Lanthanide-Mediated Shallow-to-Deep Trap Engineering in CaS Nanocrystals for Multistimulus Dynamic Anticounterfeiting

Persistent luminescent (PersL) materials have demonstrated significant potential in multistimulus-responsive anticounterfeiting by tunable trap depths, yet existing material architectures encounter substantial limitations in achieving programmable gradient engineering of defect depths. Herein, we investigate the trap depth evolution mechanism in the CaS systems by employing a lanthanide-ion codoping strategy in calcium sulfide nanocrystals, achieving a gradient-controlled trap depth modulation from 0.644 to 1.090 eV through Sm³⁺-mediated defect engineering. Thermoluminescence analysis (TL) combined with density functional theory (DFT) calculations reveals that the intrinsic sulfur vacancies act as shallow traps, enabling a persistent luminescence exceeding 600 s. Furthermore, the synergistic interactions between Sm³⁺ dopants and sulfur vacancies drive the modulation of trap depth, achieving the restructuring of defect states through the controllable doping concentration. This strategy demonstrates remarkable photostimulated luminescence (PSL) performance corresponding to deep trap states (980 nm excitation, 1 W/cm², 3800 s). The developed core-shell architecture integrates multiresponsive capabilities: the core (CaS:Eu, Sm) preserves an optimized trap hierarchy, while the spatially selective shell (CaS:Er) doping introduces Er³⁺-mediated green upconversion luminescence (UCL). This work provides a paradigm for programmable stimulus-responsive luminescent materials, significantly advancing dynamic anticounterfeiting technologies with on-demand optical response capabilities.