Facile Synthesis of Matrix‐Free Room‐Temperature Phosphorescent Nitrogen‐Doped Carbon Dots and Their Application as Security Inks

Abstract Room‐temperature phosphorescent (RTP) nitrogen‐doped carbon dots (N‐CDs) have attracted great interest but their efficiency is usually dependent on a solid matrix. Developing efficient matrix‐free RTP CDs is still a great challenge. Here, a simple strategy is reported to synthesize efficient matrix free RTP N‐CDs from citric acid (CA) and basic fuchsine (BF) via a single step hydrothermal process. The synthesized N‐CDs show strong fluorescence in aqueous solution and the solid state, and the RTP lifetime is long‐lived (51.9 ms at 298 K). The phosphorescence of the N‐CDs is attributed to the formation of an internal hydrogen bonded network by the organic polymers on the surface of the N‐CDs. This reduces the nonradiative transitions of the triplet excitons and mitigates oxygen quenching. The application of N‐CDs as security inks is demonstrated.