Enhanced emission properties of Au/SiO2/ZnO nanorod layered structure: effect of SiO2 spacer layer and role of interfacial charge transfer
SiO2 spacer layers of various thicknesses in between an Au and ZnO nanorod (NR) layer (Au/ZnO) have been introduced and the luminescence properties of the layered ensemble have been investigated. When ZnO NRs are grown directly on a granular Au layer, the ultraviolet (UV) emission of ZnO was enhanced nearly 2 times due to surface plasmon resonance (SPR) mediated charge transfer between Au and ZnO. A significant improvement is observed when the SiO2 spacer layer is introduced in between Au and ZnO. The UV/VIS emission intensity ratio of Au/SiO2/ZnO NRs' becomes ∼6 times higher than that of the pristine ZnO NRs. A SPR mediated electron transfer from Au/SiO2 to ZnO causes such an enhanced UV emission. The spacer diminishes the reverse electron transfer process from the conduction band of ZnO to the Fermi level of Au, a most competitive reason for PL quenching, which also accounts for the emission enhancement.