Injection and detection of a spin-polarized current in a light-emitting diode

Science.gov (United States)

Fiederling, R.; Keim, M.; Reuscher, G.; Ossau, W.; Schmidt, G.; Waag, A.; Molenkamp, L. W.

1999-12-01

The field of magnetoelectronics has been growing in practical importance in recent years. For example, devices that harness electronic spin-such as giant-magnetoresistive sensors and magnetoresistive memory cells-are now appearing on the market. In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts, but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a non-magnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.

Isoelectronic Ln doping in p-GaN and its effects on InGaN light-emitting diodes

International Nuclear Information System (INIS)

Kim, C. S.; Cheong, H. S.; Kang, D. S.; Kim, J. Y.; Hong, C. H.; Suh, E. K.; Lee, H. J.; Cho, H. K.; Adesida, I.

2004-01-01

The effects of isoelectronic In doping in a Mg-doped p-GaN layer on device performance of InGaN light-emitting diodes (LED) were investigated. It was found that there was a decrease of Hall resistivity and contact resistivity in p-GaN with In doping, compared to typical Mg-doped p-GaN. Isoelectronic In doping in p-GaN seems to cause a kind of surfactant effect and/or purification effect similar to the In-doped GaN case, which exhibits a decrease of non-radiative recombination centers and an enhancement of carrier concentration. Light output power and operating voltage were improved by applying an In-doped p-GaN contact layer to the LED.

Light Converting Inorganic Phosphors for White Light-Emitting Diodes

OpenAIRE

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 incand...

Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Reich, Christoph, E-mail: Christoph.Reich@tu-berlin.de; Guttmann, Martin; Wernicke, Tim; Mehnke, Frank; Kuhn, Christian [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, Berlin 10623 (Germany); Feneberg, Martin; Goldhahn, Rüdiger [Institut für Experimentelle Physik, Otto-von-Guericke-Universität, Universitätsplatz 2, Magdeburg 39106 (Germany); Rass, Jens; Kneissl, Michael [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, Berlin 10623 (Germany); Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, Berlin 12489 (Germany); Lapeyrade, Mickael; Einfeldt, Sven; Knauer, Arne; Kueller, Viola; Weyers, Markus [Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, Berlin 12489 (Germany)

2015-10-05

The optical polarization of emission from ultraviolet (UV) light emitting diodes (LEDs) based on (0001)-oriented Al{sub x}Ga{sub 1−x}N multiple quantum wells (MQWs) has been studied by simulations and electroluminescence measurements. With increasing aluminum mole fraction in the quantum well x, the in-plane intensity of transverse-electric (TE) polarized light decreases relative to that of the transverse-magnetic polarized light, attributed to a reordering of the valence bands in Al{sub x}Ga{sub 1−x}N. Using k ⋅ p theoretical model calculations, the AlGaN MQW active region design has been optimized, yielding increased TE polarization and thus higher extraction efficiency for bottom-emitting LEDs in the deep UV spectral range. Using (i) narrow quantum wells, (ii) barriers with high aluminum mole fractions, and (iii) compressive growth on patterned aluminum nitride sapphire templates, strongly TE-polarized emission was observed at wavelengths as short as 239 nm.

White top-emitting organic light-emitting diodes using one-emissive layer of the DCJTB doped DPVBi layer

Energy Technology Data Exchange (ETDEWEB)

Kim, M.S.; Jeong, C.H.; Lim, J.T. [Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of); Yeom, G.Y. [Department of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of); The National Program for Tera-level Devices, Hawolgok-dong, Sungbuk-gu, Seoul, 136-791 (Korea, Republic of)], E-mail: gyyeom@skku.edu

2008-04-01

White top-emitting organic light-emitting diodes (TEOLEDs) composed of one doped emissive layer which emits two-wavelength light though the radiative recombination were fabricated. As the emissive layer, 4,4-bis(2,2-diphenylethen-1-yl)biphenyl (DPVBi) was used as the host material and 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (DCJTB) was added as the dopant material. By optimizing the DCJTB concentration (1.2%) and the thickness of the DPVBi layer (30 nm), the intensity ratio of the two wavelengths could be adjusted for balanced white light emission. By using the device composed of glass/Ag (100 nm)/ITO (90 nm)/2-TNATA (60 nm)/NPB (15 nm)/DPVBi:DCJTB (1.2%, 30 nm)/Alq{sub 3} (20 nm)/Li (1.0 nm)/Al (2.0 nm)/Ag (20 nm)/ITO (63 nm)/SiO{sub 2} (42 nm), the Commission Internationale d'Eclairage (CIE) chromaticity coordinate of (0.32, 0.34) close to the ideal white color CIE coordinate could be obtained at 100 cd/m{sup 2}.

Self-assembly surface modified indium-tin oxide anodes for single-layer light-emitting diodes

CERN Document Server

Morgado, J; Charas, A; Matos, M; Alcacer, L; Cacialli, F

2003-01-01

We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide.

Self-assembly surface modified indium-tin oxide anodes for single-layer light-emitting diodes

International Nuclear Information System (INIS)

Morgado, Jorge; Barbagallo, Nunzio; Charas, Ana; Matos, Manuel; Alcacer, Luis; Cacialli, Franco

2003-01-01

We study the effect of indium-tin oxide surface modification by self assembling of highly polar molecules on the performance of single-layer light-emitting diodes (LEDs) fabricated with polyfluorene blends and aluminium cathodes. We find that the efficiency and light-output of such LEDs is comparable to, and sometimes better than, the values obtained for LEDs incorporating a hole injection layer of poly(3,4-ethylene dioxythiophene) doped with polystyrene sulphonic acid. This effect is attributed to the dipole-induced work function modification of indium-tin oxide

Non-doped-type white organic light-emitting diodes for lighting purpose

Energy Technology Data Exchange (ETDEWEB)

Zhu Jianzhuo [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China); Li Wenlian, E-mail: wllioel@yahoo.com.c [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Chu Bei, E-mail: beichu@163.co [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Yan Fei; Yang Dongfang; Liu Huihui; Wang Junbo [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Graduate School of Chinese Academy of Sciences, Beijing 100039 (China)

2010-05-15

We demonstrate a non-doped white organic light-emitting diode (WOLED) in which the blue-, green- and red-emissions are generated from 4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl, tris(8-hydroxyquinoline)aluminum (Alq) and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyl-julolidyl 9-enyl)-4H-pyran (DCJTB), which is used as an ultrathin layer. The DCJTB ultrathin layer plays the chromaticity tuning role in optimizing the white spectral band by modulating the location of the DCJTB ultrathin layer in the green emissive Alq layer. The optimized WOLED gives the Commission Internationale de l'Eclairage-1931 xy coordinates of (0.319, 0.335), a color rendering index of 91.2 at 10 V, a maximum brightness of 21010 cd/m{sup 2} at 12 V and a maximum current efficiency of 5.17 cd/A at 6.6 V. The electroluminescence mechanism of the white device is also discussed.

AlGaInN-based ultraviolet light-emitting diodes grown on Si(111)

International Nuclear Information System (INIS)

Kipshidze, G.; Kuryatkov, V.; Borisov, B.; Holtz, M.; Nikishin, S.; Temkin, H.

2002-01-01

Ultraviolet light-emitting diodes grown on Si(111) by gas-source molecular-beam epitaxy with ammonia are described. The layers are composed of superlattices of AlGaN/GaN and AlN/AlGaInN. The layers are doped n and p type with Si and Mg, respectively. Hole concentration of 4x10 17 cm -3 , with a mobility of 8 cm2/Vs, is measured in Al 0.4 Ga 0.6 N/GaN. We demonstrate effective n- and p-type doping of structures based on AlN/AlGaInN. Light-emitting diodes based on these structures show light emission between 290 and 334 nm

Top-emitting organic light-emitting diodes.

Science.gov (United States)

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

2011-11-07

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

Highly efficient red fluorescent organic light-emitting diodes by sorbitol-doped PEDOT:PSS

Science.gov (United States)

Zheng, Yan-Qiong; Yu, Jun-Le; Wang, Chao; Yang, Fang; Wei, Bin; Zhang, Jian-Hua; Zeng, Cheng-Hui; Yang, Yang

2018-06-01

This work shows a promising approach to improve device performance by optimizing the electron transport and hole injection layers for tetraphenyldibenzoperiflanthene (DBP):rubrene-based red fluorescent organic light-emitting diodes (OLEDs). We compared the effect of two electron transport layers (ETLs), and found that the rubrene/bathophenanthroline (Bphen) ETL-based OLED showed a much higher external quantum efficiency (EQE) (4.67%) than the Alq3 ETL-based OLED (EQE of 3.08%). The doping ratio of DBP in rubrene was tuned from 1.0 wt% to 4.5 wt%, and the 1.5 wt%-DBP:rubrene-based OLED demonstrated the highest EQE of 5.24% and lowest turn-on voltage of 2.2 V. Atomic force microscopy images indicated that 1.5 wt% DBP-doped rubrene film exhibited a regular strip shape, and this regular surface was favorable to the hole and electron recombination in the emitting layer. Finally, the sorbitol-doped poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was used to further improve the EQE; doping with 6 wt% sorbitol achieved the highest current efficiency of 7.03 cd A‑1 and an EQE of 7.50%. The significantly enhanced performance implies that the hole injection is a limiting factor for DBP:rubrene-based red fluorescent OLEDs.

High-efficiency green phosphorescent organic light-emitting diodes with double-emission layer and thick N-doped electron transport layer

Energy Technology Data Exchange (ETDEWEB)

Nobuki, Shunichiro, E-mail: shunichiro.nobuki.nb@hitachi.com [Hitachi Research Laboratory, Hitachi Ltd., 7-1-1 Omika-cho, Hitachi-city, Ibaraki 319-1292 (Japan); Wakana, Hironori; Ishihara, Shingo [Hitachi Research Laboratory, Hitachi Ltd., 7-1-1 Omika-cho, Hitachi-city, Ibaraki 319-1292 (Japan); Mikami, Akiyoshi [Dept. of Electrical Engineering, Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichimachi, Ishikawa 921-8501 (Japan)

2014-03-03

We have developed green phosphorescent organic light-emitting diodes (OLEDs) with high external quantum efficiency of 59.7% and power efficiency of 243 lm/W at 2.73 V at 0.053 mA/cm{sup 2}. A double emission layer and a thick n-doped electron transport layer were adopted to improve the exciton recombination factor. A high refractive index hemispherical lens was attached to a high refractive index substrate for extracting light trapped inside the substrate and the multiple-layers of OLEDs to air. Additionally, we analyzed an energy loss mechanism to clarify room for the improvement of our OLEDs including the charge balance factor. - Highlights: • We developed high efficiency green phosphorescent organic light-emitting diode (OLED). • Our OLED had external quantum efficiency of 59.7% and power efficiency of 243 lm/W. • A double emission layer and thick n-doped electron transport layer were adopted. • High refractive index media (hemispherical lens and substrate) were also used. • We analyzed an energy loss mechanism to clarify the charge balance factor of our OLED.

Solution-Processed n-Type Graphene Doping for Cathode in Inverted Polymer Light-Emitting Diodes.

Science.gov (United States)

Kwon, Sung-Joo; Han, Tae-Hee; Kim, Young-Hoon; Ahmed, Towfiq; Seo, Hong-Kyu; Kim, Hobeom; Kim, Dong Jin; Xu, Wentao; Hong, Byung Hee; Zhu, Jian-Xin; Lee, Tae-Woo

2018-02-07

n-Type doping with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl) dimethylamine (N-DMBI) reduces a work function (WF) of graphene by ∼0.45 eV without significant reduction of optical transmittance. Solution process of N-DMBI on graphene provides effective n-type doping effect and air-stability at the same time. Although neutral N-DMBI act as an electron receptor leaving the graphene p-doped, radical N-DMBI acts as an electron donator leaving the graphene n-doped, which is demonstrated by density functional theory. We also verify the suitability of N-DMBI-doped n-type graphene for use as a cathode in inverted polymer light-emitting diodes (PLEDs) by using various analytical methods. Inverted PLEDs using a graphene cathode doped with N-DMBI radical showed dramatically improved device efficiency (∼13.8 cd/A) than did inverted PLEDs with pristine graphene (∼2.74 cd/A). N-DMBI-doped graphene can provide a practical way to produce graphene cathodes with low WF in various organic optoelectronics.

Organic light emitting diode with light extracting electrode

Energy Technology Data Exchange (ETDEWEB)

Bhandari, Abhinav; Buhay, Harry

2017-04-18

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

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

Energy Technology Data Exchange (ETDEWEB)

Ding, Baofu, E-mail: b.ding@ecu.edu.au; Alameh, Kamal, E-mail: k.alameh@ecu.edu.au [Electron Science Research Institute, Edith Cowan University, 270 Joondalup Drive, Joondalup WA 6027 Australia (Australia); Song, Qunliang [Institute for Clean Energy and Advanced Materials, Southwest University, Chongqing 400715 (China)

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.

Doping of nano structures for light emitting diode applications

International Nuclear Information System (INIS)

Han, S. W.; Yoo, H. J.; Jeong, E. S.; Park, S. H.

2006-04-01

Lighting Emitting Diodes (LED) have been widely studied and developed for practical applications and the LED market in the world have been dramatically expended. GaN-based LEDs are mostly used. However, for diverse application, we should first solved several problems in the GaN-based LEDs, thermal heating effects and low light emitting efficiency. The thermal heating effects reduce the life time of LEDs and the low light emitting efficiency are disadvantageous in competition with electric lights. In this project, we studied the possibility of ZnO nanomaterials as LEDs. We have developed a techniques to fabricated reproducible ZnO nanorod arrays on various substrates with 40 - 100 nm diameters. We have successfully fabricated two-dimensional ZnO film growth on one-dimensional nanorods. We have also systematically studied ZnO nanorod growth on GaN and Al 2 O 3 substrated with different proton treatments to understand the ZnO nanorod growth mechanism. These techniques will be used to develop p-ZnO/n-ZnO nanomaterials as LEDs

Spin polarization of electrons in a magnetic impurity doped ...

Indian Academy of Sciences (India)

Abstract. A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different ...

Beyond conventional c-plane GaN-based light emitting diodes: A systematic exploration of LEDs on semi-polar orientations

Science.gov (United States)

Monavarian, Morteza

Despite enormous efforts and investments, the efficiency of InGaN-based green and yellow-green light emitters remains relatively low, and that limits progress in developing full color display, laser diodes, and bright light sources for general lighting. The low efficiency of light emitting devices in the green-to-yellow spectral range, also known as the "Green Gap", is considered a global concern in the LED industry. The polar c-plane orientation of GaN, which is the mainstay in the LED industry, suffers from polarization-induced separation of electrons and hole wavefunctions (also known as the "quantum confined Stark effect") and low indium incorporation efficiency that are the two main factors that contribute to the Green Gap phenomenon. One possible approach that holds promise for a new generation of green and yellow light emitting devices with higher efficiency is the deployment of nonpolar and semi-polar crystallographic orientations of GaN to eliminate or mitigate polarization fields. In theory, the use of other GaN planes for light emitters could also enhance the efficiency of indium incorporation compared to c-plane. In this thesis, I present a systematic exploration of the suitable GaN orientation for future lighting technologies. First, in order to lay the groundwork for further studies, it is important to discuss the analysis of processes limiting LED efficiency and some novel designs of active regions to overcome these limitations. Afterwards, the choice of nonpolar orientations as an alternative is discussed. For nonpolar orientation, the (1100)-oriented (mo-plane) structures on patterned Si (112) and freestanding m-GaN are studied. The semi-polar orientations having substantially reduced polarization field are found to be more promising for light-emitting diodes (LEDs) owing to high indium incorporation efficiency predicted by theoretical studies. Thus, the semi-polar orientations are given close attention as alternatives for future LED technology

Polarization methods for diode laser excitation of solid state lasers

Science.gov (United States)

Holtom, Gary R.

2008-11-25

A mode-locked laser employs a coupled-polarization scheme for efficient longitudinal pumping by reshaped laser diode bars. One or more dielectric polarizers are configured to reflect a pumping wavelength having a first polarization and to reflect a lasing wavelength having a second polarization. A Yb-doped gain medium can be used that absorbs light having a first polarization and emits light having a second polarization. Using such pumping with laser cavity dispersion control, pulse durations of less than 100 fs can be achieved.

Polymer light emitting diodes

International Nuclear Information System (INIS)

Gautier-Thianche, Emmmanuelle

1998-01-01

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

Flexible organic light-emitting diodes consisting of a platinum doped indium tin oxide anode

International Nuclear Information System (INIS)

Hsu, C-M; Huang, C-Y; Cheng, H-E; Wu, W-T

2009-01-01

This paper demonstrates that a flexible organic light-emitting diode (OLED) with a platinum (Pt)-doped indium tin oxide (ITO) anode could show superior electro-optical characteristics to those of a conventional device. The threshold voltage and turn-on voltage of an OLED device consisting of an aluminium/lithium fluoride/tris(8-hydroxyquinoline) aluminium/N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4, 4'-diamine/Pt-doped ITO/ITO structure were reduced by 1.2 V and 0.8 V, respectively. Current efficiency was found improved for a driving voltage of less than 6.5 V as a result of the enhanced hole-injection rate, attributed mainly to the elevated surface work function and partly reduced surface roughness of ITO by the incorporated Pt atoms in the ITO matrix.

Low driving voltage blue, green, yellow, red and white organic light-emitting diodes with a simply double light-emitting structure.

Science.gov (United States)

Zhang, Zhensong; Yue, Shouzhen; Wu, Yukun; Yan, Pingrui; Wu, Qingyang; Qu, Dalong; Liu, Shiyong; Zhao, Yi

2014-01-27

Low driving voltage blue, green, yellow, red and white phosphorescent organic light-emitting diodes (OLEDs) with a common simply double emitting layer (D-EML) structure are investigated. Our OLEDs without any out-coupling schemes as well as n-doping strategies show low driving voltage, e.g. white OLED, respectively. This work demonstrates that the low driving voltages and high efficiencies can be simultaneously realized with a common simply D-EML structure.

Color-converted remote phosphor prototype of a multiwavelength excitable borosilicate glass for white light-emitting diodes

International Nuclear Information System (INIS)

Tian Hua; Qiu Kun; Song Jun; Wang Da-Jian; Liu Ji-Wen

2012-01-01

We report a unique red light-emitting Eu-doped borosilicate glass to convert color for warm white light-emitting diodes. This glass can be excited from 394 nm-peaked near ultraviolet light, 466 nm-peaked blue light, to 534 nm-peaked green light to emit the desired red light with an excellent transmission in the wavelength range of 400–700 nm which makes this glass suitable for color conversion without a great cost of luminous power loss. In particular, when assembling this glass for commercial white light-emitting diodes, the tested results show that the color rendering index is improved to 84 with a loss of luminous power by 12 percent at average, making this variety of glass promising for inorganic “remote-phosphor” color conversion

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-11-30

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

Salt-Doped Polymer Light-Emitting Devices

Science.gov (United States)

Gautier, Bathilde

Polymer Light-Emitting Electrochemical Cells (PLECs) are solid state devices based on the in situ electrochemical doping of the luminescent polymer and the formation of a p-n junction where light is emitted upon the application of a bias current or voltage. PLECs answer the drawbacks of polymer light-emitting diodes as they do not require an ultra-thin active layer nor are they reliant on low work function cathode materials that are air unstable. However, because of the dynamic nature of the doping, they suffer from slow response times and poor stability over time. Frozen-junction PLECs offer a solution to these drawbacks, yet they are impractical due to their sub-ambient operation temperature requirement. Our work presented henceforth aims to achieve room temperature frozen-junction PLECS. In order to do that we removed the ion solvating/transporting polymer from the active layer, resulting in a luminescent polymer combined solely with a salt sandwiched between an ITO electrode and an aluminum electrode. The resulting device was not expected to operate like a PLEC due to the absence of an ion-solvating and ion-transporting medium. However, we discovered that the polymer/salt devices could be activated by applying a large voltage bias, resulting in much higher current and luminance. More important, the activated state is quasi static. Devices based on the well-known orange-emitting polymer MEH-PPV displayed a luminance storage half-life of 150 hours when activated by forward bias (ITO biased positively with respect to the aluminum) and 200 hours when activated by reverse bias. More remarkable yet, devices based on a green co-polymer displayed no notable decay in current density or luminance even after being stored for 1200 hours at room temperature! PL imaging under UV excitation demonstrates the presence of doping. These devices are described herein along with an explanation of their operating mechanisms.

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

International Nuclear Information System (INIS)

Guan Yunxia; Niu Lianbin

2009-01-01

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

Device characteristics of organic light-emitting diodes based on electronic structure of the Ba-doped Alq3 layer.

Science.gov (United States)

Lim, Jong Tae; Kim, Kyung Nam; Yeom, Geun Young

2009-12-01

Organic light-emitting diodes (OLEDs) with a Ba-doped tris(8-quinolinolato)aluminum(III) (Alq3) layer were fabricated to reduce the barrier height for electron injection and to improve the electron conductivity. In the OLED consisting of glass/ITO/4,4',4"-tris[2-naphthylphenyl-1-phenylamino]triphenylamine (2-TNATA, 30 nm)/4,4'-bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (NPB, 18 nm)/Alq3 (42 nm)/Ba-doped Alq3 (20 nm, x%: x = 0, 10, 25, and 50)/Al (100 nm), the device with the Alq3 layer doped with 10% Ba showed the highest light out-coupling characteristic. However, as the Ba dopant concentration was increased from 25% to 50%, this device characteristic was largely reduced. The characteristics of these devices were interpreted on the basis of the chemical reaction between Ba and Alq3 and the electron injection property by analyzing the electronic structure of the Ba-doped Alq3 layer. At a low Ba doping of 10%, mainly the Alq3 radical anion species was formed. In addition, the barrier height for electron injection in this layer was decreased to 0.6 eV, when compared to the pristine Alq3 layer. At a high Ba doping of 50%, the Alq3 molecules were severely decomposed. When the Ba dopant concentration was changed, the light-emitting characteristics of the devices were well coincided with the formation mechanism of Alq3 radical anion and Alq3 decomposition species.

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

Science.gov (United States)

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

2016-07-21

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

Investigation of p-type depletion doping for InGaN/GaN-based light-emitting diodes

Science.gov (United States)

Zhang, Yiping; Zhang, Zi-Hui; Tan, Swee Tiam; Hernandez-Martinez, Pedro Ludwig; Zhu, Binbin; Lu, Shunpeng; Kang, Xue Jun; Sun, Xiao Wei; Demir, Hilmi Volkan

2017-01-01

Due to the limitation of the hole injection, p-type doping is essential to improve the performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs). In this work, we propose and show a depletion-region Mg-doping method. Here we systematically analyze the effectiveness of different Mg-doping profiles ranging from the electron blocking layer to the active region. Numerical computations show that the Mg-doping decreases the valence band barrier for holes and thus enhances the hole transportation. The proposed depletion-region Mg-doping approach also increases the barrier height for electrons, which leads to a reduced electron overflow, while increasing the hole concentration in the p-GaN layer. Experimentally measured external quantum efficiency indicates that Mg-doping position is vitally important. The doping in or adjacent to the quantum well degrades the LED performance due to Mg diffusion, increasing the corresponding nonradiative recombination, which is well supported by the measured carrier lifetimes. The experimental results are well numerically reproduced by modifying the nonradiative recombination lifetimes, which further validate the effectiveness of our approach.

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

Energy Technology Data Exchange (ETDEWEB)

Guan Yunxia; Niu Lianbin [Key Laboratory of Optical Engineering, College of Physics and Information Technology, Chongqing Normal University, Chongqing 400047 (China)], E-mail: gyxybsy@126.com, E-mail: niulb03@126.com

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 /Alq{sub 3} /CsF/Mg:Ag/Ag. Multilayer organic devices using AND and Rubrene as an emitting layer produced white emissions with good chromaticity and luminous efficiency as high as 5.93 cd/A. This performance can be explained by Foerster energy transfer from the blue-emitting host to the orange-emitting dopant.

Enhanced Performance of Bipolar Cascade Light Emitting Diodes by Doping the Aluminum Oxide Apertures

National Research Council Canada - National Science Library

Siskaninetz, William

2004-01-01

Performance improvements in multiple-stage, single-cavity bipolar cascade light emitting diodes including reduced operating voltages, enhanced light generation, and reduced device heating are obtained...

Perovskite Materials for Light-Emitting Diodes and Lasers.

Science.gov (United States)

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

2016-08-01

Organic-inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light-emitting diodes, lasers, and light-emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light-emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A(-1) have been achieved. Although perovskite light-emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light-emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower-dimensionality layered and three-dimensional perovskites, nanostructures, charge-transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light-emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light-emitting devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Science.gov (United States)

Taniyasu, Yoshitaka; Kasu, Makoto; Makimoto, Toshiki

2006-05-18

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

Ultraviolet electroluminescence from nitrogen-doped ZnO-based heterojuntion light-emitting diodes prepared by remote plasma in situ atomic layer-doping technique.

Science.gov (United States)

Chien, Jui-Fen; Liao, Hua-Yang; Yu, Sheng-Fu; Lin, Ray-Ming; Shiojiri, Makoto; Shyue, Jing-Jong; Chen, Miin-Jang

2013-01-23

Remote plasma in situ atomic layer doping technique was applied to prepare an n-type nitrogen-doped ZnO (n-ZnO:N) layer upon p-type magnesium-doped GaN (p-GaN:Mg) to fabricate the n-ZnO:N/p-GaN:Mg heterojuntion light-emitting diodes. The room-temperature electroluminescence exhibits a dominant ultraviolet peak at λ ≈ 370 nm from ZnO band-edge emission and suppressed luminescence from GaN, as a result of the decrease in electron concentration in ZnO and reduced electron injection from n-ZnO:N to p-GaN:Mg because of the nitrogen incorporation. The result indicates that the in situ atomic layer doping technique is an effective approach to tailoring the electrical properties of materials in device applications.

Laterally injected light-emitting diode and laser diode

Science.gov (United States)

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

2015-06-16

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

High Intensity Organic Light-emitting Diodes

Science.gov (United States)

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

Influences of wide-angle and multi-beam interference on the chromaticity and efficiency of top-emitting white organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Deng, Lingling; Zhou, Hongwei; Chen, Shufen, E-mail: iamsfchen@njupt.edu.cn; Liu, Bin; Wang, Lianhui [Key Laboratory for Organic Electronics and Information Displays and Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Shi, Hongying [Jiangsu-Singapore Joint Research Center for Organic/Bio- Electronics and Information Displays and Institute of Advanced Materials, Nanjing Tech University, Nanjing 211816 (China); Huang, Wei, E-mail: iamdirector@njupt.edu.cn [Key Laboratory for Organic Electronics and Information Displays and Institute of Advanced Materials, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China); Jiangsu-Singapore Joint Research Center for Organic/Bio- Electronics and Information Displays and Institute of Advanced Materials, Nanjing Tech University, Nanjing 211816 (China)

2015-02-28

Wide-angle interference (WI) and multi-beam interference (MI) in microcavity are analyzed separately to improve chromaticity and efficiency of the top-emitting white organic light-emitting diodes (TWOLEDs). A classic electromagnetic theory is used to calculate the resonance intensities of WI and MI in top-emitting organic light-emitting diodes (TOLEDs) with influence factors (e.g., electrodes and exciton locations) being considered. The role of WI on the performances of TOLEDs is revealed through using δ-doping technology and comparing blue and red EML positions in top-emitting and bottom-emitting devices. The blue light intensity significantly increases and the chromaticity of TWOLEDs is further improved with the use of enhanced WI (the blue emitting layer moving towards the reflective electrode) in the case of a weak MI. In addition, the effect of the thicknesses of light output layer and carrier transport layers on WI and MI are also investigated. Apart from the microcavity effect, other factors, e.g., carrier balance and carrier recombination regions are considered to obtain TWOLEDs with high efficiency and improved chromaticity near white light equal-energy point.

Irradiation Pattern Analysis for Designing Light Sources-Based on Light Emitting Diodes

International Nuclear Information System (INIS)

Rojas, E.; Stolik, S.; La Rosa, J. de; Valor, A.

2016-01-01

Nowadays it is possible to design light sources with a specific irradiation pattern for many applications. Light Emitting Diodes present features like high luminous efficiency, durability, reliability, flexibility, among others as the result of its rapid development. In this paper the analysis of the irradiation pattern of the light emitting diodes is presented. The approximation of these irradiation patterns to both, a Lambertian, as well as a Gaussian functions for the design of light sources is proposed. Finally, the obtained results and the functionality of bringing the irradiation pattern of the light emitting diodes to these functions are discussed. (Author)

Evaluation of light-emitting diode beacon light fixtures.

Science.gov (United States)

2009-12-01

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

Light Converting Inorganic Phosphors for White Light-Emitting Diodes

Directory of Open Access Journals (Sweden)

Chiao-Wen Yeh

2010-03-01

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

Light Converting Inorganic Phosphors for White Light-Emitting Diodes

Science.gov (United States)

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.

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

Science.gov (United States)

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

2013-08-01

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

Optical design of adjustable light emitting diode for different lighting requirements

International Nuclear Information System (INIS)

Lu Jia-Ning; Yu Jie; Tong Yu-Zhen; Zhang Guo-Yi

2012-01-01

Light emitting diode (LED) sources have been widely used for illumination. Optical design, especially freedom compact lens design is necessary to make LED sources applied in lighting industry, such as large-range interior lighting and small-range condensed lighting. For different lighting requirements, the size of target planes should be variable. In our paper we provide a method to design freedom lens according to the energy conservation law and Snell law through establishing energy mapping between the luminous flux emitted by a Lambertian LED source and a certain area of the target plane. The algorithm of our design can easily change the radius of each circular target plane, which makes the size of the target plane adjustable. Ray-tracing software Tracepro is used to validate the illuminance maps and polar-distribution maps. We design lenses for different sizes of target planes to meet specific lighting requirements. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

DEFF Research Database (Denmark)

Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.

2003-01-01

Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...

Light-extraction enhancement of GaN-based 395  nm flip-chip light-emitting diodes by an Al-doped ITO transparent conductive electrode.

Science.gov (United States)

Xu, Jin; Zhang, Wei; Peng, Meng; Dai, Jiangnan; Chen, Changqing

2018-06-01

The distinct ultraviolet (UV) light absorption of indium tin oxide (ITO) limits the performance of GaN-based near-UV light-emitting diodes (LEDs). Herein, we report an Al-doped ITO with enhanced UV transmittance and low sheet resistance as the transparent conductive electrode for GaN-based 395 nm flip-chip near-UV LEDs. The thickness dependence of optical and electrical properties of Al-doped ITO films is investigated. The optimal Al-doped ITO film exhibited a transmittance of 93.2% at 395 nm and an average sheet resistance of 30.1  Ω/sq. Meanwhile, at an injection current of 300 mA, the forward voltage decreased from 3.14 to 3.11 V, and the light output power increased by 13% for the 395 nm near-UV flip-chip LEDs with the optimal Al-doped ITO over those with pure ITO. This Letter provides a simple and repeatable approach to further improve the light extraction efficiency of GaN-based near-UV LEDs.

Electrically driven surface plasmon light-emitting diodes

DEFF Research Database (Denmark)

Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke

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

Ce3+-Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr3 Nanocrystals Based Light-Emitting Diodes.

Science.gov (United States)

Yao, Ji-Song; Ge, Jing; Han, Bo-Ning; Wang, Kun-Hua; Yao, Hong-Bin; Yu, Hao-Lei; Li, Jian-Hai; Zhu, Bai-Sheng; Song, Ji-Zhong; Chen, Chen; Zhang, Qun; Zeng, Hai-Bo; Luo, Yi; Yu, Shu-Hong

2018-03-14

Inorganic perovskite CsPbBr 3 nanocrystals (NCs) are emerging, highly attractive light emitters with high color purity and good thermal stability for light-emitting diodes (LEDs). Their high photo/electroluminescence efficiencies are very important for fabricating efficient LEDs. Here, we propose a novel strategy to enhance the photo/electroluminescence efficiency of CsPbBr 3 NCs through doping of heterovalent Ce 3+ ions via a facile hot-injection method. The Ce 3+ cation was chosen as the dopant for CsPbBr 3 NCs by virtue of its similar ion radius and formation of higher energy level of conduction band with bromine in comparison with the Pb 2+ cation to maintain the integrity of perovskite structure without introducing additional trap states. It was found that by increasing the doping amount of Ce 3+ in CsPbBr 3 NCs to 2.88% (atomic percentage of Ce compared to Pb) the photoluminescence quantum yield (PLQY) of CsPbBr 3 NCs reached up to 89%, a factor of 2 increase in comparison with the native, undoped ones. The ultrafast transient absorption and time-resolved photoluminescence (PL) spectroscopy revealed that Ce 3+ -doping can significantly modulate the PL kinetics to enhance the PL efficiency of doped CsPbBr 3 NCs. As a result, the LED device fabricated by adopting Ce 3+ -doped CsPbBr 3 NCs as the emitting layers exhibited a pronounced improvement of electroluminescence with external quantum efficiency (EQE) from 1.6 to 4.4% via Ce 3+ -doping.

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

Energy Technology Data Exchange (ETDEWEB)

Schmidt, Tobias D., E-mail: Tobias.Schmidt@physik.uni-augsburg.de; Reichardt, Lukas J.; Wehrmeister, Sebastian; Scholz, Bert J.; Mayr, Christian; Brütting, Wolfgang, E-mail: Wolfgang.Bruetting@physik.uni-augsburg.de [Institute of Physics, University of Augsburg, 86135 Augsburg (Germany); Rausch, Andreas F.; Wehlus, Thomas; Reusch, Thilo C. G. [OSRAM OLED GmbH, Wernerwerkstrasse 2, 93049 Regensburg (Germany); Ciarnáin, Rossá Mac; Danz, Norbert [Fraunhofer Institute for Applied Optics and Precision Engineering, 07745 Jena (Germany)

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.

Highly efficient silicon light emitting diode

NARCIS (Netherlands)

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

2002-01-01

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

Growth and characterization of air annealing Tb-doped YAG:Ce single crystal for white-light-emitting diode

International Nuclear Information System (INIS)

Gong, Maogao; Xiang, Weidong; Liang, Xiaojuan; Zhong, Jiasong; Chen, Daqin; Huang, Jun; Gu, Guorui; Yang, Cheng; Xiang, Run

2015-01-01

Highlights: • We report preparation of transparent Ce,Tb:YAG single crystal by Czochralski method. • The effect of annealing on Ce,Tb:YAG single crystal had been investigated. • The Ce,Tb:YAG single crystal after annealing exhibited better optical performance. • The Ce,Tb:YAG single crystal could be used as an ideal candidate for WLED. - Abstract: We report the preparation of transparent Ce and Tb co-doped Y 3 Al 5 O 12 single crystal by the Czochralski method. The characterization of the resulting single crystal was accomplished by using X-ray powder diffractometer, scanning electron microscopy and energy dispersive X-ray spectroscopy. Absorption peak of the single crystal at about 460 nm has been obtained from ultraviolet–visible absorption spectrometer and their intensity is changed with different annealing condition. Its optical properties also have been investigated using fluorescence spectrometer. What’s more, its photoelectric parameters were studied by LED fast spectrometer. The constructed single crystal based white-light-emitting diode exhibits a high luminous efficiency of 140.89 lm/W, and a correlated color temperature of 4176 K as well as a color rendering index of 56.7, which reveal the prominent feasibility of the present single crystal material in white-light-emitting diode application

Growth and characterization of air annealing Tb-doped YAG:Ce single crystal for white-light-emitting diode

Energy Technology Data Exchange (ETDEWEB)

Gong, Maogao [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (China); Xiang, Weidong, E-mail: xiangweidong001@126.com [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (China); Liang, Xiaojuan [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (China); Zhong, Jiasong; Chen, Daqin [College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018 (China); Huang, Jun; Gu, Guorui; Yang, Cheng; Xiang, Run [College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035 (China)

2015-08-05

Highlights: • We report preparation of transparent Ce,Tb:YAG single crystal by Czochralski method. • The effect of annealing on Ce,Tb:YAG single crystal had been investigated. • The Ce,Tb:YAG single crystal after annealing exhibited better optical performance. • The Ce,Tb:YAG single crystal could be used as an ideal candidate for WLED. - Abstract: We report the preparation of transparent Ce and Tb co-doped Y{sub 3}Al{sub 5}O{sub 12} single crystal by the Czochralski method. The characterization of the resulting single crystal was accomplished by using X-ray powder diffractometer, scanning electron microscopy and energy dispersive X-ray spectroscopy. Absorption peak of the single crystal at about 460 nm has been obtained from ultraviolet–visible absorption spectrometer and their intensity is changed with different annealing condition. Its optical properties also have been investigated using fluorescence spectrometer. What’s more, its photoelectric parameters were studied by LED fast spectrometer. The constructed single crystal based white-light-emitting diode exhibits a high luminous efficiency of 140.89 lm/W, and a correlated color temperature of 4176 K as well as a color rendering index of 56.7, which reveal the prominent feasibility of the present single crystal material in white-light-emitting diode application.

Perspective: Toward efficient GaN-based red light emitting diodes using europium doping

Science.gov (United States)

Mitchell, Brandon; Dierolf, Volkmar; Gregorkiewicz, Tom; Fujiwara, Yasufumi

2018-04-01

While InGaN/GaN blue and green light-emitting diodes (LEDs) are commercially available, the search for an efficient red LED based on GaN is ongoing. The realization of this LED is crucial for the monolithic integration of the three primary colors and the development of nitride-based full-color high-resolution displays. In this perspective, we will address the challenges of attaining red luminescence from GaN under current injection and the methods that have been developed to circumvent them. While several approaches will be mentioned, a large emphasis will be placed on the recent developments of doping GaN with Eu3+ to achieve an efficient red GaN-based LED. Finally, we will provide an outlook to the future of this material as a candidate for small scale displays such as mobile device screens or micro-LED displays.

Novel Na(+) doped Alq3 hybrid materials for organic light-emitting diode (OLED) devices and flat panel displays.

Science.gov (United States)

Bhagat, S A; Borghate, S V; Kalyani, N Thejo; Dhoble, S J

2015-05-01

Pure and Na(+) -doped Alq3 complexes were synthesized by a simple precipitation method at room temperature, maintaining a stoichiometric ratio. These complexes were characterized by X-ray diffraction, Fourier transform infrared (FTIR), UV/Vis absorption and photoluminescence (PL) spectra. The X-ray diffractogram exhibits well-resolved peaks, revealing the crystalline nature of the synthesized complexes, FTIR confirms the molecular structure and the completion of quinoline ring formation in the metal complex. UV/Vis absorption and PL spectra of sodium-doped Alq3 complexes exhibit high emission intensity in comparison with Alq3 phosphor, proving that when doped in Alq3 , Na(+) enhances PL emission intensity. The excitation spectra of the synthesized complexes lie in the range 242-457 nm when weak shoulders are also considered. Because the sharp excitation peak falls in the blue region of visible radiation, the complexes can be employed for blue chip excitation. The emission wavelength of all the synthesized complexes lies in the bluish green/green region ranging between 485 and 531 nm. The intensity of the emission wavelength was found to be elevated when Na(+) is doped into Alq3 . Because both the excitation and emission wavelengths fall in the visible region of electromagnetic radiation, these phosphors can also be employed to improve the power conversion efficiency of photovoltaic cells by using the solar spectral conversion principle. Thus, the synthesized phosphors can be used as bluish green/green light-emitting phosphors for organic light-emitting diodes, flat panel displays, solid-state lighting technology - a step towards the desire to reduce energy consumption and generate pollution free light. Copyright © 2014 John Wiley & Sons, Ltd.

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-06-09

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

Organic light emitting diode with surface modification layer

Science.gov (United States)

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

2017-09-12

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

Electroluminescence enhancement for near-ultraviolet light emitting diodes with graphene/AZO-based current spreading layers

DEFF Research Database (Denmark)

Lin, Li; Ou, Yiyu; Zhu, Xiaolong

LEDs) have attracted significant research interest due to their intensive applications in various areas where indium tin oxide (ITO) is one of the most widely employed transparent conductive materials for NUV LEDs. Compared to ITO, indium-free aluminum-doped zinc oxide (AZO) has similar electrical......Near-ultraviolet light emitting diodes with different aluminum-doped zinc oxide-based current spreading layers were fabricated and electroluminescence (EL) was compared. A 170% EL enhancement was achieved by using a graphene-based interlayer. GaN-based near-ultraviolet light emitting diodes (NUV...... with a new type of current spreading layer (CSL) which combines AZO and a single-layer graphene (SLG) as an effective transparent CSL [1]. In the present work, LEDs with solo AZO CSL in Fig.1(a) and SLG/Ni/AZO-based CSL in Fig.1(b) were both fabricated for EL comparison. Standard mesa fabrication including...

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

Science.gov (United States)

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

2016-06-22

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

Lithium hydride doped intermediate connector for high-efficiency and long-term stable tandem organic light-emitting diodes.

Science.gov (United States)

Ding, Lei; Tang, Xun; Xu, Mei-Feng; Shi, Xiao-Bo; Wang, Zhao-Kui; Liao, Liang-Sheng

2014-10-22

Lithium hydride (LiH) is employed as a novel n-dopant in the intermediate connector for tandem organic light-emitting diodes (OLEDs) because of its easy coevaporation with other electron transporting materials. The tandem OLEDs with two and three electroluminescent (EL) units connected by a combination of LiH doped 8-hydroxyquinoline aluminum (Alq3) and 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) demonstrate approximately 2-fold and 3-fold enhancement in current efficiency, respectively. In addition, no extra voltage drop across the intermediate connector is observed. Particularly, the lifetime (T75%) in the tandem OLED with two and three EL units is substantially improved by 3.8 times and 7.4 times, respectively. The doping effect of LiH into Alq3, the charge injection, and transport characteristics of LiH-doped Alq3 are further investigated by ultraviolet photoelectron spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS).

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

Directory of Open Access Journals (Sweden)

Luis Morgado

2009-01-01

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

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

Science.gov (United States)

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.

Phosphorescence white organic light-emitting diodes with single emitting layer based on isoquinolinefluorene-carbazole containing host.

Science.gov (United States)

Koo, Ja Ryong; Lee, Seok Jae; Hyung, Gun Woo; Kim, Bo Young; Shin, Hyun Su; Lee, Kum Hee; Yoon, Seung Soo; Kim, Woo Young; Kim, Young Kwan

2013-03-01

We have demonstrated a stable phosphorescent white organic light-emitting diodes (WOLEDs) using an orange emitter, Bis(5-benzoyl-2-(4-fluorophenyl)pyridinato-C,N) iridium(III)acetylacetonate [(Bz4Fppy)2Ir(III)acac] doped into a newly synthesized blue host material, 2-(carbazol-9-yl)-7-(isoquinolin-1-yl)-9,9-diethylfluorene (CzFliq). When 1 wt.% (Bz4Fppy)2Ir(III)acac was doped into emitting layer, it was realized an improved EL performance and a pure white color in the OLED. The optimum WOLED showed maximum values as a luminous efficiency of 10.14 cd/A, a power efficiency of 10.24 Im/W, a peak external quantum efficiency 4.07%, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39) at 8 V.

Hybrid Light-Emitting Diode Enhanced With Emissive Nanocrystals

DEFF Research Database (Denmark)

Kopylov, Oleksii

This thesis investigates a new type of white light emitting hybrid diode, composed of a light emitting GaN/InGaN LED and a layer of semiconductor nanocrystals for color conversion. Unlike standard white LEDs, the device is configured to achieve high color conversion efficiency via non-radiative e......This thesis investigates a new type of white light emitting hybrid diode, composed of a light emitting GaN/InGaN LED and a layer of semiconductor nanocrystals for color conversion. Unlike standard white LEDs, the device is configured to achieve high color conversion efficiency via non...... of the hybrid diode fabrication including process techniques for GaN LED and incorporation of the nanocrystals are presented with the emphasis on the differences with standard LED processing. Results and analysis of optical and electrical characterization including photoluminescence (PL), micro-PL, time......-resolved PL and electroluminescence (EL) together with current-voltage characteristics are presented to evaluate the device performance. A clear evidence of non-radiative energy transfer was seen in the carrier dynamics of both the LED and the nanocrystals when the quantum well – nanocrystals separation...

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-06-15

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

Bi-layer non-doped small-molecular white organic light-emitting diodes with high colour stability

International Nuclear Information System (INIS)

Chen Shuming; Kwok, Hoi-Sing; Zhao Zujin; Tang Benzhong; Wang Zhiming; Lu Ping; Gao Zhao; Ma Yuguang

2011-01-01

Bi-layer non-doped white organic light-emitting diodes (WOLEDs) with hole-transporting layer 4-(4-(1,2,2-triphenylvinyl)phenyl)-7-(5-(4-(1,2,2-triphenylvinyl)phenyl) thiophen-2yl)benzo[c][1,2,5]thiadiazole (BTPETTD) as a red emitter and electron-transporting layer 4,4'-bis(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (DDPi) as a blue emitter are demonstrated. The blue emission is due to direct recombination of excitons in DPPi, while the red emission originates not only from the direct recombination of excitons in BTPETTD but also from a colour down-conversion process by absorbing blue emission and re-emitting red photons. The combination of blue emission and red emission yields an efficient and extremely stable white colour, regardless of driving voltages. In our demonstration, a bi-layer WOLED with an efficiency of 4.2 cd A -1 at 1000 cd m -2 , 1931 Commision International de L'Eclairage coordinates of (0.31, 0.31) and a high colour rendering index of 92 over a wide range of driving voltages is obtained.

Control of a White Organic Light Emitting Diode emission parameters using a single doped RGB active layer

Energy Technology Data Exchange (ETDEWEB)

Pereira, D. [Departamento de Ciência dos Materiais e i3N – Instituto de Nanoestruturas, Nanomodelação e Nanofabricação, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Caparica (Portugal); Pinto, A.; Califórnia, A.; Gomes, J. [CeNTI – Centro de Nanotecnologia, Materiais Técnicos, Funcionais e Inteligentes, Rua Fernando Mesquita 2785, 4760-034 Vila Nova de Famalicão (Portugal); Pereira, L., E-mail: luiz@ua.pt [Departmento de Física e i3N – Instituto de Nanoestruturas, Nanomodelação e Nanofabricação, Universidade de Aveiro, 3810-193 Aveiro (Portugal)

2016-09-15

Highlights: • A simple WOLED for Solid State Lighting is proposed with high color stability. • Energy transfer and electroluminescence dynamics of a single RGB layer for WOLEDs. • White shade modulation and stability over large emitting areas and applied voltages. - Abstract: Solid State Lighting technologies based on Organic Light Emitting Diodes, became an interesting focus due to their unique properties. The use of a unique RGB active layer for white emission, although simple in theory, shows difficulty to stabilize both CIE coordinates and color modulation. In this work, a WOLED using a simple RGB layer, was developed achieving a high color stability and shade modulation. The RGB matrix comprises a blue host material NPB, doped with two guests, a green (Coumarin 153) and a red (DCM1) in low concentrations. The RGB layer carrier dynamics allows for the white emission in low device complexity and high stability. This was also shown independent of the white shade, obtained through small changes in the red dopant resulting in devices ranging from warm to cool white i.e. an easy color tuning. A detailed analysis of the opto-electrical behavior is made.

Control of a White Organic Light Emitting Diode emission parameters using a single doped RGB active layer

International Nuclear Information System (INIS)

Pereira, D.; Pinto, A.; Califórnia, A.; Gomes, J.; Pereira, L.

2016-01-01

Highlights: • A simple WOLED for Solid State Lighting is proposed with high color stability. • Energy transfer and electroluminescence dynamics of a single RGB layer for WOLEDs. • White shade modulation and stability over large emitting areas and applied voltages. - Abstract: Solid State Lighting technologies based on Organic Light Emitting Diodes, became an interesting focus due to their unique properties. The use of a unique RGB active layer for white emission, although simple in theory, shows difficulty to stabilize both CIE coordinates and color modulation. In this work, a WOLED using a simple RGB layer, was developed achieving a high color stability and shade modulation. The RGB matrix comprises a blue host material NPB, doped with two guests, a green (Coumarin 153) and a red (DCM1) in low concentrations. The RGB layer carrier dynamics allows for the white emission in low device complexity and high stability. This was also shown independent of the white shade, obtained through small changes in the red dopant resulting in devices ranging from warm to cool white i.e. an easy color tuning. A detailed analysis of the opto-electrical behavior is made.

III-nitride based light emitting diodes and applications

CERN Document Server

Han, Jung; Amano, Hiroshi; Morkoç, Hadis

2017-01-01

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

III-nitride based light emitting diodes and applications

CERN Document Server

Han, Jung; Amano, Hiroshi; Morkoç, Hadis

2013-01-01

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

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

Science.gov (United States)

2009-12-01

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

Degradation of light emitting diodes: a proposed methodology

International Nuclear Information System (INIS)

Koh, Sau; Vam 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. (semiconductor devices)

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

International Nuclear Information System (INIS)

Feng, Shih-Wei; Liao, Po-Hsun; Leung, Benjamin; Han, Jung; Yang, Fann-Wei; Wang, Hsiang-Chen

2015-01-01

Based on quantum efficiency and time-resolved electroluminescence measurements, the effects of carrier localization and quantum-confined Stark effect (QCSE) on carrier transport and recombination dynamics of Ga- and N-polar InGaN/GaN light-emitting diodes (LEDs) are reported. The N-polar LED exhibits shorter ns-scale response, rising, delay, and recombination times than the Ga-polar one does. Stronger carrier localization and the combined effects of suppressed QCSE and electric field and lower potential barrier acting upon the forward bias in an N-polar LED provide the advantages of more efficient carrier relaxation and faster carrier recombination. By optimizing growth conditions to enhance the radiative recombination, the advantages of more efficient carrier relaxation and faster carrier recombination in a competitive performance N-polar LED can be realized for applications of high-speed flash LEDs. The research results provide important information for carrier transport and recombination dynamics of an N-polar InGaN/GaN LED

Efficient carrier relaxation and fast carrier recombination of N-polar InGaN/GaN light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Feng, Shih-Wei, E-mail: swfeng@nuk.edu.tw; Liao, Po-Hsun [Department of Applied Physics, National University of Kaohsiung, No. 700, Kaohsiung University Rd., Nan Tzu Dist., 811 Kaohsiung, Taiwan (China); Leung, Benjamin; Han, Jung [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Yang, Fann-Wei [Department of Electronic Engineering, Southern Taiwan University of Science and Technology, Tainan, Taiwan (China); Wang, Hsiang-Chen [Graduate Institute of Opto-Mechatronics and Advanced Institute of Manufacturing with High-Tech Innovations (AIM-HI), National Chung Cheng University, Chia-Yi, Taiwan (China)

2015-07-28

Based on quantum efficiency and time-resolved electroluminescence measurements, the effects of carrier localization and quantum-confined Stark effect (QCSE) on carrier transport and recombination dynamics of Ga- and N-polar InGaN/GaN light-emitting diodes (LEDs) are reported. The N-polar LED exhibits shorter ns-scale response, rising, delay, and recombination times than the Ga-polar one does. Stronger carrier localization and the combined effects of suppressed QCSE and electric field and lower potential barrier acting upon the forward bias in an N-polar LED provide the advantages of more efficient carrier relaxation and faster carrier recombination. By optimizing growth conditions to enhance the radiative recombination, the advantages of more efficient carrier relaxation and faster carrier recombination in a competitive performance N-polar LED can be realized for applications of high-speed flash LEDs. The research results provide important information for carrier transport and recombination dynamics of an N-polar InGaN/GaN LED.

Optoelectronical properties of InGaN quantum well light emitting diodes on semipolar GaN

Energy Technology Data Exchange (ETDEWEB)

Rass, Jens; Stascheit, Marcus; Ploch, Simon; Wernicke, Tim; Vogt, Patrick; Kneissl, Michael [Technische Universitaet Berlin, Institute of Solid State Physics, Secretariat EW6-1, Hardenbergstrasse 36, 10623 Berlin (Germany)

2011-07-01

The performance of GaN-based light emitting diodes (LEDs) is strongly affected by polarization fields along the c-axis of the crystal. Due to the resulting quantum-confined Stark effect the radiative transition rate is reduced and the emission wavelength is blue-shifted when carriers are injected. By growing the structures on semipolar or nonpolar planes the polarization fields can be significantly reduced or even eliminated. In this work, InGaN single quantum well LEDs have been grown by metal-organic vapor phase epitaxy on different semipolar surfaces such as the (10 anti 11) and (20 anti 21) plane. The optoelectronic properties such as the light output power, the emission wavelength and its shift with injection current as well as the operating voltage have been studied. By employing capacitance-voltage- and current-voltage measurements, the size of the depletion region, the build-in potential, the saturation current and the doping concentrations have been determined. LEDs with emission wavelengths ranging from the violet to the blue and green region are presented and their performance characteristics are compared to LEDs grown on the polar c-plane surface.

Broadband mid-infrared superlattice light-emitting diodes

Science.gov (United States)

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

2017-05-01

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

Effect of carbazole-oxadiazole excited-state complexes on the efficiency of dye-doped light-emitting diodes

Science.gov (United States)

Jiang, Xuezhong; Register, Richard A.; Killeen, Kelly A.; Thompson, Mark E.; Pschenitzka, Florian; Hebner, Thomas R.; Sturm, James C.

2002-05-01

Interactions between hole-transporting carbazole groups and electron-transporting 1,3,4-oxadiazole groups were studied by photoluminescence and electroluminescence (EL) spectroscopy, in blends of poly(N-vinylcarbazole) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK:PBD) and in random copolymers with carbazole and oxadiazole groups attached as side chains. Different excited-state complexes form in the blends, which exhibit exciplexes, and in the copolymers, which manifest electroplexes, due to topological constraints on the position of carbazole and oxadiazole units in the polymer. Both types of complex red-shift the EL spectra of the matrices compared with pure PVK homopolymer, although the shift is significantly greater for the electroplex. The presence of these complexes has a profound effect on the external quantum efficiency of dye-doped organic light-emitting diodes employing the blends or copolymers as matrices, as it strongly affects the efficiency of Förster energy transfer from the matrix to the dye. Single-layer devices doped with either coumarin 47 (C47), coumarin 6 (C6), or nile red (NR) were compared. Among the three dye-doped PVK:PBD devices, C6 doping yields the highest efficiency, while NR doping produced the most efficient copolymer devices, consistent with the degree of overlap between the EL spectrum of the matrix material and the absorption spectrum of the dye.

Slim planar apparatus for converting LED light into collimated polarized light uniformly emitted from its top surface.

Science.gov (United States)

Teng, Tun-Chien; Tseng, Li-Wei

2014-10-20

This study proposes a slim planar apparatus for converting nonpolarized light from a light-emitting diode (LED) into an ultra-collimated linearly polarized beam uniformly emitted from its top surface. The apparatus was designed based on a folded-bilayer configuration comprising a light-mixing collimation element, polarization conversion element, and polarization-preserving light guide plate (PPLGP) with an overall thickness of 5 mm. Moreover, the apparatus can be extended transversally by connecting multiple light-mixing collimation elements and polarization conversion elements in a side-by-side configuration to share a considerably wider PPLGP, so the apparatus can have theoretically unlimited width. The simulation results indicate that the proposed apparatus is feasible for the maximal backlight modules in 39-inch liquid crystal panels. In the case of an apparatus with a 480 × 80 mm emission area and two 8-lumen LED light sources, the average head-on polarized luminance and spatial uniformity over the emission area was 5000 nit and 83%, respectively; the vertical and transverse angular distributions of the emitting light were only 5° and 10°, respectively. Moreover, the average degree of polarization and energy efficiency of the apparatus were 82% and 72%, respectively. As compared with the high-performance ultra-collimated nonpolarized backlight module proposed in our prior work, not only did the apparatus exhibit outstanding optical performance, but also the highly polarized light emissions actually increased the energy efficiency by 100%.

A white organic light emitting diode based on anthracene-triphenylamine derivatives

Science.gov (United States)

Jiang, Quan; Qu, Jianjun; Yu, Junsheng; Tao, Silu; Gan, Yuanyuan; Jiang, Yadong

2010-10-01

White organic lighting-diode (WOLED) can be used as flat light sources, backlights for liquid crystal displays and full color displays. Recently, a research mainstream of white OLED is to develop the novel materials and optimize the structure of devices. In this work a WOLED with a structure of ITO/NPB/PAA/Alq3: x% rubrene/Alq3/Mg: Ag, was fabricated. The device has two light-emitting layers. NPB is used as a hole transport layer, PAA as a blue emitting layer, Alq3: rubrene host-guest system as a yellow emitting layer, and Alq3 close to the cathode as an electron transport layer. In the experiment, the doping concentration of rubrene was optimized. WOLED 1 with 4% rubrene achieved a maximum luminous efficiency of 1.80 lm/W, a maximum luminance of 3926 cd/m2 and CIE coordinates of (0.374, 0.341) .WOLED 2 with 2% rubrene achieved a maximum luminous efficiency of 0.65 lm/W, a maximum luminance of 7495cd/m2 and CIE coordinates of (0.365,0.365).

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

KAUST Repository

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

2016-01-01

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

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

KAUST Repository

Young, Erin C.

2016-01-26

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

The Light-Emitting Diode as a Light Detector

Science.gov (United States)

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

2011-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-03-31

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

Investigations of thin p-GaN light-emitting diodes

DEFF Research Database (Denmark)

Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke

2016-01-01

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

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

Indian Academy of Sciences (India)

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

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

CERN Document Server

Ohtsu, Motoichi

2016-01-01

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

Electrodeposition of Cu-doped ZnO nanowire arrays and heterojunction formation with p-GaN for color tunable light emitting diode applications

International Nuclear Information System (INIS)

Lupan, O.; Pauporté, T.; Viana, B.; Aschehoug, P.

2011-01-01

Highlights: ► High quality copper-doped zinc oxide nanowires were electrochemically grown at low temperature. ► ZnO:Cu nanowires have been epitaxially grown on Mg-doped p-GaN single-crystalline layers. ► The (ZnO:Cu NWs)/(p-GaN:Mg) heterojunction was used to fabricate a light-emitting diode structure. ► The photo- and electroluminescence emission was red-shifted to the violet spectral region compared to pure ZnO. ► The results are of importance for band-gap engineering of ZnO and for color-tunable LED. - Abstract: Copper-doped zinc oxide (ZnO:Cu) nanowires (NWs) were electrochemically deposited at low temperature on fluor-doped tin oxide (FTO) substrates. The electrochemical behavior of the Cu–Zn system for Cu-doped ZnO electrodeposition was studied and the electrochemical reaction mechanism is discussed. The synthesized ZnO arrayed layers were investigated by using SEM, XRD, EDX, photoluminescence and Raman techniques. X-ray diffraction analysis demonstrates a decrease in the lattice parameters of Cu-doped ZnO NWs. Structural analyses show that the nanomaterial is of hexagonal structure with the Cu incorporated in ZnO NWs probably by substituting zinc in the host lattice. Photoluminescence studies on pure and Cu-doped ZnO NWs shows that the near band edge emission is red-shifted by about 5 or 12 nm depending on Cu(II) concentration in the electrolytic bath solution (3 or 6 μmol l −1 ). Cu-doped ZnO NWs have been also epitaxially grown on Mg doped p-GaN single-crystalline layers and the (ZnO:Cu NWs)/(p-GaN:Mg) heterojunction has been used to fabricate a light-emitting diode (LED) structure. The emission was red-shifted to the visible violet spectral region compared to pure ZnO. The present work demonstrates the ability of electrodeposition to produce high quality ZnO nanowires with tailored optical properties by doping. The obtained results are of great importance for further studies on bandgap engineering of ZnO, for color-tunable LED applications

All-Quantum-Dot Infrared Light-Emitting Diodes

KAUST Repository

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

2015-01-01

© 2015 American Chemical Society. Colloidal quantum dots (CQDs) are promising candidates for infrared electroluminescent devices. To date, CQD-based light-emitting diodes (LEDs) have employed a CQD emission layer sandwiched between carrier transport

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

Science.gov (United States)

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

2017-06-01

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

The efficiency challenge of nitride light-emitting diodes for lighting

KAUST Repository

Weisbuch, Claude; Piccardo, Marco; Martinelli, Lucio; Iveland, Justin; Peretti, Jacques; Speck, James S.

2015-01-01

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. We discuss the challenges of light-emitting diodes in view of their application to solid-state lighting. The requirement is to at least displace the quite efficient fluorescent, sodium, and high

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

Directory of Open Access Journals (Sweden)

O. M. Hontaruk

2015-04-01

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

A white organic light emitting diode with improved stability

International Nuclear Information System (INIS)

Zhang Zhilin; Jiang Xueyin; Zhu Wenqing; Zhang Buxin; Xu Shaohong

2001-01-01

A white organic light emitting diode (OLED) has been constructed by employing a new blue material and a red dye directly doped in the blue emitting layer. For comparison, another white cell with a blocking layer has also been made. The configurations of the devices are ITO/CuPc/NPB/JBEM(P):DCJT/Alq/MgAg (device 1) and ITO/CuPc/NPB/TPBi:DCJT/Alq/MgAg (device 2) where copper phthalocyanine (CuPc) is the buffer layer, N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1.1'bipheny1-4-4'-diamine (NPB) is the hole transporting layer, 9,10-bis(3'5'-diaryl)phenyl anthracene doped with perylene (JBEM(P)) is the new blue emitting material, N,arylbenzimidazoles (TPBi) is the hole blocking layer, tris(8-quinolinolato)aluminium complex (Alq) is the electron transporting layer, and DCJT is a red dye. A stable and current independent white OLED has been obtained in device 1, which has a maximum luminance of 14 850 cd m -2 , an efficiency of 2.88 Lm W -1 , Commission Internationale de l'Eclairage coordinates of x=0.32, y=0.38 between 4-200 mA cm -2 , and a half lifetime of 2860 h at the starting luminance of 100 cd m -2 . Device 1 has a stability more than 50 times better than that of device 2. (author)

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

Energy Technology Data Exchange (ETDEWEB)

Rothberg, Lewis

2012-11-30

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

Host-free, yellow phosphorescent material in white organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Lee, Meng-Ting; Chu, Miao-Tsai; Lin, Jin-Sheng; Tseng, Mei-Rurng, E-mail: osolomio.ac89g@nctu.edu.t [Material and Chemical Research Laboratories, Industrial Technology Research Institute (ITRI), Hsinchu, Taiwan 310 (China)

2010-11-10

A white organic light-emitting diode (WOLED) with a high power efficiency has been demonstrated by dispersing a host-free, yellow phosphorescent material in between double blue phosphorescent emitters. The device performance achieved a comparable value to that of using a complicated host-guest doping system to form the yellow emitter in WOLEDs. Based on this device concept as well as the molecular engineering of blue phosphorescent host material and light-extraction film, a WOLED with a power efficiency of 65 lm W{sup -1} at a practical brightness of 1000 cd m{sup -2} with Commission Internationale d'Echariage coordinates (CIE{sub x,y}) of (0.37, 0.47) was achieved. (fast track communication)

Light-emitting diodes based on nontoxic zinc-alloyed silver-indium-sulfide (AIZS) nanocrystals

Science.gov (United States)

Bhaumik, Saikat; Guchhait, Asim; Pal, Amlan J.

2014-04-01

We report solution-processed growth of zinc-alloyed silver-indium-sulfide (AIZS) nanocrystals followed by fabrication and characterization of light-emitting diodes (LEDs) based on such nanostructures. While growing the low dimensional crystals, we vary the ratio between the silver and zinc contents that in turn tunes the bandgap and correspondingly their photoluminescence (PL) emission. We also dope the AIZS nanocrystals with manganese, so that their PL emission, which appears due to a radiative transition between the d-states of the dopants, becomes invariant in energy when the diameter of the quantum dots or the dopant concentration in the nanostructures varies. The LEDs fabricated with such undoped and manganese-doped AIZS nanocrystals emit electroluminescence (EL) that matches the PL spectrum of the respective nanomaterial. The results demonstrate examples of quantum dot LEDs (QDLEDs) based on nontoxic AIZS nanocrystals.

Improvement of carrier injection symmetry and quantum efficiency in InGaN light-emitting diodes with Mg delta-doped barriers

Energy Technology Data Exchange (ETDEWEB)

Zhang, F.; Can, N.; Hafiz, S.; Monavarian, M.; Das, S.; Avrutin, V.; Özgür, Ü., E-mail: uozgur@vcu.edu; Morkoç, H. [Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, Virginia 23284 (United States)

2015-05-04

The effect of δ-doping of In{sub 0.06}Ga{sub 0.94}N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In{sub 0.15}Ga{sub 0.85}N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ∼80 A/cm{sup 2} in the reference LED to ∼120 A/cm{sup 2} in the LEDs with Mg δ-doped barriers.

Improvement of carrier injection symmetry and quantum efficiency in InGaN light-emitting diodes with Mg delta-doped barriers

International Nuclear Information System (INIS)

Zhang, F.; Can, N.; Hafiz, S.; Monavarian, M.; Das, S.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

2015-01-01

The effect of δ-doping of In 0.06 Ga 0.94 N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In 0.15 Ga 0.85 N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ∼80 A/cm 2 in the reference LED to ∼120 A/cm 2 in the LEDs with Mg δ-doped barriers

Improvement of carrier injection symmetry and quantum efficiency in InGaN light-emitting diodes with Mg delta-doped barriers

Science.gov (United States)

Zhang, F.; Can, N.; Hafiz, S.; Monavarian, M.; Das, S.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

2015-05-01

The effect of δ-doping of In0.06Ga0.94N barriers with Mg on the quantum efficiency of blue light-emitting-diodes (LEDs) with active regions composed of 6 (hex) 3-nm In0.15Ga0.85N is investigated. Compared to the reference sample, δ-doping of the first barrier on the n-side of the LED structure improves the peak external quantum efficiency (EQE) by 20%, owing to the increased hole concentration in the wells adjacent to the n-side, as confirmed by numerical simulations of carrier distributions across the active region. Doping the second barrier, in addition to the first one, did not further enhance the EQE, which likely indicates compensation of improved hole injection by degradation of the active region quality due to Mg doping. Both LEDs with Mg δ-doped barriers effectively suppress the drop of efficiency at high injection when compared to the reference sample, and the onset of EQE peak roll-off shifts from ˜80 A/cm2 in the reference LED to ˜120 A/cm2 in the LEDs with Mg δ-doped barriers.

Enhancing the Light-Extraction Efficiency of AlGaN Nanowires Ultraviolet Light-Emitting Diode by using Nitride/Air Distributed Bragg Reflector Nanogratings

KAUST Repository

Alias, Mohd Sharizal; Janjua, Bilal; Zhao, Chao; Priante, Davide; Alhamoud, Abdullah A.; Tangi, Malleswararao; Alanazi, Lafi M.; Alatawi, Abdullah A.; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S.

2017-01-01

The performance and efficiency of AlGaN ultraviolet light-emitting diodes have been limited by the extremely low light-extraction efficiency (LEE) due to the intrinsic material properties of AlGaN. Here, to enhance the LEE of the device, we demonstrate an AlGaN nanowires light-emitting diode (NWs-LED) integrated with nitride/air Distributed Bragg Reflector (DBR) nanogratings. Compared to a control device (only mesa), the AlGaN NWs-LED with the nitride/air DBR nanogratings exhibit enhancement in the light output power and external quantum efficiency (EQE) by a factor of ∼1.67. The higher light output power and EQE are attributed mainly to the multiple reflectances laterally for the transverse magnetic (TM)-polarized light and scattering introduced by the nanogratings. To further understand the LEE enhancement, the electrical field distribution, extraction ratio and polar pattern of the AlGaN NWs-LED with and without the nitride/air DBR nanogratings were analyzed using the finite-difference-time-domain method. It was observed that the TM-field emission was confined and scattered upward whereas the polar pattern was intensified for the AlGaN NWs-LED with the nanogratings. Our approach to enhance the LEE via the nitride/air DBR nanogratings can provide a promising route for increasing the efficiency of AlGaN-based LEDs, also, to functioning as facet mirror for AlGaN-based laser diodes.

Enhancing the Light-Extraction Efficiency of AlGaN Nanowires Ultraviolet Light-Emitting Diode by using Nitride/Air Distributed Bragg Reflector Nanogratings

KAUST Repository

Alias, Mohd Sharizal

2017-09-11

The performance and efficiency of AlGaN ultraviolet light-emitting diodes have been limited by the extremely low light-extraction efficiency (LEE) due to the intrinsic material properties of AlGaN. Here, to enhance the LEE of the device, we demonstrate an AlGaN nanowires light-emitting diode (NWs-LED) integrated with nitride/air Distributed Bragg Reflector (DBR) nanogratings. Compared to a control device (only mesa), the AlGaN NWs-LED with the nitride/air DBR nanogratings exhibit enhancement in the light output power and external quantum efficiency (EQE) by a factor of ∼1.67. The higher light output power and EQE are attributed mainly to the multiple reflectances laterally for the transverse magnetic (TM)-polarized light and scattering introduced by the nanogratings. To further understand the LEE enhancement, the electrical field distribution, extraction ratio and polar pattern of the AlGaN NWs-LED with and without the nitride/air DBR nanogratings were analyzed using the finite-difference-time-domain method. It was observed that the TM-field emission was confined and scattered upward whereas the polar pattern was intensified for the AlGaN NWs-LED with the nanogratings. Our approach to enhance the LEE via the nitride/air DBR nanogratings can provide a promising route for increasing the efficiency of AlGaN-based LEDs, also, to functioning as facet mirror for AlGaN-based laser diodes.

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

Indian Academy of Sciences (India)

2018-02-02

Feb 2, 2018 ... emitting diode (OLED) can be enhanced by using light- extraction ... to grow, ω should posses a positive value, which is possible only when ∂φ/∂h < 0, .... To detect small changes, first, the source LED was sta- bilized by ...

Enhanced light extraction of GaN-based light-emitting diodes with periodic textured SiO2 on Al-doped ZnO transparent conductive layer

Science.gov (United States)

Yu, Zhao; Bingfeng, Fan; Yiting, Chen; Yi, Zhuo; Zhoujun, Pang; Zhen, Liu; Gang, Wang

2016-07-01

We report an effective enhancement in light extraction of GaN-based light-emitting diodes (LEDs) with an Al-doped ZnO (AZO) transparent conductive layer by incorporating a top regular textured SiO2 layer. The 2 inch transparent through-pore anodic aluminum oxide (AAO) membrane was fabricated and used as the etching mask. The periodic pore with a pitch of about 410 nm was successfully transferred to the surface of the SiO2 layer without any etching damages to the AZO layer and the electrodes. The light output power was enhanced by 19% at 20 mA and 56% at 100 mA compared to that of the planar LEDs without a patterned surface. This approach offers a technique to fabricate a low-cost and large-area regular pattern on the LED chip for achieving enhanced light extraction without an obvious increase of the forward voltage. ).

Enhanced light extraction of GaN-based light-emitting diodes with periodic textured SiO2 on Al-doped ZnO transparent conductive layer

International Nuclear Information System (INIS)

Zhao Yu; Fan Bingfeng; Chen Yiting; Zhuo Yi; Wang Gang; Pang Zhoujun; Liu Zhen

2016-01-01

We report an effective enhancement in light extraction of GaN-based light-emitting diodes (LEDs) with an Al-doped ZnO (AZO) transparent conductive layer by incorporating a top regular textured SiO 2 layer. The 2 inch transparent through-pore anodic aluminum oxide (AAO) membrane was fabricated and used as the etching mask. The periodic pore with a pitch of about 410 nm was successfully transferred to the surface of the SiO 2 layer without any etching damages to the AZO layer and the electrodes. The light output power was enhanced by 19% at 20 mA and 56% at 100 mA compared to that of the planar LEDs without a patterned surface. This approach offers a technique to fabricate a low-cost and large-area regular pattern on the LED chip for achieving enhanced light extraction without an obvious increase of the forward voltage. (paper)

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

International Nuclear Information System (INIS)

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

2010-01-01

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 (Alq 3 )/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/m 2 . 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

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

Science.gov (United States)

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.

Trivalent europium-doped strontium molybdate red phosphors in white light-emitting diodes: Synthesis, photophysical properties and theoretical calculations

International Nuclear Information System (INIS)

Yang, W.-Q.; Liu, H.-G.; Liu, G.-K.; Lin, Y.; Gao, M.; Zhao, X.-Y.; Zheng, W.-C.; Chen, Y.; Xu, J.; Li, L.-Z.

2012-01-01

Eu 3+ -doped strontium molybdate red phosphors (Sr 1−x MoO 4 :Eu x (x = 0.01–0.2)) for white light-emitting diodes (LED) were synthesized by the solid-state reaction method. The fluorescent intensities of the as-prepared phosphors were remarkably improved. The excitation and emission spectra demonstrate that these phosphors can be effectively excited by the near-UV light (395 nm) and blue light (466 nm). Their emitted red light peaks are located at 613 nm, and the highest quantum yield value (η) of the as-grown red phosphor, which is 95.85%, is much higher than that of commercial red phosphor (77.53%). These red phosphors plus commercial yellow powers (1:10) were successfully packaged with the GaN-based blue chips on a piranha frame by epoxy resins. The encapsulated white LED lamps show high performance of the CIE chromaticity coordinates and color temperatures. Moreover, to explain the fluorescent spectra of these phosphors, a complete 3003 × 3003 energy matrix was successfully built by an effective operator Hamiltonian including free ion and crystal field interactions. For the first time, the fluorescent spectra for Eu 3+ ion at the tetragonal (S 4 ) Sr 2+ site of SrMoO 4 crystal were calculated from a complete diagonalization (of energy matrix) method. The fitting values are close to the experimental results.

White organic light-emitting diodes from three emitter layers

Energy Technology Data Exchange (ETDEWEB)

Kim, M.S. [Department of Advanced Materials Science and Engineering, SungKyunKwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of); Lim, J.T. [Department of Advanced Materials Science and Engineering, SungKyunKwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of); Jeong, C.H. [Department of Advanced Materials Science and Engineering, SungKyunKwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of); Lee, J.H. [Department of Advanced Materials Science and Engineering, SungKyunKwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of); Yeom, G.Y. [Department of Advanced Materials Science and Engineering, SungKyunKwan University, Suwon, Gyonggi-Do, 440-746 (Korea, Republic of)]. E-mail: gyyeom@skku.edu

2006-11-23

Three-wavelength white organic light-emitting diodes (WOLEDs) were fabricated using two doped layers, which were obtained by separating the recombination zones into three emitter layers. A sky blue emission originated from the 4,4'-bis(2,2'-diphenylethen-1-yl)biphenyl (DPVBi) layer. A green emission originated from a tris(8-quinolinolato)aluminum (III) (Alq{sub 3}) host doped with a green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1] benz opyrano [6,7,8-ij]-quinolizin-11-one (C545T) dye. An orange emission was obtained from the N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) host doped with a red fluorescent dye, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4 H-pyran (DCJTB). A white light resulted from the partial excitations of these three emitter layers by controlling the layer thickness and concentration of the fluorescent dyes in each emissive layer simultaneously. The electroluminescent spectrum of the device was not sensitive to the driving voltage of the device. The white light device showed a maximum luminance of approximately 53,000 cd/m{sup 2}. The external quantum and power efficiency at a luminance of approximately 100 cd/m{sup 2} were 2.62% and 3.04 lm/W, respectively.

High-luminosity blue and blue-green gallium nitride light-emitting diodes.

Science.gov (United States)

Morkoç, H; Mohammad, S N

1995-01-06

Compact and efficient sources of blue light for full color display applications and lighting eluded and tantalized researchers for many years. Semiconductor light sources are attractive owing to their reliability and amenability to mass manufacture. However, large band gaps are required to achieve blue color. A class of compound semiconductors formed by metal nitrides, GaN and its allied compounds AIGaN and InGaN, exhibits properties well suited for not only blue and blue-green emitters, but also for ultraviolet emitters and detectors. What thwarted engineers and scientists from fabricating useful devices from these materials in the past was the poor quality of material and lack of p-type doping. Both of these obstacles have recently been overcome to the point where highluminosity blue and blue-green light-emitting diodes are now available in the marketplace.

Improved performance of quantum dot light emitting diode by modulating electron injection with yttrium-doped ZnO nanoparticles

Science.gov (United States)

Li, Jingling; Guo, Qiling; Jin, Hu; Wang, Kelai; Xu, Dehua; Xu, Yongjun; Xu, Gang; Xu, Xueqing

2017-10-01

In a typical light emitting diode (QD-LED), with ZnO nanoparticles (NPs) serving as the electron transport layer (ETL) material, excessive electron injection driven by the matching conduction band maximum (CBM) between the QD and this oxide layer usually causes charge imbalance and degrades the device performance. To address this issue, the electronic structure of ZnO NPs is modified by the yttrium (Y) doping method. We demonstrate that the CBM of ZnO NPs has a strong dependence on the Y-doping concentration, which can be tuned from 3.55 to 2.77 eV as the Y doping content increases from 0% to 9.6%. This CBM variation generates an enlarged barrier between the cathode and this ZnO ETL benefits from the modulation of electron injection. By optimizing electron injection with the use of a low Y-doped (2%) ZnO to achieve charge balance in the QD-LED, device performance is significantly improved with maximum luminance, peak current efficiency, and maximal external quantum efficiency increase from 4918 cd/m2, 11.3 cd/A, and 4.5% to 11,171 cd/m2, 18.3 cd/A, and 7.3%, respectively. This facile strategy based on the ETL modification enriches the methodology of promoting QD-LED performance.

Optimization of white organic light emitting diodes based on emitting layer charge carrier conduction properties

International Nuclear Information System (INIS)

Baek, H I; Lee, C H

2008-01-01

We have fabricated white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which 4,4'-N,N'-dicarbazole-biphenyl (CBP) layers doped with the phosphorescent dopants fac-tris(2-phenylpyridine) iridium (Ir(ppy) 3 ) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C3')iridium(acetylacetonate) (btp 2 Ir(acac)) and the fluorescent dopant 4,4'-bis[2-{4-(N,N-diphenylamino) phenyl}vinyl]biphenyl (DPAVBi) were used as green (G), red (R) and blue (B) EMLs, respectively. A higher efficiency was expected with the R/G/B EML sequence from the hole transport layer interface than with the G/R/B sequence because of the differences in the charge carrier conduction properties of the EMLs doped with phosphorescent dopants and the luminance balance between the phosphorescent and fluorescent emissions. A high efficiency of 18.3 cd A -1 (an external quantum efficiency of 8.5%) at 100 cd m -2 and good colour stability were achieved with the R/G/B EML sequence as expected, with an additional non-doped CBP interlayer used between the G and B EMLs. In addition, the OLED with this sequence was found to have the longest lifetime of the white devices we tested

Tandem white organic light-emitting diodes adopting a C60:rubrene charge generation layer

International Nuclear Information System (INIS)

Bi Wen-Tao; Wu Xiao-Ming; Hua Yu-Lin; Sun Jin-E; Xiao Zhi-Hui; Wang Li; Yin Shou-Gen

2014-01-01

Organic bulk heterojunction fullerence (C 60 ) doped 5, 6, 11, 12-tetraphenylnaphthacene (rubrene) as the high quality charge generation layer (CGL) with high transparency and superior charge generating capability for tandem organic light emitting diodes (OLEDs) is developed. This CGL shows excellent optical transparency about 90%, which can reduce the optical interference effect formed in tandem OLEDs. There is a stable white light emission including 468 nm and 500 nm peaks from the blue emitting layer and 620 nm peak from the red emitting layer in tandem white OLEDs. A high efficiency of about 17.4 cd/A and CIE coordinates of (0.40, 0.35) at 100 cd/m 2 and (0.36, 0.34) at 1000 cd/m 2 have been demonstrated by employing the developed CGL, respectively. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Tailoring of polarization in electron blocking layer for electron confinement and hole injection in ultraviolet light-emitting diodes

International Nuclear Information System (INIS)

Lu, Yu-Hsuan; Pilkuhn, Manfred H.; Fu, Yi-Keng; Chu, Mu-Tao; Huang, Shyh-Jer; Su, Yan-Kuin; Wang, Kang L.

2014-01-01

The influence of the AlGaN electron blocking layer (EBL) with graded aluminum composition on electron confinement and hole injection in AlGaN-based ultraviolet light-emitting diodes (LEDs) are investigated. The light output power of LED with graded AlGaN EBL was markedly improved, comparing to LED with conventional EBL. In experimental results, a high increment of 86.7% can be obtained in light output power. Simulation analysis shows that via proper modification of the barrier profile from the last barrier of the active region to EBL, not only the elimination of electron overflow to p-type layer can be achieved but also the hole injection into the active region can be enhanced, compared to a conventional LED structure. The dominant factor to the performance improvement is shown to be the modulation of polarization field by the graded Al composition in EBL

Tailoring of polarization in electron blocking layer for electron confinement and hole injection in ultraviolet light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Lu, Yu-Hsuan; Pilkuhn, Manfred H. [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Fu, Yi-Keng; Chu, Mu-Tao [Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu 31040, Taiwan (China); Huang, Shyh-Jer, E-mail: yksu@mail.ncku.edu.tw, E-mail: totaljer48@gmail.com [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095 (United States); Su, Yan-Kuin, E-mail: yksu@mail.ncku.edu.tw, E-mail: totaljer48@gmail.com [Department of Electrical Engineering, Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Department of Electronic Engineering, Kun-Shan University, Tainan 71003, Taiwan (China); Wang, Kang L. [Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095 (United States)

2014-03-21

The influence of the AlGaN electron blocking layer (EBL) with graded aluminum composition on electron confinement and hole injection in AlGaN-based ultraviolet light-emitting diodes (LEDs) are investigated. The light output power of LED with graded AlGaN EBL was markedly improved, comparing to LED with conventional EBL. In experimental results, a high increment of 86.7% can be obtained in light output power. Simulation analysis shows that via proper modification of the barrier profile from the last barrier of the active region to EBL, not only the elimination of electron overflow to p-type layer can be achieved but also the hole injection into the active region can be enhanced, compared to a conventional LED structure. The dominant factor to the performance improvement is shown to be the modulation of polarization field by the graded Al composition in EBL.

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

Energy Technology Data Exchange (ETDEWEB)

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

2010-09-30

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

A novel orange emissive phosphor SrWO4:Sm3+ for white light-emitting diodes

International Nuclear Information System (INIS)

Ju Zhenghua; Wei Ruiping; Ma Jingxin; Pang Chaoran; Liu Weisheng

2010-01-01

Research highlights: → A novel orange emissive phosphor SrWO 4 :Sm 3+ was firstly reported. → The optics properties of Sm 3+ -doped SrWO 4 phosphor were successfully discussed. → The temperature-dependent luminescence indicates the phosphor exhibits a small thermal-quenching property. → The phosphor is a potential candidate as orange-emitting component for white LED. - Abstract: A novel orange emissive phosphor, Sm 3+ -doped SrWO 4 , was synthesized by high temperature solid-state reaction in air atmosphere. The excitation spectra show that the phosphors can be efficiently excited by ultraviolet and near-ultraviolet light, the optimized concentration is 4 mol%. Three emission peaks locate at 562, 596 and 642 nm, corresponding to CIE chromaticity coordinates of (x = 0.54, y = 0.46), which indicates the orange light emitting. The decay curves are well fitted with triple-exponential decay models. The quantum yield of the Sr 0.96 Sm 0.04 WO 4 phosphor is about 70.65% under excitation of 377 nm. Furthermore, the temperature-dependent luminescence indicates the phosphor exhibits a small thermal-quenching property. So the phosphor is able to be applied to UV-LED chip-based white light-emitting diodes.

Aluminum-doped zinc oxide films as transparent conductive electrode for organic light-emitting devices

International Nuclear Information System (INIS)

Jiang, X.; Wong, F.L.; Fung, M.K.; Lee, S.T.

2003-01-01

Highly transparent conductive, aluminum-doped zinc oxide (ZnO:Al) films were deposited on glass substrates by midfrequency magnetron sputtering of metallic aluminum-doped zinc target. ZnO:Al films with surface work functions between 3.7 and 4.4 eV were obtained by varying the sputtering conditions. Organic light-emitting diodes (OLEDs) were fabricated on these ZnO:Al films. A current efficiency of higher than 3.7 cd/A, was achieved. For comparison, 3.9 cd/A was achieved by the reference OLEDs fabricated on commercial indium-tin-oxide substrates

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-07-27

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

White organic light emitting diodes based on fluorene-carbazole dendrimers

International Nuclear Information System (INIS)

Usluer, Özlem; Demic, Serafettin; Kus, Mahmut; Özel, Faruk; Serdar Sariciftci, Niyazi

2014-01-01

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

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

OpenAIRE

Lu, C; Bian, Z

2016-01-01

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

Fabrication of InGaN/GaN nanopillar light-emitting diode arrays

DEFF Research Database (Denmark)

Ou, Yiyu; Fadil, Ahmed; Ou, Haiyan

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

Effect of Dopant Activation on Device Characteristics of InGaN-based Light Emitting Diodes

Science.gov (United States)

Lacroce, Nicholas; Liu, Guangyu; Tan, Chee-Keong; Arif, Ronald A.; Lee, Soo Min; Tansu, Nelson

2015-03-01

Achieving high uniformity in growths and device characteristics of InGaN-based light-emitting diodes (LEDs) is important for large scale manufacturing. Dopant activation and maintaining control of variables affecting dopant activation are critical steps in the InGaN-based light emitting diodes (LEDs) fabrication process. In the epitaxy of large scale production LEDs, in-situ post-growth annealing is used for activating the Mg acceptor dopant in the p-AlGaN and p-GaN of the LEDs. However, the annealing temperature varies with respect to position in the reactor chamber, leading to severe uniform dopant activation issue across the devices. Thus, it is important to understand how the temperature gradient and the resulting variance in Mg acceptor activation will alter the device properties. In this work, we examine the effect of varying p-type doping levels in the p-GaN layers and AlGaN electron blocking layer of the GaN LEDs on the optoelectronic properties including the band profile, carrier concentration, current density, output power and quantum efficiency. By understanding the variations and its effect, the identification of the most critical p-type doping layer strategies to address this variation will be clarified.

All-Quantum-Dot Infrared Light-Emitting Diodes

KAUST Repository

Yang, Zhenyu

2015-12-22

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

Fabrication of organic light emitting diode using Molybdenum ...

Indian Academy of Sciences (India)

65

out by measuring sheet resistance, optical transmittance and surface ... role in the organic light-emitting diode (OLED) performance because it determines the .... coated glass by thermal vacuum deposition method and optimize it by using ...

Light emission mechanism of mixed host organic light-emitting diodes

Science.gov (United States)

Song, Wook; Lee, Jun Yeob

2015-03-01

Light emission mechanism of organic light-emitting diodes with a mixed host emitting layer was studied using an exciplex type mixed host and an exciplex free mixed host. Monitoring of the current density and luminance of the two type mixed host devices revealed that the light emission process of the exciplex type mixed host was dominated by energy transfer, while the light emission of the exciplex free mixed host was controlled by charge trapping. Mixed host composition was also critical to the light emission mechanism, and the contribution of the energy transfer process was maximized at 50:50 mixed host composition. Therefore, it was possible to manage the light emission process of the mixed host devices by managing the mixed host composition.

InGaN/AlGaInN-based ultraviolet light-emitting diodes with indium gallium tin oxide electrodes

International Nuclear Information System (INIS)

Kim, Sukwon; Kim, Tae Geun

2015-01-01

In this study, In- and Sn-doped GaO (IGTO) is proposed as an alternative transparent conductive electrode for indium tin oxide (ITO) to improve the performance of InGaN/AlGaInN-based near ultraviolet light-emitting diodes (NUV LEDs). IGTO films were prepared by co-sputtering the ITO and Ga_2O_3 targets under various target power ratios. Among those, IGTO films post-annealed at 700 °C under a hydrogen environment gave rise to a transmittance of 94% at 385 nm and a contact resistance of 9.4 × 10"−"3 Ω-cm"2 with a sheet resistance of 124 Ω/ϒ. Compared to ITO-based NUV LEDs, the IGTO-based NUV LED showed a 9% improvement in the light output power, probably due to IGTO's higher transmittance, although the forward voltage was still higher by 0.23 V. - Highlights: • Indium gallium tin oxide (IGTO) for near-ultraviolet light-emitting diode is proposed. • IGTO is fabricated by co-sputtering the ITO and Ga_2O_3 targets and hydrogen annealing. • IGTO shows a 94% transmittance at 385 nm and a 9.4 × 10"−"3 Ω-cm"2 contact resistance. • Near-ultraviolet light-emitting diode with IGTO shows improved optical performance.

Spin polarization of electrons in a magnetic impurity doped ...

Indian Academy of Sciences (India)

A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and ...

Preparation and luminescence properties of Ca3(VO4)2: Eu3+, Sm3+ phosphor for light-emitting diodes

International Nuclear Information System (INIS)

Huang Jiaping; Li Qiuxia; Chen Donghua

2010-01-01

Rare-earth ions co-activated red phosphors Ca 3 (VO 4 ) 2 : Eu 3+ , Sm 3+ were synthesized by modified solid-state reactions. The samples were characterized by X-ray powder diffractometer (XRD), energy-dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and luminescence spectrometer (LS). The results showed that the Eu-Sm system exhibits higher emission intensity than those of the Eu single-doped system and Sm separate-doped system under blue light. Samarium (III) ions are effective in broadening and strengthening absorptions around 467 nm. Furthermore, they exhibit enhanced luminescence emission. Luminescent measurements showed that the phosphors can be efficiently excited by ultraviolet (UV) to visible region, emitting a red light with a peak wavelength of 616 nm. The material has potential application as a phosphor for light-emitting diodes (LEDs).

White organic light emitting diodes based on fluorene-carbazole dendrimers

Energy Technology Data Exchange (ETDEWEB)

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

2014-02-15

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

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

Science.gov (United States)

Kashiwagi, Y.; Koizumi, A.; Takemura, Y.; Furuta, S.; Yamamoto, M.; Saitoh, M.; Takahashi, M.; Ohno, T.; Fujiwara, Y.; Murahashi, K.; Ohtsuka, K.; Nakamoto, M.

2014-12-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

White organic light-emitting diodes based on doped and ultrathin Rubrene layer

Science.gov (United States)

Li, Yi; Jiang, Yadong; Wen, Wen; Yu, Junsheng

2010-10-01

Based on a yellow fluorescent dye of 5, 6, 11, 12-tetraphenylnaphthacene (Rubrene), WOLEDs were fabricated, with doping structure and ultrathin layer structure utilized in the devices. By doping Rubrene into blue-emitting N,N'-bis-(1- naphthyl)-N,N'-biphenyl-1,1'-biphenyl-4,4'-diamine (NPB), the device with a structure of indium-tin-oxide (ITO)/NPB (40 nm)/NPB:Rubrene (0.25 wt%, 7 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (30 nm)/Mg:Ag exhibited a warm white light with Commissions Internationale De L'Eclairage (CIE) coordinates of (0.38, 0.41) at 12 V. The electroluminescent spectrum of the OLED consisted of blue and yellow fluorescent emissions, the intensity of blue emission increased gradually relative to the orange emission with increasing voltage. This is mainly due to the recombination zone shifted towards the anode side as the transmission rate of electrons grows faster than that of holes under higher bias voltage. A maximum luminance of 7300 cd/m2 and a maximum power efficiency of 0.57 lm/W were achieved. Comparatively, by utilizing ultrathin dopant layer, the device with a structure of ITO/NPB (40 nm)/Rubrene (0.3 nm)/NPB (7 nm)/BCP (30 nm)/Mg:Ag achieved a low turn-on voltage of 3 V and a more stable white light. The peaks of EL spectra located at 430 and 560 nm corresponding to the CIE coordinates of (0.32, 0.32) under bias voltage ranging from 5 to 15 V. A maximum luminance of 5630 cd/m2 and a maximum power efficiency of 0.6 lm/W were achieved. The balanced spectra were attributed to the stable confining of charge carriers and exciton by the thin emitting layers. Hence, with simple device structure and fabricating process, the device with ultrathin layer achieved low turn-on voltage, stable white light emitting and higher power efficiency.

Optimization of white organic light emitting diodes based on emitting layer charge carrier conduction properties

Energy Technology Data Exchange (ETDEWEB)

Baek, H I; Lee, C H [School of Electrical Engineering and Computer Science and Inter-University Semiconductor Research Center, Seoul National University, Seoul 151-744 (Korea, Republic of)], E-mail: hibaek75@snu.ac.kr

2008-05-21

We have fabricated white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which 4,4'-N,N'-dicarbazole-biphenyl (CBP) layers doped with the phosphorescent dopants fac-tris(2-phenylpyridine) iridium (Ir(ppy){sub 3}) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C3')iridium(acetylacetonate) (btp{sub 2}Ir(acac)) and the fluorescent dopant 4,4'-bis[2-{l_brace}4-(N,N-diphenylamino) phenyl{r_brace}vinyl]biphenyl (DPAVBi) were used as green (G), red (R) and blue (B) EMLs, respectively. A higher efficiency was expected with the R/G/B EML sequence from the hole transport layer interface than with the G/R/B sequence because of the differences in the charge carrier conduction properties of the EMLs doped with phosphorescent dopants and the luminance balance between the phosphorescent and fluorescent emissions. A high efficiency of 18.3 cd A{sup -1} (an external quantum efficiency of 8.5%) at 100 cd m{sup -2} and good colour stability were achieved with the R/G/B EML sequence as expected, with an additional non-doped CBP interlayer used between the G and B EMLs. In addition, the OLED with this sequence was found to have the longest lifetime of the white devices we tested.

High-efficiency pyrene-based blue light emitting diodes: Aggregation suppression using a calixarene 3D-scaffold

KAUST Repository

Chan, Khaileok

2012-01-01

An efficient blue light emitting diode based on solution processable pyrene-1,3-alt-calix[4]arene is demonstrated, providing a record current efficiency of 10.5 cd A -1 in a simple non-doped OLED configuration. Complete suppression of pyrene aggregation in the solid state is achieved by controlling chromophore dispersion using the 1,3-alt-calix[4]arene scaffold. © 2012 The Royal Society of Chemistry.

Efficient organic light emitting-diodes (OLEDs)

CERN Document Server

Chang, Yi-Lu

2015-01-01

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

Blue and white phosphorescent organic light emitting diode performance improvement by confining electrons and holes inside double emitting layers

Energy Technology Data Exchange (ETDEWEB)

Tsai, Yu-Sheng; Hong, Lin-Ann; Juang, Fuh-Shyang; Chen, Cheng-Yin

2014-09-15

In this research, complex emitting layers (EML) were fabricated using TCTA doping hole-transport material in the front half of a bipolar 26DCzPPy as well as PPT doping electron-transport material in the back half of 26DCzPPy. Blue dopant FIrpic was also mixed inside the complex emitting layer to produce a highly efficient blue phosphorescent organic light emitting diode (OLED). The hole and electron injection and carrier recombination rate were effectively increased. The fabricated complex emitting layers exhibited current efficiency of 42 cd/A and power efficiency of 30 lm/W when the luminance was 1000 cd/m{sup 2}, driving voltage was 4.4 V, and current density was 2.4 mA/cm{sup 2}. A white OLED component was then manufactured by doping red dopant [Os(bpftz){sub 2}(PPh{sub 2}Me){sub 2}] (Os) in proper locations. When the Os dopant was doped in between the complex emitting layers, excitons were effectively confined within, increasing the recombination rate and therefore reducing the color shift. The resulting Commission Internationale de L’Eclairage (CIE) coordinates shifted from 4 to 10 V is (Δx=−0.04, Δy=+0.01). The component had a current efficiency of 35.7 cd/A, a power efficiency of 24 lm/W, driving voltage of 4.6 V and a CIE{sub x,y} of (0.31,0.35) at a luminance of 1000 cd/m{sup 2}, with a maximum luminance of 15,600 cd/m{sup 2} at 10 V. Attaching an outcoupling enhancement film was applied to increase the luminance efficiency to 30 lm/W. - Highlights: • Used the complex double emitting layers. • Respectively doped hole and electron transport material in the bipolar host. • Electrons and holes are effectively confined within EMLs to produce excitons.

Blue and white phosphorescent organic light emitting diode performance improvement by confining electrons and holes inside double emitting layers

International Nuclear Information System (INIS)

Tsai, Yu-Sheng; Hong, Lin-Ann; Juang, Fuh-Shyang; Chen, Cheng-Yin

2014-01-01

In this research, complex emitting layers (EML) were fabricated using TCTA doping hole-transport material in the front half of a bipolar 26DCzPPy as well as PPT doping electron-transport material in the back half of 26DCzPPy. Blue dopant FIrpic was also mixed inside the complex emitting layer to produce a highly efficient blue phosphorescent organic light emitting diode (OLED). The hole and electron injection and carrier recombination rate were effectively increased. The fabricated complex emitting layers exhibited current efficiency of 42 cd/A and power efficiency of 30 lm/W when the luminance was 1000 cd/m 2 , driving voltage was 4.4 V, and current density was 2.4 mA/cm 2 . A white OLED component was then manufactured by doping red dopant [Os(bpftz) 2 (PPh 2 Me) 2 ] (Os) in proper locations. When the Os dopant was doped in between the complex emitting layers, excitons were effectively confined within, increasing the recombination rate and therefore reducing the color shift. The resulting Commission Internationale de L’Eclairage (CIE) coordinates shifted from 4 to 10 V is (Δx=−0.04, Δy=+0.01). The component had a current efficiency of 35.7 cd/A, a power efficiency of 24 lm/W, driving voltage of 4.6 V and a CIE x,y of (0.31,0.35) at a luminance of 1000 cd/m 2 , with a maximum luminance of 15,600 cd/m 2 at 10 V. Attaching an outcoupling enhancement film was applied to increase the luminance efficiency to 30 lm/W. - Highlights: • Used the complex double emitting layers. • Respectively doped hole and electron transport material in the bipolar host. • Electrons and holes are effectively confined within EMLs to produce excitons

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

Energy Technology Data Exchange (ETDEWEB)

Zhan, Lu; Xia, Fafa; Ye, Qiuyu; Xiang, Xishu; Xie, Bing, E-mail: bxie@des.ecnu.edu.cn

2015-12-15

Highlights: • Rare metals (Ga, In) are separated and recycled from waste light-emitting diodes. • Pyrolysis, physical disaggregation and vacuum metallurgy separation are proposed. • There is no hazardous materials produced in this process. - Abstract: 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.

Light emitting diodes as a plant lighting source

Energy Technology Data Exchange (ETDEWEB)

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

1994-12-31

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

Operation of AC Adapters Visualized Using Light-Emitting Diodes

Science.gov (United States)

Regester, Jeffrey

2016-01-01

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

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

DEFF Research Database (Denmark)

Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

Fluorescent SiC based white light-emitting diodes(LEDs) light source, as an innovative energy-efficient light source, would even have longer lifetime, better light quality and eliminated blue-tone effect, compared to the current phosphor based white LED light source. In this paper, the yellow...

Fluorescence lifetime imaging using light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

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

2008-05-07

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

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

KAUST Repository

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

2012-01-01

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

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

Science.gov (United States)

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

2012-05-06

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

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

KAUST Repository

Sun, Liangfeng

2012-05-06

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

Highly efficient and simplified phosphorescence white organic light-emitting diodes based on synthesized deep-blue host and orange emitter

Energy Technology Data Exchange (ETDEWEB)

Koo, Ja Ryong; Lee, Seok Jae; Hyung, Gun Woo; Kim, Bo Young; Lee, Dong Hyung [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of); Kim, Woo Young [Department of Green Energy and Semiconductor Engineering, Hoseo University, Asan 336-795 (Korea, Republic of); Lee, Kum Hee [Department of Chemistry, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Yoon, Seung Soo, E-mail: ssyoon@skku.edu [Department of Chemistry, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Kim, Young Kwan, E-mail: kimyk@hongik.ac.kr [Department of Information Display, Hongik University, Seoul 121-791 (Korea, Republic of)

2013-10-01

The authors have demonstrated a highly efficient and stable phosphorescent white organic light-emitting diode (WOLED), which has been achieved by doping only one orange phosphorescent emitter, Bis(5-benzoyl-2-(4-fluorophenyl)pyridinato-C,N)iridium(III) acetylacetonate into an appropriate deep blue phosphorescent host, 4,4'-bis(4-(triphenylsilyl)phenyl)-1,1'-binaphthyl as an emitting layer (EML). The WOLED has been achieved by effective confinement of triplet excitons to emit a warm white color. The optimized WOLED, with a simple structure as a hole transporting layer-EML-electron transporting layer, showed a maximum luminous efficiency of 22.38 cd/A, a maximum power efficiency of 12.01 lm/W, a maximum external quantum efficiency of 7.32%, and CIEx,y coordinates of (0.38,0.42) at 500 cd/m{sup 2}, respectively. - Highlights: • Highly efficient phosphorescent white organic light-emitting diode (WOLED) • Single emitting layer consists of synthesized deep blue host and orange emitter • The WOLED with high EL efficiencies due to efficient triplet exciton confinement.

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

Directory of Open Access Journals (Sweden)

Hsu Chih-Neng

2013-01-01

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

Efficient red phosphorescent organic light emitting diodes with double emission layers

International Nuclear Information System (INIS)

Ben Khalifa, M; Mazzeo, M; Maiorano, V; Mariano, F; Carallo, S; Melcarne, A; Cingolani, R; Gigli, G

2008-01-01

We demonstrate efficient red phosphorescent organic light emitting diodes with a bipolar emission structure (D-EML) formed by two different layers doped with a red phosphorescent dye. Due to its self-balancing character, the recombination zone is shifted far from the emission/carrier-blocking-layer interfaces. This prevents the accumulation of carriers at the interfaces and reduces the triplet-triplet annihilation, resulting in an improved efficiency of the D-EML device compared with the standard single-EML architecture. However, a current efficiency of 8.4 cd A -1 at 10 mA cm -2 is achieved in the D-EML device compared with 3.7 cd A -1 in the single-EML device

Efficient red phosphorescent organic light emitting diodes with double emission layers

Energy Technology Data Exchange (ETDEWEB)

Ben Khalifa, M; Mazzeo, M; Maiorano, V; Mariano, F; Carallo, S; Melcarne, A; Cingolani, R; Gigli, G [NNL, National Nanotechnology Laboratory of CNR-INFM, Distretto tecnologico ISUFI, Universita del Salento, Italy, Via per Arnesano, Km.5, 73100 Lecce (Italy)], E-mail: mohamed.benkhalifa@unile.it

2008-08-07

We demonstrate efficient red phosphorescent organic light emitting diodes with a bipolar emission structure (D-EML) formed by two different layers doped with a red phosphorescent dye. Due to its self-balancing character, the recombination zone is shifted far from the emission/carrier-blocking-layer interfaces. This prevents the accumulation of carriers at the interfaces and reduces the triplet-triplet annihilation, resulting in an improved efficiency of the D-EML device compared with the standard single-EML architecture. However, a current efficiency of 8.4 cd A{sup -1} at 10 mA cm{sup -2} is achieved in the D-EML device compared with 3.7 cd A{sup -1} in the single-EML device.

Optoelectronic properties of a novel fluorene derivative for organic light-emitting diode

Energy Technology Data Exchange (ETDEWEB)

Yu, Junsheng; Lou, Shuangling; Qian, Jincheng; Jiang, Yadong [University of Electronic Science and Technology of China (UESTC), State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Optoelectronic Information, Chengdu (China); Zhang, Qing [Shanghai Jiaotong University, Department of Polymer Science, School of Chemistry and Chemical Technology, Shanghai (China)

2009-03-15

We report the optoelectronic properties of a novel fluorene derivative of 6,6'-(9H-fluoren-9,9-diyl)bis(2,3-bis (9,9-dihexyl-9H-fluoren-2-yl)quinoxaline) (BFLBBFLYQ) used for organic light-emitting diode. UV-Vis absorption, photoluminescence (PL) and electroluminescence (EL) spectra of BFLBBFLYQ and the blend doped with N,N'-biphenyl-N,N'-bis-(3-methylphenyl)-1,1'-biphenyl-4,4'-di- amine (TPD) in solid state and in solution were investigated. The results showed that BFLBBFLYQ had a PL peak at 451 nm in solid and solution states and an EL peak at 483 nm with a broad emission band, resulting from fluorenone defects. Exciplex emission was observed in BFLBBFLYQ-TPD blend solid state with a green emission peaking at 530 nm. Also the blend in solution showed solvatochromism in polarity solvent upon UV irradiation. A new absorption band appeared at around 470 nm of BFLBBFLYQ-TPD blend in chloroform solution, and disappeared when diluted in absorption spectrum. Meanwhile, a low energy emission band from 530 to 580 nm appeared and increased with material concentration and UV irradiation time. (orig.)

Luminescent properties of Eu2+-doped BaGdF5 glass ceramics a potential blue phosphor for ultra-violet light-emitting diode

International Nuclear Information System (INIS)

Zhang, Weihuan; Zhang, Yuepin; Ouyang, Shaoye; Zhang, Zhixiong; Wang, Qian; Xia, Haiping

2015-01-01

Eu 2+ doped transparent oxyfluoride glass ceramics containing BaGdF 5 nanocrystals were successfully fabricated by melt-quenching technique under a reductive atmosphere. The structure of the glass and glass ceramics were investigated by differential scanning calorimetry, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The luminescent properties were investigated by transmission, excitation, and emission spectra. The decay time of the Gd 3+ ions at 312 nm excited with 275 nm were also investigated. The results of XRD and TEM indicated the existence of BaGdF5 nanocrystals in the transparent glass ceramics. The excitation spectra of Eu 2+ doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED). Compared with the as-made glass, the emission of glass ceramics is much stronger by a factor of increasing energy transfer efficiency from Gd 3+ to Eu 2+ ions, the energy transfer efficiency from Gd 3+ to Eu 2+ ions was discussed. In addition, the chromaticity coordinates of glass and glass ceramics specimens were also discussed, which indicated that the Eu 2+ doped BaGdF 5 glass ceramics may be used as a potential blue-emitting phosphor for UV-LED

1.54 μm Er3+ electroluminescence from an erbium-compound-doped organic light emitting diode with a p-type silicon anode

International Nuclear Information System (INIS)

Zhao, W Q; Wang, P F; Ran, G Z; Ma, G L; Zhang, B R; Liu, W M; Wu, S K; Dai, L; Qin, G G

2006-01-01

By doping an erbium complex, erbium (III) 2, 4-pentanedionate (Er(acac) 3 ), into the ALQ layer, we fabricate a series of infrared emission organic light emitting diodes (OLED) with structures of p-Si/SiO 2 /NPB/ALQ/ ALQ:Er(acac) 3 /ALQ/Sm/Au, where p-Si is the anode and Sm/Au is the cathode. The 1.54 μm emission from Er 3+ is observed. The impact of doping level of Er(acac) 3 in ALQ on 1.54 μm electroluminescence (EL) intensity is studied, and the best mass ratio of Er(acac) 3 to ALQ is found at 1:60. A competitive EL mechanism from the ALQ and Er(acac) 3 is found and the Er 3+ ions excitations are attributed to energy transfer from the ligands to Er ions

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

International Nuclear Information System (INIS)

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

2010-01-01

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

InGaN/AlGaInN-based ultraviolet light-emitting diodes with indium gallium tin oxide electrodes

Energy Technology Data Exchange (ETDEWEB)

Kim, Sukwon; Kim, Tae Geun, E-mail: tgkim1@korea.ac.kr

2015-09-30

In this study, In- and Sn-doped GaO (IGTO) is proposed as an alternative transparent conductive electrode for indium tin oxide (ITO) to improve the performance of InGaN/AlGaInN-based near ultraviolet light-emitting diodes (NUV LEDs). IGTO films were prepared by co-sputtering the ITO and Ga{sub 2}O{sub 3} targets under various target power ratios. Among those, IGTO films post-annealed at 700 °C under a hydrogen environment gave rise to a transmittance of 94% at 385 nm and a contact resistance of 9.4 × 10{sup −3} Ω-cm{sup 2} with a sheet resistance of 124 Ω/ϒ. Compared to ITO-based NUV LEDs, the IGTO-based NUV LED showed a 9% improvement in the light output power, probably due to IGTO's higher transmittance, although the forward voltage was still higher by 0.23 V. - Highlights: • Indium gallium tin oxide (IGTO) for near-ultraviolet light-emitting diode is proposed. • IGTO is fabricated by co-sputtering the ITO and Ga{sub 2}O{sub 3} targets and hydrogen annealing. • IGTO shows a 94% transmittance at 385 nm and a 9.4 × 10{sup −3} Ω-cm{sup 2} contact resistance. • Near-ultraviolet light-emitting diode with IGTO shows improved optical performance.

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

International Nuclear Information System (INIS)

Kashiwagi, Y.; Yamamoto, M.; Saitoh, M.; Takahashi, M.; Ohno, T.; Nakamoto, M.; Koizumi, A.; Fujiwara, Y.; Takemura, Y.; Murahashi, K.; Ohtsuka, K.; Furuta, S.

2014-01-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded

Direct transparent electrode patterning on layered GaN substrate by screen printing of indium tin oxide nanoparticle ink for Eu-doped GaN red light-emitting diode

Energy Technology Data Exchange (ETDEWEB)

Kashiwagi, Y., E-mail: kasiwagi@omtri.or.jp; Yamamoto, M.; Saitoh, M.; Takahashi, M.; Ohno, T.; Nakamoto, M. [Osaka Municipal Technical Research Institute, 1-6-50 Morinomiya, Joto-ku, Osaka 536-8553 (Japan); Koizumi, A.; Fujiwara, Y. [Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Takemura, Y.; Murahashi, K.; Ohtsuka, K. [Okuno Chemical Industries Co., Ltd., 2-1-25 Hanaten-nishi, Joto-ku, Osaka 536-0011 (Japan); Furuta, S. [Tomoe Works Co., Ltd., 7-13 Tsurumachi, Amagasaki 660-0092 (Japan)

2014-12-01

Transparent electrodes were formed on Eu-doped GaN-based red-light-emitting diode (GaN:Eu LED) substrates by the screen printing of indium tin oxide nanoparticle (ITO np) inks as a wet process. The ITO nps with a mean diameter of 25 nm were synthesized by the controlled thermolysis of a mixture of indium complexes and tin complexes. After the direct screen printing of ITO np inks on GaN:Eu LED substrates and sintering at 850 °C for 10 min under atmospheric conditions, the resistivity of the ITO film was 5.2 mΩ cm. The fabricated LED up to 3 mm square surface emitted red light when the on-voltage was exceeded.

Recent developments in white light emitting diodes

Science.gov (United States)

Lohe, P. P.; Nandanwar, D. V.; Belsare, P. D.; Moharil, S. V.

2018-05-01

because they can emit visible light strongly under blue light irradiation. These are chemically, thermally and mechanically stable materials with high efficiency to down convert blue radiation into green and red. Efficient white light can be generated by coating these phosphors on blue LED.CRI of white emitting LED lamp can be improved significantly if green and red emitting phosphors are coated on efficient blue emitting LED chips. In this approach CRI will be maintained if appropriate combination of red, green along with blue emission is used. This article reviews some recent developments in phosphors for white light emitting diodes.

Color Rendering Index Thermal Stability Improvement of Glass-Based Phosphor-Converted White Light-Emitting Diodes for Solid-State Lighting

Directory of Open Access Journals (Sweden)

Chun-Chin Tsai

2014-01-01

Full Text Available High color rendering index performance has been required for phosphor-converted warm-white light-emitting diodes (PC-WWLEDs in lighting industry. The characteristics of low-temperature fabricated phosphor (yellow: Ce3+:YAG, green: Tb3+:YAG, and red: CaAlClSiN3:Eu2+ doped glass were presented for applications to high color rendering index warm-white-light-emitting diodes. Color coordinates (x, y = (0.36, 0.29, quantum yield (QY = 55.6%, color rending index (CRI = 85.3, and correlated color temperature (CCT = 3923 K were characterized. Glass-based PC-WWLEDs was found able to maintain good thermal stability for long-time high-temperature operation. QY decay, CRI remenance, and chromaticity shift were also analyzed for glass- and silicone-based high-power PC-WLEDs by thermal aging at 150°C and 250°C for industrial test standard’s aging time 1008 hours. Better than the silicone’s, thermal stability of glass-based PC-WLEDs has been improved. The resulted high color rendering index (CRI glass phosphor potentially can be used as a phosphor layer for high-performance and low-cost PC-WLEDs used in next-generation indoor solid-state lighting applications.

Tuning the colour of white polymer light emitting diodes

NARCIS (Netherlands)

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

2010-01-01

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

4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM)-doping density dependence of luminescence spectra and white emission in polymer light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Inoue, Akinori; Hosokawa, Takeshi; Haishi, Motoki; Ohtani, Naoki [Department of Electronics, Doshisha University, Tatara-Miyakodani, Kyotanabe-shi, Kyoto (Japan)

2009-01-15

We fabricated white polymer light-emitting diodes (PLEDs), in which the active region is doped with a low-weight molecule. The host polymer material is Poly(9,9-didodecyl-fluorenyl-2,7-yleneethylnylene) (PFO), while the guest luminescent low-weight-molecule is 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). The photoluminescence (PL) and electroluminescence (EL) spectra strongly depend on DCM-doping-density. However, the most suitable DCM-doping-densities for white emissions in PL and EL are slightly different. This discrepancy is caused by the difference in excitation efficiencies. The photo-excitation system for PL measurement is better than the current injection for generating carriers efficiently. Thus, the realization of the white EL signal requires the larger DCM-doping-density than that of the white PL signal. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Light emitting diodes for today's energy conscious world

Energy Technology Data Exchange (ETDEWEB)

Papanier, J

2000-10-01

The role played by light emitting diodes in back lighting, decorative illumination, emergency lighting, and automated signage are described as indicators of the many benefits and advantages of LED technology. The basic principles underlying the functioning of LEDs are explained, including the reasons behind their high efficiency in applications requiring colour. The difference between wattage and lumens is clarified; wattage refers to power consumption, whereas lumens measure brightness or light output, the measure most significant in the case of LEDs.

Performance of injection-limited polymer light-emitting diodes

NARCIS (Netherlands)

Blom, P.W.M.; Woudenberg, T.V.; Huiberts, H.; Jabbour, GE; Carter, SA; Kido, J; Lee, ST; Sariciftci, NS

2002-01-01

The electro-optical characteristics of a polymer light emitting diode (PLED) with a strongly reduced hole injection have been investigated. The device consists of a poly-p-phenylene vinylene semiconductor with a Ag hole injecting contact, which has an injection barrier of about 1 eV. It is observed

Single component Mn-doped perovskite-related CsPb2ClxBr5-x nanoplatelets with a record white light quantum yield of 49%: a new single layer color conversion material for light-emitting diodes.

Science.gov (United States)

Wu, Hao; Xu, Shuhong; Shao, Haibao; Li, Lang; Cui, Yiping; Wang, Chunlei

2017-11-09

Single component nanocrystals (NCs) with white fluorescence are promising single layer color conversion media for white light-emitting diodes (LED) because the undesirable changes of chromaticity coordinates for the mixture of blue, green and red emitting NCs can be avoided. However, their practical applications have been hindered by the relative low photoluminescence (PL) quantum yield (QY) for traditional semiconductor NCs. Though Mn-doped perovskite nanocube is a potential candidate, it has been unable to realize a white-light emission to date. In this work, the synthesis of Mn-doped 2D perovskite-related CsPb 2 Cl x Br 5-x nanoplatelets with a pure white emission from a single component is reported. Unlike Mn-doped perovskite nanocubes with insufficient energy transfer efficiency, the current reported Mn-doped 2D perovskite-related CsPb 2 Cl x Br 5-x nanoplatelets show a 10 times higher energy transfer efficiency from perovskite to Mn impurities at the required emission wavelengths (about 450 nm for perovskite emission and 580 nm for Mn emission). As a result, the Mn/perovskite dual emission intensity ratio surprisingly elevates from less than 0.25 in case of Mn-doped nanocubes to 0.99 in the current Mn-doped CsPb 2 Cl x Br 5-x nanoplatelets, giving rise to a pure white light emission with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.35, 0.32). More importantly, the highest PL QY for Mn-doped perovskite-related CsPb 2 Cl x Br 5-x nanoplatelets is up to 49%, which is a new record for white-emitting nanocrystals with single component. These highly luminescent nanoplatelets can be blended with polystyrene (PS) without changing the white light emission but dramatically improving perovskite stability. The perovskite-PS composites are available not only as a good solution processable coating material for assembling LED, but also as a superior conversion material for achieving white light LED with a single conversion layer.

Study of photophysical processes in organic light-emitting diodes based on light-emission profile reconstruction

NARCIS (Netherlands)

Carvelli, M.

2012-01-01

Organic light-emitting diodes (OLEDs) are emerging as a promising option for energy-efficient, flexible light sources. A key factor that needs to be measured and controlled is the shape of the emission profile, i.e. the spatial distribution of the emitting excitons across the active layer thickness.

Optical and electrical improvements of semipolar (1 1 −2 2) GaN-based light emitting diodes by Si doping of n-GaN template

International Nuclear Information System (INIS)

Lee, Jae-Hwan; Han, Sang-Hyun; Song, Ki-Ryong; Lee, Sung-Nam

2014-01-01

Highlights: • In semipolar GaN, Si-doping is effective to reduce out-of plane PSFs toward [1−100]. • Interfacial quality of semipolar QWs was improved by increasing SiH4 flow of n-GaN. • Electrical properties of semipolar GaN were improved by increasing Si doping. • Light output power of semipolar LEDs were increased with SiH4 flow rate of n-type GaN. - Abstract: We report that the performance of semipolar (1 1 −2 2) GaN-based light-emitting diodes (LEDs) was improved by increasing the Si-doping concentration of n-type GaN templates. In-plane and out-of plane high-resolution X-ray diffraction demonstrated that crystal defects such as threading dislocation, partial stacking faults and basal stacking faults, were significantly decreased by increasing the Si-doping concentration. This resulted in the increase of carrier mobility due to reduction of the defect-scattering effect. Furthermore, the quality of InGaN/GaN quantum-well interfaces was improved by increasing the Si-doping concentration of the n-type GaN template. Based on these results, we suggest that the light-output power and operation voltage of semipolar (1 1 −2 2) GaN-based LEDs would be improved by increasing Si doping concentration of n-type GaN templates

p-Type modulation doped InGaN/GaN dot-in-a-wire white-light-emitting diodes monolithically grown on Si(111).

Science.gov (United States)

Nguyen, H P T; Zhang, S; Cui, K; Han, X; Fathololoumi, S; Couillard, M; Botton, G A; Mi, Z

2011-05-11

Full-color, catalyst-free InGaN/GaN dot-in-a-wire light-emitting diodes (LEDs) were monolithically grown on Si(111) by molecular beam epitaxy, with the emission characteristics controlled by the dot properties in a single epitaxial growth step. With the use of p-type modulation doping in the dot-in-a-wire heterostructures, we have demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm(2). The remarkable performance is attributed to the superior three-dimensional carrier confinement provided by the electronically coupled dot-in-a-wire heterostructures, the nearly defect- and strain-free GaN nanowires, and the significantly enhanced hole transport due to the p-type modulation doping.

Influence of dehydrated nanotubed titanic acid on charge transport and luminescent properties of polymer light-emitting diodes with fluorescent dye

Science.gov (United States)

Qian, Lei; Bera, Debasis; Jin, Zhen-Sheng; Du, Zu-Liang; Xu, Zheng; Teng, Feng; Liu, Wei

2007-09-01

In this paper, we discuss the influence of dehydrated nanotubed titanic acid (DNTA) on charge transport and luminescent properties of polymer light-emitting diodes (PLEDs) doped with fluorescent dye. Photoluminescence results confirm the efficient energy transfer from PVK to 4-(dicyanom-ethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and tris-(8-hydroxtquinoline) aluminum (Alq 3) in a DNTA-doped device. The device showed lower turn-on voltages and higher charge current by doping with DNTA, which also caused a shift in the exciton's recombination region.

Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Room-Temperature-Processed Ga-Doped ZnO Nanoparticles as the Electron Transport Layer

KAUST Repository

Cao, Sheng

2017-04-19

Colloidal ZnO nanoparticle (NP) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QD-LEDs) with good stability and high efficiency. However, because of the inherently high work function of such films, spontaneous charge transfer occurs at the QD/ZnO interface in such a QD-LED, thus leading to reduced performance. Here, to improve the QD-LED performance, we prepared Ga-doped ZnO NPs with low work functions and tailored band structures via a room-temperature (RT) solution process without the use of bulky organic ligands. We found that the charge transfer at the interface between the CdSe/ZnS QDs and the doped ZnO NPs was significantly weakened because of the incorporated Ga dopants. Remarkably, the as-assembled QD-LEDs, with Ga-doped ZnO NPs as the ETLs, exhibited superior luminances of up to 44 000 cd/m2 and efficiencies of up to 15 cd/A, placing them among the most efficient red-light QD-LEDs ever reported. This discovery provides a new strategy for fabricating high-performance QD-LEDs by using RT-processed Ga-doped ZnO NPs as the ETLs, which could be generalized to improve the efficiency of other optoelectronic devices.

Weak-microcavity organic light-emitting diodes with improved light out-coupling.

Science.gov (United States)

Cho, Sang-Hwan; Song, Young-Woo; Lee, Joon-gu; Kim, Yoon-Chang; Lee, Jong Hyuk; Ha, Jaeheung; Oh, Jong-Suk; Lee, So Young; Lee, Sun Young; Hwang, Kyu Hwan; Zang, Dong-Sik; Lee, Yong-Hee

2008-08-18

We propose and demonstrate weak-microcavity organic light-emitting diode (OLED) displays with improved light-extraction and viewing-angle characteristics. A single pair of low- and high-index layers is inserted between indium tin oxide (ITO) and a glass substrate. The electroluminescent (EL) efficiencies of discrete red, green, and blue weak-microcavity OLEDs are enhanced by 56%, 107%, and 26%, respectively, with improved color purity. Moreover, full-color passive-matrix bottom-emitting OLED displays are fabricated by employing low-index layers of two thicknesses. As a display, the EL efficiency of white color was 27% higher than that of a conventional OLED display.

High performance inkjet printed phosphorescent organic light emitting diodes based on small molecules commonly used in vacuum processes

Energy Technology Data Exchange (ETDEWEB)

Jung, Sung-Hoon [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Kim, Jang-Joo, E-mail: jjkim@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742 (Korea, Republic of); Kim, Hyong-Jun, E-mail: hkim@kongju.ac.kr [Department of Chemical Engineering, Kongju National University, Cheonan, 330-717 (Korea, Republic of)

2012-09-30

High efficiency phosphorescent organic light emitting diodes (OLEDs) are realized by inkjet printing based on small molecules commonly used in vacuum processes in spite of the limitation of the limited solubility. The OLEDs used the inkjet printed 5 wt.% tris(2-phenylpyridine)iridium(III) (Ir(ppy){sub 3}) doped in 4,4 Prime -Bis(carbazol-9-yl)biphenyl (CBP) as the light emitting layer on various small molecule based hole transporting layers, which are widely used in the fabrication of OLEDs by vacuum processes. The OLEDs resulted in the high power and the external quantum efficiencies of 29.9 lm/W and 11.7%, respectively, by inkjet printing the CBP:Ir(ppy){sub 3} on a 40 nm thick 4,4 Prime ,4 Double-Prime -tris(carbazol-9-yl)triphenylamine layer. The performance was very close to a vacuum deposited device with a similar structure. - Highlights: Black-Right-Pointing-Pointer Effective inkjet printed organic light emitting diode (OLED) technique is explored. Black-Right-Pointing-Pointer Solution process on commonly used hole transporting material (HTM) is demonstrated. Black-Right-Pointing-Pointer Triplet energy overlap of HTM and emitting material is the key to the performance. Black-Right-Pointing-Pointer Simple inkjet printed OLED provides the high current efficiency of 40 cd/A.

Using an ultra-thin non-doped orange emission layer to realize high efficiency white organic light-emitting diodes with low efficiency roll-off

Energy Technology Data Exchange (ETDEWEB)

Zhu, Liping; Chen, Jiangshan; Ma, Dongge, E-mail: mdg1014@ciac.ac.cn [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate University of the Chinese Academy of Sciences, Changchun 130022 (China); Zhao, Yongbiao [Luminous Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798 (Singapore); Zhang, Hongmei [Department of Materials Science and Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023 (China)

2014-06-28

By adopting an ultra-thin non-doped orange emission layer sandwiched between two blue emission layers, high efficiency white organic light-emitting diodes (WOLEDs) with reduced efficiency roll-off were fabricated. The optimized devices show a balanced white emission with Internationale de L'Eclairage of (0.41, 0.44) at the luminance of 1000 cd/m{sup 2}, and the maximum power efficiency, current efficiency (CE), and external quantum efficiency reach 63.2 lm/W, 59.3 cd/A, and 23.1%, which slightly shift to 53.4 lm/W, 57.1 cd/A, and 22.2% at 1000 cd/m{sup 2}, respectively, showing low efficiency roll-off. Detailed investigations on the recombination zone and the transient electroluminescence (EL) clearly reveal the EL processes of the ultra-thin non-doped orange emission layer in WOLEDs.

Effects of a highly Si-doped GaN current spreading layer at the n+-GaN/multi-quantum-well interface on InGaN/GaN blue-light-emitting diodes

International Nuclear Information System (INIS)

Kim, C. S.; Cho, H. K.; Choi, R. J.; Hahn, Y. B.; Lee, H. J.; Hong, C. H.

2004-01-01

Highly Si-doped GaN thin current spreading layer (CSL) with various carrier concentrations were inserted before the n + -GaN/multi-quantum-well (MQW) interface controlled by the growth rate and the modulated Si-doping in InGaN/GaN blue light-emitting diodes (LEDs), and their effects were investigated by using capacitance-voltage (C-V), current-voltage (I-V), and output power measurements. The LEDs with a highly Si-doped CSL show enhanced I-V characteristics and increased output power with increasing carrier concentration up to some critical point in the CSL. This means that proper high Si-doping in some limited area before the interface may enhance the device performance through the current spreading effect.

Effect of mixed hole transporting host on the mobility, Gaussian density of states and efficiencies of a heterojunction phosphorescent organic light emitting diode

International Nuclear Information System (INIS)

Talik, N A; Woon, K L; Yap, B K

2016-01-01

We present an in-depth study of the hole transport in poly(vinylcarbazole) PVK films blended with small molecule tris(4-carbazoyl-9-ylphenyl)amine (TcTa). Doping TcTa in PVK introduces shallow hole traps when the doping concentration is lower than 20 wt%. It becomes percolative at higher concentrations. The energetic disorder σ of the blended system reduces from ∼72 meV at 0 wt% TcTa to ∼41 meV at 50 wt% TcTa. A correlation between σ and the film morphologies suggests that the blending of TcTa molecules in the film does not only change the film homogeneity and roughness but also the energetic disorder. In addition to the mobility study, we fabricated a red phosphorescent organic light emitting diode with the same blending system. By doping merely 5 wt% of TcTa into PVK as mixed hole-transporting hosts, the efficiency of the deep red heterojunction phosphorescent organic light emitting diode increased from 2 cd A −1 to 4 cd A −1 , suggesting that TcTa molecules assist in hole injection. (paper)

Study of the effect of the doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymeric anode on the organic light-emitting diode performances

Energy Technology Data Exchange (ETDEWEB)

De Girolamo Del Mauro, Anna, E-mail: anna.degirolamo@enea.it; Nenna, Giuseppe; Villani, Fulvia; Minarini, Carla

2012-06-01

Bottom-emitting organic diode devices with polymeric anode were fabricated and their performances were compared to devices with different anodes. The highly transparent (transmittance Almost-Equal-To 90%) and conductive (700 S/cm) anode was poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) processed from aqueous solution and modified by addition of dimethyl sulfoxide (DMSO). The electro-optical characteristics of the DMSO-doped PEDOT:PSS based device and devices with architectures based on undoped PEDOT:PSS and/or indium tin oxide (ITO) were investigated and the effects of the different anodes were analyzed by means of electrical responses in static and dynamic regimes. The efficiency of the device with the proposed polymeric anode was comparable to that of ITO based device but reduced with respect to the device including PEDOT:PSS as hole-injection layer. These results were correlated to the film morphological properties and discussed in terms of interfacial state density modification. - Highlights: Black-Right-Pointing-Pointer Doped Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) is proposed as anode. Black-Right-Pointing-Pointer Transparent and conductive polymeric anode is used in organic light-emitting diodes. Black-Right-Pointing-Pointer Efficiency of polymeric anode device is comparable to device with indium tin oxide. Black-Right-Pointing-Pointer Lower optical switch-on and higher luminance are observed. Black-Right-Pointing-Pointer Interface state density is modified by addition of the dopant in polymeric electrode.

Multilayered phosphorescent polymer light-emitting diodes using a solution-processed n-doped electron transport layer

Energy Technology Data Exchange (ETDEWEB)

Chen, Yuehua; Zhang, Mengke [Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023 (China); Zhang, Xinwen, E-mail: iamxwzhang@njupt.edu.cn [Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023 (China); Lei, Zhenfeng; Zhang, Xiaolin; Hao, Lin; Fan, Quli [Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023 (China); Lai, Wenyong, E-mail: iamwylai@njupt.edu.cn [Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023 (China); Huang, Wei [Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023 (China); Key Laboratory of Flexible Electronics & Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816 (China)

2017-06-15

Efficient multilayered green phosphorescent polymer light-emitting devices (PhPLEDs) were successfully fabricated using a solution-processed n-doped small molecular electron transporting layer (ETL) composed of 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBi) and CsF. We found that the electroluminescence properties of the devices with n-doped ETLs are significantly improved. The maximum luminance efficiency of the device with 7.5 wt% CsF doped TPBi ETL reached 26.9 cd/A, which is 1.5 times as large as that of the undoped device. The impedance spectra of the devices and electron transport properties of the CsF doped ETLs demonstrate that doping dramatically decreases the impedance and enhances the electrical conductivity. Similarly, enhanced performance of PhPLED is also observed by use of CsF-doped 4,7-diphenyl-1,10 -phenanthroline (BPhen) ETL. These results demonstrate that CsF can be used as an effective n-dopant in solution-processed devices.

Multilayered phosphorescent polymer light-emitting diodes using a solution-processed n-doped electron transport layer

International Nuclear Information System (INIS)

Chen, Yuehua; Zhang, Mengke; Zhang, Xinwen; Lei, Zhenfeng; Zhang, Xiaolin; Hao, Lin; Fan, Quli; Lai, Wenyong; Huang, Wei

2017-01-01

Efficient multilayered green phosphorescent polymer light-emitting devices (PhPLEDs) were successfully fabricated using a solution-processed n-doped small molecular electron transporting layer (ETL) composed of 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBi) and CsF. We found that the electroluminescence properties of the devices with n-doped ETLs are significantly improved. The maximum luminance efficiency of the device with 7.5 wt% CsF doped TPBi ETL reached 26.9 cd/A, which is 1.5 times as large as that of the undoped device. The impedance spectra of the devices and electron transport properties of the CsF doped ETLs demonstrate that doping dramatically decreases the impedance and enhances the electrical conductivity. Similarly, enhanced performance of PhPLED is also observed by use of CsF-doped 4,7-diphenyl-1,10 -phenanthroline (BPhen) ETL. These results demonstrate that CsF can be used as an effective n-dopant in solution-processed devices.

True Yellow Light-Emitting Diodes as Phosphor for Tunable Color-Rendering Index Laser-Based White Light

KAUST Repository

Janjua, Bilal; Ng, Tien Khee; Zhao, Chao; Prabaswara, Aditya; Consiglio, Giuseppe Bernardo; Priante, Davide; Shen, Chao; Elafandy, Rami T.; Anjum, Dalaver H.; Alhamoud, Abdullah A.; Alatawi, Abdullah A.; Yang, Yang; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Ooi, Boon S.

2016-01-01

An urgent challenge for the lighting research community is the lack of efficient optical devices emitting in between 500 and 600 nm, resulting in the “green-yellow gap”. In particular, true green (∼555 nm) and true yellow (∼590 nm), along with blue and red, constitute four technologically important colors. The III-nitride material system, being the most promising choice of platform to bridge this gap, still suffers from high dislocation density and poor crystal quality in realizing high-power, efficient devices. Particularly, the high polarization fields in the active region of such 2D quantum confined structures prevent efficient recombination of carriers. Here we demonstrate a true yellow nanowire (NW) light emitting diode (LED) with peak emission of 588 nm at 29.5 A/cm2 (75 mA in a 0.5 × 0.5 mm2 device) and a low turn-on voltage of ∼2.5 V, while having an internal quantum efficiency of 39%, and without “efficiency droop” up to an injection current density of 29.5 A/cm2. By mixing yellow light from a NW LED in reflective configuration with that of a red, green, and blue laser diode (LD), white light with a correlated color temperature of ∼6000 K and color-rendering index of 87.7 was achieved. The nitride-NW-based device offers a robust, long-term stability for realizing yellow light emitters for tunable color-rendering index solid-state lighting, on a scalable, low-cost, foundry-compatible titanium/silicon substrate, suitable for industry uptake.

True Yellow Light-Emitting Diodes as Phosphor for Tunable Color-Rendering Index Laser-Based White Light

KAUST Repository

Janjua, Bilal

2016-10-11

An urgent challenge for the lighting research community is the lack of efficient optical devices emitting in between 500 and 600 nm, resulting in the “green-yellow gap”. In particular, true green (∼555 nm) and true yellow (∼590 nm), along with blue and red, constitute four technologically important colors. The III-nitride material system, being the most promising choice of platform to bridge this gap, still suffers from high dislocation density and poor crystal quality in realizing high-power, efficient devices. Particularly, the high polarization fields in the active region of such 2D quantum confined structures prevent efficient recombination of carriers. Here we demonstrate a true yellow nanowire (NW) light emitting diode (LED) with peak emission of 588 nm at 29.5 A/cm2 (75 mA in a 0.5 × 0.5 mm2 device) and a low turn-on voltage of ∼2.5 V, while having an internal quantum efficiency of 39%, and without “efficiency droop” up to an injection current density of 29.5 A/cm2. By mixing yellow light from a NW LED in reflective configuration with that of a red, green, and blue laser diode (LD), white light with a correlated color temperature of ∼6000 K and color-rendering index of 87.7 was achieved. The nitride-NW-based device offers a robust, long-term stability for realizing yellow light emitters for tunable color-rendering index solid-state lighting, on a scalable, low-cost, foundry-compatible titanium/silicon substrate, suitable for industry uptake.

Photoresponse of poly(para-phenylenevinylene) light-emitting diodes

International Nuclear Information System (INIS)

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

1994-01-01

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

Safety of light emitting diodes in toys.

Science.gov (United States)

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

2012-03-01

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

Safety of light emitting diodes in toys

International Nuclear Information System (INIS)

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

2012-01-01

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.

White emission from organic light-emitting diodes with a super-thin BCP layer

International Nuclear Information System (INIS)

Hao Jingang; Deng Zhenbo; Yang Shengyi

2007-01-01

We report a method to achieve white emission from organic light-emitting diodes (OLEDs) in which a super-thin (3 nm) hole blocking layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), was inserted between electron-transport layer 8-hydroxyquinoline aluminum (Alq 3 ) and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (DCJTB) doped poly-vinlycarbazole (PVK) layer. The BCP layer can not only confine exciton in the emitting layer but also control energy transfer proportion from PVK to Alq 3 and then from Alq 3 to DCJTB through BCP layer. In this way, pure white emission with CIE coordinate of (0.32, 0.32) was obtained and it was voltage independent. The brightness reached 270 cd/m 2 at 18 V with an efficiency of 0.166 cd/A

A tunable lighting system integrated by inorganic and transparent organic light-emitting diodes

Science.gov (United States)

Zhang, Jing-jing; Zhang, Tao; Jin, Ya-fang; Liu, Shi-shen; Yuan, Shi-dong; Cui, Zhao; Zhang, Li; Wang, Wei-hui

2014-05-01

A tunable surface-emitting integrated lighting system is constructed using a combination of inorganic light-emitting diodes (LEDs) and transparent organic LEDs (OLEDs). An RB two-color LED is used to supply red and blue light emission, and a green organic LED is used to supply green light emission. Currents of the LED and OLED are tuned to produce a white color, showing different Commission Internationale d'Eclairage (CIE) chromaticity coordinates and correlated color temperatures with a wide adjustable range. Such an integration can compensate for the lack of the LED's luminance uniformity and the transparent OLED's luminance intensity.

Luminescence properties of Ca2 Ga2 SiO7 :RE phosphors for UV white-light-emitting diodes.

Science.gov (United States)

Jiao, Mengmeng; Lv, Wenzhen; Lü, Wei; Zhao, Qi; Shao, Baiqi; You, Hongpeng

2015-03-16

A series of Eu(2+) -, Ce(3+) -, and Tb(3+) -doped Ca2 Ga2 SiO7 phosphors is synthesized by using a high-temperature solid-state reaction. The powder X-ray diffraction and structure refinement data indicate that our prepared phosphors are single phased and the phosphor crystalizes in a tetrahedral system with the ${P\\bar 42m}$ (113) space group. The Eu(2+) - and Ce(3+) -doped phosphors both have broad excitation bands, which match well with the UV light-emitting diodes chips. Under irradiation of λ=350 nm, Ca2 Ga2 SiO7 :Eu(2+) and Ca2 Ga2 SiO7 :Ce(3+) , Li(+) have green and blue emissions, respectively. Luminescence of Ca2 Ga2 SiO7 :Tb(3+) , Li(+) phosphor varies with the different Tb(3+) contents. The thermal stability and energy-migration mechanism of Ca2 Ga2 SiO7 :Eu(2+) are also studied. The investigation results indicate that the prepared Ca2 Ga2 SiO7 :Eu(2+) and Ca2 Ga2 SiO7 :Ce(3+) , Li(+) samples show potential as green and blue phosphors, respectively, for UV-excited white-light-emitting diodes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hybrid fluorescent layer emitting polarized light

Directory of Open Access Journals (Sweden)

Mohammad Mohammadimasoudi

2017-07-01

Full Text Available Semiconductor nanorods have anisotropic absorption and emission properties. In this work a hybrid luminescent layer is produced based on a mixture of CdSe/CdS nanorods dispersed in a liquid crystal that is aligned by an electric field and polymerized by UV illumination. The film emits light with polarization ratio 0.6 (polarization contrast 4:1. Clusters of nanorods in liquid crystal can be avoided by applying an AC electric field with sufficient amplitude. This method can be made compatible with large-scale processing on flexible transparent substrates. Thin polarized light emitters can be used in LCD backlights or solar concentrators to increase the efficiency.

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

KAUST Repository

Wu, Junbo

2010-01-26

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

Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes

Science.gov (United States)

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.

Epitaxial Sb-doped SnO_2 and Sn-doped In_2O_3 transparent conducting oxide contacts on GaN-based light emitting diodes

International Nuclear Information System (INIS)

Tsai, Min-Ying; Bierwagen, Oliver; Speck, James S.

2016-01-01

We demonstrate the growth of epitaxial (100)-oriented, rutile Sb-doped SnO_2 (ATO) and (111)-oriented, cubic Sn-doped In_2O_3 (ITO) transparent conducting oxide (TCO) contacts on top of an InGaN/GaN(0001) light emitting diode (LED) by plasma-assisted molecular beam epitaxy (PAMBE). Both oxides form rotational domains. The in-plane epitaxial alignment of the two ITO(111) rotational domains to the GaN(0001) was: GaN [21-10]|| ITO_D_o_m_a_i_n_1[‐ 211]|| ITO_D_o_m_a_i_n_2[‐ 1‐12]. A growth temperature as low as 600 °C was necessary to realize a low contact resistance between ATO and the top p-GaN layer of the LED but resulted in non-optimal resistivity (3.4 × 10"− "3 Ω cm) of the ATO. The current–voltage characteristics of a processed LED, however, were comparable to that of a reference LED with a standard electron-beam evaporated ITO top contact. At short wavelengths, the optical absorption of ATO was lower than that of ITO, which is beneficial even for blue LEDs. Higher PAMBE growth temperatures resulted in lower resistive ATO but higher contact resistance to the GaN, likely by the formation of an insulating Ga_2O_3 interface layer. The ITO contact grown by PAMBE at 600 °C showed extremely low resistivity (10"−"4 Ω cm) and high crystalline and morphological quality. These proof-of-principle results may lead to the development of epitaxial TCO contacts with low resistivity, well-defined interfaces to the p-GaN to help minimize contact losses, and enable further epitaxy on top of the TCO. - Highlights: • Plasma-assisted molecular beam epitaxy of SnO_2:Sb (ATO) and In_2O_3:Sn (ITO) contacts • Working light emitting diodes processed with the ATO contact on the top p-GaN layer • Low growth temperature ensures low contact resistance (limiting interface reaction). • ITO showed significantly better structural and transport properties than ATO. • ATO showed higher optical transmission at short wavelengths than ITO.

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

Energy Technology Data Exchange (ETDEWEB)

Qian, L., E-mail: qian_lei@126.com; Xu, Z.; Teng, F.; Duan, X.-X. [Beijing Jiaotong University, Institute of Optoelectronic Technology (China); Jin, Z.-S.; Du, Z.-L. [Henan University, Key Laboratory on special functional materials (China); Li, F.-S.; Zheng, M.-J. [State Key Laboratory for Artificial Microstructures and Mesoscopic Physics, Peking University, Department of Physics (China); Wang, Y.-S. [Beijing Jiaotong University, Institute of Optoelectronic Technology (China)

2007-06-15

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

Science.gov (United States)

Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

2007-06-01

Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

Heavy Mg-doping of (Al,Ga)N films for potential applications in deep ultraviolet light-emitting structures

Science.gov (United States)

Liang, Y. H.; Towe, E.

2018-03-01

Doping of high aluminum-containing (Al,Ga)N thin films has remained a challenging problem that has hindered progress in the development of deep ultraviolet light-emitters. This paper reports on the synthesis and use of heavily doped (Al,Ga)N films in deep ultraviolet (˜274 nm) light-emitting structures; these structures were synthesized by molecular beam epitaxy under liquid-metal growth conditions that facilitate the incorporation of extremely high density of Mg dopant impurities (up to 5 × 1019 cm-3) into aluminum-rich (Al,Ga)N thin films. Prototypical light-emitting diode structures incorporating Al0.7Ga0.3N films doped with Mg impurities that ionize to give free hole carrier concentrations of up to 6 × 1017 cm-3 exhibit external quantum efficiencies of up 0.56%; this is an improvement from previous devices made from molecular beam epitaxy-grown materials. This improvement is believed to be due to the high hole carrier concentration enabled by the relatively low activation energy of 220 meV compared to the expected values of 408-507 meV for Al0.7Ga0.3N films.

Non-radiative recombination losses in polymer light-emitting diodes

NARCIS (Netherlands)

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

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

Liquid metals as electrodes in polymer light emitting diodes

NARCIS (Netherlands)

Andersson, G.G.; Gommans, H.H.P.; Denier van der Gon, A.W.; Brongersma, H.H.

2003-01-01

We demonstrate that liquid metals can be used as cathodes in light emitting diodes (pLEDs). The main difference between the use of liquid cathodes and evaporated cathodes is the sharpness of the metal–polymer interface. Liquid metal cathodes result in significantly sharper metal–organic interfaces

Effect of nitrogen doping on the structural, optical and electrical properties of indium tin oxide films prepared by magnetron sputtering for gallium nitride light emitting diodes

Science.gov (United States)

Tian, Lifei; Cheng, Guoan; Wang, Hougong; Wu, Yulong; Zheng, Ruiting; Ding, Peijun

2017-01-01

The indium tin oxide (ITO) films are prepared by the direct current magnetron sputtering technology with an ITO target in a mixture of argon and nitrogen gas at room temperature. The blue transmittance at 455 nm rises from 63% to 83% after nitrogen doping. The resistivity of the ITO film reduces from 4.6 × 10-3 (undoped film) to 5.7 × 10-4 Ω cm (N-doped film). The X-ray photoelectron spectroscopy data imply that the binding energy of the In3d5/2 peak is declined 0.05 eV after nitrogen doping. The high resolution transmission electron microscope images show that the nitrogen loss density of the GaN/ITO interface with N-doped ITO film is smaller than that of the GaN/ITO interface with undoped ITO film. The forward turn-on voltage of gallium nitride light emitting diode reduces by 0.5 V after nitrogen doping. The fabrication of the N-doped ITO film is conducive to modify the N component of the interface between GaN and ITO layer.

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

KAUST Repository

Wu, Junbo; Agrawal, Mukul; Becerril, Héctor A.; Bao, Zhenan; Liu, Zunfeng; Chen, Yongsheng; Peumans, Peter

2010-01-01

Theoretical estimates indicate that graphene thin films can be used as transparent electrodes for thin-film devices such as solar cells and organic light-emitting diodes, with an unmatched combination of sheet resistance and transparency. We

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

Science.gov (United States)

Saikia, Dhrubajyoti; Sarma, Ranjit

2018-01-01

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

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

Directory of Open Access Journals (Sweden)

Boucar Diouf

2012-01-01

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

Current path in light emitting diodes based on nanowire ensembles

International Nuclear Information System (INIS)

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

2012-01-01

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

Tandem organic light-emitting diodes with KBH4 doped 9,10-bis(3-(pyridin-3-yl)phenyl) anthracene connected to the charge generation layer.

Science.gov (United States)

Duan, Lian; Tsuboi, Taiju; Qiu, Yong; Li, Yanrui; Zhang, Guohui

2012-06-18

Tandem organic light emitting diodes (OLEDs) are ideal for lighting applications due to their low working current density at high brightness. In this work, we have studied an efficient electron transporting layer of KBH(4) doped 9,10-bis(3-(pyridin-3-yl)phenyl)anthracene (DPyPA) which is located adjacent to charge generation layer of MoO(3)/NPB. The excellent transporting property of the DPyPA:KBH(4) layer helps the tandem OLED to achieve a lower voltage than the tandem device with the widely used tris-(8-hydroxyquinoline)aluminum:Li. For the tandem white OLED with a fluorescent blue unit and a phosphorescent yellow unit, we've achieved a high current efficiency of 75 cd/A, which can be further improved to 120 cd/A by attaching a diffuser layer.

Reduced Graphene Oxide/Single-Walled Carbon Nanotube Hybrid Films Using Various p-Type Dopants and Their Application to GaN-Based Light-Emitting Diodes.

Science.gov (United States)

Lee, Byeong Ryong; Kim, Tae Geun

2017-01-01

This article reports the electrical and optical properties of the reduced graphene oxide (RGO)/single-walled carbon nanotube (SWCNT) films using various p-type dopants and their application to GaN-based light-emitting diodes. To enhance the current injection and spreading of the RGO/SWCNT films on the light-emitting diodes (LEDs), we increased the work function (Φ) of the films using chemical doping with AuCl₃, poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and MoO₃; thereby reduced the Schottky barrier height between the RGO/SWCNT films and p-GaN. By comparison, LEDs fabricated with work-function-tuned RGO/SWCNT film doped with MoO₃ exhibited the decrease of the forward voltage from 5.3 V to 5.02 V at 20 mA and the increase of the output power up to 1.26 times. We also analyzed the current injection mechanism using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy.

Reduced Graphene Oxide/Single-Walled Carbon Nanotube Hybrid Film Using Various p-Type Dopants and Its Application to GaN-Based Light-Emitting Diodes.

Science.gov (United States)

Lee, Byeong Ryong; Kim, Tae Geun

2016-06-01

This paper reports the electrical and optical properties of the reduced graphene oxide (RGO)/single-walled carbon nanotube (SWNT) films using various p-type dopants and its application to GaN-based light-emitting diodes. To enhance the current injection and spreading of the RGO/SWNT films on the light-emitting diodes (LEDs), we increased the work function (φ) of the films using chemical doping with AuCl3, poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) ( PSS) and MoO3; thereby reduced the Schottky barrier height between the RGO/SWNT films and p-GaN. By comparison, LEDs fabricated with work-function-tuned RGO/SWNT film doped with MoO3 exhibited the decrease of the forward voltage from 5.3 V to 5.02 V at 20 mA and the increase of the output power up to 1.26 times. We also analyzed the current injection mechanism using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy.

Light-emitting diodes - Their potential in biomedical applications

Energy Technology Data Exchange (ETDEWEB)

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

2010-10-15

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

Carrier transport assisted by dopants in doped poly(N-vinylcarbozole) light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Chen Xiaohong [Institute of Optoelectronic Technology, Bejing Jiaotong University, Beijing 100044 (China); Liu Ming [Institute of Optoelectronic Technology, Bejing Jiaotong University, Beijing 100044 (China); Xu Zheng [Institute of Optoelectronic Technology, Bejing Jiaotong University, Beijing 100044 (China); Hou Yanbing [Institute of Optoelectronic Technology, Bejing Jiaotong University, Beijing 100044 (China); Teng Feng [Institute of Optoelectronic Technology, Bejing Jiaotong University, Beijing 100044 (China); Xu Xurong [Institute of Optoelectronic Technology, Bejing Jiaotong University, Beijing 100044 (China)

2004-04-07

We have investigated the transient electroluminescence (EL) onset of the double-layer light-emitting devices made from poly(N-vinylcarbozole) (PVK) doped with 4-(dicyanomethylene)-2-t-butyl-6(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and tris(8-hydroxy-quinoline) aluminium (Alq{sub 3}). For the double-layered device in which PVK was doped with 0.1 wt% DCJTB, the EL onset of PVK lags that of DCJTB and Alq{sub 3}, while the EL onset of DCJTB and Alq{sub 3} is simultaneous. However, the EL emission of the double-layered device of PVK/Alq{sub 3} originates only from Alq{sub 3}. The results show that DCJTB dopants can not only help to tunnel electrons from Alq{sub 3} zone to PVK but can also assist electrons transfer in PVK under high electric field by hopping between DCJTB molecules or from DCJTB to PVK sites at a low doping concentration of 0.1 wt%. When the DCJTB doping concentration is 4.0 wt%, the EL onset of Alq{sub 3} lags that of DCJTB. The difference in the EL onsets of DCJTB, Alq{sub 3} and PVK is attributed to the slow build-up of the internal space charge in the vicinity of the interface between PVK and Alq{sub 3}. The electron potential difference of the interface between Alq{sub 3} and PVK doped by DCJTB can be adjusted by changing the DCJTB doping concentration in double-layer devices.

White emission from organic light-emitting diodes with a super-thin BCP layer

Energy Technology Data Exchange (ETDEWEB)

Hao Jingang [Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Deng Zhenbo [Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China)]. E-mail: zbdeng@center.njtu.edu.cn; Yang Shengyi [Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China)

2007-01-15

We report a method to achieve white emission from organic light-emitting diodes (OLEDs) in which a super-thin (3 nm) hole blocking layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), was inserted between electron-transport layer 8-hydroxyquinoline aluminum (Alq{sub 3}) and 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran (DCJTB) doped poly-vinlycarbazole (PVK) layer. The BCP layer can not only confine exciton in the emitting layer but also control energy transfer proportion from PVK to Alq{sub 3} and then from Alq{sub 3} to DCJTB through BCP layer. In this way, pure white emission with CIE coordinate of (0.32, 0.32) was obtained and it was voltage independent. The brightness reached 270 cd/m{sup 2} at 18 V with an efficiency of 0.166 cd/A.

Effects of electron blocking and hole trapping of the red guest emitter materials on hybrid white organic light emitting diodes

International Nuclear Information System (INIS)

Hong, Lin-Ann; Vu, Hoang-Tuan; Juang, Fuh-Shyang; Lai, Yun-Jr; Yeh, Pei-Hsun; Tsai, Yu-Sheng

2013-01-01

Hybrid white organic light emitting diodes (HWOLEDs) with fluorescence and phosphorescence hybrid structures are studied in this work. HWOLEDs were fabricated with blue/red emitting layers: fluorescent host material doped with sky blue material, and bipolar phosphorescent host emitting material doped with red dopant material. An electron blocking layer is applied that provides hole red guest emitter hole trapping effects, increases the charge carrier injection quantity into the emitting layers and controls the recombination zone (RZ) that helps balance the device color. Spacer layers were also inserted to expand the RZ, increase efficiency and reduce energy quenching along with roll-off effects. The resulting high efficiency warm white OLED device has the lower highest occupied molecule orbital level red guest material, current efficiency of 15.9 cd/A at current density of 20 mA/cm 2 , and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39)

Effects of electron blocking and hole trapping of the red guest emitter materials on hybrid white organic light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Hong, Lin-Ann; Vu, Hoang-Tuan [National Formosa University, Institute of Electro-Optical and Materials Science, Huwei, Yunlin County, Taiwan (China); Juang, Fuh-Shyang, E-mail: fsjuang@seed.net.tw [National Formosa University, Institute of Electro-Optical and Materials Science, Huwei, Yunlin County, Taiwan (China); Lai, Yun-Jr [National Formosa University, Institute of Electro-Optical and Materials Science, Huwei, Yunlin County, Taiwan (China); Yeh, Pei-Hsun [Raystar Optronics, Inc., 5F No. 25, Keya Rd. Daya Township, Taichung County, Taiwan (China); Tsai, Yu-Sheng [National Formosa University, Institute of Electro-Optical and Materials Science, Huwei, Yunlin County, Taiwan (China)

2013-10-01

Hybrid white organic light emitting diodes (HWOLEDs) with fluorescence and phosphorescence hybrid structures are studied in this work. HWOLEDs were fabricated with blue/red emitting layers: fluorescent host material doped with sky blue material, and bipolar phosphorescent host emitting material doped with red dopant material. An electron blocking layer is applied that provides hole red guest emitter hole trapping effects, increases the charge carrier injection quantity into the emitting layers and controls the recombination zone (RZ) that helps balance the device color. Spacer layers were also inserted to expand the RZ, increase efficiency and reduce energy quenching along with roll-off effects. The resulting high efficiency warm white OLED device has the lower highest occupied molecule orbital level red guest material, current efficiency of 15.9 cd/A at current density of 20 mA/cm{sup 2}, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39)

Reduced-droop green III-nitride light-emitting diodes utilizing GaN tunnel junction

Science.gov (United States)

Alhassan, Abdullah I.; Young, Erin C.; Alyamani, Ahmed Y.; Albadri, Abdulrahman; Nakamura, Shuji; DenBaars, Steven P.; Speck, James S.

2018-04-01

We report the fabrication of low-droop high-efficiency green c-plane light-emitting diodes (LEDs) utilizing GaN tunnel junction (TJ) contacts. The LED epitaxial layers with a top p-GaN layer were grown by metal organic chemical vapor deposition and an n++-GaN layer was deposited by molecular beam epitaxy to form a TJ. The TJ LEDs were then compared with equivalent LEDs having a tin-doped indium oxide (ITO) contact. The TJ LEDs exhibited a higher performance and a lower efficiency droop than did the ITO LEDs. At 35 A/cm2, the external quantum efficiencies for the TJ and ITO LEDs were 31.2 and 27%, respectively.

High color rendering index white organic light-emitting diode using levofloxacin as blue emitter

International Nuclear Information System (INIS)

Miao Yan-Qin; Zhang Ai-Qin; Li Yuan-Hao; Wang Hua; Jia Hu-Sheng; Liu Xu-Guang; Gao Zhi-Xiang; Tsuboi Taijuf

2015-01-01

Levofloxacin (LOFX), which is well-known as an antibiotic medicament, was shown to be useful as a 452-nm blue emitter for white organic light-emitting diodes (OLEDs). In this paper, the fabricated white OLED contains a 452-nm blue emitting layer (thickness of 30 nm) with 1 wt% LOFX doped in CBP (4,4’-bis(carbazol-9-yl)biphenyl) host and a 584-nm orange emitting layer (thickness of 10 nm) with 0.8 wt% DCJTB (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7, 7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran) doped in CBP, which are separated by a 20-nm-thick buffer layer of TPBi (2,2’,2”-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole). A high color rendering index (CRI) of 84.5 and CIE chromaticity coordinates of (0.33, 0.32), which is close to ideal white emission CIE (0.333, 0.333), are obtained at a bias voltage of 14 V. Taking into account that LOFX is less expensive and the synthesis and purification technologies of LOFX are mature, these results indicate that blue fluorescence emitting LOFX is useful for applications to white OLEDs although the maximum current efficiency and luminance are not high. The present paper is expected to become a milestone to using medical drug materials for OLEDs. (paper)

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

DEFF Research Database (Denmark)

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

2013-01-01

we show that it is feasible to carry out Monte Carlo simulations including all of these molecular-scale processes for a hybrid multilayer organic light-emitting diode combining red and green phosphorescent layers with a blue fluorescent layer. The simulated current density and emission profile......In multilayer white organic light-emitting diodes the electronic processes in the various layers--injection and motion of charges as well as generation, diffusion and radiative decay of excitons--should be concerted such that efficient, stable and colour-balanced electroluminescence can occur. Here...

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

International Nuclear Information System (INIS)

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

2014-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-01-31

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

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

Science.gov (United States)

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.

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

Science.gov (United States)

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

2014-10-01

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

Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p-n diodes and InGaN LEDs

Science.gov (United States)

Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

2017-12-01

Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal-organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p-n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm-3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10-3-3.4 × 10-3 Ω·cm2, and the turn-on voltages of the diodes.

Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

KAUST Repository

Mughal, Asad J.

2017-11-27

Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

KAUST Repository

Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

2017-01-01

Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

Efficient light harvesting from flexible perovskite solar cells under indoor white light-emitting diode illumination

NARCIS (Netherlands)

Lucarelli, G.; Di Giacomo, F.; Zardetto, V.; Creatore, M.; Brown, T.M.

2017-01-01

This is the first report of an investigation on flexible perovskite solar cells for artificial light harvesting by using a white light-emitting diode (LED) lamp as a light source at 200 and 400 lx, values typically found in indoor environments. Flexible cells were developed using either

Atom probe tomography of a commercial light emitting diode

International Nuclear Information System (INIS)

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

2013-01-01

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

Optical investigation of microscopic defect distribution in semi-polar (1-101 and 11-22) InGaN light-emitting diodes

Science.gov (United States)

Hafiz, Shopan; Andrade, Nicolas; Monavarian, Morteza; Izyumskaya, Natalia; Das, Saikat; Zhang, Fan; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

2016-02-01

Near-field scanning optical microscopy was applied to investigate the spatial variations of extended defects and their effects on the optical quality for semi-polar (1-101) and (11-22) InGaN light emitting diodes (LEDs). (1-101) and (11-22) oriented InGaN LEDs emitting at 450-470 nm were grown on patterned Si (001) 7° offcut substrates and m-sapphire substrates by means of nano-epitaxial lateral overgrowth (ELO), respectively. For (1-101) structures, the photoluminescence (PL) at 85 K from the near surface c+ wings was found to be relatively uniform and strong across the sample. However, emission from the c- wings was substantially weaker due to the presence of high density of threading dislocations (TDs) and basal plane stacking faults (BSFs) as revealed from the local PL spectra. In case of (11-22) LED structures, near-field PL intensity correlated with the surface features and the striations along the direction parallel to the c-axis projection exposed facets where the Indium content was higher as deduced from shift in the PL peak energy.

Effect of gold nanorods and nanocubes on electroluminescent performances in organic light-emitting diodes and its working mechanism

Directory of Open Access Journals (Sweden)

Ying Xu

2015-06-01

Full Text Available In this manuscript we investigated the influence of Au nanoparticles on electrical and electroluminescent (EL performances in organic light-emitting diodes (OLEDs via doping as-synthesized Au nanorods (NRs or nanocubes (NCs into hole transport layer (HTL. Through accurately controlling the distance between the Au NRs and the emitting layer, altering the guest emitter’s lifetime, and replacing Au NRs with Au NCs to satisfy a better spectrum overlap with the emission guest, we got a conclusion that doping Au NRs or NCs into HTL has no significant influence on the device’s electrical and EL performances, although we observed an increase in the spontaneous emission rate in a fluorescent material by the exciton-surface plasmon-coupling. Our results suggest that a further research on emission mechanism in surface plasmon-enhanced OLEDs is still in process.

A phosphor-free white light-emitting diode using In2O3 : Tb transparent conductive light converter

International Nuclear Information System (INIS)

Chen, Lung-Chien; Tien, Ching-Ho; Liao, Wei-Chian

2011-01-01

Tb-doped indium oxide (In 2 O 3 : Tb) films were deposited on a GaN-based near-ultraviolet (NUV) light-emitting diode (LED) as a transparent conductive light converter to form a white LED. The transmittance of the In 2 O 3 : Tb film (Tb at 10 wt%) exceeded 80% in visible light and the resistivity was 0.325 Ω cm. The In 2 O 3 : Tb transparent conductive light converter was also employed on GaN-based LEDs. GaN-based NUV-LEDs with In 2 O 3 : Tb film (Tb at 10 wt%) produced forward biases of 3.42 V at an injection current of 20 mA. With increasing temperature, increasing Tb 3+ concentration and increasing injection current from 20 to 100 mA, the chromaticity coordinates barely changed in the white light area. Therefore, the GaN-based NUV-LED with In 2 O 3 : Tb film had a stable white light colour, when temperature and injection current changed, and is suitable for solid-state lighting.

Carrier-injection studies in GaN-based light-emitting-diodes

Science.gov (United States)

Nguyen, Dinh Chuong; Vaufrey, David; Leroux, Mathieu

2015-09-01

Although p-type GaN has been achieved by Mg doping, the low hole-mobility still remains a difficulty for GaN-based light-emitting diodes (LEDs). Due to the lack of field-dependent-velocity model for holes, in GaN-based LED simulations, the hole mobility is usually supposed to remain constant. However, as the p-GaN-layer conductivity is lower than the n-GaN-layer conductivity, a strong electric-field exists in the p-side of an LED when the applied voltage exceeds the LED's built-in voltage. Under the influence of this field, the mobilities of electrons and holes are expected to decrease. Based on a field-dependent-velocity model that is usually used for narrow-bandgap materials, an LED structure is modelled with three arbitrarily chosen hole saturation-velocities. The results show that a hole saturation-velocity lower than 4x106 cm/s can negatively affect the LED's behaviors.

Progress in Piezo-Phototronic-Effect-Enhanced Light-Emitting Diodes and Pressure Imaging.

Science.gov (United States)

Pan, Caofeng; Chen, Mengxiao; Yu, Ruomeng; Yang, Qing; Hu, Youfan; Zhang, Yan; Wang, Zhong Lin

2016-02-24

Wurtzite materials exhibit both semiconductor and piezoelectric properties under strains due to the non-central symmetric crystal structures. The three-way coupling of semiconductor properties, piezoelectric polarization and optical excitation in ZnO, GaN, CdS and other piezoelectric semiconductors leads to the emerging field of piezo-phototronics. This effect can efficiently manipulate the emission intensity of light-emitting diodes (LEDs) by utilizing the piezo-polarization charges created at the junction upon straining to modulate the energy band diagrams and the optoelectronic processes, such as generation, separation, recombination and/or transport of charge carriers. Starting from fundamental physics principles, recent progress in piezo-phototronic-effect-enhanced LEDs is reviewed; following their development from single-nanowire pressure-sensitive devices to high-resolution array matrices for pressure-distribution mapping applications. The piezo-phototronic effect provides a promising method to enhance the light emission of LEDs based on piezoelectric semiconductors through applying static strains, and may find perspective applications in various optoelectronic devices and integrated systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

DEFF Research Database (Denmark)

Fadil, Ahmed; Ou, Yiyu; Iida, Daisuke

2016-01-01

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

Overshoot effects of electron on efficiency droop in InGaN/GaN MQW light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Huang, Yang; Liu, Zhiqiang, E-mail: lzq@semi.ac.cn, E-mail: spring@semi.ac.cn; Yi, Xiaoyan, E-mail: lzq@semi.ac.cn, E-mail: spring@semi.ac.cn; Guo, Yao; Wu, Shaoteng; Yuan, Guodong; Wang, JunXi; Wang, Guohong; Li, Jinmin [R& D Center for Semiconductor Lighting, Chinese Academy of Sciences, Beijing 100083 (China); State Key Laboratory of Solid State Lighting, Beijing 100083 (China); Beijing Engineering Research Center for the 3rd Generation Semiconductor Materials and Application, Beijing 100083 (China)

2016-04-15

To evaluate electron leakage in InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs), analytic models of ballistic and quasi-ballistic transport are developed. With this model, the impact of critical variables effecting electron leakage, including the electron blocking layer (EBL), structure of multiple quantum wells (MQWs), polarization field, and temperature are explored. The simulated results based on this model shed light on previously reported experimental observations and provide basic criteria for suppressing electron leakage, advancing the design of InGaN/GaN LEDs.

Improved efficiency of organic light-emitting diodes based on a europium complex by fluorescent dye

Energy Technology Data Exchange (ETDEWEB)

You Han [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, Changchun 130022 (China); Fang Junfeng [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, Changchun 130022 (China); Gao Jia [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, Changchun 130022 (China); Ma Dongge [State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of Chinese Academy of Sciences, Changchun 130022 (China)]. E-mail: mdg1014@ciac.jl.cn

2007-01-15

Improved efficiency of organic light-emitting diodes (OLEDs) based on europium complexes have been realized by using a fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6 (1,1,7,7-tetramethyljulolidyl-9-enyl))-4H-pyran (DCJTB) doping .The luminous efficiency of the devices with a fluorescent dye in the emissive layer was found to improve two times of that in devices without fluorescent dye. The devices showed pure red light, which is the characteristic emission of trivalent europium ion with a full-width at half-maximum of 3 nm.The maximum brightness and luminous efficiency reached 1200 cd/m{sup 2} at 23 V and 7.3 cd/A (2.0 lm/w), respectively, at a current density of 0.35 mA/cm{sup 2}.

Investigation of organic light emitting diodes for interferometric purposes

Science.gov (United States)

Pakula, Anna; Zimak, Marzena; Sałbut, Leszek

2011-05-01

Recently the new type of light source has been introduced to the market. Organic light emitting diode (OLED) is not only interesting because of the low applying voltage, wide light emitting areas and emission efficiency. It gives the possibility to create a light source of a various shape, various color and in the near future very likely even the one that will change shape and spectrum in time in controlled way. Those opportunities have not been in our reach until now. In the paper authors try to give an answer to the question if the new light source -OLED - is suitable for interferometric purposes. Tests cover the short and long term spectrum stability, spectrum changes due to the emission area selection. In the paper the results of two OLEDs (red and white) are shown together with the result of an attempt to use them in an interferometric setup.

Highly efficient white top-emitting organic light-emitting diodes with forward directed light emission

Energy Technology Data Exchange (ETDEWEB)

Freitag, Patricia; Reineke, Sebastian; Furno, Mauro; Luessem, Bjoern; Leo, Karl [Institut fuer Angewandte Photophysik, TU Dresden (Germany)

2010-07-01

The demand for highly efficient and energy saving illumination has increased considerably during the last decades. Organic light emitting diodes (OLEDs) are promising candidates for future lighting technologies. They offer high efficiency along with excellent color quality, allowing substantially lower power consumption than traditional illuminants. Recently, especially top-emitting devices have attracted high interest due to their compatibility with opaque substrates like metal sheets. In this contribution, we demonstrate top-emitting OLEDs with white emission spectra employing a multilayer hybrid cavity structure with two highly efficient phosphorescent emitter materials for orange-red (Ir(MDQ)2(acac)) and green (Ir(ppy)3) emission as well as the stable fluorescent blue emitter TBPe. To improve the OLED performance and modify the color quality, two different electron blocking layers and anode material combinations are tested. Compared to Lambertian emission, our devices show considerably enhanced forward emission, which is preferred for most lighting applications. Besides broadband emission and angle independent emission maxima, power efficiencies of 13.3 lm/W at 3 V and external quantum efficiencies of 5.3% are achieved. The emission shows excellent CIE coordinates of (0.420,0.407) at approx. 1000 cd/m{sup 2} and color rendering indices up to 77.

Efficient textured colour conversion layer of a down-converted white organic light-emitting diode by transfer imprinting

International Nuclear Information System (INIS)

Zhu, Wenqing; Xiao, Teng; Qian, Bingjie; Sun, Liangliang

2015-01-01

In this paper, we demonstrated an efficient textured colour conversion layer (CCL) of a down-converted white organic light-emitting diode (WOLED), which was fabricated by a very simple transfer imprinting method based on silicon wafer. The textured CCL not only helped to extract wave-guided light in the device, but also had an outstanding performance in enhancing the colour conversion rate, which was 1.75 times greater than that of flat CCL. Compared to flat CCL, the lower-doped textured CCL produced better white emission and higher efficiency simultaneously. Moreover, the WOLED with textured CCL also exhibited good colour stability at various voltages. (paper)

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

Science.gov (United States)

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

2017-05-09

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

Highly efficient single-layer dendrimer light-emitting diodes with balanced charge transport

Science.gov (United States)

Anthopoulos, Thomas D.; Markham, Jonathan P. J.; Namdas, Ebinazar B.; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.

2003-06-01

High-efficiency single-layer-solution-processed green light-emitting diodes based on a phosphorescent dendrimer are demonstrated. A peak external quantum efficiency of 10.4% (35 cd/A) was measured for a first generation fac-tris(2-phenylpyridine) iridium cored dendrimer when blended with 4,4'-bis(N-carbazolyl)biphenyl and electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene at 8.1 V. A maximum power efficiency of 12.8 lm/W was measured also at 8.1 V and 550 cd/m2. These results indicate that, by simple blending of bipolar and electron-transporting molecules, highly efficient light-emitting diodes can be made employing a very simple device structure.

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

Science.gov (United States)

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%.

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

Science.gov (United States)

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

2013-01-01

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

Trap effect of an ultrathin DCJTB layer in organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Wang Yuanmin [Institute of Optoelectronic Technology, Key Laboratory for Information Storage, Displays and Materials, Beijing Jiaotong University, Beijing 100044 (China); Teng Feng [Institute of Optoelectronic Technology, Key Laboratory for Information Storage, Displays and Materials, Beijing Jiaotong University, Beijing 100044 (China)]. E-mail: advanced9898@126.com; Xu Zheng [Institute of Optoelectronic Technology, Key Laboratory for Information Storage, Displays and Materials, Beijing Jiaotong University, Beijing 100044 (China); Hou Yanbing [Institute of Optoelectronic Technology, Key Laboratory for Information Storage, Displays and Materials, Beijing Jiaotong University, Beijing 100044 (China); Yang Shengyi [Institute of Optoelectronic Technology, Key Laboratory for Information Storage, Displays and Materials, Beijing Jiaotong University, Beijing 100044 (China); Xu Xurong [Institute of Optoelectronic Technology, Key Laboratory for Information Storage, Displays and Materials, Beijing Jiaotong University, Beijing 100044 (China)

2005-08-15

An improved performance of organic light-emitting diodes has been obtained by using 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) -4Hpyran (DCJTB) as an ultrathin emitting layer. When 0.1 nm DCJTB was inserted between the hole-transporting layer and electron-transporting layer, for an unoptimized device indium-tin oxide (ITO)/naphtylphenyliphenyl diamine (NPB)/DCJTB (0.1 nm)/8-hydroxyquinoline aluminum (Alq{sub 3})/Al, the maximum brightness was 1531 cd m{sup -2} at 15 V. Compared with doped devices ITO/NPB/Alq{sub 3}:DCJTB (1%)/Alq{sub 3}/LiF/Al, a higher efficiency has been achieved. Compared with the conventional device ITO/NPB/Alq{sub 3}/Al, the inserted device has a slightly higher current efficiency and lower turn-on voltage. We suggest the ultrathin DCJTB layer acts as trap for carriers, and the accumulated holes at the hole-transport layer/electron-transport layer interface have enhanced the electric field in the electron-transport layer and improved the electron injection at the cathode.

Storage of charge carriers on emitter molecules in organic light-emitting diodes

Science.gov (United States)

Weichsel, Caroline; Burtone, Lorenzo; Reineke, Sebastian; Hintschich, Susanne I.; Gather, Malte C.; Leo, Karl; Lüssem, Björn

2012-08-01

Organic light-emitting diodes (OLEDs) using the red phosphorescent emitter iridium(III)bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate) [Ir(MDQ)2(acac)] are studied by time-resolved electroluminescence measurements. A transient overshoot after voltage turn-off is found, which is attributed to electron accumulation on Ir(MDQ)2(acac) molecules. The mechanism is verified via impedance spectroscopy and by application of positive and negative off-voltages. We calculate the density of accumulated electrons and find that it scales linearly with the doping concentration of the emitter. Using thin quenching layers, we locate the position of the emission zone during normal OLED operation and after voltage turn-off. In addition, the transient overshoot is also observed in three-color white-emitting OLEDs. By time- and spectrally resolved measurements using a streak camera, we directly attribute the overshoot to electron accumulation on Ir(MDQ)2(acac). We propose that similar processes are present in many state-of-the-art OLEDs and believe that the quantification of charge carrier storage will help to improve the efficiency of OLEDs.

Numerical study on electronic and optical properties of organic light emitting diodes.

Science.gov (United States)

Kim, Kwangsik; Hwang, Youngwook; Won, Taeyoung

2013-08-01

In this paper, we present a finite element method (FEM) study of space charge effects in organic light emitting diodes. Our model includes a Gaussian density of states to account for the energetic disorder in organic semiconductors and the Fermi-Dirac statistics to account for the charge hopping process between uncorrelated sites. The physical model cover all the key physical processes in OLEDs, namely charge injection, transport and recombination, exciton diffusion, transfer and decay as well as light coupling, and thin-film-optics. The exciton model includes generation, diffusion, and energy transfer as well as annihilation. We assumed that the light emission originates from oscillating and thus embodied as excitons and embedded in a stack of multilayer. The out-coupled emission spectrum has been numerically calculated as a function of viewing angle, polarization, and dipole orientation. We discuss the accumulation of charges at internal interfaces and their signature in the transient response as well as the electric field distribution.

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

Science.gov (United States)

Brummer, Gordon

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

Azimuthal anisotropy of light extraction from photonic crystal light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Lai, Chun-Feng; Lu, T.C.; Wang, S.C. [Department of Photonics and Institute of Electro-Optical Engineering, National Chiao-Tung University, Hsinchu 300, Taiwan (China); Chao, C.H.; Hsueh, H.T.; Wang, J.F.T.; Yeh, W.Y.; Chi, J.Y. [Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute, Hsinchu 310, Taiwan (China); Kuo, H.C.

2008-07-01

Photonic crystal (PhC) light-emitting diodes (LEDs) exhibiting anisotropic light extraction have been investigated experimentally and theoretically. It is found that the anisotropic light extraction strongly depends on the lattice constant and orientation. Optical images of the anisotropy in the azimuthal direction are obtained using annular structure with triangular lattice. 6-fold symmetric light extraction patterns with varying number of petals are observed. More petals in multiple of 6 appear in the observed image with lattice constant increasing. This anisotropic behavior suggests a new means to optimize the PhC design of GaN LED for light extraction. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

Science.gov (United States)

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%.

SPECTRAL CHARACTERISTICS OF MID-INFRARED LIGHT-EMITTING DIODES BASED ON InAs (Sb,P

Directory of Open Access Journals (Sweden)

N. K. Zhumashev

2016-01-01

Full Text Available Subject of Study. We consider spectral characteristics of mid-infrared light-emitting diodes with heterostructures based on InAs(Sb,P emitting at T=300 K in the wavelength range 3.4–4.1 micrometers. The aim of the study was to search for the ways of increasing the diode efficiency. Methods. The heterostructures were grown from metal-organic chemical compounds with the use of vapor-phase epitaxial technique. The spectra were recorded under pulse excitation with the use of computer-controlled installation employing MDR-23 grating monochromator and a lock-in amplifier. InSb photodiode was used as a detector. Comparative study of electroluminescence spectra of the diodes was carried out at the temperatures equal to 300 K and 77 K. We compared the obtained data with the calculation results of the band diagrams of the heterostructures. Main Results. As a result of comparative study of the electroluminescence spectra of the diodes recorded at 300 K and 77 K we have established that increasing of their efficiency is hindered by substantial influence of Auger recombination. For the first time at 77 К we have observed the effect of stimulated emission from InAsSb active layer in light-emitting structures made of InAs/InAsSb/InAsSbP. For heterostructures with quantum wells InAs/(InAs/InAsSb/InAsSbP we have found out that at 77 К the carrier recombination occurs outside quantum wells, which points out to the insufficient carrier localization in the active layer. Thus, we have shown that the efficiency of mid-infrared light-emitting diodes based on InAs(Sb,P can be increased via suppression of Auger-recombination and improvement of carrier localization in the active region. Practical Relevance. The results of the study can be used for development of heterostructures for mid-infrared light-emitting diodes.

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

KAUST Repository

Park, Jihoon; Kim, Eugene

2015-01-01

© 2015 Copyright Taylor & Francis Group, LLC. Floating-off film-transfer technique was used for the formation of semiconducting polymer multi-layers and the effect on the performance of polymer light-emitting diode (PLED) was studied. This method

Study of different roles phosphorescent material played in different positions of organic light emitting diodes

Science.gov (United States)

Keke, Gu; Jian, Zhong; Jiule, Chen; Yucheng, Chen; Ming, Deng

2013-09-01

Phosphorescent materials are crucial to improve the luminescence and efficiency of organic light emitting diodes (OLED), because its internal quantum efficiency can reach 100%. So the studying of optical and electrical properties of phosphorescent materials is propitious for the further development of phosphorescent OLED. Phosphorescent materials were generally doped into different host materials as emitting components, not only played an important role in emitting light but also had a profound influence on carrier transport properties. We studied the optical and electrical properties of the blue 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DPVBi)-based devices, adding a common yellow phosphorescent material bis[2-(4- tert-butylphenyl)benzothiazolato- N,C2'] iridium(acetylacetonate) [( t-bt)2Ir(acac)] in different positions. The results showed ( t-bt)2Ir(acac) has remarkable hole-trapping ability. Especially the ultrathin structure device, compared to the device without ( t-bt)2Ir(acac), had increased the luminance by about 60%, and the efficiency by about 97%. Then introduced thin 4,4'-bis(carbazol-9-yl)biphenyl (CBP) host layer between DPVBi and ( t-bt)2Ir(acac), and got devices with stable white color.

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

Science.gov (United States)

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

2012-06-01

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

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

Science.gov (United States)

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

2017-02-01

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.

Photoluminescence studies of organic phosphor coated diffusing surface using blue inorganic light-emitting diode as excitation source

International Nuclear Information System (INIS)

Singh, Gyanendra; Mehta, Dalip Singh

2013-01-01

We report the studies on photoluminescence (PL) of organic phosphor coated on a diffusing surface using a blue inorganic light-emitting diode (LED) array as an excitation source. The organic phosphor composite coated diffuser was used to scatter the directional blue light from the LED array. Some of the blue light is absorbed by the organic phosphor composite and the phosphor molecules are excited and re-emit light at longer wavelengths due to the PL process. The output light consists of scattered blue light plus phosphor generated broadband yellow light, thus making white light. The diffuser was made up of a plastic substrate coated with an organic composite of small molecule fluorescent material zinc(II)bis(8-hydroxyquinoline) (Znq 2 ) doped with different percentages of electro-phosphorescent metal complex iridium(III)bis(2-methyldibenzo-[f, h] quinoxaline) (acetylacetonate) ([Ir(MDQ) 2 (acac)]). By means of changing the concentration and the thickness of the phosphor composite material the colour coordinates of white light were achieved. The CIE coordinates and correlated colour temperature were calculated for various thicknesses and phosphor composite concentrations and the results are reported. (paper)

[A novel yellow organic light-emitting device].

Science.gov (United States)

Ma, Chen; Wang, Hua; Hao, Yu-Ying; Gao, Zhi-Xiang; Zhou, He-Feng; Xu, Bing-She

2008-07-01

The fabrication of a novel organic yellow-light-emitting device using Rhodamine B as dopant with double quantum-well (DQW) structure was introduced in the present article. The structure and thickness of this device is ITO/CuPc (6 nm) /NPB (20 nm) /Alq3 (3 nm)/Alq3 : Rhodamine B (3 nm) /Alq3 (3 nm) /Al q3 : Rhodamine B(3 nm) /Alq3 (30 nm) /Liq (5 nm)/Al (30 nm). With the detailed investigation of electroluminescence of the novel organic yellow-light-emitting device, the authors found that the doping concentration of Rhodamine B (RhB) had a very big influence on luminance and efficiency of the organic yellow-light-emitting device. When doping concentration of Rhodamine B (RhB) was 1.5 wt%, the organic yellow-light-emitting device was obtained with the maximum current efficiency of 1.526 cd x A(-1) and the maximum luminance of 1 309 cd x m(-2). It can be seen from the EL spectra of the devices that there existed energy transferring from Alq3 to RhB in the organic light-emitting layers. When the doping concentration of RhB increased, lambda(max) of EL spectra redshifted obviously. The phenomenon was attributed to the Stokes effect of quantum wells and self-polarization of RhB dye molecules.

Highly efficient deep-blue organic light emitting diode with a carbazole based fluorescent emitter

Science.gov (United States)

Sahoo, Snehasis; Dubey, Deepak Kumar; Singh, Meenu; Joseph, Vellaichamy; Thomas, K. R. Justin; Jou, Jwo-Huei

2018-04-01

High efficiency deep-blue emission is essential to realize energy-saving, high-quality display and lighting applications. We demonstrate here a deep-blue organic light emitting diode using a novel carbazole based fluorescent emitter 7-[4-(diphenylamino)phenyl]-9-(2-ethylhexyl)-9H-carbazole-2-carbonitrile (JV234). The solution processed resultant device shows a maximum luminance above 1,750 cd m-2 and CIE coordinates (0.15,0.06) with a 1.3 lm W-1 power efficiency, 2.0 cd A-1 current efficiency, and 4.1% external quantum efficiency at 100 cd m-2. The resulting deep-blue emission enables a greater than 100% color saturation. The high efficiency may be attributed to the effective host-to-guest energy transfer, suitable device architecture facilitating balanced carrier injection and low doping concentration preventing efficiency roll-off caused by concentration quenching.

Low temperature preparation of Ag-doped ZnO nanowire arrays for sensor and light-emitting diode applications

Science.gov (United States)

Lupan, O.; Viana, B.; Cretu, V.; Postica, V.; Adelung, R.; Pauporté, T.

2016-02-01

Transition metal doped-oxide semiconductor nanostructures are important to achieve enhanced and new properties for advanced applications. We describe the low temperature preparation of ZnO:Ag nanowire/nanorod (NW/NR) arrays by electrodeposition at 90 °C. The NWs have been characterized by SEM, EDX, transmittance and photoluminescence (PL) measurements. The integration of Ag in the crystal is shown. Single nanowire/nanorod of ZnO:Ag was integrated in a nanosensor structure leading to new and enhanced properties. The ultraviolet (UV) response of the nanosensor was investigated at room temperature. Experimental results indicate that ZnO:Ag (0.75 μM) nanosensor possesses faster response/recovery time and better response to UV light than those reported in literature. The sensor structure has been also shown to give a fast response for the hydrogen detection with improved performances compared to pristine ZnO NWs. ZnO:Ag nanowire/nanorod arrays electrochemically grown on p-type GaN single crystal layer is also shown to act as light emitter in LED structures. The emission wavelength is red-shifted compared to pristine ZnO NW array. At low Ag concentration a single UV-blue emission is found whereas at higher concentration of dopant the emission is broadened and extends up to the red wavelength range. Our study indicates that high quality ZnO:Ag NW/NR prepared at low temperature by electrodeposition can serve as building nanomaterials for new sensors and light emitting diodes (LEDs) structures with low-power consumption.

A hole accelerator for InGaN/GaN light-emitting diodes

Science.gov (United States)

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; Demir, Hilmi Volkan

2014-10-01

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.

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

Science.gov (United States)

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

2012-03-01

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

Edge and defect luminescence of powerful ultraviolet InGaN/GaN light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Shamirzaev, V. T., E-mail: tim@isp.nsc.ru; Gaisler, V. A. [Novosibirsk State Technical University (Russian Federation); Shamirzaev, T. S. [Russian Academy of Science, Siberian Branch, Rzhanov Institute of Semiconductor Physics (Russian Federation)

2016-11-15

The spectrum of ultraviolet (UV) InGaN/GaN light-emitting diodes and its dependence on the current flowing through the structure are studied. The intensity of the UV contribution to the integrated diode luminescence increases steadily with increasing density of current flowing through the structure, despite a drop in the emission quantum efficiency. The electroluminescence excitation conditions that allow the fraction of UV emission to be increased to 97% are established. It is shown that the nonuniform generation of extended defects, which penetrate the active region of the light-emitting diodes as the structures degrade upon local current overheating, reduces the integrated emission intensity but does not affect the relative intensity of diode emission in the UV (370 nm) and visible (550 nm) spectral ranges.

Alternative p-doped hole transport material for low operating voltage and high efficiency organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Murawski, Caroline, E-mail: caroline.murawski@iapp.de; Fuchs, Cornelius; Hofmann, Simone; Leo, Karl [Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Str. 1, 01062 Dresden (Germany); Gather, Malte C. [Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Str. 1, 01062 Dresden (Germany); SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS Scotland (United Kingdom)

2014-09-15

We investigate the properties of N,N′-[(Diphenyl-N,N′-bis)9,9,-dimethyl-fluoren-2-yl]-benzidine (BF-DPB) as hole transport material (HTL) in organic light-emitting diodes (OLEDs) and compare BF-DPB to the commonly used HTLs N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD), 2,2′,7,7′-tetrakis(N,N′-di-p-methylphenylamino)-9,9′-spirobifluorene (Spiro-TTB), and N,N′-di(naphtalene-1-yl)-N,N′-diphenylbenzidine (NPB). The influence of 2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6-TCNNQ p-dopant) concentration in BF-DPB on the operation voltage and efficiency of red and green phosphorescent OLEDs is studied; best results are achieved at 4 wt. % doping. Without any light extraction structure, BF-DPB based red (green) OLEDs achieve a luminous efficacy of 35 .1 lm/W (74 .0 lm/W) at 1000 cd/m{sup 2} and reach a very high brightness of 10 000 cd/m{sup 2} at a very low voltage of 3.2 V (3.1 V). We attribute this exceptionally low driving voltage to the high ionization potential of BF-DPB which enables more efficient hole injection from BF-DPB to the adjacent electron blocking layer. The high efficiency and low driving voltage lead to a significantly lower luminous efficacy roll-off compared to the other compounds and render BF-DPB an excellent HTL material for highly efficient OLEDs.

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

Science.gov (United States)

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

2013-05-01

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

High efficient white organic light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Seidel, Stefan; Krause, Ralf [Department of Materials Science VI, University of Erlangen-Nuremberg (Germany); Siemens AG, CT MM 1, Erlangen (Germany); Kozlowski, Fryderyk; Schmid, Guenter; Hunze, Arvid [Siemens AG, CT MM 1, Erlangen (Germany); Winnacker, Albrecht [Department of Materials Science VI, University of Erlangen-Nuremberg (Germany)

2007-07-01

Due to the rapid progress in the last years the performance of organic light emitting diodes (OLEDs) has reached a level where general lighting presents a most interesting application target. We demonstrate, how the color coordinates of the emission spectrum can be adjusted using a combinatorial evaporation tool to lie on the desired black body curve representing cold and warm white, respectively. The evaluation includes phosphorescent and fluorescent dye approaches to optimize lifetime and efficiency, simultaneously. Detailed results are presented with respect to variation of layer thicknesses and dopant concentrations of each layer within the OLED stack. The most promising approach contains phosphorescent red and green dyes combined with a fluorescent blue one as blue phosphorescent dopants are not yet stable enough to achieve long lifetimes.

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

Science.gov (United States)

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.

Using rare earth doped thiosilicate phosphors in white light emitting LEDs: Towards low colour temperature and high colour rendering

International Nuclear Information System (INIS)

Smet, P.F.; Korthout, K.; Haecke, J.E. van; Poelman, D.

2008-01-01

Rare earth doped thiosilicates are promising materials for use in phosphor converted light emitting diodes (pcLEDs). These phosphors (including the hosts Ca 2 SiS 4 , BaSi 2 S 5 and Ba 2 SiS 4 in combination with Ce 3+ and/or Eu 2+ doping) cover the entire visible part of the spectrum, as the emission colour can be changed from deep blue to red. The photoluminescence emission spectrum and the overlap of the excitation spectrum with the emission of pumping LEDs is evaluated. The trade-off between high colour rendering and high electrical-to-optical power efficiency is discussed by simulation with both blue and UV emitting LEDs. Finally, a phosphor combination with low colour temperature (3000 K) and high colour rendering (CRI = 93) is proposed

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

International Nuclear Information System (INIS)

Coenen, Michiel J.J.; Slaats, Thijs M.W.L.; Eggenhuisen, Tamara M.; Groen, Pim

2015-01-01

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

Epitaxial Sb-doped SnO{sub 2} and Sn-doped In{sub 2}O{sub 3} transparent conducting oxide contacts on GaN-based light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Tsai, Min-Ying [Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106 (United States); Bierwagen, Oliver, E-mail: bierwagen@pdi-berlin.de [Materials Department, University of California, Santa Barbara, CA 93106 (United States); Paul-Drude-Insitut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Speck, James S. [Materials Department, University of California, Santa Barbara, CA 93106 (United States)

2016-04-30

We demonstrate the growth of epitaxial (100)-oriented, rutile Sb-doped SnO{sub 2} (ATO) and (111)-oriented, cubic Sn-doped In{sub 2}O{sub 3} (ITO) transparent conducting oxide (TCO) contacts on top of an InGaN/GaN(0001) light emitting diode (LED) by plasma-assisted molecular beam epitaxy (PAMBE). Both oxides form rotational domains. The in-plane epitaxial alignment of the two ITO(111) rotational domains to the GaN(0001) was: GaN [21-10]|| ITO{sub Domain1}[‐ 211]|| ITO{sub Domain2}[‐ 1‐12]. A growth temperature as low as 600 °C was necessary to realize a low contact resistance between ATO and the top p-GaN layer of the LED but resulted in non-optimal resistivity (3.4 × 10{sup −} {sup 3} Ω cm) of the ATO. The current–voltage characteristics of a processed LED, however, were comparable to that of a reference LED with a standard electron-beam evaporated ITO top contact. At short wavelengths, the optical absorption of ATO was lower than that of ITO, which is beneficial even for blue LEDs. Higher PAMBE growth temperatures resulted in lower resistive ATO but higher contact resistance to the GaN, likely by the formation of an insulating Ga{sub 2}O{sub 3} interface layer. The ITO contact grown by PAMBE at 600 °C showed extremely low resistivity (10{sup −4} Ω cm) and high crystalline and morphological quality. These proof-of-principle results may lead to the development of epitaxial TCO contacts with low resistivity, well-defined interfaces to the p-GaN to help minimize contact losses, and enable further epitaxy on top of the TCO. - Highlights: • Plasma-assisted molecular beam epitaxy of SnO{sub 2}:Sb (ATO) and In{sub 2}O{sub 3}:Sn (ITO) contacts • Working light emitting diodes processed with the ATO contact on the top p-GaN layer • Low growth temperature ensures low contact resistance (limiting interface reaction). • ITO showed significantly better structural and transport properties than ATO. • ATO showed higher optical transmission at short

Luminescence and squeezing of a superconducting light-emitting diode

Science.gov (United States)

Hlobil, Patrik; Orth, Peter P.

2015-05-01

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

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

Science.gov (United States)

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.

Optical characterization of magnesium incorporation in p-GaN layers for core–shell nanorod light-emitting diodes

Science.gov (United States)

Gîrgel, I.; Šatka, A.; Priesol, J.; Coulon, P.-M.; Le Boulbar, E. D.; Batten, T.; Allsopp, D. W. E.; Shields, P. A.

2018-04-01

III-nitride nanostructures are of interest for a new generation of light-emitting diodes (LEDs). However, the characterization of doping incorporation in nanorod (NR) structures, which is essential for creating the p-n junction diodes, is extremely challenging. This is because the established electrical measurement techniques (such as capacitance–voltage or Hall-effect methods) require a simple sample geometry and reliable ohmic contacts, both of which are difficult to achieve in nanoscale devices. The need for homogenous, conformal n-type or p-type layers in core–shell nanostructures magnifies these challenges. Consequently, we demonstrate how a combination of non-contact methods (micro-photoluminescence, micro-Raman and cathodoluminescence), as well as electron-beam-induced-current, can be used to analyze the uniformity of magnesium incorporation in core–shell NRs and make a first estimate of doping levels by the evolution of band transitions, strain and current mapping. These techniques have been used to optimize the growth of core–shell nanostructures for electrical carrier injection, a significant milestone for their use in LEDs.

Organic light emitting diodes on ITO-free polymer anodes

Energy Technology Data Exchange (ETDEWEB)

Fehse, Karsten; Schwartz, Gregor; Walzer, Karsten; Leo, Karl [Institut fuer Angewandte Photophysik, TU Dresden, D-01062 Dresden (Germany)

2007-07-01

The high material cost of indium, being the main component of the commonly used indium-tin-oxide anodes (ITO) in organic light emitting diodes (OLEDs), is an obstacle for the production of efficient low-cost OLEDs. Therefore, new anode materials are needed for large scale OLED production. Recently, we demonstrated that the polymer PEDOT:PSS can substitute ITO as anode. Another highly conductive polymer is polyaniline (PANI) that provides 200 S/cm with a work function of 4.8 eV. In this study, we use PANI as anode for OLEDs (without ITO layer underneath the polymer) with electrically doped hole- and electron transport layers and intrinsic materials in between. Fluorescent blue (Spiro-DPVBi) as well as phosphorescent green (Ir(ppy){sub 3}) and red emitters (Ir(MDQ){sub 2}(acac)) were used for single colour and white OLEDs. Green single and double emission OLEDs achieve device efficiencies of 34 lm/W and 40.7 lm/W, respectively. The white OLED shows a power efficiency of 8.9 lm/W at 1000 cd/m{sup 2} with CIE coordinates of (0.42/0.39).

Origin of colour stability in blue/orange/blue stacked phosphorescent white organic light-emitting diodes

International Nuclear Information System (INIS)

Kim, Sung Hyun; Jang, Jyongsik; Yook, Kyoung Soo; Lee, Jun Yeob

2009-01-01

The origin of colour stability in phosphorescent white organic light-emitting diodes (PHWOLEDs) with a blue/orange/blue stacked emitting structure was studied by monitoring the change in a recombination zone. A balanced recombination zone shift between the blue and the orange light-emitting layers was found to be responsible for the colour stability in the blue/orange/blue stacked PHWOLEDs.

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

NARCIS (Netherlands)

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

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

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

KAUST Repository

Al-Saggaf, Abeer

2015-05-01

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

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

KAUST Repository

Al-Saggaf, Abeer

2015-01-01

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

Red organic light-emitting diodes based on wide band gap emitting material as the host utilizing two-step energy transfer

International Nuclear Information System (INIS)

Haq Khizarul; Shanpeng Liu; Khan, M A; Jiang, X Y; Zhang, Z L; Zhu, W Q

2008-01-01

We demonstrated efficient red organic light-emitting diodes based on a host emitting system of 9,10-di(2-naphthyl)anthracene (ADN) co-doped with 4-(dicyano-methylene)-2-t-butyle-6- (1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran (DCJTB) as a red dopant and 2,3,6,7- tetrahydro-1,1,7,7-tetramethyl-1H,5H,1 1H-10(2-benzothiazolyl)-quinolizine-[9,9a,1gh] coumarin (C545T) as an assistant dopant. The typical device structure was glass substrate/ITO/4,4',4''-tris(N-3-methylphenyl-N-phenylamino) triphenylamine(m-MTDATA)/N,N'-bis-(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB)/[ADN: DCJTB: C545T/Alq 3 /LiF/Al]. It was found that C545T dopant did not emit by itself but did assist the energy transfer from the host (ADN) to the red emitting dopant. The red OLEDs realized by this approach not only enhanced the emission color, but also significantly improved the EL efficiency. The EL efficiency reached 3.5 cd A −1 at a current density of 20 mA cm −2 , which is enhanced by three times compared with devices where the emissive layer is composed of the DCJTB doped ADN. The saturated red emission was obtained with CIE coordinates (x = 0.618, y = 0.373) at 621 nm, and the device driving voltage is decreased as much as 38%. We attribute these improvements to the assistant dopant (C545T), which leads to the more efficient energy transfer from ADN to DCJTB. These results indicate that the co-doped system is a promising method for obtaining high-efficiency red OLEDs

Yellow emitting Iridium (III) phenyl-benzothiazole complexes with different β-diketone ancillary ligands as dopants in white organic light-emitting diodes

Science.gov (United States)

Ivanov, P.; Petrova, P.; Tomova, R.

2018-03-01

We discuss the influence of the type of β-diketone ancillary ligand in Iridium (III) bis phenyl-benzothiazole complexes ((bt)2Ir(β-diketone)) on their photophysical and electroluminescent properties when they are used as dopants in white organic light-emitting diodes (WOLED). For this purpose, we investigated four novel yellow cyclometalated complexes: (bt)2Ir(dbm), (bt)2Ir(fmtdbm), (bt)2Ir(tta) and (bt)2Ir(bsm), where dbm = 1,3-diphenylpropane-1,3-dionate; fmtdbm = 1-(4-fluorophenyl)-3-(4-methoxyphenyl)propane-1,3-dionate; tta = 4,4,4-trifluoro-1-(thiophene-2-yl)butane-1,3-dionate; and bsm = 1-phenylicosane-1,3-dionate). To obtain white light by mixing emissions of two complementary colors (yellow emitted by the dopant and blue, by another emitter), we chose the following OLED structure: ITO/doped HTL/ElL/ETL/M, where ITO was a transparent anode of In2O3:SnO2; M, a metallic Al cathode; HTL, 4,4’-Bis(9H-carbazol-9-yl)biphenyl (CBP) involved in a poly(N-vinylcarbazole) (PVK) matrix; ElL, an electroluminescent layer of aluminum(III)bis(2-methyl-8-quninolinato)-4-phenylphenolate (BAlq); and ETL, an electron-transporting layer of zinc(II)bis(2-2-hydroxyphenyl)benzothiazole. We found that all complexes are suitable candidates for fabrication of WOLED. The best results were demonstrated by the device doped with 2 wt % of (bt)2Ir(bsm), which had twice as high luminescence (1100 cd/m2) and one-and-a-half as high current efficiency (5 cd/A) as the device doped with 1.25 wt % of the known (bt)2Ir(acac), with its 580 cd/m2 and 3.4 cd/A at approximately the same CIE (Commission Internationale de L’Eclairage) (x/y) coordinates of the warm white light emitted by the two devices.

Optimization of emission color and efficiency of organic light emitting diodes for lighting applications

Energy Technology Data Exchange (ETDEWEB)

Seidel, Stefan; Krause, Ralf [Department of Materials Science VI, University of Erlangen-Nuernberg (Germany); Siemens AG, CT MM 1, Erlangen (Germany); Kozlowski, Fryderyk; Schmid, Guenter; Hunze, Arvid [Siemens AG, CT MM 1, Erlangen (Germany); Winnacker, Albrecht [Department of Materials Science VI, University of Erlangen-Nuernberg (Germany)

2008-07-01

In recent years the performance of organic light emitting diodes (OLEDs) has reached a level where OLED lighting presents an interesting application target. Research activities therefore focus amongst other things on the development of high efficient and stable white light emitting devices. We demonstrate how the color coordinates can be adjusted to achieve a warm white emission spectrum, whereas the OLED stack contains phosphorescent red and green dyes combined with a fluorescent blue one. Detailed results are presented with respect to a variation of layer thicknesses and dopant concentrations of the emission layers. Furthermore the influence of various dye molecules and hence different energy level alignments between host and dopants on color and efficiency will be discussed.

A hole modulator for InGaN/GaN light-emitting diodes

Science.gov (United States)

Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

2015-02-01

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ˜332 meV to ˜294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.

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

DEFF Research Database (Denmark)

Thorseth, Anders

2012-01-01

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

Effect of inserting of thin Rubrene layer on performance of Organic Light-Emitting Diodes based on Zn(BTz)2

Science.gov (United States)

Tomova, R. L.; Petrova, P. K.; Stoycheva-Topalova, R. T.

2010-11-01

Organic light-emitting diodes (OLEDs) with improved performances are fabricated using a thin (1 nm) yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene (Rubrene) inserted at different position in green emitting electroluminescent (EL) layer of bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTz)2) in configuration: ITO/PVK:TPD/ Zn(BTz)2 (x nm)/ Rubrene (1 nm)/ Zn(BTz)2 (75-x nm)/Al, where PVK:TPD is a hole transporting layer of N, N'-bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD) incorporated in poly(N-vinylcarbazole) (PVK) matrix and Al is a cathode. EL spectra predominantly influenced by Rubrene emission when the doping layer is close to (PVK:TPD)/ Zn(BTz)2 (x→ 0-15 nm) and to Zn(BTz)2/Al (x→ 70-75 nm) interfaces and shift toward emission of Zn(BTz)2 increasing the distance of Rubrene from both interfaces (x→35 nm). The same dependence of the EL efficiency on the position of the doping Rubrene layer in the OLED structure was found.

Printable candlelight-style organic light-emitting diode

Science.gov (United States)

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

2017-06-01

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

Color optimization of conjugated-polymer/InGaN hybrid white light emitting diodes by incomplete energy transfer

International Nuclear Information System (INIS)

Chang, Chi-Jung; Lai, Chun-Feng; Madhusudhana Reddy, P.; Chen, Yung-Lin; Chiou, Wei-Yung; Chang, Shinn-Jen

2015-01-01

By using the wavelength conversion method, white light emitting diodes (WLEDs) were produced by applying mixtures of polysiloxane and fluorescent polymers on InGaN based light emitting diodes. UV curable organic–inorganic hybrid materials with high refractive index (1.561), compromised optical, thermal and mechanical properties was used as encapsulants. Red light emitting fluorescent FABD polymer (with 9,9-dioctylfluorene (F), anthracene (A) and 2,1,3-benzothiadiazole (B), and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (D) repeating units) and green light emitting fluorescent FAB polymer were used as wavelength converters. The encapsulant/fluorescent polymer mixture and InGaN produce the white light by incomplete energy transfer mechanism. WLEDs with high color rendering index (CRI, about 93), and tunable correlated color temperature (CCT) properties can be produced by controlling the composition and chemical structures of encapsulating polymer and fluorescent polymer in hybrid materials, offering cool-white and neutral-white LEDs. - Highlights: • Highly efficient white light-emitting diodes (WLEDs) were produced. • Conjugated-polymer/InGaN hybrid WLEDs by incomplete energy transfer mechanism. • WLEDs with high color-rendering index and tunable correlated color temperature. • Polysiloxane encapsulant with superior optical, mechanical and thermal properties

InGaN/GaN disk-in-nanowire white light emitting diodes on (001) silicon

KAUST Repository

Guo, Wei; Banerjee, Animesh; Bhattacharya, Pallab K.; Ooi, Boon S.

2011-01-01

High density (? 1011 cm-2) GaN nanowires and InGaN/GaN disk-in-nanowire heterostructures have been grown on (001) silicon substrates by plasma-assisted molecular beam epitaxy. The nanowires exhibit excellent uniformity in length and diameter and a broad emission is obtained by incorporating InGaN disks of varying composition along the length of the nanowires. Monolithic lighting emitting diodes were fabricated with appropriate n- and p-doping of contact layers. White light emission with chromaticity coordinates of x=0.29 and y=0.37 and a correlated color temperature of 5500-6500 K at an injection current of 50 A/ cm2 is measured. The measured external quantum efficiency of the devices do not exhibit any rollover (droop) up to an injection current density of 400 A/ cm2. © 2011 American Institute of Physics.

Investigation of phosphorescent blue organic light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Chiu, Chien-Shu [Department of Electrical Engineering and Information Technology, Technical University of Braunschweig (Germany); Siemens AG, CT MM 1, Erlangen (Germany); Krause, Ralf [Department of Materials Science VI, University of Erlangen-Nuernberg (Germany); Siemens AG, CT MM 1, Erlangen (Germany); Kozlowski, Fryderyk; Hunze, Arvid [Siemens AG, CT MM 1, Erlangen (Germany); Kowalsky, Wolfgang [Department of Electrical Engineering and Information Technology, Technical University of Braunschweig (Germany)

2008-07-01

Recently, rapid development of phosphorescent materials has significantly improved the efficiency of organic light emitting diodes (OLEDs). By using efficient phosphorescent emitter materials white OLEDs with high power efficiency values could be demonstrated. But especially blue phosphorescent devices, due to stability issues, need to be further investigated und optimized. In this work, blue OLED devices based on the phosphorescent emitter FIrpic were investigated. Single-carrier hole-only as well as electron-only devices were fabricated and characterized to study the impact of charge carriers on device performance.

Aggregation in organic light emitting diodes

Science.gov (United States)

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.

Rosin-enabled ultraclean and damage-free transfer of graphene for large-area flexible organic light-emitting diodes

Science.gov (United States)

Zhang, Zhikun; Du, Jinhong; Zhang, Dingdong; Sun, Hengda; Yin, Lichang; Ma, Laipeng; Chen, Jiangshan; Ma, Dongge; Cheng, Hui-Ming; Ren, Wencai

2017-02-01

The large polymer particle residue generated during the transfer process of graphene grown by chemical vapour deposition is a critical issue that limits its use in large-area thin-film devices such as organic light-emitting diodes. The available lighting areas of the graphene-based organic light-emitting diodes reported so far are usually transfer method using rosin as a support layer, whose weak interaction with graphene, good solubility and sufficient strength enable ultraclean and damage-free transfer. The transferred graphene has a low surface roughness with an occasional maximum residue height of about 15 nm and a uniform sheet resistance of 560 Ω per square with about 1% deviation over a large area. Such clean, damage-free graphene has produced the four-inch monolithic flexible graphene-based organic light-emitting diode with a high brightness of about 10,000 cd m-2 that can already satisfy the requirements for lighting sources and displays.

Red emitting phosphors of Eu3+ doped Na2Ln2Ti3O10 (Ln = Gd, Y) for white light emitting diodes

International Nuclear Information System (INIS)

Zhang, Niumiao; Guo, Chongfeng; Yin, Luqiao; Zhang, Jianhua; Wu, Mingmei

2015-01-01

Highlights: • Layered red phosphors Na 2 Ln 2 Ti 3 O 10 (Ln = Gd, Y):Eu 3+ were prepared. • The synthesis parameters of phosphors were optimized. • PL and thermal stability of the samples were investigated. • LED devices were also fabricated including the present red phosphor. - Abstract: A series of Eu 3+ doped Na 2 Ln 2 Ti 3 O 10 (Ln = Gd, Y) red-emitting phosphors for application in ultraviolet based light emitting diodes (LEDs) were successfully synthesized by a modified sol–gel method. Their structure and luminescent properties were characterized by powder X-ray diffraction (XRD), photoluminescence excitation (PLE) and emission (PL) spectra and absorption spectra, according to these results the optimal compositions and synthesis parameters were determined. In addition, the thermal stabilities of the phosphors were investigated according to the temperature-dependent PL spectra. The red and white-LEDs (W-LEDs) comprising the Na 2 Ln 2 Ti 3 O 10 :Eu 3+ (Ln = Gd, Y) red emitting phosphors were fabricated with a near-ultraviolet (n-UV) chip. In comparison with Na 2 Y 1.4 Eu 0.6 Ti 3 O 10 , the Na 2 Gd 0.6 Eu 1.4 Ti 3 O 10 phosphor offers higher brightness, quantum efficiency, and excellent thermal stability. W-LEDs comprising Na 2 Gd 0.6 Eu 1.4 Ti 3 O 10 showed bright white emission with a color rendering index (Ra) of 82, a color temperature of 2151 K, and Commission Internationale de I’Eclairage (CIE) color coordinates of (0.34, 0.37). The phosphor Na 2 Gd 0.6 Eu 1.4 Ti 3 O 10 is more suitable candidate for application in LEDs

GaN-Based Multiple-Quantum-Well Light-Emitting Diodes Employing Nanotechnology for Photon Management

KAUST Repository

Hsiao, Yu Hsuan; Tsai, Meng Lin; He, Jr-Hau

2015-01-01

Nanostructures have been proved to be an efficient way of modifying/improving the performance of GaN-based light-emitting diodes (LEDs). The achievements in photon management include strain relaxation, light extraction enhancement, radiation pattern

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

NARCIS (Netherlands)

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

2011-01-01

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

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

NARCIS (Netherlands)

Kuik, Martijn; Nicolai, Herman T.; Lenes, Martijn; Wetzelaer, Gert-Jan A. H.; Lu, Mingtao; Blom, Paul W. M.

2011-01-01

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

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

NARCIS (Netherlands)

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

2011-01-01

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

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

International Nuclear Information System (INIS)

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

1998-01-01

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

The efficiency challenge of nitride light-emitting diodes for lighting

KAUST Repository

Weisbuch, Claude

2015-03-13

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

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

Science.gov (United States)

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 (PAK. MAL PDT using red light-emitting diode light is an appropriate treatment alternative for multiple AK lesions.

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

Energy Technology Data Exchange (ETDEWEB)

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

1999-06-01

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

Three-dimensional modeling of charge transport, injection and recombination in organic light-emitting diodes

NARCIS (Netherlands)

Holst, van der J.J.M.

2010-01-01

Organic light-emitting diodes (OLEDs) are ideally suited for lighting and display applications. Commercial OLED displays as well as OLED white-light sources are presently being introduced to the market. Essential electronic processes in OLEDs are the injection of electrons and holes into an organic

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

International Nuclear Information System (INIS)

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

2012-01-01

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

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

DEFF Research Database (Denmark)

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

1999-01-01

Recently developed blue light emitting diodes (LEDs) for the optical stimulation of quartz for use in routine optically stimulated luminescence (OSL) dating and retrospective dosimetry have been tested. For similar power densities, it was found that the higher energy light provided by the blue LE......, preliminary results from ramping the blue light power output with time are demonstrated. It is shown that this technique enables the separation of OSL components with differing stimulation rates.......Recently developed blue light emitting diodes (LEDs) for the optical stimulation of quartz for use in routine optically stimulated luminescence (OSL) dating and retrospective dosimetry have been tested. For similar power densities, it was found that the higher energy light provided by the blue LEDs...... (470 nm) gives order of magnitude greater rate of stimulation in quartz than that from conventional blue-green light filtered from a halogen lamp. A practical blue LED OSL configuration is described. From comparisons of OSL decay curves produced by green and blue light sources, and by examination...

Synthesis and Electroluminescent Property of New Orange Iridium Compounds for Flexible White Organic Light Emitting Diodes.

Science.gov (United States)

Lee, Ho Won; Jeong, Hyunjin; Kim, Young Kwan; Ha, Yunkyoung

2015-10-01

Recently, white organic light-emitting diodes (OLEDs) have aroused considerable attention because they have the potential of next-generation flexible displays and white illuminated applications. White OLED applications are particularly heading to the industry but they have still many problems both materials and manufacturing. Therefore, we proposed that the new iridium compounds of orange emitters could be demonstrated and also applied to flexible white OLEDs for verification of potential. First, we demonstrated the chemical properties of new orange iridium compounds. Secondly, conventional two kinds of white phosphorescent OLEDs were fabricated by following devices; indium-tin oxide coated glass substrate/4,4'-bis[N-(napthyl)-N-phenylamino]biphenyl/N,N'-dicarbazolyl-3,5-benzene doped with blue and new iridium compounds for orange emitting 8 wt%/1,3,5-tris[N-phenylbenzimidazole-2-yl]benzene/lithium quinolate/aluminum. In addition, we fabricated white OLEDs using these emitters to verify the potential on flexible substrate. Therefore, this work could be proposed that white light applications can be applied and could be extended to additional research on flexible applications.

Determination of illuminants representing typical white light emitting diodes sources

DEFF Research Database (Denmark)

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

2017-01-01

is to develop LED-based illuminants that describe typical white LED products based on their Spectral Power Distributions (SPDs). Some of these new illuminants will be recommended in the update of the CIE publication 15 on colorimetry with the other typical illuminants, and among them, some could be used......Solid-state lighting (SSL) products are already in use by consumers and are rapidly gaining the lighting market. Especially, white Light Emitting Diode (LED) sources are replacing banned incandescent lamps and other lighting technologies in most general lighting applications. The aim of this work...... to complement the CIE standard illuminant A for calibration use in photometry....

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

Science.gov (United States)

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

2018-02-01

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

Nonpolar a-plane light-emitting diode with an in-situ SiNx interlayer on r-plane sapphire grown by metal-organic chemical vapour deposition

International Nuclear Information System (INIS)

Fang Hao; Long Hao; Sang Li-Wen; Qi Sheng-Li; Xiong Chang; Yu Tong-Jun; Yang Zhi-Jian; Zhang Guo-Yi

2011-01-01

We report on the growth and fabrication of nonpolar a-plane light emitting diodes with an in-situ SiN x interlayer grown between the undoped a-plane GaN buffer and Si-doped GaN layer. X-ray diffraction shows that the crystalline quality of the GaN buffer layer is greatly improved with the introduction of the SiN x interlayer. The electrical properties are also improved. For example, electron mobility and sheet resistance are reduced from high resistance to 31.6 cm 2 /(V·s) and 460 Ω/□ respectively. Owing to the significant effect of the SiN x interlayer, a-plane LEDs are realized. Electroluminescence of a nonpolar a-plane light-emitting diode with a wavelength of 488nm is demonstrated. The emission peak remains constant when the injection current increases to over 20 mA. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Extraction of surface plasmons in organic light-emitting diodes via high-index coupling.

Science.gov (United States)

Scholz, Bert J; Frischeisen, Jörg; Jaeger, Arndt; Setz, Daniel S; Reusch, Thilo C G; Brütting, Wolfgang

2012-03-12

The efficiency of organic light-emitting diodes (OLEDs) is still limited by poor light outcoupling. In particular, the excitation of surface plasmon polaritons (SPPs) at metal-organic interfaces represents a major loss channel. By combining optical simulations and experiments on simplified luminescent thin-film structures we elaborate the conditions for the extraction of SPPs via coupling to high-index media. As a proof-of-concept, we demonstrate the possibility to extract light from wave-guided modes and surface plasmons in a top-emitting white OLED by a high-index prism.

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

International Nuclear Information System (INIS)

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

2013-01-01

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

Pyridine substituted spirofluorene derivative as an electron transport material for high efficiency in blue organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Jeon, Soon Ok; Yook, Kyoung Soo; Lee, Jun Yeob, E-mail: leej17@dankook.ac.k

2010-11-01

The quantum efficiency of blue fluorescent organic light-emitting diodes was enhanced by 20% using a pyridine substituted spirofluorene-benzofluorene derivative as an electron transport material. 2',7'-Di(pyridin-3-yl)spiro[benzofluorene-7,9'-fluorene] (SPBP) was synthesized and it was used as the electron transport material to block the hole leakage from the emitting layer. The improvement of the quantum efficiency and power efficiency of the blue fluorescent organic light-emitting diodes using the SPBP was investigated.

Characterization of 12CaO x 7Al2O3 doped indium tin oxide films for transparent cathode in top-emission organic light-emitting diodes.

Science.gov (United States)

Jung, Chul Ho; Hwang, In Rok; Park, Bae Ho; Yoon, Dae Ho

2013-11-01

12CaO x 7Al2O3, insulator (C12A7) doped indium tin oxide (ITO) (ITO:C12A7) films were fabricated using a radio frequency magnetron co-sputtering system with ITO and C12A7 targets. The qualitative and quantitative properties of ITO:C12A7 films, as a function of C12A7 concentration, were examined via X-ray photoemission spectroscopy and synchrotron X-ray scattering as well as by conducting atomic force microscopy. The work function of ITO:C12A7 (1.3%) films of approximately 2.8 eV obtained by high resolution photoemission spectroscopy measurements make them a reasonable cathode for top-emission organic light-emitting diodes.

The application of the light emitting diode in MR room lighting

International Nuclear Information System (INIS)

Cao Jun; Wang Chunhong

2009-01-01

Objective: To investigate the application of white light emitting diode (LED) in magnetic resonance room, in order to resolve the damageable problem of incandescent lights under the high magnetic field. Methods: The white LEDs and the incandescent lights were installed in MR room, the number of damaged lights was compared after 300 hours. Chi-square test was used for the statistical analysis. And the illuminance and 50 000 hours electricity consumption between LED and incandescent lights were calculated. Results: The number of damaged LED and incandescent lights was 2 and 32, respectively and there was a significant difference (χ 2 =48.813, P=0.000). The illuminance of the LED and incandescent lights was 155 lx and 100 lx at the 0.75 m horizontal level and the 50 000 hour's electricity consumption was 200 kW and 5000 kW, respectively. Conclusion: It is feasible and a great advantage to use the white LEDs in MR room lighting. (authors)

Effect of inserting of thin Rubrene layer on performance of Organic Light-Emitting Diodes based on Zn(BTz){sub 2}

Energy Technology Data Exchange (ETDEWEB)

Tomova, R L; Petrova, P K; Stoycheva-Topalova, R T, E-mail: reni@clf.bas.b [Institute of optical materials and technologies ' Acad. J. Malinowski' , Bulgarian Academy of Sciences, ' Acad. G. Bonchev' str. bl. 109, 1113 Sofia (Bulgaria)

2010-11-01

Organic light-emitting diodes (OLEDs) with improved performances are fabricated using a thin (1 nm) yellow-emitting layer of 5,6,11,12-tetraphenylnaphthacene (Rubrene) inserted at different position in green emitting electroluminescent (EL) layer of bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTz){sub 2}) in configuration: ITO/PVK:TPD/ Zn(BTz){sub 2} (x nm)/ Rubrene (1 nm)/ Zn(BTz){sub 2} (75-x nm)/Al, where PVK:TPD is a hole transporting layer of N, N'-bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD) incorporated in poly(N-vinylcarbazole) (PVK) matrix and Al is a cathode. EL spectra predominantly influenced by Rubrene emission when the doping layer is close to (PVK:TPD)/ Zn(BTz){sub 2} (x{yields} 0-15 nm) and to Zn(BTz){sub 2}/Al (x{yields} 70-75 nm) interfaces and shift toward emission of Zn(BTz){sub 2} increasing the distance of Rubrene from both interfaces (x{yields}35 nm). The same dependence of the EL efficiency on the position of the doping Rubrene layer in the OLED structure was found.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

KAUST Repository

Yan, Long

2018-05-03

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

KAUST Repository

Yan, Long; Zhang, Yuantao; Han, Xu; Deng, Gaoqiang; Li, Pengchong; Yu, Ye; Chen, Liang; Li, Xiaohang; Song, Junfeng

2018-01-01

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.

Micro-light-emitting diodes with III–nitride tunnel junction contacts grown by metalorganic chemical vapor deposition

KAUST Repository

Hwang, David

2017-12-13

Micro-light-emitting diodes (µLEDs) with tunnel junction (TJ) contacts were grown entirely by metalorganic chemical vapor deposition. A LED structure was grown, treated with UV ozone and hydrofluoric acid, and reloaded into the reactor for TJ regrowth. The silicon doping level of the n++-GaN TJ was varied to examine its effect on voltage. µLEDs from 2.5 × 10−5 to 0.01 mm2 in area were processed, and the voltage penalty of the TJ for the smallest µLED at 20 A/cm2 was 0.60 V relative to that for a standard LED with indium tin oxide. The peak external quantum efficiency of the TJ LED was 34%.

Micro-light-emitting diodes with III–nitride tunnel junction contacts grown by metalorganic chemical vapor deposition

KAUST Repository

Hwang, David; Mughal, Asad J.; Wong, Matthew S.; Alhassan, Abdullah I.; Nakamura, Shuji; DenBaars, Steven P.

2017-01-01

Micro-light-emitting diodes (µLEDs) with tunnel junction (TJ) contacts were grown entirely by metalorganic chemical vapor deposition. A LED structure was grown, treated with UV ozone and hydrofluoric acid, and reloaded into the reactor for TJ regrowth. The silicon doping level of the n++-GaN TJ was varied to examine its effect on voltage. µLEDs from 2.5 × 10−5 to 0.01 mm2 in area were processed, and the voltage penalty of the TJ for the smallest µLED at 20 A/cm2 was 0.60 V relative to that for a standard LED with indium tin oxide. The peak external quantum efficiency of the TJ LED was 34%.

Micro-light-emitting-diode array with dual functions of visible light communication and illumination

International Nuclear Information System (INIS)

Huang Yong; Guo Zhi-You; Sun Hui-Qing; Huang Hong-Yong

2017-01-01

We demonstrate high-speed blue 4 × 4 micro-light-emitting-diode (LED) arrays with 14 light-emitting units (two light-emitting units are used as the positive and negative electrodes for power supply, respectively) comprising multiple quantum wells formed of GaN epitaxial layers grown on a sapphire substrate, and experimentally test their applicability for being used as VLC transmitters and illuminations. The micro-LED arrays provide a maximum −3-dB frequency response of 60.5 MHz with a smooth frequency curve from 1 MHz to 500 MHz for an optical output power of 165 mW at an injection current of 30 mA, which, to our knowledge, is the highest response frequency ever reported for blue GaN-based LEDs operating at that level of optical output power. The relationship between the frequency and size of the device single pixel diameter reveals the relationship between the response frequency and diffusion capacitance of the device. (paper)

Topology optimisation of passive coolers for light-emitting diode lamps

DEFF Research Database (Denmark)

Alexandersen, Joe

2015-01-01

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

Improvement of white organic light emitting diode performances by an annealing process

International Nuclear Information System (INIS)

Sepeai, Suhaila; Salleh, Muhamad Mat; Yahaya, Muhammad; Umar, Akrajas Ali

2009-01-01

White organic light emitting diode (OLED) devices with the structure ITO/PHF:rubrene/Al, in which PHF (poly(9,9-di-n-hexylfluorenyl-2,7-diyl)) is used as blue light emitting host and rubrene (5,6,11,12-tetraphenylnapthacene) as an orange dye dopant, have been fabricated. Indium tin oxide (ITO) coated-glass and aluminium were used as anode and cathode, respectively. The devices were fabricated with various rubrene-dopant to obtain a white light emission. The OLED device that composed of several concentrations of rubrene-doped PHF film was prepared in this study. It was found that the concentration of rubrene in the PHF-rubrene thin film matrix plays a key role in producing the white color emission. In a typical result, the device composed of 0.06 wt.% rubrene-dopant produced the white light emission with the Commission Internationale de L'Eclairage (CIE) coordinate of (0.30,0.33). The turn-on voltage and the brightness were found to be as low as 14.0 V and as high as 6540 cd/m 2 , respectively. The annealing technique at relatively low temperature (50 o C, 100 o C, and 150 o C) was then used to optimize the performance of the device. In a typical result, the turn-on voltage of the device could be successfully reduced and the brightness could be increased using the annealing technique. At an optimum condition, for example, annealed at 150 o C, the turn-on voltage as low as 8.0 V and the brightness as high as 9040 cd/m 2 were obtained. The mechanism for the improvement of the device performance upon annealing will be discussed.

Demonstration Assessment of Light-Emitting Diode (LED) Post-Top Lighting at Central Park in New York City

Energy Technology Data Exchange (ETDEWEB)

Myer, Michael; Goettel, Russell T.; Kinzey, Bruce R.

2012-09-30

A review of five post-top light-emitting diode (LED) pedestrian luminaires installed in New York City's Central Park for possible replacement to the existing metal halide post-top luminaire. This report reviews the energy savings potential and lighting delivered by the LED post-top luminaires.

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

NARCIS (Netherlands)

Monat, C.; Alloing, B.; Zinoni, C.; Li, L.; Fiore, A.

2006-01-01

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-temp. electroluminescence spectra evidence discrete narrow lines around 1300 nm (line width ~ 75 micro

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

KAUST Repository

Prabaswara, Aditya

2017-05-08

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

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

KAUST Repository

Prabaswara, Aditya; Ng, Tien Khee; Zhao, Chao; Janjua, Bilal; Alyamani, Ahmed; El-desouki, Munir; Ooi, Boon S.

2017-01-01

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

Highly Conductive PEDOT:PSS Films with 1,3-Dimethyl-2-Imidazolidinone as Transparent Electrodes for Organic Light-Emitting Diodes.

Science.gov (United States)

Kim, Jin Hee; Joo, Chul Woong; Lee, Jonghee; Seo, Yoon Kyung; Han, Joo Won; Oh, Ji Yoon; Kim, Jong Su; Yu, Seunggun; Lee, Jae Hyun; Lee, Jeong-Ik; Yun, Changhun; Choi, Bum Ho; Kim, Yong Hyun

2016-09-01

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PSS) films as transparent electrodes for organic light-emitting diodes (OLEDs) are doped with a new solvent 1,3-dimethyl-2-imidazolidinone (DMI) and are optimized using solvent post-treatment. The DMI doped PSS films show significantly enhanced conductivities up to 812.1 S cm(-1) . The sheet resistance of the PSS films doped with DMI is further reduced by various solvent post-treatment. The effect of solvent post-treatment on DMI doped PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PSS films with the new solvent of DMI can be a promising transparent electrode for low-cost, efficient ITO-free white OLEDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Directory of Open Access Journals (Sweden)

Fengbing Wu

2012-01-01

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

Prediction and design of efficient exciplex emitters for high-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes.

Science.gov (United States)

Liu, Xiao-Ke; Chen, Zhan; Zheng, Cai-Jun; Liu, Chuan-Lin; Lee, Chun-Sing; Li, Fan; Ou, Xue-Mei; Zhang, Xiao-Hong

2015-04-08

High-efficiency, thermally activated delayed-fluorescence organic light-emitting diodes based on exciplex emitters are demonstrated. The best device, based on a TAPC:DPTPCz emitter, shows a high external quantum efficiency of 15.4%. Strategies for predicting and designing efficient exciplex emitters are also provided. This approach allow prediction and design of efficient exciplex emitters for achieving high-efficiency organic light-emitting diodes, for future use in displays and lighting applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Science.gov (United States)

Fina, Michael Dane

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

Doping-free white organic light-emitting diodes without blue molecular emitter: An unexplored approach to achieve high performance via exciplex emission

Science.gov (United States)

Luo, Dongxiang; Xiao, Ye; Hao, Mingming; Zhao, Yu; Yang, Yibin; Gao, Yuan; Liu, Baiquan

2017-02-01

Doping-free white organic light-emitting diodes (DF-WOLEDs) are promising for the low-cost commercialization because of their simplified device structures. However, DF-WOLEDs reported thus far in the literature are based on the use of blue single molecular emitters, whose processing can represent a crucial point in device manufacture. Herein, DF-WOLEDs without the blue single molecular emitter have been demonstrated by managing a blue exciplex system. For the single-molecular-emitter (orange or yellow emitter) DF-WOLEDs, (i) a color rendering index (CRI) of 81 at 1000 cd/m2 can be obtained, which is one of the highest for the single-molecular-emitter WOLEDs, or (ii) a high efficiency of 35.4 lm/W can be yielded. For the dual-molecular-emitter (yellow/red emitters) DF-WOLED, a high CRI of 85 and low correlated color temperature of 2376 K at 1000 cd/m2 have been simultaneously achieved, which has not been reported by previous DF-WOLEDs. Such presented findings may unlock an alternative avenue to the simplified but high-performance WOLEDs.

Interference phenomenon determines the color in an organic light emitting diode

Science.gov (United States)

Granlund, Thomas; Pettersson, Leif A. A.; Anderson, Mats R.; Inganäs, Olle

1997-06-01

We report on electroluminescence from two-layer organic diodes made of poly(3-methyl-4-octylthiophene) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,2,4-oxadiazole films between electrodes of indium tin oxide and Ca/Al. The diodes emitted light in the green-blue range; the electroluminescence spectra varied between diodes with different thicknesses of the polymer and molecular layers. The optical phenomena were simulated with a model accounting for interference effects; simulated results showed that the electroluminescence from the organic diode can be due neither to luminescence of the polymer nor of the molecular layer. These model simulations, together with electrochemical measurements, can be interpreted as evidence for an indirect optical transition at the polymer/molecule interface that only occurs in a strong electric field. We label this transition an electroplex.

A hole modulator for InGaN/GaN light-emitting diodes

International Nuclear Information System (INIS)

Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

2015-01-01

The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm 2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs

Recycling of Gallium from End-of-Life Light Emitting Diodes

Directory of Open Access Journals (Sweden)

Nagy S.

2017-06-01

Full Text Available Nowadays Light Emitting Diodes (LEDs are widely utilized. They are applied as backlighting in Liquid Crystal Displays (LCD and TV sets or as lighting equipments in homes, cars, instruments and street-lightning. End of life equipments are containing more and more LEDs. The recovery of valuable materials – such as Ga, Au, Cu etc. – from the LEDs is essential for the creating the circular economy. First task is the development of a proper recycling technology. Most of the researchers propose fully chemical or thermal-chemical pathway for the recycling of LEDs.

Top-Emitting White Organic Light-Emitting Diodes Based on Cu as Both Anode and Cathode

International Nuclear Information System (INIS)

Mu Ye; Zhang Zhen-Song; Wang Hong-Bo; Qu Da-Long; Wu Yu-Kun; Yan Ping-Rui; Li Chuan-Nan; Zhao Yi

2015-01-01

It is still challenging to obtain broadband emission covering visible light spectrum as much as possible with negligible angular dependence. In this work, we demonstrate a low driving voltage top-emitting white organic light-emitting diode (TEWOLED) based on complementary blue and yellow phosphor emitters with negligible angular dependence. The bottom copper anode with medium reflectance, which is compatible with the standard complementary metal oxide semiconductor (CMOS) technology below 0.13 μm, and the semitransparent multilayer Cs2CO3/Al/Cu cathode as a top electrode, are introduced to realize high-performance TEWOLED. Our TEWOLED achieves high efficiencies of 15.4 cd/A and 12.1 lm/W at a practical brightness of 1000 cd/m 2 at low voltage of 4 V. (paper)

Recent advances in light outcoupling from white organic light-emitting diodes

Science.gov (United States)

Gather, Malte C.; Reineke, Sebastian

2015-01-01

Organic light-emitting diodes (OLEDs) have been successfully introduced to the smartphone display market and have geared up to become contenders for applications in general illumination where they promise to combine efficient generation of white light with excellent color quality, glare-free illumination, and highly attractive designs. Device efficiency is the key requirement for such white OLEDs, not only from a sustainability perspective, but also because at the high brightness required for general illumination, losses lead to heating and may, thus, cause rapid device degradation. The efficiency of white OLEDs increased tremendously over the past two decades, and internal charge-to-photon conversion can now be achieved at ˜100% yield. However, the extraction of photons remains rather inefficient (typically physics of outcoupling in white OLEDs and review recent progress toward making light extraction more efficient. We describe how structures that scatter, refract, or diffract light can be attached to the outside of white OLEDs (external outcoupling) or can be integrated close to the active layers of the device (internal outcoupling). Moreover, the prospects of using top-emitting metal-metal microcavity designs for white OLEDs and of tuning the average orientation of the emissive molecules within the OLED are discussed.

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

Science.gov (United States)

Sharma, Pratibha; Kwok, Harry

2006-08-01

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

Highly transparent and conductive double-layer oxide thin films as anodes for organic light-emitting diodes

International Nuclear Information System (INIS)

Yang Yu; Wang Lian; Yan He; Jin Shu; Marks, Tobin J.; Li Shuyou

2006-01-01

Double-layer transparent conducting oxide thin film structures containing In-doped CdO (CIO) and Sn-doped In 2 O 3 (ITO) layers were grown on glass by metal-organic chemical vapor deposition and ion-assisted deposition (IAD), respectively, and used as anodes for polymer light-emitting diodes (PLEDs). These films have a very low overall In content of 16 at. %. For 180-nm-thick CIO/ITO films, the sheet resistance is 5.6 Ω/□, and the average optical transmittance is 87.1% in the 400-700 nm region. The overall figure of merit (Φ=T 10 /R sheet ) of the double-layer CIO/ITO films is significantly greater than that of single-layer CIO, IAD-ITO, and commercial ITO films. CIO/ITO-based PLEDs exhibit comparable or superior device performance versus ITO-based control devices. CIO/ITO materials have a much lower sheet resistance than ITO, rendering them promising low In content electrode materials for large-area optoelectronic devices

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

International Nuclear Information System (INIS)

Gassmann, Andrea; Yampolskii, Sergey V.; Klein, Andreas; Albe, Karsten; Vilbrandt, Nicole; Pekkola, Oili; Genenko, Yuri A.; Rehahn, Matthias; Seggern, Heinz von

2015-01-01

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

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

Science.gov (United States)

Jackson, David L.; And Others

1985-01-01

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

An anode with aluminum doped on zinc oxide thin films for organic light emitting devices

International Nuclear Information System (INIS)

Xu Denghui; Deng Zhenbo; Xu Ying; Xiao Jing; Liang Chunjun; Pei Zhiliang; Sun Chao

2005-01-01

Doped zinc oxides are attractive alternative materials as transparent conducting electrode because they are nontoxic and inexpensive compared with indium tin oxide (ITO). Transparent conducting aluminum-doped zinc oxide (AZO) thin films have been deposited on glass substrates by DC reactive magnetron sputtering method. Films were deposited at a substrate temperature of 150-bar o C in 0.03 Pa of oxygen pressure. The electrical and optical properties of the film with the Al-doping amount of 2 wt% in the target were investigated. For the 300-nm thick AZO film deposited using a ZnO target with an Al content of 2 wt%, the lowest electrical resistivity was 4x10 -4 Ωcm and the average transmission in the visible range 400-700 nm was more than 90%. The AZO film was used as an anode contact to fabricate organic light-emitting diodes. The device performance was measured and the current efficiency of 2.9 cd/A was measured at a current density of 100 mA/cm 2

Metasurface integrated high energy efficient and high linearly polarized InGaN/GaN light emitting diode.

Science.gov (United States)

Wang, Miao; Xu, Fuyang; Lin, Yu; Cao, Bing; Chen, Linghua; Wang, Chinhua; Wang, Jianfeng; Xu, Ke

2017-07-06

We proposed and demonstrated an integrated high energy efficient and high linearly polarized InGaN/GaN green LED grown on (0001) oriented sapphire with combined metasurface polarizing converter and polarizer system. It is different from those conventional polarized light emissions generated with plasmonic metallic grating in which at least 50% high energy loss occurs inherently due to high reflection of the transverse electric (TE) component of an electric field. A reflecting metasurface, with a two dimensional elliptic metal cylinder array (EMCA) that functions as a half-wave plate, was integrated at the bottom of a LED such that the back-reflected TE component, that is otherwise lost by a dielectric/metal bi-layered wire grids (DMBiWG) polarizer on the top emitting surface of the LED, can be converted to desired transverse magnetic (TM) polarized emission after reflecting from the metasurface. This significantly enhances the polarized light emission efficiency. Experimental results show that extraction efficiency of the polarized emission can be increased by 40% on average in a wide angle of ±60° compared to that with the naked bottom of sapphire substrate, or 20% compared to reflecting Al film on the bottom of a sapphire substrate. An extinction ratio (ER) of average value 20 dB within an angle of ±60° can be simultaneously obtained directly from an InGaN/GaN LED. Our results show the possibility of simultaneously achieving a high degree of polarization and high polarization extraction efficiency at the integrated device level. This advances the field of GaN LED toward energy efficiency, multi-functional applications in illumination, display, medicine, and light manipulation.

Effects of electron transport material on blue organ light-emitting diode with fluorescent dopant of BCzVBi.

Science.gov (United States)

Meng, Mei; Song, Wook; Kim, You-Hyun; Lee, Sang-Youn; Jhun, Chul-Gyu; Zhu, Fu Rong; Ryu, Dae Hyun; Kim, Woo-Young

2013-01-01

High efficiency blue organic light emitting diodes (OLEDs), based on 2-me-thyl-9,10-di(2-naphthyl) anthracene (MADN) doped with 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi), were fabricated using two different electron transport layers (ETLs) of tris(8-hydroxyquinolino)-aluminum (Alq3) and 4,7-di-phenyl-1,10-phenanthroline (Bphen). Bphen ETL layers favored the efficient hole-electron recombination in the emissive layer of the BCzVBi-doped blue OLEDs, leading to high luminous efficiency and quantum efficiency of 8.34 cd/A at 100 mA/cm2 and 5.73% at 100 cd/m2, respectively. Maximum luminance of blue OLED with Bphen ETL and Alq3 ETL were 10670 cd/m2, and CIExy coordinates of blue OLEDs were (0.180, 0279) and (0.155, 0.212) at 100 cd/m2.

Understanding the role of ultra-thin polymeric interlayers in improving efficiency of polymer light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Bailey, Jim; Wang, Xuhua; Bradley, Donal D. C.; Kim, Ji-Seon, E-mail: ji-seon.kim@imperial.ac.uk [Department of Physics and Centre for Plastic Electronics, South Kensington Campus, Imperial College London, London SW7 2AZ (United Kingdom); Wright, Edward N.; Walker, Alison B. [Department of Physics, University of Bath, Bath BA2 7AY (United Kingdom)

2014-05-28

Insertion of ultra-thin polymeric interlayers (ILs) between the poly(3,4-ethylenedioxythiophene):polystyrene sulphonate hole injection and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) light emission layers of polymer light emitting diodes (PLEDs) can significantly increase their efficiency. In this paper, we investigate experimentally a broad range of probable causes of this enhancement with an eye to determining which IL parameters have the most significant effects. The importance of hole injection and electron blocking was studied through varying the IL material (and consequently its electronic energy levels) for both PLED and hole-only diode structures. The role of IL conductivity was examined by introducing a varying level of charge-transfer doping through blending the IL materials with a strong electron-accepting small molecule in concentrations from 1% to 7% by weight. Depositing ILs with thicknesses below the exciton diffusion length of ∼15 nm allowed the role of the IL as a physical barrier to exciton quenching to be probed. IL containing PLEDs was also fabricated with Lumation Green Series 1300 (LG 1300) light emission layers. On the other hand, the PLEDs were modeled using a 3D multi-particle Kinetic Monte Carlo simulation coupled with an optical model describing how light is extracted from the PLED. The model describes charge carrier transport and interactions between electrons, holes, singlets, and triplets, with the current density, luminance, and recombination zone (RZ) locations calculated for each PLED. The model shows F8BT PLEDs have a narrow charge RZ adjacent to the anode, while LG 1300 PLEDs have a wide charge RZ that is evenly distributed across the light emitting layer. Varying the light emitting layer from F8BT to Lumation Green Series 1300, we therefore experimentally examine the dependence of the IL function, specifically in regard to anode-side exciton quenching, on the location of the RZ. We found an exponential dependence of

Phosphorescent Organic Light Emitting Diodes Implementing Platinum Complexes

Science.gov (United States)

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

Analytic formalism for current crowding in light emitting diodes

International Nuclear Information System (INIS)

Lee, Kyu-Seok

2012-01-01

This paper presents an analytic approach to simulating current crowding (CC) in light-emitting diodes with parallel p- and n-contacts. The electrical potential difference across the p-i-n layers is derived from the Laplace equation, whereas the current density through the p-i-n layers is obtained from the current density - voltage relation of a single-diode model. Since these two properties influence each other, they are calculated iteratively. It is found that CC depends on the applied voltage (or the average current density), the sheet resistances of the p- and the n-contact layers, the width of the active region, and the specific series resistance and ideality factor of the p-i-n layers. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Structural design and optimization of near-ultraviolet light-emitting diodes with wide wells

Energy Technology Data Exchange (ETDEWEB)

Kuo, Yen-Kuang, E-mail: ykuo@cc.ncue.edu.tw [Department of Physics, National Changhua University of Education, Changhua 500, Taiwan (China); Chen, Fang-Ming [Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan (China); Chang, Jih-Yuan [Center for Teacher Education, National Changhua University of Education, Changhua 500, Taiwan (China); Shih, Ya-Hsuan [Department of Photonics, National Cheng Kung University, Tainan 701, Taiwan (China)

2016-03-07

The characteristics of the near-ultraviolet (NUV) light-emitting diodes (LEDs) with wide (14-nm-thick) and narrow (2-nm-thick) wells under the situations of different numbers of wells and degree of polarization are systematically investigated. The simulation results show that the Auger recombination can be efficiently suppressed with the increase of number of wells in NUV LEDs. For the LEDs with wide wells, the quantum-confined Stark effect and Shockley–Read–Hall recombination play an important role when the number of wells increases, especially when the LED is under low current injection or high degree of polarization. In order to take the advantage of using wide wells, it is proposed that the quaternary Al{sub 0.1}In{sub 0.05}Ga{sub 0.85}N barriers be used in wide-well NUV LEDs along with the use of Al{sub 0.3}Ga{sub 0.7}N/Al{sub 0.1}Ga{sub 0.9}N superlattice electron-blocking layer to mitigate the polarization effect and electron overflow. With this band-engineering structural design, the optical performance of the wide-well NUV LEDs is much better than its thin-well counterpart even under the situation of high degree of polarization.

Effect of 670-nm Light-Emitting Diode Light On Neuronal Cultures

Science.gov (United States)

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.

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

NARCIS (Netherlands)

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

2017-01-01

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

Manipulating Ion Migration for Highly Stable Light-Emitting Diodes with Single-Crystalline Organometal Halide Perovskite Microplatelets.

Science.gov (United States)

Chen, Mingming; Shan, Xin; Geske, Thomas; Li, Junqiang; Yu, Zhibin

2017-06-27

Ion migration has been commonly observed as a detrimental phenomenon in organometal halide perovskite semiconductors, causing the measurement hysteresis in solar cells and ultrashort operation lifetimes in light-emitting diodes. In this work, ion migration is utilized for the formation of a p-i-n junction at ambient temperature in single-crystalline organometal halide perovskites. The junction is subsequently stabilized by quenching the ionic movement at a low temperature. Such a strategy of manipulating the ion migration has led to efficient single-crystalline light-emitting diodes that emit 2.3 eV photons starting at 1.8 V and sustain a continuous operation for 54 h at ∼5000 cd m -2 without degradation of brightness. In addition, a whispering-gallery-mode cavity and exciton-exciton interaction in the perovskite microplatelets have both been observed that can be potentially useful for achieving electrically driven laser diodes based on single-crystalline organometal halide perovskite semiconductors.

High color rendering index white organic light-emitting diode using levofloxacin as blue emitter

Science.gov (United States)

Miao, Yan-Qin; Gao, Zhi-Xiang; Zhang, Ai-Qin; Li, Yuan-Hao; Wang, Hua; Jia, Hu-Sheng; Liu, Xu-Guang; Tsuboi, Taijuf

2015-05-01

Levofloxacin (LOFX), which is well-known as an antibiotic medicament, was shown to be useful as a 452-nm blue emitter for white organic light-emitting diodes (OLEDs). In this paper, the fabricated white OLED contains a 452-nm blue emitting layer (thickness of 30 nm) with 1 wt% LOFX doped in CBP (4,4’-bis(carbazol-9-yl)biphenyl) host and a 584-nm orange emitting layer (thickness of 10 nm) with 0.8 wt% DCJTB (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran) doped in CBP, which are separated by a 20-nm-thick buffer layer of TPBi (2,2’,2”-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole). A high color rendering index (CRI) of 84.5 and CIE chromaticity coordinates of (0.33, 0.32), which is close to ideal white emission CIE (0.333, 0.333), are obtained at a bias voltage of 14 V. Taking into account that LOFX is less expensive and the synthesis and purification technologies of LOFX are mature, these results indicate that blue fluorescence emitting LOFX is useful for applications to white OLEDs although the maximum current efficiency and luminance are not high. The present paper is expected to become a milestone to using medical drug materials for OLEDs. Project supported by the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-13-0927), the International Science & Technology Cooperation Program of China (Grant No. 2012DFR50460), the National Natural Science Foundation of China (Grant Nos. 21101111 and 61274056), and the Shanxi Provincial Key Innovative Research Team in Science and Technology, China (Grant No. 2012041011).

Dr. Harry Whelan With the Light Emitting Diode Probe

Science.gov (United States)

1999-01-01

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

Synthesis and characterization of pure and Li⁺ activated Alq₃ complexes for green and blue organic light emitting diodes and display devices.

Science.gov (United States)

Bhagat, S A; Borghate, S V; Kalyani, N Thejo; Dhoble, S J

2014-08-01

Pure and Li(+)-doped Alq3 complexes were synthesized by simple precipitation method at room temperature, maintaining the stoichiometric ratio. These complexes were characterized by X-ray diffraction, ultraviolet-visible absorption and Fourier transform infrared and photoluminescence (PL) spectra. X-ray diffraction analysis reveals the crystalline nature of the synthesized complexes, while Fourier transform infrared spectroscopy confirm the molecular structure, the completion of quinoline ring formation and presence of quinoline structure in the metal complex. Ultraviolet-visible and PL spectra revealed that Li(+) activated Alq3 complexes exhibit the highest intensity in comparison to pure Alq3 phosphor. Thus, Li(+) enhances PL emission intensity when doped into Alq3 phosphor. The excitation spectra lie in the range of 383-456 nm. All the synthesized complexes other than Liq give green emission, while Liq gives blue emission with enhanced intensity. Thus, he synthesized phosphors are the best suitable candidates for green- and blue-emitting organic light emitting diode, PL liquid-crystal display and solid-state lighting applications. Copyright © 2013 John Wiley & Sons, Ltd.

Degradation of phosphorescent blue organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Chiu, Chien-Shu [Department of Electrical Engineering and Information Technology, Technical University of Braunschweig (Germany); Siemens AG, CT MM 1, Erlangen (Germany); Steinbacher, Frank [Department of Materials Science VI, University of Erlangen-Nuernberg (Germany); Siemens AG, CT MM 1, Erlangen (Germany); Krause, Ralf; Hunze, Arvid [Siemens AG, CT MM 1, Erlangen (Germany); Kowalsky, Wolfgang [Department of Electrical Engineering and Information Technology, Technical University of Braunschweig (Germany)

2009-07-01

Development of phosphorescent materials has significantly improved the efficiency of organic light-emitting diodes (OLEDs). By using efficient red, green and blue phosphorescent emitter materials high efficient white OLEDs can be achieved. However, due to low stability of blue phosphorescent materials the lifetime of phosphorescent white OLEDs remains an issue. As a result, degradation of blue phosphorescent materials needs to be further investigated and improved. In this work, blue OLED devices based on the phosphorescent emitter FIrpic were investigated. Single-carrier hole-only as well as electron-only devices were fabricated. For investigation of degradation process the devices were stressed with electrical current and UV-light to study the impact of charge carriers as well as excitons and exciton-polaron quenching on the stability of the blue dye.

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

Science.gov (United States)

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

2014-01-01

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

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

KAUST Repository

Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Banavoth, Murali; Sarmah, Smritakshi P.; Yuan, Mingjian; Sinatra, Lutfan; AlYami, Noktan; 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

2016-01-01

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-paircapped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs.

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

KAUST Repository

Pan, Jun

2016-08-16

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

Manipulating the Local Light Emission in Organic Light-Emitting Diodes by using Patterned Self-Assembled Monolayers

NARCIS (Netherlands)

Mathijssen, S.G.J.; Hal, P.A. van; Biggelaar, T.J.M. van den; Smits, E.C.P.; Boer, B. de; Kemerink, M.; Janssen, R.A.J.; Leeuw, D.M. de

2008-01-01

In organic light-emitting diodes (OLEDs), interface dipoles play an important role in the process of charge injection from the metallic electrode into the active organic layer.[1,2] An oriented dipole layer changes the effective work function of the electrode because of its internal electric field.

Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

KAUST Repository

Shervin, Shahab

2018-01-26

Deep ultraviolet (DUV) light at the wavelength range of 250‒280 nm (UVC spectrum) is essential for numerous applications such as sterilization, purification, sensing, and communication. III-nitride-based DUV light-emitting diodes (DUV LEDs), like other solid-state lighting sources, offer a great potential to replace the conventional gas-discharged lamps with short lifetimes and toxic-element-bearing nature. However, unlike visible LEDs, the DUV LEDs are still suffering from low quantum efficiencies (QEs) and low optical output powers. In this work, reported is a new route to improve QEs of AlGaN-based DUV LEDs using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency (IQE) is enhanced higher than three times, when the DUV LEDs are moderately bent to induce in-plane compressive strain in the heterostructure. Furthermore, efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

KAUST Repository

Shervin, Shahab; Oh, Seung Kyu; Park, Hyun Jung; Lee, Keon Hwa; Asadirad, Mojtaba; Kim, Seung Hwan; Kim, Jeomoh; Pouladi, Sara; Lee, Sung-Nam; Li, Xiaohang; Kwak, Joon-Seop; Ryou, Jae-Hyun

2018-01-01

Deep ultraviolet (DUV) light at the wavelength range of 250‒280 nm (UVC spectrum) is essential for numerous applications such as sterilization, purification, sensing, and communication. III-nitride-based DUV light-emitting diodes (DUV LEDs), like other solid-state lighting sources, offer a great potential to replace the conventional gas-discharged lamps with short lifetimes and toxic-element-bearing nature. However, unlike visible LEDs, the DUV LEDs are still suffering from low quantum efficiencies (QEs) and low optical output powers. In this work, reported is a new route to improve QEs of AlGaN-based DUV LEDs using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency (IQE) is enhanced higher than three times, when the DUV LEDs are moderately bent to induce in-plane compressive strain in the heterostructure. Furthermore, efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

Highly efficient exciplex organic light-emitting diodes incorporating a heptazine derivative as an electron acceptor.

Science.gov (United States)

Li, Jie; Nomura, Hiroko; Miyazaki, Hiroshi; Adachi, Chihaya

2014-06-11

Highly efficient exciplex systems incorporating a heptazine derivative () as an electron acceptor and 1,3-di(9H-carbazol-9-yl)benzene () as an electron donor are developed. An organic light-emitting diode containing 8 wt% : as an emitting layer exhibits a maximum external quantum efficiency of 11.3%.

Improvement of white organic light emitting diode performances by an annealing process

Energy Technology Data Exchange (ETDEWEB)

Sepeai, Suhaila, E-mail: suhaila_sepeai@yahoo.co [Solar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 UKM Bangi Selangor (Malaysia); Salleh, Muhamad Mat, E-mail: mms@pkrisc.cc.ukm.m [Institute Of Microengineering And Nanoelectronic, Universiti Kebangsaan Malaysia, 43600 UKM Bangi Selangor (Malaysia); Yahaya, Muhammad; Umar, Akrajas Ali [Institute Of Microengineering And Nanoelectronic, Universiti Kebangsaan Malaysia, 43600 UKM Bangi Selangor (Malaysia)

2009-06-30

White organic light emitting diode (OLED) devices with the structure ITO/PHF:rubrene/Al, in which PHF (poly(9,9-di-n-hexylfluorenyl-2,7-diyl)) is used as blue light emitting host and rubrene (5,6,11,12-tetraphenylnapthacene) as an orange dye dopant, have been fabricated. Indium tin oxide (ITO) coated-glass and aluminium were used as anode and cathode, respectively. The devices were fabricated with various rubrene-dopant to obtain a white light emission. The OLED device that composed of several concentrations of rubrene-doped PHF film was prepared in this study. It was found that the concentration of rubrene in the PHF-rubrene thin film matrix plays a key role in producing the white color emission. In a typical result, the device composed of 0.06 wt.% rubrene-dopant produced the white light emission with the Commission Internationale de L'Eclairage (CIE) coordinate of (0.30,0.33). The turn-on voltage and the brightness were found to be as low as 14.0 V and as high as 6540 cd/m{sup 2}, respectively. The annealing technique at relatively low temperature (50 {sup o}C, 100 {sup o}C, and 150 {sup o}C) was then used to optimize the performance of the device. In a typical result, the turn-on voltage of the device could be successfully reduced and the brightness could be increased using the annealing technique. At an optimum condition, for example, annealed at 150 {sup o}C, the turn-on voltage as low as 8.0 V and the brightness as high as 9040 cd/m{sup 2} were obtained. The mechanism for the improvement of the device performance upon annealing will be discussed.

Gigabit-per-second white light-based visible light communication using near-ultraviolet laser diode and red-, green-, and blue-emitting phosphors

KAUST Repository

Lee, Changmin; Shen, Chao; Cozzan, Clayton; Farrell, Robert M.; Speck, James S.; Nakamura, Shuji; Ooi, Boon S.; DenBaars, Steven P.

2017-01-01

Data communication based on white light generated using a near-ultraviolet (NUV) laser diode (LD) pumping red-, green-, and blue-emitting (RGB) phosphors was demonstrated for the first time. A III-nitride laser diode (LD) on a semipolar (2021

Fabrication and properties of light-emitting diodes based on self-assembled multilayers of poly(phenylene vinylene)

Science.gov (United States)

Fou, A. C.; Onitsuka, O.; Ferreira, M.; Rubner, M. F.; Hsieh, B. R.

1996-05-01

Light-emitting diodes have been fabricated from self-assembled multilayers of poly(p-phenylene vinylene) (PPV) and two different polyanions; polystyrene sulfonic acid (SPS) and polymethacrylic acid (PMA). The type of polyanion used to assemble the multilayer thin films was found to dramatically influence the behavior and performance of devices fabricated with indium tin oxide and aluminum electrodes. Light-emitting devices fabricated from PMA/PPV multilayers were found to exhibit luminance levels in the range of 20-60 cd/m2, a thickness dependent turn-on voltage and classical rectifying behavior with rectification ratios greater than 105. In sharp contrast, the devices based on SPS/PPV exhibited near symmetric current-voltage curves, thickness independent turn-on voltages and much lower luminance levels. The significant difference in device behavior observed between these two systems is primarily due to a doping effect induced either chemically or electrochemically by the sulfonic acid groups of SPS. It was also found that the performance of these devices depends on the type of layer that is in contact with the Al top electrode thereby making it possible to manipulate device efficiency at the molecular level.

Sharp green electroluminescence from 1H-pyrazolo[3,4-b]quinoline-based light-emitting diodes

Science.gov (United States)

Tao, Y. T.; Balasubramaniam, E.; Danel, A.; Jarosz, B.; Tomasik, P.

2000-09-01

A multilayer organic light-emitting diode was fabricated using a fluorescent compound {6-N,N-diethylamino-1-methyl-3-phenyl-1H-pyrazolo[3,4-b]quinoline} (PAQ-NEt2) doped into the hole-transporting layer of NPB {4,4'-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl}, with the TPBI {2,2',2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole]} as an electrontransporting material. At 16% PAQ-NEt2 doping concentration, the device gave a sharp, bright, and efficient green electroluminescence (EL) peaked at around 530 nm. The full width at half maximum of the EL is 60 nm, which is 60% of the green emission from typical NPB/AlQ [where AlQ=tris(8-hydroxyquinoline) aluminum] device. For the same concentration, a maximum luminance of 37 000 cd/m2 was obtained at 10.0 V and the maximum power, luminescence, and external quantum efficiencies were obtained 4.2 lm/W, 6.0 cd/A, and 1.6%, respectively, at 5.0 V.

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

Science.gov (United States)

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

2010-10-25

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-04-28

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

III-nitride Photonic Integrated Circuit: Multi-section GaN Laser Diodes for Smart Lighting and Visible Light Communication

KAUST Repository

Shen, Chao

2017-04-01

The past decade witnessed the rapid development of III-nitride light-emitting diodes (LEDs) and laser diodes (LDs), for smart lighting, visible-light communication (VLC), optical storage, and internet-of-things. Recent studies suggested that the GaN-based LDs, which is free from efficiency droop, outperform LEDs as a viable high-power light source. Conventionally, the InGaN-based LDs are grown on polar, c-plane GaN substrates. However, a relatively low differential gain limited the device performance due to a significant polarization field in the active region. Therefore, the LDs grown on nonpolar m-plane and semipolar (2021)-plane GaN substrates are posed to deliver high-efficiency owing to the entirely or partially eliminated polarization field. To date, the smart lighting and VLC functionalities have been demonstrated based on discrete devices, such as LDs, transverse-transmission modulators, and waveguide photodetectors. The integration of III-nitride photonic components, including the light emitter, modulator, absorber, amplifier, and photodetector, towards the realization of III-nitride photonic integrated circuit (PIC) offers the advantages of small-footprint, high-speed, and low power consumption, which has yet to be investigated. This dissertation presents the design, fabrication, and characterization of the multi-section InGaN laser diodes with integrated functionalities on semipolar (2021)-plane GaN substrates for enabling such photonic integration. The blue-emitting integrated waveguide modulator-laser diode (IWM-LD) exhibits a high modulation efficiency of 2.68 dB/V. A large extinction ratio of 11.3 dB is measured in the violet-emitting IWM-LD. Utilizing an integrated absorber, a high optical power (250mW), droop-free, speckle-free, and large modulation bandwidth (560MHz) blue-emitting superluminescent diode is reported. An integrated short-wavelength semiconductor optical amplifier with the laser diode at ~404 nm is demonstrated with a large gain of 5

Application of Surface Plasmonics for Semiconductor Light-Emitting Diodes

DEFF Research Database (Denmark)

Fadil, Ahmed

This thesis addresses the lack of an efficient semiconductor light source at green emission colours. Considering InGaN based quantum-well (QW) light-emitters and light-emitting diodes (LEDs), various ways of applying surface plasmonics and nano-patterning to improve the efficiency, are investigated....... By placing metallic thin films or nanoparticles (NPs) in the near-field of QW light-emitters, it is possible to improve their internal quantum efficiency (IQE) through the Purcell enhancement effect. It has been a general understanding that in order to achieve surface plasmon (SP) coupling with QWs......-QW coupling does not necessarily lead to emission enhancement. The findings of this work show that the scattering and absorption properties of NPs play a crucial role in determining whether the implementation will improve or degrade the optical performance. By applying these principles, a novel design...

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

CERN Document Server

Krier, A

2003-01-01

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

Tunable light extraction efficiency of GaN light emitting diodes by ZnO nanorod arrays

International Nuclear Information System (INIS)

Chao, C H; Lin, W H; Lin, C F; Chen, C H; Changjean, C H

2009-01-01

We report the influence of ZnO nanorod arrays (NRAs) on the light extraction efficiency of GaN light emitting diodes (LEDs). Our investigation indicates that the output light intensity of the device exhibits a periodic oscillation as a function of the rod length. The variation of light extraction efficiency is caused by the Fabry–Perot resonance of the film composed of the nanorods. The theoretical analysis shows a good agreement with the measurement results. Our study reveals a method to control the output light extraction efficiency of GaN LEDs via a simple solution-based synthesized ZnO NRAs

Flexible bottom-emitting white organic light-emitting diodes with semitransparent Ni/Ag/Ni anode.

Science.gov (United States)

Koo, Ja-Ryong; Lee, Seok Jae; Lee, Ho Won; Lee, Dong Hyung; Yang, Hyung Jin; Kim, Woo Young; Kim, Young Kwan

2013-05-06

We fabricated a flexible bottom-emitting white organic light-emitting diode (BEWOLED) with a structure of PET/Ni/Ag/Ni (3/6/3 nm)/ NPB (50 nm)/mCP (10 nm)/7% FIrpic:mCP (10 nm)/3% Ir(pq)(2) acac:TPBi (5 nm)/7% FIrpic:TPBi (5 nm)/TPBi (10 nm)/Liq (2 nm)/ Al (100 nm). To improve the performance of the BEWOLED, a multilayered metal stack anode of Ni/Ag/Ni treated with oxygen plasma for 60 sec was introduced into the OLED devices. The Ni/Ag/Ni anode effectively enhanced the probability of hole-electron recombination due to an efficient hole injection into and charge balance in an emitting layer. By comparing with a reference WOLED using ITO on glass, it is verified that the flexible BEWOLED showed a similar or better electroluminescence (EL) performance.

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

Science.gov (United States)

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

2012-07-01

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

Efficient white organic light emission by single emitting layer

Energy Technology Data Exchange (ETDEWEB)

Ko, Young Wook; Chung, Choong-Heui; Lee, Jin Ho; Kim, Yong-Hae; Sohn, Choong-Yong; Kim, Bong-Chul; Hwang, Chi-Sun; Song, Yoon-Ho; Lim, Jongtae; Ahn, Young-Joo; Kang, Gi-Wook; Lee, Namheon; Lee, Changhee

2003-02-24

Stable organic white light-emitting diodes are successfully fabricated by a single organic white emitting layer, which is Bis (2-methyl-8-quinolinato) (triphenylsiloxy) aluminum (III) (SAlq) doped red fluorescent dye of 4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)- 4H-pyran (DCJTB). The incomplete energy transfer from blue-emitting SAlq to red-emitting DCJTB enables to obtain a stable white balanced light-emission by the DCJTB doping concentration of 0.5%. A device with the structure of ITO/TPD (50 nm)/SAlq:DCJTB (30 nm, 0.5%)/Alq{sub 3} (20 nm)/LiF (0.5 nm)/Al (110 nm) shows maximum luminance of 20 400 cd/m{sup 2} at 810 mA/cm{sup 2}, external quantum efficiency of 2% at 200 cd/m{sup 2} ({approx}3 mA/cm{sup 2}), power efficiency of 2.3 lm/W at 67 cd/m{sup 2} ({approx}1 mA/cm{sup 2}), and a Commission Internationale de l'Eclairage chromaticity coordinates of (0.34, 0.39) at 1.8 mA/cm{sup 2} to (0.31, 0.38) at 36 mA/cm{sup 2}.

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

Science.gov (United States)

Yang, Pao-Keng

2011-09-01

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

Light-Emitting Diode-Based Illumination System for In Vitro Photodynamic Therapy

OpenAIRE

Defu Chen; Huifen Zheng; Zhiyong Huang; Huiyun Lin; Zhidong Ke; Shusen Xie; Buhong Li

2012-01-01

The aim of this study is to develop a light-emitting diode- (LED-) based illumination system that can be used as an alternative light source for in vitro photodynamic therapy (PDT). This illumination system includes a red LED array composed of 70 LEDs centered at 643 nm, an air-cooling unit, and a specific-designed case. The irradiance as a function of the irradiation distance between the LED array and the sample, the homogeneity and stability of irradiation, and the effect of long-time irrad...

Influence of doping location and width of dimethylquinacridone on the performance of organic light emitting devices

International Nuclear Information System (INIS)

Li Jingze; Yahiro, Masayuki; Ishida, Kenji; Matsushige, Kazumi

2005-01-01

The influence of doping location and width of fluorescent dimethylquinacridone (DMQA) molecules on the performance of organic light emitting devices has been systematically investigated. While the doped zone is located at the interface of the hole transport layer (HTL) and the light emitting layer (EML), doping in the HTL leads to significant improvement of the external quantum efficiency relative to the undoped device, whereas the efficiency is lower than that of doping in the EML. This phenomenon is explained according to the electroluminescence (EL) process of the doped DMQA, which is dominated by Foerster energy transfer. Additionally, a device with dual doping in both HTL and EML exhibits the highest efficiency. The EL and photoluminescence spectra are also dependent on the doping sites

Performance Improvement of GaN-Based Flip-Chip White Light-Emitting Diodes with Diffused Nanorod Reflector and with ZnO Nanorod Antireflection Layer

Directory of Open Access Journals (Sweden)

Hsin-Ying Lee

2014-01-01

Full Text Available The GaN-based flip-chip white light-emitting diodes (FCWLEDs with diffused ZnO nanorod reflector and with ZnO nanorod antireflection layer were fabricated. The ZnO nanorod array grown using an aqueous solution method was combined with Al metal to form the diffused ZnO nanorod reflector. It could avoid the blue light emitted out from the Mg-doped GaN layer of the FCWLEDs, which caused more blue light emitted out from the sapphire substrate to pump the phosphor. Moreover, the ZnO nanorod array was utilized as the antireflection layer of the FCWLEDs to reduce the total reflection loss. The light output power and the phosphor conversion efficiency of the FCWLEDs with diffused nanorod reflector and 250 nm long ZnO nanorod antireflection layer were improved from 21.15 mW to 23.90 mW and from 77.6% to 80.1% in comparison with the FCWLEDs with diffused nanorod reflector and without ZnO nanorod antireflection layer, respectively.

Photoemission spectroscopy study on interfacial energy level alignments in tandem organic light-emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Ou, Qing-Dong; Li, Chi; Li, Yan-Qing, E-mail: yqli@suda.edu.cn; Tang, Jian-Xin, E-mail: jxtang@suda.edu.cn

2015-10-01

Highlights: • The interface energetics of tandem OLEDs is overviewed. • Energy level alignment in CGLs is addressed via photoemission spectroscopy. • The n-type doping effect with cesium compounds is discussed. • Hole injection barrier is dependent on oxygen vacancies in transition metal oxides. • Device lifetime of tandem OLEDs is sensitive to interfacial stability of CGLs. - Abstract: Organic light-emitting diodes (OLEDs) using a tandem structure offer a highly attractive option for the applications of next-generation flat panel displays and solid-state lighting due to the extremely high brightness and efficiency along with the long operational lifetime. In general, reliable information about interface energetics of the charge generation layers (CGLs), which plays the central role in charge generation and carrier injection into the stacked emission units, is highly desirable and advantageous for interface engineering and the performance optimization of tandem OLEDs. In this review, our recent studies on tandem OLEDs are overviewed, especially from interface energetics perspective via photoemission spectroscopy. The electronic structures of various transition metal oxide (TMO)-based CGLs and their role in charge generation process are reviewed, addressing the n-type doping impact of organic layers in CGLs, thermal annealing-induced oxygen vacancy in TMOs, and the interfacial stability of CGLs on the device operational lifetime. The resulting energy level alignments are summarized in correspondence with tandem OLED performance.

Ultraviolet light-emitting diodes in water disinfection.

Science.gov (United States)

Vilhunen, Sari; Särkkä, Heikki; Sillanpää, Mika

2009-06-01

The novel system of ultraviolet light-emitting diodes (UV LEDs) was studied in water disinfection. Conventional UV lamps, like mercury vapor lamp, consume much energy and are considered to be problem waste after use. UV LEDs are energy efficient and free of toxicants. This study showed the suitability of LEDs in disinfection and provided information of the effect of two emitted wavelengths and different test mediums to Escherichia coli destruction. Common laboratory strain of E. coli (K12) was used and the effects of two emitted wavelengths (269 and 276 nm) were investigated with two photolytic batch reactors both including ten LEDs. The effects of test medium were examined with ultrapure water, nutrient and water, and nutrient and water with humic acids. Efficiency of reactors was almost the same even though the one emitting higher wavelength had doubled optical power compared to the other. Therefore, the effect of wavelength was evident and the radiation emitted at 269 nm was more powerful. Also, the impact of background was studied and noticed to have only slight deteriorating effect. In the 5-min experiment, the bacterial reduction of three to four log colony-forming units (CFU) per cubic centimeter was achieved, in all cases. When turbidity of the test medium was greater, part of the UV radiation was spent on the absorption and reactions with extra substances on liquid. Humic acids can also coat the bacteria reducing the sensitivity of the cells to UV light. The lower wavelength was distinctly more efficient when the optical power is considered, even though the difference of wavelengths was small. The reason presumably is the greater absorption of DNA causing more efficient bacterial breakage. UV LEDs were efficient in E. coli destruction, even if LEDs were considered to have rather low optical power. The effect of wavelengths was noticeable but the test medium did not have much impact. This study found UV LEDs to be an optimal method for bacterial

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

Science.gov (United States)

Thorseth, Anders

2012-03-01

Given the problem of metamerisms inherent in color mixing in light-emitting diode (LED) systems with more than three distinct colors, a method for optimizing the spectral output of multicolor LED system with regards to standardized light quality parameters has been developed. The composite spectral power distribution from the LEDs are simulated using spectral radiometric measurements of single commercially available LEDs for varying input power, to account for the efficiency droop and other non-linear effects in electrical power vs. light output. The method uses electrical input powers as input parameters in a randomized steepest decent optimization. The resulting spectral power distributions are evaluated with regard to the light quality using the standard characteristics: CIE color rendering index, correlated color temperature and chromaticity distance. The results indicate Pareto optimal boundaries for each system, mapping the capabilities of the simulated lighting systems with regard to the light quality characteristics.

A triphenylamine substituted quinacridone derivative for solution processed organic light emitting diodes

NARCIS (Netherlands)

Pilz da Cunha, M.; Do, T.T.; Yambem, S.D.; Pham, H.D.; Chang, S.; Manzhos, S.; Katoh, R.; Sonar, P.

2018-01-01

We report on a novel quinacridone derivative design, namely, 2,9-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-5,12-bis(2-ethylhexyl)-5,12-dihydroquinolino[2,3-b]acridine-7,14-dione (TPA-QA-TPA) for possible use as a solution processable emissive layer in organic light emitting diodes (OLEDs). TPA-QA-TPA

High tunability and superluminescence in InAs mid-infrared light emitting diodes

International Nuclear Information System (INIS)

Sherstnev, V.V.; Krier, A.; Hill, G.

2002-01-01

We report on the observation of super luminescence and high spectral current tunability (181 nm) of InAs light emitting diodes operating at 3.0 μm. The source is based on an optical whispering gallery mode which is generated near the edges of the mesa and which is responsible for the superluminescence. (author)

The photocatalytic degradation of methylene blue by green semiconductor films that is induced by irradiation by a light-emitting diode and visible light.

Science.gov (United States)

Yang, Chih-Chi; Doong, Ruey-An; Chen, Ku-Fan; Chen, Giin-Shan; Tsai, Yung-Pin

2018-01-01

This study develops a low-energy rotating photocatalytic contactor (LE-RPC) that has Cu-doped TiO 2 films coated on stainless-steel rotating disks, to experimentally evaluate the efficiency of the degradation and decolorization of methylene blue (MB) under irradiation from different light sources (visible 430 nm, light-emitting diode [LED] 460 nm, and LED 525 nm). The production of hydroxyl radicals is also examined. The experimental results show that the photocatalytic activity of TiO 2 that is doped with Cu 2+ is induced by illumination with visible light and an LED. More than 90% of methylene blue at a 10 mg/L concentration is degraded after illumination by visible light (430 nm) for 4 hr at 20 rpm. This study also demonstrates that the quantity of hydroxyl radicals produced is directly proportional to the light energy intensity. The greater the light energy intensity, the greater is the number of hydroxyl radicals produced. The CuO-doped anatase TiO 2 powder was successfully synthesized in this study by a sol-gel method. The catalytic abilities of the stainless-steel film were enhanced in the visible light regions. This study has successfully modified the nano-photocatalytic materials to drop band gap and has also successfully fixed the nano-photocatalytic materials on a substratum to effectively treat dye wastewater in the range of visible light. The results can be useful to the development of a low-energy rotating photocatalytic contactor for decontamination purposes.

Light-emitting diode street lights reduce last-ditch evasive manoeuvres by moths to bat echolocation calls

Science.gov (United States)

Wakefield, Andrew; Stone, Emma L.; Jones, Gareth; Harris, Stephen

2015-01-01

The light-emitting diode (LED) street light market is expanding globally, and it is important to understand how LED lights affect wildlife populations. We compared evasive flight responses of moths to bat echolocation calls experimentally under LED-lit and -unlit conditions. Significantly, fewer moths performed ‘powerdive’ flight manoeuvres in response to bat calls (feeding buzz sequences from Nyctalus spp.) under an LED street light than in the dark. LED street lights reduce the anti-predator behaviour of moths, shifting the balance in favour of their predators, aerial hawking bats. PMID:26361558

Photonic effects in microstructured conjugated polymer films and light emitting diodes

International Nuclear Information System (INIS)

Matterson, B.J.

2002-03-01

This thesis reports an investigation into the photonic effects caused by wavelength scale microstructure patterned onto films of conjugated polymers. The efficiency of light emitting diodes (LEDs) made from conjugated polymers is limited in part by the trapping of light into waveguide modes caused by the high refractive index of these materials. Waveguide modes in films of poly(p,-phenylene vinylene) (PPV) and poly(2-methoxy, 5-(2'ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) are analysed and the refractive index of these materials is calculated. The photoluminescence of conjugated polymer films that have been spun onto textured substrates is analysed. It is found that the photoluminescence quantum yield of a film spun onto a substrate inscribed with a grating is increased. It is also found that the photoluminescence spectrum of the film is dramatically altered and varies substantially with viewing angle. The features in the spectrum caused by the grating are strongly polarized. These effects are analysed and are attributed to the scattering of waveguided light out of the film. It is found that films spun onto metal gratings exhibit especially strong scattering. The effect of metal gratings with various grating depths is analysed. The possible contribution of band gaps to the photoluminescence spectrum from polymers on strong metal gratings is discussed. LEDs that include grating structures are constructed and analysed. It is found that having grating structures on the metal layers that are used as electrodes in the LED does not adversely affect the electrical properties of the LED. It is demonstrated that grating in the LED is able to substantially increase the light emission without using extra electrical power. The emission spectra from LEDs are observed to vary with angle, and exhibit considerable polarization. (author)

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

Directory of Open Access Journals (Sweden)

Margit Olle

2013-06-01

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

Dominant transverse-electric polarized emission from 298 nm MBE-grown AlN-delta-GaN quantum well ultraviolet light-emitting diodes

Science.gov (United States)

Liu, Cheng; Ooi, Yu Kee; Islam, S. M.; Xing, Huili Grace; Jena, Debdeep; Zhang, Jing

2017-02-01

III-nitride based ultraviolet (UV) light emitting diodes (LEDs) are of considerable interest in replacing gas lasers and mercury lamps for numerous applications. Specifically, AlGaN quantum well (QW) based LEDs have been developed extensively but the external quantum efficiencies of which remain less than 10% for wavelengths UV wavelengths is by the use of the AlGaN-delta-GaN QW where the insertion of the delta-GaN layer can ensure the dominant conduction band (C) - heavyhole (HH) transition, leading to large transverse-electric (TE) optical output. Here, we proposed and investigated the physics and polarization-dependent optical characterizations of AlN-delta- GaN QW UV LED at 300 nm. The LED structure is grown by Molecular Beam Epitaxy (MBE) where the delta-GaN layer is 3-4 monolayer (QW-like) sandwiched by 2.5-nm AlN sub-QW layers. The physics analysis shows that the use of AlN-delta-GaN QW ensures a larger separation between the top HH subband and lower-energy bands, and strongly localizes the electron and HH wave functions toward the QW center and hence resulting in 30-time enhancement in TEpolarized spontaneous emission rate, compared to that of a conventional Al0.35Ga0.65N QW. The polarization-dependent electroluminescence measurements confirm our theoretical analysis; a dominant TE-polarized emission was obtained at 298 nm with a minimum transverse-magnetic (TM) polarized emission, indicating the feasibility of high-efficiency TEpolarized UV emitters based on our proposed QW structure.

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

Science.gov (United States)

2004-01-01

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

New Optoelectronic Technology Simplified for Organic Light Emitting Diode (OLED

Directory of Open Access Journals (Sweden)

Andre F. S. Guedes

2014-06-01

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

Employing exciton transfer molecules to increase the lifetime of phosphorescent red organic light emitting diodes

Science.gov (United States)

Lindla, Florian; Boesing, Manuel; van Gemmern, Philipp; Bertram, Dietrich; Keiper, Dietmar; Heuken, Michael; Kalisch, Holger; Jansen, Rolf H.

2011-04-01

The lifetime of phosphorescent red organic light emitting diodes (OLEDs) is investigated employing either N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB), TMM117, or 4,4',4″-tris(N-carbazolyl)-triphenylamine (TCTA) as hole-conducting host material (mixed with an electron conductor). All OLED (organic vapor phase deposition-processed) show similar efficiencies around 30 lm/W but strongly different lifetimes. Quickly degrading OLED based on TCTA can be stabilized by doping exciton transfer molecules [tris-(phenyl-pyridyl)-Ir (Ir(ppy)3)] to the emission layer. At a current density of 50 mA/cm2 (12 800 cd/m2), a lifetime of 387 h can be achieved. Employing exciton transfer molecules is suggested to prevent the degradation of the red emission layer in phosphorescent white OLED.

Nanoengineering of organic light-emitting diodes

International Nuclear Information System (INIS)

Lupton, J.M.

2000-11-01

This thesis reports nanoengineerging of the emission and transport properties of organic light-emitting diodes (LEDs). This is achieved by a control of the electronic material properties and the photonic device properties. A novel class of conjugated materials for electroluminescence (EL) applications is presented, based on successively branching, or dendritic, materials comprising an emissive core and a shielding dendritic architecture. Exciton localisation at the centre of these dendrimers is observed in both luminescence and absorption. A detailed quantum chemical investigation using an exciton model supports these findings and accurately describes the energies and oscillator strengths of transitions in the core and branches. The dendrimer generation describes the degree of branching and gives a direct measure of the separation and interaction between chromophores. Increasing generation is found to lead to a reduction in red tail emission. This correlates with an increase in operating field and LED efficiency. Dendrimer blends with triplet harvesting dendritic phosphors are also investigated and found to exhibit unique emission properties. A numerical device model is presented, which is used to describe the temperature dependence of single layer polymer LEDs by fitting the field-dependent mobility and the barrier to hole injection. The device model is also used to obtain mobility values for the dendrimer materials, which are in excellent agreement with results obtained from time-of-flight measurements. The dendrimer generation is shown to provide a direct control of hopping mobility, which decreases by two orders of magnitude as the dendrimer generation increases from 0 to 3. The photonic properties and spontaneous emission of an LED are modified by incorporating a periodic wavelength scale microstructure into the emitting film. This is found to double the amount of light emitted with no effect on the device current. An investigation of the angular dependence

Monolithic Flexible Vertical GaN Light-Emitting Diodes for a Transparent Wireless Brain Optical Stimulator.

Science.gov (United States)

Lee, Han Eol; Choi, JeHyuk; Lee, Seung Hyun; Jeong, Minju; Shin, Jung Ho; Joe, Daniel J; Kim, DoHyun; Kim, Chang Wan; Park, Jung Hwan; Lee, Jae Hee; Kim, Daesoo; Shin, Chan-Soo; Lee, Keon Jae

2018-05-18

Flexible inorganic-based micro light-emitting diodes (µLEDs) are emerging as a significant technology for flexible displays, which is an important area for bilateral visual communication in the upcoming Internet of Things era. Conventional flexible lateral µLEDs have been investigated by several researchers, but still have significant issues of power consumption, thermal stability, lifetime, and light-extraction efficiency on plastics. Here, high-performance flexible vertical GaN light-emitting diodes (LEDs) are demonstrated by silver nanowire networks and monolithic fabrication. Transparent, ultrathin GaN LED arrays adhere to a human fingernail and stably glow without any mechanical deformation. Experimental studies provide outstanding characteristics of the flexible vertical μLEDs (f-VLEDs) with high optical power (30 mW mm -2 ), long lifetime (≈12 years), and good thermal/mechanical stability (100 000 bending/unbending cycles). The wireless light-emitting system on the human skin is successfully realized by transferring the electrical power f-VLED. Finally, the high-density GaN f-VLED arrays are inserted onto a living mouse cortex and operated without significant histological damage of brain. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Semi-transparent all-oxide ultraviolet light-emitting diodes based on ZnO/NiO-core/shell nanowires

Science.gov (United States)

Shi, Zhi-Feng; Xu, Ting-Ting; Wu, Di; Zhang, Yuan-Tao; Zhang, Bao-Lin; Tian, Yong-Tao; Li, Xin-Jian; Du, Guo-Tong

2016-05-01

Semi-transparent all-oxide light-emitting diodes based on ZnO/NiO-core/shell nanowire structures were prepared on double-polished c-Al2O3 substrates. The entire heterojunction diode showed an average transparency of ~65% in the ultraviolet and visible regions. Under forward bias, the diode displayed an intense ultraviolet emission at ~382 nm, and its electroluminescence performance was remarkable in terms of a low emission onset, acceptable operating stability, and the ability to optically excite emissive semiconductor nanoparticle chromophores.Semi-transparent all-oxide light-emitting diodes based on ZnO/NiO-core/shell nanowire structures were prepared on double-polished c-Al2O3 substrates. The entire heterojunction diode showed an average transparency of ~65% in the ultraviolet and visible regions. Under forward bias, the diode displayed an intense ultraviolet emission at ~382 nm, and its electroluminescence performance was remarkable in terms of a low emission onset, acceptable operating stability, and the ability to optically excite emissive semiconductor nanoparticle chromophores. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07236k

Contact light-emitting diodes based on vertical ZnO nanorods