Cs₂Cd1–xMnxCl₄ Nanoplatelets for Thermal Quenching Resistance and Luminescence Tuning

Two-dimensional (2D) metal halides exhibit unique optical properties, attracting significant attention. Cs2CdCl4 with a 2D layered Ruddlesden–Popper (R–P) phase demonstrates poor optical characteristics, limiting its potential application. The introduction of Mn2+ doping improved its luminescence. The weak-blue emission of pure Cs2CdCl4 shifts to an orange-red color after Mn doping, which is caused by Mn2+ and Mn–Mn ferromagnetic coupling in the point–point connection between neighbored octahedra by increasing the feed ratio of Mn2+. Under strong quantum confinement effects, the introduction of Mn2+ into the 2D Cd–Cl lattice leads to the formation of exciton magnetic polarons (EMPs) and localized exciton magnetic polarons (LEMPs), significantly influencing their optical properties and resulting in a gradual red shift in their emission bands. The photoluminescence quantum yield (PLQY) is tremendously increased to 46% in the doped samples, accompanied by tunable emissions achieved through an increasing amount of Mn doping. This enhancement and shift in luminescence are attributed to an energy transfer pathway from the defect state luminescence of Cs2CdCl4 to the dominant luminescence via single Mn2+ and Mn–Mn pair d–d transitions. This study indicates the spin–spin coupling effect of doped metal ions on the luminescence enhancement and shift in 2D layered halides, thereby presenting new prospects for practical applications of R–P phase 2D layered nanoplatelets.