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

• Published in: Journal of sol-gel science and technology 2022-12, Vol.104 (3), p.702-710
• Main Authors: Suzuki, Kazumasa, Nabata, Haruka, Ueno, Saya, Morita, Shu, Miyamura, Hiroshi, Balachandran, Jeyadevan
• Format: Article
• Language: English
• Subjects: Carbon; Carbon dots; Ceramics; Chemistry and Materials Science; Composites; Fluorescence; Functional groups; Glass; Inorganic Chemistry; Invited Paper: Sol-gel and hybrid materials with surface modification for applications; Materials Science; Nanotechnology; Natural Materials; Optical and Electronic Materials; Physical properties; Sol-gel processes; Sol-Gel Research in Japan; Structural analysis; Surface properties; Surface reactions
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-022-05901-1

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. Graphical abstract Highlights Contribution of C-dot surface and core structures to fluorescence was experimentally investigated. Several C-dots with different surface states and similar fluorescence were synthesized. C-dots were functionalized with organoalkoxysilane changing their surface structures. The surface and core states of C-dots contribute to different fluorescence. Fluorescence peak shift behavior indicates common local structures for the different C-dots.