Tunable wavelength of fluorescence and afterglow in super-bright carbon dot-based composite materials

The afterglow material based on carbon dots (CDs), with boric acid (BA) serving as the matrix, demonstrates outstanding structural rigidity. The covalent bond structure is particularly advantageous for stabilizing the triplet states of CDs, thus shielding the triplet excitons from quenching. Urea, on the other hand, harbors numerous CO and –NH2 functional groups, fostering the creation of hydrogen bond structures with CDs. This impedes the non-radiative recombination of CDs, thereby enhancing the production of afterglow. Here, we blend two substrate materials with distinct structural characteristics, utilizing their combined effect on restricting CDs. By employing this method, we have successfully synthesized afterglow materials with an exceptional absolute quantum yield (QY) of 61.22% and an afterglow delay time surpassing 5 s. Urea is employed to modulate the size and graphitization degree of CDs, thereby adjusting the emission wavelength in both solid state fluorescence (S-FL) and afterglow within composite materials. Furthermore, by adjusting the mixed ratio of BA and urea, thus altering their respective proportions in interacting with CDs, the brightness of S-FL and the delay time of afterglow are adjusted.