3 research outputs found
Nano-engineered electronâhole exchange interaction controls exciton dynamics in coreâshell semiconductor nanocrystals
A strong electronâhole exchange interaction (EI) in semiconductor nanocrystals (NCs) gives rise to a large (up to tens of meV) splitting between optically active ('bright') and optically passive ('dark') excitons. This darkâbright splitting has a significant effect on the optical properties of band-edge excitons and leads to a pronounced temperature and magnetic field dependence of radiative decay. Here we demonstrate a nanoengineering-based approach that provides control over EI while maintaining nearly constant emission energy. We show that the darkâbright splitting can be widely tuned by controlling the electronâhole spatial overlap in coreâshell CdSe/CdS NCs with a variable shell width. In thick-shell samples, the EI energy reduces to <250 ÎŒeV, which yields a material that emits with a nearly constant rate over temperatures from 1.5 to 300 K and magnetic fields up to 7 T. The EI-manipulation strategies demonstrated here are general and can be applied to other nanostructures with variable electronâhole overlap