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 LuBO₃:Ce³⁺ 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.