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Gallium-doped aluminum oxide (Al 1-x Ga x ) 2 O 3 with γ-Al 2 O 3 (spinel) structure has been synthesized by the precursor method using the formate Al 1-x Ga x (OH)(HCOO) 2 as a precursor. The examination of Al 1-x Ga 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-x Ga x ) 2 O 3 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 -x Ga x ) 2 O 3 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-Al 2 O 3 ., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Simultaneous emission lines around 1.05μm, 1.3μm, 1.8μm, 2.1μm and 2.7μm have been observed in Li 7 La 3-x Nd x Hf 2 O 12 :Ho 3+ (x=0.00-0.15) under 808nm laser diode excitation. Near-infrared luminescence due to holmium ions with residual concentration in the Li 7 La 3 Hf 2 O 12 host has been studied. The intensity of 2.1 and 2.7μm lines associated with 5 I 7 → 5 I 8 and 5 I 6 → 5 I 7 transitions in Ho 3+ depends on the neodymium codopant concentration. This result indicates that Nd 3+ ions can be potentially used as sensitizers for Ho 3+ ions to stimulate the intense near-infrared emission in this system. Possible energy transfer mechanisms between lanthanide ions have been briefly discussed., (Copyright © 2017 Elsevier B.V. All rights reserved.)