Photoluminescence and thermal stability of 5.5 eV and Ti centres in gamma irradiated LiF : Mg,Ti crystals

Photoluminescence (PL) and thermoluminescence (TL) measurements of LiF: Mg, Ti (DTG-4) single crystals, previously gamma irradiated with 500 Gy and the rmally treated, were performed. The behaviour of the Mg centres, related to the known 5.5 eV optical absorption band, PL emission after repeated heati ng cycles with a heating rate of 1 K/s up to 373-653 K indicate that these centres are created simultaneously with the destruction of TL peaks. The de cay of the PL emission after repeated heating cycles followed by 10 min ann ealing at 643 K coincides with the decreasing of the TL sensitisation facto rs of peaks 2, 3 and 5. Both these facts support the point of view that the precursors of the 5.5 eV centres. act as competitive traps during TL reado ut. The behaviour of the Ti-related PL emission was found to be unexpectedl y complex. Noticeable change of the Ti band shape and ambiguous behaviour o f the Ti emission during subsequent heating indicate the possible presence of an additional Ti band. (C) 2001 Elsevier Science Ltd. All rights reserve d.