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

► Optical decay of free 2D excitons is induced by exciton-acoustic phonon interaction. ► Exciton radiative lifetime is found as a function of effective temperature T. ► There is a characteristic T⁎ at which the lifetime is minimal. ► The lifetime is linear over T at T>T⁎ that fits known experiments. ► At T