Effects of bleaching on the thermoluminescence of gamma-irradiated LiF crystals

Light emitted as a function of temperature by crystalline materials, which have been exposed to ionizing radiation, is commonly known as thermoluminescence. Its structured shape, which is often resolved in narrow bands called glow peaks, is related to the material, the impurities and the defect centers generated by the irradiation. Several efforts have been made to associate these peaks to the defect centers, but up to now in the majority of the cases and in particular in LiF, there is not any certain attribution. In order to overcome this situation, pure LiF samples have been irradiated with gamma rays and treated thermally and optically in order to produce samples with different known concentrations of color centers. By comparing the glow curves from ambient temperature to 450°C, and optical absorption and emission spectra in the visible region, it has been possible to establish a link between F3+ centers and the low temperature region of the glow curve below about 200°C.