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.