Expanding the Toolbox of All‐Inorganic Perovskite‐Like Rare‐Earth‐Based Metal Halides for Photonic Applications

Abstract All‐inorganic perovskite‐like rare‐earth‐based metal halides (RE‐MHs) have emerged as promising alternatives to the popular lead‐based counterparts, owing to the rich types of RE ions, excellent structural tunability, and their tailored optoelectronic properties enabled by the 5d/4f orbital transitions. The striking optoelectronic properties make RE‐MHs a versatile material platform for fundamental spectroscopic study and applications. This review systematically summarizes synthesis methodologies, including hydrothermal growth, hot‐injection, and mechanochemical routes, with emphasis on crystallinity control and structural tuning. The photoluminescence mechanisms underpinning RE‐MHs are then dissected, covering band‐edge emissions, f–f and d–f transitions, self‐trapped excitons, and synergistic energy transfer processes. Recent advances in device integration, spanning light‐emitting diodes, optical sensing, information encryption, and X‐ray imaging, are highlighted to demonstrate the transformative potential of RE‐MHs. Finally, current challenges and future directions are discussed, aiming to guide material innovations and expand practical applications.