Medidas de parâmetros termo-ópticos e de eficiência quântica da fluorescência em líquidos por interferometria e difração cônica de origem fototérmica.

Abstract

In this work, was applied the Conical Diffraction technique (DC) to determine the fluorescence quantum efficiency (η) of liquid samples based on the number of rings observed in the plane of observation due to self-phase modulation induced thermally (SPM). The thermally induced SPM effect consists of the possibility of the excitation beam inducing a nonlinear phase variation (Δφ) at its own wavefront due to the transverse variation in the refractive index, generating an interference pattern in the form of rings. When thermal properties are known in the investigated material, it is possible to determine directly value of the η by measuring the optical absorption of the sample and counting the number of rings produced by the DC. Otherwise, it is necessary to use a method that does not depend on these properties. In this way, the Normalized Conical Diffusion (DCN) method was proposed, which eliminates the dependence of the thermal conductivity (K) and the thermo-optical coefficient (dn/dT) of the investigated liquid sample. In this method, it is possible to calculate η of the fluorescent material using a non-fluorescent reference sample diluted in the same solvent of interest. Besides the determination of η, the thermal conductivity (K) of the unknown solvent can also be found, since the thermo-optical coefficient dn/dT is measured independently. To determine the dn/dT of the samples investigated in this work, a Mach-Zehnder interferometer type was used. The values of K obtained with this approach are in agreement with the literature. The DC technique was applied to a chromophore derived from vitamin B6 diluted in different solvents, in anthocyanin extracted in three different solvents, and in CdSe/CdS and CdSe/ZnS core/shell QDs with different sizes (1,9,2,0 and 4,0 nm) functionalized with the hydroxyl (R-OH) and carboxyl (R-COOH) group, or nonfunctionalized in aqueous solution. Therefore, the proposed method was applied in the characterization of thermo-optical parameters, and it can serve as a low cost optical approach for the determination of the K value in unknown liquid samples.