Crystal structure and luminescence properties of lead-free metal halides (C₆H₅CH₂NH₃)₃MBr₆(M = Bi and Sb)

Organic-inorganic hybrid metal halides have received extensive attention owing to their versatile structures and optoelectronic properties. Herein, we report two lead-free metal halides, (PMA)₃BiBr₆and (PMA)₃SbBr₆[PMA⁺: (C₆H₅CH₂NH₃)⁺, as the abbreviation of phenylmethylammonium], which possess iso-structural zero-dimensional structures and crystallize in the monoclinic space groupP2₁/c. (PMA)₃BiBr₆and (PMA)₃SbBr₆exhibit optical band gaps of ∼3.50 and 3.40 eV, respectively, and density functional theory calculations reveal their indirect bandgap behaviors. Upon 350 and 425 nm excitation, (PMA)₃BiBr₆and (PMA)₃SbBr₆exhibit broadband emission peaking at 510 nm and 625 nm with wide full-widths at half-maximum of ∼153 and 175 nm, respectively. The emission mechanism of the metal halides is attributed to self-trapped exciton emission. The relationship between the crystal structure and luminescence intensity is also discussed. Finally, both metal halides have high decomposition temperatures and are stable for long-term storage under ambient conditions, demonstrating their potential for optoelectronic applications.