First-principles electronic structure of Cu+ luminescence centers in Cu-doped ZnS

The electronic structures of various Cu+ luminescence centers in wurtzite ZnS are studied by using first-principles linear muffin-tin-orbital method combining atomic sphere approximation. The results for ZnS:Cu:CI and ZnS:Cu:Al show that Cu acceptor states are anomalously deep (beyond 2.7 eV above the top of valence band) and located near the bottom of conduction band in these two cases. On the other hand, the results for ZnS:Cu with sulfur vacancies manifest that the Cu+ center is an associated center, whose Cu d-like states are situated above the top of valence band.