Alkaline-Earth-Site Confinement Enables 98% Quantum Yield Orange Emission in Mn-Doped Cadmium Halide

The luminescence efficiency of Mn2+-doped metal halides is often limited by concentration quenching caused by Mn-Mn interactions. In this work, the alkaline-earth cadmium chloride BaCd2Cl6·6H2O:Mn2+was synthesized via a mechanical grinding method. The three-dimensional network framework of this compound effectively isolates Mn2+ions with a Mn-Mn separation of 4.87 Å, thereby suppressing concentration quenching. Under 254 nm ultraviolet excitation, the sample exhibits efficient orange emission centered at 588 nm with a photoluminescence quantum yield (PLQY) as high as 98%. Temperature-dependent photoluminescence studies reveal that the optimal emission temperature of this system is 320 K, demonstrating good thermal stability. This work achieves, for the first time, near-unity Mn2+luminescence efficiency in a Ba-site alkaline-earth cadmium halide system, demonstrating that alkaline-earth-site confinement provides an effective strategy for achieving highly efficient Mn-doped halide luminescence.