鹼土鋁硼酸鹽螢光體電荷轉移與發光特性之研究

Abstract

本論文主要探討分別摻雜Eu2+、Eu3+、Tb3+與Ce3+等活化劑離子的SrAl2B2O7螢光體之發光特性。另一方面，SrAl2B2O7：Eu, Tb電荷轉移機制、SrAl2B2O7：Ce3+, Tb3+能量轉移機制與(Sr1-xBax)Al2B2O7：Eu2+主體組成對其發光特性之效應，也在研究範圍之內。 本研究發現以SrAl2B2O7為主晶格螢光體，具有自身還原的機制， SrAl2B2O7：R（R= Eu2+, Ce3+, Tb3+）等螢光體之合成無需還原製程，其中SrAl2B2O7：Eu2+（或Tb3+）等更呈現強烈放射強度。 紫外光致發光光譜研究顯示SrAl2B2O7：Eu2+螢光體呈現一6P7/2→8S7/2陡峭放射峰與另一寬廣 4f7→4f65d 放射峰；而SrAl2B2O7：Ce3+螢光體則呈現無分裂之單一寬廣放射峰；另一方面SrAl2B2O7：Tb3+螢光體則呈現5D3→7F6與5D4→7FJ ( J = 3, 4, 5, 6)陡峭放射峰，其中對應於5D3→7F6遷移之發光行為，不受到螢光濃度猝滅效應的影響。 另一方面，SrAl2B2O7：R（R= Tb3+, Ce3+）螢光體中螢光濃度猝滅效應較SrAl2B2O7：Eu2+（或Eu3+）更為顯著，此可能與Eu3+ → Eu2+自我還原或Eu2+激發態與基態能階間具有過渡能態所致。 未經還原SrAl2B2O7：Eu, Tb螢光體電荷轉移研究中，本論文發現Eu2+離子6P7/2→8S7/2陡峭放射峰之強度，並未隨Tb3+離子摻雜量遞增而呈現隨之增加的現象。此外，SrAl2B2O7：Ce3+, Tb3+能量轉移機制使得Tb3+最佳光致發光強度（λex = 329 nm）相對於SrAl2B2O7：Tb3+ （λex = 220 nm）最佳發光強度二倍以上，因此以SrAl2B2O7作為主晶格的螢光體中，經由Ce3+ →Tb3+可望具有良好的能量轉移效率。 另一方面，本研究亦藉著系統化調變(Sr1-xBax)Al2B2O7：Eu2+系列螢光體之組成，以探討主體組成對其發光特性之效應。

The research is attempted to investigate the luminescent properties of SrAl2B2O7：R (R = Eu2+, Eu3+, Tb3+, and Ce3+) phosphors. In addition, the mechanism of charge transfer in SrAl2B2O7：Eu, Tb and energy transfer in SrAl2B2O7：Ce3+, Tb3+, and the host compositional dependence of photoluminescence(PL) of (Sr1-xBax)Al2B2O7：Eu2+ have also been investigated. Our data have revealed that SrAl2B2O7：R (R = Eu2+, Tb3+, Ce3+) phosphors can be synthesized without the presence of reducing atmosphere. This fact can probably be attributed to the self-reduction property of SrAl2B2O7 that was probably related to low-melting B2O3 used as one of the reactants when being synthesized. Ultraviolet photoluminescent emission spectra indicate that (a) in SrAl2B2O7：Eu2+, a broad band emission attributed to 4f65d → 4f7 and another line attributed to 6P7/2→8S7/2 transition was also observed；(b) in SrAl2B2O7：Ce3+ non-split broad band emission was observed；(c) in SrAl2B2O7：Tb3+ a sharp emission peak (whose intensity is independent of concentration quenching) attributed to 5D3→7F6 transition was also observed. We have also found that SrAl2B2O7 doped with Ce3+ or Tb3+ exhibited significant concentration quenching effect compared to that doped with Eu2+ or Eu3+, as indicated by the PL emission spectra. The study on the charge transfer mechanism in non-reduced SrAl2B2O7：Eu0.025, xTb indicated that the emission intensity due to 6P7/2→8S7/2 was found to be independent of the codoped Tb3+ content. On the other hand, with codoping of Ce3+ in SrAl2B2O7：Tb3+ phase the fluorescent intensity was found to be enhanced by twice as much as that of SrAl2B2O7：Tb3+ phase. The observation has been rationalized with an efficient energy transfer mechanism from Ce3+ to Tb3+. In addition, the host compositional dependence of luminescence for (Sr1-xBax)Al2B2O7：Eu2+ phase indicated that the emission wavelength of Eu2+ exhibited blue shift with increasing Ba2+ dopant contents. We also found that with increasing Ba2+ content the hue of (Sr1-xBax)Al2B2O7：Eu2+ phosphors changed from blue to whitish.