Synthesis Of Rare Earth/Carbon Dots Composites And Application In Anti-Counterfeiting Field

With the increasing of counterfeit goods on the market,the anti-counterfeiting technology is becoming more and more important.Currently,common anti-counterfeiting technologies on the market have been well known and can be easily copied,including laser holography,texture,digital and two-dimensional codes(QR Code)and so on.Fluorescent materials have received extensive attention as an anti-counterfeiting material with unique optical properties.Fluorescence anti-counterfeiting technology,that is invisible under visible light and displays information under specific excitation light.Therefore,it can avoid to be duplicated.However,with the common365 nm UV light excited fluorescent materials are widely used in vary fields,single-mode fluorescent materials and anti-counterfeiting technique are familiar to people.Therefore,how to develop a new type of fluorescent anti-counterfeiting material and anti-counterfeiting technology is still a major problem.In this paper,we developed two types of dual-mode fluorescent materials to solve current anti-counterfeiting problem.Firstly,we propose to combine the up conversion luminescent Na YF₄:Er,Yb(Tm)material with the down conversion fluorescent CDs material by simple hydrothermal method.The composite material can emit fluorescence under 980 nm NIR and 365 nm UV light,respectively.Then we propose to use a short-wavelength(254 nm)UV source to replace high-heat NIR source.We composite high fluorescence intensity,light stability and non-toxic Y₂O₃:Eu material(254 nm UV fluorescent material)and CDs material(365 nm UV fluorescent material)by simple physical mixing.Then morphology and fluorescent properties are studied.The main contents are as follows:1)Firstly,we synthesize Na YF₄:Er,Yb(Tm)/CDs composites by simple hydrothermal method,then carry out morphological characterization of Na YF₄:Yb,Er,CDs and Na YF₄:Yb,Er/CDs materials by SEM,TEM and HRTEM.The result presents the shape of Na YF₄:Yb,Er materials become uniform circle shape after composition from uniform hexagonal shape,and some nanodots are found in surface of Na YF₄:Yb,Er/CDs composites.In addition,the XPS and FTIR spectra of both pure up conversion and composites materials are measured.Compared pure Na YF₄:Yb,Er up conversion materials,the content of C,N and O element of composites obviously increases.And the absorption peaks of FTIR are consistent with that of pure CDs.It is confirmed that the composites are successfully prepared.Then the UV-vis absorption and fluorescent spectra are tested,and the composites can emit light under both 980 nm NIR and 365nm UV light excitation.Finally,the dual-mode fluorescent effect is achieved through screen printing technique.2)Firstly,we synthesize Y₂O₃:Eu nanorods and CDs nanodots materials by simple hydrothermal method.Then the morphology of both materials are measured by SEM,TEM and HRTEM,respectively,and the XRD of Y₂O₃:Eu is also tested.Additionally,the UV-vis absorption and fluorescent spectra of both materials are measured.According to the unique fluorescent property of both materials,36 types of composites are prepared by simple physical mixing.Then 36 types of fluorescent color blocks are printed by screen printing,and the fluorescent spectra of them are measured to study the relationship between fluorescent intensity and concentration.The result shows that with the increasing of concentration the intensity increases.Finally,different fluorescent patterns are printed by screen printing to achieve UV-switchable dual-mode anti-counterfeiting effect.This type of fluorescent material and technology can realize the need of low cost,easy operation and difficult copy and can be applied in the field of anti-counterfeiting on a large scale.