Realizing Near-Unity Quantum Efficiency of Zero-Dimensional Antimony Halides through Metal Halide Structural Modulation.

Zero-dimensional (0D) organic metal halides have attracted significant attention because of their exceptional structure tunability and excellent optical characteristics. However, controllable synthesis of a desirable configuration of metal halide species in a rational way remains a formidable challenge, and how the unique crystal structures affect the photophysical properties are not yet well understood. Here, a reasonable metal halide structural modulation strategy is proposed to realize near-unity photoluminescence quantum efficiency (PLQE) in 0D organic antimony halides. By carefully controlling the reaction conditions, both 0D (C12H28N)2SbCl5 and (C12H28N)SbCl4 with different metal halide configurations can be prepared. (C12H28N)2SbCl5 with pyramid-shaped [SbCl5]2- species exhibits yellow emission with a near-unity PLQE of 96.8%, while (C12H28N)SbCl4 with seesaw-shaped [SbCl4]- species is not emissive at room temperature. Theoretical calculations indicate that the different photophysical properties of these two crystals can be attributed to the different symmetries of their crystal structures. (C12H28N)2SbCl5 adopts a triclinic structure with P-1 symmetry, while (C12H28N)SbCl4 possesses a monoclinic structure with P21/c symmetry, which has an inversion center, and thus the optical transitions between their band-edge states give a minimal dipole intensity because of their similar parity character. In addition, we also successfully synthesized (C12H28N)2SbCl5 nanocrystals for the first time, which are particularly appealing for their solution processibility and excellent optical properties. Furthermore, (C12H28N)2SbCl5 nanocrystals flexible composite film shows bright yellow emission under β-ray excitation, suggesting a strong potential of (C12H28N)2SbCl5 for β-ray detection.