Effects of Transition-Metal-Doping on the Radio-Luminescence Properties of Magnesium Aluminate Spinel Crystals

The use of the radio-luminescence (RL) method for radiation-induced processes in magnesium aluminates spinel crystals (MgO•nAl2O3) of different composition doped with transition metals (Mn, Cr, and Fe) was investigated.The RL spectra demonstrate bands related to the intrinsic defects, such as anti-site defects (263 nm) and F-type centers (~360 nm).Transition metal (TM) ions substituting the crystal-forming ions in the tetra-and octahedral sites show the emission due to electron transitions in doped ions, particularly, band at 520 nm identified with the transition in Mn 2+ in tetrahedral positions and the emission in the red spectral region (consisting of zerophonon line at 686.6 nm and phonon-assisted lines) related to the transition in Cr 3+ ions at the octahedral position.Based on the data on the quenching UV luminescence in stoichiometric crystals doped with TM, we suggest the partial ordering of this type of crystals.The enhancement of Cr 3+ luminescence in stoichiometric spinel crystals doped with manganese and iron supports this suggestion on the ordering of the spinel crystals by doping with some TM's.The existence of a large number of non-stoichiometric cationic vacancies in non-stoichiometric spinel crystals prevents the formation of an ordered structure.