Unlocking Phonon‐Assisted Emission in the UV Using Visible‐Excitable Phosphors for Security Applications

Abstract UV luminescence holds great promise for secure optical anti‐counterfeiting but is often limited by the need for shorter‐wavelength excitation sources. In this study, an intriguing phonon‐assisted luminescence phenomenon is introduced, enabling anti‐Stokes UV (AS‐UV) emission through the use of visible light to excite various phosphors. By leveraging lattice vibrations (phonons) to bridge the energy gap, a 330‐fold increase in UV emission intensity is achieved at 200 °C compared to room temperature in the model system LuBO 3 :Ce 3+ under 405 nm excitation. This thermally activated nature of this phenomenon is extended to additional phosphors, demonstrating its potential for UV imaging and anti‐counterfeiting applications. Importantly, distinctive patterns emerge only under specific thermal conditions, adding an extra layer of security. These findings establish a class of UV phosphors excitable by visible light, providing insights into phonon‐assisted luminescence and offering significant advancements for security features and optical imaging technologies.