Formation of Cu-related emission centers under thermal doping of ZnS powders with CuCl and CuCl2

The photoluminescence (PL), PL excitation and electron paramagnetic resonance spectra of powderlike ZnS doped with Cu from CuCl and CuCl2 compounds at 800 °C with restricted access of atmospheric air or in He flow were investigated. It is shown that the contribution of blue and green PL bands to PL spectra depends on the compounds used for doping and on the annealing conditions. The appearance of Cu clusters on the surface of ZnS microcrystals for both doping compounds is found. These clusters manifest themselves in the presence of broad line in electron paramagnetic resonance spectra and are the additional source for the doping of ZnS powder. The chemical reactions upon doping are analyzed. It is shown that these reactions control the concentration of the recombination centers responsible for blue and green PL bands and are also the reason of Cu clusters appearance. Under annealing in He flow when volatile components are removed by flowing gas, the dominant process can be the doping of ZnS from Cu clusters. This allows obtaining the blue band mainly. The localization of recombination centers responsible for blue and green emissions is discussed.