Photoluminescence in semiconductor quantum dots: Enhanced probablities of phonon-assisted transitions

A theory of photoluminescence in semiconductor quantum dots is developed which takes into account non-adiabaticity of the exciton-phonon system. The role of non-adiabaticity is shown to be of paramount importance in spherical quantum dots, where the lowest one-exciton state can be degenerate or quasi-degenerate. In quantum dots of lower symmetry, the effects of non-adiabaticity reveal themselves mainly due to the phonon-induced mixing of states, which belong to different energy levels. We show that the proposed non-adiabatic treatment of phonon-assisted optical transitions can provide an explanation for the remarkably high intensities of phonon satellites observed in the photoluminescence spectra of various quantum-dot structures.