First-order induced Raman scattering fromNi2+ions and cation vacancies in LiCl

Abstract

First-order induced Raman scattering has been observed from single crystals of LiCl containing ${\mathrm{Ni}}^{2+}$ ions. Sharp bands at 247, 216, 161, and 122 ${\mathrm{cm}}^{\ensuremath{-}1}$ are assigned to ${A}_{1g}$, ${T}_{2g}$, ${E}_{g}$, and ${T}_{2g}$ modes, respectively, on the basis of polarization measurements with 100> and 110> crystals. No differences were observed in the experimental peak positions, bandwidths, or relative intensities for crystals in which the ${\mathrm{Ni}}^{2+}$ concentration differed by a factor of 2. Theoretical calculations suggest that the ${A}_{1g}$ and the higher frequency ${T}_{2g}$ bands are due to vibrations about the ${\mathrm{Ni}}^{2+}$ ions, while the ${E}_{g}$ and possibly the lower-frequency ${T}_{2g}$ bands can be assigned to the local modes about the cation vacancies.