Crystal structure, electronic structure, temperature-dependent optical and scintillation properties of CsCe2Br7

Abstract

CsCe₂Br₇ is a self-activated inorganic scintillator that shows promising performance, but the understanding of the important structure–property relationships is lacking. In this work, we conduct a comprehensive study on CsCe₂Br₇. The crystal structure of CsCe₂Br₇ is refined using single crystal X-ray study for the first time. It crystallizes into the orthorhombic crystal system with Pmnb space group. Its electronic structure is revealed by density functional theory (DFT) calculations. Two cerium emission centers are identified and the energy barriers related to the thermal quenching to 4f ground states of Ce³⁺ for these two Ce centers are evaluated. CsCe₂Br₇ single crystal has better light yield and energy resolution than CsCe₂Cl₇, but with an additional slow decay component of 1.7 μs. The existence of a deep trap with a depth of 0.9 eV in CsCe₂Cl₇ contributes to its higher afterglow level in comparison to that of CsCe₂Br₇. The most possible point defects in CsCe₂Cl₇ and CsCe₂Br₇ are proposed by considering the vapour pressure in the growth atmosphere upon melting point.