ZnS Covering of ZnO Nanorods for Enhancing UV Emission from ZnO

Enhancing the ultraviolet (UV) emission from zinc oxide (ZnO) is of special significance for fabricating ZnO-based short-wavelength light-emitting devices. Herein, we report the enhancement of the UV near-band-edge (NBE) emission of ZnO by covering the surface of ZnO nanorods with a thin ZnS coating. The ZnO nanorods were grown via hydrothermal reactions, and the ZnS covering was realized by pulsed laser deposition. The prepared samples were characterized for morphology and structure by field emission scanning electron microscopy, transmission electron microscopy, Raman scattering spectroscopy, and Fourier-transform infrared spectroscopy measurements. Photoluminescence of the samples was measured at room temperature and reduced temperatures for a systematic examination of the effect of the ZnS covering on the NBE emission of ZnO. The bare ZnO NRs without ZnS covering can emit a strong UV NBE emission at room temperature along with a very weak visible emission ascribed to deep level defects. After being covered with a 4 nm thick ZnS coating, the ZnO NBE emission was enhanced about 2.5 times at room temperature. The ZnO NBE emission of the bare and ZnS-covered ZnO nanorods increases as the temperature decreases, with the ZnO NBE emission of the latter increasing more evidently. At a low temperature of 100 K, an about 4-fold enhancement in the UV ZnO NBE emission is obtained for the 4 nm thick ZnS-coverd ZnO nanorods compared with the bare ZnO nanorods.