銪鏑共摻鋁酸鍶系長餘輝螢光體之溶膠/凝膠合成、雜質摻雜與其餘輝與熱發光特性之研究

Abstract

本研究以溶膠-凝膠法合成以銪、鏑或銪、釹共摻鋁酸鍶為主體之長餘輝螢光體，並藉硼或矽之添加以改善餘輝性質。本研究除了以X光繞射鑑定結晶相、微結構分析與熱分析做為材料特性研究外，並以光致發光與餘輝光譜、餘輝衰減量測及熱螢光分析等技術，探討材料中缺陷陷阱之束縛能及陷坑性質。 以溶膠凝膠法與固態反應法所分別合成之樣品比較顯示：前者材料結晶性較差且粒徑較小，由於兩者主體中銪離子晶場效應差異，造成前者餘輝發射波長短於後者。在組成效應探討方面，本研究改變不同Al/Sr比值，則發現當主體前驅物組成的Al/Sr比值＜1時，產物大都為Sr3Al2O6；當其組成中2＜Al/Sr＜3時，則形成SrAl2O4產物，若組成為9＜Al/Sr≦12時，則可製得含95%以上SrAl12O19結晶相的產物。在銪、鏑共摻且前驅物中Al/Sr組成不同的鋁酸鍶餘輝光譜中。SrAl2O4的含量為影響餘輝強度與持續時間的重要因素，主體中所含Sr3Al2O6則不利於餘輝時間；反之， SrAl12O19之共存則不影響餘輝持續時間。 添加硼或矽於鋁酸鍶磷光體中，除可增加晶格缺陷外，餘輝強度亦產生增強之效果，尤其以摻雜硼者餘輝強度及持續時間均較佳。硼摻雜鋁酸鍶磷光體具有優越的餘輝性質的主因，可能與非均勻分佈於材料表面能促進Eu2+還原並能提高陷阱深度的玻璃態硼酸鍶有關，硼之摻雜造成SrAl2O4:Eu,Dy產生餘輝雙峰光譜，此可能分別源自於不同性質陷阱的貢獻。 以熱螢光圖譜探討鋁酸鍶磷光體陷阱特性結果顯示：Dy3+ 之摻雜所誘導之電洞陷阱，須經氮氫混合氣高溫還原處理才會發揮作用，否則和未摻雜Dy3+之SrAl2O4:Eu2+的陷阱狀態相似。此外，本研究發現若以Nd3+代替Dy3+做為輔助活化劑，則SrAl2O4:Eu, Nd亦有長餘輝性，但 Nd3+之摻雜僅提昇餘輝強度，但未增加陷阱之深度，故其陷阱性質與未摻雜輔助活化劑之SrAl2O4:Eu2+相近。 以The effect of impurity doping, photoluminescent, afterglow, and thermoluminescent properties and for long phosphorescent SrAl2O4:Eu2+, Dy3+ (SAED) and some analogous phosphors derived from a sol-gel synthetic route have been investigated. The improvement on phosphorescence intensity and the lengthening of afterglow persistent time has been observed in the SAED phases with the addition of boron or silicon. In order to investigate the photoluminescence, afterglow, defects and the depth energy of the traps, we have measured the X-ray diffraction (XRD) profiles, SEM and DTA/TGA, photoluminescence (PL), afterglow (AG) and thermoluminescence (TL) spectra to characterize the microstructure and luminescent properties that are relevant to the nature of defects present in long afterglow SAED phases. The SAED phases derived from sol-gel route exhibit smaller grain size and poorer crystallinity, as compared to those synthesized by solid-state method. The wavelength of afterglow (lAG) for SAED derived from sol-gel processes was found to be shorter than lAG for those prepared via solid-state route, which was attributed to difference in host crystal field strength for Eu2+. The effect of host compositions on the PL and AG spectra of SAED phases has also been investigated for samples prepared from starting host precursors with different Al/Sr compositions. We found that Sr3Al2O6 dominated in strontium aluminate with the host precursors with Al/Sr < 1; SrAl2O4 was observed in those with 2 < Al/Sr < 3; however, more than 95% of SrAl12O19 was discovered in those with 9 < Al/Sr ≦12. The amount of SrAl2O4 present in the host with various Al/Sr ratios was found to be critical in the determining the afterglow intensity and the afterglow persistent time, as indicated by the AG curves for SAED phases. The coexistence of SrAl12O19 in the SAED host was found to affect the afterglow duration, whereas that of the Sr3Al2O6 phase was found to be independent of the afterglow persistence. The effect of boron and silicon doping in the SAED phosphors was found to not only increase the crystal defects but also enhance the afterglow intensity. The boron-doped SAED (BSAED) sample was observed to exhibit stronger phosphorescence intensity and longer afterglow duration. This observation can be attributed to the non-homogeneous distribution of glassy strontium borates that promotes the reduction of Eu2+ and increases the trap depth energy, as indicated by surface microstructure analysis of BSAED. The twin peaks observed in the afterglow curves for BSAED phases could probably be attributed to two different traps with different depth energies, as compared to one singlet emission observed in the PL spectra. The hole trapping effect due to Dy3+ codoping in SrAl2O4:Eu2+,Dy3+ phase can be effective only when the samples were reduced under a reducing H2/N2 atmosphere at 1,300℃, as indicated by the TL curve analysis. Otherwise, shallow traps will form as that found in SrAl2O4:Eu2+. In addition, the codoping of Nd3+ coactivator in the SrAl2O4:Eu2+,Nd3+ phase indicated that the Nd3+-doping only increases the afterglow intensity, but doesn’t increase the trap depth, which is similar to the shallow traps present in the SrAl2O4:Eu2+ phase. Based on the experimental Hoogenstraaten’s plots, the calculated trap depth energy was found to be 0.57–0.76 eV, 0.43 eV, and 0.18 eV for SrAl2O4:Eu2+0.05,Dy3+0.05,B0.3, SrAl2O4: Eu2+0.05, Dy3+0.05, and SrAl2O4:Eu2+0.05, respectively, as compared to 0.59 – 0.72 eV for BG-300M.manufactured by Nemoto Co. These results indicate the similarity of nature of the trap levels for all strontium aluminate phosphors described in this research. 計算所得SrAl2O4:Eu2+0.05,Dy3+0.05,B0.3、SrAl2O4:Eu2+0.05,Dy3+0.05與SrAl2O4:Eu2+0.05等長餘輝螢光體之陷坑阱深能分別為：0.57~ 0.76eV、0.43eV及 0.18eV，此項結果與日本根本化學所產製BG300M之阱深能 0.59~0.72eV比較，十分相近，證明此類物質陷坑本質之相似性。

The effect of impurity doping, photoluminescent, afterglow, and thermoluminescent properties and for long phosphorescent SrAl2O4:Eu2+, Dy3+ (SAED) and some analogous phosphors derived from a sol-gel synthetic route have been investigated. The improvement on phosphorescence intensity and the lengthening of afterglow persistent time has been observed in the SAED phases with the addition of boron or silicon. In order to investigate the photoluminescence, afterglow, defects and the depth energy of the traps, we have measured the X-ray diffraction (XRD) profiles, SEM and DTA/TGA, photoluminescence (PL), afterglow (AG) and thermoluminescence (TL) spectra to characterize the microstructure and luminescent properties that are relevant to the nature of defects present in long afterglow SAED phases. The SAED phases derived from sol-gel route exhibit smaller grain size and poorer crystallinity, as compared to those synthesized by solid-state method. The wavelength of afterglow (lAG) for SAED derived from sol-gel processes was found to be shorter than lAG for those prepared via solid-state route, which was attributed to difference in host crystal field strength for Eu2+. The effect of host compositions on the PL and AG spectra of SAED phases has also been investigated for samples prepared from starting host precursors with different Al/Sr compositions. We found that Sr3Al2O6 dominated in strontium aluminate with the host precursors with Al/Sr < 1; SrAl2O4 was observed in those with 2 < Al/Sr < 3; however, more than 95% of SrAl12O19 was discovered in those with 9 < Al/Sr ≦12. The amount of SrAl2O4 present in the host with various Al/Sr ratios was found to be critical in the determining the afterglow intensity and the afterglow persistent time, as indicated by the AG curves for SAED phases. The coexistence of SrAl12O19 in the SAED host was found to affect the afterglow duration, whereas that of the Sr3Al2O6 phase was found to be independent of the afterglow persistence. The effect of boron and silicon doping in the SAED phosphors was found to not only increase the crystal defects but also enhance the afterglow intensity. The boron-doped SAED (BSAED) sample was observed to exhibit stronger phosphorescence intensity and longer afterglow duration. This observation can be attributed to the non-homogeneous distribution of glassy strontium borates that promotes the reduction of Eu2+ and increases the trap depth energy, as indicated by surface microstructure analysis of BSAED. The twin peaks observed in the afterglow curves for BSAED phases could probably be attributed to two different traps with different depth energies, as compared to one singlet emission observed in the PL spectra. The hole trapping effect due to Dy3+ codoping in SrAl2O4:Eu2+,Dy3+ phase can be effective only when the samples were reduced under a reducing H2/N2 atmosphere at 1,300℃, as indicated by the TL curve analysis. Otherwise, shallow traps will form as that found in SrAl2O4:Eu2+. In addition, the codoping of Nd3+ coactivator in the SrAl2O4:Eu2+,Nd3+ phase indicated that the Nd3+-doping only increases the afterglow intensity, but doesn’t increase the trap depth, which is similar to the shallow traps present in the SrAl2O4:Eu2+ phase. Based on the experimental Hoogenstraaten’s plots, the calculated trap depth energy was found to be 0.57–0.76 eV, 0.43 eV, and 0.18 eV for SrAl2O4:Eu2+0.05,Dy3+0.05,B0.3, SrAl2O4: Eu2+0.05, Dy3+0.05, and SrAl2O4:Eu2+0.05, respectively, as compared to 0.59 – 0.72 eV for BG-300M.manufactured by Nemoto Co. These results indicate the similarity of nature of the trap levels for all strontium aluminate phosphors described in this research.