Two different mechanisms on UV emission enhancement in Ag-doped ZnO thin films

Ag-doped ZnO thin films were prepared by a sol-gel method. The structural, morphological and optical properties of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis and photoluminescence spectra. The results show that the Ag in the ZnO thin films annealed at 500 °C for 1 h substitutes for Zn and exists in the form of Ag+ ion (AgZn) while the Ag in the ZnO thin films without a post-annealing mainly exists in the form of simple substance (Ag0). The incorporation of Ag indeed can improve the ultraviolet emission of ZnO thin films and suppress the visible emissions at the same time. However, the mechanisms on the ultraviolet emission enhancement in the annealed and unannealed Ag-doped ZnO thin films are very different. As for the post-annealed Ag-doped ZnO thin films, the UV emission enhancement maybe mainly results from more electron-hole pairs (excitons) due to Ag-doping while for the unannealed Ag-doped ZnO thin films; the UV emission enhancement is attributed to the resonant coupling between exciton emission in ZnO and localized surface plasmon in Ag nanoparticles.