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

We have studied changes in optical absorption of MgAl2O4 spinel crystals im planted 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 i n optical absorption, especially in the vicinity of two absorption bands: o ne 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) i ons/m(2). This is the same dose range in which formation of a metastable ph ase of spinel has been reported previously. The band at 6.9 eV grows with i ncreasing dose and saturates at 1.10(20) -3.10(20) ions/m(2). Previous stud ies have shown that spinel is amorphized by Xe ion irradiation in this dose range. Annealing studies were also conducted on the Xe ion implanted spine l crystals. By optical absorption, F-centers were found to anneal at 500 de grees 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.