Kohei MIZOI1, Miki ARAI, Yutaka FUJIMOTO, Daisuke NAKAUCHI, Masanori KOSHIMIZU, Takayuki YANAGIDA and Keisuke ASAI
Abstract
Photoluminescence and scintillation properties are reported for SrCl2¹xBrx:Yb2+ (x = 0, 0.3, 1.4, 1.6, and 2.0) crystals grown by a self-seeding solidification method. SrCl2¹xBrx have been reported to crystallize in some structural types with different local site symmetries depending on the Cl/Br ratio. Taking advantage of this property, we can control the crystal structure and the local Yb2+ site symmetry of SrCl2¹xBrx:Yb2+ by changing the compositions and investigate the behaviors of the spin-allowed and spin-forbidden transitions dependent on the local site symmetry. For photoluminescence and scintillation, both spin-allowed and spin-forbidden Yb2+ 5d4f transitions were observed for SrCl2:Yb2+ with local Oh symmetry and SrCl0.4Br1.6:Yb2+ and SrBr2:Yb2+ with local C4h symmetry, whereas only spin-forbidden Yb2+ 5d4f transition was observed for SrCl1.7Br0.3:Yb2+ and SrCl0.6Br1.4:Yb2+ with local D2h symmetry. The spin-allowed transitions were observed in crystals with higher local site symmetry. Light yields of SrCl2¹xBrx:Yb2+ (x = 0, 0.3, 1.4, 1.6, and 2.0) were (21000 to 71000) photons/MeV. Crystals with higher local site symmetry, which showed the spin-allowed transitions, had relatively high light yields. Among them, SrCl0.4Br1.6:Yb2+ showed a light yield of 71000 photons/MeV, which is higher than those of previously reported Yb2+-doped scintillators, for example, SrI2:Yb2+ (56000 photons/MeV) and CsBa2I5:Yb2+ (54000 photons/MeV).
