Photonic crystal films with upconversion luminescence based on the self-assembly of polystyrene encapsulated NaYF4:Ln3+ composite microspheres for dual-mode optical code

The design and fabrication of advanced materials with multiple optical states for constructing security code are of great value in anti-counterfeiting. Herein, novel upconversion photonic crystal (UCPC) films with tunable luminescence and structural color were prepared by vertical deposition of polystyrene encapsulated NaYF4:Ln3+ ([email protected]2/PS) composite microspheres. The composite microspheres were synthesized by sequential coating technology. Firstly, NaYF4:Ln3+@NaYF4 core/shell nanoparticles (CSNPs) were synthesized and served as upconversion luminescent emission centers. Then, the CSNPs were further coated by a SiO2 shell with pendant double bond to form [email protected]2-MPS. Afterward, mono-dispersed [email protected]2/PS composite microspheres were synthesized by emulsion polymerization of styrene in the presence of [email protected]2-MPS. By tailoring the doped lanthanide ions in CSNPs and adjusting the diameter of the composite microspheres, UCPC films with diverse upconversion fluorescence and structural color can be obtained. As a proof of concept, these different kinds of UCPC films were employed as information coding units to construct dual-mode anti-counterfeiting code. Our protocol provided a new security strategy for information storage.