The influences of monovalent ions on the stability of scintillation properties and radiation hardness of PbWO 4:Y 3+ crystals

Abstract

Some Y 3+-doped PbWO 4 crystals grown by modified Bridgmann method showed exceptional behaviors, namely, light yield increased after low dose rate irradiation, and the radiation-induced absorption coefficient was negative around 430 nm. In this paper, the influences of monovalent ion impurities (Na + and K +) on the stability of scintillation properties and radiation hardness were studied. The experimental results show that Na + ion enhances the absorption band at cut-off edge and at 430 nm, while K + ion only makes optical transmission unstable around 430 nm when the crystals were annealed at high temperatures. The contamination by Na + and K + ions makes scintillation properties and radiation hardness more unstable in the temperature range from 50°C to 350°C. The radiation-induced absorption coefficient is also negative around 430 nm. The charge compensation mode of K + ion along the crystal does not change, but those of Na + ion are different along the crystal. The concentrated Na +, K + and Y 3+ ions, which occupied Pb sublattice, lead to the shortage of Pb vacancies ( V Pb″). Thus instead of the formation of [2(Y 3+ Pb) — V Pb″] ((Y 3+ Pb) stands for the Y 3+ ion occupying the Pb sublattice), Na + and K + ions compel the defect (Y 3+ Pb) to form cluster [2(Y 3+ Pb) —O i″] or [(Y 3+ Pb) —O i″+hole] in which the interstitial oxygen (O i″) was considered to be the origin of light yield increase after low dose rate irradiation.