Luminescent transitions at divalent copper impurities in ZnO give rise to a close-spaced, no-phonon doublet at ∼2.8590 eV, as well as a broad multiphonon side band. The transition is found to be an optical charge transfer between a highly shielded localized level of the copper impurity and a level which is strongly perturbed by the valence-band states of the crystal. The analysis provides information about the role of deep acceptor states in electronic processes in covalent solids.

• Received 25 July 1969

DOI:https://doi.org/10.1103/PhysRevLett.23.579