Surface modification effect on photoluminescence of individual ZnO nanorods with different diameters

Abstract

Optical properties of Al₂O₃ coated individual ZnO nanorods (NRs) with different diameters were studied by confocal micro-photoluminescence spectroscopy. The one-dimensional ZnO/Al₂O₃ core–shell NRs showed enhanced near band-edge emission compared with the same ZnO NRs before Al₂O₃ coating at room temperature. Besides, the relative intensity of the deep-level emission with respect to the near band-edge emission was reduced. A model was proposed to explain these spectral changes. For ZnO NRs with diameters above 360 nm, a multi-mode behavior resulting from whispering gallery resonance was observed. In addition, selective enhancement or quenching of different whispering gallery modes in ultraviolet (UV) emission was observed after Al₂O₃ coating at room temperature, which is due to the larger refractive index of Al₂O₃ compared with air. We proposed a model to explain these spectral changes as well. By comparing the optical properties before and after surface coating, our results suggest that surface coating of an Al₂O₃ layer is an effective way to tailor the optical properties of ZnO NRs.