相变及空位缺陷对SrF2在高压下光学性质的影响

本文采用第一性原理方法, 计算了SrF2的理想晶体和含锶、氟空位点缺陷晶体在100 GPa压力范围内的光学性质. 吸收谱数据表明, 压力因素引起的两个结构相变对SrF2的吸收谱均有影响: 第一个相变将导致其吸收边蓝移, 第二个相变将导致其吸收边红移. 空位点缺陷的存在将使得SrF2的吸收边红移, 其中氟空位点缺陷引起的红移行为更显著. 尽管如此, 这些红移并未使得SrF2晶体在可见光区出现光吸收的现象(是透明的). 波长在532 nm处的折射率数据指明, 在SrF2的三个结构相区, 其折射率均随压力的增加而增大, 且SrF2的高压结构相变也使得其折射率增大. 锶空位点缺陷将导致SrF2的折射率降低, 但氟空位点缺陷的存在对其基本没有影响. 分析表明, SrF2晶体有成为冲击窗口材料的可能.

Influences of phase transitions and vacancy defects on optical properties of SrF2 at high pressure

The optical properties of SrF2 crystal with and without and vacancy defects within pressure 100 GPa were calculated using the first-principles method. The absorption data show that the two pressure-induced structural transitions in SrF2 have influences on its absorption spectra: the first structural transition leads to a blue-shift of its absorption edge, and the second one results in its absorption edge a red-shift. The existence of vacancy point defects causes the red-shifts in the absorption edge, and the influence of the vacancy defect is more significant. However, all these red-shift behaviors do not give rise to its light absorption in the visible region. The refractive-index data at 532 nm show that, in its three structural phase regions, the refractive-index increases with increasing pressure. Moreover, the high-pressure structural transitions in SrF2 also result in an increase in its refractive index. The vacancy defect causes a reduction in its refractive index, but the influence of the vacancy defect is very little. Our analysis indicates that SrF2 crystal is likely to be a shock window material.