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

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Abstract
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.

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