Polarized Raman spectra of silver halide crystals

Abstract

Second-order Raman spectra of AgCl and AgBr single crystals have been measured at 77 K. By using oriented crystals and different polarizations of the incident and scattered light the separate contributions of ${\Gamma }_1$, ${\Gamma }_{12}$, and ${\Gamma }_{{25}^{\prime }}$ symmetries are determined for the first time in these materials. These data are compared with calculated two-phonon dispersion curves. A few van Hove singularities are identified and the relative contribution of different branches inferred. The longitudinal-optic-phonon-overtone (2LO) peak shows significant quasiresonant enhancement for the argon-laser lines used.