Surface-enhanced fluorescence , plasmonic molecule-plasmon coupling

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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