Physics & Astronomy Colloquium – Fall 2021 – Fedin

Speaker: Igor Fedin (University of Alabama, Department of Chemistry and Biochemistry)

Title: Enhanced Emission from the Bright Exciton and Locating the Dark Exciton in Asymmetrically Strained CdSe/Cd_xZn_1–xSe Quantum Dots

Colloidal CdSe/Cd_xZn_1-xSe quantum dots (QDs) designed with a high degree of asymmetric internal strain have recently been shown to host a number of desirable optical properties including subthermal room-temperature line widths, suppressed spectral diffusion, and high photoluminescence (PL) quantum yields. It remains an open question, however, whether they are well-suited for applications requiring emission of identical single photons. Temperature-dependent PL dynamics measured from ensembles of these QDs reveals the radiative recombination rates of bright and dark excitons, and the relaxation rate between the two. Polarization-resolved fluorescence line narrowing (FLN) spectra reveal the quantized acoustic phonons in the QDs that can contribute to relaxation processes. In addition, we identify the signature of the dark exciton in the FLN spectra. In comparison to conventional colloidal CdSe/ZnS core/shell QDs, we find that in asymmetrically strained CdSe QDs over six times more light is emitted directly by the bright exciton. These results are therefore encouraging for the prospects of chemically synthesized colloidal QDs as emitters of single indistinguishable photons. Currently, my group is working to expand these superior photonic properties from the visible to the near-IR spectrum range using cadmium phosphide (Cd₃P₂) QDs.

Homepage: http://chemistry.ua.edu/people/igor-fedin/