Previous experiments on blinking statistics of various semiconductor quantum dots (QDs) revealed that the close packing of QDs at distances of 1 nm (or smaller) results in a significant increase in “on” time corresponding to the system’s state with the high quantum efficiency. However, understanding of physical processes governing this behavior is still incomplete. We use linear-responce time-dependent density functional theory (TDDFT) to calculate non-radiative energy transfer rates between 1-1.5 nm Si QDs and dependence of these rates on the QD size, surface defects, passivating ligands, and the charge. Our calculations demonstrate that the energy transfer between Si QDs separated at the distance of 1 nm happens at 100 ps - 10 ns range, depending on the excitation energy and the surface defects. Imperfect ligand passivation and a charge on the QD significantly accelerate the energy transfer between the QDs. Although the fastest energy transfer happens between optically allowed states, semi-dark trap states with weak oscillator strength also efficiently contribute to the energy transfer, if their energies are in resonance range.  As such, the ultrafast energy transfer between closely packed QDs provide additional channel for rapid population of lower-energy dark states with long lifetime, allowing for only higher-energy bright states contributing to emission, which increase the overall ‘on’ blinking time in QDs aggregates.

Energy transfer in closely packed Si quantum dots: The role of surface defects

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.