An analysis of the three-valence model of photorefraction

In this paper we present an analysis of the three-valence model of photoref raction. The basic equations of the model are studied and solved to find ze ro- and first-order solutions in the steady state, including expressions fo r the space-charge field and the effective trap density. The intensity depe ndence of the solutions for the population densities and space-charge field are analysed and discussed for varying proportions of the different valenc e states in the material, and the influence of some important material para meters considered. The possible applications of these results to the experi mental characterisation of three-valence-state materials are discussed and some comparisons are made between the three-valence and the two-independent -centre models of photorefraction.