Covert Information Storage and Encryption Using Temporal Emissions from Lanthanide-Doped LiYF₄ Nanoparticles

The long-lived excited state lifetimes from lanthanide ions add a temporal dimension to the two spatial dimensions used in printed information storage devices. A system using lanthanide-doped LiYF 4 nanoparticles was designed, where a pattern and mask emit in the same region of the visible spectrum but with different lifetimes. After excitation has ceased, the emission from the mask decays, allowing the pattern to be imaged. A pattern employing Eu 3+ -doped nanoparticles was masked using CsMnCl 3 nanoparticles, and a pattern using LiYF 4:Yb 3+, Ho 3+ upconverting nanoparticles was masked using LiYF 4:Yb 3+, Er 3+ nanoparticles. This demonstrates a method to enhance the encryption capacity of information storage devices that rely on lanthanide luminescence.