Organic ultralong room-temperature phosphorescence (RTP)
has attracted
extensive attention and has been a sparklingly heated topic due to
its promising applications in bioimaging, encryption, and optoelectronic
devices. However, the synthesis procedures for these materials are
always cumbersome, costly, and involve toxic substances as well. Herein,
a facile, low-cost, and hypotoxic strategy has been developed to achieve
green RTP by the hydrothermal reaction of carbon source together with
boric acid, resulting in the in situ rigidification
of carbon dots into the B2O3 matrix. The designed
green RTP carbon dots (CDs@B2O3) exhibited an
ultralong lifetime of 905.5 ms, lasting more than 8 s. This excellent
performance was mainly due to the restricted vibration and rotation
of CDs by the covalent bond formation and the suppressed nonradiative
recombination of triplet excitons via B2O3 matrix
rigidification. Moreover, we demonstrated the practical applications
of the prepared CDs for bioimaging, anti-counterfeiting, and information
encryption. This work provides design principles to construct metal-free
RTP materials with ultralong lifetime and high stability for promising
remarkable applications.