Preparation And Anti-counterfeiting Application Of Rare Earth Doped Sodium Yttrium Fluoride With Dual-mode Emission

Counterfeiting of goods and documents is a global issue causing tremendous lost to governments and businesses.Due to its advantages in design ability,unique optical properties,and handling convenience,luminescent ink has been widely applied in anti-counterfeiting technology.In order to against counterfeiting,several traditional luminescent materials are developed,such as quantum dots(QDs),metal-organic frameworks,and lanthanide doped materials.However,these luminescent materials applied in anti-counterfeiting are generally exhibiting sing-mode emission upon near-infrared(NIR) or ultraviolet(UV) light excitation.Currently,no matter what excitation light source is used,the strategy of using single-mode emission materials has been well known for luminescent security inks and can be easily replicated.Among these luminescent materials,the lanthanide doped materials are much preferred to confect luminescent security inks,based on their excellent optical features,chemical stability,ease in bulk production and low toxicity.For further elevating difficulty of illegal imitation as well as improving anti-fake ability,dual-mode or multi-mode emission from fluorescent anti-counterfeiting materials is one of the important research directions.In this paper,in order to improve the applicability of inorganic luminescent materials in high-level anti-counterfeiting applications,the lanthanide-doped single-mode luminescent materials based on sodium yttrium fluoride were modified to prepare dual-mode luminescent material at the single-particle level.X-ray Powder Diffractometer(XRD),Scanning Electron Microscope(SEM),Transmission Electron Microscope(TEM),High Revolution Translation Electron Microscopy(HRTEM),Ultraviolet-visible Spectrophotometer(UV-Vis),Fluorospectrophotometer and Fourier Transform Infrared spectroscopy(FTIR) have been utilized to analyze the crystal structure,morphology and fluorescence properties.The major research contents include:(1)Single-mode emission NaYF₄:Er³⁺,Tm³⁺ microcrystals were prepared by hydrothermal method and surface treated.Under hydrothermal environment,NaYF₄:Er³⁺,Tm³⁺@NaYF₄:Ce³⁺,Tb³⁺luminescent microcrystals were synthesized via an epitaxial growth technique.The structure and morphology of these microcrystals are examined by SEM,TEM,EDS and XRD measurements.These particles show dual-mode emissions with red upconversion(UC) and green downconversion(DC) as single particles level.The mean length and diameter of these microparticles increases from 0.43?m to 2.26?m and from1.33?m to 1.86?m,respectively.Most interestingly,the photoluminescence properties of NaYF₄:Er³⁺,Tm³⁺@NaYF₄:Ce³⁺,Tb³⁺phosphor crystals are highly dependent on the crystallite size.The microcrystals fluoresce emit dual-mode emissions when they are solid or dispersed in solvents.(2)NaYF₄:Ce³⁺,Tb³⁺ nanoparticles and carbon dots(CDs) were synthesized by solvothermal and hydrothermal method,respectively.Under room temperature,NaYF₄:Ce³⁺,Tb³⁺@CDs nanocrystals were obtained via the classic EDC-NHS coupling.The structure and morphology of these nanocrystals are examined by XRD,TEM,and FTIR measurements.These particles show dual-mode emissions with blue and green light.After fabricated the NaYF₄:Ce³⁺,Tb³⁺@CDs nanostructures,these nanoparticles retained the cubic phase crystal form of NaYF₄.When the mass ratio of NaYF₄ nanoparticles to CDs is1.0,the highest emission of blue light can be obtained.(3)These dual-mode emitting NaYF₄:Er³⁺,Tm³⁺@NaYF₄:Ce³⁺,Tb³⁺microcrystals were utilized to fabricate fluorescent inks and light conversion film.These inks are employed to fabricate various invisible patterns and Chinese characters using conventional screen printing technique as well as pen-on-paper process.These patterns and LCF present strong concealment under ambient lighting,while exhibit high identifiability with red and green fluorescence patterns under 254 nm UV-lamp and 980 nm NIR laser.In this paper,the research of lanthanide-doped sodium yttrium fluoride luminescent materials with dual-mode emission provide a significant reference for the selection of inorganic luminescent materials in high-level anti-counterfeiting applications.