(C16H28N)2SbCl5: A new lead-free zero-dimensional metal-halide hybrid with bright orange emission

Zero-dimensional (0D) metal halides are in a blossoming status for their fascinating optoelectronic properties. Herein, an antimony-based metal halide of (C16H28N)2SbCl5 (C16H28N+ = benzyltripropylammonium cations), where the isolated [SbCl5]2− clusters are surrounded by C16H28N+ to form a 0D square-pyramidal structure, was synthesized and investigated. The (C16H28N)2SbCl5 exhibited a broadband orange emission at 633 nm upon the low-energy irradiation (400 nm) with a near-unity photoluminescence quantum efficiency (97.8%). Interestingly, (C16H28N)2SbCl5 showed an additional emission peak at 477 nm upon the higher-energy irradiation (300 nm), which is attributed to the transformation of the doublet of spin-orbit couplings into two independent self-trapped excitons (STEs). Temperature-dependent Raman spectra clearly revealed the characteristics of multi-phonon coupling, demonstrating a strong anharmonic electron-phonon interaction in (C16H28N)2SbCl5. Temperature-dependent emission spectra and density functional theory results illustrated that the observed dual-band emission originated from singlet and triplet STEs in [SbCl5]2− units. Combined with the efficient emission and excellent stability of (C16H28N)2SbCl5, a stable white-light-emitting diode with an ultra-high color rendering index of 96.6 was fabricated.