Influence of Pb2+ ions on the optical properties of gamma irradiated BaF2 crystals

BaF2 crystals were obtained in our Crystal Research Laboratory using Bridgman method. Various raw materials were used to test the influence of the trace amount of Pb2+ in BaF2 crystals on the radiation damage. BaF2:1 mol % PbF2 crystal was also obtained in order to use it as comparative sample. The optical absorption spectra after irradiation are quite similar in band structure for all samples, except the intensities of the absorption bands. After gamma rays irradiation many new absorption bands have been observed in the entire investigated spectral domain (200 divided by 900 nm) and these absorption bands remain stable during the time even for trace amount of Pb2+ ions. The magnitude of the induced absorption bands depends on the oxygen content in BaF2. The most intense bands is at 220 nm that corresponds to Pb3+ ions and similar to 470 nm that corresponds to Pb+ ions and F center. The BaF2 crystals are used as fast scintillator involving emission in the UV domain around 195-220 nm and as window over a wide wavelength domain. The absorption band in the UV can attenuate the fast component. Thus, the study of the sensitivity to the radiation damage of the BaF2 crystals are practical importance. The lead ions need to be carefully investigated, because they can be in the raw material and during the crystal growth process are incorporated in BaF2 crystals, changing the optical properties of the crystal. The radiation damage depends more on the level of the oxygen content than on the trace amount of PbF2.