Lignin-Based Temperature Phosphorescent Material Composites: Long Afterglow & Water Stability

Room-temperature phosphorescence (RTP) materials are severely limited by emission quenching in aqueous environments, which restricts their practical utility. To address this, we present a hierarchical rigidification and encapsulation strategy to fabricate ultralong and water-resistant RTP materials from lignin-derived carbon dots (CDs). At the molecular level, lignin was selectively depolymerized using a computationally guided deep eutectic solvent (DES) to yield CDs with tailored surface chemistry. At the nanoscale, the heteroatom-doped CDs were immobilized within a rigid polyacrylamide (PAM) network, which restricted molecular motion and produced a phosphorescence lifetime of 451 ms. At the macroscopic level, a continuous crystalline isophthalic acid (IPA) layer was introduced as a protective barrier, effectively shielding the phosphors from quenchers such as water and oxygen. This multilevel design suppresses nonradiative decay and extends the phosphorescence lifetime to 729 ms. It also enables a visible afterglow lasting more than 6 s in aqueous solution, which, to our knowledge, has not been reported previously for lignin-based RTP systems. The resulting composite exhibits excellent stability across various solvents and demonstrates considerable potential for advanced anticounterfeiting applications.