Exploration of Room-Temperature Phosphorescence and New Mechanism on Carbon Dots in a Polyacrylamide Platform and their Applications for Anti-Counterfeiting and Information Encryption

This is the first report of full-color afterglow composites composed of four multicolored (blue, green, orange, and red) carbon dots (CDs) in polyacrylamide (PAM) matrix. Thus, adjustable four-color room-temperature phosphorescence (RTP) CDs@PAM composites are prepared on a PAM platform. The abundant amide groups in PAM are connected to the functional groups in CDs by hydrogen bonds, which promote the intersystem crossover and inhibit the non-radiative relaxation of triple states (T₁) in CDs@PAM and effectively shield the quenching agents such as oxygen. Furthermore, the rigid hydrogen bond mesh structure is beneficial to the stability of T₁ in CDs@PAM. In addition, the results of electron spin resonance reveal that the afterglow of CDs@PAM composites is not caused by oxygen defects and the increase of oxygen defects hinders the emission of phosphorescence. The CDs@PAM composites display not only multi-color fluorescence from blue to red, but also display full-color RTP emission from blue to red with average phosphorescence lifetime in the range of 637–478.97 ms. These composites, in addition to the full-color RTP performance, are promising for multi-color pattern anti-counterfeiting and information encryption.