Who make transparent ZnO colorful? – Ion implantation and thermal annealing effects

ZnO has re-attracted considerable interest as a wide band gap semiconductor and energy material in recent years. When most of the near-band-edge exciton sharp lines in the ultraviolet spectral region have been firmly identified, defect origins of broad color emissions are still open to debate. By implanting Cu⁺ and Zn⁺ ions into high quality ZnO single crystal, respectively, and investigating their photoluminescence spectra at different temperatures, we firmly show that the structured green emission band is indeed associated with copper impurity. Incorporation of excess Zn ions into ZnO results in a structureless red emission band with a nearly perfect Gaussian lineshape. The pure electronic level locations of these two color emission bands were inclusively determined by using generalized multiple Brownian oscillator model when the simultaneous multiphonon emission was taken into account. The nature of the two colorful luminescent centers, including their charge states, was discussed with the aid of the latest theoretical results on different point defects and their optical transitions in ZnO.