Metal-Cap Composite Nanoparticle for

Jul 12, 2018 - The core radius (r) and the thicknesses of the shell (t1) and the ... we average the enhancement factor of the electric field (|E/E0|av...
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C: Plasmonics; Optical, Magnetic, and Hybrid Materials

Metal-Core/Dielectric-Shell/Metal-Cap Composite Nanoparticle for Upconversion Enhancement Tatsuki Hinamoto, Hiroshi Sugimoto, and Minoru Fujii J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b05211 • Publication Date (Web): 12 Jul 2018 Downloaded from http://pubs.acs.org on July 13, 2018

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The Journal of Physical Chemistry

Metal-Core/Dielectric-Shell/Metal-Cap Composite Nanoparticle for Upconversion Enhancement Tatsuki Hinamoto, Hiroshi Sugimoto, and Minoru Fujii* Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan

ABSTRACT

We have developed an upconversion composite nanoparticle composed of a metal core, an upconversion shell, and a metal cap. Numerical simulation of the nanocomposite revealed that hybridization of the localized surface plasmon modes of the core and the cap results in the emergence of novel bonding and antibonding modes. The latter mode has wide tunability in the resonance wavelength and strong field confinement at the position of the upconversion shell. For the fabrication of the composite nanoparticle, we developed a process that combines liquid phase synthesis and vapor deposition processes. The scattering spectra of single composite nanoparticles agreed well with those in the numerical simulation. The comparison of the upconversion intensity between the metal-core/dielectric-shell structure and the metalcore/dielectric-shell/metal-cap structure revealed that the cap formation increases the intensity several fold.

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INTRODUCTION Photon upconversion, which converts low-energy photons into a high-energy photon, has applications in a variety of fields including fluorescent probes for bio-imaging1, wavelength conversion layers in solar cells2,3, full-color 3D displays4 and security inks5.6–9 Among several upconversion systems, those utilizing long-lived intermediate states of rare-earth ions have superior properties such as high chemical stability and sharp emission bands.6,10 However, the upconversion fluorescence intensity is usually not high enough for practical applications due to the small excitation cross section of parity forbidden intra-4f transitions of rare-earth ions and due to the low quantum efficiency (