a The Normalized PL intensity of ZnO films with and without Ag NPs. b XPS spectra corresponding the O-1s core level of ZnO film with and without Ag NPs. c The cross-section electric field distributions and d the top view electric field distributions of Ag NPs on ZnO film simulated by FDTD. e The absorption curves of ZnO film with and without Ag NPs calculated by FDTD. Liu et al.