Strong Exciton Confinement Enabling Near-Unity Photoluminescence Quantum Efficiency in Hybrid Bimetallic Halides

Development of efficient and structurally stable zero-dimensional (0D) hybrid antimony halide materials still encounters huge challenges due to the limited and time-consuming trial-and-error design principle. Here, a host-guest chemistry strategy is employed at the A-site to design a series of hybrid antimony-based bimetallic halides (HABHs) with a general formula of [A(L)₆][BCl_<i>n</i>] (A = lanthanide and alkaline earth metals; B = Sb, In, and Bi; and L = urea ligands with different substituents). Controllable structural regulation is achieved by adjusting the steric effect of large [A(L)₆]^2+/3+ clusters, realizing a wide photoluminescence (PL) spectral modulation and high photoluminescence quantum efficiency (PLQY) over 98%. Some photophysical properties could be well correlated with specific structural changes. The PL spectral profile and emission energy are mainly dependent on the distortion of the SbCl_<i>n</i> polyhedra. In particular, a quantitatively exponential relationship between PLQY and structural parameters (bond distortion, angle deviation, and the defined effective Cl number describing the integrity of the hydrogen bonding network) related to the [SbCl_<i>n</i>]^{(<i>n</i>-3)-} sublattice has been reasonably established. As supported by theoretical calculations and photophysical analysis, strong exciton localization with negligible nonradiative recombination has been demonstrated for high PLQY, which results from a highly symmetrical rigid structure and the "shielding effect" of a complete hydrogen bonding network. Environmental stability and unique temperature-dependent PL behaviors enable multiapplications. This work proposes a quantitative "structure-property" correlation insight for new hybrid antimony halides, providing a direction for advancing the design of efficient hybrid metal halide materials.