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

Room-temperature phosphorescence (RTP) plays an importantrolein the field of information encryption due to its ability to effectivelyeliminate interference caused by background fluorescence (FL). Herein,a series of RTP carbon dots (CDs) containing different nitrogen contentswere prepared via a molten salt method. In the reaction system, magnesiumchloride and potassium nitrate were used as doping salts to form saltshells, and potassium nitrate was used as salt medium to promote thereaction. By adjusting the amount of melamine, the synthesized CDs-3exhibit cyan FL and yellow phosphorescence, with a long phosphorescencelifetime of 673.29 ms. It is worth noting that the yellow RTP canbe maintained either in dry or wet state, which facilitates for theinformation encryption. It is suggested that the salt shell composedof magnesium salt with high charge density has a rigid structure,which inhibits the nonradiative transition process of the triplet-stateexciton and enhances the phosphorescence intensity. Unfortunately,when the amount of melamine increases to a certain extent, due tothe incomplete encapsulation of the salt shell, the phosphorescenceof the prepared CDs quenches accordingly. In addition, CDs-3 can alsobe mixed with epoxy resin to obtain the desired fluorescent/phosphorescentcomposites. These excellent optical properties indicate that the synthesizedCD materials have great development prospects in fields such as anti-counterfeitingand luminescent materials.