Lattice Compressibility versus Emission Properties: A Trade-Off in Zero-Dimensional Hybrid Bimetallic Halides

Hybrid metal halide perovskites exhibit interesting optoelectronic properties that are highly tunable and sensitive via structural manipulation, whether intrinsically designed or induced by pressure stimuli. Their soft lattices are generally easy to compress, where the bulk modulus (B₀) decreases with decreasing dimensionality from 3D to 0D. Here, we show that an unusually large B₀ of 119 GPa beyond 2 GPa can be achieved through the control of coordinated solvent ligand in a 0D hybrid bimetallic bromides series, namely La(L)_n[SbBr₆] (L = dimethyl sulfoxide, 1-methylurea, and 1,3-dimethylurea). We identify a striking inverse relation between B₀ and photoluminescence (PL) under pressure, mediated by hydrogen-bonding strength. Stronger hydrogen bonds create a more rigid structure (high B₀), which causes a rapid quenching of emission. This phenomenon is generally observed in the La(L)_n[SbBr₆] series, with all undergoing a universal quenching of PL intensity once a compressibility limit is reached at ∼2 GPa. This work provides a paradigm for controlling the compressibility in low-dimensional hybrid materials and establishes a fundamental principle regarding the compressibility and optical property evolutions.