Surface-enhanced Raman scattering and fluorescence near metal nanoparticles

TL;DR

This paper models the enhancement of Raman scattering and fluorescence near silver nanoparticles, showing significant increases in scattering cross sections due to electromagnetic effects and the interplay with molecular dynamics.

Contribution

It introduces a comprehensive model combining electromagnetic effects and molecular dynamics to analyze surface-enhanced Raman scattering and fluorescence near metal nanoparticles.

Findings

Raman scattering cross section can increase by about 10 orders of magnitude.

Fluorescence enhancement grows with EM but stalls due to non-radiative decay.

Anti-Stokes Raman scattering is achievable with strong laser intensities.

Abstract

We present a general model study of surface-enhanced resonant Raman scattering and fluorescence, focusing on the interplay between electromagnetic (EM) effects and the molecular dynamics as treated by a density matrix calculation. The model molecule has two electronic levels, is affected by radiative and non-radiative damping mechanisms, and a Franck-Condon mechanism yields electron-vibration coupling. The coupling between the molecule and the electromagnetic field is enhanced by placing it between two Ag nanoparticles. The results show that the Raman scattering cross section can, for realistic parameter values, increase by some 10 orders of magnitude (to $\sim10^{-14}$ cm$^2$) compared with the free-space case. Also the fluorescence cross section grows with increasing EM enhancement, however, at a slower rate, and this increase eventually stalls when non-radiative decay processes become important. Finally, we find that anti-Stokes Raman scattering is possible with strong incident laser intensities, $\sim 1$ mW/$\mu$m.