**5. Conclusions of the experimental analysis**

The linear absorbance, nonlinear absorption coefficient and nonlinear refractive index measurements of the four distinct plasmonic shapes, namely colloidal gold nanoflowers, colloidal gold nanopebbles colloidal gold nanospheres and gold nanoislands film confirmed that not only size but the geometry of the plasmonic structures plays a vital role in determining their linear as well as nonlinear optical

**Figure 12.** *(a) Raman spectra of Eosin Yellow dye and its hybrids illustrating morphology directed SERS effect [68].*

**Figure 13.** *Z-scan representation of Eosin Yellow dye (a) open aperture and (b) closed aperture scan [67].*

coefficients. A strong mutual interaction between the organic dye Eosin Yellow and plasmonic structures has been inferred from the Raman spectroscopic analysis. Further, the observed results deduce that the nanostructures with sharp edges, offering plenty of hotspots, may be competitive candidates for highly sensitive SERS probes. Nonlinear transmission measurements of colloidal plasmonic shapes, organic fluorophore EY and their colloidal plasmonic organic hybrids show that they possess excellent saturable absorption properties at 532 nm wavelength. Further, the Two Photon Absorption coefficients reported for colloidal plasmonic organic hybrids reveal that the enhancement induced by the plasmonic structures in the in the third order nonlinearity of the organic dye Eosin Yellow critically depends on the morphology of the plasmonic structures. Further, the results based on the spectral and temporal modulations of EY hybrids in solution and film demonstrated that the excitonic states of molecular hybrids tend to modify drastically due to strong coupling between molecular excitons and plasmons. The energy transfer mechanism delineated for all the four EY-gold nanoshapes hybrids depicts that Forster resonance energy transfer

*Types of Nonlinear Interactions between Plasmonic-Excitonic Hybrids DOI: http://dx.doi.org/10.5772/intechopen.105833*

**Figure 14.**

*Transient absorption spectra at various time delays measured for EY when hybridized with (a) colloidal gold nanospheres; (b) colloidal gold nanopebbles; (c) colloidal gold nanoflowers and (d) nanoislands film pumped at visible wavelength (420 nm, power = 1.5 mW) [69].*

(FRET) took place between EY-GNS, EY-GNP and EY-Au islands while nanometal surface energy transfer (NSET) existed between EY-GNF.

These findings may find importance in fabrication of energy transfer based active photonic devices.
