Optical absorption and thermoluminescence of MgAl2O4 spinel crystals implanted with Xe++ ions

We have studied changes in optical absorption of MgAl2O4 spinel crystals implanted with 340 keV Xe++ ions at about 120 K, to fluences ranging from 10(15)-10(21) ions/m(2). With increasing ion fluence, we observe an increase in optical absorption, especially in the vicinity of two absorption bands: one centered at 5.3 eV. the other at 6.9 eV. The absorption band at 5.3 eV, caused by F-centers, saturates at a fluence between 1.10(18) and 1.10(19) ions/m(2). This is the same dose range in which formation of a metastable phase of spinel has been reported previously. The band at 6.9 eV grows with increasing dose and saturates at 1.10(20) -3.10(20) ions/m(2). Previous studies have shown that spinel is amorphized by Xe ion irradiation in this dose range. Annealing studies were also conducted on the Xe ion implanted spinel crystals. By optical absorption, F-centers were found to anneal at 500 degrees C. Thermoluminescence measurements revealed a temperature dependence of luminescence that correlates well with the optical absorption. (C) 1999 Elsevier Science B.V. All rights reserved.