Investigation of photoluminescence mechanisms of ZnO through experimental and first-principles calculation methods

The photoluminescence properties of ZnO were investigated experimentally and by a first-principles method. Thermal treatment of ZnO in various atmospheres provides insight into the ultraviolet (UV) and green emission mechanisms. These mechanisms were investigated in detail from the thermal quenching behavior of the emission spectra of ZnO. The negative thermal quenching of the green emission could be fitted exactly with a model equation based on the assumption that UV emission loss by thermal quenching affects green emission. The electronic states of ZnO clusters with and without an oxygen vacancy were calculated by first-principles calculations using the discrete variational (DV) Xα molecular orbital method. This method gave a reasonably accurate calculation of band-gap energy. The energy levels calculated by the DV-Xα method agree well with experimentally measured thermal quenching activation energy and the zero-phonon energy of green emission. The results indicate that oxygen vacancies function as luminescent centers for green emission.