Electroluminescence Emission Spectra of ZnS Single Crystals

According to the Sch5n-Klasens model (1, 2) for the luminescence centers in Cu-activated zinc sul-fide, the "blue " and "green " emission bands are due to recombination at two different hole-traps, the "blue " and "green " centers. Electroluminescence (EL) excitation is usually interpreted in the frame-work of this model by impact-ionization of the luminescence centers with accelerated conduction-band electrons (3). In recent papers objections were raised both to the SchSn-Klasens model and to the impact-ioni-zation theory of EL excitation (4-6). As a contribu-tion to this discussion, experiments on the voltage dependence of the EL emission spectra of ZnS are reported here