Chemical Composition Engineering Boosting Luminescent Efficiency and Thermostability in Dy ³⁺ ‐Activated Borotellurate Phosphors for Multifunctional Security and Identification Applications

Dy 3+ ‐activated phosphors offer cost‐effective potential for optical security and forensic applications but are typically hindered by low luminescent efficiency, thermal instability, and poor compatibility with flexible matrices. To address these limitations, the chemical composition of LnTeBO 5 :Dy 3+ (Ln = La, Y, Gd) phosphors is engineered via lanthanide substitution to modulate the [LnO 8 ] coordination environment and enhance the Dy 3+ emission. Gd 3+ incorporation enables precise control over the 4 F 9/2 → 6 H 15/2 (blue) and 4 F 9/2 → 6 H 13/2 (yellow) transitions, achieving a 3.5‐fold increase in internal quantum efficiency (IQE). The optimized GTBO:5%Dy 3+ phosphor exhibits the highest structural rigidity and maintains a 96% emission intensity at 423K. It also shows excellent compatibility with polyvinylpyrrolidone (PVP) and polydimethylsiloxane (PDMS), supporting fabrication in both flexible and rigid formats. Its intense and stable luminescence enables high‐contrast latent fingerprint (LFP) visualization and durable anti‐counterfeiting markings under UV and visible light, demonstrating its multifunctionality for security and identification applications.