**4. Experimental realizations**

With an aim to circumvent the material bottleneck limitations hindering the realization of an on chip all optical switch, our experimental work presents a detailed insight into the morphology directed third order NLO properties of four distinct gold nanoshapes and their hybrids with an organic fluorescent dye Eosin Yellow (EY). The ultrafast structural dynamics of the gold nanoshapes and their hybrids has been delineated in terms of their spectral and temporal modulations to deconvolute the excited state dynamics responsible for the coupling between the transient states of gold nanoshapes and various intermediate states of the Eosin Yellow photocycle. Finally, the work is concluded with a mechanistic interpretation of the observed phenomenon in terms of the energy transfer within the hybrids.

In our investigations, colloidal gold nanoshapes were synthesized using chemical reduction method (**Figure 7**) while, the DC sputtering technique has been employed for fabricating the gold nanoislands film [67, 68].

Apart from this, films of Eosin Yellow having different concentrations were spin coated on a glass substrate. The shape and lattice parameters of colloidal gold

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

**Figure 7.**

*TEM micrographs (a) GNP (gold nanopebbles); (b) GNF (gold nanoflowers) and (c) GNS (gold nanospheres). While, the insets represents the HR-TEM image of the corresponding nanoparticles [67].*

nanostructures were estimated using high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) respectively. Atomic force microscopy (AFM), field-emission scanning electron Microscopy (FESEM) and near field scanning optical microscopy (NSOM) were employed to examine the morphology of the epitaxial gold film and its interaction with the organic counterpart respectively **Figures 8**–**10** [67, 68].

Further, various standard spectroscopic characterizations namely absorption spectroscopy (UV-Vis), surface enhanced Raman spectroscopy (SERS), third order

#### **Figure 8.**

*FESEM image of (a) gold Nanoislands film at high magnification (inset represents the particle size distribution) and (b) EY-gold nanoislands hybrid [68].*

#### **Figure 9.**

*(a) Powder X-ray diffraction pattern and (b) selected area electron diffraction pattern of Au colloids demonstrating FCC structure [67].*

#### **Figure 10.**

*(a, b) AFM representation of bare Au-islands and EY-Au islands hybrid, respectively and (c, d) 2-D NSOM image of the raw gold nanoislands and EY-Gold nanoislands film, respectively (inset represents the intensity of field in terms of oscillation with maxima and minima in the x–z plane) [68].*

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

#### **Figure 11.**

*Normalized extinction spectra of free Eosin Yellow (EY) and its hybrid with (a) GNP; (b) GNF and (c) GNS. The insets represent peak extinction maxima (normalized w.r.t 1:1 (v/v) gold nanoparticles-EY ratio) of the hybrid structures [67].*

nonlinear spectroscopy (Z-Scan), photoluminance spectroscopy (PL) and ultrafast time resolved pump probe spectroscopy (UTRPPS) have been used to unveil the steady state as well as the excited state dynamics of all four distinct gold nanoshapes and their hybrids with EY (**Figures 11**–**14**). For a detailed explanation regarding the synthesis, experimental setups employed and the experimental results the corresponding papers may be referred [67–69].
