Abstract: All-inorganic metal halides have shown significant applications in solid-state optoelectronics because of their flexible structures and impressive fluorescence emissions. In this study, a heterovalent cation substitution strategy was used to partially replace the divalent cadmium ions in CsCdCl₃ with trivalent antimony ions to promote the production of self-trapped excitons, resulting in a bright broadband green photoluminescence of CsCdCl₃∶Sb³⁺ with a central wavelength of 530 nm. Mechanism researches results show that the adjacent SbCl₆ octahedra in CsCdCl₃∶Sb³⁺ are isolated, forming a low-dimensional electronic configuration that promotes Sb³⁺ localization and achieves efficient photoluminescence with a quantum efficiency of up to 95.5%. Furthermore, although both CsCdCl₃ and RbCdCl₃ belong to ACdCl₃ (A is an alkali metal family), they have distinctly different crystal structures. RbCdCl₃ crystallizes in the orthorhombic crystal system with space group of Pnma; while CsCdCl₃ crystallizes in the hexagonal phase crystal system with space group of P6₃/mmc. The structural symmetry of CsCdCl₃ is higher than that of RbCdCl₃, indicating that its crystal structure is less distorted away from the cubic phase than that of RbCdCl₃, resulting in a smaller Stokes shift and corresponding blue shift of the emission spectrum in CsCdCl₃∶Sb³⁺ than in RbCdCl₃∶Sb³⁺. This work not only provides a method for designing new photoluminescence materials by heterovalent cation substitution but also paves an avenue for modulating the luminescent properties of metal halides through crystal structure symmetry.

Key words: metal halide, heterovalent cation substitution, self-trapped exciton, high quantum efficiency, cadmium, green photoluminescence