Ga-doped ZnS nanowires are used as precursors for the preparation of ZnO/ZnGa2O4 composite nanotubes, as shown in the figure. Oxidation of the nanowires induces phase separation resulting in the formation of ZnO/ ZnGa2O4 phosphor heterostructures. The nanowires essentially serve as both precursors and templates for the fabrication of the nanotubes.