Strategy for Activating Room-Temperature Phosphorescence of Carbon Dots in Aqueous Environments

Activating room-temperature phosphorescence (RTP) emission in aqueous environments is a challenging feat because of the releasing of nonradiative decay pathways. Here, a design strategy was presented that effectively promotes the presence of RTP of carbon dots (CDs) in aqueous solutions by utilizing CDs and melamine to construct hydrogen-bonded networks to form a polymer (M-CDs). The obtained M-CDs not only enjoy an ultralong phosphorescence lifetime of 664 ms, but also relatively high quantum yield of 25% in an aqueous environment at 468 nm excitation. This is also a rare example of achieving RTP of CDs with a solid state in an aqueous environment. Further investigations reveal that the hydrogen-bonded networks are critical to the implementation of RTP in an aqueous environment. The existence of covalent bonds in CDs and melamine further stabilizes the hydrogen-bond skeleton and triplet state. Furthermore, the bound water formed inside the M-CDs also plays an indispensable role in stabilizing the RTP in the aqueous solution. Given the feature, the M-CDs are used to effectively implement double data encryption and decryption. In addition, this strategy is universal for most phosphorescence materials. This result will pave the way toward expanding RTP materials and their applications in aqueous environments.