Vertically aligned ZnO–ZnGa₂O₄ core–shell nanowires: from synthesis to optical properties

Dense and vertically aligned ZnO–ZnGa₂O₄ core–shell nanowires were synthesized in large scale on a-plane sapphire substrates by a simple two-step chemical vapor deposition method. The synthesized ZnO–ZnGa₂O₄ core–shell nanowires were connected through their base by a thick underlayer of the same material realizing electrical contact of the nanostructured array. X-ray diffraction and transmission electron microscopy analyses of the core–shell nanowires reveal that the ZnO cores and ZnGa₂O₄ shells of the core–shell nanowires are of single-crystal quality and have aligned crystallographic orientations. The ultraviolet–visible diffuse reflectance spectra of the core–shell nanowires showed two sharp edges corresponding to near-band-edge absorption contributed by the ZnO cores and the ZnGa₂O₄ shells. Moreover, the room-temperature photoluminescence spectra of the core–shell nanowires gave three UV emission peaks coming from the ZnGa₂O₄ shells and the ZnO cores. The dense and vertically aligned ZnO–ZnGa₂O₄ core–shell nanowires showing promising photoelectric properties offer an ideal structure for light harvesting applications such as a photoanode in a photoelectrochemical water splitting cell.