Exceptional Optical Anisotropy Enhancement Achieved Through Dual-Ions Cosubstitution Strategy in Novel Hybrid Bismuth Halides.

Abstract

Guided by a superb dual-ions cosubstitution strategy, two novel, highly optically anisotropic hybrid bismuth halides are designed and synthesized. The first compound, Gu3 Bi2 NO3 Cl8 (Gu = C(NH2 )3 ), is developed using the 2D perovskite halide Cs3 Bi2 Cl9 as the maternal structure. This involved substituting all Cs+ cations with organic Gu+ and replacing some Cl- anions with [NO3 ]- . Further substitution of Cl- with additional [NO3 ]- resulted in the formation of nitrate-rich Gu2 Bi(NO3 )3 Cl2 crystal, exhibiting a 3.4-fold increase in [NO3 ]- per unit volume. Both compounds have a structurally 0D nature, comprising bismuth-centered polyhedra formed by coordinated chlorides and monodentate/bidentate nitrate moieties, with Gu+ serving as a separator and linker. Notably, the presence of superb optically anisotropic dual-ions, i.e., planar Gu+ and [NO3 ]- , enables these crystals to possess sharply enhanced optical anisotropy, with birefringence values more than 1 order of magnitude higher than that of the initial crystal Cs3 Bi2 Cl9 (0.162/0.186vs 0.011 at 546nm). The discovery and characterization of Gu3 Bi2 NO3 Cl8 and Gu2 Bi(NO3 )3 Cl2 crystals provide new insights into achieving expected modifications in optical properties through the utilization of a dual-ions cosubstitution strategy.