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

Lanthanide (Ln 3+ )-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 Ln 3+ -doped RP-phase Cs 2 CdCl 4 nanoplatelets (NPLs) via a hot-injection method. Doping with Pr 3+, Ce 3+, Tb 3+, and Eu 3+ yields stable, well-defined 2D NPLs with emissions ranging from UV–C to red spectral ranges. Co-doping systems (Ce 3+ /Tb 3+ and Tb 3+ /Eu 3+ ) exhibit efficient interdopant energy transfer and the record photoluminescence quantum yield (up to 70%) is reported for the Ce 3+ /Tb 3+ 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 Cs 2 CdCl 4 NPLs as versatile hosts for dopant engineering and next-generation optoelectronic applications.