Tailoring light emission in colloidal nanocrystals through lattice distortion engineering

Colloidal semiconductor nanocrystals (quantum dots) exhibit bright, narrowband, and spectrally tunable emission, making them attractive for photonic applications. Their emission properties are governed by closely spaced exciton fine structure, whose thermal mixing complicates control over key characteristics such as color purity, radiative rate, and polarization. Moreover, the lowest-energy excitonic state is typically non-emissive (dark), suppressing emission rates, particularly at cryogenic temperatures. Here we show that these limitations can be addressed by inducing controlled lattice distortion in zinc blende CdSe nanocrystals through pseudomorphic epitaxial growth of a ZnSe shell. This approach modifies the exciton fine structure by placing an emissive (bright) state at the lowest energy and increasing the separation between bright states derived from light- and heavy-hole subbands. These changes reduce thermal mixing, resulting in accelerated emission at low temperatures, sub-thermal linewidths, and polarization. These findings establish lattice distortion engineering as a strategy for controlling emission properties in colloidal nanocrystals.