A crosslinking network and nanoconfinement synergistic strategy for achieving white-light excited long-lived room-temperature phosphorescence in transparent aqueous carbon dot solutions.

Aqueous phosphorescent carbon dots (CDs) have shown great promise for solution-based practical applications. However, dissolved oxygen in water can severely quench triplet excitons, resulting in unstable phosphorescence emission in aqueous solution. Moreover, most reported aqueous phosphorescent CDs mainly rely on UV excitation and exhibit turbid colloidal solutions. Herein, we for the first time report that white light excitable high-transparency aqueous room-temperature phosphorescence (RTP) CD-based nanomaterials (N,P-CDs@SiO2) can be rationally designed and synthesized via a crosslinking network and nanoconfinement synergistic strategy. Compared with the undoped system, the introduction of phosphorus atoms generated abundant functional groups on the CD surface, significantly enhancing the spin-orbit coupling effect between excited singlet and triplet states and promote intersystem crossing, resulting in an order-of-magnitude increase in phosphorescence lifetime (from 47.87 ms to 629.34 ms) and an approximately 7-fold improvement in phosphorescence quantum yield (from 3.6% to 25.34%) in N,P-CDs@SiO2 nanomaterials. The three-dimensional siloxane (Si-O-Si) network formed by the crosslinking precursor and silica effectively suppresses the non-radiative decay of triplet excitons, thus stabilizing the phosphorescence emission in aqueous solution. Leveraging their unique advantage of being excitable by visible light, the RTP CD-based nanomaterials have been successfully applied to warning signs that can be activated by automotive headlights and multifunctional RTP hydrogels, demonstrating great application potential in the fields of advanced anti-counterfeiting technology and flexible luminescent materials.