Optically dark excited states are generators of long-lived excitons and are generally created from the non-radiative decay of bright excited states. Low-energy electron scattering followed by electron capture by quantum dots provides an alternate pathway to study these dark unoccupied levels. Resonance electron capture from an incident electron beam also bypasses optical selection rules for populating these excited states. This theoretical and computational study uses the many-body perturbation theory and 1-particle Green’s function method to investigate dark excited states in quantum dots. The developed method was applied to study the generation of hot-electron states in PbS, PbSe, CdS and CdSe quantum dots by scattering from a 5 eV electron beam, and results on these systems will be presented. The radiative decay of the hot-electron states to low-energy states by the inverse photoemission process will be discussed. Unlike the 2-photon transient absorption process, which also involves unoccupied-to-unoccupied level transitions, the inverse photoemission process does not involve generation of a hole-state in the occupied level. This allows for a unique opportunity to analyze hot-electron states without interferences from electron-hole coupling interaction. The impact of electron-correlation in the presence and absence of hole states will be discussed, and comparisons with 2-photon transient excitation will be presented.

Characterization of dark excited states in quantum dots from low-energy resonant electron capture and inverse photoemmision processes

ACS Spring 2022

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