Effect of the Host Lattice Environment on the Expression of 5s 2 Lone-Pair Electrons in a 0D Bismuth-Based Metal Halide.

n s 2 -Metal halide perovskites have attracted wide attention due to their fascinating photophysical properties. However, achieving high photoluminescence (PL) properties is still an enormous challenge, and the relationship between the lattice environment and n s 2 -electron expression is still elusive. Herein, an organic-inorganic Bi 3+ -based halide (C 5 H 14 N 2 ) 2 BiCl 6 ·Cl·2H 2 O (C 5 H 14 N 2 2+ = doubly protonated 1-methylpiperazine) with a six-coordinated structure has been successfully prepared, which, however, exhibits inferior PL properties due to the chemically inert expression of Bi 3+ -6s 2 lone-pair electrons. After reasonably embedding Sb 3+ with 5s 2 electrons into the lattice of (C 5 H 14 N 2 ) 2 BiCl 6 ·Cl·2H 2 O, the host lattice environment induces the Sb-Cl moiety to change from the original five-coordinated to six-coordinated structure, thereby resulting in a broad-band yellow emission with a PL efficiency up to 50.75%. By utilizing the host lattice of (C 5 H 14 N 2 ) 2 BiCl 6 ·Cl·2H 2 O, the expression of Sb 3+ -5s 2 lone-pair electrons is improved and thus promotes the radiative recombination from the Sb 3+ - 3 P 1 state, resulting in the enhanced PL efficiency. This work will provide an in-depth insight into the effect of the local structure on the expression of Sb 3+ -5s 2 lone-pair electrons.