The influences of monovalent ions on the stability of scintillation properties and radiation hardness of PbWO4:Y3+ crystals

Some Y3+-doped PbWO4 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 deg. C to 350 deg. 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 Y3+ ions, which occupied Pb sublattice, lead to the shortage of Pb vacancies (VPb''). Thus instead of the formation of [2(Y3+Pb)·--VPb''] ((Y3+Pb)· stands for the Y3+ ion occupying the Pb sublattice), Na+ and K+ ions compel the defect (Y3+Pb)· to form cluster [2(Y3+Pb)·--Oi''] or [(Y3+Pb)·--Oi''+hole] in which the interstitial oxygen (Oi'') was considered to be the origin of light yield increase after low dose rate irradiation