Non-plasmonic enhancement of the near band edge luminescence from ZnO using Ag nanoparticles

The effect of Ag nanoparticles (NPs) on the optical properties of ZnO has been investigated. Samples of pure and Ag doped ZnO were synthesized by the combustion method. X-ray diffraction, transmission electron microscope and UV-vis spectrophotometer measurements confirmed the growth of Ag NPs in the ZnO matrix. The near band edge (NBE) emission from ZnO excited by a 325 nm He-Cd laser was significantly enhanced in the presence of ~5 nm diameter Ag NPs. The experimental results suggest that the origin of enhanced NBE emission is due to direct interaction between the laser photons and Ag NPs, which in turn leads to photoemission transfer of electrons from the Ag NPs to the conduction band of ZnO. This is different from previously reported mechanisms where the photoemission transfer of electrons was mediated by plasmon decay.