Disordered plasmonic nanostructures for advanced absorber, emitter, detector, and guide of light

Plasmonics have focused on controlling electromagnetic field inside dielectric-metal interface to enhance light absorption, emission, conversion, and detection. For particular applications, periodic nano-scale plasmonic structures such as lattice-type 2D array of metal nanoparticles and/or uniformly patterned 2D/3D grating structures have been intensively studied. However, these periodic plasmonic nanostructures are generally limited to be applicable for wideband as well as far from being cost-effectiveness of fabrication. In this study, we instead demonstrated disordered plasmonic nanostructures comprised by sub-wavelength metallic nanoparticles or nanowires network. The disordered nanostructures are deliberately designed to induce and localize a few orders of magnitude enhanced intesity of near-field. The induced field finally results in two- or three-order enhanced intensity of emitted light by the near IR (NIR)-to-visible light upconversion (UCL). In order to form plasmonic ‘hot-spots’, we fabricated self-assembled array of sub-100 nm Ag nanoparticles over a plasmonic substrate containing β-NaYF4:Yb3+/Er3+ UC nanoparticles. We also employed a randomly aligned network of micrometer-long Ag nanowires as sub-wavelength platform for Fabry-Perot resonance. We experimentally and computationally observed and confirmed the formation of strong near-field of incident NIR around in the nanostructures. We also observed strong emission of visible (green and red) light driven by nano-antenna effects. Based on enhanced upconversion properties, we also observed notable photo-detection performances at NIR. We finally applied the disordered plasmonic nanostructures to construct a micro-strip-type waveguide to effectively confine and deliver NIR light over long range while filtering visible spectrum. The disordered plasmonic nanostructures are expected to be applicable to a variety of purposes such as bio- and chemical sensors and terahertz communication.