Crystal Structure and Optical Properties Characterization in Quasi-0D Lead-Free Bromide Crystals (CHN)BiBr·HO and (CHN)SbBr.

Low dimensional organic inorganic metal halide materials have shown broadband emission and large Stokes shift, making them widely used in various fields and a promising candidate material. Here, the zero-dimensional lead-free bromide single crystals (CHN)BiBr·HO () and (CHN)SbBr () were synthesized. They crystallized in the monoclinic crystal system with the space group of 2 and 2/, respectively. Through ultraviolet-visible-near-infrared (UV-vis-NIR) absorption analysis, the band gaps of (CHN)BiBr·HO and (CHN)SbBr are found to be 2.75 and 2.83 eV, respectively. Upon photoexcitation, (CHN)BiBr·HO exhibit broad-band red emission peaking at 640 nm with a large Stokes shift of 180 nm and a lifetime of 2.94 ns, and the emission spectrum of (CHN)SbBr are similar to those of (CHN)BiBr·HO. This exclusive red emission is ascribed to the self-trapping exciton transition caused by lattice distortion, which is confirmed through both experiments and first-principles calculations. In addition, due to the polar space group structure and the large spin-orbit coupling (SOC) associated with the heavy elements of Bi and Br of crystal , an obvious Rashba effect was observed. The discovery of organic inorganic metal bromide material provides a critical foundation for uncovering the connection between 0D metal halide materials' structures and properties.