Mechanism of infrared stimulation and quenching in ZnS: Cu,Al Phosphors

To investigate the mechanism of the stimulation and quenching of the green luminescence in ZnS: Cu, Al phosphors by infrared (IR) light of 0.7–1.5 μm, stimulation and quenching spectra, IR effects on time-resolved emission spectra, and IR-induced photoconductivity are measured at 4.2 K, 77 K, and room temperature. Both the stimulation and quenching are caused by the IR transitions ascribed to excited copper acceptors. It is concluded that the stimulation is induced by the process in which holes produced by IR light migrate among copper acceptors, so that the statistical distribution of the intrapair separations of excited copper-aluminum pairs are changed to shorter distances. It is found that at low temperatures the holes migrate from one copper acceptor to another without being thermally released to the valence band. It is confirmed that the quenching is caused by the recombination of holes released to the valence band with electrons in the conduction band via some kind of nonradiative recombination centers.