Blue Light-Excitable Broadband Yellow Emission in a Zero-Dimensional Hybrid Bismuth Halide with Type-II Band Alignment

Zero-dimensional (0D) organic–inorganic hybrid metal halides have captured broad interest in the lighting and display fields because of their unique electronic structures and splendid broadband emission properties. However, the blue light-excitable broadband yellow emissions have been rarely reported in 0D hybrid metal halides. Here, we design a new 0D bismuth hybrid, (4cmpyH)2BiCl5 (1, 4cmpy = 4-(chloromethyl)pyridine), featuring isolated edge-sharing bioctahedral [Bi2Cl10]4– dimers surrounded by rigid, conjugated, and luminescent organic [4cmpyH]+ cations. This material is able to show intrinsic broadband yellow emissions under blue light (468 nm) excitation with a long lifetime of 22.33 μs and a photoluminescence (PL) quantum yield of 5.56%. Solid-state UV–vis spectroscopy studies prove that introducing organic π-conjugated groups into hybrid systems leads to absorption in the visible light region, in favor of photoexcitation by visible light. By comparing the PL data of 1 and the organic template at room temperature and measuring variable-temperature PL spectra of 1, the blue light-excited broadband emission of 1 can be attributed to the synergistic emissions of intramolecular π → π* and n → π* transitions in the organic cations and triple self-trapped exciton (STE) states centralized at the highly distorted Bi–Cl lattices. Moreover, density functional theory calculations reveal a type-II band alignment in 1 with an indirect band gap of 2.64 eV, which is together determined by organic cations and inorganic bioctahedral units. To the best of our knowledge, our work represents the first report on the blue light-excitable STE emission in 0D Bi-based metal halides, which will largely promote the rapid development of novel high-performance yellow light-emitting materials.