Inelastic scattering and emission correlated with enormous SERS of dye adsorbed on Ag nanoparticles

With respect to the enormous enhancement in SERS of dye molecules adsorbed on hot Ag nanoparticles, two distinct inelastic and emission peaks were observed at 550-600 and 600-750 nm. Based on the spectral variations for different surface coverage and for different dye species, the shorter and longer wavelength peaks were originated from excited electron on metal, and from fluorescence of molecules, respectively. Furthermore, we found the shorter wavelength peak shows invariant Stokes shift irrespective of excitation wavelengths, indicating it arises from inelastic scattering of excited electron by surface roughness or by adsorbed molecules.