Influence of a dopant source on the structural and optical properties of Mn doped ZnGa2O4 thin films

Thin films of ZnGa2O4:Mn2+ were deposited on quartz substrates using an rf magnetron sputtering technique. The sputtering target, ZnGa2O4 doped with 2 at. % manganese, was synthesized by a high temperature solid state reaction. Two different dopant sources were used to incorporate the dopant ions into the target, namely, manganese acetate and manganese oxide. The structural and optical properties of the thin films were studied using XRD, PL and transmission spectra. Polycrystalline ZnGa2O4:Mn with a spinel structure could be grown at an optimized substrate-target distance even at room temperature. No luminescence was observed in the as-deposited films grown using (CH3COO)(2)Mn as the dopant source in the target. Substrate heating or post-deposition annealing in the reducing ambient didn't impart any luminescence to the films, ruling out the possibility of Mn2+ incorporation in the films. However, when using MnO as the manganese source in the target, the as-deposited films exhibited green photoluminescent emission (peak maximum at 508 nm) for substrate temperatures at and above 500 degrees C. This suggests that, in thin films, Mn incorporation and subsequent luminescent outcome is strongly influenced by the dopant source, which is quite different from the bulk phosphor behavior.