Photoswitchable lanthanide-doped core-multishell nanoparticles for tunable triple-mode information encryption and dynamic anti-counterfeiting patterns

Photoresponsive luminescent materials with high-capacity information storage and multilevel anti-counterfeiting capability are attracting much interest in many fields including information encryption and anti-counterfeiting. Herein, a class of novel photoswitchable upconversion luminescent nanoparticles (PUCNPs) with core-multishell structure that shows switchable dual-colored emission is described. The PUCNPs is successively built up from lanthanide-doped NaYF4 nanoparticles and a photochromic spiropyrane (SP) monomer by grafting of poly(glycidyl methacrylate-co-SPMA) on the nanoparticles via surface reversible addition-fragmentation chain transfer (RAFT) polymerization. The as-prepared PUCNPs with triple-mode optical features displayed green upconversion luminescence under a 980 nm laser, red downconervsion fluorescence and purple color under a 365 nm UV light irradiation and turning off, respectively. Furthermore, they enable dynamic reversible changes in color between colorless and purple states with 365 nm UV and white light stimuli. Their potential in complex information encryption and dynamic anti-counterfeiting patterns is described and its great potential in data storage, and rewritable optical materials is foreseen.