Browsing by Author "Cai, Yiyu"

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    Light Emission from Single Plasmonic Nanoparticles
    (2019-07-19) Cai, Yiyu; Link, Stephan
    The precise mechanism of light emission from metallic plasmonic nanoparticles is a contested issue. Photoluminescence and electronic Raman scattering are two different views proposed to explain the observed emission from plasmonic nanostructures. The Stokes and anti-Stokes emission spectroscopy studies of single gold nanorods are reported. A model was developed to quantitatively simulate the experimental emission spectra of gold nanorods. Correlated emission spectra and quantum yields of single gold nanorods with different excitation wavelengths and varied excitation powers demonstrate the underlying effects of hot carrier dynamics following interband and intraband transitions. The plasmonic resonance quality factors, modified by nanorod crystallinity, determine the Purcell enhancement effect and have a linear relation with the emission quantum yield. The central role of hot carriers in the systematical study on gold nanorods as a model system supports a Purcell effect enhanced hot carrier photoluminescence mechanism. The emission spectra of single copper and gold nanocubes are compared, unveiling the synergistic effects of interband transitions and plasmonic enhancement. The excitation wavelength dependent quantum yields are explained by the energy dependent lifetime of d-band holes.
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    Single-Particle Absorption Spectroscopy by Photothermal Contrast
    (American Chemical Society, 2015) Yorulmaz, Mustafa; Nizzero, Sara; Hoggard, Anneli; Wang, Lin-Yung; Cai, Yiyu; Su, Man-Nung; Chang, Wei-Shun; Link, Stephan; Laboratory for Nanophotonics
    Removing effects of sample heterogeneity through single-molecule and single-particle techniques has advanced many fields. While background free luminescence and scattering spectroscopy is widely used, recording the absorption spectrum only is rather difficult. Here we present an approach capable of recording pure absorption spectra of individual nanostructures. We demonstrate the implementation of single-particle absorption spectroscopy on strongly scattering plasmonic nanoparticles by combining photothermal microscopy with a supercontinuum laser and an innovative calibration procedure that accounts for chromatic aberrations and wavelength-dependent excitation powers. Comparison of the absorption spectra to the scattering spectra of the same individual gold nanoparticles reveals the blueshift of the absorption spectra, as predicted by Mie theory but previously not detectable in extinction measurements that measure the sum of absorption and scattering. By covering a wavelength range of 300 nm, we are furthermore able to record absorption spectra of single gold nanorods with different aspect ratios. We find that the spectral shift between absorption and scattering for the longitudinal plasmon resonance decreases as a function of nanorod aspect ratio, which is in agreement with simulations.