Excessive acid reagent-induced luminescent blue shift: A strategy for synthesizing full-color carbon dots and its application in information encryption and multicolor LEDs

Due to their unique fluorescence properties and wide range of applications, carbon dots (CDs) have emerged as a prominent research subject. Acid reagents have traditionally been regarded as versatile means to facilitate the carbonization and polymerization of CDs, resulting in increased carbonization and polymerization levels, which in turn cause a redshift in the luminescence of CDs. However, there has been limited investigation into the impact of excess acid reagents on CDs luminescence. In this study, we discovered that the addition of excess acid reagent, in the presence of oxygen-containing functional groups, does not enhance the graphitization of CDs, but rather, it has the opposite effect. Excess acid reagents prevent CDs polymerization and reduce the content of graphite-N in the CDs. Simultaneously, excess acid reagent leads to an increase in oxygen-containing functional groups on the surface of the CDs, resulting in a blueshift in luminescence. Building upon these findings, we have devised a synthesis scheme for full-color CDs that cover nearly the entire visible light spectrum. Furthermore, leveraging the diverse color range, we have also employed these CDs for anti-counterfeiting encryption and LEDs applications.