The Knowles group is interested in studying the fundamental properties of nanoscale materials in both their ground and photoexcited states. Initial projects will focus on developing colloidal mixed-metal oxide semiconductor nanocrystals and nanostructured thin films that absorb visible and near-infrared light for use in solar energy conversion. Mixed-metal oxide semiconductors are a richly diverse class of materials with optical, electronic, chemical, and magnetic properties that vary widely depending on composition and stoichiometry. By specifically targeting mixed-metal oxide materials with small band gaps, we will take advantage of the superior redox stability of metal oxides relative to chalcogenide semiconductor nanocrystals, while simultaneously avoiding the complication of having to use sensitizers in order to absorb visible light. Ultimately, we wish to use these materials to achieve improved performance in homogeneous and heterogeneous photocatalytic systems.
We will develop new solution-phase colloidal syntheses of mixed-metal oxide nanocrystals that allow us to control their sizes, shapes, compositions, and surface chemistries. Fabrication of nanostructured thin films of these materials by well-established techniques such as sol-gel, chemical bath deposition, and electrochemical deposition will provide benchmark model systems for comparison with colloidal films. One of our primary goals is to understand structure-function relationships between the morphology and chemistry of nanostructured oxide surfaces and their photoelectrochemical behavior.
Students in the Knowles group will gain interdisciplinary experience at the interfaces of physical, inorganic, and materials chemistry. In addition to standard techniques for characterization of solution-phase and nanostructured inorganic materials (i.e. electron microscopy, X-ray diffraction, and NMR, infrared, electronic absorption, Raman, and photoluminescence spectroscopy), the core techniques used in our lab include spectroelectrochemistry, photoconductivity, diffuse reflectance spectroscopy, and time-resolved optical spectroscopies.
- Knowles, K. E.; Nelson, H. D.; Kilburn, T. B.; Gamelin, D. R. "Singlet-Triplet Splittings in the Luminescent Excited States of Colloidal Cu+:CdSe, Cu+:InP, and CuInS2 Nanocrystals: Charge-Transfer Configurations and Self-Trapped Excitons," J. Am. Chem. Soc. 2015, 137, 13138-13147.
- Knowles, K. E.; Kilburn, T. B.; Alzate, D. G.; McDowall, S.; Gamelin, D. R. "Bright CuInS2/CdS Nanocrystal Phosphors for High-Gain Full-Spectrum Luminescent Solar Concentrators," Chem. Commun 2015, 51, 9129-9132.
- Bradshaw, L. R.; Knowles, K. E.; McDowall, S.; Gamelin, D. R. "Nanocrystals for Luminescent Solar Concentrators," Nano Lett. 2015, 15, 1315-1323.
*Featured in Nature: News and Views: Debije, M. “Renewable Energy: Better luminescent solar panels in prospect.” Nature 2015, 519, 298-299.
- Knowles, K. E.; Tagliazucchi, M.; Malicki, M.; Swenson, N. K.; Weiss, E. A. "Electron Transfer as a Probe of the Permeability of Organic Monolayers on the Surfaces of Colloidal PbS Quantum Dots," J. Phys. Chem. C 2013, 117, 15849-15857.
- Knowles, K. E.; Malicki, M.; Parameswaran, R.; Cass, L. C.; Weiss, E. A. "Spontaneous Multi-Electron Transfer from the Surfaces of PbS Quantum Dots to Tetracyanoquinodimethane," J. Am. Chem. Soc. 2013, 135, 7264-7271.
- Knowles, K. E.; McArthur, E. A.; Weiss, E. A "A Multi-Timescale Map of Radiative and Nonradiative Decay Pathways for Excitons in CdSe Quantum Dots," ACS Nano 2011, 5, 2026-2035.
- Knowles, K. E.; Tice, D. B.; McArthur, E. A.; Solomon, G. C.; Weiss, E. A. "Chemical Control of the Photoluminescence of CdSe Quantum Dot-Organic Complexes with a Series of Para-Substituted Aniline Ligands," J. Am. Chem. Soc. 2010, 132, 1041-1050.