新穎供真空紫外光激發螢光體製備與發光特性之研究

Abstract

本論文利用固態合成法於氫氣的還原氣氛下，成功合成了YBa3(BO3)3:Tb3+、Ca5Al6O14:Eu2+、MCaPO4:Eu2+ (M = Na, K)、Li4SrCa(SiO4)2:Eu2+與LiZnBO3:Mn2+等五系列螢光體，並利用X光粉末繞射及掃描式電子顯微鏡進行結構鑑定及晶相分析，並使用國家同步輻射研究中心所提供的真空紫外光光源，以探討各螢光體於波長147 nm及172 nm的激發下，其所表現的發光特性和能量轉移機制，試圖開發新穎且應用於電漿平面顯示器的螢光材料。 YBa3(BO3)3:Tb3+為源自於Tb3+的5D4→7F5躍遷的窄峰放射，放射波長為543 nm。此系列中，主體因含有硼酸根BO33-陰離子團，因此可以有效吸收真空紫外光光源，並且與活化劑之間表現了良好的能量傳遞現象。 Ca5Al6O14:Eu2+、NaCaPO4:Eu2+、KCaPO4:Eu2+及Li4SrCa(SiO4)2:Eu2+等螢光體皆來自Eu2+的4f65d1→4f7躍遷之寬帶放射，放射波長隨主體及結晶場環境而不同。其中，研究發現Ca5Al6O14:Eu2+主體對真空紫外光源的吸收度相當良好，但由於晶格中過短的Ca-Ca距離，使得濃度淬滅效應特別顯著。而KCaPO4:Eu2+及Li4SrCa(SiO4)2:Eu2+的主體於真空紫外光的吸收度較低或因主體與活化劑之間能量傳遞效率低，因此降低了螢光體發光強度。 LiZnBO3:Mn2+之發光也為寬帶放射，但由於主體吸收光源的效率低，且Mn2+的激發為d-d躍遷，因此發光強度較(Y,Gd)BO3:Eu3+商品為弱。

The thesis attempts to investigate novel phosphors for the application in Plasma Display Panel. The novel vacuum ultraviolet (VUV) excited phosphors with chemical compositions of YBa3(BO3)3:Tb3+, Ca5Al6O14:Eu2+, NaCaPO4:Eu2+, KCaPO4:Eu2+, Li4SrCa(SiO4)2:Eu2+ and LiZnBO3:Mn2+ were successfully synthesized by solid state method. X-ray diffraction and electron microscopy were used to verify the phase purity, respectively. By using synchrotron radiation as a light source, photoluminescence spectra were used to study the luminescence performance and energy transfer mechanism of the phosphors. We found under 172 nm excitation, YBa3(BO3)3:Tb3+ phosphors showed a intense and sharp yellowish-green emission at 543 nm corresponding to the electric dipole 5D4 →7F5 transition of Tb3+. The observation can be rationalized by the presence of BO33- anionic group in the host that generally shows strong absorption in the VUV region. In addition, such good energy transfer efficiency is observed from host to activator Tb3+. Ca5Al6O14:Eu2+, NaCaPO4:Eu2+, KCaPO4:Eu2+ and Li4SrCa(SiO4)2:Eu2+ phosphors showed the broad emission due to the well-known transitions between the ground state 4f7 and the crystal-field split 4f65d configuration, which is strongly affected by the environments surrounding Eu2+ ions. It is found that the host of Ca5Al6O14:Eu2+ absorbed the excitation energy efficiently, but the unusual short Ca-Ca distances lead to significant fluorescence quenching. Furthermore, the observed reduced PL intensity of KCaPO4:Eu2+ and Li4SrCa(SiO4)2:Eu2+ may correspond to the poor host absorption of VUV radiation and/or the low efficiency of energy transfer between host and Eu2+. The spectroscopic results of LiZnBO3:Mn2+ red phosphor also showed the broad emission with lower intensity, which affiliated with the 3d–3d forbidden transitions of Mn2+.