Boosted photochromic properties by carbon dots based on Förster resonance energy transfer

Photochromic materials with rapid response and high stability are essential for progressive anti-counterfeiting and secure information encryption technologies. Herein, we report a Förster resonance energy transfer (FRET)-assisted strategy to boost the photochromic properties of highly crystalline C₃N₅ nanosheets (HC-C₃N₅) by integrating carbon dots (CDs). The incorporation of CDs significantly increased light absorption, fluorescence intensity, and energy transfer efficiency, leading to an ultrafast and reversible color transition from dark yellow to green under UV irradiation, with complete recovery within 180 s and excellent cycling stability. The transient photovoltage technique (TPV) test confirms a non-radiative energy transfer pathway between CDs and HC-C₃N₅, excluding the possibility of electron transfer. Building on the distinct photo response characteristics of bulk C₃N₅ (B-C₃N₅), HC-C₃N₅, and CDs/HC-C₃N₅, this study further explores their potential in multi-layered anti-counterfeiting labels and a time-resolved encryption system, enabling dynamic optical information encoding. This work not only reveals the key role of the FRET mechanism over CDs in modified photochromic materials, but also paves the way for next-generation anti-counterfeiting and secure data storage applications.