AlF3-confined carbon dots with lanthanide-ion-mediated dynamic afterglow for multilevel information encryption

The development of dynamic optical materials with time-dependent afterglow color (TDAC) is crucial for advanced anti-counterfeiting and information encryption but remains a formidable challenge. This work introduces a novel aluminum fluoride (AlF 3 ) matrix for the rigid confinement of carbon dots (CDs), yielding a CDs@AlF 3 composite that exhibits intense blue thermally activated delayed fluorescence (TADF) with a long lifetime of 994 ms and a high photoluminescence quantum yield of up to 23.4%. Remarkably, incorporation of lanthanide ions (Eu 3+ or Tb 3+ ) into the CDs@AlF 3 system fundamentally alters the emission mechanism, suppressing TADF and activating room-temperature phosphorescence from the CDs while simultaneously establishing a phosphorescence resonance energy transfer (PRET) pathway to the lanthanide acceptors. This creates dual afterglow centers with distinct decay kinetics. The resultant CDs@AlF 3 /Eu 3+ (or CDs@AlF 3 /Tb 3+ ) composites demonstrate fascinating TDAC phenomena, visually transitioning from red (or green) to blue over time after ceasing the excitation source. The PRET efficiency and emission color are precisely tunable by varying the lanthanide concentration. Furthermore, the composites exhibit exceptional stability against UV irradiation, harsh chemicals, and solvents. This matrix-based confinement and energy transfer strategy paves the way for designing smart optical materials with programmable temporal features for high-level security applications.