Correlations between surface-excitonic emission bands in ZnO nanowires

We report on the investigation of correlated spectral properties of two different surface-related photoluminescence bands in ZnO nanowires. We show that the spectral position and the temperature-dependent intensity of the surface-related emission band A are directly correlated with the emission of the surface-exciton band SX. We measure the thermal activation energies of both emission bands and present time-resolved photoluminescence data to deduce the photoluminescence decay time of the A emission band. We propose a model to explain the experimental observations and assign the A emission band to excitons bound to structural defects in the surface layer of the nanowires.