Research / 2021 / Article / Fig 2

Review Article

Afterglow Carbon Dots: From Fundamentals to Applications

Figure 2

(a) Schematic representation of four stages in the preparation of CDs via a high-temperature carbonization strategy. (i) Formation of cross-linked amorphous CDs. (ii and iii) Formation of CDs with a controlled graphitized core and an amorphous shell. (iv) Formation of over-carbonized CDs. This kind of CDs is produced at high temperatures, endowing them with poor surface chemistry and inability to luminesce upon excitation (adapted and copyright permission [35], American Chemical Society). (b) Schematic energy level diagrams showing the generation of luminescence of CDs, including fluorescence, DF, and phosphorescence. The afterglow luminescence mechanism for CDs mainly comprises TADF, phosphorescence, and a combination of the two. (c) Photographs of CDs@SBT-1 under sunlight, UV-on, and UV-off states. (d) The corresponding emission profiles of fluorescence and phosphorescence. (e) Temperature-dependent decay behaviors of the phosphorescence (at 525 nm). (f) Photographs of CDs@SBT-2 under sunlight, UV-on, and UV-off states. (g) The corresponding emission profiles of fluorescence and DF. (h) Temperature-dependent decay behaviors of the DF (at 440 nm) (adapted and copyright permission [57] (c–h), American Chemical Society).