Effect of the surface-plasmon-exciton coupling and charge transfer process on the photoluminescence of metal-semiconductor nanostructures

The effect of direct metal coating on the photoluminescence (PL) properties of ZnO nanorods (NRs) has been investigated in detail in this work. The direct coating of Ag nanoparticles (NPs) induces remarkable enhancement of the surface exciton (SX) emissions from the ZnO NRs. Meanwhile, the charge transfer process between ZnO and Ag also leads to notable increment of blue and violet emissions from Zn interstitial defects. A thin SiO2 blocking layer inserted between the ZnO and Ag has been demonstrated to be able to efficiently suppress the defect emission enhancement caused by the direct contact of metal-semiconductor, without weakening the surface-plasmon-exciton coupling effect. A theoretical model considering the type of contacts formed between metals, ZnO and blocking layer is proposed to interpret the change of the PL spectra.