A Zero-Dimensional Organic Lead Bromide of (TPA)₂PbBr₄ Single Crystal with Bright Blue Emission

Blue-luminescence materials are needed in urgency. Recently, zero-dimensional (0D) organic metal halides have attractive much attention due to unique structure and excellent optical properties. However, realizing blue emission with near-UV-visible light excitation in 0D organic metal halides is still a great challenge due to their generally large Stokes shifts. Here, we reported a new (0D) organic metal halides (TPA)₂PbBr₄ single crystal (TPA⁺ = tetrapropylammonium cation), in which the isolated [PbBr₄]^2- tetrahedral clusters are surrounded by organic ligand of TPA⁺, forming a 0D framework. Upon photoexcitation, (TPA)₂PbBr₄ exhibits a blue emission peaking at 437 nm with a full width at half-maximum (FWHM) of 50 nm and a relatively small Stokes shift of 53 nm. Combined with density functional theory (DFT) calculations and spectral analysis, it is found that the observed blue emission in (TPA)₂PbBr₄ comes from the combination of free excitons (FEs) and self-trapped exciton (STE), and a small Stokes shift of this compound are caused by the small structure distortion of [PbBr₄]^2- cluster in the excited state confined by TPA molecules, in which the multi-phonon effect take action. Our results not only clarify the important role of excited state structure distortion in regulating the STEs formation and emission, but also focus on 0D metal halides with bright blue emission under the near-UV-visible light excitation.