• Title, Summary, Keyword: Light Emitting Diodes

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AC-Based Characterization of Quantum-Dot Light-Emitting Diodes

  • Hwang, Hee-Soo;Lee, Ki-Hun;Park, Chan-Rok;Yang, Heesun;Hwang, Jinha
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.466-466
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    • 2013
  • Quantum-dot materials have introduced novel applications in organic light-emitting diodes and solar cells. The size controllability and structure modifications have continuously been upgrading the applicability to optoelectronic and flat-panel displays. In particular, quantum-dot organic light-emitting diodes (QLEDs) are a device driven through the electrical field applied to the electrical diodes. The QLEDs are affected by the constituent materials and the corresponding device structures. Conventionally, the electrical properties are characterized only in terms of dc-based current-voltage characteristics. The dynamic change in light-emitting diodes should be characterized in emitted and non-emitted states. Therefore, the frequency-dependent impedance can offer different information on the electrical performance in QLED. The current work reports an auxiliary information on the electrical and optical features originating from quantum-dot organic light-emitting diodes. The empirical characterizations are discussed towards an experimental tool in optimizing the light-emitting diodes.

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Charge Trapping Host Structure for High Efficiency in Phosphorescent Organic Light-Emitting Diodes

  • Lee, Jun-Yeob
    • Journal of Information Display
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    • v.9 no.2
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    • pp.14-17
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    • 2008
  • A charge trapping host structure was developed to improve the light-emitting efficiency of green phosphorescent organic light-emitting diodes. N, N'-dicarbazolyl-3,5-benzene(mCP) and a spirobifluorene based triplet host(PHl) were co-deposited as hosts in the emitting layer and the device performance was examined according to the composition mCP and PH1. The results showed that the quantum efficiency could be improved by 30 % using a mixed host of mCP and PH1.

Wear Of Resin Composites Polymerized By Conventional Halogen Light Curing And Light Emitting Diodes Curing Units (HALOGEN LIGHT CURING UNIT 과 LIGHT EMITTING DIODES CURING UNIT 을 이용하여 중합되어진 복합레진의 마모 특성 비교)

  • 이권용;김환;박성호;정일영;전승범
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.1057-1060
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    • 2004
  • In this study, the wear characteristics of five different dental composite resins cured by conventional halogen light and LED light sources were investigated. Five different dental composite resins of Surefil, Z100, Dyract AP, Fuji II LC and Compoglass were worn against a zirconia ceramic ball using a pin-on-disk type wear tester with 15 N contact force in a reciprocal sliding motion with sliding distance of 10 mm/cycle at 1Hz under the room temperature dry condition. The wear variations of dental composite resins were linearly increased as the number of cycles increased. It was observed that the wear resistances of these specimens were in the order of Dyract AP > Surefil > Compoglass > Z100 > Fuji II LC. On the morphological observations by SEM, the large crack formation on the sliding track of Fuji II LC specimen was the greatest among all resin composites. Dyract AP showed the least wear with few surface damage. There is no significant difference in wear performance between conventional halogen light curing and light emitting diodes curing sources. It indicates that a light emitting diodes (LED) source can replace a halogen light source as a curing unit for composite resin restorations.

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Wear of Resin Composites Polymerized by Conventional Halogen Light Curing and Light Emitting Diodes Curing Units (Halogen Light Curing Unit과 Light Emitting Diodes Curing Unit을 이용하여 중합되어진 복합레진의 마멸 특성 비교)

  • Lee Kwon-Yong;Kim Hwan;Park Sung-Ho;Jung Il-Young;Jeon Seung-Beom
    • Tribology and Lubricants
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    • v.21 no.6
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    • pp.268-271
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    • 2005
  • In this study, the wear characteristics of five different dental composite resins cured by conventional halogen light and LED light sources were investigated. Five different dental composite resins of Surefil, Z100, Dyract AP, Fuji II LC and Compoglass were worn against a zirconia ceramic ball using a pin-on-disk type wear tester with 15N contact force in a reciprocal sliding motion of sliding distance of 10mm/cycle at 1Hz under the room temperature dry condition. The wear variations of dental composite resins were linearly increased as the number of cycles increased. It was observed that the wear resistances of these specimens were in the order of Dyract AP > Surefil > Compoglass > Z100 > Fuji II LC. On the morphological observations by SEM, the large crack formation on the sliding track of Fuji II LC specimen was the greatest among all resin composites. Dyract AP showed less wear with few surface damage. There is no significant difference in wear performance between conventional halogen light curing and light emitting diodes curing sources. It indicates that a light emitting diodes (LED) source can replace a halogen light source as curing unit for composite resin restorations.

Simplified Bilayer White Phosphorescent Organic Light-Emitting Diodes

  • Lee, Jonghee;Sung, Woo Jin;Joo, Chul Woong;Cho, Hyunsu;Cho, Namsung;Lee, Ga-Won;Hwang, Do-Hoon;Lee, Jeong-Ik
    • ETRI Journal
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    • v.38 no.2
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    • pp.260-264
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    • 2016
  • We report on highly efficient blue, orange, and white phosphorescent organic light-emitting diodes consisting only two organic layers. Hole transporting 4, 4,' 4"-tris (N-carbazolyl)triphenylamine (TcTa) and electron transporting 2-(diphenylphosphoryl) spirofluorene (SPPO1) are used as an emitting host for orange light-emitting bis(3-benzothiazol-2-yl-9-ethyl-9H-carbazolato) (acetoacetonate) iridium ((btc)2(acac)Ir) and blue light-emitting iridium(III)bis(4,6-difluorophenyl-pyridinato-N,C2') picolinate (FIrpic) dopant, respectively. Combining these two orange and blue light-emitting layers, we successfully demonstrate highly efficient white PHOLEDs while maintaining Commission internationale de l'eclairage coordinates of (x = 0.373, y = 0.443). Accordingly, we achieve a maximum external quantum, current, and power efficiencies of 12.9%, 30.3 cd/A, and 30.0 lm/W without out-coupling enhancement.

Development of Colloidal Quantum Dots for Electrically Driven Light-Emitting Devices

  • Han, Chang-Yeol;Yang, Heesun
    • Journal of the Korean Ceramic Society
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    • v.54 no.6
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    • pp.449-469
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    • 2017
  • The development of quantum dots (QDs) has had a significant impact on various applications, such as solar cells, field-effect transistors, and light-emitting diodes (LEDs). Through successful engineering of the core/shell heterostructure of QDs, their photoluminescence (PL) quantum yield (QY) and stability have been dramatically enhanced. Such high-quality QDs have been regarded as key fluorescent materials in realizing next-generation display devices. Particularly, electrically driven (or electroluminescent, EL) QD light-emitting diodes (QLED) have been highlighted as an alternative to organic light-emitting diodes (OLED), mostly owing to their unbeatably high color purity. Structural optimizations in QD material as well as QLED architecture have led to substantial improvements of device performance, especially during the past decade. In this review article, we discuss QDs with various semiconductor compositions and describe the mechanisms behind the operation of QDs and QLEDs and the primary strategies for improving their PL and EL performances.

Luminescence Properties of $Y_2SiO_5:Eu^{3+}$ as Red-Emitting Phosphor for White Light Emitting Diodes

  • Song, Y.H.;Park, W.J.;Yoon, D.H.
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.1303-1304
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    • 2009
  • In order to apply to the White light emitting diodes (WLEDs), The $Y_2SiO_5:Eu^{3+}$ as red phosphor was synthesized by solid state reaction method. The highest emission of $Y_2SiO_5:Eu^{3+}$ was shown when the $Eu^{3+}$ concentration was 0.02. A single phase was observed from X-ray diffraction (XRD) analysis of synthesized samples and secondary phase wasn't found.

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The use of ZrO2 as an electron-injecting layer in hybrid metal-oxide/polymer light-emitting diodes

  • Tokmoldin, Nurlan;Bradley, Donal D.C.;Haque, Saif
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.779-780
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    • 2009
  • New inverted architecture of a hybrid inorganic-organic light-emitting diode, utilizing ZrO2 electron-injecting layer, is presented. The thickness of the ZrO2, as well as the annealing of the light-emitting polymer, is found critical to obtain good performance. A range of light-emitting polymers is shown to operate efficiently in the proposed architecture.

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High efficiency deep blue and pure white phosphorescent organic light emitting diodes

  • Yook, Kyoung-Soo;Jeon, Soon-Ok;Joo, Chul-Woong;Kim, Myung-Seop;Choi, Hong-Seok;Lee, Seok-Jong;Han, Chang-Wook;Tak, Yoon-Heung;Lee, Nam-Yang;Lee, Jun-Yeob
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.486-488
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    • 2009
  • High efficiency deep blue and pure white phosphorescent organic light emitting diodes were developed using a new deep blue phosphorescent dopant, tris((3,5-difluoro-4-cyanophenyl)pyridine) iridium (FCNIr). A high quantum efficiency of 9.1 % with a color coordinate of (0.15, 0.16) at 1,000 cd/$m^2$ was obtained in the deep blue device and a high quantum efficiency of 15.2 % with a color coordinate (0.30, 0.32) was obtained in the pure white organic light-emitting diodes. The quantum efficiency of the pure white device is the best quantum efficiency value reported in the pure white device up to now.

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Numerical Modeling and Simulations of Electrical Characteristics of Multi-layer Organic Light Emitting Diodes

  • Lee, Hyun-Jung;Lee, Yong-Soo;Park, Jae-Hoon;Choi, Jong-Sun
    • Journal of Information Display
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    • v.8 no.3
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    • pp.11-16
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    • 2007
  • Theoretical simulations of spatial distribution of charge carriers and recombination rate, and J-V characteristics of the multi-layer organic light emitting diodes are carried out. Drift-diffusion current transport, field-dependent carrier mobility, exponential and Gaussian trap distribution, and Langevin recombination models are included in this computer model. The simulated results show good agreement with the experimental data confirming the validity of the physical models for organic light emitting diodes.