Boron-doped carbon dots with long lifetime phosphorescence usable in anti-counterfeiting applications

Room-temperature phosphorescent (RTP) materials have received broad interest for their promising applications in information encryption, bioimaging, and anti-counterfeiting. Carbon dots (CDs), as a new carbon-based luminescent nanomaterial have been found to have multicolor afterglow and ultralong luminescence. In this study, using o-phenylenediamine (OPD) and citric acid (CA) as precursors, carbon dots denoted as OC-CDs were synthesized via a hydrothermal method. The OC-CDs were then embedded into a boric acid (BA) matrix, yielding a carbon dot composite material (denoted as OC-CDs@BA). The composite was chemically characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The phosphorescence properties of the OC-CDs@BA composite were systematically investigated. The study demonstrates that the material exhibits excitation-wavelength-dependent RTP behavior. Under 254 nm excitation, the material exhibits deep-blue phosphorescence at 418 nm with a long phosphorescence lifetime of 1.61 s and a quantum yield of 7.7%; under 365 nm excitation, it switches to green phosphorescence at 533 nm with a lifetime of 201 ms and a quantum yield of 3.25%. Finally, the excitation and time-dependent phosphorescence property of the composite was used in anti-counterfeiting. This work provides a new approach for designing multifunctional RTP carbon dot materials for high-security optical anti-counterfeiting applications.