Localized Surface Plasmon Resonance-Enhanced Two-Photon Excited Ultraviolet Emission of Au-Decorated ZnO Nanorod Arrays

ZnO nanorod arrays and their Au-decorated counterparts are fabricated. The two-photon excited ultraviolet emissions of these two samples are studied by selecting different excitation wavelengths according to the localized surface plamsmon resonance (LSPR) position of Au nanoparticles (NPs). It is found that the two-photon excitation threshold of Au-decorated ZnO sample is much lower than that of the as-grown sample under an excitation corresponding to the LSPR absorption of Au NPs, such as 520 nm. Under the same excitation power, the UV emission intensity is strongly enhanced after the Au NPs are assembled on the surfaces of ZnO nanorods. This improvement is attributed to a strong local field enhancement generated by the LSPR of Au NPs. Experiments demonstrate that the resonant process depends on the excitation wavelength near or far from the LSPR peak of Au NPs. These studies provide direct evidence for the mechanism of LSPR-enhanced UV emission of ZnO, and are helpful to design proper metal-semiconductor nanostructures with high luminescence efficiency.