Deep-blue thermally activated delayed fluorescence carbon dots with ultralong lifetime

Carbon dots (CDs) with deep-blue thermally activated delayed fluorescence (TADF) of more than 2 s were developed, exhibiting the longest lifetime to date. In contrast to the established deep-blue TADF systems, this developed CD-based system (BNCDs) could be facilely and effectively synthesized, and more impressively, the emission lasted for more than 16 s (to the naked eye). XRD, TEM, FT-IR, and XPS analyses were conducted, and structural characterizations indicated that the CDs formed hydrogen bonding with B2O3. The temperature-dependent photoluminescence (PL) spectra demonstrated the existence of thermally activated delayed fluorescence in the composite. Further studies revealed that the B2O3 matrix restricted the vibration and rotation of CD chromophores and suppressed the non-radiative recombination of triplet excitons. Last but not least, potential applications in bioimaging, anti-counterfeiting, and information encryption were also explored. This work can provide new insights for developing metal-free and ultralong lifetime afterglow materials.