Effects of annealing on the optical and scintillation properties of reddish Bi4Ge3O12 single crystals

Abstract Large-size and -scale bismuth germanate (Bi4Ge3O12, BGO) crystals were grown in an oxidizing atmosphere using the modified Bridgman method. Although the growth condition has been optimized, we found a few reddish crystals, resulting in poor performance. In this work, the red-color-induced characteristic absorption bands corresponding to 506, 389, and 332 nm were studied by measuring the optical transmission and absorption spectra. A modified oxygen-annealing was applied to eliminate the reddish in BGO single crystal. Based on the comparison of the optical performance, the absorption band in the visible range of the reddish crystals disappeared after annealing. This phenomenon greatly improved the light output and energy resolution. The effects of annealing in reducing atmosphere were studied. The formation mechanism of crystal coloration was also discussed.