Near-infrared emitting metal halide materials: Luminescence design and applications

Near-infrared (NIR) luminescent metal halide (LMH) materials have attracted great attention in various optoelectronic applications due to their low-temperature solution-processable synthesis, abundant crystallographic/electronic structures, and unique optoelectronic properties. However, some challenges still remain in their luminescence design, performance improvement, and application assignments. This review systematically summarizes the development of NIR LMHs through classifying NIR luminescent origins into four major categories: band-edge emission, self-trapped exciton (STE) emission, ion emission, and defect-related emission. The luminescence mechanisms of different types of NIR LMHs are discussed in detail by analyzing typical examples. Reasonable strategies for designing and optimizing luminescence/optoelectronic properties of NIR LMHs are summarized, including bandgap engineering, self-trapping state engineering, chemical composition modification, energy transfer, and other auxiliary strategies such as improvement of synthesis scheme and post-processing. Furthermore, application prospects based on the optoelectronic devices are revealed, including phosphor-converted light-emitting diodes (LEDs), electroluminescent LEDs, photodetectors, solar cells, and x-ray scintillators, as well as demonstrations of some related practical applications. Finally, the existing challenges and future perspectives on the development of NIR LMH materials are critically proposed. This review aims to provide general understanding and guidance for the design of high-performance NIR LMHs materials.