Achieving Near-Unity Photoluminescence Quantum Yield in Lead-Free Cerium (III) Halides Cs3CeX6 (X = Cl, Br, I) for Multifunctional Applications

Rare-earth metal halides have emerged as a compelling class of luminescent materials, offering an environmentally benign alternative to toxic lead-based halides. This work reports the successful synthesis of Cs 3 CeX 6 (X = Cl, Br, I) with tunable emission and excellent photoluminescence quantum yield (PLQY) of Cs 3 CeCl 6 . Through controlled halogen substitution in the Cs 3 CeX 6 (X = Cl, Br, I) system, composition-dependent emission redshift (Cl→Br→I) is observed. Among them, Cs 3 CeCl 6 achieves a photoluminescence quantum yield (PLQY) of 99.89%, significantly surpassing the 92.57% PLQY of Cs 3 CeBr 6 and the 7.53% PLQY of Cs 3 CeI 6 , meanwhile surpassing that of most previously reported lead-free metal halides, highlighting its exceptional potential for efficient luminescent applications. Thermal stability analysis reveals that Cs 3 CeCl 6 maintains remarkable emission efficiency at elevated temperatures, retaining > 85% of its room-temperature luminescence intensity at 438 K, compared to only 60% for Cs 3 CeBr 6 and a mere 10% for Cs 3 CeI 6 . The exceptional thermal robustness originates from their characteristically high activation energies for thermal quenching, which effectively suppress non-radiative relaxation pathways. White light-emitting diodes (LEDs) based on Cs 3 CeI 6 exhibit a remarkable color rendering index (R a ) of 95.1, in contrast to those based on Cs 3 CeCl 6 (R a = 77.6) and Cs 3 CeBr 6 (R a = 79.6); all WLEDs based on Cs 3 CeX 6 (X = Cl, Br, I) demonstrate excellent atmospheric stability. With near-unity PLQY and remarkable thermal stability of Cs 3 CeCl 6 , coupled with the outstanding white LEDs performance of Cs 3 CeI 6 , Cs 3 CeX 6 (X = Cl, Br, I) compounds emerge as promising candidates for next-generation environmentally friendly optoelectronic applications, particularly in advanced display technologies and solid-state lighting systems. This work contributes to the advancement of eco-friendly emitters with both high efficiency and practical utility in next-generation optical technologies.