Controlling the Afterglow of Carbon Dot Composite Materials Through pH Value and the Application in Information Encryption

Abstract Phosphorescence (Phos) materials with tunable delay time can provide more modes of anti‐counterfeiting and information encryption. Carbon dots (CDs), a novel nanomaterial, exhibit remarkable optical properties and potential. Matrix assistance is an effective method to realize CDs delayed emission. Here, a new CDs composite material (AB‐CDs) is prepared using biuret and 2,4,6‐Triphenylboroxin by hydrothermal treatment, which achieves fluorescence (FL) emission at 296 nm and Phos emission at 456 nm under 260 nm excitation. Under 365 nm excitation, delayed luminescence peaked at 456 nm can be observed with the naked eye for up to 5 s. By utilizing various spectra analysis, the origin of Phos is investigated, revealing luminescence mechanism of AB‐CDs and the energy transfer (ET) process between the matrix and CDs. Simultaneously, tunable Phos delayed time from 2 to 7 s can be obtained at different pH. AB‐CDs can also maintain a high stable Phos lifetime and intensity under the same pH over 300 h, demonstrating reversible cycling at pH value between 3 and 11. Based on the unique tunable Phos characteristic of AB‐CDs, it shows potential applications in anti‐counterfeiting, information encryption and recyclable pH test.