Carbon Dots‐Inked Paper with Single/Two‐Photon Excited Dual‐Mode Thermochromic Afterglow for Advanced Dynamic Information Encryption

Abstract Achieving thermochromic afterglow (TCAG) in a single material for advanced information encryption remains a significant challenge. Herein, TCAG in carbon dots (CDs)‐inked paper (CDs@Paper) is achieved by tuning the temperature‐dependent dual‐mode afterglow of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). The CDs are synthesized through thermal treatment of levofloxacin in melting boric acid with postpurification via dialysis. CDs@Paper exhibit both TCAG and excitation‐dependent afterglow color properties. The TCAG of CDs@Paper exhibits dynamic color changes from blue at high temperatures to yellow at low temperatures by adjusting the proportion of the temperature‐dependent TADF and phosphorescence. Notably, two‐photon afterglow in CDs‐based afterglow materials and time‐dependent two‐photon afterglow colors are achieved for the first time. Moreover, leveraging the opposite emission responses of phosphorescence and TADF to temperature, CDs@Paper demonstrate TCAG with temperature‐sensing capabilities across a wide temperature range. Furthermore, a CDs@Paper‐based 3D code containing color and temperature information is successfully developed for advanced dynamic information encryption.