Two state model for sub-exponential fluorescence revisited

A two-state model for the stretched exponential law found in the asymptotic decay of the fluorescence is generalized. By assuming a modification of the Arrhenius law for the detrapping process we find that the exponent characterizing the stretched exponential decay, β, exhibits a number of different behaviors, in qualitative agreement with some recent experimental results. The microscopic origin of these modified Arrhenius-type laws is considered. It is shown that multiphonon absorption can lead to a β which is a decreasing function of temperature, as found experimentally.