Photophysics of Cationic and Anionic Dye Mixed by Sodium-2-Diethylhexyl Sulfosuccinate–Water–Hexane at Low Molar Ratio (X ≤ 8)

The fluorescence, absorption spectra, and Z-scan (open aperture) were studied in mixture of anionic dye (fluorescein sodium salt-FSS) and cationic dye (Rhodamine B-RhB) with low size of water droplets. The droplet was prepared by sodium-2-diethylhexyl sulfosuccinate/water/hexane microemulsion (MEs) at water to the surfactant molar ratio less than 8. The absorbance and fluorescence intensity was studied at different dye-doped droplet size and concentration. The results evidenced that the fluorescence spectra of FSS in MEs are less than water, but the fluorescence intensity of Rhodamine B in MEs is higher than bulk water. The results evidenced that the fluorescence depends on the size (molar ratio) of the droplet. The Rhodamine B in MEs with X = 3 (middle size) has a higher fluorescence intensity than other X. However, the fluorescence intensity of FSS reduces with reduction of droplet size. The red shift of fluorescence was studied by the Bilot and Kawski theory; the excited dipole moment over the ground state value (μ_e/μ_g) was determined. The results indicated that in the same dye in solution concentration, the μ_e/μ_g depends on molar ratio. The nonlinear optical properties of dye/sodium-2-diethylhexyl sulfosuccinate/hexane/water MEs for two types of dye (FSS and RhB) at constant X = 8 were investigated. The results show that two-photon absorption coefficient for both dyes increased with the increase of the droplet concentration.