Enhanced surface-excitonic emission in ZnO/Al2O3 core-shell nanowires

We report the influence of an Al(2)O(3) shell on the photoluminescence emission of ZnO nanowires. At room temperature, the spectrum of the core-shell nanowires shows a strong reduction of the relative intensity of the green defect emission with respect to the near-band-edge emission. At 5 K an increase of the relative intensity of the surface exciton band with respect to the donor-bound exciton emission is observed. Annealing the core-shell nanowires at 500 degrees C does not increase the green defect luminescence at 5 K. We propose a model explaining the spectral changes.