**6. Summary**

The work reported herein, presents a significant enhancement in the third-order nonlinearity of a technologically promising organic dye Eosin yellow (EY) when hybridized with three distinct colloidal gold nanoshapes, namely, gold nanospheres (GNS), gold nanopebbles (GNP) and gold nanoflowers (GNF) and a gold nanoislands film (Au islands). Indeed, up to 400% increase in the NLO response of EY when hybridized with Au islands was demonstrated when excited with a 532 nm, 20 ps laser. Further, a 50% reduction in the response time been attained. Herein, the role of resonant interactions within the hybrids especially in terms of nonradiative energy in altering the steady state as well as excited state dynamics due to the spectral overlap between the extinction spectra of the gold nanoshapes and the emission spectra of the dye has been emphasized. Finally, a descriptive uncertainty budget for the precise measurement of the third order NLO coefficients has been documented.

Based on the hypothesis that the nonradiative energy transfer has the ability to significantly alter steady state as well as excited state dynamics of plasmonic organic hybrids and a unique relationship exists between the efficiency of energy transfer and the enhancement in the third order NLO coefficients, this study may be safely extended to a wide range of energy transfer-based plasmonic-organic hybrids.
