Browsing by Author "Lo, CL"

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Low temperature sintering and crystallisation behaviour of low loss anorthite-based glass-ceramics
(2003-02-15)
Lo, CL
;
Duh, JG
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Anorthite-based glass-ceramics including TiO2 as nucleating agent were melted and quenched in this study. The effect of particle size on the sintering behaviour of glass powders was investigated in order to obtain low-temperature sintered glass-ceramics. Anorthite glass-ceramic starts to densify at the transition temperature of glass (T-g = 770degreesC) and is fully sintered before the crystallisation occurrence (880degreesC). Therefore, a dense and low-loss glass-ceramic with predominant crystal phase of anorthite is achieved by using fine glass powders (D-50 = 0.45 mum) fired at 900degreesC. The as-sintered density approaches 99% theoretical density and the apparent porosity is as low as 0.05 Vol%. The dense and crystallized anorthite-based glass-ceramic exhibits a fairly low dielectric loss of 4 x 10(-4) at 1 MHz and a thermal expansion coefficient of 4.5 x 10(-6)degreesC(-1). Furthermore, the microwave characteristics were measured at 10 GHz with the results of K = 9.8, Of = 2250, and temperature coefficient of resonant frequency tau(f) = -30 ppm/degreesC. (C) 2003 Kluwer Academic Publishers.
Low-voltage cathodoluminescence properties of the Y2O2S : Eu red light emitting phosphor screen in field-emission environments
(2002-07-01)
Lo, CL
;
Duh, JG
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Y2O2S: Eu phosphors doped with different concentrations of Eu were fabricated by a high-temperature flux fusion method. For applications in field emission displays, phosphor powders were electrophoretically deposited on an indium-tin oxide coated glass substrate to form a phosphor screen. Cathodoluminescence properties of phosphor screens were examined at a low excitation voltage of 5 kV in a high-vacuum chamber (5 x 10(-8) Torr), and characteristics of Y2O2S: Eu phosphors, including brightness and wavelength data, are presented and discussed. The red emission brightness for the Y2O2S: Eu phosphor screens can be significantly improved by adjustment of the Eu additions, which decrease the x coordinate slightly, while having no significant influence on the color performance. Considering the effects of Eu concentrations on red light emission spectra and brightness for Y2O2S: Eu phosphor screens, it is found that brightness for Y2O2S: Eu phosphor screens could be obtained up to 120 cd/m(2) with chromaticity of x = 0.63 and y = 0.36, and the Eu dopant concentration is suggested to be in the range 6-7.5 wt %. (C) 2002 The Electrochemical Society.
Microstructure characteristics for anorthite composite glass with nucleating agents of TiO2 under non-isothermal crystallization
(2002-10-03)
Lo, CL
;
Duh, JG
;
Chiou, BS
;
Lee, WH
;
電子工程學系及電子研究所
The anorthite-based composite glass doped with TiO2 and B2O3 was prepared by quenching of molten droplets. Phase development and crystals microstructure of glass were investigated under non-isothermal conditions. A glass transition temperature of 770degreesC and an exothermal peak around 870degreesC in the DTA trace was associated with anorthite crystallization (CaAl2Si2O8). For glass specimens under nucleation and crystallization heat-treatment, the final predominant phase was identified as anorthite. Anorthite crystals show preferential nucleation at specific sites with rutile TiO2 crystals precipitated from the glassy matrix and anorthite crystallization is governed by heterogeneous volume nucleation. The introduced TiO2 plays the role of nucleating agents to reduce the crystallization temperature lower than 900degreesC for anorthite-based glass-ceramics. Chemical compositions could be related to the crystal microstructures on different characteristic regions. It was observed that the sintering aid of B2O3 neither reacted with nor dissolved in the anorthite or rutile TiO2 crystals, and remained a glassy phase in the matrix. Occurrence of acicular precipitations was attributed to the orientation growth of TiO2 crystals. Anorthite crystals were observed to grow with the forms of feathery-spherical particles, having a tendency to coalescence into a huge domain. (C) 2002 Elsevier Science Ltd. All rights reserved.
Synthesis of Eu3+-activated yttrium oxysulfide red phosphor by flux fusion method
(2001-08-15)
Lo, CL
;
Duh, JG
;
Chiou, BS
;
Peng, CC
;
Ozawa, L
Synthesis of the yttrium oxysulfide red phosphor by the flux fusion method was presented. Effects of flux compositions and sintering conditions on the shape and size distribution of phosphor were studied. In addition, the optimization of firing conditions was also conducted. After firing phosphor with a flux containing (S + Na2CO3 + Li3PO4 + K2CO3)/(S + Li2CO3 + K2CO3) at a ratio of 3:1 at 1150 degreesC for 2.5 h, Y2O2S:Eu3+ phosphor was obtained without any Y2O3 as a second phase. The nearly spherical phosphor powder exhibited a mean particle size of 3 mum and a rather sharp particle size distribution. Y2O2S:Eu3+ red phosphor illuminated the most red color light with an applied probe current density of 0.51 muA/cm(2). (C) 2001 Elsevier Science BN. All rights reserved.