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 assign-ments.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 design-ing 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,pho-todetectors,solar cells,and x-ray scintillators,as well as demonstrations of some related practical applications.Finally,the existing challenges and future perspec-tives 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.