Two characterization methods (photodepolarization spectroscopy and the voltage dependence of the transferred charge) have been used to study the energy depth of defect states in ZnS : Mn electroluminescent structures showing a hysteresis in the charge-voltage and luminance-voltage characteristics. The hysteresis effects are accompanied by the formation of self-organized patterns. We show that there is a correlation between the concentration and the energy depth of the defects in the film, on the one hand, and the hysteresis width as well as the patterns observed, on the other hand. The influence of defect states on the hysteresis and self-organization phenomena is discussed.