Effect of Microemulsion Structure on Fluorescence and Nonlinear Optical Properties of Rhodamine 6G

This study is conducted to investigate the effect of nano-droplets concentration and size on linear and nonlinear optical properties of Rhodamine 6G by UV-Vis, spectrofluorometer and Z-Scan techniques. Nano-droplets were prepared by mixture of AOT, n-Decane and Water at three different water to surfactant molar ratios (W = 3, 6.7 and 40) and two dye to water mass ratios (R). At high enough dye concentration, the fluorescence intensity and its red shift depend on the concentration of dye in water nano-droplets (R). Moreover, the fluorescence spectra of R6G can be enhanced by confined water nano-droplets (microemulsion) at higher dye to water mass ratios. The Raman Spectra reveal no dependence of R6G local polarity in the AOT reversed micelles to nano-droplet size. From the Bakhshiev equation, the excited to ground state dipole moment ratio (mu (e) /mu (g) ) was calculated through solvatochromic shift method for different nano-droplet concentrations. The results show that mu (e) /mu (g) of R6G in water nano-droplets is smaller than that of bulk water. At high enough dye concentration, mu (e) /mu (g) depends on the nano-droplets' dye content. The dye aggregation can affect the dipole moment R6G in microemulsion. Two photon absorption coefficient (beta), nonlinear refractive index (n (2)), the real third order susceptibility () and the second order hyperpolarizability () were measured using the Z-Scan technique at different nano-droplet concentration and two sizes of nano-droplet. The results show a good compatibility with the attained consequence by Quantum Perturbation theory. In this content, the interaction of nano-droplet was studied by dynamic light scattering, whose results indicate an ascending trend in mobility of nano-droplets by the increase of nano-droplets dye content. Hence increase of dye in nano-droplets influences the dye aggregation, fluorescence red shift and dipole moment ratio (mu (e) /mu (g) ) by the nano-droplet collision.