[Study on the elements of the fluorescence spectra emitted from ethanol-water mixture]

The 236 nm UV-light was adopted to excite the 10 ethanol-water mixture samples in which the volume percent of ethanol ranges from 10% to 95%, and the Gaussian decomposition method was used to decompose the fluorescence spectra obtained above to Gaussian curves, where every Gaussian curve can be attributed to the fluorescence emission of a certain kind of luminescent ethanol-water cluster, which is formed by the association between water molecules and ethanol molecules. It was found that every spectrum of the certain binary mixture contains 8 Gaussian elements, and the emission density and peak wavelength of each element were also obtained. The authors studied the mechanism of the fluorescence emission of the mixtures based on the structural characters of fluorescence substances and concluded that the water molecules play an important role in the fluorescence emission: they enlarge the conjugate system as the electron donors; they bridge the ethanol molecules to form 8 kinds of new clusters at the same time, and the conformation of the clusters is rings and chains composed by several rings. Through the peak wavelengths of the Gaussian elements decomposed from the certain concentration spectrum the authors got the information about the relative size of the new clusters, i.e. the clusters are bigger or show chain structures when the peak wavelength of the Gaussian curves is located at the longer positions. The emission transition energies of the 8 kinds of new clusters were also calculated. In addition, it was found that there was a certain relation between the half-width and the association situation. The research contributes to the study of ethanol-water cluster structures and their physical and chemical characteristics.