Pressure induced Raman and fluorescence singularities in $LiYF_4$

TL;DR

This study investigates how pressure affects the Raman and fluorescence properties of $LiYF_4$, revealing multiple phase transitions and irreversible changes at high pressures, with implications for understanding its structural behavior under extreme conditions.

Contribution

It provides detailed experimental evidence of pressure-induced singularities and phase transitions in $LiYF_4$ using Raman and fluorescence spectroscopy up to 40 GPa.

Findings

Identified three Raman singularities at 6, 10-12, and 16-17 GPa.

Observed irreversible phase change at 23 GPa.

High-pressure spectra show broad bands indicating amorphization.

Abstract

The pressure effect on the fluoride scheelite laser host $LiYF_4$ is studied at room temperature up to 26 GPa by Raman scattering and up to 40 GPa by $P^{3+}$ fluorescence of doped sample. The Raman spectra exhibit three singularities at the vicinity of 6 GPa, 10-12 GPa and 16-17 GPa. The samples pressurized to 21 GPa or higher do not recover the original phase after being released, giving more Raman lines than original samples. The luminescence spectra of $P^{3+}$ are collected in the energy range corresponding to following transitions $^3P_{0,1}--^3H_{4,5,6}$, $^1D_2--^3H_4$ and $^3P_0--^3F_2$. Singularities are observed in the vicinity of 6 GPa, 10 GPa, 16 GPa, 23 GPa in agreement with the Raman study. Moreover, an irreversible transition occurs at 23 GPa. The samples pressurized to above 26 GPa become amorphous when released and all the sharp lines disappear. Above 31 GPa, the spectra at high pressures show only some broad bands corresponding to transitions between two multiplets of the $^4F_2$ configuration of $Pr^{3+}$. These singularities suggest possible phase transformations leading to lowering of the lattice symmetry.