Facile Preparation of Light Emitting Organic Metal Halide Crystals with Near-Unity Quantum Efficiency

We
report the synthesis and characterization of (Ph4P)2SbCl5, a novel ionically bonded organic
metal halide hybrid with a zero-dimensional (0D) structure at the
molecular level. By cocrystallization of tetraphenylphosphonium (Ph4P+) and antimony (Sb3+) chloride salts,
(Ph4P)2SbCl5 bulk single crystals
can be prepared in high yield, which exhibit a highly efficient broadband
red emission peaked at 648 nm with a photoluminescence quantum efficiency
(PLQE) of around 87%. Density functional theory (DFT) calculations
reveal the origin of emission as phosphorescence from the excitons
localized at SbCl52– with strong excited-state
structural distortion. Interestingly, (Ph4P)2SbCl5 bulk crystals with a PLQE of around 100% can be
prepared via a rapid crystal growth process within minutes, followed
by a spontaneous structural transformation. It was found that the
rapid growth process yielded a yellow emitting kinetically favored
metastable product containing solvent molecules, which turned into
the red emitting thermodynamically stable product slowly at room temperature
or quickly upon thermal treatment.