Accessing persistent high temperature phosphorescence from lignin through in situ double matrix confinement

Achieving high temperature phosphorescence (HTP), particularly using biomass as precursors, is intriguing but faces significant challenges due to the violent non-radiative decay. Here, lignin is converted to carbon dots (L-CD) in the urea-boric acid (UB) matrix through an in situ double matrix confinement strategy. The rigid UB matrix can provide multiple chemical and non-covalent interactions with L-CD, thus the triplet excitons are protected against quenching by strong confinement effect. The L-CD-UB demonstrates outstanding room temperature phosphorescence (RTP) lifetime of 1256.99 ms and quantum yield of 7.43% at ambient environment. Because of the high stability of the triplet excitons and reduced energy gap between singlet state and triplet state, the L-CD-UB shows thermally activated delayed fluorescence (TADF) and high temperature phosphorescence dual emission phenomenon, with a striking phosphorescence lifetime of 304.33 ms at 453 K. The work provides an effective method to achieve HTP of lignin and affords a promising eco-friendly material for high temperature anti-counterfeiting, encryption and smart sensing.