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.