Evaluation of photoluminescence and scintillation properties of Yb²⁺-doped SrCl_2−xBr_x crystals

Abstract

Photoluminescence and scintillation properties are reported for SrCl_2−xBr_x:Yb²⁺ (x = 0, 0.3, 1.4, 1.6, and 2.0) crystals grown by a self-seeding solidification method. SrCl_2−xBr_x 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 SrCl_2−xBr_x: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⁺ 5d–4f transitions were observed for SrCl₂:Yb²⁺ with local O_h symmetry and SrCl_0.4Br_1.6:Yb²⁺ and SrBr₂:Yb²⁺ with local C_4h symmetry, whereas only spin-forbidden Yb²⁺ 5d–4f transition was observed for SrCl_1.7Br_0.3:Yb²⁺ and SrCl_0.6Br_1.4:Yb²⁺ with local D_2h symmetry. The spin-allowed transitions were observed in crystals with higher local site symmetry. Light yields of SrCl_2−xBr_x: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, SrCl_0.4Br_1.6: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).