Influence of Temperature Gradient on Radiation Damage of BGO Crystals

In this work, we grew two types of Bi4Ge3O12 (BGO) crystals in different temperature gradient by Bridgmen-Stockbarger technology and compared the optical transmissions and energy resolutions of the two types of BGO crystals before and after ultraviolet irradiation. It was found that the optical transmissions and energy resolutions of the two types of BGO crystals are similar before UV-irradiation. After UV-irradiation the optical transmissions at 480nm of the first type of BGO crystals which were grown in high temperature gradient cut down about 20% and their energy resolutions obviously changed bad from about 12% to 18%. But the optical transmissions and energy resolutions of the second type of BGO crystals which were grown in low temperature gradient keep unchanged on the whole. After 250℃/4h annealing, the optical transmissions and energy resolutions of the second type of BGO crystals can completely be recovered. Whereas the optical transmissions and energy resolutions of the first type of BGO crystals can't completely be recovered until through 800℃/8h annealing. The thermoluminescence curves of the two types of BGO crystals show that there is a luminescence peak at 85℃for second type of BGO crystal, whereas for the first type of BGO crystals, besides at 85℃, there are also two luminescence peaks at 130℃and at 170℃ which may show that there exist defects with deeper traps in the first type of BGO crystals. The reason for the difference between the first and second type of BGO crystals may be that if the temperature drop dawn too fast during crystal growing, the defects in the melt can not spread out to the surface and so the defects easily exist in the first type of BGO crystals.