Carbon Dot-Based Room-Temperature Phosphorescent Materials for Information Encryption

Room-temperature phosphorescence (RTP) plays an important role in the field of information encryption due to its ability to effectively eliminate interference caused by background fluorescence (FL). Herein, a series of RTP carbon dots (CDs) containing different nitrogen contents were prepared via a molten salt method. In the reaction system, magnesium chloride and potassium nitrate were used as doping salts to form salt shells, and potassium nitrate was used as salt medium to promote the reaction. By adjusting the amount of melamine, the synthesized CDs-3 exhibit cyan FL and yellow phosphorescence, with a long phosphorescence lifetime of 673.29 ms. It is worth noting that the yellow RTP can be maintained either in dry or wet state, which facilitates for the information encryption. It is suggested that the salt shell composed of magnesium salt with high charge density has a rigid structure, which inhibits the nonradiative transition process of the triplet-state exciton and enhances the phosphorescence intensity. Unfortunately, when the amount of melamine increases to a certain extent, due to the incomplete encapsulation of the salt shell, the phosphorescence of the prepared CDs quenches accordingly. In addition, CDs-3 can also be mixed with epoxy resin to obtain the desired fluorescent/phosphorescent composites. These excellent optical properties indicate that the synthesized CD materials have great development prospects in fields such as anti-counterfeiting and luminescent materials.