On the radiative lifetime of free-moving two-dimensional excitons

A simple microscopic mechanism explaining the linear dependence of the radiative lifetime of free-moving two-dimensional excitons on their effective temperature is suggested. It is shown that there exists a characteristic effective temperature (of about few Kelvin) defined by the exciton-acoustic phonon interaction at which the radiative lifetime is minimal. Below this temperature the lifetime starts to increase with decreasing temperature. The correspondence with previous theoretical and experimental results is discussed.