Highly Emissive Lanthanide-Doped Ruddlesden–Popper Cs ₂ CdCl ₄ Nanoplatelets for White Light-Emitting Diode Applications

Lanthanide (Ln3+)-doped halide perovskite nanocrystals offer a compelling platform for tunable photoluminescence, yet their integration into Ruddlesden–Popper (RP) phases remains largely unexplored. Here, we report the first colloidal synthesis of Ln3+-doped RP-phase Cs2CdCl4 nanoplatelets (NPLs) via a hot-injection method. Doping with Pr3+, Ce3+, Tb3+, and Eu3+ yields stable, well-defined 2D NPLs with emissions ranging from UV–C to red spectral ranges. Co-doping systems (Ce3+/Tb3+ and Tb3+/Eu3+) exhibit efficient interdopant energy transfer and the record photoluminescence quantum yield (up to 70%) is reported for the Ce3+/Tb3+ codoped sample. A prototype UV-pumped white-light LED fabricated from a blend of these NPLs achieves balanced emission near ideal white-light coordinates. These results establish RP-phase Cs2CdCl4 NPLs as versatile hosts for dopant engineering and next-generation optoelectronic applications.