Localized surface plasmon resonance (LSPR) in metal nanoparticles permits strong light absorption and near-field enhancement within the visible wavelengths (400~700nm). Gold or Silver nanoparticles have thus been widely studied and practically used to manipulate visible light.

Recently, it was found that degenerately doped metal oxide nanocrystals could also host LSPR with their mobile charge careers. Unlike in metals, the largely variable career density in doped metal oxides extends the accessible spectral range of LSPR across the entire infrared (IR) region, while the interest in IR-optics is rapidly growing for applications to solar energy harvesting, biomedical imaging & therapy, telecommunication, and night/thermal imaging. ​

We investigate how compositional and structural attributes of doped metal oxide nanocrystals influence their infrared LSPR properties that are unseen from noble metal nanoparticles. For instance, a highly anisotropic crystal structure of Cs-tungsten bronze (Cs:WO3-δ) originates dual-mode LSPR [1]. ​We explore novel methods to control the nanostructure of individual Cs:WO3-δ nanocrystals and their collective assemblies, which allow to exquisitely tune their LSPR spectra [2]. We have found that the anisotropic crystal structure and surface chemistry offer key advantages in controlling particle shape [3], facilitating reversible oriented assemblies [4] promoting directional (ex. polarized) and switchable LSPR. Tailoring the shape of Cs:WO3-δ nanocrystals has expanded 

their LSPR spectral range across the entire NIR-SWIR-MIR region (above figure). 

Currently, we explore how these tunable plasmonic properties can be harnessed for energy saving and harvesting devices [5] as well as for next generation biomedical imaging and therapy 

applications. 

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[1] J Kim*, A Agrawal, F Krieg, A Bergerud, D J Milliron*, “The interplay of Shape and Crystalline Anisotropies in Plasmonic Semiconductor Nanocrystals” Nano Letters 16, 3879-3884 (2016)  [Link]​​​

​[2] Y. Cheref, F. Lochon, L. Daugas, C. C-Langavant, E. Larquet, A. Baron, T. Gacoin, J. Kim* “Dual-band LSPR of tungsten bronze nanocrystals tunable over NIR and SWIR ranges” Chemistry of Materials 34 (21), 9795 (2022). [Link]

[3] J. Oh, J. Davis, S. Tusseau-Nenez, M. Plapp, A. Baron, T. Gacoin*, J. Kim* “Continuous anisotropic growth of plasmonic CsxWO3–δ nanocrystals into rods and platelets” under review at ACS Nano [Link] 

[4] C. Cleret, J. Oh, F. Lochon, S. Tusseau-Nenez, V. Ponsinet, A. Baron, T. Gacoin*, J. Kim* “Near-Infrared Dual-Band LSPR Coupling in Oriented Assembly of Doped Metal Oxide Nanocrystal Platelets” Nano Letters 24 (10) 3074-3081 (2024). [Link]

[5] L. Daugas, K. Lahlil, C. Langavant, I. Florea, E. Larquet, H. Henry, J. Kim*, T. Gacoin* “Investigation of LSPR Coupling Effects toward the Rational Design of CsxWO3–δ Based Solar NIR Filtering Coatings” Advanced Functional Materials 33 2212845 (2023). [Link]​​​​

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