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.