Characterization of complex defects which were formed by ionizing radiation in monocrystals of the Tl-doped halide was carried out by using optical spectroscopic and thermoluminescence methods. Aggregates, which were formed by the association of color centers with Tl+ ions, were found to be responsible for new absorption bands in the 240 to 260 and 180 to 340nm regions. Under excitation, photoluminescence was observed at 293nm in the former case and at 435nm in the latter case. Studies of the dependence of emission spectra upon dopant concentration, irradiation dose and temperature permitted the identification of 2 different types of complex center and of an energy transfer process between them. Spectrally resolved thermoluminescence data confirmed the coexistence of aggregate centers, which involved Tl+ impurity ions and intrinsic defects which were induced by irradiation in the host lattice, revealed evidence of complex emission dynamics, and gave further support to the suggestion that luminescence at 240nm was due to intrinsic emission that was caused by excitation in the fundamental absorption of this halide.

C.Furetta, G.Ramogida, A.Scacco, M.Martini, S.Paravisi: Journal of the Physics and Chemistry of Solids, 1994, 55[11], 1337-45