Gradient Deep-Trap Engineering in Terbium-Doped LiYF ₄ Nanocrystals for Reconfigurable Multiplexed Encrypted Data Storage

The rapid expansion of digital data requires storage with high capacity, long-term stability, and secure encryption. Persistent luminescence (PersL) is promising for optical storage, but flexible multilevel encoding and efficient readout remain challenging. Here, we report gradient deep-trap engineering in LiYF₄:Tb³⁺ nanocrystals for multiplexed encrypted storage. The distorted coordination of scheelite-type LiYF₄ and fluoride displacement under X-ray irradiation promote charge-compensating defects, generating a broad distribution of deep traps (0.8-1.4 eV) that exceeds conventional sodium-based fluorides. Besides long-lasting PersL, LiYF₄:Tb³⁺ exhibits pronounced photostimulated and thermally stimulated luminescence (PSL and TSL). Thermoluminescence (TL) analysis reveals a gradient trap profile enabling temperature-selective carrier release. Utilizing this controllable trap distribution with strong charge retention and thermal cyclability, we demonstrate multilayer optical encryption within a single medium, where distinct information can be selectively decoded. These findings hold great promise for advanced optical data storage, enabling scalable encoding and retrieval for high-density, secure data.