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The Dukovic lab studies what happens to electrons and holes in semiconductor nanomaterials after they absorb light, and how that understanding can be used to drive useful chemical reactions and control light emission. Our approach combines colloidal synthesis, femtosecond-to-microsecond spectroscopy, kinetic modeling, and structural characterization by electron microscopy. Our work falls roughly in three areas.

Photoexcited carrier dynamics in semiconductor nanocrystals

We combine colloidal synthesis, femtosecond-to-microsecond spectroscopy, and kinetic modeling to build quantitative physical descriptions of carrier dynamics in semiconductor nanocrystals. For example, with theory from the Eaves group, we showed that holes trapped at nanorod surfaces are not stationary but diffuse across the surface ( and related papers). Consequently, the rates of a photochemical oxidation may be limited by hole diffusion to the acceptor rather than by the rate of the transfer step itself. More recently, by removing the hole and generating negatively charged CdS quantum dots, we isolated the cooling of hot electrons and, with theory from the , revealed the phonon bottleneck limited lifetime that is 2000-fold longer than in the presence of the hole, perhaps long enough to support hot-electron photochemistry (, ).

Driving multielectron chemistry with light

Reactions such as the reduction of N₂ to ammonia and the formation of carbon–carbon bonds from CO₂ require the delivery of many electrons to a catalyst, which is challenging to do with synthetic catalysts. Nature carries out these reactions using redox enzymes. With enzyme collaborators , , , and their groups, we have been using semiconductor nanocrystals to supply those electrons after they absorb light (e.g., , , , ). We have been characterizing the kinetics of the many steps involved in photochemical catalysis of these multielectron reactions as well as the details of the nanocrystal-enzyme binding to identify the efficiency-limiting processes, with the goal of tuning the nanocrystal properties to adapt them for enzyme catalysis.

Beyond enzymes, we study how to extend the lifetimes of photogenerated charges in nanocrystals and deliver them to molecular acceptors and catalysts in the Energy Frontier Research Center . Recent results include exceptionally long-lived charge-separated states in CdS nanocrystals with a covalently bound hole acceptor () and the effect of binding motifs on electron transfer and recombination in CdSe quantum dots functionalized with modified viologens ().

Relating structure and composition to optical properties

Many semiconductors of interest for optoelectronic applications are solid solutions whose properties depend on how their elements are distributed, not only on their average composition. We study how the distribution of elements within individual nanocrystals arises during synthesis and how it determines their optical properties. To do so, we combine optical spectroscopy with electron microscopy, elemental mapping, and electron energy-loss spectroscopy of single particles, which reveal heterogeneity that ensemble measurements cannot detect. Our work has focused on (Ga_1–xZn_x)(N_1–xO_x) oxynitrides for solar water splitting (, ) and, with the , on In_1–xGa_xP_{1–γ}As_γ nanocrystals for near-infrared optoelectronics (). We have also contributed structural insights into the optical properties of materials studied in the NSF Science and Technology Center for Integration of Modern Optoelectronic Materials on Demand () (e.g., ). Our electron microscopy work is done in close collaboration with Sadegh Yazdi (Â鶹Ãâ·Ñ°æÏÂÔØBoulder Facility for Electron Microscopy of Materials).

A complete list of our publications is on the Publications page and on .