Tuning Plasmon Resonance of In₂O₃ Nanocrystals throughout the Mid-Infrared Region by Competition between Electron Activation and Trapping

Abstract

Controlling plasmonic properties of aliovalently doped semiconductor nanocrystals in mid-infrared (MIR) spectral region is of a particular current interest, because of their potential application in heat-responsive devices and near-field enhanced spectroscopies. However, a lack of detailed understanding of the correlations among the electronic structure of the host lattice, dopant ions, and surface properties hampers the development of MIR-tunable plasmonic nanocrystals (NCs). In this article, we report the colloidal synthesis and spectroscopic properties of two new plasmonic NC systems based on In2O3, antimony- and titanium-doped In2O3 NCs, and comparative investigation of their electronic structure using the combination of the Drude–Lorenz model and density functional theory. The localized surface plasmon resonances (LSPRs) lie at lower energies and have smaller bandwidths for Ti-doped than for Sb-doped In2O3 NCs with similar doping levels, indicating lower free electron density. Surprisingly, the Fermi level is found to be higher in Ti-doped In2O3 than in Sb-doped In2O3, suggesting the formation of electron trap states on nanocrystal surfaces, which reduce carrier density without significantly impacting their mobility. Controlling the competition between doping concentration and electron trapping allowed us to generate LSPR in Ti-doped In2O3 nanocrystals deep in the MIR region, and tune the absorption spectra from 650 cm–1 to 8000 cm–1. We also demonstrated the possibility to enhance the intensity of LSPR in these new plasmonic NCs by adjusting the synthesis and post-synthesis treatment conditions. The results of this work allow for an expansion of the tuning range of LSPR of colloidal metal oxide NCs by controlling the electronic structure of aliovalent dopant and charge carrier trapping.

Plasmon-induced carrier polarization in semiconductor nanocrystals

“…9 Subsequently, different dopants were introduced into In2O3, including, Ti, Sb, Ce and Mo, to tune to plasmon frequency from NIR to MIR. 12,[30][31] Many other types of metal oxides substitutionally doped with high-valence-cations have been extensively studied in the search of plasmonic semiconductor nanomaterials, including ZnO doped with Al, Ga, and In; 16 CdO doped with Dy, In, and Sn; 17,[32][33] TiO2 doped with Nb; 19 SnO2 doped with Sb, 18 etc. In these degenerately doped semiconductor NCs, the dopants substitute the lattice cations and cause the shift of the Fermi level depending on the energetic alignment of the dopant orbitals with the conduction band of metal oxides.…”

“…Furthermore, the ability to control carrier activation, trapping, and scattering via NC composition and/or surface chemistry allows for fine tuning of the energy, band width, and quality factor of the LSPR. [12][13][14][15]…”

Rapid, facile synthesis of InSb twinning superlattice nanowires with a high-frequency photoconductivity response

“…57 Additionally, the scattering peaks at 113.9 and 132.5 cm À1 are corresponding to In 2 O 3 due to the partial surface oxidation of InSb NWs, which further conrmed by high-resolution X-ray photoelectron spectroscopy (XPS) spectra (Fig. S1 † 58 although the oxide impurities cannot be characterized by X-ray diffraction (Fig. 1a).…”

Sustainable Nanoplasmon‐Enhanced Photoredox Reactions: Synthesis, Characterization, and Applications

“…In a work reported by Fang et al, the LSPR of Ti and Sb doped In 2 O 3 nanocrystals was tuned in the mid‐infrared region. [ 135 ] Synthesized by a dispersion‐precipitation method, the two systems (Ti:In 2 O 3 and Sb:In 2 O 3 ) had discrete electronic structures. The absorption bands of Ti:In 2 O 3 exhibit red shifts are symmetric and narrower and have a low free electron concentration.…”