Abstract: A method for regulating the trap levels of matrix-free carbon dots (CDs) through boron (B) doping is demonstrated, significantly prolonging their afterglow duration. Further studies reveal that B is incorporated into the CDs in the forms of B-N and B-C bonds when the CDs are synthesized from 1,4-phenylenediboronic acid, sodium hydroxide, and melamine. The B content increases with the proportion of the B source (i.e., 1,4-phenylenediboronic acid). This process not only enhances the trap density in the CDs but also increases the energy level difference between the trap energy level and the excited triplet state. Moreover, the elevated levels of C=O and C=N bonds facilitate the generation of triplet excitons and intersystem crossing. As traps capture and store triplet excitons for gradual release, the afterglow lifetime of CDs is successfully extended from 0.764 seconds to 1.224 seconds, effectively quadrupling the afterglow duration. Finally, based on variations in their afterglow durations, potential applications for information storage and encryption using these CDs are demonstrated.

Key words: Carbon dots, Room temperature afterglow, Traps; Element doping, Dynamic information encryption