Plasmonic Nanoparticles and Fluorescence
Metallic nanoparticles are apt to modify the luminescence yield from organic molecules in their immediate nano-environment. In case of photoluminescence, they influence both the nonradiative and the radiative rate . The latter can be tuned that much that even Purcell-like changes of the fluorescence spectra can be observed . Thinking one step further, from the Purcell effect, which influences spontaneous transitions, to stimulated transitions, one may end up with nanoscale lasers or even the “spaser”, which however faces fundamental limitations form the materials point of view . Star shaped plasmonic nanoparticles have been shown to improve the yield of electroluminescence in organic light emitting diodes .
Plasmons can also substantially improve the quantum efficiency of the intrinsic luminescence from gold stemming from the recombination of d-band holes with sp electrons . Recently, we have observed an anticorrelation of the intensity of the d-band luminescence with the intensity of the hot spots between two gold nanoparticles  and we have found that gold nanosponges, while showing highly polarized scattering spectra , produce much less polarized luminescence spectra.
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