Exciton—LO-Phonon Interaction and the Anti-Stokes Emission Line in CdS

Abstract

Phonon interaction with the $I_1$ (4888-Å) emission line in CdS (exciton bound to a neutral acceptor site) has often been observed. For the first time the optical frequency anti-Stokes transition, involving the collapse of a bound exciton, has been observed in the emission from selected platelets at 1.2°K. Since the thermally excited phonon field at this temperature is negligible, the observation of anti-Stokes emission directly supports the conclusion that LO phonons are generated to a nonthermal level of distribution as the excitons decay.