Optical and X-ray absorption spectroscopy in lead doped lithium fluoride crystals

LiF:Pb doped crystals were successfully grown by Kyropoulos method, starting with drying powders. The presence of Pb²⁺ ions in the LiF crystals were evidenced by the absorption band at 278 nm and by 375 nm photoluminescence. The presence of some other Pb structures with oxygen compounds in the as made samples was evidenced, decreasing after some annealing procedures. The local environment and valence state of Pb in LiF were studied by X-ray Absorption Spectroscopy at the Pb L_III and L_I edges. XANES data reveal that Pb is present as Pb²⁺ whereas EXAFS data show that it is incorporated in the crystal and not forming PbF₂ precipitates. Identical spectra are obtained for samples as prepared and after thermal annealing up to 650 °C demonstrating the stability of the incorporation site. Also the concentration of Pb in the crystal has no effect on the location site of the metal as the same spectrum is obtained for specimens with different dopant concentrations.