC at 266 nm irradiations was quantified by counting colony-forming units. The survival of less mature biofilms (24 h grown) was studied as a function of UV-radiant exposure. All treatments were performed on three different biological replicates to test reproducibility. It was shown that UVB irradiation was significantly more effective than UVC irradiation in inactivating P. aeruginosa biofilms. UVC irradiation induced insignificant inactivation on mature biofilms. The fact that the UVB at 296 nm exists in daylight and has such disinfection ability on biofilms provides perspectives for the treatment of infectious diseases.

  14. 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).

  15. Study of ethanolamine surface treatment on the metal-oxide electron transport layer in inverted InP quantum dot light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Jang, Ilwan; Kim, Jiwan; Park, Chang Jun; Ippen, Christian; Greco, Tonino; Oh, Min Suk; Lee, Jeongno; Kim, Won Keun; Wedel, Armin; Han, Chul Jong; Park, Sung Kyu

    2015-11-01

    The present work shows the effect of ethanolamine surface treatment on inverted InP quantum dot light-emitting diodes (QD-LEDs) with inorganic metal oxide layers. In the inverted structure of ITO/ZnO/InP QDs/CBP/MoO3/Al, a sol-gel derived ZnO film was used as an electron transport layer (ETL) and MoO3 was used as a hole injection layer (HIL). First, ethanolamine was treated as a surface modifier on top of the ZnO electron transport layer. The optical performance of the QD-LED device was improved by the ethanolamine surface treatment. Second, low temperature annealing (<200°C) was performed on the ZnO sol-gel electron transport layer, followed by an investigation of the effect of the ZnO annealing temperature. The efficiency of the inverted QD-LEDs was significantly enhanced (more than 3-fold) by optimization of the ZnO annealing temperature. [Figure not available: see fulltext.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1999-01-01

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

  18. Light emitting diodes as a plant lighting source

    SciTech Connect

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

    1994-12-31

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

  19. Ultraviolet nanoimprinted polymer nanostructure for organic light emitting diode application

    NASA Astrophysics Data System (ADS)

    Jeon, Sohee; Kang, Jae-Wook; Park, Hyung-Dol; Kim, Jang-Joo; Youn, Jae R.; Shim, Jongyoup; Jeong, Jun-ho; Choi, Dae-Geun; Kim, Ki-Don; Altun, Ali Ozhan; Kim, Se-Heon; Lee, Yong-Hee

    2008-06-01

    Light extraction efficiency of a conventional organic light emitting diode (OLED) remains limited to approximately 20% as most of the emission is trapped in the waveguide and glass modes. An etchless simple method was developed to fabricate two-dimensional nanostructures on glass substrate directly by using ultraviolet (UV) curable polymer resin and UV nanoimprint lithography in order to improve output coupling efficiency of OLEDs. The enhancement of the light extraction was predicted by the three-dimensional finite difference time domain method. OLEDs integrated on nanoimprinted substrates enhanced electroluminance intensity by up to 50% compared to the conventional device.

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

    PubMed

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

    2012-03-02

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

  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. 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.

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

    PubMed

    O'Toole, Martina; Diamond, Dermot

    2008-04-07

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

  4. 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.

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

    PubMed

    Nishi, Kazuki; Matsuda, Yuichi

    2017-01-23

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

  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. PMID:27879829

  7. Enhancing the electroluminescence efficiency of Si NC/SiO2 superlattice-based light-emitting diodes through hydrogen ion beam treatment.

    PubMed

    Fu, Sheng-Wen; Chen, Hui-Ju; Wu, Hsuan-Ta; Chen, Shao-Ping; Shih, Chuan-Feng

    2016-04-07

    This paper presents a novel method for enhancing the electroluminescence (EL) efficiency of ten-period silicon-rich oxide (SRO)/SiO2 superlattice-based light-emitting diodes (LEDs). A hydrogen ion beam (HIB) was used to irradiate each SRO layer of the superlattices to increase the interfacial roughness on the nanoscale and the density of the Si nanocrystals (Si NCs). Fowler-Nordheim (F-N) tunneling was the major mechanism for injecting the carriers into the Si NCs. The barrier height of the F-N tunneling was lowered by forming a nano-roughened interface and the nonradiative Pb centers were passivated through the HIB treatment. Additionally, the reflectance of the LEDs was lowered because of the nano-roughened interface. These factors considerably increased the slope efficiency of EL and the maximum output power of the LEDs. The lighting efficiency increased by an order of magnitude, and the turn-on voltage decreased considerably. This study established an efficient approach for obtaining bright Si NC/SiO2 superlattice-based LEDs.

  8. Enhancing the electroluminescence efficiency of Si NC/SiO2 superlattice-based light-emitting diodes through hydrogen ion beam treatment

    NASA Astrophysics Data System (ADS)

    Fu, Sheng-Wen; Chen, Hui-Ju; Wu, Hsuan-Ta; Chen, Shao-Ping; Shih, Chuan-Feng

    2016-03-01

    This paper presents a novel method for enhancing the electroluminescence (EL) efficiency of ten-period silicon-rich oxide (SRO)/SiO2 superlattice-based light-emitting diodes (LEDs). A hydrogen ion beam (HIB) was used to irradiate each SRO layer of the superlattices to increase the interfacial roughness on the nanoscale and the density of the Si nanocrystals (Si NCs). Fowler-Nordheim (F-N) tunneling was the major mechanism for injecting the carriers into the Si NCs. The barrier height of the F-N tunneling was lowered by forming a nano-roughened interface and the nonradiative Pb centers were passivated through the HIB treatment. Additionally, the reflectance of the LEDs was lowered because of the nano-roughened interface. These factors considerably increased the slope efficiency of EL and the maximum output power of the LEDs. The lighting efficiency increased by an order of magnitude, and the turn-on voltage decreased considerably. This study established an efficient approach for obtaining bright Si NC/SiO2 superlattice-based LEDs.

  9. 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.

  10. Broadband mid-infrared superlattice light-emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  11. 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.

  12. 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

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

    NASA Astrophysics Data System (ADS)

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

    1998-01-01

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

  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. Improved UV Nitride Light Emitting Diode With Engineered Spontaneous and Piezoelectric Charges

    DTIC Science & Technology

    2008-12-01

    Shen, Y. C., Chen, G., Watanabe, S., Goetz, W., and Krames, M. R., 2007, Blue- emitting InGaN –GaN double-heterostructure light- emitting diodes...IMPROVED UV NITRIDE LIGHT EMITTING DIODE WITH ENGINEERED SPONTANEOUS AND PIEZOELECTRIC CHARGES Paul Hongen Shen, Meredith L. Reed, Eric D...nitride light emitting diodes have an n-type down structure with Ga polarity. In such a device, the active layer is grown on top of the n-cladding

  16. A controlled trial of the Litebook light-emitting diode (LED) light therapy device for treatment of Seasonal Affective Disorder (SAD).

    PubMed

    Desan, Paul H; Weinstein, Andrea J; Michalak, Erin E; Tam, Edwin M; Meesters, Ybe; Ruiter, Martine J; Horn, Edward; Telner, John; Iskandar, Hani; Boivin, Diane B; Lam, Raymond W

    2007-08-07

    Recent research has emphasized that the human circadian rhythm system is differentially sensitive to short wavelength light. Light treatment devices using efficient light-emitting diodes (LEDs) whose output is relatively concentrated in short wavelengths may enable a more convenient effective therapy for Seasonal Affective Disorder (SAD). The efficacy of a LED light therapy device in the treatment of SAD was tested in a randomized, double-blind, placebo-controlled, multi-center trial. Participants aged 18 to 65 with SAD (DSM-IV major depression with seasonal pattern) were seen at Baseline and Randomization visits separated by 1 week, and after 1, 2, 3 and 4 weeks of treatment. Hamilton Depression Rating Scale scores (SIGH-SAD) were obtained at each visit. Participants with SIGH-SAD of 20 or greater at Baseline and Randomization visits were randomized to active or control treatment: exposure to the Litebook LED treatment device (The Litebook Company Ltd., Alberta, Canada) which delivers 1,350 lux white light (with spectral emission peaks at 464 nm and 564 nm) at a distance of 20 inches or to an inactivated negative ion generator at a distance of 20 inches, for 30 minutes a day upon awakening and prior to 8 A.M. Of the 26 participants randomized, 23 completed the trial. Mean group SIGH-SAD scores did not differ significantly at randomization. At trial end, the proportions of participants in remission (SIGH-SAD less than 9) were significantly greater (Fisher's exact test), and SIGH-SAD scores, as percent individual score at randomization, were significantly lower (t-test), with active treatment than with control, both in an intent-to-treat analysis and an observed cases analysis. A longitudinal repeated measures ANOVA analysis of SIGH-SAD scores also indicated a significant interaction of time and treatment, showing superiority of the Litebook over the placebo condition. The results of this pilot study support the hypothesis that light therapy with the Litebook is an

  17. 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

    2014-03-07

    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.

  18. Magnetoresistance in organic light-emitting diode structures under illumination

    NASA Astrophysics Data System (ADS)

    Desai, P.; Shakya, P.; Kreouzis, T.; Gillin, W. P.

    2007-12-01

    We have investigated the effect of illumination on the organic magnetoresistance (OMR) in organic light-emitting diode (OLED) structures. The results show that it is possible to obtain OMR at voltages below “turn-on,” where no OMR was visible for devices operated in the dark. The photoinduced OMR has a field dependence that is identical to that obtained for OLEDs containing very thin layers, where triplet dissociation at the cathode was a major component of the OMR. At voltages around the open circuit voltage, where the current through the device is very small, very large OMRs of ˜300% can be observed. The results support our proposed model for organic magnetoresistance as being caused in part by the interaction of free carriers with triplet excitons within the device. The results suggest that the introduction of a low field magnet could provide a simple means of improving the efficiency of organic photovoltaic cells.

  19. Organic light-emitting diodes having carbon nanotube anodes.

    PubMed

    Li, Jianfeng; Hu, Liangbing; Wang, Lian; Zhou, Yangxin; Grüner, George; Marks, Tobin J

    2006-11-01

    Single-walled carbon nanotube (SWNT) films on flexible PET (polyethyleneterephthalate) substrates are used as transparent, flexible anodes for organic light-emitting diodes (OLEDs). For polymer-based OLEDs having the structure: SWNT/PEDOT-PSS:MeOH/TFB (poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine)) + TPD-Si(2) (4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl) /BT (poly(9,9-dioctylfluorene-co-benzothiadiazole))/CsF/Al, a maximum light output of 3500 cd/m(2) and a current efficiency of 1.6 cd/A have been achieved. The device operational lifetime is comparable to that of devices with Sn-doped In(2)O(3) (ITO)/PET anodes. The advantages of this novel type of anode over conventional ITO are discussed.

  20. 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.

  1. 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.

  2. 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

  3. High efficiency quantum dot light emitting diodes from positive aging.

    PubMed

    Acharya, Krishna P; Titov, Alexandre; Hyvonen, Jake; Wang, Chenggong; Tokarz, Jean; Holloway, Paul H

    2017-10-05

    Colloidal quantum dot-polymer hybrid light emitting diodes (QLEDs) that exhibit external quantum efficiencies >12% for all three primary colors (21% from green) have been demonstrated. These high efficiencies result in part from a positive aging effect reported here for the first time, where positive aging means the efficiency of the QLED increased with time. We have achieved 470 h operational life time (T90) at 2550 nits for red QLEDs. At longer times, negative aging phenomena lead to lower luminance and limit the lifetime of the QLEDs. It is concluded that we have reasonable control over the efficiency of QLEDs. The next challenge is to achieve lifetimes sufficiently long for all three primary colors for applications such as in television and illumination.

  4. 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.

  5. High illuminance light-emitting diode headlight for medical applications

    NASA Astrophysics Data System (ADS)

    Lee, Ui-Hyung; Jung, Jae-hun; Park, Seung Hyun; Lee, Gye Seon; Ju, Young-Gu

    2010-11-01

    High brightness light emitting diodes have been used to develop high illuminance headlight for medical applications. It provides various advantages such as high illuminance, long life time, reduced infra red light, extended operation time with battery and light weight. A 3 W LED was employed to achieve the high performance medical headlight. The optical design includes two lenses for high energy transmission and high illuminance. The LED headlight shows 42,000 lux with spot diameter of 80 mm at the distance of 300 mm. For comparison purpose, 5 W LED was also used to obtain the high illuminance headlight. However, the large divergence angle and large spot size of the 5 W LED limits the illuminance to 31,000 lux with increased burden on heat dissipation. The thermal images of the heat sinks indicate that the temperature of the headlight using a 3 W LED is below 50 degree C, which is suitable for medical applications.

  6. LIGHT-EMITTING DIODE TECHNOLOGY IMPROVES INSECT TRAPPING

    PubMed Central

    GILLEN, JONATHON I.; MUNSTERMANN, LEONARD E.

    2008-01-01

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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2000-02-01

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

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Römer, Friedhard; Witzigmann, Bernd

    2015-01-01

    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.

  12. Indoor localization system utilizing two visible light emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    Indoor positioning or localization based on visible light communications (VLC) is an emerging technology with wide applications. In conventional localization schemes, the trilateration technique is widely used with at least three separate lighting sources to determine the user's location. An indoor VLC positioning scheme based on the optical power distributions of only two light emitting diodes (LEDs) is reported for different environments. We have used two received signal strength indications to determine the user's position based on the LEDs configuration offering less complexity. We propose comprehensive mathematical models for the VLC localization system considering the noise and its impact on the user's location, and numerically evaluated it over a range of signal-to-noise ratios (SNRs). In addition, it is compared to the results with the exiting trilateration technique. The performance of the proposed system is evaluated with a reported accuracy of <20 cm for an SNR of >13 dB.

  13. Kinetics of transient electroluminescence in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

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

    2008-08-01

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

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

    PubMed

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

    2012-11-23

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

  15. Light extraction by Lambertian sources from light emitting diodes

    NASA Astrophysics Data System (ADS)

    Nagel, James R.

    2013-03-01

    Internal back-and-forth propagation of photons within a light emitting diode (LED) will naturally tend towards a Lambertian intensity profile when surface texturing is sufficiently rough. Novel designs in light extraction efficiency (LEE) can therefore benefit by optimizing under this expectation. This paper develops a framework for calculating LEE from a planar LED structure with textured surface features under the assumption of Lambertian intensity within the substrate. The method can estimate the total LEE value when given a substrate width w, an attenuation constant α, and the transmittance function T(θ,Φ) through the top interface. We demonstrate our theory on a pyramidal surface texture over a GaSb substrate at 4.5 μm wavelength by computing the expected LEE as a function of w.

  16. Origin of electrophosphorescence from a doped polymer light emitting diode

    NASA Astrophysics Data System (ADS)

    Lane, P. A.; Palilis, L. C.; O'brien, D. F.; Giebeler, C.; Cadby, A. J.; Lidzey, D. G.; Campbell, A. J.; Blau, W.; Bradley, D. D.

    2001-06-01

    The origin of electrophosphorescence from a doped polymer light emitting diode (LED) has been investigated. A luminescent polymer host, poly(9,9-dioctylfluorene) (PFO), was doped with a red phosphorescent dye, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (PtOEP). The maximum external quantum efficiency of 3.5% was obtained at a concentration of 4% PtOEP by weight. Energy transfer mechanisms between PFO and PtOEP were studied by absorption, photoluminescence, and photoinduced absorption spectroscopy. Even though electroluminescence spectra were dominated by PtOEP at a concentration of only 0.2 wt % PtOEP, Förster transfer of singlet excitons was weak and there was no evidence for Dexter transfer of triplet excitons. We conclude that the dominant emission mechanism in doped LED's is charge trapping followed by recombination on PtOEP molecules.

  17. Origin of electrophosphorescence from a doped polymer light emitting diode

    SciTech Connect

    Lane, P. A.; Palilis, L. C.; O {close_quote}Brien, D. F.; Giebeler, C.; Cadby, A. J.; Lidzey, D. G.; Campbell, A. J.; Blau, W.; Bradley, D. D. C.

    2001-06-15

    The origin of electrophosphorescence from a doped polymer light emitting diode (LED) has been investigated. A luminescent polymer host, poly(9,9-dioctylfluorene) (PFO), was doped with a red phosphorescent dye, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (PtOEP). The maximum external quantum efficiency of 3.5% was obtained at a concentration of 4% PtOEP by weight. Energy transfer mechanisms between PFO and PtOEP were studied by absorption, photoluminescence, and photoinduced absorption spectroscopy. Even though electroluminescence spectra were dominated by PtOEP at a concentration of only 0.2 wt% PtOEP, Forster transfer of singlet excitons was weak and there was no evidence for Dexter transfer of triplet excitons. We conclude that the dominant emission mechanism in doped LED{close_quote}s is charge trapping followed by recombination on PtOEP molecules.

  18. Inorganic Halide Perovskites for Efficient Light-Emitting Diodes.

    PubMed

    Yantara, Natalia; Bhaumik, Saikat; Yan, Fei; Sabba, Dharani; Dewi, Herlina A; Mathews, Nripan; Boix, Pablo P; Demir, Hilmi Volkan; Mhaisalkar, Subodh

    2015-11-05

    Lead-halide perovskites have transcended photovoltaics. Perovskite light-emitting diodes (PeLEDs) emerge as a new field to leverage on these fascinating semiconductors. Here, we report the first use of completely inorganic CsPbBr3 thin films for enhanced light emission through controlled modulation of the trap density by varying the CsBr-PbBr2 precursor concentration. Although pure CsPbBr3 films can be deposited from equimolar CsBr-PbBr2 and CsBr-rich solutions, strikingly narrow emission line (17 nm), accompanied by elongated radiative lifetimes (3.9 ns) and increased photoluminescence quantum yield (16%), was achieved with the latter. This is translated into the enhanced performance of the resulting PeLED devices, with lower turn-on voltage (3 V), narrow electroluminescence spectra (18 nm) and higher electroluminescence intensity (407 Cd/m(2)) achieved from the CsBr-rich solutions.

  19. 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.

  20. Lifetime of organic light emitting diodes on polymer anodes

    NASA Astrophysics Data System (ADS)

    Fehse, Karsten; Meerheim, Rico; Walzer, Karsten; Leo, Karl; Lövenich, Wilfried; Elschner, Andreas

    2008-08-01

    We report on the use of a thin layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) as anode for bottom emission organic light emitting diodes (OLEDs). The combination of polymer anodes with OLEDs having either electrically doped or undoped hole transport layers in direct contact with the polymer is shown. We discuss the impact of the annealing conditions of the polymer on the OLED lifetime in comparison to indium tin oxide anodes. Supported by a differential thermal analysis of PEDOT:PSS, a strong influence of residual water in the polymer on the device lifetime is found. Additional heating of the polymer anode in a dry ambient prior to OLED deposition is necessary to achieve high device lifetimes. At a luminance of 260 cd/m2, pin-OLEDs on a PEDOT:PSS anode show no measurable device degradation during 5200 h of operation.

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

    PubMed

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

    2014-08-01

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

  2. 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.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

    Craine, Eric R.

    2016-05-01

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

  6. 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.

  7. Electrically detected magnetic resonance in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Boehme, Christoph

    2013-03-01

    Due to the built-in weak spin-orbit coupling of carbon based materials, electronic transitions in organic semiconductors are subjected to strong spin-selection rules that are responsible for a number of interesting electron spin- and even nuclear spin-dependent electrical and optical properties of these materials, including device efficiencies of organic light emitting diodes and solar cells or magnetoresistive and magneto-optic effects. In recent years, we have studied how these effects work and how they can be utilized for organic semiconductor device improvement and new device applications. Our focus has been in particular on the effects of spin on π-conjugated polymer based bipolar injection devices (more commonly known as organic light emitting diodes, OLEDs). In OLEDs, spin-interactions between recombining charge carriers do not only control electroluminescence rates but also the magnetoresistance. We have shown that spin-coherence can be observed through current measurements and that these effects can be utilized for a coherent, pulsed electrically detected magnetic resonance spectroscopy (pEDMR) which enables us to encode the qualitative nature of spin-dependent mechanisms (the polaron pair mechanism and the triplet polaron recombination) and the their dynamical nature (spin-relaxation, electronic relaxation, hopping times). The insights gained from these studies have led to the invention of a robust absolute magnetic field sensor based on organic thin film materials with absolute sensitivities of <50nT/Hz1/2. Acknowledgment is made to the DOE (#DESC0000909) and NSF through a MRSEC Project (#1121252) and a CAREER Project (#0953225).

  8. Theoretical study of phosphorescence in dye doped light emitting diodes.

    PubMed

    Minaev, Boris; Jansson, Emil; Agren, Hans; Schrader, Sigurd

    2006-12-21

    Phosphorescence of platinum(II) octaethyl porphyrin (PtOEP), which has been used in organic light emitting diodes to overcome the efficiency limit imposed by the formation of triplet excitons, is studied by time-dependent (TD) density functional theory (DFT). The spin-orbit coupling (SOC) effects and the phosphorescence radiative lifetime (tau(p) (r)), calculated by the TD DFT method with the quadratic response technique, are analyzed for a series of porphyrins in order to elucidate the internal heavy atom effect on tau(p) (r). While the significance of the d(pi) orbital admixture into the lowest unoccupied molecular orbital e(g)(pi(*)), proposed by Gouterman et al. [J. Chem. Phys. 56, 4073 (1972)], is supported by our SOC calculations, we find that the charge-transfer (CT) mechanism is more important; the CT state of the (3)A(2g) symmetry provides effective SOC mixing with the ground state, and a large (3)A(2g)-(3)E(u) transition dipole moment gives the main contribution to the radiative phosphorescence rate constant. The IR and Raman spectra in the ground state and first excited triplet state (T(1)) are studied for proper assignment of vibronic patterns. An orbital angular momentum of the T(1) state is not quenched completely by the Jahn-Teller effect. A large zero-field splitting is predicted for PtP and PtOEP which results from a competition between the SOC and Jahn-Teller effects. A strong vibronic activity is found for the e(g) mode at 230 cm(-1) in PtP phosphorescence which is shifted to 260 cm(-1) in PtOEP. This out-of-plane vibration of the Pt atom produces considerable change of the SOC mixing. The role of charge-transfer state of d(pi)pi(*) type is stressed for the explanation of the electroluminescent properties of the dye doped light emitting diode.

  9. Theoretical study of phosphorescence in dye doped light emitting diodes

    NASA Astrophysics Data System (ADS)

    Minaev, Boris; Jansson, Emil; Ågren, Hans; Schrader, Sigurd

    2006-12-01

    Phosphorescence of platinum(II) octaethyl porphyrin (PtOEP), which has been used in organic light emitting diodes to overcome the efficiency limit imposed by the formation of triplet excitons, is studied by time-dependent (TD) density functional theory (DFT). The spin-orbit coupling (SOC) effects and the phosphorescence radiative lifetime (τpr), calculated by the TD DFT method with the quadratic response technique, are analyzed for a series of porphyrins in order to elucidate the internal heavy atom effect on τpr. While the significance of the dπ orbital admixture into the lowest unoccupied molecular orbital eg(π*), proposed by Gouterman et al. [J. Chem. Phys. 56, 4073 (1972)], is supported by our SOC calculations, we find that the charge-transfer (CT) mechanism is more important; the CT state of the A2g3 symmetry provides effective SOC mixing with the ground state, and a large A2g3-Eu3 transition dipole moment gives the main contribution to the radiative phosphorescence rate constant. The IR and Raman spectra in the ground state and first excited triplet state (T1) are studied for proper assignment of vibronic patterns. An orbital angular momentum of the T1 state is not quenched completely by the Jahn-Teller effect. A large zero-field splitting is predicted for PtP and PtOEP which results from a competition between the SOC and Jahn-Teller effects. A strong vibronic activity is found for the eg mode at 230cm-1 in PtP phosphorescence which is shifted to 260cm-1 in PtOEP. This out-of-plane vibration of the Pt atom produces considerable change of the SOC mixing. The role of charge-transfer state of dππ* type is stressed for the explanation of the electroluminescent properties of the dye doped light emitting diode.

  10. New materials for organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Robinson, Matthew R.

    A number of materials exist for organic light-emitting diodes (OLEDs). These include small molecules and conjugated polymers. Small molecules can be precisely identified and purified but typically require vapor depositon and have a tendency towards microcrystallinity. Conjugated polymers can be easily and cheaply deposited by spin-casting or printing from solution, however they are difficult to obtain in strict purity resulting in inconsistent properties. Furthermore, many OLEDs require the use of multi-layers for sufficient efficiency. This dissertation describes a number of strategies to obtain materials with the attributes of both small molecules and conjugated polymers while avoiding drawbacks such as microcrystallinity. In addition these materials are designed for use as the single layer in an OLED. This dissertation begins by describing sate-of-the-art methods for OLED fabrication and measurement. The rest describes the design, synthesis, and characterization of a number of well-defined, small molecules and intermediate-sized macromolecules. One class of molecules has four conjugated oligomers attached to a carbon atom providing a tetrahedral shape that discourages crystallization in thin films. Films are characterized by atomic force microscopy (AFM), fluorescence microscopy, and are compared to OLED performance as a function of casting solvent and heat treatment. Another class of molecules uses small molecules blended into conjugated polymers thereby taking advantage of the electrical properties of the polymer (host) and the emission properties of the small molecule (guest). For example, lanthanides blended into conjugated polymers give a narrow emission spectra. Both red (612 nm) and infrared (1100 nm, 1540 nm) emission can be obtained in this manner. By insulating the guest from the host using by adding tert-butyl groups, reduced charge trapping is acheived. By blending iridium complexes designed to be miscible with conjugated polymer hosts through the

  11. Vertical Stand Transparent Light-Emitting Diode Architecture for High-Efficiency and High-Power Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Pan, Chih-Chien; Koslow, Ingrid; Sonoda, Junichi; Ohta, Hiroaki; Ha, Jun-Seok; Nakamura, Shuji; DenBaars, Steven P.

    2010-08-01

    Using a transparent ZnO vertical stand as a submount, a novel Light-emitting diode architecture, which is similar to conventional lighting bulbs, was proposed. The emission power of a blue LED based on c-plane (0001) bulk GaN was increased by 14.2 and 5.1% compared with those of conventional and suspended die packages, respectively. The output power and external quantum efficiency of LEDs respectively reached 31.7 mW and 57.1% at a forward current of 20 mA under direct current conditions. The high thermal conductivity and refractive index of the transparent submount simultaneously resulted in high current operation and high external efficiency.

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

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-09

    ... Parts 429 and 430 RIN 1904-AC67 Energy Conservation Program: Test Procedures for Light-Emitting Diode... light-emitting diode (LED) lamps to support implementation of labeling provisions by the Federal Trade... light) to project the rated lifetime of LED lamps. The rated lifetime of the LED lamp is the...

  15. 77 FR 75190 - Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-19

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

  16. 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

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

  17. 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.

  18. 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.

  19. 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

  20. 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

  1. 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.

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  4. New material options for light-emitting diode packaging

    NASA Astrophysics Data System (ADS)

    Zweben, Carl H.

    2004-06-01

    As light-emitting diode (LED) power levels and chip sizes increase, thermal management and thermal stresses, which affect performance, power conversion efficiency nad lifetime, are becoming increasingly serious problems. Traditional materials have serious deficiencies in meeting requirements for thermal management and minimization of thermal stresses in high-brightness (HB) LED packaging. Copper, the standard material for applications requiring high thermal conductivity, has a coefficient of thermal expansion (CTE) that is much larger than those of ceramics and semiconductor materials, giving rise to thermal stresses when packages are subjected to thermal excursions. Aluminum has a larger CTE than copper. Traditional materials with low CTEs have thermal conductivites that are little or no better than that of aluminum. There are an increasing number of new packaging materials with low, tailorable CTEs and thermal conductivities up to four times those of copper that overcome thise limitations. The ability to tailor material CTE has been used to solve critical warping problems in manufacturing, increasing yield from 5% to over 99%. Advanced materials fall into six categories: monolithic carbonaceous materials, metal matrix compsites, carbon/carbon composites, ceramic matrix composites, polymer matrix composites, and advanced metallic alloys. This paper provides an overview of the state of the art of advanced packaging materials, including their key properties, state of maturity, cost and applications.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  6. 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.

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

    PubMed Central

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

    2004-01-01

    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. PMID:14704283

  8. Applications of Light Emitting Diodes in Health Care.

    PubMed

    Dong, Jianfei; Xiong, Daxi

    2017-09-25

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

  9. Silk-hydrogel Lenses for Light-emitting Diodes.

    PubMed

    Melikov, Rustamzhon; Press, Daniel Aaron; Kumar, Baskaran Ganesh; Dogru, Itir Bakis; Sadeghi, Sadra; Chirea, Mariana; Yılgör, İskender; Nizamoglu, Sedat

    2017-08-03

    Today the high demand for electronics leads to massive production of waste, thus green materials based electronic devices are becoming more important for environmental protection and sustainability. The biomaterial based hydrogels are widely used in tissue engineering, but their uses in photonics are limited. In this study, silk fibroin protein in hydrogel form is explored as a bio-friendly alternative to conventional polymers for lens applications in light-emitting diodes. The concentration of silk fibroin protein and crosslinking agent had direct effects on optical properties of silk hydrogel. The spatial radiation intensity distribution was controlled via dome- and crater-type silk-hydrogel lenses. The hydrogel lens showed a light extraction efficiency over 0.95 on a warm white LED. The stability of silk hydrogel lens is enhanced approximately three-folds by using a biocompatible/biodegradable poly(ester-urethane) coating and more than three orders of magnitude by using an edible paraffin wax coating. Therefore, biomaterial lenses show promise for green optoelectronic applications.

  10. 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.

  11. 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.

  12. 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.

  13. Perovskite energy funnels for efficient light-emitting diodes.

    PubMed

    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.

  14. Printable candlelight-style organic light-emitting diode

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  15. Near-field photometry for organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Li, Rui; Harikumar, Krishnan; Isphording, Alexandar; Venkataramanan, Venkat

    2013-03-01

    Organic Light Emitting Diode (OLED) technology is rapidly maturing to be ready for next generation of light source for general lighting. The current standard test methods for solid state lighting have evolved for semiconductor sources, with point-like emission characteristics. However, OLED devices are extended surface emitters, where spatial uniformity and angular variation of brightness and colour are important. This necessitates advanced test methods to obtain meaningful data for fundamental understanding, lighting product development and deployment. In this work, a near field imaging goniophotometer was used to characterize lighting-class white OLED devices, where luminance and colour information of the pixels on the light sources were measured at a near field distance for various angles. Analysis was performed to obtain angle dependent luminous intensity, CIE chromaticity coordinates and correlated colour temperature (CCT) in the far field. Furthermore, a complete ray set with chromaticity information was generated, so that illuminance at any distance and angle from the light source can be determined. The generated ray set is needed for optical modeling and design of OLED luminaires. Our results show that luminance non-uniformity could potentially affect the luminaire aesthetics and CCT can vary with angle by more than 2000K. This leads to the same source being perceived as warm or cool depending on the viewing angle. As OLEDs are becoming commercially available, this could be a major challenge for lighting designers. Near field measurement can provide detailed specifications and quantitative comparison between OLED products for performance improvement.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  17. 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.

  18. InGaN-based flexible light emitting diodes

    NASA Astrophysics Data System (ADS)

    Bayram, C.

    2017-02-01

    Novel layer release and transfer technology of single-crystalline GaN semiconductors is attractive for enabling many novel applications including flexible photonics and hybrid device integration. To date, light emitting diode (LED) research has been primarily focused on rigid devices due to the thick growth substrate. This prevented fundamental research in flexible inorganic LEDs, and limited the applications of LEDs in the solid state lighting (due to the substrate cost) and in biophotonics (i.e. optogenetics) (due to LED rigidness). In the literature, a number of methods to achieve layer transfer have been reported including the laser lift-off, chemical lift-off, and Smartcut. However, the release of films of LED layers (i.e. GaN semiconductors) has been challenging since their elastic moduli and chemical resistivity are much higher than most conventional semiconductors. In this talk, we are going to review the existing technologies and new mechanical release techniques (i.e. spalling) to overcome these problems.

  19. Phosphorescent Organic Light-Emitting Diodes with Simplified Device Architecture

    NASA Astrophysics Data System (ADS)

    Seo, Ji Hyun; Kim, Hoe Min; Choi, Eun Young; Choi, Dae Hyuk; Park, Jung Hwan; Yoo, Han Seong; Kang, Hyun Ju; Lee, Kum Hee; Yoon, Seung Soo; Kim, Young Kwan

    2010-08-01

    We demonstrated that single-layered red phosphorescent organic light-emitting diodes (OLEDs) can have high a efficiency without carrier transport and injection layers. This high efficiency is caused by the direct injection of carriers from electrodes into a dopant, bis(2-phenylquinoline) iridium(III) (acetylacetonate) [Ir(ppy)2(acac)]. This mechanism is proved by analyzing the single-layered devices with various hosts, 4,4'-N,N'-dicarbazole-biphenyl (CBP), 9-phenyl-3-[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-9H-carbazole (LPGH 114), 9-(naphthalen-2-yl)-3-[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-9H-carbazole (LPGH 124), and 9-phenyl-3,6-bis[4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl]-9H-carbazole (LPGH 153). Among the devices, the single-layered device with LPGH 153 shows a luminous efficiency, a power efficiency, and a quantum efficiency of 9.3 cd/A, 5.2 lm/W, and 6.2%, respectively. The single-layered device with CBP was compared with a multilayered device with CBP. As a result, the single-layered device shows a reduced operating voltage, an enhanced roll-off efficiency, and a pure emitting color in comparison with the multilayered device owing to the direct injection of carriers into a dopant and the suppression of exciplex formation.

  20. Temperature-dependent photoluminescence in light-emitting diodes

    PubMed Central

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

    2014-01-01

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

  1. A multi-source portable light emitting diode spectrofluorometer.

    PubMed

    Obeidat, Safwan; Bai, Baolong; Rayson, Gary D; Anderson, Dean M; Puscheck, Adam D; Landau, Serge Y; Glasser, Tzach

    2008-03-01

    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 using a light weight (<1.5 kg) spectrometer. Limits of detection for rhodamine 6G, rhodamine B, and fluorescein were 2.9, 3.2, and 11.0 nM, respectively. Generation of excitation-emission matrices (EEMs) enabled the analysis of samples containing mixtures of rhodamine B and fluorescein. Buffered saline plant and animal feed extracts were also analyzed using this instrument. These samples included the woody plants Pistacia lentiscus (Evergreen pistache or Mastic) and Philyria latifolia, and the herbaceous species Medicago sativa (alfalfa), Trifolium spp. (clover), and a feed concentrate. Application of multi-way principal component analysis (MPCA) to the resulting three-dimensional data sets enabled discernment among these various diet constituents.

  2. 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.

  3. Carrier modulation layer-enhanced organic light-emitting diodes.

    PubMed

    Jou, Jwo-Huei; Kumar, Sudhir; Singh, Meenu; Chen, Yi-Hong; Chen, Chung-Chia; Lee, Meng-Ting

    2015-07-17

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

  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. Frequency domain fluorometry with pulsed light-emitting diodes.

    PubMed

    Herman, Petr; Vecer, Jaroslav

    2008-01-01

    We present a simple way to extend the time resolution of a standard frequency domain (FD) fluorometer by use of pulsed light-emitting diodes (LEDs) as an excitation source. High temporal resolution of the multifrequency FD method requires the excitation light to be modulated up to the highest possible frequencies with high modulation depth. We used harmonic content of subnanosecond-pulsed LEDs for generation of modulated excitation light. By a replacement of the light source, the upper frequency limit increased to 500-600 MHz, which is almost triple the frequency limit of the standard FD fluorometer equipped with an ordinary photomultiplier tube and an electro-optical modulator. Besides the increased time resolution, this approach allowed for elimination of a light modulator with an associated synthesizer and radio frequency power amplifier that are normally required for FD measurements with continuous wave light sources. Performance of the instrument with pulsed LED excitation is demonstrated on several examples of ultraviolet-excited fluorescence decays. We show that pulsed LEDs can serve as an inexpensive alternative to pulsed laser sources for FD fluorescence spectroscopy.

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  7. 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.

  8. Organic light-emitting diodes with direct contact-printed red, green, blue, and white light-emitting layers

    NASA Astrophysics Data System (ADS)

    Chen, Sun-Zen; Peng, Shiang-Hau; Ting, Tzu-Yu; Wu, Po-Shien; Lin, Chun-Hao; Chang, Chin-Yeh; Shyue, Jing-Jong; Jou, Jwo-Huei

    2012-10-01

    We demonstrate the feasibility of using direct contact-printing in the fabrication of monochromatic and polychromatic organic light-emitting diodes (OLEDs). Bright devices with red, green, blue, and white contact-printed light-emitting layers with a respective maximum luminance of 29 000, 29 000, 4000, and 18 000 cd/m2 were obtained with sound film integrity by blending a polymeric host into a molecular host. For the red OLED as example, the maximum luminance was decreased from 29 000 to 5000 cd/m2 as only the polymeric host was used, or decreased to 7000 cd/m2 as only the molecular host was used. The markedly improved device performance achieved in the devices with blended hosts may be attributed to the employed polymeric host that contributed a good film-forming character, and the molecular host that contributed a good electroluminescence character.

  9. NiOx Electrode Interlayer and CH3 NH2 /CH3 NH3 PbBr3 Interface Treatment to Markedly Advance Hybrid Perovskite-Based Light-Emitting Diodes.

    PubMed

    Chih, Yi-Kai; Wang, Jian-Chih; Yang, Rei-Ting; Liu, Chi-Ching; Chang, Yun-Chorng; Fu, Yaw-Shyan; Lai, Wei-Chi; Chen, Peter; Wen, Ten-Chin; Huang, Yu-Ching; Tsao, Cheng-Si; Guo, Tzung-Fang

    2016-10-01

    The performance of hybrid perovskite-based light-emitting diodes (LEDs) is markedly enhanced by the application of a NiOx electrode interlayer and moderate methylamine treatment. A hybrid perovskite-based LED exhibits a peak luminous efficiency of 15.9 cd A(-1) biased at 8.5 V, 407.65 mA cm(-2) , and 65 300 cd m(-2) , showing a distinctive impact for future applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Development of Mid-infrared GeSn Light Emitting Diodes on a Silicon Substrate

    DTIC Science & Technology

    2015-04-22

    Final 3. DATES COVERED 13-01-2013 to 30-07-2014 4. TITLE AND SUBTITLE Development of Mid-infrared GeSn Light Emitting Diodes on a Silicon...to develop 1) direct-bandgap Sn-based group-IV material with very low defect densities and 2) a new type of Sn-based group-IV light - emitting diode ...infrared GeSn Light Emitting Diodes on a Silicon Substrate” 22/4/2015 PI and Co-PI information: - Name of Principal Investigators: Prof. H

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

    PubMed

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Wildeson, Isaac H.

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

  13. 77 FR 75189 - Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-19

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION Certain Light-Emitting Diodes and Products Containing Same; Commission Determination Not To Review... importation, importation, or sale after importation into the United States of certain light-emitting...

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

    PubMed

    Tada, Kaoru; Ikeda, Kazuo; Tomita, Katsuro

    2009-11-01

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

  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. An organic light-emitting diode display for use in neuroendoscopic surgery in the ventricle.

    PubMed

    Nishiyama, Kenichi; Sano, Masakazu; Jinguji, Shinya; Harada, Atsuko; Yoshimura, Junichi; Fujii, Yukihiko

    2012-08-01

    The organic light-emitting diode (OLED) display delivers a bright and high-contrast image compared to the liquid crystal display. The first experience of neuroendoscopic surgery using an OLED display was reported and its stereoscopic effect emphasized.

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

    DTIC Science & Technology

    2016-03-31

    Super-Lattice Light Emitting Diodes (SLEDS) on GaAs Kassem Nabha1, Russel Ricker2, Rodney McGee1, Nick Waite1, John Prineas2, Sydney Provence2...infrared light emitting diodes (LEDs). Typically, the LED arrays are mated with CMOS read-in integrated circuit (RIIC) chips using flip-chip bonding. In...CMOS RIIC Introduction Infrared imaging (IR) systems are widely used in law enforcement, military, and industrial applications . They operate in a

  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. 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

  20. Development of ultraviolet nitride-based light emitting diodes

    NASA Astrophysics Data System (ADS)

    Katona, Thomas Matthew

    2003-10-01

    Deep ultraviolet light emitting diodes, with emission wavelengths shorter than 360 nm, have attracted interest due to their potential applications as replacement white light sources, in non-line of sight communication, for chemical and biological weapons detection, medical applications, water purification, and counterfeit detection. Light emitters in this wavelength range require AlGaN based active regions with increasing Al composition as the wavelength is decreased. High Al composition AlGaN based devices have been challenged by difficulty in growth, low electron and hole mobilities, and deep dopant levels resulting in low carrier concentrations. The combination of these factors has resulted in UV optoelectronic devices with quantum efficiency several orders of magnitude lower than their GaN/InGaN based visible counterparts. This work will details studies on alternative selective area growth techniques for dislocation reduction and the development of ultraviolet LEDs ranging from 292--340 nm. Lateral overgrowth of GaN on patterned Si (111) substrates was developed with the hope of developing seed material for bulk GaN growth. The effect of growth conditions on both the crystallographic wing tilt and crack density in the AlN/GaN films was studied. By controlling the lateral to vertical growth rate at the beginning of lateral overgrowth, the wing tilt can be effectively eliminated. We also demonstrate the first lateral overgrowth of AlN to create low threading dislocation density AlN template layers for optoelectronic device development. Deep UV quantum wells grown on this material were studied with cathodoluminescence to study the effect of dislocations on radiative recombination in deep UV devices. In addition to work on lateral overgrowth of GaN and AlN, 292, 340 nm LEDs were grown on AlN on sapphire and GaN on sapphire respectively. AlN strain relief interlayers were developed to prevent cracking of the 340 nm AlGaN based LEDs that were grown in tension on Ga

  1. 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

  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. 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…

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  5. 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.

  6. 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. %.

  7. Light-emitting diodes based on conjugated polymers

    NASA Astrophysics Data System (ADS)

    Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; Mackay, K.

    1990-10-01

    It is shown here that poly(p-phenylene vinylene), prepared by way of a solution-processable precursor, can be used as the active element in a large-area LED. The combination of good structural properties of this polymer, its ease of fabrication, and light emission in the green-yellow part of the spectrum with reasonably high efficiency suggest that the polymer can be used for the development of large-area light-emitting displays.

  8. 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.

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

    PubMed

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

    2017-02-20

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

  10. 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.

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

    PubMed

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

    2017-02-01

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

  12. 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.

  13. The Organic-Oxide Interfacial Layer on the Studies of Organic Electronics (Light-Emitting Diodes and Solar Cells)

    DTIC Science & Technology

    2008-10-09

    polymer light - emitting diodes …………….... 6 V. Sulfonated poly(diphenylamine) as a novel hole...oxide cathode buffer layer in fabricating high-performance polymer light - emitting diodes " Adv. Funct. Mater. 18, 3036 (2008). (AOARD-07-4068) SCI...cathode buffer layer in fabricating high-performance polymer light - emitting diodes Abstract Spin-casting or thermal evaporation in vacuum of a

  14. 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.

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

    PubMed

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

    2014-05-30

    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.

  16. Highly efficient exciplex phosphorescence from organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Virgili, D.; Cocchi, M.; Fattori, V.; Sabatini, C.; Kalinowski, J.; Williams, J. A. G.

    2006-12-01

    The efficiency of organic exciplex light-emitting-devices (EXLEDs) can be greatly improved by introduction of a phosphorescent sensitizer with a high electronic affinity. In the electron-hole combination process at the electron donor/acceptor interface, solely singlet exciplexes are generated producing the exciplex fluorescence. A phosphor sensitizer allows the formation in the emitter bulk of triplet exciplexes, which yield highly efficient exciplex phosphorescence. As an example, we use a Pt-based phosphor (PtL 2Cl) doped into a star-burst amine hole transporting donor (m-MTDATA) and bathophenanthroline (BPT) electron-transporting acceptor system which in a bi-layer EXLED reveals an exciplex high electro-phosphorescence external quantum yield of 2.4% photon/carrier.

  17. Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor Deposition.

    PubMed

    Leyden, Matthew R; Meng, Lingqiang; Jiang, Yan; Ono, Luis K; Qiu, Longbin; Juarez-Perez, Emilio J; Qin, Chuanjiang; Adachi, Chihaya; Qi, Yabing

    2017-07-20

    Organo-lead-halide perovskites are promising materials for optoelectronic applications. Perovskite solar cells have reached power conversion efficiencies of over 22%, and perovskite light-emitting diodes have recently achieved over 11% external quantum efficiency. To date, most research on perovskite light-emitting diodes has focused on solution-processed films. There are many advantages of a vapor-based growth process to prepare perovskites, including ease of patterning, ability to batch process, and material compatibility. We investigated an all-vapor perovskite growth process by chemical vapor deposition and demonstrated luminance up to 560 cd/m(2).

  18. 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.

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

    DOEpatents

    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.

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

    DOEpatents

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

    2017-05-09

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

  1. 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.

  2. Synthesis and characterization of organic/inorganic heterostructure films for hybrid light emitting diode

    NASA Astrophysics Data System (ADS)

    Toyama, Toshihiko; Ichihara, Tokuyuki; Yamaguchi, Daisuke; Okamoto, Hiroaki

    2007-10-01

    Thin-film light emitting devices based on organic materials have been gathering attentions for applying a flat-panel display and a solid-state lighting. Alternatively, inorganic technologies such as Si-based thin-film technology have been growing almost independently. It is then expected that combining the Si-based thin-film technology with the organic light emitting diode (OLED) technology will develop innovative devices. Here, we report syntheses of the hybrid light emitting diode (LED) with a heterostructure consisting of p-type SiC x and tris-(8-hydroxyquinoline) aluminum films and characterization for the hybrid LEDs. We present the energy diagram of the heterostructure, and describe that the use of high dark conductivities of the p-type SiC x as well as inserting wide-gap intrinsic a-SiC x at the p-type SiC x/Alq interface are effective for improving device performance.

  3. The effect of light-emitting diode and laser on mandibular growth in rats.

    PubMed

    El-Bialy, Tarek; Alhadlaq, Adel; Felemban, Nayef; Yeung, Jasper; Ebrahim, Amal; Hassan, Ali H

    2015-03-01

    To evaluate the effect of a light-emitting diode (LED) and/or low-level laser (LLL) with or without the use of anterior bite jumping appliances (also known as functional appliances [FAs]) on mandibular growth in rats. Thirty-six 8-week-old male Sprague-Dawley rats weighing 200 g were obtained from Charles River Canada (St. Constant, QC, Canada) and were divided into six groups of six animals each. Groups were as follows: group 1: LLL; group 2: LLL + FA; group 3: LED; group 4: LED + FA; group 5: FA; and group 6: control (no treatment). Mandibular growth was evaluated by histomorphometric and micro computed tomographic (microCT) analyses. The LED and LED + FA groups showed an increase in all condylar tissue parameters compared with other groups. The LED-treated groups showed more mandibular growth stimulation compared with the laser groups.

  4. 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.

  5. 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.

  6. 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.

  7. Highly flexible silver nanowire electrodes for shape-memory polymer light-emitting diodes.

    PubMed

    Yu, Zhibin; Zhang, Qingwu; Li, Lu; Chen, Qi; Niu, Xiaofan; Liu, Jun; Pei, Qibing

    2011-02-01

    Shape-memory polymer light-emitting diodes (PLEDs) using a new silver nanowire/polymer electrode are reported. The electrode can be stretched by up to 16% with only a small increase in sheet resistance. Large deformation shape change and recovery of the PLEDs to various bistable curvatures result in minimal loss of electroluminescence performance.

  8. 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…

  9. 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…

  10. Light Emitting Diode Flashlights as Effective and Inexpensive Light Sources for Fluorescence Microscopy

    PubMed Central

    Robertson, J. Brian; Zhang, Yunfei; Johnson, Carl Hirschie

    2009-01-01

    Summary Light-emitting diodes (LEDs) are becoming more commonly used as light sources for fluorescence microscopy. We describe the adaptation of a commercially available LED flashlight for use as a source for fluorescence excitation. This light source is long-lived, inexpensive, and is effective for excitation in the range of 440–600 nm. PMID:19772530

  11. 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.

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

    USDA-ARS?s Scientific Manuscript database

    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...

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

    PubMed

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

    2012-05-06

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

  14. 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…

  15. 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…

  16. 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.

  17. Low-threshold light-emitting-diode laser

    NASA Technical Reports Server (NTRS)

    Hawrylo, F. Z.; Kressel, H.

    1976-01-01

    Technique, which consists of reducing bandgap change at heterojunction to 0.1 eV and avoiding deep-level impurities such as Si and Ge, produces low-threshold laser diodes which are made from (AlGa)As and emit in visible spectrum.

  18. 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.

  19. 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

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

  20. 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...

  1. 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...

  2. 76 FR 64108 - In the Matter of Certain Light-Emitting Diodes and Products Containing Same; Notice of Commission...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-17

    ... COMMISSION In the Matter of Certain Light-Emitting Diodes and Products Containing Same; Notice of Commission..., the sale for importation, and the sale within the United States after importation of certain light-emitting diodes and products containing same by reason of infringement of certain claims of U.S. Patent...

  3. 77 FR 75446 - Certain Light-Emitting Diodes and Products Containing the Same; Commission Determination To Grant...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-20

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

  4. 77 FR 807 - Certain Light-Emitting Diodes and Products Containing the Same; Determination Not To Review...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-06

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

  5. 76 FR 60082 - In the Matter of Certain Light-Emitting Diodes and Products Containing Same; Notice of Commission...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-28

    ... From the Federal Register Online via the Government Publishing Office INTERNATIONAL TRADE COMMISSION In the Matter of Certain Light-Emitting Diodes and Products Containing Same; Notice of Commission... within the United States after importation of certain light-emitting diodes and products containing...

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

    PubMed

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

    2017-01-01

    Photomodulation therapy (PBMT) using light-emitting diode (LED) has been proposed as an alternative to conventional osteoporosis therapies. Our aim was to determine the effect of irradiation with a light-emitting diode on receptor activator of NF-κB ligand (RANKL)-mediated differentiation of mouse bone marrow macrophages into osteoclasts and compare it to alendronate treatment. The cells were irradiated with LED at 635±10 nm, 9-cm spot size, 5 mW/cm(2), and 18 J for 60 min/day in a CO2 incubator. The differentiation of irradiated and untreated RANKL-stimulated bone marrow macrophages into osteoclasts was evaluated by tartrate-resistant acid phosphatase (TRAP) staining and by molecular methods. These included assessing messenger RNA (mRNA) expression of osteoclastic markers such as TRAP, c-Fos, Atp6v0d2, DC-STAMP, NFATc1, cathepsin K, MMP9 and OSCAR; phosphorylation of various MAPKs, including extracellular signal-regulated kinase ERK1/2, P38, and JNK; NF-κB translocation; and resorption pit formation. Results were compared to those obtained with sodium alendronate. Production of reactive oxygen species was measured by a 2',7'-dihydrodichlorofluorescein diacetate assay. LED irradiation and alendronate inhibited mRNA expression of osteoclast-related genes, such as TRAP, c-Fos, and NFATc1, and reduced the osteoclast activity of RANKL-stimulated bone marrow macrophages. LED irradiation, but not alendronate, also inhibited the production of reactive oxygen species (ROS); phosphorylation of ERK, P38, and IκB; and NF-κB translocation. These findings suggest that LED irradiation downregulates osteoclastogenesis by ROS production; this effect could lead to reduced bone loss and may offer a new therapeutic tool for managing osteoporosis.

  7. 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

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

    PubMed

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

    2013-09-01

    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). 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. 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/m(2), but in FS the luminance of white saturated at 162 cd/m(2). Due to different saturation levels, the luminance of FS green and FS yellow could exceed the luminance of FS white for identical DDLs. The OLED temporal characteristics are excellent and superior to those of LCDs. However, the OLEDs revealed severe perceptually relevant artifacts with

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

    PubMed

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

    2017-04-01

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

  10. 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.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  14. The Combination of Resveratrol and High-Fluence Light Emitting Diode-Red Light Produces Synergistic Photobotanical Inhibition of Fibroblast Proliferation and Collagen Synthesis: A Novel Treatment for Skin Fibrosis.

    PubMed

    Mamalis, Andrew; Jagdeo, Jared

    2017-01-01

    Skin fibrosis is a debilitating condition that significantly impacts patient quality of life. Ultraviolet phototherapy is currently used to treat several diseases featuring skin fibrosis. High-fluence light-emitting diode-generated red light (HF-LED-RL) does not cause DNA damage associated with skin cancer, and it is generally regarded as safe, portable, and cost-effective. Early clinical observations suggest that LED-generated light may possess antifibrotic effects, although these findings are largely unexplored. Previously published research demonstrated that HF-LED-RL decreases fibroblast proliferation and collagen in vitro. The goal of this study was to compare the combination effects of HF-LED-RL alone with HF-LED-RL in combination with resveratrol. It is hypothesized that resveratrol, an active ingredient in red wine, a potent antioxidant scavenger of reactive oxygen species, and an inhibitor of collagen production, may synergistically decrease fibroblast proliferation and collagen production when combined with HF-LED-RL. In this study, evidence is provided that resveratrol combined with HF-LED-RL acts synergistically to decrease fibroblast proliferation and procollagen 1A1 production, and this represents a new potential therapeutic modality that is termed the "photobotanical" effect due to the combined light and botanical properties observed. The study, discovery, and use of photobotanical combinations may usher in new therapeutics or phototherapy adjuvants for the treatment of dermatologic diseases.

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

    PubMed

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

    2017-07-25

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

  16. Effect of light emitting diode (LED) therapy on the survival of photoreceptors following argon laser injury

    NASA Astrophysics Data System (ADS)

    DiCarlo, Cheryl D.; Brown, Jeremiah; Hacker, Henry D.; Cheramie, Rachel; Schuschereba, Steven; Valo, Lynn; Clarkson, Donna R.; Sankovich, James; Zwick, Harry; Lund, David J.; Stuck, Bruce E.

    2005-04-01

    Due to the increasing number of optic systems that military personnel are exposed, the development of countermeasures for laser eye injury is of significant concern. Recent reports in the literature suggest some benefit form the use of Light Emitting Diode (LED) therapy on the retina that received a toxic insult. The purpose of this study was to compare retinal cell survival and multifocal electroretinography (mfERG) in a laser retinal injury model following treatment with LED photoillumination. Control and LED array (670 nm) illuminated cynomolgus monkeys received macular Argon laser lesions (514 nm, 130 mW, 100 ms). LED array exposure was accomplished for 4 days for a total dose of 4 J/cm2 per day. Baseline and post-laser exposure mfERGs were performed on most of the subjects. Ocular tissues were collected from four animals at Day 4 poast laser exposure and from two animals at 4 months post laser exposure. The tissues were processed for plastic embedding. Retinal cell counts were performed on the lesion sections. Analysis of Variance (ANOVA) results yielded no significant difference in the sparing of photoreceptors, inner nuclear and ganglion cells between the control and LED illuminated subjects. Although pathology showed no significant support for diode therapy, our early mfERG observations previously reported suggested a more rapid functional recovery. Since there is still no uniform therapy for laser retinal injury, research is continuing to determine novel therapies that may provide retinal cell sparing and functional retinal return.

  17. 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.

  18. 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.

  19. 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.

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

    SciTech Connect

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

    2016-04-04

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

  1. The fabrication of high density nanochannel organic light emitting diodes with reduced charge spreading

    NASA Astrophysics Data System (ADS)

    Trivedi, K.; Bhansali, U. S.; Gnade, B.; Hu, W.

    2009-10-01

    This study reports fabrication and characterization of nanoscale organic light emitting diodes with reduced charge spreading. Nanoimprint lithography is used to make SU-8 nanochannels with ~90° sidewalls into which N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) and tris-(8-hydroxyquinoline) aluminum (Alq3) are thermally evaporated, to avoid charge spreading. Micron grating devices are fabricated for comparison. Device characteristics show that performance is retained while scaling down to nanochannels, as no geometry dependent trend is observed. Surface potential microscopy (SPM) measurements reveal an identical periodic difference in surface potential for nanochannel and microscale grating devices. The SPM results, together with cross-sectional scanning electron microscopy observation of the physical separation of nanoscale organic light emitting diodes (OLEDs), indicate electrical separation and isolated light emission from nanoscale confined OLEDs with minimized charge spreading.

  2. 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.

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

    PubMed

    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

    2015-12-04

    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. Copyright © 2015, American Association for the Advancement of Science.

  4. Near-infrared organic light-emitting diodes with very high external quantum efficiency and radiance

    NASA Astrophysics Data System (ADS)

    Tuong Ly, Kiet; Chen-Cheng, Ren-Wu; Lin, Hao-Wu; Shiau, Yu-Jeng; Liu, Shih-Hung; Chou, Pi-Tai; Tsao, Cheng-Si; Huang, Yu-Ching; Chi, Yun

    2017-01-01

    Bright and efficient organic emitters of near-infrared light would be of use in applications ranging from biological imaging and medical therapy to night-vision devices. Here we report how a new class of Pt(II) complex phosphors have enabled the fabrication of organic light-emitting diodes that emit light at 740 nm with very high efficiency and radiance due to a high photoluminescence quantum yield of ∼81% and a highly preferred horizontal dipole orientation. The best devices exhibited an external quantum efficiency of 24 ± 1% in a normal planar organic light-emitting diode structure. The incorporation of a light out-coupling hemisphere structure further boosts the external quantum efficiency up to 55 ± 3%.

  5. Polymer light-emitting diodes: from materials to devices

    NASA Astrophysics Data System (ADS)

    Berntsen, Arjan J. M.; Croonen, Yvo; Cuijpers, Raymond; Habets, Boris; Liedenbaum, Coen T. H. F.; Schoo, Herman F. M.; Visser, Robert J.; Vleggaar, Jeroen J. M.; van de Weijer, Peter

    1997-12-01

    In this paper on polymer LEDs we discuss the formation of black spots, surface treatments of the anode, and photochemical degradation of the emissive polymer. We find that small pinholes in the cathode layer are the origin of the black spots. The black spots form when H2O or O2 diffuse through the pinholes and react with the cathode at the polymer-cathode interface.A model is presented that describes the growth of the spots. We find that for both indium-tin-oxide (ITO) and Au anodes, an UV/O3 or an O2 plasma cleaning treatment increases the work function by 0.8-0.9 eV. A higher work function may lead to a better hole injection and a reduction in the operating voltage. We present a method to measure the quantum yield for bleaching, (gamma) equals 1.6$MN4 and (gamma) equals 1.7 10-7 for bleaching of dialkoxy-PPV in air and vacuum, respectively, indicating that the polymer is 1000 times more stable in vacuum than in air.

  6. Light therapy for seasonal affective disorder with blue narrow-band light-emitting diodes (LEDs).

    PubMed

    Glickman, Gena; Byrne, Brenda; Pineda, Carissa; Hauck, Walter W; Brainard, George C

    2006-03-15

    While light has proven an effective treatment for Seasonal Affective Disorder (SAD), an optimal wavelength combination has not been determined. Short wavelength light (blue) has demonstrated potency as a stimulus for acute melatonin suppression and circadian phase shifting. This study tested the efficacy of short wavelength light therapy for SAD. Blue light emitting diode (LED) units produced 468 nm light at 607 microW/cm2 (27 nm half-peak bandwidth); dim red LED units provided 654 nm at 34 microW/cm2 (21 nm half-peak bandwidth). Patients with major depression with a seasonal pattern, a score of > or =20 on the Structured Interview Guide for the Hamilton Depression Rating Scale-SAD version (SIGH-SAD) and normal sleeping patterns (routine bedtimes between 10:00 pm and midnight) received 45 minutes of morning light treatment daily for 3 weeks. Twenty-four patients completed treatment following random assignment of condition (blue vs. red light). The SIGH-SAD was administered weekly. Mixed-effects analyses of covariance determined that the short wavelength light treatment decreased SIGH-SAD scores significantly more than the dimmer red light condition (F = 6.45, p = .019 for average over the post-treatment times). Narrow bandwidth blue light at 607 microW/cm2 outperforms dimmer red light in reversing symptoms of major depression with a seasonal pattern.

  7. 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.

  8. Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light-Emitting Diodes.

    PubMed

    Yuan, Fanglong; Wang, Zhibin; Li, Xiaohong; Li, Yunchao; Tan, Zhan'ao; Fan, Louzhen; Yang, Shihe

    2017-01-01

    Multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% are synthesized using a solvothermal method. For the first time, monochrome electroluminescent light-emitting diodes (LEDs) with MCBF-CQDs directly as an active emission layer are fabricated. The maximum luminance of blue LEDs reaches 136 cd m(-2) , which is the best performance for CQD-based monochrome electroluminescent LEDs.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  10. 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.

  11. 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.

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

    Treesearch

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

    2013-01-01

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

  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. 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

  15. Blue-green variable light-emitting diode based on organic-molecule-doped polymer

    NASA Astrophysics Data System (ADS)

    Xu, Chunxiang; Cui, Yiping; Shen, Yingzhong; Gu, Hongwei; Pan, Yi; Li, Yinkui

    1999-09-01

    Monolayer organic light-emitting diodes based on the organic molecule [(3,4-dimethoxybenzyldehycle-2'-hydroxy naphthylimine)dimethyl gallium]-doped [poly(2-mehtyoxy-5-ethyloxy)-4-di-(2-methyoxy-5'-octaoxy)phenylene vinylene] have been fabricated by a spin-coating method. Color variation from green to blue has been observed. The results have been attributed to the variation of the recombination zone and the charge transfer between the materials.

  16. 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.

  17. Ultra-violet light-emitting diode calibration system for timing large area scintillation detectors

    NASA Astrophysics Data System (ADS)

    Naumov, P. Yu; Runtso, M. F.; Naumov, P. P.; Maklyaev, E. F.; Kaplin, V. A.; Fomin, V. S.; Razzhivin, I. S.; Melikyan, Yu A.

    2017-01-01

    Timing large area plastic scintillation detectors are developing for the space gamma-ray telescopes now. For the in-flight calibration of these detectors the use of ultra-violet light-emitting diode, irradiating the 1 m long detector module at the center of its lateral side is suggested. The results of the measurements show the possibility of this calibration system implementation as for amplitude as for timing properties monitoring.

  18. Variable-color light-emitting diodes using GaN microdonut arrays.

    PubMed

    Tchoe, Youngbin; Jo, Janghyun; Kim, Miyoung; Heo, Jaehyuk; Yoo, Geonwook; Sone, Cheolsoo; Yi, Gyu-Chul

    2014-05-21

    Microdonut-shaped GaN/Inx Ga1-x N light-emitting diode (LED) microarrays are fabricated for variable-color emitters. The figure shows clearly donut-shaped light emission from all the individual microdonut LEDs. Furthermore, microdonut LEDs exhibit spatially-resolved blue and green EL colors, which can be tuned by either controlling the external bias voltage or changing the size of the microdonut LED.

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

    PubMed

    Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Murali, Banavoth; Sarmah, Smritakshi P; Yuan, Mingjian; Sinatra, Lutfan; Alyami, Noktan M; Liu, Jiakai; Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Comin, Riccardo; Hedhili, Mohamed N; Mohammed, Omar F; Lu, Zheng Hong; Kim, Dong Ha; Sargent, Edward H; Bakr, Osman M

    2016-10-01

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

  20. 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.

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

    PubMed

    Bui, Duy Anh; Hauser, Peter C

    2015-01-01

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

  2. 10 Mb/s visible light transmission system using a polymer light-emitting diode with orthogonal frequency division multiplexing.

    PubMed

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

    2014-07-01

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

  3. Visible Red Light Emitting Diode Photobiomodulation for Skin Fibrosis: Key Molecular Pathways.

    PubMed

    Mamalis, Andrew; Siegel, Daniel; Jagdeo, Jared

    Skin fibrosis, also known as skin scarring, is an important global health problem that affects an estimated 100 million persons per year worldwide. Current therapies are associated with significant side effects and even with combination therapy, progression, and recurrence is common. Our goal is to review the available published data available on light-emitting diode-generated (LED) red light phototherapy for treatment of skin fibrosis. A search of the published literature from 1 January 2000 to present on the effects of visible red light on skin fibrosis, and related pathways was performed in January 2016. A search of PubMed and EMBASE was completed using specific keywords and MeSH terms. "Fibrosis" OR "skin fibrosis" OR "collagen" was combined with ("light emitting diode," "LED," "laser," or "red light"). The articles that were original research studies investigating the use of visible red light to treat skin fibrosis or related pathways were selected for inclusion. Our systematic search returned a total of 1376 articles. Duplicate articles were removed resulting in 1189 unique articles, and 133 non-English articles were excluded. From these articles, we identified six articles related to LED effects on skin fibrosis and dermal fibroblasts. We augmented our discussion with additional in vitro data on related pathways. LED phototherapy is an emerging therapeutic modality for treatment of skin fibrosis. There is a growing body of evidence demonstrating that visible LED light, especially in the red spectrum, is capable of modulating key cellular characteristic associated with skin fibrosis. We anticipate that as the understanding of LED-RL's biochemical mechanisms and clinical effects continue to advance, additional therapeutic targets in related pathways may emerge. We believe that the use of LED-RL, in combination with existing and new therapies, has the potential to alter the current treatment paradigm of skin fibrosis. There is a current lack of clinical trials

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m-2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

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

    PubMed Central

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

    2017-01-01

    Inorganic perovskites such as CsPbX3 (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr3 lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m−2 and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs0.87MA0.13PbBr3 as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date. PMID:28589960

  6. 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.

  7. 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.

  8. 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.

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

    SciTech Connect

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

    2016-07-18

    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.

  10. Nanostructured current-confined single quantum dot light-emitting diode at 1300 nm.

    PubMed

    Monat, Christelle; Alloing, Blandine; Zinoni, Carl; Li, Lianhe H; Fiore, Andrea

    2006-07-01

    A novel light-emitting-diode structure is demonstrated, which relies on nanoscale current injection through an oxide aperture to achieve selective excitation of single InAs/GaAs quantum dots. Low-temperature electroluminescence spectra evidence discrete narrow lines around 1300 nm (line width approximately 75 microeV) at ultralow currents, which are assigned to the emission from single excitons and multiexcitons. This approach, which enables the fabrication of efficient nanoscale active devices at 1300 nm, can provide single-photon-emitting diodes for fiber-based quantum cryptography.

  11. Thermal behavior and carrier injection of GaAs/GaP quantum dots light emitting diodes

    NASA Astrophysics Data System (ADS)

    Golz, Christian; Dadgostar, Shabnam; Masselink, W. Ted; Hatami, Fariba

    2017-02-01

    Thermal behavior and carrier injection of GaAs/GaP quantum-dot light-emitting diodes are investigated. The diodes emit red light between 1.8 eV and 2 eV and operate at room temperature. Adding aluminum to the quantum structures shifts the emission wavelength towards green. Thermal filling and high injection of the carriers in GaAs/GaP quantum dots result in contributions of different radiative recombination channels with higher emission energies and hence a blueshift of the electroluminescence with increasing temperature and very small thermal quenching of the light output.

  12. Wireless Power Transmission to Organic Light Emitting Diode Lighting Panel with Magnetically Coupled Resonator

    NASA Astrophysics Data System (ADS)

    Kim, Yong-Hae; Han, Jun-Han; Kang, Seung-Youl; Cheon, Sanghoon; Lee, Myung-Lae; Ahn, Seong-Deok; Zyung, Taehyoung; Lee, Jeong-Ik; Moon, Jaehyun; Chu, Hye Yong

    2012-09-01

    We are successful to lit the organic light emitting diode (OLED) lighting panel through the magnetically coupled wireless power transmission technology. For the wireless power transmission, we used the operation frequency 932 kHz, specially designed double spiral type transmitter, small and thin receiver on the four layered printed circuit board, and schottky diodes for the full bridge rectifier. Our white OLED is a hybrid type, in which phosphorescent and fluorescent organics are used together to generate stable white color. The total efficiency of power transmission is around 72%.

  13. 850nm light-emitting-diode phototherapy plus low-dose tacrolimus (FK-506) as combination therapy in the treatment of Dermatophagoides farinae-induced atopic dermatitis-like skin lesions in NC/Nga mice.

    PubMed

    Kim, Chang-Hyun; Cheong, Kyung Ah; Lee, Ai-Young

    2013-11-01

    Light emitting diode (LED) phototherapy is an effective alternative for the treatment of inflammatory skin disorders. Tacrolimus (FK-506) is a potent immunomodulating agent, which has been used to treat AD. Combination therapy is often used in the treatment of AD to improve therapeutic efficacy or to reduce the dose of each drug. To investigate the therapeutic efficacy of monotherapy with either 850nm LED phototherapy or low-dose FK-506, and combination therapy in Dermatophagoides farina (Df)-induced AD-like skin lesions in NC/Nga mice. The Df-induced NC/Nga mice with a clinical score of 7 were used for treatment with LED (10 and 25J/cm(2)) alone, low-dose FK-506 (1mg/kg) or in combination. The synergistic effects of combined therapy were evaluated by dermatitis scores, skin histology, skin barrier function, and immunological parameters, such as IgE, NO, Th2-mediated cytokines and chemokines. Combination therapy with 850nm (25J/cm(2)) LED and low-dose FK-506 showed a significant reduction in the severity of skin lesions. Combined therapy decreased in the serum level of IgE, NO, and in the splenic level of Th2-mediated cytokines and chemokines. Combination therapy significantly also reduced the inflammatory cellular infiltrate into the skin lesions. Moreover, combination therapy led to recovery of skin barrier function in the skin lesions. The use of combination of LED phototherapy and low-dose immunosuppressant improved Df-induced AD-like skin lesions in an NC/Nga mouse model by dominantly reducing IgE, NO, suppressing Th2-mediated immune responses, and inhibiting inflammatory cells, as well as improving skin barrier function. Copyright © 2013 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.

  14. 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.

  15. Point-of-use water disinfection using UV light-emitting diodes to reduce bacterial contamination.

    PubMed

    Nelson, Kristina Y; McMartin, Dena W; Yost, Christopher K; Runtz, Ken J; Ono, Takaya

    2013-08-01

    The treatment process described in this research explores the impact of exposing water samples containing fecal coliforms to the radiation produced by single ultraviolet (UV) light-emitting diodes (LEDs) operating at 265 nm. UV LEDs are long lasting, compact in size and produce more efficient light output than traditional mercury-vapour bulbs, making them ideal for application in point-of-use disinfection systems, such as in remote areas. In this study, contaminated water samples containing either a pure culture of Escherichia coli or tertiary effluent from the City of Regina Wastewater Treatment Plant were used to study the application and efficiency of using UV LEDs for water disinfection. The results indicate that bacterial inactivation was achieved in a time-dependent manner, with 1- and 2.5-log E. coli reductions in water following 20 and 50 min of UV LED exposure, respectively. Ultraviolet radiation was less effective in reducing coliform bacteria in wastewater samples due to the elevated turbidity levels. Further work remains to be completed to optimize the application of UV LEDs for point-of-use disinfection systems; however, the results from this study support that bacterial inactivation using UV LEDs is possible, meriting further future technological development of the LEDs.

  16. Pulsed Light-Emitting Diodes for a Higher Phytochemical Level in Microgreens.

    PubMed

    Vaštakaitė, Viktorija; Viršilė, Akvilė; Brazaitytė, Aušra; Samuolienė, Giedrė; Jankauskienė, Julė; Novičkovas, Algirdas; Duchovskis, Pavelas

    2017-08-09

    A novel research of pulsed light-emitting diode (LED) lighting versus continuous lighting was conducted by analyzing phytochemical levels in microgreens. Red pak choi (Brassica rapa var. chinensis), mustard (Brassica juncea L.), and tatsoi (Brassica rapa var. rosularis) were grown indoors under HPS lamps supplemented with monochromatic (455, 470, 505, 590, and 627 nm) LEDs [total photosynthetic photon flux density (PPFD) of 200 ± 10 μmol m(-2) s(-1), for 16 h day(-1)]. For pulsed light treatments, the frequencies at 2, 32, 256, and 1024 Hz with a duty cycle of 50% monochromatic LEDs were applied. The results were compared to those under the continuous light (0 Hz) condition in terms of total phenolic content, anthocyanins, and antiradical activity (DPPH). The summarized data suggested that pulsed light affected accumulation of secondary metabolites both positive and negative in microgreens. The significant differences in the response of phytochemicals between pulsed light at several frequencies and continuous light were determined. The most positive effects of 2, 256, and 1024 Hz for total phenolic compounds in mustard under all wavelength LEDs were achieved. The LED frequencies at 2 and 32 Hz were the most suitable for accumulation of anthocyanins in red pak choi and tatsoi. The highest antiradical activity under the treatments of 32, 256, and 1024 Hz in mustard and under the 2 Hz frequency in red pak choi and tatsoi was determined.

  17. Cuban experience for therapy in dentistry with light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Sopena, Esperanza P.; Serra, Mayra C.; Sopena, Maria d. l. A.; Lopez Silva, Sonnia M.

    1996-01-01

    Interest in the interaction of low power light with tissues has increased in the last few years. Very often, the stimulating effects of irradiation have been explained by the role of the coherence of laser radiation as it acts upon biological objects. This argument is not convincing and the purpose of the present report is to describe the experiences during two years working with infrared (IR) GaAs light emitting diodes (LED) as clinical light for the therapy of some dental diseases. Equipment was designed and built, FOTOTER, which was approved by the National Health Office (registration No. 7910B). The treatment was practiced on 360 patients. They presented pain on buccal or facial structures and disorders on buccal tissues. Pathologies, number of patients treated, application time in each trigger point, number of sessions, and the relief pain patients are summarized. We conclude that the therapy with IR LED has the same effects as the HeNe and GaAs laser therapy on the biological buccal tissues. We recommend LED therapy for the treatment of these dentistry diseases.

  18. 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.

  19. 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.

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

    SciTech Connect

    Vashchenko, A. A.; Goriachiy, D. O.; Vitukhnovsky, A. G.; Tananaev, P. N.; Vasnev, V. A.; Rodlovskaya, E. N.

    2016-01-15

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

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

  5. Enhancement of Barrier Properties Using Ultrathin Hybrid Passivation Layer for Organic Light Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Bae, Sung Jin; Lee, Joo Won; Park, Jung Soo; Kim, Dong Young; Hwang, Sung Woo; Kim, Jai‑Kyeong; Ju, Byeong‑Kwon

    2006-07-01

    The hybrid thin-film (HTF) passivation layer composed of the UV curable acrylate layer and MS-31 (MgO:SiO2=3:1 wt %) layer was adopted in organic light emitting diode (OLED) to protect organic light emitting materials from penetrations of oxygen and water vapors. The moisture resistance of the deposited HTF layer was measured by the water vapor transmission rate (WVTR). The results showed that the HTF layer possessed a very low WVTR value of lower than 0.007 g/(m2 \\cdot day) at 37.8 °C and 100% RH. Therefore, the HTF on the OLED was found to be very effective in protect what from the penetrations of oxygen and moisture.

  6. All-solution-processed inverted quantum-dot light-emitting diodes.

    PubMed

    Castan, Alice; Kim, Hyo-Min; Jang, Jin

    2014-02-26

    Quantum dots are a promising new candidate for the emissive material in light-emitting devices for display applications. The fabrication of such devices by solution processing allows considerable cost reduction and is therefore very attractive for industrial manufacturers. We report all solution-processed colloidal quantum-dot light-emitting diodes (QLEDs) with an inverted structure. The red, green, and blue devices showed maximum luminances of 12 510, 32 370, and 249 cd/m(2) and turn-on voltages of 2.8, 3.6, and 3.6 V, respectively. We investigate the effect of a surfactant addition in the hole injection layer (HIL), with the aim of facilitating layer deposition and thereby enhancing device performance. We demonstrate that in the device structure presented in this study, a small amount of surfactant in the HIL can significantly improve the performance of the QLED.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    PubMed

    Oh, Phil-Sun; Kim, Hyun-Soo; Kim, Eun-Mi; Hwang, Hyosook; Ryu, Hyang Hwa; Lim, SeokTae; Sohn, Myung-Hee; Jeong, Hwan-Jeong

    2017-01-18

    The aim of this study was to determine the effects and molecular mechanism of blue light emitting diode (LED) in tumor cells. A migration and invasion assay for the metastatic behavior of mouse colon cancer CT-26 and human fibrosarcoma HT-1080 cells was performed. Cancer cell migration-related proteins were identified by obtaining a 2-dimensional gel electrophoresis (2-DE) in total cellular protein profile of blue LED-irradiated cancer cells, followed by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis of proteins. Protein levels were examined by immunoblotting. Irradiation with blue LED inhibited CT-26 and HT-1080 cell migration and invasion. The anti-metastatic effects of blue LED irradiation were associated with inhibition of matrix metalloproteinase (MMP)-2 and MMP-9 expression. P38 MAPK phosphorylation was increased in blue LED-irradiated CT-26 and HT-1080 cells, but was inhibited after pretreatment with SB203580, a specific inhibitor of p38 MAPK. Inhibition of p38 MAPK phosphorylation by SB203580 treatment increased number of migratory cancer cells in CT-26 and HT-1080 cells, indicating that blue LED irradiation inhibited cancer cell migration via phosphorylation of p38 MAPK. Additionally blue LED irradiation of mice injected with CT-26 cells expressing luciferase decreased early stage lung metastasis compared to untreated control mice. These results indicate that blue LED irradiation inhibits cancer cell migration and invasion in vitro and in vivo.

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

    PubMed

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

    2016-12-01

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

  14. 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.

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

    PubMed

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

    2016-03-22

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

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

    PubMed

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

    2017-07-21

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

  17. 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.

  18. Light emitting fabric for photodynamic treatment of actinic keratosis

    NASA Astrophysics Data System (ADS)

    Thecua, E.; Vicentini, C.; Vignion, A.-S.; Lecomte, F.; Deleporte, P.; Mortier, L.; Szeimies, R.-M.; Mordon, S.

    2017-02-01

    The integration of optical fibers into flexible textile structures, by using knitting or weaving processes can allow the development of flexible light sources. The paper aims to present a new technology: Light Emitting Fabrics (LEF), which can be used for example for PDT of Actinic Keratosis in Dermatology. The predetermined macro-bending of optical fibers, led to a homogeneous side emission of light over the entire surface of the fabric. Tests showed that additional curvatures when applying the LEF on non-planar surfaces had no impact on light delivery and proved that LEF can adapt to the human morphology. The ability of the LEF, coupled with a 635nm LASER source, to deliver a homogeneous light to lesions is currently assessed in a clinical trial for the treatment of AK of the scalp by PDT. The low irradiance and progressive activation of the photosensitizer ensure a pain reduction, compared to discomfort levels experienced by patients during a conventional PDT session.

  19. Colloidal metal oxide nanocrystals as charge transporting layers for solution-processed light-emitting diodes and solar cells.

    PubMed

    Liang, Xiaoyong; Bai, Sai; Wang, Xin; Dai, Xingliang; Gao, Feng; Sun, Baoquan; Ning, Zhijun; Ye, Zhizhen; Jin, Yizheng

    2017-02-28

    Colloidal metal oxide nanocrystals offer a unique combination of excellent low-temperature solution processability, rich and tuneable optoelectronic properties and intrinsic stability, which makes them an ideal class of materials as charge transporting layers in solution-processed light-emitting diodes and solar cells. Developing new material chemistry and custom-tailoring processing and properties of charge transporting layers based on oxide nanocrystals hold the key to boosting the efficiency and lifetime of all-solution-processed light-emitting diodes and solar cells, and thereby realizing an unprecedented generation of high-performance, low-cost, large-area and flexible optoelectronic devices. This review aims to bridge two research fields, chemistry of colloidal oxide nanocrystals and interfacial engineering of optoelectronic devices, focusing on the relationship between chemistry of colloidal oxide nanocrystals, processing and properties of charge transporting layers and device performance. Synthetic chemistry of colloidal oxide nanocrystals, ligand chemistry that may be applied to colloidal oxide nanocrystals and chemistry associated with post-deposition treatments are discussed to highlight the ability of optimizing processing and optoelectronic properties of charge transporting layers. Selected examples of solution-processed solar cells and light-emitting diodes with oxide-nanocrystal charge transporting layers are examined. The emphasis is placed on the correlation between the properties of oxide-nanocrystal charge transporting layers and device performance. Finally, three major challenges that need to be addressed in the future are outlined. We anticipate that this review will spur new material design and simulate new chemistry for colloidal oxide nanocrystals, leading to charge transporting layers and solution-processed optoelectronic devices beyond the state-of-the-art.

  20. 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.

  1. 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

    2015-04-08

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

  2. Application of highly ordered carbon nanotubes templates to field-emission organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Li, Chi-Shing; Su, Shui-Hsiang; Chi, Hsiang-Yu; Yokoyama, Meiso

    2009-01-01

    An anodic aluminum oxide (AAO) template was formed by a two-step anodization process. Carbon nanotubes (CNTs) were successfully synthesized along with AAO pores and the diameters of CNTs equaled those of AAO pores. The lengths of CNTs during a chemical vapor deposition synthesized process on the AAO template were effectively controlled. These AAO-CNTs exhibit excellent field emission with a low turn-on field (0.7 V/μm) and a low threshold field (1.4 V/μm). The field enhancement factor, calculated from the non-saturated region of the Fowler-Nordheim (F-N) plot, is about 8237. A novel field-emission organic light-emitting diode (FEOLED) combining AAO-CNTs cathodes as electron source with organic electroluminescent (EL) light-emitting layers coated on indium-tin-oxide (ITO) is produced. The uniform and dense luminescence image is obtained in the FEOLEDs. Organic EL light-emitting materials have lower working voltage than inorganic phosphor-coated fluorescent screens.

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  4. 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.

  5. Modelling the spatial colour distribution of phosphor-white high power light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Keppens, A.; Denijs, S.; Wouters, S.; Ryckaert, W. R.; Deconinck, G.; Hanselaer, P.

    2010-05-01

    In contrast to the spatial (luminous) intensity distribution of high power light-emitting diodes (LEDs), little effort has been made to examine the spatial colour distribution of these light sources, i.e. the values of CIE colour coordinates as a function of direction in space. The spatial colour variation is negligible for single colour emitters, but this is not the case for bichromatic white LEDs using phosphor for wavelength conversion. As the latter diode types are most often used for high colour rendering applications, a quantitative description of their colour distribution is necessary. Therefore, photogoniometer measurements have been performed on a variety of white light-emitting diodes incorporating a planar (remote) phosphor. In this paper measurement results are used to discuss and model the spatial colour distribution of phosphor-white LEDs. Such LEDs appear to show an intrinsic and inevitable spatial colour variation. Furthermore, the measurement data and constructed model allow evaluating the visibility of spatial colour differences and the relevance of colour binning measurements at the end of LED package production lines. Using insights on spatial colour distribution gathered throughout this paper, a design proposal is made to vastly decrease the colour variation of phosphor-white LEDs.

  6. 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).

  7. Color-tunable multilayer light-emitting diodes based on conjugated polymers

    NASA Astrophysics Data System (ADS)

    Huang, C. C.; Meng, H. F.; Ho, G. K.; Chen, C. H.; Hsu, C. S.; Huang, J. H.; Horng, S. F.; Chen, B. X.; Chen, L. C.

    2004-02-01

    Wide-range low-voltage continuous color tuning is achieved in multilayer light-emitting diodes based exclusively on the commonly used high-efficiency electroluminescent conjugated polymers. There are three layers for red, green, and blue emission, and one extra layer for electron blocking. The color of the emitted photon depends on the position of the electron-hole recombination. Due to the stronger field dependence of the electron mobility relative to the hole mobility, the recombination zone is pushed away from the cathode and concentrated in different emissive layers as the voltage increases.

  8. MM/T program for three color light emitting diode display modules

    NASA Astrophysics Data System (ADS)

    David, R. F.; Lewis, G. W.

    1981-10-01

    This report provides a complete description of the LED panel, along with a discussion of the processes and tooling required for its production at reasonable cost. An 'LED Panel Exerciser' (test system) which was delivered to the government is described. Suggested changes to ERADCOM TECHNICAL REQUIREMENTS NO. MMT-799938 are presented based on analysis and present practice. Sample processes, operator's manuals, and drawings are included. Problems involving the quality of procurred light emitting diodes and collimators are discussed, along with actions which are being taken to resolve them.

  9. 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.

  10. Optical design of tunnel lighting with white light-emitting diodes.

    PubMed

    Tsai, Ming-Shiou; Lee, Xuan-Hao; Lo, Yi-Chien; Sun, Ching-Cherng

    2014-10-10

    This paper presents a tunnel lighting design consisting of a cluster light-emitting diode and a free-form lens. Most of the energy emitted from the proposed luminaire is transmitted onto the surface of the road in front of drivers, and the probability that that energy is emitted directly into drivers' eyes is low. Compared with traditional fluorescent lamps, the proposed luminaire, of which the optical utilization factor, optical efficiency, and uniformity are, respectively, 44%, 92.5%, and 0.72, exhibits favorable performance in energy saving, glare reduction, and traffic safety.

  11. Indium Tin Oxide Electrode with an Ultrathin Al Buffer Layer for Flexible Organic Light Emitting Diode

    NASA Astrophysics Data System (ADS)

    Sim, Boyeon; Hwang, Hyeonseok; Ryu, Seungyoon; Baik, Hongkoo; Lee, Myeongkyu

    2010-06-01

    This paper reports that the mechanical and electrical stability of indium tin oxide (ITO) film deposited on flexible plastic substrate can be much enhanced with a thin Al buffer layer while maintaining a visible transmittance over 75%. The improved stability is attributed to the effective elastic mismatch between the film and the substrate reduced by a ductile interlayer. A polymer light emitting diode fabricated using an ITO/Al anode exhibited a luminance of 13,000 cd/m2 with a current efficiency of 16 cd/A. Bending-induced degradation of the device performance was also alleviated when a mechanical buffer layer was inserted.

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

    PubMed

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

    2012-04-01

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

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

    SciTech Connect

    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.

  14. 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.

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

    DOE PAGES

    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.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

  19. Microcavity organic light-emitting diodes for strongly directed pure red, green, and blue emissions

    NASA Astrophysics Data System (ADS)

    Tokito, Shizuo; Tsutsui, Tetsuo; Taga, Yasunori

    1999-09-01

    In this article we demonstrate strongly directed pure red, green, and blue emissions in the organic light-emitting diodes (OLEDs) with a planar microcavity defined by a pair of dielectric mirror and a metal mirror. By careful control of the cavity mode and the position of the resonance wavelength, the strong directionality in the forward direction as well as the spectral narrowing and the intensity enhancement are realized in the microcavity OLEDs. The intensity enhancements at the resonance wavelength are 1.5-5 compared to the noncavity OLEDs, and the chromaticity coordinates of the emission colors are the ideal primary colors. The experimental results are compared to theoretically calculated ones.

  20. 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

  1. 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.

  2. 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.

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

    SciTech Connect

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

    2014-06-09

    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).

  4. 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.

  5. High efficiency light emitting diode with anisotropically etched GaN-sapphire interface

    NASA Astrophysics Data System (ADS)

    Lo, M. H.; Tu, P. M.; Wang, C. H.; Hung, C. W.; Hsu, S. C.; Cheng, Y. J.; Kuo, H. C.; Zan, H. W.; Wang, S. C.; Chang, C. Y.; Huang, S. C.

    2009-07-01

    We report the fabrication and study of high efficiency ultraviolet light emitting diodes with inverted micropyramid structures at GaN-sapphire interface. The micropyramid structures were created by anisotropic chemical wet etching. The pyramid structures have significantly enhanced the light output efficiency and at the same time also improved the crystal quality by partially relieving the strain and reducing the dislocation defects in GaN. The electroluminescent output power at normal direction was enhanced by 120% at 20 mA injection current and the output power integrated over all directions was enhanced by 85% compared to a reference sample.

  6. InGaN light-emitting diode stripes with reduced luminous exitance.

    PubMed

    Cheung, W S; Cheung, Y F; Chen, H T; Hui, R S Y; Waffenschmidt, E; Choi, H W

    2015-06-01

    InGaN light-emitting diodes of stripe geometries have been demonstrated. The elongated geometry facilitates light spreading in the longitudinal direction. The chips are further shaped by laser-micromachining to have partially-inclined sidewalls. The light extraction efficiencies of such 3D chip geometries are enhanced by ~12% (~8% according to ray-trace simulations), leading to a reduction of junction temperatures. The effective emission area is also increased four times compared to a cubic chip. The stripe LEDs are thus more efficient emitters with reduced luminous exitance, making them more suitable for a wide range of lighting applications.

  7. 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.

  8. Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes.

    PubMed

    Elfström, D; Guilhabert, B; McKendry, J; Poland, S; Gong, Z; Massoubre, D; Richardson, E; Rae, B R; Valentine, G; Blanco-Gomez, G; Gu, E; Cooper, J M; Henderson, R K; Dawson, M D

    2009-12-21

    We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370 nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8 W/cm2 per imaged pixel in circular spots of diameter approximately 8 microm. We show example structures written in positive as well as in negative photoresist.

  9. Miniaturized optoelectronic tweezers controlled by GaN micro-pixel light emitting diode arrays.

    PubMed

    Zarowna-Dabrowska, Alicja; Neale, Steven L; Massoubre, David; McKendry, Jonathan; Rae, Bruce R; Henderson, Robert K; Rose, Mervyn J; Yin, Huabing; Cooper, Jonathan M; Gu, Erdan; Dawson, Martin D

    2011-01-31

    A novel, miniaturized optoelectronic tweezers (OET) system has been developed using a CMOS-controlled GaN micro-pixelated light emitting diode (LED) array as an integrated micro-light source. The micro-LED array offers spatio-temporal and intensity control of the emission pattern, enabling the creation of reconfigurable virtual electrodes to achieve OET. In order to analyse the mechanism responsible for particle manipulation in this OET system, the average particle velocity, electrical field and forces applied to the particles were characterized and simulated. The capability of this miniaturized OET system for manipulating and trapping multiple particles including polystyrene beads and live cells has been successfully demonstrated.

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

    PubMed

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

    2015-09-01

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

  11. Doping effects of vanadium pentoxide in hole injection layer for quantum dot light emitting diodes

    NASA Astrophysics Data System (ADS)

    Song, Suk-Ho; Song, Dae-Ho; Lee, Jun-Seo; Kim, Sang-Soo; Song, Jang-Kun

    2017-05-01

    We report the doping effect of V2O5 into hole injection layer (HIL) for quantum dot light emitting diodes (QD-LEDs). We used PEDOT:PSS for HIL, and by doping 0.1 wt% of V2O5 into PEDOT:PSS layer, the maximum external quantum efficiency was increased from 1 % to 1.28 % and the turn-on voltage was reduced from 14.65 V to 12.72 V, when compared to pure PEDOT:PSS. This indicates that V2O5 enhances the hole injection property for PEDOT:PSS layer.

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

    PubMed

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

    2015-04-01

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

  13. 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.

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

    PubMed

    Su, Jung-Chieh; Lu, Chun-Lin

    2009-11-23

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  16. High performance inverted top-emitting organic light-emitting diodes with enhanced intrinsic quantum yield

    NASA Astrophysics Data System (ADS)

    Wu, Yukun; Guo, Runda; Wang, Hongbo; Zhang, Zhensong; Zhao, Yi

    2015-09-01

    Inverted top-emitting organic light-emitting diodes (ITOLEDs) with aluminum as cathode and semitransparent silver as anode are investigated. Comparing the blue, green and red ITOLEDs with conventional BEOLEDs based on iridium complex, it is surprising that the red ITOLED exhibits a higher efficiency nearly twice as that of the bottom-emitting counterpart, while blue and green ITOLEDs are comparable to BEOLEDs. We explain that the role of the strong microcavity effect improved the spontaneous emission of emitters in all ITOLEDs, however, only the intrinsic quantum yield of the red emitters is improved due to its comparable radiative and nonradiative decay rates.

  17. 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

  18. Monolithic integration of individually addressable light-emitting diode color pixels

    NASA Astrophysics Data System (ADS)

    Chung, Kunook; Sui, Jingyang; Demory, Brandon; Teng, Chu-Hsiang; Ku, Pei-Cheng

    2017-03-01

    Monolithic integration of individually addressable light-emitting diode (LED) color pixels is reported. The integration is enabled by local strain engineering. The use of a nanostructured active region comprising one or more nanopillars allows color tuning across the visible spectrum. In the current work, integration of amber, green, and blue pixels is demonstrated. The nanopillar LEDs exhibit an electrical performance comparable to that of a conventional thin-film LED fabricated on the same wafer. The proposed platform uses only standard epitaxy and a similar process flow as a conventional LED. It is also shown that the emission intensity can be linearly tuned without shifting the color coordinate of individual pixels.

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

    PubMed

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

    2012-07-01

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

  20. Efficiency enhancement of blue phosphorescent organic light-emitting diodes using mixed electron transport layer

    NASA Astrophysics Data System (ADS)

    Yoo, Seung Il; Yoon, Ju-An; Kim, Nam Ho; Kim, Jin Wook; Lee, Ho Won; Kim, Young Kwan; He, Gufeng; Kim, Woo Young

    2015-01-01

    Blue phosphorescent organic light-emitting diodes (OLED) using mixed electron transport layer (ETL) were fabricated with the device structure of ITO/NPB/mCP:Firpic-8%/TPBi:BCP or TPBi:3TPYMB/Liq/Al to observe mixed ETL's influence on their electrical and optical characteristics. OLED device with mixed ETL of TPBi with BCP or 3TPYMB significantly improved its current efficiency to 30.4 and 34.2 cd/A comparing to 19.8 cd/A of single ETL with BCP only. We examined mixed ETL's capability of electron transport and triplet exciton confinement enhancing phosphorescent OLED's luminance and luminous efficiency.

  1. Electroluminescence enhancement in polymer light-emitting diodes through hole injection layer insertion

    NASA Astrophysics Data System (ADS)

    Li, Sheng; Tong, Guo-Ping; George, Thomas F.

    2009-10-01

    After a hole injection layer is inserted into a polymer light-emitting diode (PLED), the positive polaron is easily injected into the polymer layer. An applied electrical field drives the positive polaron to approach and collide with the nonemissive triplet exciton. The collision between the positive polaron and neutral triplet exciton induces the exciton to emit light. Based on this physical picture, the maximum quantum efficiency of the PLEDs, 61.6%, is consistent with the experimental result of 60%. With the help of an external magnetic field, a structure of PLEDs with high electroluminescent efficiency is designed.

  2. 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.

  3. Organic light emitting diodes using a Ga:ZnO anode

    SciTech Connect

    Berry, J. J.; Ginley, D. S.; Burrows, P. 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 compared. Relative to ITO, the GZO anodes have a slightly better sheet resistance and transparency in the visible spectral region. Device data suggest that GZO effectively injects holes into an aromatic triamine hole transporting layer. Indium-free anodes such as GZO are expected to improve OLED stability while lowering the cost per unit area, which is crucial for OLED based lighting applications.

  4. Wideband antireflective circular polarizer exhibiting a perfect dark state in organic light-emitting-diode display.

    PubMed

    Kim, Bong Choon; Lim, Young Jin; Song, Je Hoon; Lee, Jun Hee; Jeong, Kwang-Un; Lee, Joong Hee; Lee, Gi-Dong; Lee, Seung Hee

    2014-12-15

    We proposed wideband antireflective circular polarizer for realizing a true black state in all viewing directions in organic light-emitting-diode displays (OLEDs). Present commercialized wideband circular polarizer consisted of a half wave and a quarter wave plates having the refractive index parameter (Nz) of 1.5 in both films exhibits light leakage in the oblique viewing directions, deteriorating image quality of a black state. We evaluated Nzs of both films and proposed a new wideband antireflective circular polarizer with a perfect dark state in all viewing directions with Nz = 0.5 in both plates, which will greatly improve image quality of OLEDs.

  5. GaN-based light-emitting diodes on origami substrates

    NASA Astrophysics Data System (ADS)

    Jung, Younghun; Wang, Xiaotie; Kim, Jiwan; Hyun Kim, Sung; Ren, Fan; Pearton, Stephen J.; Kim, Jihyun

    2012-06-01

    GaN-based light-emitting diodes (LEDs) were transferred to paper substrates after a laser lift-off (LLO) process with an ArF excimer laser system (λ = 193 nm) to remove the sapphire substrate and produce freestanding blue LED templates. The threshold voltage (˜2.7 V), current-voltage characteristics, and peak emission wavelength (442 nm) were not changed after the paper substrate was subsequently wrinkled. We were able to demonstrate transfers to both planar and folded (origami) paper structures, showing the promise of the LLO process for transferring LEDs to arbitrary surfaces.

  6. Low-cost high-power light emitting diodes for photoacoustic imaging

    NASA Astrophysics Data System (ADS)

    Dai, Xianjin; Yang, Hao; Jiang, Huabei

    2017-03-01

    We present a photoacoustic imaging system based on a low-cost high-power miniature light emitting diode (LED), which has the capability of in vivo mapping vasculature networks in biological tissue. Phantoms were used to demonstrate the feasibility of the system, while in vivo imaging the vasculature of mouse ear shows that LED-based photoacoustic imaging (LED-PAI) could have great potential for label-free biomedical imaging applications, overcoming the practical limitations of the use of bulky and expensive pulsed lasers.

  7. Realistic model for the output beam profile of stripe and tapered superluminescent light-emitting diodes.

    PubMed

    Causa, Frederica; Sarma, Jayanta

    2003-07-20

    We present a new model to analyse the spatial characteristics of the output beam of conventional (straight-stripe) and tapered superluminescent light-emitting diodes. The device model includes both spontaneous and stimulated emission processes as well as a nonuniform carrier density distribution to correctly represent current spreading and carrier diffusion effects. Near- and far-field intensity profiles computed with this model are accurately verified over a wide range of injection currents by comparisons with experimental results measured from in-house fabricated devices.

  8. Tailoring of self-assembled monolayer for polymer light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Choi, Beomrak; Rhee, Jungsoo; Lee, Hong H.

    2001-09-01

    The choice of a self-assembled monolayer (SAM) is tailored to specifically remove water on an indium-tin oxide electrode and to reduce barrier height for long-term stability of polymer light-emitting diodes. Water, which is a major cause of long-term degradation, is shown to have entirely reversible effects on the power efficiency of the device. It is shown that the use of a SAM for the specific purposes results in a more than an order of magnitude increase in the half lifetime of the device based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene].

  9. 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.

  10. 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%.

  11. Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light-Emitting Diodes.

    PubMed

    Di, Dawei; Yang, Le; Richter, Johannes M; Meraldi, Lorenzo; Altamimi, Rashid M; Alyamani, Ahmed Y; Credgington, Dan; Musselman, Kevin P; MacManus-Driscoll, Judith L; Friend, Richard H

    2017-04-01

    Solution-processed polymer organic light-emitting diodes (OLEDs) doped with triplet-triplet annihilation (TTA)-upconversion molecules, including 9,10-diphenylanthracene, perylene, rubrene and TIPS-pentacene, are reported. The fraction of triplet-generated electroluminescence approaches the theoretical limit. Record-high efficiencies in solution-processed OLEDs based on these materials are achieved. Unprecedented solid-state TTA-upconversion quantum yield of 23% (TTA-upconversion reaction efficiency of 70%) at electrical excitation well below one-sun equivalent is observed.

  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. 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.

  14. Efficient inverted organic light-emitting devices by amine-based solvent treatment (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Song, Myoung Hoon; Choi, Kyoung-Jin; Jung, Eui Dae

    2015-10-01

    The efficiency of inverted polymer light-emitting diodes (iPLEDs) were remarkably enhanced by introducing spontaneously formed ripple-shaped nanostructure of ZnO (ZnO-R) and amine-based polar solvent treatment using 2-methoxyethanol and ethanolamine (2-ME+EA) co-solvents on ZnO-R. The ripple-shape nanostructure of ZnO layer fabricated by solution process with optimal rate of annealing temperature improves the extraction of wave guide modes inside the device structure, and 2-ME+EA interlayer enhances the electron injection and hole blocking and reduces exciton quenching between polar solvent treated ZnO-R and emissive layer. As a result, our optimized iPLEDs show the luminous efficiency (LE) of 61.6 cd A-1, power efficiency (PE) of 19.4 lm W-1 and external quantum efficiency (EQE) of 17.8 %. This method provides a promising method, and opens new possibilities for not only organic light-emitting diodes (OLEDs) but also other organic optoelectronic devices such as organic photovoltaics, organic thin film transistors, and electrically driven organic diode laser.

  15. 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

  16. Proliferation of chicken fibroblasts induced by light-emitting diodes: a comparative trial for different wavelengths

    NASA Astrophysics Data System (ADS)

    Vinck, Elke; Cagnie, B.; Declercq, H.; Cornelissen, R.; Cambier, D.

    2003-12-01

    The effectiveness and applicability of a variety of light sources, in the treatment of wounds has thoroughly been investigated, in vitro as well as in vivo. The current commercial availability of Light Emitting Diode (LED) sources therefore also invites research to explore the effect of low power infrared, red and green light on wound healing, e.g. by means of fibroblast proliferation. Therefore a controlled and randomized study on cultured embryonic chicken fibroblasts was conducted. The fibroblasts were irradiated during three consecutive days, at several wavelengths (950 nm, 660 nm and 570 nm) and a respective power output of 160 mW, 80 mW or 10 mW. Treatment duration varied from 1 minute to 3 minutes to obtain a surface energy density of 0.9 J/cm2 (infrared and red light) or 0.2 J/cm2 (green light). Statistical analysis revealed that LED irradiation for all three wavelengths induced a higher rate of proliferation in comparison of the control group. This difference was statistically significant (p < .001). With regard to the amount of proliferation the green probe yielded a significantly higher number of cells, than the red (p < .001) an the infrared probe (p < .001). Furthermore, the red probe provided a higher increase (p < .001) than the IR probe. LED irradiation results in an increased fibroblast proliferation in vitro. This outcome postulates beneficial stimulatory effects of LED at the applied wavelength, energy density and power output on wound healing in vivo. Further investigation is necessary to examine this hypothesis.

  17. Light-emitting diode therapy reduces persistent inflammatory pain: Role of interleukin 10 and antioxidant enzymes.

    PubMed

    Martins, D F; Turnes, B L; Cidral-Filho, F J; Bobinski, F; Rosas, R F; Danielski, L G; Petronilho, F; Santos, A R S

    2016-06-02

    During the last decades, the use of light-emitting diode therapy (LEDT) has increased significantly for the treatment of wound healing, analgesia and inflammatory processes. Nevertheless, scientific data on the mechanisms responsible for the therapeutic effect of LEDT are still insufficient. Thus, this study investigated the analgesic, anti-inflammatory and anti-oxidative effect of LEDT in the model of chronic inflammatory hyperalgesia. Mice injected with Complete Freund's Adjuvant (CFA) underwent behavioral, i.e. mechanical and hot hyperalgesia; determination of cytokine levels (tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-10), oxidative stress markers (protein carbonyls and thiobarbituric acid reactive species (TBARS)) and antioxidant enzymes (catalase (CAT) and superoxide dismutase (SOD)). Additionally, mice were pretreated with either naloxone or fucoidin and mechanical hyperalgesia was assessed. LEDT inhibited mechanical and thermal hyperalgesia induced by CFA injection. LEDT did not reduce paw edema, neither influenced the levels of TNF-α and IL1-β; although it increased the levels of IL-10. LEDT significantly prevented TBARS increase in both acute and chronic phases post-CFA injection; whereas protein carbonyl levels were reduced only in the acute phase. LEDT induced an increase in both SOD and CAT activity, with effects observable in the acute but not in the chronic. And finally, pre-administration of naloxone or fucoidin prevented LEDT analgesic effect. These data contribute to the understanding of the neurobiological mechanisms involved in the therapeutic effect of LEDT as well as provides additional support for its use in the treatment of painful conditions of inflammatory etiology. Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed

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

    2017-02-22

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

  1. Hydrogenated aluminium-doped zinc oxide semiconductor thin films for polymeric light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Hao, X. T.; Zhu, F. R.; Ong, K. S.; Tan, L. W.

    2006-01-01

    Highly conducting transparent thin films of aluminium(Al)-doped zinc oxide (ZnO:Al) were deposited by a radio frequency magnetron-sputtering technique using an argon and hydrogen gas mixture at room temperature. Hydrogen serves as a shallow donor and plays a critical role in improving the Al doping efficiency to enhance the conductivity of thin films. The effect of hydrogen partial pressure on the properties of ZnO:Al films was investigated in detail. Polycrystalline ZnO:Al films with a surface roughness of about 2 nm, conductivity of 1.97 × 103 S cm-1, transmittance of over 83% in the visible wavelength region and an optical band gap of 3.93 eV were achieved at a hydrogen partial pressure of 7.5 × 10-4 Pa. A ZnO:Al film with the desired properties was used as an anode contact in a bi-layer polymeric light-emitting diode. A polyethylene dioxythiophene-polystyrene sulfonate doped with poly(styrenesulfonic acid) (PEDOT: PSS) and phenyl-substituted poly(p-phenylene vinylene) (Ph-PPV) were employed as a hole transport layer and a light-emitting layer, respectively. The electro-luminescence performance of the aforementioned diode was studied and compared to a control device with an indium tin oxide anode.

  2. Electrically tunable excitonic light-emitting diodes based on monolayer WSe2 p–n junctions

    SciTech Connect

    Ross, Jason S.; Klement, Philip; Jones, Aaron M.; Ghimire, Nirmal J.; Yan, Jiaqiang; Mandrus, D. G.; Taniguchi, Takashi; Watanabe, Kenji; Kitamura, Kenji; Yao, Wang; Cobden, David H.; Xu, Xiaodong

    2014-03-09

    The development of light-emitting diodes with improved efficiency, spectral properties, compactness and integrability is important for lighting, display, optical interconnect, logic and sensor applications1, 2, 3, 4, 5, 6, 7, 8. Monolayer transition-metal dichalcogenides have recently emerged as interesting candidates for optoelectronic applications due to their unique optical properties9, 10, 11, 12, 13, 14, 15, 16. Electroluminescence has already been observed from monolayer MoS2 devices17, 18. However, the electroluminescence efficiency was low and the linewidth broad due both to the poor optical quality of the MoS2 and to ineffective contacts. Here, we report electroluminescence from lateral p–n junctions in monolayer WSe2 induced electrostatically using a thin boron nitride support as a dielectric layer with multiple metal gates beneath. This structure allows effective injection of electrons and holes, and, combined with the high optical quality of WSe2, yields bright electroluminescence with 1,000 times smaller injection current and 10 times smaller linewidth than in MoS2 (refs 17,18). Furthermore, by increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged and neutral excitons. This system has the required ingredients for new types of optoelectronic device, such as spin- and valley-polarized light-emitting diodes, on-chip lasers and two-dimensional electro-optic modulators.

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

    SciTech Connect

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

    2010-09-28

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

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

  6. Extracting and directing light out of organic light emitting diodes (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Lemmer, Uli; Egel, Amos; Hecht, Matthias; Preinfalk, Jan B.; Gomard, Guillaume

    2015-10-01

    Light extraction from organic light emitting diodes (OLEDs) is attracting considerable interest as being crucial for enhancing the energy efficiency in lighting applications. Light extraction can be realized by lithographically defined internal diffraction gratings or stochastic scattering centers. The former approach needs in addition an external optical layer for scrambling the angularly dependent emission spectra in order to avoid color shifts [1]. Micro lens arrays cannot only be used for fulfilling this task but they can also be used for enhancing the luminosity into a specific direction. We demonstrate recent advances towards high efficiency OLEDs with high directionality. In addition to the relevant technologies we have also developed a comprehensive simulation software for the quantitative description of the light propagation inside the devices. Here, a particular challenging task is the description of multiple and coherent optical scattering. We have recently developed a software for the exact simulation based on a scattering matrix formalism [2]. [1] T. Bocksrocker, J. B. Preinfalk, J. Asche-Tauscher, A. Pargner, C. Eschenbaum, F. Maier-Flaig and U. Lemmer, White organic light emitting diodes with enhanced internal and external outcoupling for ultra-efficient light extraction and Lambertian emission Opt. Expr. 20, A932 (2012). [2] A. Egel, U. Lemmer, Dipole emission in stratified media with multiple spherical scatterers: Enhanced outcoupling from OLEDs, Journal of Quantitative Spectroscopy and Radiative Transfer 148, 165 (2014).

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

    PubMed

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

    2011-02-04

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

  8. 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.

  9. 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.

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

    PubMed

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

    2013-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

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

    PubMed Central

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

    2017-01-01

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

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

    PubMed

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

    2013-07-01

    In multilayer white organic light-emitting diodes the electronic processes in the various layers--injection and motion of charges as well as generation, diffusion and radiative decay of excitons--should be concerted such that efficient, stable and colour-balanced electroluminescence can occur. Here we show that it is feasible to carry out Monte Carlo simulations including all of these molecular-scale processes for a hybrid multilayer organic light-emitting diode combining red and green phosphorescent layers with a blue fluorescent layer. The simulated current density and emission profile are shown to agree well with experiment. The experimental emission profile was obtained with nanometre resolution from the measured angle- and polarization-dependent emission spectra. The simulations elucidate the crucial role of exciton transfer from green to red and the efficiency loss due to excitons generated in the interlayer between the green and blue layers. The perpendicular and lateral confinement of the exciton generation to regions of molecular-scale dimensions revealed by this study demonstrate the necessity of molecular-scale instead of conventional continuum simulation.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    The development of Organic Light Emitting Diode (OLED), using an optically transparent substrate material and organic semiconductor materials, has been widely utilized by the electronic industry when producing new technological products. The OLED are the base Poly(3,4-ethylenedioxythiophene), PEDOT, Poly(p-phenylenevinylene), PPV, and Polyaniline, PANI, were deposited in Indium Tin Oxide, ITO, and characterized by UV-Visible Spectroscopy (UV-Vis), Optical Parameters (OP) and Scanning Electron Microscopy (SEM). In addition, the thin film obtained by the deposition of PANI, prepared in perchloric acid solution, was identified through PANI-X1. The result obtained by UV-Vis has demonstrated that the PET/ITO/PEDOT/PPV/PANI-X1/Al layer does not have displacement of absorption for wavelengths greaters after spin-coating and electrodeposition. Thus, the spectral irradiance of the OLED informed the irradiance of 100 W/m2, and this result, compared with the standard Light Emitting Diode (LED), has indicated that the OLED has higher irradiance. After 1200 hours of electrical OLED tests, the appearance of nanoparticles visible for images by SEM, to the migration process of organic semiconductor materials, was present, then. Still, similar to the phenomenon of electromigration observed in connections and interconnections of microelectronic devices, the results have revealed a new mechanism of migration, which raises the passage of electric current in OLED.

  17. External efficiency and thermal reliability enhanced multi-chip package design for light emitting diodes

    NASA Astrophysics Data System (ADS)

    Tang, Meng-Han; Wu, Tsung-Han; Su, Guo-Dung J.

    2008-08-01

    With the power of light emitting diodes (LEDs) getting higher and higher, the issue of thermal management is getting much more important. In this paper, we discussed a new idea to get white light without using traditional phosphor and to enhance its extraction efficiency. Microlens is used for increasing external efficiency and shaping light pattern. The location of micro-lens is designed carefully by considering cup reflection. We also revealed that it is important to consider the angle of exit light from LEDs. The result shows our design is suitable for high color rendering index (CRI) application. At the same time, the uniform white light is approached as the light has been strongly diffused. Furthermore, we try to decrease the junction temperature as low as possible so as to increase stability and lifetime of LEDs. In order to maintain color mixing and dissipate heat, multi-chip or four pairs of electrodes which are electroplated with copper after bulk micromachining process within a silicon-based package are used. This novel packaging technique needs just a few processing steps and could be mass produced for nowadays high brightness light emitting diodes (HBLEDs).

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

    PubMed

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

    2012-09-01

    As light-emitting diodes become more common as the light source for low vision aids, the effect of illumination colour temperature on magnifier reading performance was investigated. Reading ability (maximum reading speed, critical print size, threshold near visual acuity) using Radner charts and subjective preference was assessed for 107 participants with visual impairment using three stand magnifiers with light emitting diode illumination colour temperatures of 2,700 K, 4,500 K and 6,000 K. The results were compared with distance visual acuity, prescribed magnification, age and the primary cause of visual impairment. Reading speed, critical print size and near visual acuity were unaffected by illumination colour temperature (p > 0.05). Reading metrics decreased with worsening acuity and higher levels of prescribed magnification but acuity was unaffected by age. Each colour temperature was preferred and disliked by a similar number of patients and was unrelated to distance visual acuity, prescribed magnification and age (p > 0.05). Patients had better near acuity (p = 0.002), critical print size (p = 0.034) and maximum reading speed (p < 0.001), and the improvement in near from distance acuity was greater (p = 0.004) with their preferred rather than least-liked colour temperature illumination. A range of colour temperature illuminations should be offered to all visually impaired individuals prescribed with an optical magnifier for near tasks to optimise subjective and objective benefits. © 2012 The Authors. Clinical and Experimental Optometry © 2012 Optometrists Association Australia.

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

    PubMed

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

    2012-05-27

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

  20. 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.

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

    PubMed

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

    2012-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  3. Effects of colored light-emitting diode illumination on behavior and performance of laying hens.

    PubMed

    Huber-Eicher, B; Suter, A; Spring-Stähli, P

    2013-04-01

    The best method for lighting poultry houses has been an issue for many decades, generating much interest in any new systems that become available. Poultry farmers are now increasingly using colored LED (light-emitting diodes) to illuminate hen houses (e.g., in Germany, Austria, the Netherlands, and England). In Switzerland all newly installed systems are now equipped with LED, preferably green ones. The LED give monochromatic light from different wavelengths and have several advantages over conventional illuminants, including high energy efficiency, long life, high reliability, and low maintenance costs. The following study examines the effects of illumination with white, red, and green LED on behavior and production parameters of laying hens. Light intensities in the 3 treatments were adjusted to be perceived by hens as equal. Twenty-four groups of 25 laying hens were kept in identical compartments (5.0 × 3.3 m) equipped with a litter area, raised perches, feed and drinking facilities, and nest boxes. Initially, they were kept under white LED for a 2-wk adaptation period. For the next 4 wk, 8 randomly chosen compartments were lit with red LED (640 nm) and 8 others with green LED (520 nm). Behavior was monitored during the last 2 wk of the trial. Additionally weight gain, feed consumption, onset of lay, and laying performance were recorded. The results showed minor effects of green light on explorative behavior, whereas red light reduced aggressiveness compared with white light. The accelerating effect of red light on sexual development of laying hens was confirmed, and the trial demonstrated that this effect was due to the specific wavelength and not the intensity of light. However, an additional effect of light intensity may exist and should not be excluded.

  4. Is light-emitting diode phototherapy (LED-LLLT) really effective?

    PubMed Central

    Kim, Won-Serk; Calderhead, R Glen

    2011-01-01

    Background: Low level light therapy (LLLT) has attracted attention in many clinical fields with a new generation of light-emitting diodes (LEDs) which can irradiate large targets. To pain control, the first main application of LLLT, have been added LED-LLLT in the accelerated healing of wounds, both traumatic and iatrogenic, inflammatory acne and the patient-driven application of skin rejuvenation. Rationale and Applications: The rationale behind LED-LLLT is underpinned by the reported efficacy of LED-LLLT at a cellular and subcellular level, particularly for the 633 nm and 830 nm wavelengths, and evidence for this is presented. Improved blood flow and neovascularization are associated with 830 nm. A large variety of cytokines, chemokines and macromolecules can be induced by LED phototherapy. Among the clinical applications, non-healing wounds can be healed through restoring the collagenesis/collagenase imbalance in such examples, and ‘normal’ wounds heal faster and better. Pain, including postoperative pain, postoperative edema and many types of inflammation can be significantly reduced. Experimental and clinical evidence: Some personal examples of evidence are offered by the first author, including controlled animal models demonstrating the systemic effect of 830 nm LED-LLLT on wound healing and on induced inflammation. Human patients are presented to illustrate the efficacy of LED phototherapy on treatment-resistant inflammatory disorders. Conclusions: Provided an LED phototherapy system has the correct wavelength for the target cells, delivers an appropriate power density and an adequate energy density, then it will be at least partly, if not significantly, effective. The use of LED-LLLT as an adjunct to conventional surgical or nonsurgical indications is an even more exciting prospect. LED-LLLT is here to stay. PMID:24155530

  5. Effect of NASA light-emitting diode irradiation on wound healing.

    PubMed

    Whelan, H T; Smits, R L; Buchman, E V; Whelan, N T; Turner, S G; Margolis, D A; Cevenini, V; Stinson, H; Ignatius, R; Martin, T; Cwiklinski, J; Philippi, A F; Graf, W R; Hodgson, B; Gould, L; Kane, M; Chen, G; Caviness, J

    2001-12-01

    The purpose of this study was to assess the effects of hyperbaric oxygen (HBO) and near-infrared light therapy on wound healing. Light-emitting diodes (LED), originally developed for NASA plant growth experiments in space show promise for delivering light deep into tissues of the body to promote wound healing and human tissue growth. In this paper, we review and present our new data of LED treatment on cells grown in culture, on ischemic and diabetic wounds in rat models, and on acute and chronic wounds in humans. In vitro and in vivo (animal and human) studies utilized a variety of LED wavelength, power intensity, and energy density parameters to begin to identify conditions for each biological tissue that are optimal for biostimulation. LED produced in vitro increases of cell growth of 140-200% in mouse-derived fibroblasts, rat-derived osteoblasts, and rat-derived skeletal muscle cells, and increases in growth of 155-171% of normal human epithelial cells. Wound size decreased up to 36% in conjunction with HBO in ischemic rat models. LED produced improvement of greater than 40% in musculoskeletal training injuries in Navy SEAL team members, and decreased wound healing time in crew members aboard a U.S. Naval submarine. LED produced a 47% reduction in pain of children suffering from oral mucositis. We believe that the use of NASA LED for light therapy alone, and in conjunction with hyperbaric oxygen, will greatly enhance the natural wound healing process, and more quickly return the patient to a preinjury/illness level of activity. This work is supported and managed through the NASA Marshall Space Flight Center-SBIR Program.

  6. Effects of light-emitting diode (LED) therapy on skeletal muscle ischemia reperfusion in rats.

    PubMed

    Takhtfooladi, Mohammad Ashrafzadeh; Shahzamani, Mehran; Takhtfooladi, Hamed Ashrafzadeh; Moayer, Fariborz; Allahverdi, Amin

    2015-01-01

    Low-level laser therapy has been shown to decrease ischemia-reperfusion injuries in the skeletal muscle by induction of synthesis of antioxidants and other cytoprotective proteins. Recently, the light-emitting diode (LED) has been used instead of laser for the treatment of various diseases because of its low operational cost compared to the use of a laser. The objective of this work was to analyze the effects of LED therapy at 904 nm on skeletal muscle ischemia-reperfusion injury in rats. Thirty healthy male Wistar rats were allocated into three groups of ten rats each as follows: normal (N), ischemia-reperfusion (IR), and ischemia-reperfusion + LED (IR + LED) therapy. Ischemia was induced by right femoral artery clipping for 2 h followed by 2 h of reperfusion. The IR + LED group received LED irradiation on the right gastrocnemius muscle (4 J/cm(2)) immediately and 1 h following blood supply occlusion for 10 min. At the end of trial, the animals were euthanized and the right gastrocnemius muscles were submitted to histological and histochemical analysis. The extent of muscle damage in the IR + LED group was significantly lower than that in the IR group (P < 0.05). In comparison with other groups, tissue malondialdehyde (MDA) levels in the IR group were significantly increased (P < 0.05). The muscle tissue glutathione (GSH), superoxide dismutases (SOD), and catalase (CAT) levels in the IR group were significantly lower than those in the subjects in other groups. From the histological and histochemical perspective, the LED therapy has alleviated the metabolic injuries in the skeletal muscle ischemia reperfusion in this experimental model.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  10. Low-level light emitting diode (LED) therapy suppresses inflammasome-mediated brain damage in experimental ischemic stroke.

    PubMed

    Lee, Hae In; Lee, Sae-Won; Kim, Nam Gyun; Park, Kyoung-Jun; Choi, Byung Tae; Shin, Yong-Il; Shin, Hwa Kyoung

    2017-02-06

    Use of photostimulation including low-level light emitting diode (LED) therapy has broadened greatly in recent years because it is compact, portable, and easy to use. Here, the effects of photostimulation by LED (610 nm) therapy on ischemic brain damage was investigated in mice in which treatment started after a stroke in a clinically relevant setting. The mice underwent LED therapy (20 min) twice a day for 3 days, commencing at 4 hours post-ischemia. LED therapy group generated a significantly smaller infarct size and improvements in neurological function based on neurologic test score. LED therapy profoundly reduced neuroinflammatory responses including neutrophil infiltration and microglia activation in the ischemic cortex. LED therapy also decreased cell death and attenuated the NLRP3 inflammasome, in accordance with down-regulation of pro-inflammatory cytokines IL-1β and IL-18 in the ischemic brain. Moreover, the mice with post-ischemic LED therapy showed suppressed TLR-2 levels, MAPK signaling and NF-kB activation. These findings suggest that by suppressing the inflammasome, LED therapy can attenuate neuroinflammatory responses and tissue damage following ischemic stroke. Therapeutic interventions targeting the inflammasome via photostimulation with LED may be a novel approach to ameliorate brain injury following ischemic stroke. Effect of post-ischemic low-level light emitting diode therapy (LED-T) on infarct reduction was mediated by inflammasome suppression.

  11. A study of interfaces between organic and metal materials and their application in polymer light-emitting diodes and polymer photovoltaic solar cells

    NASA Astrophysics Data System (ADS)

    Li, Juo-Hao

    2009-12-01

    In the past few decades, it attracts a lot of attention for the researches of organic semiconductor due to its new and interesting properties, compared with conventional soft material and inorganic semiconductor. Several kinds of electronic devices such as light emitting diodes, thin film transistors and photovoltaic solar cell based on these organic semiconductors are also proposed and studied. This dissertation will focus on interface between organic and metal, which is one of the mysteries and critical issues remaining in the material properties and limiting the device performance. In the first chapter, a brief review and introduction of the organic semiconductor and organic electronics will be described. The purpose is to introduce the research background, motivation and methodology. Chapter two demonstrates the concept of top-emitting light-emitting diodes and the research focus on the interfaces between the light-emitting polymer and electrodes. An interfacial layer is introduced to improve the hole-injection from the anode. Except for alternating the electrode architecture, surface treatment or modification also have significant influences on interfacial electronic structure. Chapter three describes the discovery of solvent treatment on top of the light-emitting polymer and its application on organic electrophosphorescent devices. To further study the interfaces in organic electronics, an interface layer of sol-gel processed titanium oxide is introduced into organic electronic devices. Chapter four describes the amorphous titanium oxide and its application on polymer light-emitting diodes, while Chapter five demonstrates nanocrystalline titanium dioxide and its application in both light-emitting devices and polymer photovoltaic solar cells.

  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. 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.

  14. Deep ultraviolet emitting polarization induced nanowire light emitting diodes with AlxGa1-xN active regions

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    In this report, we demonstrate band gap tuning of the active region emission wavelength from 365 nm to 250 nm in light emitting diodes fashioned from catalyst-free III-nitride nanowires. Optical characteristics of the nanowire heterostructures and fabricated devices are studied via electroluminescence (EL) and photoluminescence spectroscopy over a wide range of active region compositions. It is observed that for typical nanowire plasma assisted molecular beam epitaxy growth conditions, tuning of emission to wavelengths shorter than 300 nm is hampered by the presence of an optically active defect level. We show that by increasing the AlGaN nanowire growth temperatures this defect emission can be suppressed. These findings are applied to growth of the active region of a nanowire light emitting diode, resulting in a polarization-induced nanowire light emitting diode with peak EL at 250 nm.

  15. [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.

  16. 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

  17. 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.

  18. Omnidirectional multiview three-dimensional display based on direction-selective light-emitting diode array

    NASA Astrophysics Data System (ADS)

    Yan, Caijie; Liu, Xu; Liu, Di; Xie, Jing; Xia, Xin Xing; Li, Haifeng

    2011-03-01

    A volumetric display system based on a rotating light-emitting diode (LED) array panel can realize a three-dimensional (3-D) display truthfully in the space, but the drawback is missing the occlusion of a 3-D image. We propose an omnidirectional 3-D display with correct occlusion based on a direction-selective LED array panel, which is realized by setting a direction-convergent diaphragm array in front of the LED array. Every diaphragm restricts a light-emitting characteristic of every LED. By using direction-convergent diaphragm array, the observer around the display system can only see one image displayed by the LED array at the corresponding position. With the high-speed rotation of the LED panel, a series of views of a 3-D scene are displayed every angle patch in one circle. We set up an acquisition system to record 180 views of the 3-D scene with a rotating camera along a circle, and then the 180 images are displayed sequentially on the rotating direction-selective LED array to get a 360 deg 3-D display. This 3-D display technology has two main advantages: easy to get viewer-position-dependent correct occlusion and simplify the 3-D data preprocessing process which is helpful to real-time 3-D display.

  19. White organic light-emitting diodes based on electroplex from polyvinyl carbazole and carbazole oligomers blends

    NASA Astrophysics Data System (ADS)

    Chen, Fei-Peng; Xu, Bin; Zhao, Zu-Jin; Tian, Wen-Jing; Lü, Ping; Im, Chan

    2010-03-01

    White organic light-emitting diodes with a blue emitting material fluorene-centred ethylene-liked carbazole oligomer (Cz6F) doped into polyvinyl carbazole (PVK) as the single light-emitting layer are reported. The optical properties of Cz6F, PVK, and PVK:Cz6F blends are studied. Single and double layer devices are fabricated by using PVK: Cz6F blends, and the device with the configuration of indium tin oxide (ITO)/PVK:Cz6F/tris(8-hydroxyquinolinate)aluminium (Alq3)/LiF/A1 exhibits white light emission with Commission Internationale de l'Éclairage chromaticity coordinates of (0.30, 0.33) and a brightness of 402 cd/m2. The investigation reveals that the white light is composed of a blue-green emission originating from the excimer of Cz6F molecules and a red emission from an electroplex from the PVK:Cz6F blend films.

  20. 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.

  1. Numerical study of the light output intensity of the bilayer organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Lu, Feiping

    2017-02-01

    The structure of organic light-emitting diodes (OLEDs) is one of most important issues that influence the light output intensity (LOI) of OLEDs. In this paper, based on a simple but accurate optical model, the influences of hole and electron transport layer thickness on the LOI of bilayer OLEDs, which with N,N0- bis(naphthalen-1-yl)-N,N0- bis(phenyl)- benzidine (NPB) or N,N'- diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4-diamine (TPD) as hole transport layer, with tris(8-hydroxyquinoline) aluminum (Alq3) as electron transport and light emitting layers, were investigated. The laws of LOI for OLEDs under different organic layer thickness values were obtained. The results show that the LOI of devices varies in accordance with damped cosine or sine function as the increasing of organic layer thickness, and the results show that the bilayer OLEDs with the structure of Glass/ITO/NPB (55 nm)/Alq3 (75 nm)/Al and Glass/ITO/TPB (60 nm)/Alq3 (75 nm)/Al have most largest LOI. When the thickness of Alq3 is less than 105 nm, the OLEDs with TPD as hole transport layer have larger LOI than that with NPB as hole transport layer. The results obtained in this paper can present an in-depth understanding of the working mechanism of OLEDs and help ones fabricate high efficiency OLEDs.

  2. 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.

  3. Efficient and extremely long-lived organic light-emitting diodes based on dinaphthylperylene

    NASA Astrophysics Data System (ADS)

    Jarikov, Viktor V.; Kondakov, Denis Y.; Brown, Christopher T.

    2007-11-01

    We describe a synergistic effect of a lifetime-extending light-emitting-layer (LEL) additive and improved electron injection and transport in organic light-emitting diodes (OLEDs). Previously reported di(2-naphthyl)perylene (DNP) serves as the LEL additive capable of extending the operating lifetime of OLEDs by over two orders of magnitude. Using 2-phenyl-9,10-di(2-naphthyl)anthracene (PADN) as an electron-transport layer (ETL) and a separate layer of 4,7-diphenyl-1,10-phenanthroline (BPhen) as an electron-injection layer (EIL) significantly improves electron delivery into the charge recombination zone relative to traditional ETL made of tris(8-quinolinolate)aluminum (Alq). This ETL∣EIL combination not only results in approximately seven times lower electric field in the ETL and, thus, lower drive voltage and higher efficiency devices, but can also increase device lifetime substantially. In a representative device containing a red-emitting LEL dopant [Commission Internationale de l'Eclairage 1931 2° color chromaticity coordinates (CIEx ,y) of 0.65, 0.35], the external quantum efficiency, electroluminescence yield, drive voltage, and operating half-life (t50) can reach 5.8%, 6.5cd/A, 4.5V, and ˜1000000h, respectively, all at 20mA/cm2 current density.

  4. 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

  5. ITO-free large-area organic light-emitting diodes with an integrated metal grid.

    PubMed

    Choi, Seungkeun; Kim, Sung-Jin; Fuentes-Hernandez, Canek; Kippelen, Bernard

    2011-07-04

    We report on ITO-free large-area organic light-emitting diodes (OLEDs) fabricated on glass substrates comprising α-NPD as a hole transport layer (HTL) and coevaporated CBP:Ir(ppy)(3) as the emission layer. Indium-tin-oxide (ITO) was replaced with a conductive polymer electrode and an electroplated thick metal grid was used to improve the homogeneity of the potential distribution over the transparent polymer electrode. An electrical model of a metal grid integrated OLED shows the benefits of the use of metal grids in terms of improving the uniformity of the light emitted as the area of the OLED increases as well as the conductivity of the transparent electrode decreases. By integrating metal grids with polymer electrodes, the luminance increases more than 24% at 6 V and 45% at 7 V compared to the polymer electrode devices without a metal grid. This implies that a lower voltage can be applied to achieve the same luminance, hence lowering the power consumption. Furthermore, metal grid integrated OLEDs exhibited less variation in light emission compared to devices without a metal grid.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  7. 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.

  8. 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.

  9. Sb-doped p-ZnO /Ga-doped n-ZnO homojunction ultraviolet light emitting diodes

    NASA Astrophysics Data System (ADS)

    Chu, S.; Lim, J. H.; Mandalapu, L. J.; Yang, Z.; Li, L.; Liu, J. L.

    2008-04-01

    ZnO p-n homojunction light emitting diodes were fabricated based on p-type Sb-doped ZnO /n-type Ga-doped ZnO thin films. Low resistivity Au /NiO and Au /Ti contacts were formed on top of p-type and n-type ZnO layers, respectively. Au /NiO contacts on p-type ZnO exhibited a low specific resistivity of 7.4×10-4Ωcm2. The light emitting diodes yielded strong near-band-edge emissions in temperature-dependent and injection current-dependent electroluminescence measurements.

  10. Optical logic inverter and AND elements using laser or light-emitting diodes and photodetectors in a bistable system.

    PubMed

    Okumura, K; Ogawa, Y; Ito, H; Inaba, H

    1984-11-01

    Fundamental optical digital data-processing functions of optical inverter and optical AND elements are proposed and demonstrated experimentally for the first reported time using light-emitting diodes and a photodetector in a hybrid optoelectronic bistable system. The inherent simplicity of these bistable optical devices that use either a laser or a light-emitting diode should make it possible to realize these optical logic functions by monolithic optoelectronic integration. Specific integration schemes are also proposed, and future interesting and useful applications are discussed.

  11. 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.

  12. Enhanced Optical and Electrical Properties of Polymer-Assisted All-Inorganic Perovskites for Light-Emitting Diodes.

    PubMed

    Ling, Yichuan; Tian, Yu; Wang, Xi; Wang, Jamie C; Knox, Javon M; Perez-Orive, Fernando; Du, Yijun; Tan, Lei; Hanson, Kenneth; Ma, Biwu; Gao, Hanwei

    2016-10-01

    Highly bright light-emitting diodes based on solution-processed all-inorganic perovskite thin film are demonstrated. The cesium lead bromide (CsPbBr3 ) created using a new poly(ethylene oxide)-additive spin-coating method exhibits photoluminescence quantum yield up to 60% and excellent uniformity of electrical current distribution. Using the smooth CsPbBr3 films as emitting layers, green perovskite-based light-emitting diodes (PeLEDs) exhibit electroluminescent brightness and efficiency above 53 000 cd m(-2) and 4%: a new benchmark of device performance for all-inorganic PeLEDs.

  13. The enhancement of light-emitting efficiency using GaN-based multiple quantum well light-emitting diodes with nanopillar arrays

    NASA Astrophysics Data System (ADS)

    Wan, Tu-Tu; Ye, Zhan-Qi; Tao, Tao; Xie, Zi-Li; Zhang, Rong; Liu, Bin; Xiu, Xiang-Qian; Li, Yi; Han, Ping; Shi, Yi; Zheng, You-Dou

    2013-08-01

    The quest for higher modulation speed and lower energy consumption has inevitably promoted the rapid development of semiconductor-based solid lighting devices in recent years. GaN-based light-emitting diodes (LEDs) have emerged as promising candidates for achieving high efficiency and high intensity, and have received increasing attention among many researchers in this field. In this paper, we use a self-assembled array-patterned mask to fabricate InGaN/GaN multi-quantum well (MQW) LEDs with the intention of enhancing the light-emitting efficiency. By utilizing inductively coupled plasma etching with a self-assembled Ni cluster as the mask, nanopillar arrays are formed on the surface of the InGaN/GaN MQWs. We then observe the structure of the nanopillars and find that the V-defects on the surface of the conventional structure and the negative effects of threading dislocation are effectively reduced. Simultaneously, we make a comparison of the photoluminescence (PL) spectrum between the conventional structure and the nanopillar arrays, achieved under an experimental set-up with an excitation wavelength of 325 mm. The analysis demonstrates that MQW-LEDs with nanopillar arrays achieve a PL intensity 2.7 times that of conventional LEDs. In response to the PL spectrum, some reasons are proposed for the enhancement in the light-emitting efficiency as follows: 1) the improvement in crystal quality, namely the reduction in V-defects; 2) the roughened surface effect on the expansion of the critical angle and the attenuated total reflection; and 3) the enhancement of the light-extraction efficiency due to forward scattering by surface plasmon polariton modes in Ni particles deposited above the p-type GaN layer at the top of the nanopillars.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  15. Broadband localized surface-plasmon-enhanced green light-emitting diodes by silver nanocone array

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Li, Yufeng; Huang, Yaping; Wang, Shuai; Feng, Lungang; Gong, Zhina; Wang, Jiangteng; Ding, Wen; Zhang, Ye; Yun, Feng

    2015-12-01

    Green light-emitting diodes (LEDs) with silver nanocone-shaped structures embedded in p-GaN have been demonstrated with the surface plasmon (SP) enhancement effect. The resonance frequency has been broadened and the strength of coupling has been considerably enhanced. Compared with the LED without Ag nanocones, the integrated photoluminescence (PL) intensity of the SP-enhanced LED was improved by ∼275%, and the electroluminescence (EL) enhancement ratio at a different wavelength was evaluated at an injection current of 50 mA/mm2. At the same time, a reduction in the recombination lifetime indicated an increased internal quantum efficiency of LEDs. The results of simulation using nanocones as well as nanorods indicate good correlation with the experimental observation of the broadening effect. This structure is promising for converting incident photons into the localized surface plasmon (LSP) mode, to enhance the emission of LEDs within a broad wavelength range.

  16. 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.

  17. Blue inorganic light emitting diode on flexible polyimide substrate using laser lift-off process.

    PubMed

    Barange, Nilesh; Kim, Young Dong; Ko, Hyungduk; Park, Joon-Suh; Park, Byoungnam; Ko, Doo-Hyun; Han, Ii Ki

    2014-11-01

    The fabrication process for the blue GaN inorganic light emitting diode (ILED) on flexible polyimide (PI) substrate by laser lift off (LLO) method was demonstrated. The GaN epi-structure was grown on patterned sapphire wafer. GaN samples were temporary bonded with polyimide substrate by flexible silver epoxy. Separation of the whole GaN LED film from GaN/sapphire wafer was accomplished using a single KrF excimer (248 nm) laser pulse directed through the transparent sapphire wafer. Device fabrication was carried out on both rigid silicon and flexible polyimide substrate, and I-V performance for both devices was measured. The optimized LLO process for the whole GaN LED film transfer would be applicable in flexible LED applications without compromising electrical properties.

  18. GaN-based high-voltage light-emitting diodes with backside reflector

    NASA Astrophysics Data System (ADS)

    Huamao, Huang; Hong, Wang; Xiaosheng, Huang; Jinyong, Hu

    2014-07-01

    High-voltage light-emitting diodes (HV-LED) withbackside reflector, including Ti3O5/SiO2 distributed Bragg reflector (DBR) or hybrid reflector combining DBR and Al or Ag metal layer, are investigated using Monte Carlo ray tracing method. The hybrid reflector leads to more enhancement of light-extraction efficiency (LEE). Moreover, the LEE can also be improved by redesigning the thicknesses of DBR. HV-LED with four redesigned DBR pairs (4-MDBR), and those with a hybrid reflector combining 4-MDBR and Al metal layer (4-MDBR-Al), are fabricated. Compared to 4-MDBR, the enhancement of light-output power induced by 4-MDBR-Al is 4.6%, which is consistent with the simulated value of 4.9%.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1992-12-01

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

  2. Er-Pr doped tellurite glass nanocomposites for white light emitting diodes

    NASA Astrophysics Data System (ADS)

    Kityk, I. V.; AlZayed, N. S.; El-Naggar, A. M.; Reben, M.; Wasylak, J.; Lakshminarayana, G.; Reshak, Ali H.; Brik, M. G.

    2012-03-01

    In this paper, optical glass nanocomposites (nanoparticles sizes up to 100 nm) with composition TeO 2-WO 3-PbO-xEr 2O 3-yPr 6O 11 (x = 0.30 mol%, y = 0.70 mol%) embedded into polymer matrices was reported. The two types of polymers chosen for present study were: photopolymer oligoetheracryalte (OEA) and polymethylmethacrylate (PMMA), respectively. The incorporation of the titled nanoparticles into the polymer matrices is analyzed optically. The fluorescence spectra of the nanocomposites were compared with the fluorescence spectra of bulk glasses. Based on the comparison of Er 3 + and Pr 3 + ions' energy level schemes, possible energy transfer processes were identified. The prepared glasses are promising candidates for the white light emitting diodes applications.

  3. III-N light emitting diodes fabricated using RF nitrogen gas source MBE

    NASA Astrophysics Data System (ADS)

    Van Hove, J. M.; Carpenter, G.; Nelson, E.; Wowchak, A.; Chow, P. P.

    1996-07-01

    Homo- and heterojunction III-N light emitting diodes using RF atomic nitrogen plasma molecular beam epitaxy have been grown. GaN films deposited on sapphire using this growth technique exhibited an extremely sharp X-ray diffraction with a full width half maximum of 112 arc sec. p-type doping of the nitride films was done with elemental Mg and resulted in as-grown p-type material with resistivities as low as 2 Ω · cm. Both homo- and heterojunction LEDs showed clear rectification. Emission from the GaN homojunction deposited on n-type SiC was peaked at 410 nm while the AlGaNGaN(Zn)AlGaN double heterojunction LEDs emission was centered about 520 nm.

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

    PubMed

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

    2009-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    PubMed

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

    2014-09-21

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

  7. Thin-type integral imaging method with an organic light emitting diode panel.

    PubMed

    Kim, Youngmin; Kim, Joohwan; Kim, Yunhee; Choi, Heejin; Jung, Jae-Hyun; Lee, Byoungho

    2008-09-20

    A thin and lensless two-dimensional (2D) to three-dimensional (3D) convertible display based on integral imaging using an organic light emitting diode (OLED) panel as a direct emissive light source is proposed with improved optical efficiency. A point light source array for 2D-3D convertible display is formed on the surface light source, i.e., the OLED panel. However, a blurring effect and color separation result from the finite (nonzero) size of point light sources since each point light source is generated by a pixel of the OLED panel. Simulation results for a blurring effect and color separation in terms of rays from a light source with finite size is presented. The proposed system has a thin structure and simple convertibility because it does not need any additional optical element to provide 2D-3D convertibility.

  8. 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.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    Shi, Xiao-Bo; Qian, Min; Wang, Zhao-Kui; Liao, Liang-Sheng

    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 SiO2 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.

  11. Wavelength-stable rare earth-free green light-emitting diodes for energy efficiency.

    PubMed

    Wetzel, Christian; Detchprohm, Theeradetch

    2011-07-04

    Solid state lighting seeks to replace both, incandescent and fluorescent lighting by energy efficient light-emitting diodes (LEDs). Just like compact fluorescent tubes, current white LEDs employ costly rare earth-based phosphors, a drawback we propose to overcome with direct emitting LEDs of all colors. We show the benefits of homoepitaxial LEDs on bulk GaN substrate for wavelength-stable green spectrum LEDs. By use of non-polar growth orientation we avoid big color shifts with drive current and demonstrate polarized light emitters that prove ideal for pairing with liquid crystal display modulators in back light units of television monitors. We further offer a comparison of the prospects of non-polar a- and m-plane growth over conventional c-plane growth.

  12. 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%.

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

    SciTech Connect

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

    2016-06-14

    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.

  14. 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.

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

    PubMed

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

    2014-12-15

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

  16. 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.

  17. Optical design of color light-emitting diode ring light for machine vision inspection

    NASA Astrophysics Data System (ADS)

    Dong, Jing-Tao; Lu, Rong-Sheng; Shi, Yan-Qiong; Xia, Rui-Xue; Li, Qi; Xu, Yan

    2011-04-01

    Uniform irradiance and color adjustability are the key features in the design of lighting for machine vision inspection systems. A simple and practical design tool of angled light-emitting-diode (LED) ring arrays for uniform near-field irradiance has been developed by introducing a simple model to simplify the complexity of nonrotational symmetric irradiance distribution of angled LEDs. The color distribution and color uniformity of the ring array assembled with RGB LEDs are analyzed based on the analytical model of color mixing. According to the theoretical analysis, the simulated results, and the design exemplifications, the practical design tool offers an easy way to estimate the performance of an RGB LED ring array and can be considered as a starting point to reduce the computation time for exact designs that must use a realistic LED model.

  18. A hole accelerator for InGaN/GaN light-emitting diodes

    SciTech Connect

    Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Wang, Liancheng; Zhu, Binbin; Zhang, Yiping; Lu, Shunpeng; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei E-mail: VOLKAN@stanfordalumni.org; Demir, Hilmi Volkan E-mail: VOLKAN@stanfordalumni.org

    2014-10-13

    The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED.

  19. 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%.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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)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)2(acac). The lifetime of device (t95: 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.

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

    PubMed

    Ito, Hiroyuki; Ogawa, Masaki; Sunaga, Shoji

    2013-06-11

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

  2. 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.

  3. 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.

  4. Blue fluorescent emitters: design tactics and applications in organic light-emitting diodes.

    PubMed

    Zhu, Minrong; Yang, Chuluo

    2013-06-21

    Organic light-emitting diodes (OLEDs) are competitive candidates for the next generation flat-panel displays and solid state lighting sources. Efficient blue-emitting materials have been one of the most important prerequisites to kick off the commercialization of OLEDs. This tutorial review focuses on the design of blue fluorescent emitters and their applications in OLEDs. At first, some typical blue fluorescent materials as dopants are briefly introduced. Then nondoped blue emitters of hydrocarbon compounds are presented. Finally, the nondoped blue emitters endowed with hole-, electron- and bipolar-transporting abilities are comprehensively reviewed. The key issues on suppressing close-packing, achieving pure blue chromaticity, improving thermal and morphological stabilities, manipulating charge transporting abilities, simplifying device structures and the applications in panchromatic OLEDs are discussed.

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

    PubMed

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

    2017-10-11

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

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

    PubMed

    Chen, Shuming; Kwok, Hoi Sing

    2010-01-04

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. Fabrication of polymer light-emitting diodes using doped silicon electrodes

    NASA Astrophysics Data System (ADS)

    Parker, I. D.; Kim, Helen H.

    1994-04-01

    The paper presents the manufacture of light emitting diodes on Si substrates using semiconducting electroluminescent polymers. The substrate which serves as an electrode material is a doped n and p Si. Device characteristics can be explained by a simple band-based model with little or no band bending, as a result of low doping levels. Electrons tunnel through a triangular barrier caused by the offset between the Fermi level of the cathode and the lowest unoccupied molecular orbital (LUMO) of the MEH-PPV. Holes tunnel through a similar barrier due to the offset between the anode and the highest occupied molecular orbital (HOMO). Electroluminescence occurs through the radiative recombination of charged polarons generated by self-localization of charge on the polymer chain. The forward and reverse bias characteristics for both n- and p- Si/MEH-PPV/Ca device is illustrated.

  9. 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%.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  11. Highly Convergent Simulations of Transport Dynamics in Organic Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    deMello, J. C.

    2002-09-01

    We present a method-of-lines solution procedure for modelling charge transport and recombination in organic light-emitting diodes operating in the trap-free space-charge-limited regime. The numerical procedure employs a spatial remeshing algorithm based on equidistribution principles as reported by Sanz-Serna and Christie (1986, J. Comput. Phys.67, 348) and incorporates additional refinements proposed by Revilla (1986, Int. J. Numer. Methods Eng.23, 2263) and Saucez et al. (1996, J. Comput. Phys.128, 274). The method, which does not give rise to ill-conditioned series of differential equations, offers rapid convergence to the steady state and is especially well suited to systems of equations displaying steep moving solution fronts. The technique is readily extended to more complex systems.

  12. 3D thermal analysis of rectangular microscale inorganic light-emitting diodes in a pulsed operation

    NASA Astrophysics Data System (ADS)

    Cui, Yun; Bian, Zuguang; Li, Yuhang; Xing, Yufeng; Song, Jizhou

    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.

  13. Fabrication of near-infrared polymer light-emitting-diodes using dispersed laser dye

    NASA Astrophysics Data System (ADS)

    Jitsui, Yusuke; Ohtani, Naoki

    2012-05-01

    The purpose of this research is to fabricate polymer light-emitting diodes (PLEDs) operating in the near-infrared (NIR) region. IR-140 is a laser-dye, whose emission wavelength is 870 nm. This NIR dye was dispersed as an emissive dopant within poly(2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO -PPV) and poly(N-vinylcarbazole) (PVK). In addition, 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) was dispersed in the active layer. We fabricated the following two types of samples: (A) indium tin oxide (ITO)/MDMO-PPV:IR-140/aluminum (Al) and (B) ITO/IR-140:PBD:PVK/Al. Sample A successfully showed NIR emissions. However, sample A also revealed EL signals in the visible light region. In sample B, however, the undesired visible light was successfully eliminated due to the improved carrier-balance in the active region.

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

    PubMed

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

    2014-11-01

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

  15. 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.

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

    PubMed

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

    2017-01-06

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

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-07-01

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

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

    PubMed

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

    2010-10-01

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