Self-assembly Of NaYF4:Ln³⁺@PS Microsphere To Construct Biomimetic Photonic Crystal And Their Application In Optical Coding

Bionics takes the functions and behaviors of biological systems as learning objects,learns from nature,and has achieved good results in many engineering and technical fields.By imitating the biological structure of butterfly wings and insect carapace,combined with artificial synthetic materials and preparation technology,the preparation of biomimetic photonic crystals has been realized.Different from traditional chemical coloring technology,the structural colors of PCs are derived from the visual effects generated by the interaction between their periodic arranged physical structures and light diffraction,etc.,and they are characterized by gorgeous colors,vivid and changeable colors,and anti-fading properties.Therefore,PCs has a broad application prospect in the field of optical information coding.However,a single optical mode photonic crystal is not enough for encoding to meet the needs of multi-dimensional protection of information and high encoding security level.Therefore,the development of dual-mode fluorescence photonic crystal materials with adjustable upconversion fluorescence and structural color has important research significance for optical information encoding.This thesis aims to design and synthesize a novel type of fluorescence photonic crystal combined with information encoding technology to develop a dual-mode optical encoding system.The main research content is divided into the following three aspects:(1)Synthesis and characterization of fluorescence-enhanced NaYF₄:Ln³⁺@NaYF₄ core-shell nanoparticles.NaYF₄:Ln³⁺@NaYF₄core-shell nanoparticles(CSNPs)were synthesized via two-pot thermal decomposition using oleic acid(OA)as the ligand.The effects of the reaction temperature of the shell coating and the different thickness of the shell on the crystal phase,morphology and fluorescence properties of CSNPs were systematically explored.The results show that:the best shell growth temperature was 310?and the best shell precursor addition amount was 3 mmol,the pure hexagonal rod-shaped CSNPs have the highest fluorescence intensity.Subsequently,the doping of rare earth ions was adjusted,and Er³⁺/Tm³⁺,Yb³⁺/Er³⁺,Yb³⁺/Tm³⁺were doped to realize the preparation of red,green and blue fluorescence-enhanced core-shell nanoparticles,which laid a foundation for the subsequent preparation of upconversion fluorescence composite microspheres.(2)Synthesis and characterization of photonic crystal material NaYF₄:Ln³⁺@NaYF₄@PS(CSNPs@PS)composite microspheres.CSNPs were coated and modified with Si O₂ modified with 3-(Trimethoxysilyl)propyl methacrylate(MPS).Make CSNPs water-dispersible and give them double bonds that can participate in the polymerization reaction.Then placed in the emulsion polymerization reaction system,using styrene polymerization,the CSNPs@Si O₂-MPS particles were wrapped in PS to prepare CSNPs@PS composite microspheres.Explored the surface properties,morphology,and UC fluorescence intensity of the products at each stage of the preparation process of composite microspheres.The results show that the preparation method can prepare composite microspheres with good monodispersity and uniform particle size.Further by adjusting the amount of styrene monomer added,the particle size of the microspheres can be controlled,and for the subsequent construction of red,green and blue photonic crystal films with three primary colors,the composite microspheres with particle sizes close to 185 nm,230 nm,and 290 nm were prepared.By changing the type of upconversion fluorescence nanoparticle cores in the microspheres,the upconversion fluorescence luminescence adjustment of the microspheres was realized.(3)Self-assembly of CSNPs@PS composite microspheres to construct fluorescent photonic crystal film and its application in optical coding.The upconversion fluorescence photonic crystal(UCPC)film was constructed via the self-assemble of CSNPs@PS through the vertical deposition method.The photonic crystal films assembled by the composite microspheres have different bandgap wavelengths due to their different particle sizes.The UCPC films prepared by composite microspheres with particle sizes close to 185 nm,230 nm,and 290 nm have pink,green,and blue structural colors,respectively.Because the composite microspheres were coated with fluorescence-enhancing core-shell upconversion nanoparticles,the UCPC film exhibits upconversion fluorescence of different colors under the excitation of a 980 nm laser.By changing the types of CSNPs in the composite microspheres and the particle size of the composite microspheres,the constructed UCPC film not only has bright red,green and blue structural colors,but also emits red,green and blue fluorescence when excited by a 980 nm laser.Adjustable structural color and upconversion fluorescence can be used for information coding.The constructed dual-mode optical coding system has high information capacity and high security,and is expected to have potential application prospects in color display,anti-counterfeiting,and multiplexing detection.