Broadband Absorbing Exciton–Plasmon Metafluids
with Narrow Transparency Windows
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Abstract
Optical
metafluids that consist of colloidal solutions of plasmonic and/or
excitonic nanomaterials may play important roles as functional working
fluids or as means for producing solid metamaterial coatings. The
concept of a metafluid employed here is based on the picture that
a single ballistic photon, propagating through the metafluid, interacts
with a large collection of specifically designed optically active
nanocrystals. We demonstrate water-based metafluids that act as broadband
electromagnetic absorbers in a spectral range of 200–3300 nm
and feature a tunable narrow (∼100 nm) transparency window
in the visible-to-near-infrared region. To define this transparency
window, we employ plasmonic gold nanorods. We utilize excitonic boron-doped
silicon nanocrystals as opaque optical absorbers (“optical
wall”) in the UV and blue-green range of the spectrum. Water
itself acts as an opaque “wall” in the near-infrared
to infrared. We explore the limits of the concept of a “simple”
metafluid by computationally testing and validating the effective
medium approach based on the Beer–Lambert law. According to
our simulations and experiments, particle aggregation and the associated
decay of the window effect are one example of the failure of the simple
metafluid concept due to strong interparticle interactions