Visible light-excited full-color phosphorescent material realized by carbon dots dispersed in polyacrylamide and applied to anti-counterfeiting

Carbon dots-based phosphorescent composites have excellent room-temperature phosphorescent properties. However, the development of carbon dots-based phosphorescent materials that are excited by visible light and have adjustable colors remains a challenge. Here, we report on phosphorescent composites based on multicolored fluorescent carbon dots (CDs) and polyacrylamide (PAM) with four phosphorescent colors (blue, green, yellow and red). The phosphorescence of CDs@PAM composites is mainly derived from the C=O bonds of CDs. Electron transition of n-π* in the C=O bonds facilitates the intersystem crossover that are necessary to generate phosphorescence. In addition, the hydrogen bond actions between the amide groups of PAM polymer and the functional groups on CDs surface also promote the intersystem crossover and inhibit the non-radiative relaxation of triple states (T₁) in CDs@PAM. Meanwhile, the PAM matrix provides a rigid protective environment (hydrogen bond mesh structure) that inhibits vibrations, rotations and collisions of the CDs' luminescent clusters (C=O), avoiding the rapid decay of phosphorescence. Four kinds of CDs based phosphorescence materials can produce brilliant phosphorescence under the excitation of visible light (flashlight). Finally, their colorful phosphorescent colors were used to achieve a naked-eye observable anti-counterfeit pattern, demonstrating the potential application of these materials.