掺铌钨酸铅晶体缺陷的理论研究

Theoretical Study on Defects of Nb^(5+)∶PbWO_4 Crystal

采用基于相对论性密度泛函理论的离散变分和嵌入团簇方法计算了PbWO4∶Nb晶体中Nb缺陷态的态密度分布和能量 ,并运用过渡态方法计算了其激发能。通过计算掺Nb缺陷态电子态密度分布 ,发现与VO 相关的F+ 心是晶体掺Nb的主要补偿机制。 (NbO3 +F+ ) 2 -缺陷在掺铌钨酸铅晶体各相关缺陷形式中存在所需能量最低。计算结果表明VO 有关的F+ 的存在是有效消除晶体中 35 0nm吸收的主要原因。而F+ →W5d轨道的跃迁能量为 2 .8eV ,对应晶体中 4 2 0nm吸收。

The electronic structure and crystal energy of defects related to Nb 5+ dopants in lead tungstate crystals (PbWO 4) were investigated by the relativistic self-consistent discrete variational embedded cluster method.The excitated energy was calculated by the transition state method.We focused on the density of states associated with Nb 5+ related defects.It is found that the F + center is mainly charge compensatory form in PbWO 4∶Nb crystal.The results show that (NbO 3+F +) 2- is more stable than the other Nb 5+ related defects.In addition,the calculation results show that the exist of F + center related to V O vacancy results in the diminution of the absorption at 350nm.The transition state energy of F +→W 5d is about 2.8eV. This signifies that Nb doped crystal can't banish the absorption at 420nm.