Plasmon states damping

In atomic-molecular media the damping of plasmon states is due to the interaction of plasmon waves with electrons, lattice vibrations, and impurities. The electron-plasmon interaction is a long-range one. With absorption of a plasmon, the momentum q is transferred to the electron, resulting in a decay of the collective state into a single-particle one. The latter process is identical with absorption of a photon with the same energy. Wolff102 (see also Ref. 103) has shown that in this case the lifetime can be expressed in terms of two optical constants the absorption coefficient k and the refractive index nT, namely,... 

An additional effect to consider for SERRS is that of the fluorescence which can occur simultaneously with a RRS process. This is the so-called delayed fluorescence, " which is a radiative decay process for molecules which have relaxed from their initial excited vibrational state of the excited electronic state to the lowest vibrational level of the excited state. Delayed fluorescence can be additionally damped on a rough Ag surface for the same reasons that the RRS process is additionally damped, i.e., by coupling to the surface plasmon resonances. On the other hand, the electromagnetic enhancement factors L (o)L (Oip), will also cause an enhancement of the fluorescence in a similar manner to the Raman process. However, the decay of excited molecules by the surface channel will tend to mitigate the EM fluorescence enhancement effect. Two cases have been discussed in the literature " (a) the case of a molecule with a fluorescence quantum efficiency near unity in the free state, i.e., QE 1, and (b) the case with QE 1. If QE is low (<0.01), the fluorescent emission is estimated to be enhanced by ca. 10 whereas, for QE 1, a surface quenching of fluorescent emission by ca. 10" has been... 

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