Photo‐Induced Fluorescence Discoloration of Carbon Dots for Advanced Dynamic Information Encryption

Abstract The fluorescence discoloration of carbon dots (CDs) induced by UV irradiation without chemical modification has proved to be difficult to achieve. Herein, the synthesis of UV‐sensitive CDs with photo‐induced discoloration is reported using a heteroatom co‐doped hydrothermal method and the fluorescence of the red‐emitting CDs (R‐CDs) can be tuned under UV irradiation from red to yellow to green, showing a new strategy for simpler and easier modulating the luminescence of CDs. The UV‐induced fluorescence color change of CDs involves the changes of molecular fluorophores and oxygen defects on the surface of CDs under UV irradiation. Results show that the photo‐induced fluorescence discoloration of CDs results in the transformation of part of the internal groups, such as C─O and CO. Based on the unique UV‐induced fluorescence color‐changing property of the R‐CDs, a UV‐sensing film is fabricated, which is expected to be further applied in the field of UV detection. Furthermore, by combining CDs fluorescent ink with binary code and Morse code, it can encrypt and decrypt the information of specific text. This new concept of photo‐induced fluorescence discoloration in CDs provides strong technical support for the next generation of advanced information encryption.