Photoluminescence and Raman spectroscopy studies of low-temperature γ-Al2O3 phases synthesized from different precursors

Spectroscopic features of the local structure of high purity (with the content of impurities <10(-3) wt.%) spinel-like gamma- and gamma*-Al2O3 phases differing in the unit cell parameters were studied. Samples of these phases were synthesized from crystalline boehmite and nanodispersed pseudoboehmite, respectively. For each of the phases, photoluminescence of transition metal ions and oxygen vacancies - F- and F-2-centers - was detected, and Raman scattering spectra were recorded. The photoluminescence study of gamma*-Al2O3 revealed octahedrally coordinated ions Me. Values of the crystal field strength and Racah parameters for Me ions in gamma*-Al2O3 were determined. Manifestation of PL of Mn4+ ions in gamma*-Al2O3 and its absence in gamma-Al2O3 can serve as the indicator for distinguishing between these phases. It was found that gamma- and gamma*-Al2O3 samples have individual Raman spectra. The revealed spectroscopic features in the local structure of gamma- and gamma*-Al2O3 phases confirm the differences between these spinel-like structures. (C) 2016 Elsevier B.V. All rights reserved.