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 CDs-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 CDs 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 CDs-based composites and highlights their potential for time-resolved optical security applications.