Localized surface plasmon resonance (LSPR) in semiconductor nanocrystals (NCs) that results in resonant absorption, scattering, and near field enhancement around the NC can be tuned across a wide optical spectral range from visible to far-infrared by synthetically varying doping level. Cube-shaped NCs of conventional metals like gold and silver generally exhibit LSPR in the visible region with spectral modes determined by their faceted shapes. However, faceted NCs exhibiting LSPR response in the infrared (IR) region are relatively rare. We describe the colloidal synthesis of nanoscale fluorine-doped indium oxide (F:In₂O₃) cubes with LSPR response in the IR region, wherein fluorine was found to both direct the cubic morphology and act as an aliovalent dopant. The presence of fluorine was found to impart higher stabilization to the (100) facets, suggesting that the cubic morphology results from surface binding of F-atoms. In addition, fluorine acts as an anionic aliovalent dopant in the cubic bixbyite lattice of In₂O₃, introducing a high concentration of free electrons leading to LSPR. The cubes exhibit narrow, shape-dependent multimodal LSPR extinction peaks due to corner- and edge-centered modes. The spatial origin of these different contributions to the spectral response are directly visualized by electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM). A synthetic challenge in faceted metal oxide NCs is realizing tunable LSPR near-field response in the IR. We expand to colloidal synthesis of fluorine, tin co-doped indium oxide (F,Sn:In₂O₃) NC cubes with tunable IR range LSPR. Free carrier concentration is tuned through controlled Sn dopant incorporation, where Sn is an aliovalent n-type dopant in the In₂O₃ lattice. Monolayer NC arrays are fabricated through liquid-air interface assembly, NC film nanocavities with heightened near-field enhancement (NFE). The tunable F,Sn:In₂O₃ NC near-field is coupled with PbS quantum dots, via the Purcell effect. The detuning frequency between the nanocavity and exciton is varied, resulting in IR near-field dependent enhanced exciton lifetime decayChemical Engineerin
