Tb3+-tuned afterglow in CDs@Al2O3 for dynamic information encryption and slow-fade indicators

Abstract

Achieving controllable afterglow dynamics in carbon-based phosphors without reconstructing the host matrix remains challenging. Here, we develop a Tb³⁺-regulated carbon dots (CDs)@Al₂O₃ composite in which increasing Tb³⁺ incorporation continuously shortens the visible room-temperature phosphorescence (RTP) duration from 11 s to 1 s and reduces the RTP lifetime from 1.20 s to 0.82 s within a fixed host platform. Under UV excitation, the steady-state emission evolves from CD-dominated blue to Tb³⁺-dominated green, whereas a green afterglow persists after excitation ceases. Spectroscopic analysis and time-resolved decay measurements support a Tb³⁺-involved competitive triplet-state pathway, in which the CD triplet population is redistributed toward Tb³⁺ emission, enabling controlled modulation of afterglow kinetics. The optimized composite reaches a photoluminescence quantum yield of 36.6%. Leveraging this tunable temporal response, we demonstrate slow-fade optical indicators, time-evolving anti-counterfeiting patterns, and a UV on/off-switchable optical encryption system with distinct decoded outputs. This work establishes a simple lanthanide-regulation strategy for tailoring afterglow dynamics in CD-based composites and highlights their potential for time-resolved optical security applications.