Neutron irradiation effects in magnesium-aluminate spinel doped with transition metals

We present data on optical properties for stoichiometric (MgO . Al2O3) and non-stoichiometric (MgO . 2Al(2)O(3)) spinel crystals: (1) nominally pure; (2) doped with transition metals Mn, Cr, and Fe to a concentration of 0.01 wt%; (3) irradiated with neutrons to a fluence of 1.8x10(21) m(-2); (4) pos t-annealed at 650 K. The temperature during neutron irradiation was 350 K. Optical absorption and thermoluminescence measurements were performed on ir radiated and annealed samples at room temperature. Results of absorption me asurements show spectra with the following features: (1) a prominent band a t 2.33 eV (for stoichiometric spinel); (2) overlapping bands attributed to hole centers (3.17 eV); (3) optical centers on antisite defects (3.78 and 4 .14 eV); (4) F+-;and F-centers (4.75 and 5.3 eV); (5) bands related to defe ct complexes. For nominally pure samples, the efficiency of optical center formation in stoichiometric spinel is half that in non-stoichiometric spine l. Doped crystals exhibit high efficiencies for defect creation, independen t of spinel composition. All dopants enhance the efficiency of defect creat ion in spinel. Doping with Mn has the least effect on increasing the number of radiation-induced stable defects. Apparently, impurities in spinel serv e as centers for stabilization of irradiation-induced interstitials or vaca ncies. (C) 2000 Elsevier Science B.V. All rights reserved.