The Rb₇ Bi_3-3x Sb_3x Cl₁₆ Family: A Fully Inorganic Solid Solution with Room-Temperature Luminescent Members

Low-dimensional ns² -metal halide compounds have received immense attention for applications in solid-state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb²⁺ or unstable Sn²⁺ , and a stable inorganic luminescent material has yet to be found. Here, the zero-dimensional Rb₇ Sb₃ Cl₁₆ phase, comprised of isolated [SbCl₆ ]^3- octahedra and edge-sharing [Sb₂ Cl₁₀ ]^4- dimers, shows room-temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature-dependent PL lifetime rivals that of previous low-dimensional materials with a specific temperature sensitivity above 0.06 K^-1 at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi³⁺ in the Rb₇ Bi_3-3x Sb_3x Cl₁₆ (x≤1) family, we present the edge-shared [Sb₂ Cl₁₀ ]^4- dimer as a design principle for Sb-based luminescent materials.