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

Abstract

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.

Bismuth trihalide based coordination polymers with the N‐donor cyanopyridine as source for charge transfer based luminescence

“…[3,16,17] However, a precise assignment of optical spectra of Bi 3 + compounds is a problematic task, even if supported by additional DFT-calculations. [2,5,8,13,18] A significant part of luminescent Bi(III) compounds are coordination polymers of halidobismutates (BiX 3 , X = Cl, Br) with N-donor ligands, for example, pyridine-containing ligands. [1][2][3]5,6,8] It is worth noting that the halide nature plays a significant role in charge transfer processes and can affect the optical properties of compounds, i. e. intensity or position of bands.…”

“…[2,5,8,13,18] A significant part of luminescent Bi(III) compounds are coordination polymers of halidobismutates (BiX 3 , X = Cl, Br) with N-donor ligands, for example, pyridine-containing ligands. [1][2][3]5,6,8] It is worth noting that the halide nature plays a significant role in charge transfer processes and can affect the optical properties of compounds, i. e. intensity or position of bands. [2,13] One promising ligand for pyridine-containing coordination polymers is 4-cyanopyridine (4-cypy), as it also contains a cyano group and thereby has two different N-donor atoms and the possibility to act as interlinking ligand.…”

“…Bi(III) coordination polymers (CPs) and inorganic-organic hybrid materials are considered as luminescence materials, [1][2][3][4][5][6][7][8][9][10] even reporting the possibility of achieving white light emission. [6] They are also discussed for perspective applications as host lattices for lanthanide ions [11][12][13] and as topological insulators with noble metals such as rhodium.…”

“…Given that the luminescence spectra of bismuth compounds are characterized by broad bands, their nature is usually described by various possible mechanisms, such as LMCT (ligand‐to‐metal charge transfer) or MLCT (metal‐to‐ligand charge transfer), [2–4,6–8,13] and in some cases, when several different Bi‐centers are presented, IVCT (intervalence charge transfer) [3,16,17] . However, a precise assignment of optical spectra of Bi 3+ compounds is a problematic task, even if supported by additional DFT‐calculations [2,5,8,13,18] …”

“…A significant part of luminescent Bi(III) compounds are coordination polymers of halidobismutates (BiX 3 , X=Cl, Br) with N‐donor ligands, for example, pyridine‐containing ligands [1–3,5,6,8] . It is worth noting that the halide nature plays a significant role in charge transfer processes and can affect the optical properties of compounds, i. e. intensity or position of bands [2,13] …”