Phonon‐assisted exciton annihilation in CdSe crystals

Emission spectra of exciton annihilation are measured in CdSe crystals from 2 to 77 °K. Especially the line‐shape, due to exciton annihilation with simultaneous creation of one or two phonons is considered. This shape can adequately be described on the basis of energy and momentum conservation laws only if the momentum dependence of the exciton‐phonon interaction probability is properly taken into account. As a result analytical expressions E 3/2 exp (– E/kT ) for the one‐phonon line and E 1/2 exp (– E/kT ) for the two‐phonon line, where E is the exciton kinetic energy, are obtained. An additional broadening of exciton emission lines, clearly observed at lower temperatures, is assigned to the inherent width of exciton levels.