高压下LiYF4晶体光学性质的第一性原理研究

本文采用第一性原理方法，在100 GPa的压力范围内, 计算了LiYF4理想晶体和含空位点缺陷晶体的光学性质.吸收谱数据表明，在100 GPa范围内，压力和相变因素的存在不会改变LiYF4晶体在250-1000 nm的波段内没有光吸收的事实. 氟、钇空位点缺陷的出现会使得LiYF4的吸收边蓝移，而锂空位点缺陷将导致它的吸收边微弱红移(但在250-1000 nm的波段内它仍不具有光吸收行为).波长在532 nm处的折射率数据显示, 在LiYF4的三个结构相区，其折射率均随压力的增加而增大. LiYF4从白钨矿结构到褐钇铌矿结构的相变会使得其折射率略微增加，但从褐钇铌矿结构到类黑钨矿结构的相变将导致其折射率显著降低. 同时，空位缺陷的存在将引起LiYF4的折射率明显增大. 分析指明，LiYF4有成为冲击窗口材料的可能. 本文所获得的信息对未来的实验研究有参考作用.

Optical properties of LiYF4 crystal under high pressure: a first principles study

The optical properties of LiYF4 crystal without and with vacancy defects within pressure 100 GPa were calculated using the first-principles method. The absorptive data suggest that pressures and structural transitions cannot alter the fact that there is no light absorption for LiYF4 at 250-1000 nm within pressure 100 GPa. The fluorous and yttric vacancy defects in LiYF4 causes a blue-shift in its absorption edge. The lithic vacancy defect in LiYF4 leads to a red-shift in its absorption edge (but there is still no light absorption in the 250-1000 nm region). The refractive-index data at 532 nm show that the refractive index in the three structural phase regions of LiYF4 increases with increasing pressure, and the scheelite to fergusonite structural transition in LiYF4 will slightly increase its refractive index, but the fergusonite to wolframite-like structural transition in LiYF4 will significantly reduce its refractive index. Meanwhile, the vacancy defect will cause its refractive index a significant increase. Our analysis indicates that LiYF4 is likely to be a shock window material, and the calculated results would provide some important information for further experimental study.