Enhanced two-photon fluorescence of molecules adsorbed on silver particle films

The two-photon fluorescence intensity from Rhodamine $B$ molecules adsorbed onto silver particle films is enhanced 150-fold compared with molecules in solution. This is accounted for in terms of local-field amplification of the incident intensity when the absorbing state of the molecules lies within the plasma resonance bandwidth of the silver particles. For diphenylanthracene and Nile Blue, when the absorbing state lies above the particle resonance, no enhancement is observed, even though the luminescence falls within the resonance bandwidth.