Tm ³⁺ Activated Dual‐Emission Ratiometric Mechanoluminescence With Energy Transfer‐Induced Dual‐Peak Ratio Change for Secure Sensing and Encryption

ABSTRACT Ratiometric mechanoluminescence (RML) improves accuracy and stability over absolute emission intensity by encoding mechanical information into the intensity ratio of multiple emission channels. However, existing RML approaches mainly rely on multi‐ion doping or multi‐component systems with limited controllability, spectral overlap, and complex energy transfer. Here, we report a single‐ion Tm 3+ activated RML material, YVO 4 :Tm 3+ , showing sharp dual emissions in the visible and near‐infrared (NIR) under mechanical stress. Two well‐resolved peaks at 474 nm and 800 nm arise from distinct intra‐4f transitions of Tm 3+ activators, with a large spectral separation of 326 nm for high‐fidelity discrimination. Mechanistic studies indicate that ratiometric behavior originates from stress‐modulated energy transfer between the YVO 4 lattice and Tm 3+ activators. Under low stress, energy transfer from the 3 T 1 host level populates the 3 H 4 level of Tm 3+ , enhancing NIR emission. Under high stress, electron transfer to the 1 G 4 level restores emission to the intrinsic photoluminescence state, enabling robust RML. The visible‐NIR RML is demonstrated for train wheel damage detection and a mechanically activated, spectrally gated information encryption‐decryption platform. This strategy advances single‐ion RML for secure sensing, structural diagnostics, and optical encryption.