第一性原理铽掺杂钙钛矿型钆铝酸盐的电子结构计算

The Electronic Structures of Tb-doped Gadolinium Aluminate Perovskite by First-principles Calculation

基于局域密度近似(LSDA,Local spin-density approximation)和有效库仑相关能(U approach),采用第一性原理计算软件VASP,计算了钙钛矿型钆铝酸盐(GdAlO3,GAP)电子结构,并研究了铽离子(Tb3+)掺杂后(GdAlO3∶Tb,GAP∶Tb)对能带带隙(Eg,Energy of gap)的影响。计算结果表明:GAP为直接带隙半导体,带隙宽度主要由价带(VB,Valence band)顶部的O-2p和导带(CB,conduction band)底部Al-3(s+p)、Gd-(s+d)(p)决定,Eg值为4.8eV;随着Tb3+的掺入,当掺入量为1/4原子比时(GAP∶Tb0.25)出现杂质能级,为3eV、2.3eV,分别对应Tb3+的5 D3-7FJ(J=3,4,5,6)电子跃迁和5 D4-7FJ(J=3,4,5,6)电子跃迁。当掺入量为1/16时(GAP∶Tb0.0625),仅杂质能级2.3eV较为明显,这一计算结果与GAP∶Tb0.7荧光粉在紫外激发下绿色荧光发射明显这一实验现象相符合(荧光发射主峰对应5 D4→7F5(544nm))。

The electronic structures of gadolinium aluminate perovskite（GdAlO3,GAP）and Tb-doped gadolinium aluminate perovskite（GdAlO3∶Tb,GAP∶Tb）have been calculated in this paper by local spin-density approximation（LSDA）and U approach,with VASP software.The Tb3＋doping influence on the energy of gap（Eg）was also discussed.The first principle calculation results show：GAP is a direct semiconductor,and Egis 4.8eV,the gap is consisted by O-2p at the top of the valence band（VB）and Al-3（s＋p）,Gd-（s＋d）（p）at the bottom of conductor band（CB）.When Tb3＋substituting into GAP by 1/4atomic ratio,the added energy levels are 3eV,2.3eV,correspond to Tb3＋5 D3-7FJ（J=3,4,5,6）and5 D4-7FJ（J=3,4,5,6）.While Tb3＋substituting by 1/16 atomic ratio,the added energy level 2.3eV is more obviously,which is coherent to GAP∶Tb phosphor green emission under UV excitation（The strongest peak of green emission is 554 nm,correspond to Tb3＋5 D4→7F5）.