Ultraviolet Emission from Cerium‐Based Organic‐Inorganic Hybrid Halides and Their Abnormal Anti‐Thermal Quenching Behavior

Abstract Rare earth elements are widely employed and investigated as dopants in luminescent materials because of their ability to modulate hosts’ specific physical and chemical properties. However, stable phosphors crystallized with pure rare earth elements are few and hence their potential for wider utilization is largely limited. Herein, two examples of cerium (Ce)‐based organic–inorganic hybrid halides, (DFPD)₄CeX₇ (DFPD⁺ = 4,4‐difluoropiperidinium; X⁻ = Cl⁻ and Br⁻) and (DFPD)CeCl₄·2MeOH are demonstrated. The Cl compositions of both examples are capable of emitting the fascinating ultraviolet (UV) light (350–375 nm), which represents the shortest emission wavelength ever reported in existing metal halide perovskites. Moreover, the resulting crystals are of high quality, which have intrinsic photoluminescence quantum yields of 95%–100%. Besides, in contrast to their all‐inorganic counterparts like Ce₃CeBr₆, the proposed two forms of Ce³⁺‐based halides show abnormal anti‐thermal quenching behavior (≈128% of emission intensity at 420 K relative to 80 K), being particularly applicable for practical use in a heated environment. A phosphor‐converted light‐emitting diode fabricated with (DFPD)₄CeCl₇ demonstrates stable UV emission (840 min) and has a high external quantum efficiency of 1%. This study opens up the way to a possible design of robust UV‐emitting structures based on rare earth hybrid metal halides.