Browsing by Author "Chiu, Chuang-Hung"

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Luminescence and Spectroscopic Properties of Yellow-Emitting Carbonitride Phosphors and Their Application in White LEDs
(2010)
Wu, Yun-Chen
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Chen, Teng-Ming
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Chiu, Chuang-Hung
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Mo, Chi-Neng
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應用化學系
A series of yellow-emitting carbonitride phosphors with compositions of (Y(1-x)Ce(x))(2)(CN(2))(3) (x = 0-0.1) was synthesized by using exothermic solid-state metathesis reactions. The wavelength of the broad band yellow emission was tunable, varying from 570 to 577 nm. The photoluminescence (PL) intensity enhanced with increasing Ce(3+) dopant content and was optimized at 3 mol % under excitation at 415 nm. We analyzed the 5d energy levels of Ce(3+) in a capped trigonal prismatic complex and estimated the vibronic coupling parameters and Stokes shifts. To understand the thermal quenching behavior, the temperature-dependent PL for (Y(1.97)Ce(0.03))(2)(CN(2))(3) was investigated. To demonstrate its potential application, we fabricated a warm white light-emitting diode (LED) using (Y(1.97)Ce(0.03))(2)(CN(2))(3), pumped with a 420 nm GaInN LED chip, and the electroluminescence data were also presented. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3476307] All rights reserved.
Structural, spectroscopic and photolurninescence studies of LiEu(WO4)(2-x)(MoO4), as a near-UV convertible phosphor
(2007-02-01)
Chiu, Chuang-Hung
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Wang, Ming-Fang
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Lee, Chi-Shen
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Chen, Teng-Ming
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應用化學系
A series of lithium europium double tungsto-molybdate phosphors LiEu(WO4)(2-),(MoO4), (X = 0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the D-5(0) -> F-7(2) emission of Eu3+ activated at wavelength of 396 mn was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the D-5(0) -> F-7(2) transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photolumineseent properties of LiEu(WO4)(2-x)(MoO4), is investigated and discussed. (c) 2006 Elsevier Inc. All rights reserved.
Synthesis and luminescence properties of intensely red-emitting M5Eu(WO4)(4-x)(MoO4)(x) (M = Li, Na, K) phosphors
(2008)
Chiu, Chuang-Hung
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Liu, Chih-Hsuan
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Huang, Sheng-Bang
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Chen, Teng-Ming
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應用化學系
We have investigated the luminescence of a series of M5Eu(WO4)(4-x)(MoO4)(x) (M = Li, Na, K) phosphors and discovered that Na5Eu(WO4)(4-x)(MoO4)(x) (0 <= x <= 4.0) exhibit the most intense red emission among the three investigated. Powder X-ray diffraction investigations show that a complete solid solution can be formed in the indicated composition range. The effect of chemical compositions on the luminescence properties of Na5Eu(WO4)(4-x)(MoO4)(x) has been investigated and discussed. The Commission International de l'Eclairage chromaticity coordinates were found to be (0.66,0.33) for Na5Eu(WO4)(4-x)(MoO4)(x), which reaches the same level as that of the Y2O2S:Eu3+ commodity. The color-rendering index (Ra) of a typical white-light-light emitting diode (WL-LED) based on Na5Eu(WO4)(2)(MoO4)(2) was found to be 82.3, higher than that (i.e., Ra similar to 70.8) obtained for the WL-LED fabricated using the commodity of La2O2S:Eu3+ when the WL-LEDs were operated at a forward-bias current (I-f) of 20 mA at room temperature. Na5Eu(WO4)(4-x)(MoO4)(x) is therefore suggested to be a potential red-emitting phosphor for WL-LED. (c) 2008 The Electrochemical Society.
White-light-emitting diodes using red-emitting LiEu(WO4)(2-x)(MoO4)(x) phosphors
(2007)
Chiu, Chuang-Hung
;
Liu, Chih-Hsuan
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Huang, Sheng-Bang
;
Chen, Teng-Ming
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應用化學系
The fundamental luminescence and chromaticity properties of a class of red-emitting phosphors LiEu(WO4)(2-x)(MoO4)(x) under near-UV excitation have been investigated. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra reveal that the absorption is mainly attributed to O -> Mo(W) charge transfer at 300 nm and the Eu3+ transitions in near-UV and visible regions, and red emissions are assigned to intraconfigurational 4f-4f transitions of Eu3+. Both PL and PLE intensity were found to increase with increasing doped Mo content. The intensity of the D-5(0) -> F-7(2) emission of Eu3+ activated at 394 nm was found to reach a maximum when the relative ratio of Mo/W was 2:0. The CIE chromaticity coordinates were found to be (0.66, 0.33) for LiEu(MoO4)(2) and it reached the same level as the commodity phosphor Y2O2S:Eu3+. A white-light-emitting diode fabricated using the composition-optimized LiEu(MoO4)(2) and the matching green- and blue-emitting phosphors shows that the quality of red color reproduction based on LiEu(MoO4)(2) was found to be much higher and improved than that using La2O2S:Eu3+. (C) 2007 The Electrochemical Society.