Indirect‐Forbidden Exciton Transitions in AgBr

Abstract

Abstract Observation of low temperature resonant Raman scattering in AgBr involving the TA(L) momentum‐conserving phonon for the first time, allows symmetry‐forbidden indirect exciton transitions to be studied in silver halides. From analyzing the energy dependence of scattered intensity, in terms of impurity trapping and intra‐ and intervalley exciton scattering, relative scattering probabilities are determined for these relaxation processes. The exciton‐TA(L)‐phonon matrix element obtained with respect to that for the allowed TO(L) process is 5.5 × 10 −3 (meV) −1 . Taking into account the TA(L)‐assisted component, from a lineshape analysis of the indirect exciton edge a value of 28 meV is derived for the Is exciton binding energy.