Influence of growth conditions on the optical spectra of gamma irradiated BaF2 and CaF2 crystals

Abstract

A comparative study of the gamma irradiated BaF2 and CaF2 crystals obtained under different growth conditions, using the Bridgman technique, is presented. A special attention was attributed to the influence of trace amount of three impurities: lead, ytterbium and oxygen ions, on the γ–rays induced color centers. The small amount of Pb ions comes from the different raw materials used. The oxygen content is due to the low vacuum level during the growth process. The crystals with Yb content were intentionally doped with a small amount of YbF3. The CaF2 crystal is more sensitive to a trace amount of lead ions than the BaF2 host. The oxygen, in addition of the lead ions in the BaF2 host, is more harmful than the trace amount of PbF2. The small amount of YbF3 is useful in eliminating the color centers in visible range. The induced color centers are stable in time. The lead ions contaminated BaF2 and CaF2 crystals are not good materials for applications in which the radiation induced absorption bands are undesirable.