Upconversion Fluorescence Performance Modulation And Anticounterfeiting Application Of NaYF₄:Re³⁺ Thin Films

Counterfeiting of commercial goods is a challenger which exhibit serious economic ramifications for customers,companies and governments.Thus,until today,various anticounterfeiting technologies have been developed to label and track commercial luxury products.Although the traditional anticounterfeiting techniques including hologram attachment,QR codes and radio-frequency identification(RFID)have been well developed and commercial applicated,there are several limitations such as complicated fabrication process,costly raw materials and easy to copy.Therefore,it has become an important development trend to develop ant-counterfeiting technology with the characteristics of cost-effective fabrication,difficulty in copying and high concealment.Fluorescent anticounterfeiting labels using UV irradiated fluorescent ink to print coded patterns for authenticity identification.They are economical and easy to identify,and have been commercialized and is widely known to the public.Organic dyes,the component of fluorescence ink,have the advantages of high luminous efficiency and adjustable color,while most of them are colorful and confronted with the phenomenon of light bleaching,which leads to poor concealment of patterns and unstable fluorescence.Therefore,it is of great theoretical and practical significance to explore new luminescent materials and design new fluorescent labels with strong concealment and not easy to copy for promoting the development of fluorescent anticounterfeiting technology.In this paper,the transparent Na YF₄:20%Yb³⁺,2%Er³⁺green upconverting(UC)fluorescent film was deposited by a solution electrochemical deposition method,and the red-green-blue(RGB)primary color fluorescence of Na YF₄:Re³⁺(Yb³⁺,Tm³⁺,Er³⁺)UC fluorescent films were modulated by the doping ions.After that,the patterned films were realized by microelectronic lithography.Under the illumination of near-infrared invisible light at 980 nm,the coded patterned films emits visible fluorescence of various colors,which is characterized by concealment and difficulty in reproduction.The specific research contents and results are as follows:(1)Electrochemical deposition growth mechanism of Na YF₄:Re³⁺UC fluorescent films.The preparation of pure?-Na YF₄green UC fluorescent film was realized by solution electrochemical deposition,and the thickness could be well modulated from 1.58 to 6.09?m by the deposition time.Through comparison experiments,it is found that the p H of the solution plays important roles in the growth of the film.Under the environment of p H 6.5-8.5,the Re³⁺and EDTA(Y)molecules are highly complexed to form a stable Re³⁺-YH molecule,which distributed throughout the solution uniformly.The applied electric field drives the sodium ascorbate molecule to oxidize on the surface of the anode to produce H⁺,which causes the Re³⁺-YH molecule to release Re³⁺ions in the micro-area of the anode surface.In the final step,Re³⁺react with the Na⁺and F^-ions near the surface of the anode,resulting in the deposition of Na YF₄:Re³⁺particles onto the FTO substrate.(2)Optical properties of Na YF₄:Re³⁺green UC fluorescent films.Na YF₄:20%Yb³⁺,2%Er³⁺film was obtained by co-doping with 20%Yb³⁺,2%Er³⁺.It was found that the film had no fluorescence emission before annealing and the crystallinity increased after annealing at 300?.They can emit bright green fluorescence of 510-570 nm under 980 nm NIR light excitation.Further studies found that the deposition time had a great influence on the transparency and fluorescence properties of the film.As the deposition time increased,the transparency of the film in the visible band increases gradually after annealing,and found that the UC emission intensity of film electrochemical deposited for 30 minutes was the strongest.By investigating the influence of excitation light on the fluorescence performance of the film in the power range of 0.339?0.894 W,it is found that the UC fluorescence intensity(I_v)and the excitation light power(P)is approximately expressed by the following equation:I_V?P ⁿ,and n=2.06,which reveals the green upconversion luminescence of the Na YF₄:20%Yb³⁺,2%Er³⁺film is a two-photon luminescence process.(3)Synthesis and optical properties of red and blue UC fluorescent Na YF₄:Re³⁺films.On the basis of the above deposition process,the controllable preparation of Na YF₄:60%Yb³⁺,2%Er³⁺and Na YF₄:20%Yb³⁺,0.2%Tm³⁺films was achieved by adjusting the type,concentration and proportion of doping ions.Red UC emission band at 640-700 nm and blue UC emission band at 450-510 nm were generated under the excitation of 980 nm NIR light,respectively.By investigating the influence of excitation light on the fluorescence performance of the films in the power range of 0.115-1.220 W,it is found that both the red and blue UC fluorescence intensity(I_v)and the excitation light power(P)is approximately expressed by the following equation:I_V?P ⁿ,and n=1.63 and 2.51 respectively,which reveals the red and blue UC luminescence of the Na YF₄:60%Yb³⁺,2%Er³⁺film and the Na YF₄:20%Yb³⁺,0.2%Tm³⁺film are two-photon and three-photon luminescence processes,respectively.(4)Anticounterfeiting application of RGB UC fluorescent Na YF₄:Re³⁺Patterns.In combination with electrochemical deposition and microelectronic lithography,the process was optimized to achieve the preparation of a patterned Na YF₄:Re³⁺film with a resolution of50?m.The patterned Na YF₄:Re³⁺film with high fluorescence pixels and spatial resolution were found to emit bright RGB fluorescent patterns under the excitation of 980 nm NIR.Further,through the camera recognition,the APP corrects the fluorescent pattern and recognizes the code,compares it with the information base,and then decodes the anti-counterfeiting information to realize the authenticity of the commodity.