Origin of carbon dot fluorescence in organosilica films explored experimentally by surface functionalization

Carbon dots (C-dots) are nanocarbon materials that exhibit a range of fluorescence and chemical/physical properties depending on the precursors employed and the conditions under which they were synthesized. However, the structural factors responsible for C-dot fluorescence remain unknown. This is because C-dots exhibit a wide distribution of sizes, structures, functional groups, heteroatoms, and defects, making structural analysis challenging. Therefore, a different experimental approach is necessary to explore the factors affecting the fluorescence. As a physicochemical approach, the surface properties of C-dots were altered by surface modification using organosilane, and the differences in fluorescence wavelength caused by the functionalization of C-dots were investigated in an organosilica matrix in this study. To explore the impact of varying chemical states of the C-dots surface on the fluorescence properties, it is necessary to evaluate them in a stable solid-state matrix that eliminates the effects of changes in the surrounding chemical state, dispersion state, and mobility. To compare the fluorescence properties, homogeneous hybrid organosilica films containing surface-functionalized C-dots were prepared using sol-gel method. For comparison, three types of C-dots were synthesized, each with a different fraction of surface reaction sites for functionalization. The fluorescence peak shift from pristine C-dots to functionalized C-dots in films was investigated for each. The reasons behind the fluorescence peak shifts and the local structures responsible for the fluorescence of the C-dots were explored based on the peak shift behavior and differences in the structural features of the as-prepared pristine C-dots.