Engineering Bicolor Emission in 2D Core/Crown CdSe/CdSei1-xTex Nanoplatelet Heterostructures Using Band-Offset Tuning

Colloidal 2D nanoplatelets (NPLs) are a class of nanoparticles that offer the possibility of forming two types of heterostructures, by growing either in the confined direction or perpendicular to the confined direction, called core/crown NPLs. Here, we demonstrate that bicolor emission can be obtained from 2D NPLs with a core/crown geometry. To date, for CdSe/CdTe NPLs with type-II band alignment, only charge transfer emission has been observed due to the very fast (<picoseconds) transfer of the electrons toward the CdSe core. Here, we show that using CdSei(1-x)Te(x) alloys crowned with the right composition and lateral extension enables the observation of bicolor emission at the single-particle level. One source of emission originates from recombination at the core/crown interface (X-int), and the other emission source originates from direct recombination in the crown (X-crown). This crown emission, which isnonvisible in pure CdSe/CdTe core crown NPLs, results from the large binding energy compared to the reduced conduction band offset existing in the alloy with intermediate (60%) Te content. These observations are only made possible by the 2D geometry of the NPLs.