Effect of Charge and Dielectric Constant on Linear and Nonlinear Optical Properties of Two Dyes

Abstract

The enhancement of nonlinear optical properties of dye with surfactant can be applied in photodynamic therapy and medicine. The nonlinear optical properties of alizarin red S and rhodamine B mixed with cationic and anionic surfactant are studied by Z-scan technique. The nonlinear absorption coefficient values of cationic dye (rhodamine B) in aqueous solution are reduced with the increase of anionic surfactant concentration, while the nonlinear absorption coefficient values are enhanced by the interaction between anionic dye (alizarin red S) with anionic surfactant. The nonlinear refractive index (n2) of cationic and anionic dye is reduced with an increase of surfactant concentration. The nonlinear absorption coefficient values of a rhodamine B-doped droplet is reduced by the increase of cationic surfactant in the water droplet. In general, the nonlinear absorption coefficient values are reduced with an increase of dye solubility, and the value of n2 is reduced with an increase of dye solubility in solution. The fluorescence intensity is higher when dye and surfactant have the same charge. This effect can be due to the increase of solubility of cationic (anionic) dye with an increase of anionic (cationic) surfactant in the solution. The reduction of nonlinear absorption coefficient values with an increase of droplet size can be due to the change of rhodamine B solubility in microemulsion.