Optical absorption and thermoluminescence of Tb3+-doped phosphate scintillating glasses

We present a study of the optical properties of Tb3+-doped NaPO3-GdPO4-based glasses by means of optical absorption measurements performed at room temperature both before and after x-ray irradiation. A numerical decomposition of the absorption spectra is performed, and the possible nature of the defects responsible for the observed absorption bands is discussed; namely, it is proposed that both intrinsic defects and Tb4+ ions are responsible for the optical absorption pattern. Moreover, the thermal stability of the radiation-induced absorption bands has also been studied in the temperature range 20-280degreesC, and the results are compared with a parallel investigation, of trap levels in the glasses, measured by means of wavelength-resolved thermally stimulated luminescence. From the observed phenomenology, it can be proposed that the recovery of optical absorption bands is governed by the de-trapping of charge carriers from defect trap states. The de-trapping should be followed by recombination at activators and/or at defect sites, and at radiation-induced centres responsible for absorption bands, which in this way return to their preirradiation configuration.