Spectroscopic Characterization of the Fluorescence of Paper at the Wet-Dry Interface

Abstract

Changes in the fluorescence of an additive-free cotton cellulose paper in which a wet-dry interface has been created by capillary action using distilled water under static air have been characterised spectroscopically. Fluorescence was measured on the surface of the paper at the wet-dry interface, where a fluorescent tide line developed. Measurements were also carried out on the areas both above (original paper) and below (extracted paper) the wet-dry boundary. The fluorescence spectra recorded on the three different areas showed the same spectral distribution with excitation maxima at 260, 340, and 385 nm (λEm = 500 nm), and a single emission maximum at 440 nm (λEx = 254 and 340 nm). The intensities of the spectra recorded at the wet-dry boundary were approximately three times higher than those recorded on the original paper. Furthermore, a decrease in fluorescence intensity was observed for the extracted paper in comparison to the original paper. These results show that the migration and concentration of a fluorescent compound already present within the paper contributed to the enhanced fluorescence observed at the wet-dry interface. Spectroscopic analysis of the aqueous extract of the fluorescent tide line confirmed the presence of a water-soluble fluorescent compound. The results of this study are discussed in relation to the more general phenomenon of fluorescence accompanying the discoloration of paper.