Plasmonic Thermally‐Assisted Optical Memory at 77 K

Cryogenic optical storage offers a compelling route toward high‐density, quantum‐compatible, and permanent data preservation, yet it imposes critical challenges on readout sensitivity and stability. Here, we present a cryogenic optical storage platform based on a composite film of self‐assembled gold nano‐islands and rare‐earth‐doped nanoparticles. Under optical excitation, the localized surface plasmon resonance of Au nano‐islands drives crystal phase transformation of rare‐earth‐doped nanoparticles via plasmonic nano‐heating, enabling efficient data writing and reading at 77 K. The system exhibits reversible luminescence switching with a high contrast ratio of 99.9%, allowing robust binary encoding into bright (“1”) and quenched (“0”) states. Operating at cryogenic temperatures without the need for external manipulation or specialized instrumentation, this all‐optical approach is both simple to implement and highly promising for applications in secure communication, anti‐counterfeiting, and protected data transmission.