ODMR investigations of IR photoluminescence in ZnS:Cu

The results of ODMR measurements are presented for IR emissions of copper doped ZnS. An analysis of these experiments enables the authors to interpret the nature of the PL processes observed. In particular, it has been found that the same copper centres are active in the IR as in the visible regions of the PL. This is due to the possibility of two recombination channels; the direct process (visible PL) and the indirect (IRPL), two-step process, via the excited states of these centres. All experimental results are interpreted within the framework of a simple two-dimensional configuration coordinate model. The role of iron impurities as 'killers' of the visible PL in ZnS and as radiative centres in the IR is also discussed.