利用同步輻射光源探討非氟化物量子剪裁螢光體之發光特性與機制

Abstract

量子剪裁係指螢光體吸收一真空紫外光光子後，將其能量分割為兩可見光光子能量的過程，在無汞照明與電漿平面顯示器(PDP)領域，可藉由發光效率之提升，改善其低能量轉換效率之缺失，故極具應用潛力。近十年來，一些具有可見光量子剪裁特性的氟化物螢光體已被開發，但因合成不易且化學穩定性，導致發展受限制；因此本論文針對具有可見光量子剪裁的非傳統氟化物的稀土金屬磷酸鹽與稀土金屬氧化物，進行合成、發光及螢光衰減特性之探討。 本論文中所有光譜的量測皆使用國家同步輻射研究中心的真空紫外光源設備，探討包括：放射綠光的GdPO4:Tb3+、KCaGd(PO4)2:Tb3+；以及放射紅光的Gd¬3Ga5O12:Eu3+、Gd¬3Al5O12:Eu3+、Y¬3Al5O12:Gd3+，Eu3+共五種非氟化物的螢光粉。利用螢光放射(PL)、螢光激發光譜(PLE)以及瞬態螢光衰減曲線等的量測結果確立Tb3+-Tb3+及Eu3+-Eu3+能量傳遞及量子剪裁的模型；此外，本論文也分析了溫度與活化劑摻雜濃度等變因，對於螢光粉之量子剪裁及發光特性的影響。

Quantum cutting (QC), a new route to highly efficient luminescence via downconversion processes, refers to a phenomenon, in which more than one visible photon emit for each vacuum ultraviolet (VUV) photon absorbed. This phenomenon is potentially useful in improving the luminescence efficiency of phosphors for mercury-free lighting and plasma display panel (PDP). Over the last decade, there have been numerous fluoride and some oxide phosphors investigated to exhibit QC behavior. However, fluoride phosphors tend to exhibit poor chemical stability, which limits their applications and, therefore, developing non-fluoride QC phosphors appears to be imminent. In this work, by using synchrotron radiation as a light source, we have discovered and investigated and several unconventional non-fluoride quantum-cutting phosphors, such as GdPO4:Tb3+ , KCaGd(PO4)2:Tb3+, Y3Al5O12:Gd3+,Eu3+ ,Gd3Al5O12:Eu3+ and Gd3Ga5O12:Eu3+. Based on the analysis of the experimental photoluminescence (PL), PL excitation (PLE) and transient luminescence spectra, We have also proposed plausible mechanisms and energy level diagrams involving Tb3+-Tb3+ or Eu3+-Eu3+ energy transfer model to rationalize the observed QC processes. Furthermore, this work discuessed with the dependence of the efficiency on the temperature and dopant concentration .