Understanding the Relation between the Structure and Emission Properties in 0D (2-ABI)3Bi1-x Sb x Cl6<middle dot>H2O: Impact of Structural Distortion and Stereoactivity of ns2 Lone Pairs

Zero-dimensional (0D) organic-inorganic metal halides (OIMHs) have emerged as a fascinating class of materials, offering unprecedented opportunities for the development of low-cost solid-state lighting devices. Herein, we report two novel 0D Bi/Sb-based OIMHs, (2-ABI)3MCl6<middle dot>H2O (M = Bi, Sb), crystallizing in the monoclinic P21/n space group. Under 365 nm UV light irradiation, the Sb-analogue displays a bright and broad yellow emission band at 580 nm with a photoluminescence (PL) quantum yield of 34.6%, which may be attributed to the distortion-induced self-trapped excitons (STEs). Theoretical study of (2-ABI)3SbCl6<middle dot>H2O in the ground state and excited state shows specific bonds are distorted significantly indicating the role of the stereoactivity of the 5s2 lone pair. To understand the effect of gradual Sb substitution on the structure and the optical properties of (2-ABI)3BiCl6<middle dot>H2O, a series of mixed compounds, (2-ABI)3Bi1-x Sb x Cl6<middle dot>H2O (refined x = 0, 0.11, 0.40, 0.53, 0.87, 1) was prepared. This work provides important insight into the correlation between the PL properties and local structure distortion in the ground and excited states induced by the expression of 5s2 lone-pair electrons of Sb3+, thus providing an efficient tool for exploring highly emissive 0D OIMHs and further modulating their structures to enhance the luminescent properties for practical optoelectronic applications.