Expanding the color palette of bicolor-emitting nanocrystals

Owing to their bright and tunable luminescence spectra, nanocrystals appear as a unique playground for light source design. Displays and lighting require white light sources that combine several narrow lines. As Kasha's rule prevents the emission of hot carriers, blends of multiple nanocrystal populations are currently the obvious strategy for broad-band source design. However, a few reports suggest that bicolor emission can also be obtained from a single particle even under weak excitation if a careful design of the exciton scattering mechanism sufficiently slows down its relaxation pathways. A key challenge remains to maintain quantum confinement for color tunability in the same structure, while simultaneously achieving a large size to leverage the critical, slower exciton diffusion or relaxation down to the ground state. Herein, we demonstrate that 2D nanoplatelets offer an original opportunity for the design of confined and large heterostructures. We demonstrate that bicolor emission is not limited to green-red pair and show that blue-yellow and purple-green emissions can be obtained from CdSe/CdTe/CdSe core/crown/crown and CdSe/CdS core/crown heterostructures, respectively.