Manipulation of the Plasmonic Properties of n-Type Doped Colloidal Indium Oxide Nanocrystals

Abstract

Plasmonic nanocrystals (NCs) have been a focus of intense research over the past decade due to their unique optical properties and wide applications. Indium (III) oxide (In2O3) is an ideal host lattice for plasmonic NCs, owing to its high charge carrier concentration and mobility. In this project, one pot colloidal synthesis has been utilized to prepare antimony-doped In2O3 (AIO) NCs and titanium-doped In2O3 (TIO) NCs. It is shown that both of these doped NC samples exhibit the tunability of the plasmon resonance in the mid-infrared (MIR). For AIO NCs, it is revealed that the plasmon resonance can be well-tuned from 0.25 eV to 0.37 eV, with the maximum electron concentration of ca. 1.24 × 10^20 cm^-3 determined for 10.6 % of Sb. Compared to the broad plasmon of AIO NCs, relatively narrow plasmon of TIO NCs can be tuned from 0.13 eV to 0.28 eV by varying the doping concentration of Ti from 1.12 % to 7.8 %. Furthermore, the highest electron concentration determined for TIO NCs (7.8 % of Ti) is ca. 6.85 × 10^19 cm^-3. Both XRD patterns and high-resolution TEM images indicate that all synthesized AIO and TIO NCs retain the body-centered cubic (bcc)-In2O3 structure. UV-visible absorption spectra confirm the blue shift of the band gap for both AIO NCs and TIO NCs, because of the Burstein-Moss effect. Post treatment of as-synthesized NCs by rapid annealing under H2 or Ar illustrates that the intensity of the plasmon band can be improved appreciably. Finally, electronic and optical properties of AIO and TIO NCs were further investigated by the Density Functional Theory (DFT) calculations. It is expected that AIO and TIO NCs broadly tunable in the MIR can be employed in a variety of potential applications, including sensing, enhanced spectroscopy, and thermal imaging.