Doped metal oxide nanocrystals (NCs) attract immense attention because they exhibit a localized surface plasmon resonance (LSPR) that can be tuned extensively across the infrared region. This makes them potential contenders to be implemented in a variety of applications such as photothermal therapy, sensing, and smart windows. While LSPR tunability triggered through compositional and morphological changes during the synthesis (size, shape, and doping percentage) is well-known and relatively easy to accomplish, practical applications actually require a dynamic modulation of LSPR that is fundamentally less explored and less understood. Since LSPR is a consequence of high carrier density, dynamic modulation of LSPR is achieved by modifying the carrier density through an external stimulus such as electric potential, light, or a chemical redox agent. Recent electrochemical investigations suggested that the extent of LSPR modulation attained in NCs is influenced extensively by the presence of depletion layer on the surface, however, different complications have so far prevented a provide a clear description of the strength of these depletion effects. Here, through chemical titrations on colloidal solutions of Sn-doped In<sub>2</sub>O<sub>3</sub> NCs with decamethylcobaltocene, we realize the full potential of depletion effects and illustrate that the strength of depletion effects in determining the LSPR modulation has been significantly underestimated. Furthermore, utilizing both experiments and mathematical fitting models, we demonstrate that different methods of charging the NCs are not equivalent and chemical doping has the ability to transfer a much higher carrier density than electrochemical doping or photodoping. This will improve the candidacy of LSPR materials for an application and help understand the fundamental changes that happen in the electronic structure during carrier injection and extraction in doped metal oxide NCs.

Modulating plasmonics in doped metal oxide nanocrystals through chemical doping

ACS Spring Meeting 2021

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