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 NaYF 4 :Ln 3+ (CSNPs@SiO 2 /PS) composite microspheres . The composite microspheres were synthesized by sequential coating technology . Firstly, NaYF 4 :Ln 3+ @NaYF 4 core/shell nanoparticles (CSNPs) were synthesized and served as upconversion luminescent emission centers. Then, the CSNPs were further coated by a SiO 2 shell with pendant double bond to form CSNPs@SiO 2 -MPS. Afterward, mono-dispersed CSNPs@SiO 2 /PS composite microspheres were synthesized by emulsion polymerization of styrene in the presence of CSNPs@SiO 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.