Browsing by Subject "Plasmonic nanocrystals"

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Spectroscopic analysis of the thermal and optical effects of plasmon absorption in semiconductor metal oxide nanocrystals
(2022-08-30) Blemker, Michelle Ann; Roberts, Sean T.; Milliron, Delia; Henkleman, Graeme; Baiz, Carlos; Korgel, Brian
Plasmonically active materials have the unique ability to use photons to drive a collective multi-electronic oscillatory response. On the nanoscale, this plasmon response gives rise to absorption features previously unseen in bulk materials. This brilliant optical effect has been seen for centuries; suspensions of metallic nanocrystals have been used as a way to achieve beautiful coloration in glassware and art. The nature of this phenomena has only recently been explained in the last century, however, the physics behind the relaxation of electrons driven by this response, and how to exploit them, still desire elucidation. Here, the energetic pathways of electronic absorption and relaxation in plasmonically-active doped semiconductor nanocrystals are studied using spectroscopic and computational methods. We explore the material-dependent properties of the localized surface plasmon resonance in doped metal-oxide nanoparticles, and how to optimize a material for a desired effect. We find that compared to their metallic counterparts, metal oxide nanoparticles have the unique ability to absorb near-infrared light while elevating their electrons to exceedingly high energies. The intense changes in electronic temperatures result in various optical and thermal changes necessary for applications such as electron transfer, biological phototherapies, and optical switching. Next, observable variations to the material’s extinction profile driven by plasmon excitation, whether absorption or reflectivity, are detected using ultrafast spectroscopic methods. The changes are due to alterations in the nanocrystal’s dielectric function due to heating of its electronic and lattice temperatures. We are able to successfully model the ultrafast response of these materials by determining several material constants, that allows us to predict how different materials will behave under plasmon excitation. Lastly, utilization of these plasmonically-active charge carriers for photocatalytic processes is explored. Knowledge of the physics behind how plasmonically-driven electrons respond to photoexcitation allows us to confidently move forward complexing these semiconductors with organic molecules with the goal of directing electron and/or hole transfer with low-energy photons. We find there is much to explore in this area, as the preliminary data suggests plasmonically-enhanced multiphoton absorption by organic semiconductors. The fundamentals of plasmon resonances in semiconductor nanoparticles is vast, yet current research, including this work, suggests their future as a photoactive material is bright.