Enhancing blue phosphorescence in matrix-free carbon dots through covalent crosslinking

Room temperature phosphorescence (RTP) of carbon dots (CDs) has received extensive attention due to its excellent performance and promising application. Here, a novel kind of matrix-free CDs with blue phosphorescence emission was synthesized by a simple one-step hydrothermal method of heating (3-Aminopropyl) trimethoxysilane (APTMS) and phosphoric acid in aqueous solution. The obtained CDs show a phosphorescence lifetime of 315.73 ms, and the absolute photoluminescence quantum yield (PLQY) and the phosphorescence quantum yield (PQY) can reach up to 37.8 % and 12.4 %, respectively. From the experimental results, we speculate that the generation of RTP is attributed to the restriction effect of the covalent crosslinking structure of Si–O–Si, Si–O–C, or Si–C bonds formed on the CDs surface. In addition, phosphoric acid as a crosslinking agent and heteroatom dopant can promote the formation of cross-linked structures and facilitate the intersystem crossing (ISC) process, thus enhancing room temperature phosphorescence. Finally, the CDs were successfully used in information encryption and anti-counterfeiting.