N -Doped Carbon Dots Based on Benzoguanamine/Triphenyltriazine: Borate Matrix Confinement for High-Yield Synthesis of Ultralong Room-Temperature Phosphorescence

Room-temperature phosphorescence (RTP) materials, capable of sustained emission after excitation ceases, hold great potential in optoelectronics, information security, and bioimaging. However, conventional RTP materials often suffer from complex synthesis, high cost, poor biocompatibility, or suboptimal phosphorescence. Carbon dots (CDs) have emerged as promising alternatives due to their excellent biocompatibility, low toxicity, and tunable optical properties. This study presents a one-step synthesis strategy combining N-doping and rigid matrix confinement. Using benzoguanamine and 2,4,6-triphenyltriazine as nitrogen-rich precursors within a boric acid matrix, we successfully fabricated high-performance N-doped RTP carbon dots. The rigid B2O3 network and hydrogen-bonding network effectively suppressed nonradiative transitions and stabilized triplet excitons. N-doping, along with B–C covalent bonds and hydrogen bonds, promoted intersystem crossing (ISC) and reduced the singlet–triplet energy gap (ΔEST). The resulting Ben-CDs@BA exhibited an ultralong phosphorescence lifetime of 2.03 s, while Tri-CDs@BA achieved a high phosphorescence quantum yield of 59.6%, both displaying intense blue afterglow. Based on their distinct RTP properties, we demonstrated their application in multilevel static information encryption and dynamic anticounterfeiting. This work provides a feasible strategy for designing carbon-based RTP materials with both long lifetime and high quantum yield.