CsCe 2 Br 7 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 CsCe 2 Br 7 . The crystal structure of CsCe 2 Br 7 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 Ce 3+ for these two Ce centers are evaluated. CsCe 2 Br 7 single crystal has better light yield and energy resolution than CsCe 2 Cl 7 , but with an additional slow decay component of 1.7 ms. The existence of a deep trap with a depth of 0.9 eV in CsCe 2 Cl 7 contributes to its higher afterglow level in comparison to that of CsCe 2 Br 7 . The most possible point defects in CsCe 2 Cl 7 and CsCe 2 Br 7 are proposed by considering the vapour pressure in the growth atmosphere upon melting point.ionic activators (in particular Bi 3+ , Ce 3+ and Eu 2+ ), is a constituent of the crystal, for example CaWO 4 and Self-activated single crystals of CsCe 2 X 7 (X = Cl, Br) were developed in 2010. 9-11 The CsCe 2 Cl 7 with a density of 3.6 g cm À3 can reach a gamma-ray excited light yield of 26 000 photons per MeV, but a 50% higher light yield is achieved in CsCe 2 Br 7 with a higher density of 4.0 g cm À3 . The phase diagrams of CsCe 2 Cl 7 12 and CsCe 2 Br 7 13,14 indicate that they both melt congruently. Recently, the crystal structure refinement revealed that CsCe 2 Cl 7 crystallizes in the monoclinic space group P112 1 /b. 15 However, despite the fact that the CsCe 2 Br 7 single crystal showed more promising scintillation properties, several fundamental questions, including structureproperty relationship, are still not understood: (i) the crystal structure and electronic structure; (ii) temperature dependent luminescent behaviors; (iii) the scintillation property comparisons between CsCe 2 Cl 7 and CsCe 2 Br 7 , including non-proportionality and afterglow; (iv) the trapping effect of point defects and their possible origins. All these questions lead us to carry out an in-depth study of CsCe 2 Br 7 . The paper is organized as follows. Firstly, the crystal