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Colloquium: Dr. Svetlana Kilina

Dr. Svetlana Kilina
Department of Chemistry and Biochemistry
North Dakota State University

Role of Surface Chemistry

 

An Interface on Photophysics of Quantum Dots

The significance of the surface passivation (protection) of colloidal quantum dots (QDs) on their photophysical properties is discussed. Optically forbidden nature of surface-associated states makes their direct measurements challenging. We present several examples, where calculations based on time dependent density functional theory (TDDFT) succeed in providing insights into these issues allowing for explanations of experimental trends and observables sensitive to surface defects and ligand passivation. Thus, our investigations of QD-ligand and QD-QD interactions provide an explanation of experimentally detected enhancement of on-blinking times in closely packed Si QDs and reveal the role of Cl ligands in formation of PbSe nanoplates growing along a specific crystal lattice direction. Our calculations show that photophysics of stoichiometric, magic-size CdnSen QDs is less sensitive to their passivation, compared to non-stoichiometric CdnmSem. In the last, surface-driven optically inactive midgap states can be eliminated by anionic ligands, such as carboxylates, thiolates, and even hydrides, explaining better emission of metal-enriched than nonmetal-enriched QDs. Additionally, we found that electron cooling is happening much faster in PbS/CdS than in PbSe/CdSe core/shell QDs due to stronger electron coupling to ‘softer’ phonons in structures of lighter elements (S vs. Se).

Overall, our calculations provide insights into the surface chemistry of QDs and offering guidance for controlling the optical response of nanostructures by means of core-shell, QD-QD and QD-ligand engineering.

Department of Physics & Astrophysics
Witmer Hall Room 213
101 Cornell St Stop 7129
Grand Forks, ND 58202-7129
P 701.777.2911
physics@UND.edu
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