Photoluminescence of Carbon Dots Obtained by Hydrothermal Treatment of Polysaccharide Solutions

Carbon dots (C-dots) with violet photoluminescence (PL) were synthesized by ecologically clean one-pot hydrothermal treatment of aqueous solutions of natural polysaccharides. N-, S, and N/S-doped C-dots were obtained from cationic polysaccharide chitosan, anionic polysaccharide fucoidan, and their 50/50 complexes, respectively. As compared with the surface ς-potential of initial polysaccharides, the ς-potentials of their C-dots dispersions were lower due to the negatively charged -COO- groups originating from hydrolysis of polysaccharides during the hydrothermal treatment. All C-dots exhibited qualitatively similar UV/VIS absorption, PL excitation, and PL emission spectra. The influence of dopants on the spectral shifts was small (the PL emission spectra slightly shifted red from N- to N/S-, and, finally, to S-C-dots). The highest PL emission was observed for N-C-dots. Large Stokes shifts between the UV sp3-absorption and the violet PL of the C-dots are beneficial for the C-dots application in fluorescence imaging.