Direct formation of spinel-structured γ-Ga2O3-Al2O3 nanoparticles by a mild hydrothermal method

Spinel-structured γ-Ga2O3-based nanoparticles doped with Al2O3 component, i.e., (AlxGa1.00−x)2O3, x=0–0.85, with crystallite size of spinel phase in the range of 4–5 nm were directly synthesized from the aqueous precursor solutions of Ga(NO3)3 and Al2(SO4)3 under weakly basic conditions using aqueous ammonia in the presence of citric acid by the mild hydrothermal method at 180 °C for 5 h. A broad-band visible violet–blue light emission with a peak wavelength at 410–415 nm was observed in each of the as-prepared (AlxGa1.00−x)2O3 samples under excitation at 325 nm Xe lamp. The as-prepared spinel-structured nanoparticles with composition (Al0.50Ga0.50)2O3 showed the most intense emission. The spinel-type structure of nanoparticles in all composition ranges was maintained after heating at 600 °C. The β-Ga2O3 structure that was transformed from the spinel structure was observed in the nanoparticles with compositions from Ga2O3 to (Al0.50Ga0.50)2O3 after heat treatment at 1000 °C. The spinel-type structure was still maintained in the (Al0.75Ga0.25)2O3 nanoparticles after heat treatment at 1000 °C in contrast with a single phase of θ-Al2O3 in the case of pure Al2O3 composition.