Abstract
Light emission from gold nanoparticles was investigated with ultra-narrow-band notch filters to obtain the complete spectral shape. The anti-Stokes emission band was observed at all excitation wavelengths. The spectral shape of the anti-Stokes emission could be well fitted by a Fermi–Dirac-like line shape, while the spectral profile of the Stokes emission could be fitted by a Lorentzian line shape. The electron distribution and local surface plasmon resonance jointly determined the spectral shape. Additionally, we found that the anti-Stokes emission intensity increased more rapidly compared with that of the Stokes emission as illumination power was increased. This phenomenon can be understood from the temperature dependence of the electron distribution owing to photothermal effects.
Highlights
Photoluminescence was first supposed to arise from interband transitions, and it is enhanced by localized surface plasmon (LSP) resonance
Previous reports on the emission spectra of gold nanoparticles have been collected mainly with the use of interference optical filters, which prevent extraction of the complete spectral shape near the excitation wavelength.[4,10,11]
To elucidate the spectral line shape, two spectra of the gold nanorods (GNRs) emission measured with two different volume Bragg Grating (VBG)-based filters are shown in Fig.2a, revealing the separation between the LSP band maximum and the excitation wavelength
Summary
Photoluminescence (PL), is a well-known phenomenon.[1,2,3] Photoluminescence was first supposed to arise from interband transitions, and it is enhanced by localized surface plasmon (LSP) resonance. To obtain the full-spectra line shape with an ultra-narrow notch band, VBG-based notch filters (OptiGrate Corp.) were applied in a Jobin-Yvon HR800 Raman system with laser excitation at 633 and 676 nm, as shown schematically in Fig.1b.14 This experimental configuration allowed for ultralow frequency Raman spectroscopy measurements; full details of this technique have been described elsewhere.[14] The gold nanorods were synthesized by a seed-mediated method.
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