  A distribution function for localized carriers,
$f(E,T)=\frac{1}{e^{(E-E_a)/k_BT}+\tau_{tr}/\tau_r}$, is proposed by solving a
rate equation, in which, electrical carriers' generation, thermal escape,
recapture and radiative recombination are taken into account. Based on this
distribution function, a model is developed for luminescence from localized
state ensemble with a Gaussian-type density of states. The model reproduces
quantitatively all the anomalous temperature behaviors of localized state
luminescence. It reduces to the well-known band-tail and luminescence quenching
models under certain approximations.
