Radiation effects on BaF2 crystals

lNominally pure BaF2, BaF2:Sm (1 mol%), BaF2:Gd (0.05 mol%) and BaF2:Eu (0. 02, 0.1 and 1 mol%) single crystals were investigated at room temperature w ith optical absorption (OA) and electron paramagnetic resonance (EPR) to un derstand the mechanism of radiation damage. Irradiation of the samples at r oom temperature with gamma-rays resulted in the electron capture by trivale nt impurity ions, Sm3+ and Eu3+, forming the divalent impurity ions. Howeve r, no noticeable change in the valency of Gd ions could be observed. One of the nominally pure BaF2 crystals showed a band at 6.10 eV both before and after irradiation, which is due to Pb2+ ions. On irradiation two additional bands at 4.25 and 5.58 eV are observed. A correlation is found between the se bands and the EPR spectrum. These OA bands and EPR spectrum are attribut ed to Pb3+ ions.