| Summary: | 碩士 === 國立交通大學 === 應用化學系碩博士班 === 99 === In an attempt to investigate phosphors for light emitting diode (LED) application, we have successfully synthesized four series of thiogallate and oxythiogallate phosphors with compositions of SrLaGa3S6O:Ln (Ln = Ce3+, Eu2+, Ce3+/Li+ or Ce3+/Eu2+), (Sr1-xAx)LaGa3S6O:Ce3+ (A = Ca, Ba), Ca(La1-yMy)Ga3S6O:Ce3+ (or Eu2+) with M = Y, Gd,, and Sr2Ga2S5:Ce3+, respectively, by solid-state method under reduction atmosphere of H2S/Ar. .The crystal structure, luminescence, chromaticity and thermal luminescence quenching properties have been characterized by using X-ray diffraction (XRD), diffuse reflectance, and fluorescence spectroscopy.
We first investigated the optimization of synthetic conditions of all phosphors and carried out phase identification using XRD. We then investigated luminescence spectra of thiogallate and oxythiogallate and found that both can be excited in the range of 300-450 nm with optimal excitation at 397 nm (Ce3+-activated phases) and 405 nm (Eu2+-activated phases), respectively. The effect of crystal field strength on the luminescence of the (Sr1-xAx)LaGa3S6O:Ce3+ (A = Ca, Ba) and Ca(La1-yMy)Ga3S6O:Ce3+ (M = Y, Gd) systems has also been studied by cation substitution for Sr2+ and La3+, respectively. The energy transfer from Ce3+ to Eu2+ in SrLaGa3S6O:Ce3+,Eu2+ was investigated and found to occur via a resonance-type dipole-dipole mechanism. The chromaticity coordinates of SrLaGa3S6O:5%Ce3+,xEu2+was observed to shift from blue to yellowish-green with x increasing from to 0.10. Furthermore, the charge compensation study revealed that the emission spectrum of charge-compensated SrLaGa3S6O:Ce3+,Li+ red-shifted as compared to that of the uncompensated (Sr1-nCen)LaGa3S6O phase. Finally, we have studied the temperature-dependent luminescence intensity for the SrLaGa3S6O:Ln (Ln = Ce3+, Eu2+) and Sr2Ga2S5:Ce3+ phosphors and discovered that the thermal quenching was observed to be more serious in Sr2Ga2S5:Ce3+ than that observed in SrLaGa3S6O:Ln.
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