title: Broadband Absorbing Exciton-Plasmon Metafluids with Narrow Transparency Windows.
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.
authors.affiliation: Department of Mechanical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Jihua
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Mechanical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Nicolaas J
authors.initials: NJ
authors.lastname: Kramer
authors.affiliation: Department of Mechanical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Katelyn S
authors.initials: KS
authors.lastname: Schramke
authors.affiliation: Department of Mechanical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Lance M
authors.initials: LM
authors.lastname: Wheeler
authors.affiliation: Department of Physics and Astronomy, Ohio University , Athens, Ohio 45701, United States.
authors.forename: Lucas V
authors.initials: LV
authors.lastname: Besteiro
authors.affiliation: Department of Mechanical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hogan
authors.affiliation: Department of Physics and Astronomy, Ohio University , Athens, Ohio 45701, United States.
authors.forename: Alexander O
authors.initials: AO
authors.lastname: Govorov
authors.affiliation: Department of Mechanical Engineering, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Uwe R
authors.initials: UR
authors.lastname: Kortshagen
keywords: Colloidal boron-doped silicon nanocrystals; exciton−plasmon metafluid; gold nanorods; transparency window