Dependence of photoluminescence of carbon dots with different surface functionalization on hydrogen factor of water

The pH dependences of the photoluminescence of carbon dots synthesized by the hydrothermal method with polyfunctional and monofunctional (carboxylated and hydroxylated) surfaces have been studied. As a result of the analysis of the obtained photoluminescence and absorption spectra of aqueous suspensions of all studied types of carbon dots at different pH values, a significant effect of the acidity of the environment of nanoparticles on their optical properties was found. It has been found that the greatest changes in the spectral characteristics of absorption and photoluminescence of carbon dots with COOH, OH, and NH$_2$ surface groups appear in the pH ranges of 2–5 and 8–12. The obtained results are explained are explained by the processes of protonation/deprotonation of the surface groups of carbon dots.