Multicolor fluorescent/room temperature phosphorescent carbon dot composites for information encryption and anti-counterfeiting

Abstract

Room temperature phosphorescent (RTP) materials have a place in information encryption and anti-counterfeiting applications due to features such as long-life luminescence. In this work, three different colors (blue, cyan and green) carbon dots, named B-CDs, C-CDs, and G-CDs, were prepared via a one-step hydrothermal method using glutathione, m-phenylenediamine and p-phenylenediamine as raw materials. B-CDs, C-CDs, and G-CDs generate more n-π* transitions due to the doping of N atoms, which promotes inter-system crossing (ISC) and thus effectively populates triplet excitons. In addition, the corresponding fluorescent/phosphorescent solid powders were obtained by dispersing B-CDs, C-CDs, and G-CDs in sodium alginate (SA). After turning off the UV lamp, several seconds of RTP were able to be observed with phosphorescence lifetimes of 165.8, 284.5, and 186.1 ms, respectively. Moreover, RTP is easily quenched by atmospheric oxygen and water molecules, so green RTP can only be observed in a dry condition by printing C-CDs@SA gels on filter paper. Based on this feature, the prepared CDs can be effectively used for message encryption and advanced anti-counterfeiting. As well as, C-CDs@SA powder also has important applications in fingerprint detection.