| Abstract: | This paper summarizes the results obtained by fluorescence spectroscopic techniques with conventional and laser light sources for the characterization of the spectral luminescent properties of aquatic humic substances (AHS). The band profiles of corrected absorption, fluorescence emission, and fluorescence excitation spectra are compared in graphical form with unique functions used for the axes. In order to calculate the quantum efficiency of fluorescence, we used the Raman signal from water molecules as an internal reference. The temperature dependence of the fluorescence spectra of humic matter has been recorded in solid (?160°C to 0°C) and in liquid (0°C to +300°C) aqueous solutions. The behavior of the fluorescence band shape is discussed. A new method of nonlinear fluorimetry is proposed to enhance the capabilities of fluorescence spectroscopy. This method is based on the fluorescence saturation effect manifesting itself under powerful laser pumping (excitation) conditions. The use of the technique allows one to determine certain photophysical properties of molecules, as a complement to the normal spectral data. Using three different samples of aquatic humic substances with very similar fluorescence band shapes, it is demonstrated that these compounds have distinct molecular luminescent parameters and therefore, can be identified. The similarity of the fluorescence band shapes of humic substances in natural water of different types; the absence of any noticeable effect of temperature across a wide range and the fluorescence saturation on the fluorescence band contour can be explained. This assumes that in all of the samples of aquatic humic substances studied, with different molecular weight fractions, that there is a single dominant fluorescent functionality present. |
