Contributions of Scattering of Polaritons by Phonons to Emission of Radiation by Solids

A brief discussion of the coupled exciton-photon (polariton) fields is given. Probabilities per unit time associated with the scattering of polaritons by acoustical and optical phonons are calculated to terms of first order in the exciton-phonon interaction. Results applicable to cadmium sulfide at 77°K are obtained. Two phonon-assisted emission bands are found. One is positioned approximately one longitudinal optical (LO) phonon below the exciton-photon resonance energy $E_A$, and is due to the inelastic scattering of polaritons above the knee of the lowest-lying polariton branch to states below the knee with the simultaneous creation of LO phonons. The second band is positioned very close to $E_A$ and is also due primarily to LO-phonon scattering.