The plasmonic engineering of metal nanoparticles for enhanced fluorescence and Raman scattering

We have investigated the effects of tuning the localized surface plasmon resonance (LSPR) of a silver film on the extinction spectrum, Raman signal, and fluorescence intensity from nearby fluorophores. We observe the formation of hybridized modes due to strong coupling between the plasmonic and molecular excitations. The Raman spectra of R6G on these films show an enhancement of many orders of magnitude due to surface enhanced scattering mechanisms; we find a maximum signal when a hybridized mode lies in the middle of the Stokes shifted emission band. The effect of fluorophore-film separation on fluorescence intensity has been investigated using an alumina spacer layer. An enhancement in detected signal of up to 18× is observed relative to that detected from a bare Ag film. Overall, we observe a greater than 40× increase in detected intensity from the alumina-coated Ag film relative to fluorophores on glass; this is a result of increased collection efficiency and a greater radiative emission rate.

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