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Pohang, South Korea

Park W.B.,Sejong University | Kwon T.H.,Daejoo Electronic Materials Co. | Sohn K.-S.,Sejong University
Journal of the American Ceramic Society | Year: 2014

Ce3+-activated light emitting diode (LED) phosphors have been extensively examined for photoluminescence, and have been the focus of many detailed structural studies. However, reports of the decay curves of Ce3+-activated LED phosphors are rare. Although we have reported the decay behaviors of several Eu2+-activated LED phosphors such as Sr2SiO4, Sr2Si5N8, and CaAlSiN3, we have never conducted an in-depth study into the decay behavior for Ce3+-activated LED phosphors. For this study, we investigated the decay curves of well-known Ce3+-activated LED phosphors such as La3Si6N11 and Lu3Al5O12. Similar to Eu2+-activated LED phosphors, the decay behavior of Ce3+-activated LED phosphors was sensitive to the Ce3+ concentration and to the detection wavelength. There was active nonradiative energy transfer between the Ce3+ activators located at different sites. © 2014 The American Ceramic Society. Source

Lee W.,Inha University | Choi S.,Seoul National University | Oh S.-M.,Daejoo Electronic Materials Co. | Park D.-W.,Inha University
Thin Solid Films | Year: 2013

Spherical hollow particles were prepared from solid alumina powders using DC arc thermal plasma, and then spray coating was performed with the as-prepared particles. Operating variables for the hollow particle preparation process were additional plasma gas, input power, and carrier gas flow rate. The spherical hollow alumina particles were produced in the case of using additive gas of H2 or N2, while alumina surface was hardly molten in the pure argon thermal plasma. In addition, the hollow particles were well produced in high power and low carrier gas conditions due to high melting point of alumina. Hollow structure was confirmed by focused ion beam-scanning electron microscopy analysis. Morphology and size distribution of the prepared particles that were examined by field emission-scanning electron microscopy and phase composition of the particles was characterized by X-ray diffraction. In the spray coating process, the as-prepared hollow particles showed higher deposition rate. © 2012 Elsevier B.V. Source

Jeon J.H.,Kyung Hee University | Cha S.J.,Kyung Hee University | Jeon Y.M.,Daejoo Electronic Materials Co. | Lee J.-H.,Korea National University of Transportation | Suh M.C.,Kyung Hee University
Organic Electronics: physics, materials, applications | Year: 2014

Laser Induced Thermal Imaging (LITI) is a laser addressed thermal patterning technology with unique advantages such as an excellent uniformity of transfer film thickness, a capability of multilayer stack transfer and a possibility to fabricate high resolution as well as large-area display. Nevertheless, it has been an obstacle to use such a laser imaging process as a commercial technology so far because of serious deterioration of the device performances plausibly due to a re-orientation of the molecular stacking especially in the emitting layer during thermal transfer process. To improve device performances, we devised a new concept to suppress the thermal degradation during such kind of thermal imaging process by using a high molecular weight small molecular species with large steric hindrance as well as high thermostability as a thermal buffer layer to realize highly efficient LITI devices. As a result, we obtained very high relative efficiency (by EQE) up to 91.5% at 1000 cd/m2 from the LITI devices when we utilize 10-(naphthalene-2-yl)-3-(phenanthren-9-yl)spiro[benzo[ij]tetraphene-7, 9′-fluorene] as a thermal buffer material. © 2014 Elsevier B.V. All rights reserved. Source

Kwona S.H.,Kyonggi University | Kwona S.H.,Daejoo Electronic Materials Co. | Kim Y.J.,Kyonggi University
ECS Journal of Solid State Science and Technology | Year: 2013

NaYF4:Yb3+/Er3+ up-conversion phosphors were prepared by a solvothermal method. The dependence of the green emission intensity on the changes in the particle shapes and the structure was investigated. Both the ratio of oleic acid to NaF (RO/N) and the concentration of the reactants strongly influenced the particle shapes. The strongest green emission originated from the powders containing slightly irregular hexagonal rods. The significant enhancement in the green emission (~150%) was observed by substituting 1 mol% Al3+ ions for Y3+ ions. It is speculated that the Al3+-doping correlates with the particle morphology and the modification of the crystal field surrounding the Yb 3+/Er3+ ions. © 2013 The Electrochemical Society. Source

Park J.,Kyonggi University | Lee S.J.,Kyonggi University | Lee S.J.,Daejoo Electronic Materials Co. | Kim Y.J.,Kyonggi University
Crystal Growth and Design | Year: 2013

Sr2-y-zCazSi(O1-xNx) 4:yEu2+ (SCSON:Eu2+) solid solutions were prepared by substituting N3-, Eu2+, and Ca2+ ions into Sr2SiO4 (SSO). These ions contributed differently to the evolution of luminescence of SCSON:Eu2+. SSON:Eu2+ (z = 0) has two activation centers: Eu(I) and Eu(II). The nitridation effects led to a dramatic change in the crystal field surrounding the Eu(II) site but rarely affected the Eu(I) site. Accordingly, SSON:Eu 2+ exhibited broad excitation spectra from ultraviolet to visible wavelengths. In comparison with the Eu(II) green emissions of SSO:Eu 2+, the dominant peak wavelengths (DPWs) of the Eu(II) emissions were at red emission regions (605-630 nm), depending on the amount of Eu 2+ ions. The Ca2+ ions of SCSON:Eu2+ preferentially changed the emission wavelength assigned to Eu(I) and affected the Eu(II) emission intensity. In addition to the spectral properties, the chromaticity coordinates and a low thermal quenching behavior of SCSON:Eu 2+ powders demonstrated that they can be a novel red phosphors for use in white light emitting diodes. © 2013 American Chemical Society. Source

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