ZnO and ZnO/Agfilms are grown on Si(111) substrates by rf magnetron sputtering at room temperature.After annealing,it is found that the ultraviolet(UV) emission of ZnO/Ag films strongly depends on the thickness of the initial inteal Ag layer.During the annealing process,Ag nanoparticles are formed and diffused into the ZnO film.The resonant coupling between localized surface plasmons(LSPs) of Ag nanoparticles and ZnO enhances the UV emission.The largest UV enhancement over 12 times is found when the initial inteal Ag layer is 10nm.It is also observed that the diffusion of Ag nanoparticles destroys the ZnO crystal quality in different grades,depending on the sizes of the Ag nanoparticles.The poor crystal quality induces bad UV emission.It is concluded that the UV emission is the result of the competition between the LSP enhancement and the thermal diffusion destroying effect from Ag nanoparticles.