Study of optical non-linearity from structural perspective in Rhodamine using z-scan technique co-related to luminescence spectroscopy

Molecular structures of dyes differ with substituent and can result in different forms of a dye. For instance, Rhodamine gives Rh 6G, Rh B, Rh 123, Rh 110, etc., with varying properties that depend on the substituent. Most studies in the literature on optical non-linearity of dyes overlook the effect of substituent/molecular structure on non-linearity and confine their investigations to the dependence of non-linear properties on concentration of dyes, solvents, wavelength and intensity of the interacting laser. In this study, the effect of substituent on optical cubic non-linearity is demonstrated through a comparative investigation in Rh 6G and Rh B using the single beam z-scan technique, with an incident laser beam intensity I 0 = 7.83 kW/cm 2 and wavelength 532 nm. The closed aperture (CA) and open aperture (OA) z-scans of aqueous solutions of Rh 6G and Rh B are strikingly different. Variations in the results are analysed from a structural perspective and non-linear refractive index ( n 2 ) , non-linear absorption coefficient (β) and optical third-order susceptibility χ 3 of the dyes are calculated. The present study also examines the non-linearity in Rh 6G and Rh B in correlation to their fluorescence and up-converted emission. The possibility of quintet non-linearity in Rh 6G and Rh B is indicated for interactions with intense 1000 nm wavelength. • Substituents in the molecular structure of Rh 6G and Rh B can determine the non-linear index of refraction (n 2 ). • OA z-scan analysis of dyes co-related to fluorescence spectra; confirms phenomena involved in non-linear absorption. • Evidence of quintet non-linearity in Rh 6G and Rh B at 1000 nm wavelength obtained from up-conversion study.