Copper-Catalyzed Cation Exchange in CdSe/ZnSe Colloidal Nanoplatelets Enables Spectrally Tunable Narrow-Linewidth...

2D colloidal nanoplatelets (NPLs) are highly attractive for light-emitting devices (LEDs) due to their thickness-dependent electronic structure and distinct excitonic properties. However, most heterostructured core/shell NPLs predominantly emit in the red spectral region and extending their emission toward shorter wavelengths while preserving optical properties remains a major challenge. Here, we demonstrate a copper-catalyzed cation exchange strategy in CdSe/ZnSe core/shell NPLs that enables continuous spectral tuning. By introducing trace amounts of copper to promote cation diffusion, the emission wavelength can be tuned from 620 to 484 nm, while achieving emission linewidths as narrow as ∼12 nm, among the lowest reported for CdZnSe-based NPLs. The copper concentration serves as an additional key parameter to control the extent of the cation exchange process and the resulting optical properties. Subsequent ZnS shell deposition significantly enhances the photoluminescence quantum yield, reaching near-unity values for red-emitting NPLs and increasing to ∼70% and ∼20% for green- and blue-emitting NPLs, respectively. Using these spectrally tunable and narrow-emitting NPLs, we further demonstrate color-conversion white LEDs with an external quantum efficiency of 30%. These results establish copper-catalyzed cation exchange as a powerful strategy for engineering spectrally tunable NPLs with narrow emission linewidth, providing a viable pathway toward next-generation display technologies.