Pressure-induced changes in Cr3+-doped elpasolites and LiCaAlF6: Interpretation of macroscopic data

In the research of pressure effects on Cr3+-doped insulating lattices, it is crucial to understand the dependence of the 10Dq parameter on the sample volume, V. This problem is explored in the present work through ab initio calculations on Cr3+-doped K2NaScF6, Cs2NaYCl6, and Cs2NaYBr6 elpasolite lattices as a function of pressure in the 0–5 GPa range. From the calculated values of the lattice parameter and the Cr3+-X− (X=F, Cl, and Br) distance, R, it is found that R varies with the cell volume, vc, as vc(1/3β) where β lies around 2.6. These results allow one to understand quantitatively the 10Dq dependence on V−m/3 for LiCaAlF6:Cr3+ where the measured exponent m=2.3 is seemingly anomalous when compared to the values found for ruby (m=4.5) or NiO (m=5).