Enhanced photosensing and tunable luminescence from ZnO/NiO and ZnO/Ni core–shell nanorods

A high-performance ZnO/NiO photosensor is fabricated by depositing Ni nanoshells onto the surface of ZnO nanorods (NRs) followed by annealing to transform ZnO/Ni into ZnO/NiO core–shell NR arrays. Photoluminescence spectra show that the ultraviolet (UV) emission of NRs is blue-shifted from 385 nm to 374 nm after the deposition of Ni nanoshells, and further splits into two peaks, at 360 nm and 384 nm, respectively, after the oxidation of Ni. Absorption spectra support the shift characteristic, which is ascribed to the doping and de-doping of Ni ions, consistent with the diffraction peak shifts in X-ray diffraction patterns. Photosensing measurements show that the ZnO/NiO NR devices have high sensitivity at a low bias. NiO nanoshells improve the UV sensitivity of ZnO NRs by 70-fold, which is attributed to the extended carrier depletion region near n-ZnO/p-NiO junctions and the enhanced absorption of UV.