Aliovalent Doping-Induced Enhancement of Self-Trapped Exciton Emission in Ruddlesden–Popper Perovskite

Self-trapped exciton (STE) emission stands out for its large Stokes shift, broad emission spectrum, and high photoluminescence quantum yield (PLQY). In this work, we developed an Sb3+-doped low-dimensional layered halide, Cs2CdBr2Cl2, as a system to achieve efficient broadband emission. By fine-tuning the Sb3+ doping concentration, we induced moderate lattice distortion, resulting in a suitable Huang–Rhys factor (S = 18.00) and a high exciton binding energy (Eb = 144.73 meV), which collectively enabled strong yellow STE emission with a PLQY of nearly 80%. Experimental and theoretical investigations reveal that the emission originates from STE states associated with distorted [SbCl4Br2]3– octahedra. This highly efficient luminescent material, when combined with commercial phosphors, achieves a high color rendering index (Ra) of 90.8 and exhibits excellent radiation resistance and great potential for X-ray imaging applications.