Temperature-Responsive Red-Phosphorescent Carbon Dots for Anticounterfeiting Applications

The preparation of temperature-responsive phosphorescent materials with a high color contrast from a single emission source is still a challenging area of research. In this study, for the first time, we present a red composite phosphorescent material that is temperature-responsive and exhibits high color contrast. This material is synthesized via microwave synthesis to prepare carbon dots (CDs) in a one-step process using pyrene as the raw material and citric acid and biuret as the control materials. These materials undergo different reaction behaviors with poly(methyl methacrylate) (PMMA). Notably, the formation of large conjugated structures and the limitation of nonradiative transitions through PMMA are responsible for the achievement of high-performance red-phosphorescent phosphorus materials. PMMA pyrolysis at a high temperature produces a large number of hydroxyl groups, and the amino and carboxyl groups on the surfaces of different CDs undergo different hydrogen bonding or fracture behaviors, resulting in a temperature-stimulated response to the generation of phosphorescence. Due to the combined effect of CDs and PMMA, which greatly reduces the proportion of nonradiative transitions, the composite exhibits photophysical behavior characterized by blue fluorescence under UV irradiation and red phosphorescence when the UV light is turned off. This red-phosphorescent material is well-suited for information security applications due to its advantages of clear contrast, high visibility, and simple identification. By using different arrangement orders in the same model, three different pieces of information can be obtained and three-dimensional models and dynamic trademarks can enhance anticounterfeiting applications with double security.