Direct formation and phase stability of luminescent γ-Ga2O3 spinel nanocrystals via hydrothermal method

Abstract

Nanocrystals of γ-gallium oxide (γ-Ga2O3) were directly synthesized as a single phase of spinel-type structure from the aqueous precursor solution of Ga(NO3)3 or Ga2(SO4)3 under weakly basic conditions in the presence of citric acid by mild hydrothermal method. The crystallite size of γ-Ga2O3 spinel that was hydrothermally formed at 180–240 °C for 5 h was in the dimension range from 5 to 9 nm. The optical band gap of the as-prepared γ-Ga2O3 was 4.88 eV. The γ-Ga2O3 nanocrystals synthesized at 180 °C showed a broad-band visible violet–blue light emission with a peak wavelength at 410 nm, centered at around 425 nm under excitation at 325 nm. The emission intensity of γ-Ga2O3 synthesized at 210 and 240 °C was lower than that of 180 °C. The spinel-type structure of γ-Ga2O3 was maintained up to 600 °C. The γ-Ga2O3 phase fully transformed into β-Ga2O3 after heating at 800 °C. The luminescence intensity of gallium oxide decreased, and the peak wavelength of emission spectrum shifted into lower wavelengths via heat treatment at 600 and 800 °C for 1 h in air.