Large-area (1 cm2), vertically aligned ZnGa2O4, Mn2+ doped ZnGa2O4 (ZnGa2O4:Mn2+) and Cr3+ doped ZnGa2O4 (ZnGa2O4:Cr3+ ) nanowire arrays were synthesized by a two-step thermal evaporation method using ZnO nanowire arrays as the templates followed by reaction with Ga and/or dopant (Mn ...