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.