Achieving Near-Unity Red Light Photoluminescence in Antimony Halide Crystals via Polyhedron Regulation

Exploration of efficient red emitting antimony hybrid halide with large Stokes shift and zero self-absorption is highly desirable due to its enormous potential for applications in solid light emitting, and active optical waveguides. However, it is still challenging and rarely reported. Herein, a series of (TMS)2SbCl5 (TMS=triphenylsulfonium cation) crystals have been prepared with diverse [SbCl5]2- configurations and distinctive emission color. Among them, cubic-phase (TMS)2SbCl5 shows bright red emission with a large Stokes shift of 312 nm. In contrast, monoclinic and orthorhombic (TMS)2SbCl5 crystals deliver efficient yellow and orange emission, respectively. Comprehensive structural investigations reveal that larger Stokes shift and longer-wavelength emission of cubic (TMS)2SbCl5 can be attributed to the larger lattice volume and longer Sb⋅⋅⋅Sb distance, which favor sufficient structural aberration freedom at excited states. Together with robust stability, (TMS)2SbCl5 crystal family has been applied as optical waveguide with ultralow loss coefficient of 3.67 ⋅ 10-4 dB μm-1, and shows superior performance in white-light emission and anti-counterfeiting. In short, our study provides a novel and fundamental perspective to structure-property-application relationship of antimony hybrid halides, which will contribute to future rational design of high-performance emissive metal halides.

Mapping Uncharted Lead-Free Halide Perovskites and Related Low-Dimensional Structures

Research on perovskites has grown exponentially in the past decade due to the potential of methyl ammonium lead iodide in photovoltaics. Although these devices have achieved remarkable and competitive power conversion efficiency, concerns have been raised regarding the toxicity of lead and its impact on scaling up the technology. Eliminating lead while conserving the performance of photovoltaic devices is a great challenge. To achieve this goal, the research has been expanded to thousands of compounds with similar or loosely related crystal structures and compositions. Some materials are "re-discovered", and some are yet unexplored, but predictions suggest that their potential applications may go beyond photovoltaics, for example, spintronics, photodetection, photocatalysis, and many other areas. This short review aims to present the classification, some current mapping strategies, and advances of lead-free halide double perovskites, their derivatives, lead-free perovskitoid, and low-dimensional related crystals.

Effects of Electron-Phonon Coupling and Spin-Spin Coupling on the Photoluminescence of Low-Dimensional Metal Halides

Low-dimensional metal halides (LDMHs), as a derivative of three-dimensional lead halide perovskites, have attracted much attention because of their unique crystal structures and fascinating photonic properties. The simple synthesis and rich photonic properties of LDMHs make them striking candidates for the development of lighting, photodetectors, biological imaging, etc. Although many novel LDMHs have been achieved with strong electron-phonon coupling related to their self-trapped excitons (STEs) and excellent optical responses, transition-metal halides or doped halides have not been covered in regard to their rich spin characteristics. In this Perspective, we aim to deeply understand the role of electron-phonon coupling and STEs with magnetic coupling effects in regulating the optical properties of LDMHs and try to provide a novel way or a series of novel systems for the realization of next-generation high-performance luminescent materials with spin-coupling-involved photonics. Finally, an outlook toward potential challenges and applications of such ionic semiconducting LDMHs is also presented.