Highly efficient, ultralong-lifetime, phosphorescent nitrogen-doped carbon dots via multi-confinement for anticounterfeiting applications

The highly efficient emission of carbon dots continues to attract significant interest due to their vast potential in optoelectronic and anticounterfeiting applications. Despite their exceptional fluorescence, their room-temperature phosphorescence (RTP) remains deficient. Herein, nitrogen doped carbon dots (NCDs) were designed using a simple molecular engineering approach, achieving an impressive phosphorescence quantum yield (PQY) of 48.50 % and a prolonged lifetime of 2.06 s, visible to the naked eye for approximately 22 s. The proposed methodology enhances the formation of high-density (n, π^∗) configurations within the CDs by incorporating numerous functional groups such as –NH₂ and C[dbnd]O/C[dbnd]N. These functional groups induce robust spin-orbit coupling, thereby facilitating efficient intersystem crossing from singlet to triplet states and promoting radiative recombination from triplet states to ground states. Utilizing NCDs as triplet donors, yellow and red phosphorescent composites were successfully fabricated through effective phosphorescence Förster resonance energy transfer. These multicolor phosphorescent CDs enable advanced applications in time-dependent information storage and encryption. Their dual fluorescent and phosphorescent properties facilitate multilevel authentication through distinct color changes under varying lighting conditions, enhancing security features and rendering these composites highly effective for sophisticated anticounterfeiting solutions.