Tuning Energy Splitting and Recombination Dynamics of Dark and Bright Excitons in CdSe/CdS Dot-in-Rod Colloidal Nanostructures

We report on a time-resolved study of the photoluminescence of core/shell CdSe/CdS dot-in-rod colloidal nanocrystals having various geometries. By studying the exciton recombination dynamics, we unveil a quadratic dependence of the bright dark exciton energy splitting and the dark exciton radiative recombination rate on the inverse CdS rod width, regardless of the CdSe core size. We also evidence a strong dependence of the spin-flip rate between bright and dark exciton states on the shell thickness that suggests an acoustic phonon bottleneck. This work highlights the possibility to fully control and tune the optical properties of colloidal nano crystals by shape engineering of the CdS shell.