Synthesis And Fluorescence Performance Control Of NaYF₄:Ln³⁺ Hollow Microtube And Its Application In Anti-counterfeiting Printing

In the 21st century,where the economy is developing at a high speed,counterfeit and shoddy products have seriously damaged the global economy and even harmed human health.Therefore,the development of advanced anti-counterfeiting technology is particularly important.Fluorescent anti-counterfeiting technology has become a "new darling" for anti-counterfeiting researchers with its unique photoluminescence properties.Rare earth doped NaYF₄ has become a research hotspot for upconversion or downconversion matrix materials due to its excellent chemical stability and low phonon energy.However,the problem of low fluorescence efficiency has always been the primary problem that plagues scientists,especially in the field of anti-counterfeiting.Therefore,how to synthesize a fluorescent material with excellent fluorescence performance and high anti-counterfeiting level has great research significance for anti-counterfeiting applications.Based on this,this dissertation has carried out a series of research on high-fluorescence intensity dual-mode rare earth doped NaYF₄.The main research contents are divided into the following three aspects:（1）Yb³⁺/Er³⁺ co-doped NaYF₄ was synthesized by hydrothermal method using polyacrylic acid（PAA）as a surfactant.The effects of hydrothermal temperature,pH value,the ratio of alcohol to water,PAA concentration and PAA molecular weight on the crystal form,morphology and size of the product were systematically studied.The results showed thatβ-NaYF₄ hollow microtubes exhibiting the highest luminous intensity.（2）In this chapter,PAA was used as a surfactant to synthesize PAA modified NaYF₄:Yb³⁺,Er³⁺ upconvertion hollow microtubes（UCHMs）.The morphology,crystal phase,element composition and surface properties of UCHMs were further characterized.The growth mechanism of UCHMs was investigated in detail by analyzing the crystal phase and morphology of the intermediate products with different hydrothermal time.Subsequently,NaYF₄ UCHMs with red,green and blue colors were prepared by doping different rare earth ions,and dispersed in ethanol/molecular water/glycerol system to make printing inks.The inkjet printing technology was used to verify the UCHMs fluorescent inks in multiple stages.Great potential for image encryption and anti-counterfeiting without background images.（3）In the era of high information sharing,single-mode fluorescent anti-counterfeiting has gradually become a low-end anti-counterfeiting form that is easy to imitate.More advanced dual-mode fluorescent anti-counterfeiting materials are becoming a hot research topic.Therefore,in this chapter,PAA was used as a structure-directing agent to synthesize PAA-modified up/down conversion NaYF₄:Yb³⁺,Tm³⁺@NaGdF₄:Ce³⁺,Eu³⁺ dual-mode hollow microtubes（DMHMs）by hydrothermal method.The product has dual-mode fluorescence and the up-conversion fluorescence intensity is enhanced by 1.76 times.Finally,it has been demonstrated by inkjet printing techniques that dual mode fluorescent inks can be used to print hidden optical images on non-fluorescent paper.In summary,this dissertation is devoted to the preparation of fluorescent materials with excellent fluorescence properties by simple hydrothermal synthesis method,and its application in the field of anti-counterfeiting has been laid,which lays a foundation for the application of such materials in the field of anti-counterfeiting.At the same time,this dissertation developed a preparation method of polymer PAA-induced core-shell structure inorganic materials,which provided a reference for the multilayer composite preparation of other inorganic materials.