Lignin-derived carbon dots with molten salt confinement for ultra-stable room-temperature phosphorescence.

In response to the critical challenges of high toxicity, complex synthesis, and poor environmental stability in conventional room-temperature phosphorescent materials, this study presents a sustainable biomass-derived strategy through the development of lignin-based carbon dot/inorganic salt composites (CDSLX-T). By employing a one-step molten salt approach, we construct a hierarchical architecture featuring lignin-derived sp2-hybridized carbon cores and a rigid crystalline shell comprising multi-component inorganic salts (MgO/Mg3(PO4)2/KCl/KNO3). The inherent conjugated moieties of lignin facilitate efficient intersystem crossing, while nitrogen doping optimizes (n, π*) electronic configurations to enhance spin-orbit coupling effects. In situ characterization elucidates the synergistic mechanism of high-temperature-induced carbon core aromatization and salt matrix crystallization. A dual confinement strategy-combining covalent bonding (C-K/C-Cl/C-Mg) and spatial restriction-effectively suppresses carbon dot vibrations and non-radiative triplet exciton transitions, enabling stable phosphorescence emission in aqueous environments. Leveraging time-resolved luminescence characteristics with tunable lifetimes, the material demonstrates unique potential in fingerprint visualization and multilevel information encryption. This work establishes an eco-friendly synthetic paradigm for high-performance bio-based optical materials, bridging sustainable chemistry with advanced photonic applications.