All-Inorganic Luminescent Ternary Cadmium Halide Cs7Cd3Br13 with Two Types of Cd-Centered Polyhedrons

All-inorganic metal halides comprise a class of semiconductor material with a wide range of applications. In these materials, cadmium-related materials have excellent optical properties in the field of binary quantum dots. However, ternary cadmium halides have not attracted much attention until now. Here, we successfully synthesize a ternary all-inorganic cesium cadmium bromide, Cs7Cd3Br13, and obtained its acicular single crystals through a simple solvent evaporation method. Cadmium atoms are found to be coordinated with bromine atoms in two different polyhedrons including isolated [CdBr4]2- tetrahedrons and corner-shared [CdBr6]4- octahedral chains in the unit cells of Cs7Cd3Br13. Optical properties are then measured and the needlelike single crystals are found to have an orange emission at 630 nm upon 365 nm UV light with a photoluminescence quantum yield (PLQY) of 9.85%. The orange luminescence with large Stokes shift (255 nm) and broad full width at half-maximum (fwhm = 147 nm) is derived from self-trapped excitons, and it is further evidenced by temperature-variable photoluminescence spectra. The PL decay spectrum shows the lifetime of Cs7Cd3Br13 is 1.26 μs. Finally, DFT calculation reveals that Cs7Cd3Br13 has a direct band gap with a value of 3.09 eV.