Unambiguous identification of the role of a single Cu atom in the ZnO structured green band

High quality and purity single crystal ZnO samples doped with single isotopes of 63Cu and 65Cu, with equal concentrations of both these isotopes, and with natural Cu using a wet chemical atomic substitution reaction and anneal were studied using low temperature optical spectroscopy. Our data on the zero phonon line of the structured green band in ZnO confirm unambiguously the involvement of a single Cu atom in this defect emission. These data allow us to confirm the main features of the assignment proposed by Dingle in 1969 and to comment further on the defect structure. (paper)