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.