Exciton-exciton interaction and cascade relaxation of excitons in colloidal CdSe nanoplatelets

The exciton-exciton interaction and phonon-induced cascade relaxation of free electrons and holes determine the dynamic of stationary resonantly excited excitons in CdSe/CdS nanoplatelets. Along with saturation of the heavyhole and light-hole exciton transitions explained by the phase space filling effect the exciton-exciton interaction increases and starts to play a significant role in excitons dynamic. The lowest four band structure of CdSe/CdS nanoplatelets at the Gamma point of Brillouin zone and its modification with CdS shell thickness changing are experimentally investigated for the first time. Bleaching of the two additional to the heavyand light-hole exciton transitions with the energies higher than the absorbed photons energy can occur at room temperature due to rapid cascade relaxation of free electrons and holes formed as a result of the exciton-exciton interaction. To analyze the recombination and interaction of excitons in the colloidal nanoplatelets under high excitation densities the rate equations describing the exciton-exciton and exciton-electron interactions are applied.

Automated summary

The dynamics of resonantly excited excitons in CdSe/CdS nanoplatelets are determined by exciton-exciton interaction and phonon-induced cascade relaxation. The study also reveals the significance of exciton-exciton interaction in exciton dynamics, particularly in relation to the saturation of heavy-hole and light-hole exciton transitions. Additionally, the study experimentally investigates the lowest four band structure of CdSe/CdS nanoplatelets and the bleaching of higher energy transitions due to rapid cascade relaxation of electrons and holes.