Synthesis And Anti-counterfeiting Application Of Two-Color Up-Conversion NaYF₄:Yb³⁺/Ln³⁺(Ln=Er,Tm) Nanorods

The prevalence of counterfeit and shoddy has seriously harmed the health of the people and the image of the government.For example,food,banknotes,documents,valuables,etc.are often illegally forged.This poses a serious security threat to individuals,companies,society,and the country,so it is urgently needed for development A safe,reliable and simple technology to distinguish the authenticity.Among many anti-counterfeiting technologies,fluorescent anti-counterfeiting technology is widely used because of its low cost,strong recognition ability,non-toxicity,and difficulty in imitating.Among them,up-conversion fluorescent materials have been developed for high-density fluorescent anti-counterfeiting and identification due to their near-infrared excitation and visible emission,large anti-stokes shift,rich and adjustable spectrum,and high chemical stability.In order to improve the anti-counterfeiting level of fluorescent anti-counterfeiting materials,this subject uses hydrothermal epitaxial growth control to synthesize a series of single-particle two-color luminescent nanorods,and is committed to developing a new high-density fluorescent anti-counterfeiting encryption technology.The research content is divided into the following three section:Using oleic acid(OA)as the complexing agent,optimize the hydrothermal reaction temperature,hydrothermal time,and F^-concentration to determine the best synthesis conditions for single-particle nanorod seed crystals.The final resultant average length is 1.7?m and uniform morphology NaYF₄:Yb³⁺/Ln³⁺single-particle nanorod seed crystals.Nanorods seed crystal C-axis epitaxial growth:EDTA was used as the complexing agent to prepare NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Yb³⁺/Tm³⁺and a series of single-particle and two-color luminescent nanorods under the conditions of hydrothermal temperature,hydrothermal time and p H.SEM and TEM testing of the nanorods found that the two ends of the nanorods had obvious epitaxial protrusions.At the same time,the EDS-mapping test confirmed that the element distribution was completely consistent with the originally designed two-color single-particle nanorods.The up-conversion fluorescence spectrum test results showed that the emission peaks of Er³⁺and Tm³⁺existed simultaneously,indicating that the nanorods have dual-color luminescence characteristics.The prepared two-color nanorods were further observed by using a laser scanning confocal microscope.The nanorod seed crystals in the middle and the epitaxial protrusions at both ends respectively emitted green and blue up-conversion fluorescence,which confirmed that the synthesis of single-particle two-color luminescent nanorods was successfully controlled.Great,lay the foundation for high-density anti-counterfeiting applications.Fluorescence anti-counterfeiting application:first use NaYF₄:Yb³⁺/Er³⁺monochromatic luminescent nanorods to construct a monochromatic fluorescent anti-counterfeiting pattern under 980 nm single wavelength excitation.Then use NaYF₄:Yb³⁺/Er³⁺@NaYF₄:Yb³⁺/Tm³⁺two-color nanorods to form a two-color fluorescent anti-counterfeiting pattern under a single wavelength of 980nm excitation,and use a laser confocal microscope to observe the micro-area single-particle nanorod luminescence to compare its anti-counterfeiting performance.Both can display the same fluorescent anti-counterfeiting pattern under 980 nm excitation,but there is a clear difference in the single-particle emission color.Finally,use the NaYF₄:Yb³⁺/Er³⁺/Nd³⁺@NaYF₄:Yb³⁺/Tm³⁺two-color nanorods to construct the two-color up-conversion fluorescent anti-counterfeiting pattern under the excitation of the980nm and 808nm dual-wavelength lasers respectively.The particle nanorod luminescence was observed to compare its anti-counterfeiting performance.The complete anti-counterfeiting pattern can be seen under 980 nm excitation and part of the anti-counterfeiting pattern can still be seen under 808 nm excitation.At the same time,the single-particle luminescence color also has a significant difference with the change of excitation wavelength.