(272d) Influence of Crystalline Anisotropy on Localized Surface Plasmon Resonance of Semiconductor Nanocrystals
Unlike typical plasmonic metals like Ag or Au, doped semiconductors can have anisotropic crystal structures for example, Cu2-xS (layered) or Cs:WO3 (hexagonal), which is the focus of our current study. Here in this study, we have shown that colloidally synthesized hexagonal phase Cs:WO3 nanocrystals exhibit strong aspect ratio-dependent LSPR absorption peaks that can only be explained via a cooperative influence of crystalline and shape anisotropies. We demonstrate the dominant influence of crystalline anisotropy, which uniquely causes strong LSPR band-splitting into two distinct peaks with comparable intensities. This finding highlights the limitations of conventional treatments of LSPR that assume isotropic dielectric constants and attribute multimodal peaks uniquely to shape anisotropy effects. This understanding extends our ability to rationally tune LSPR lineshape and near-field enhancement via synthetic control of shape and crystalline anisotropies of semiconductor nanocrystals. In particular, the demonstrated multimodal LSPR with near-equal intensities of h-Cs:WO3 nanocrystals covers the near-infrared (NIR) region of great importance in photonic, solar, and clinical applications while maintaining high visible transparency due to its wide band gap.