Application of INAA for investigation of magnesium and aluminium oxide materials

The paper presents investigations of changes in optical absorption and photo luminescence spectra of magnesium oxide, and natural and synthetic magnesium aluminium spinel related with the content of transition metal ions (Cr, Fe, Mn) and the irradiation with fast neutrons. Six synthetic single magnesium aluminium spinel crystals with different stoichiometry (MgO·nAl₂O₃), five natural crystals from Ural and Pamir deposits, and seven MgO crystals were studied. Micro impurities (Cr, Fe, and Mn) and macro component (Mg, Al) quantities have been determined using the instrumental neutron activation analysis technique. Concentrations of impurities in different spinels were found in following ranges: for Cr - 1 × 10 ^-4 to 8 × 10^-2 %, for Mn - 2 × 10^-5 to 23 %, for Fe - 1 × 10^-4 to 1.2 %. Three ranges of luminescence: 380-460, 650-850 and 850-1,050 nm, were established in the most part of the investigated MgO samples. Analysis shows that the intensity of emission in each of these regions is strongly dependent on the concentration of transition metal ions. Great deviation from the stoichiometry of the irradiated MgO·2.8Al₂O₃ crystal leads to the local structure of α-Al₂O₃ formation around Cr³⁺ ions. The orange emission is attributed to Mn²⁺ in octahedral coordination, it can be assumed that the band at 570 nm is belonging to the complex centre "Mn²⁺-F⁺ (or F centre)".