A 1-D model of the photoluminescent decay of ZnS phosphors as a function of excitation conditions

We present measurements of the time-resolved photoluminescence of ZnS:Cu,Al that demonstrate how the lifetime and form of the strongly non-exponential decay depend on excitation conditions, such as pulse width and amplitude. To give some insight into the experimental observations we propose a phenomenological, correlated state model intended to describe aspects of the relaxation behavior of acceptor–donor luminescent materials. A comparison of simulation and experiment show that this simple model successfully describes many of our observations, such as a crossover from stretched exponential to power-law decay, and lifetimes that depend strongly on the excitation pulse width and amplitude. These effects are shown to be due to the development of spatial correlations between the electrons and holes. These correlations develop both during emission and continuous excitation.