Furthermore, their versatility to display plasmon modes in the first, second, or both NIR windows is particularly advantageous for bioapplications, especially considering their strong absorbing and near-field enhancing properties. Therefore, they can serve as an ideal platform to evaluate the crosstalk between plasmonic metals and plasmonic semiconductors at the nanoscale. Such well-defined nanosized colloidal assemblies feature the unique ability of holding an all-metallic, a metallic/semiconductor, or an all-semiconductor plasmonic response in the NIR.
The optical properties of the NPCs can be reversibly switched back to a purely metallic plasmonic character upon reversible conversion of 2– xSe into 2Se. Conversely, for high vacancy doping levels their NIR optical response is dominated by the two most intense plasmon modes from the shell: the transverse (along the shortest transversal axis) and longitudinal (along the major longitudinal axis) modes. For low vacancy doping levels the NIR optical properties of the dually plasmonic NPCs are determined by the LPBs of the semiconductor shell (along its major longitudinal axis) and of the metal core. Under aerobic conditions the shell undergoes vacancy doping ( x > 0), leading to the plasmon-rich NIR spectrum of the 2– xSe NPCs. The spectral response of the 2Se NPCs is governed by the transverse and longitudinal plasmon bands (LPB) of the anisotropic metallic core, since the Cu 2Se shell is nonplasmonic. Here we combine electrostatic self-assembly and Cd 2+/Cu + cation exchange to obtain an anisotropic core–shell nanoparticle cluster (NPC) whose optical properties stem from two dissimilar plasmonic materials: a gold nanorod (AuNR) core and a copper selenide (Cu 2– xSe, x ≥ 0) supraparticle shell. Exerting control over the near-infrared (NIR) plasmonic response of nanosized metals and semiconductors can facilitate access to unexplored phenomena and applications.
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