变价元素铋掺杂钨酸铅晶体辐照损伤的研究

Study on Irradiation Damage of Bi-Doped PbWO_4 Crystal

采用剂量为 4Mrad的γ射线辐照Bridgman法生长的未掺杂和掺铋钨酸铅晶体 ,研究了辐照前后晶体的透射光谱、X射线激发发射光谱 (XSL)的变化 .利用正电子湮没寿命谱 (PAT)和X光电子能谱 (XPS)的实验手段 ,对钨酸铅晶体辐照前后的微观缺陷进行了研究 ,并对其抗辐照损伤性能及微观机理进行了初步探讨 .研究表明 ,铋掺杂使得晶体中的正电子捕获中心和低价氧浓度下降 ;辐照后 ,未掺杂晶体中正电子捕获中心浓度下降 ,低价氧浓度上升 ,掺铋晶体则出现了与之完全相反的情况 ,正电子捕获中心浓度上升 ,低价氧浓度下降 .提出掺铋钨酸铅晶体中铋的掺杂辐照前主要以Bi3+占据VPb的形式存在 ,辐照使变价元素铋发生Bi3+→Bi5+的变价行为 ,Bi5+可以替代W6+格位并使得晶体内部分 (WO4 ) 2 -根团形成 (BiO3+Vo) -.

The luminescence and point defects of pure lead tungstate crystals (PbWO 4) and Bismuth (Bi) doping crystal (PbWO 4:Bi)grown by modified Bridgman method are studied. It is found that irradiation results in the great change of the transmission and X-ray excited emission after γ-ray irradiation about 4 Mrad dose. The defects in PbWO 4 crystal have been studied by means of positron annihilation lifetime and X-ray photoelectron spectra. The results show that Bi dopant suppresses the concentrations of positron capture centers and low-valent oxygen ions.After γ-ray irradiation,in the pure crystal the concentration of lead vacancy (V Pb) is decreased and that of low-valent oxygen increased; on the contrary,in Bi dopant crystal the concentrations of positron capture centers increased and that of low-valent oxygen ions suppressed. It is tentatively proposed that Bi 3+ dopants would mainly occupy the sites of lead vacancies resulted from Pb volatilization. And irradiation changes the chemical valence of Bi element,which is Bi 3+→Bi 5+.The Bi 5+ will replace the lattice W 6+ ions and it will cause some (WO 4) 2- replaced by (BiO 3+V O) -.