EMPIRICAL ONE-ELECTRON MODEL OF OPTICAL-TRANSITIONS IN CU-DOPED ZNS AND CDS

Optical absorption and emission processes in the paradigmatic wide-gap II-VI compounds ZnS:Cu and CdS:Cu find an unconstrained interpretation in a plain strong-field model of light-induced electronic processes which depicts the charge states Cu2+(d9) and Cu+(d10), viz. their internal and charge transfer transitions. A variety of observed spectroscopic features between the UV and the IR regions are included, supplemented by some tentative assignments and/or predictions. Among the phenomena covered are the blue (B-Cu), green (G-Cu) and orange-red (R-Cu) emission bands of ZnS and their homologues in CdS. Novel near-infrared luminescence bands ih ZnS peaking near 7200 and 9200 cm-1 are tentatively assigned to radiative hole-recombination at a Cu acceptor state and to the t2(5)e-->t2(4)e4 internal transitions of Cu3+ (d8), respectively. Participation of a native donor turns out to be essential for some of the processes covered. Formation of deep-acceptor-bound excitons is demonstrated for several absorptive and emissive optical transitions.