We systematically investigate visible defect-related photoluminescence (PL) properties of ZnO films with Ag nanostructures by changing the size of Ag and the power densities of excitation-laser light. We find that the PL intensity and the recombination rate are enhanced and peak at a particular size of a Ag nanostructure where its surface-plasmon resonance corresponds to the defect-emission band. The enhancements are due to the excitation of surface plasmons in Ag nanostructures and resultant local-field enhancement in the recombination energy of the defect-emission band. Furthermore, the saturation intensity of the defect-related emission in the higher-excitation power-density regime ($>\text{approximately}$ $10\mathrm{MW}/{\mathrm{cm}}^2$) is found to be strongly enhanced in the presence of Ag nanostructures, and the enhancement degree depends on the size of the nanostructures. The enhanced saturation behavior in the excitation power dependence of the emission intensity is well reproduced by the theoretical calculation based on a simple rate-equation model considering the surface-plasmon-induced enhancement of the radiative recombination rate. This result indicates that the saturation-intensity enhancement originates from the inhibition of the filling effect of defect states with excited carriers via plasmon-induced modification of their radiative processes.

• Received 4 July 2016

DOI:https://doi.org/10.1103/PhysRevApplied.6.044009