新穎真空紫外光激發螢光體合成與發光特性之研究

Abstract

本研究利用高溫固態反應法成功合成A: Tb3+、B: Tb3+、C: Tb3+、D: Tb3+、E: Eu2+ 與F: Eu2+等六系列螢光體。我們利用X-ray粉末繞射和掃描式電子顯微鏡來進行晶相分析與結構鑑定，並且使用國家同步輻射中心所提供之真空紫外光光源(波長短於200 nm)以探討各系列螢光體於紫外-可見光波段的發光現象和能量轉移機制，以期可開發新穎真空紫外激發螢光材料，並評估其應用價值。 B: Tb3+、C: Tb3+和D: Tb3+等三系列螢光體之主體以172 nm波長真空紫外光激發皆可得到高強度的綠光放射，其分別源自於Tb3+的5D4→7F5躍遷之窄帶發射，此三種主體中因皆含有磷酸根PO43-或硼酸根BO33-等陰離子團，因此在真空紫外光激發下表現良好的吸收度。此外，主體與Tb3+的吸收峰有所重疊，造成其兩者間的能量傳遞效率增加，進而提高發光效率。此外，A: Tb3+亦為綠光螢光體，但其主體之吸收度較差，因此放光強度較弱。 而Eu2+所摻雜E: Eu2+和F: Eu2+之發光主要源自4f65d1→4f7之發射躍遷，兩者皆為寬帶放射綠光螢光體，但因主體於真空紫外光之吸收度較差或因主體與Eu2+活化劑間能量傳遞效率低，因此降低了螢光體發光強度。 觀察上述六種螢光體之微結構，其中D:Tb3+之表面形貌呈現最為平滑，且粒徑大小分布最為均勻，此與其高發光強度與輝度有密切關係，經評估發現可與商品匹敵。

By using solid-state reactions we have successfully synthesized six series of phosphors for vacuum ultraviolet (VUV) excitation with chemical compositions of A: Tb3+, B: Tb3+, C: Tb3+, D: Tb3+, E: Eu2+ and F: Eu2+. X-ray diffraction and electron microscopy were used to carry out phase identification and microstructure characterizations of the phosphors, respectively. Most importantly, the VUV light source (wavelength < 200 nm) and research facilities used to investigate the photoluminescence (PL) spectra, energy transfer mechanism and application evaluation of VUV phosphors are provided by National Synchrotron Radiation Research Center (NSRRC). The optimal excitation wavelength used to pump the B: Tb3+, C: Tb3+and D: Tb3+ phosphors to generate strong but narrow yellowish-green luminescence, attributed to 5D4→7F5 transition of Tb3+, has been found to be 172 nm. These observations can be rationalized by the presence of PO43- or BO33- anionic groups in the host that generally show strong absorption in the VUV range. In addition, the enhanced luminescence intensity can also be attributed to the overlapping of absorption peaks between host and Tb3+ that is considered to improve the energy transfer efficiency from the host to the activator. However, the green-emitting VUV phosphor A: Tb3+ was found to exhibit weaker luminescence, which was attributed to poor VUV absorption of the host matrix. Furthermore, the broad green luminescence observed in both E: Eu2+ and F: Eu2+ is attributed to the emissive 4f65d1→4f7 transition. However, the observed reduced PL intensity has been attributed to the poor host absorption of VUV radiation and/or the low efficiency of energy transfer between host and the Eu2+ activator. Based on the analysis on the microstructure of the six series of VUV phosphors, we found that, among the phosphors investigated, D: Tb3+ shows the smoothest surface morphology, the most homogeneous grain size distribution and the strongest PL intensity and relative brightness that were found to be comparable with those of commodity phosphors.