Synthesis, spectroscopic and luminescence properties of Ga-doped γ-Al₂O₃

Gallium-doped aluminum oxide (Al_1-xGa_x)₂O₃ with γ-Al₂O₃ (spinel) structure has been synthesized by the precursor method using the formate Al_1-xGa_x(OH)(HCOO)₂ as a precursor. The examination of Al_1-xGa_x(OH)(HCOO)₂ (x = 0.0, 0.1, 0.2, 0.3, 0.4) was carried out by X-ray powder diffraction, Infrared, Raman spectroscopy and differential-thermal methods. The solid solutions γ-(Al_1-xGa_x)₂O₃ with х≤0.2 have been synthesized by thermolysis of precursors in helium atmosphere at 700 °C; they exhibit white-blue emission under UV excitation, whose intensity lowers with increasing dopant concentration. As an independent method, the DFT calculations confirmed thermodynamically the stability field of γ-(Al_1-xGa_x)₂O₃ solid solutions and the NMR data on relative abundance of Al and Ga within the tetrahedral and octahedral sites in the metal sublattice. Furthermore, the structural and thermodynamic properties of carbon-containing impurities within these compounds were suggested theoretically as possible models of luminescence emission centers. The experimentally observed Ga-dependent quenching of luminescence was explained using the competition between C2p and Ga4p states within the band gap of γ-Al₂O₃.