The Uv-Vis, fluorescence, Raman spectroscopy and Z-scan were used to study optical properties of fluorescein sodium salt (FSS) in AOT/Oil/Water microemaulsion. The FSS-microemulsion was prepared by two types of Oil (Heptane and Hexane) at two molar ratios of water to surfactant (X = 3 and 8), different droplet concentrations at constant ratios of dye in water (Y = FSS/water). In the AOT microemulsion media, both the emission and absorption spectra of the FSS present a red shift with respect to droplet concentration and water droplet size. A change is molecular structure was observed from Anion to Dianionic by increase of droplet concentration. The Raman spectra shows, the polarity of samples doesn’t change with change of droplet concentration. The ratios of the excited state to the ground state of dipole moments (μe/μg) of FSS-microemulsion were determined by perturbation theory. At the same dye concentrations in samples, the μe/μg depending on the oil type (Oil polarity) and size of water droplet (X) of the microemulsion. The dipole moment of the ground sate is decreasing by decrease of the droplet size and increase of the droplet concentration. The FSS in both microemulsion systems is localized in the interface of droplet because of the negative interface of AOT and the probabilities, the dye aggregation inside of the droplets change by the size of droplet and it can change the dipole moment of the ground state. The photophysics properties tend to bulk water with the increase of the droplet size. The nonlinear optical properties of FSS/AOT/Heptane/Water microemaulsion were investigated. The magnitude of the third-order nonlinear refractive index (n2) and nonlinear absorption coefficient (ß) the second order hyperpolarizabilities (γR) and the real third order susceptibilities (χR) were measured using single-beam z-scan at different droplet concentration and two molar ratio. The results shows, the ratio of dipole moment (μe/μg) has behavior similar to the 1/γR.

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