Résumé
Carbon dots (CDs) have recently attracted enormous attention in different research fields as superior luminescent alternatives for inorganic nanostructures and organic dyes. CDs can be prepared using low-cost synthesis approaches and provide, inter alia, excellent biocompatibility with chemical stability, and strongly linear optical properties (i.e. one-photon excited emission, OPE). Their non-linear optical activity (two-photon excited emission, TPE) are not fully explored yet.1Inspired by our recent results, we discuss here the optical responses of various subgroups of CDs in correlation to their versatile internal designs, including the graphitization degree. The first subgroup is represented by acetone-derived polymeric dots (PDs), fabricated following alkali-assisted aldol reaction.2 As-prepared PDs reveal excitation-dependent, broad greenish-blue OPE and TPE fluorescence (with two-photon absorption cross-section (σTPA) estimated to be ca. 20 GM). Both: OPE and TPE fluorescence increase when PDs interact with serum albumins at physiological conditions. We have also prepared nitrogen-doped folic acid-based (FA) CNDs were produced (according to green hydrothermal synthesis), providing bright blue emission (λmax = 445 nm) upon OPE and TPE, high fluorescence quantum yield (FLQY, up to 56%) and high σTPA values (??? Ile?). The most intriguing subclass of CD constitute highly-ordered CQDs, synthesized following the solvothermal treatment strategy. These CQDs give strong (FLQY~60%) and ultranarrow (~30 nm) OPE and TPE emissions in blue, green, or yellow (depending on the dots’ size). In conclusion, the aforementioned examples evidence the great applicative potential of all CDs in nano- and biophotonics.