Preparation,Photoluminescence Mechanisms Of NaYF₄ Upconversion Fluorescence Materials For Printing Anti-Counterfeiting Application

Data storage and anti-counterfeiting performance have become hot topics in the background of cloud computing and big data.Rare earth doped upconversion materials based on anti-Stocks mechanism have opened new avenues in the fields of display and anti-counterfeiting application,because of its unique fluorescence emissions under near-infrared（NIR）excitation,long fluorescence lifetime,high resistance to photobleaching and photoblinking.However,there are some limitations in the existing optical anti-counterfeiting devices based on upconversion materials,including complex preparation process,low concealment,failure to realize self-healing mechanical damage.Hence,in order to solve these problems,the single-mode/dual-mode NaYF₄upconversion materials are designed in this work,and the luminescence mechanism are deeply investigated.By combining with disulfide crosslinked polyurethane self-healing elastomers,the fluorescence-responsive self-healing elastomers are fabricated and studied.Moreover,the low-cost of screen-printing technology,spin-coating,stamping technology are used for patterning upconversion fluorescent inks and achieving anti-counterfeiting application.Specific works have been carried out in the following areas.1.Synthesis,photoluminescence mechanism of single-mode NaYF₄ upconversion materials for transparent anti-counterfeiting labels application.Firstly,single-mode NaYF₄ upconversion materials are prepared through a facile solvothermal method,which can exhibit tunable red,green and blue upconversion emissions by doping different lanthanide ions Er³⁺/Tm³⁺,Yb³⁺/Er³⁺and Yb³⁺/Tm³⁺in NaYF₄ hosts,respectively.The red and green upconversion process are two-photon process,while the blue upconversion process is a three-photon process.Secondly,The NaYF₄upconversion particles are used as pigments and then mixed with polyacrylic acid and ethanol solution to formulate fluorescence inks.The optimal fluorescence inks are deposited on flexible polyethylene terephthalate（PET）substrate to fabricate transparent security labels,which possess higher transmittance,stronger upconversion fluorescence intensity and good photostability.Finally,a series of transparent patterns are developed by simple and low-cost techniques including spin-coating,stamping and screen printing.There is no information here that is recognized by the naked eye under natural light,but can be performed multicolor patterns under 980 nm excitation.The transparent patterns based on single-mode NaYF₄ upconversion materials can be used as the die-cutting package anti-counterfeiting labels,showing low-cost,easy-manufactured and versatile merits and underlying the practical application in security field.2.Synthesis,photoluminescence mechanism of dual-mode NaYF₄ upconversion materials for anti-counterfeiting application.Firstly,three kinds of core-shell NaYF₄upconversion materials are prepared through thermal decomposition,which exhibit differential upconversion emissions under 808 nm and 980 nm excitation.Secondly,by additive mixing the suspended solution of 808 nm emitted red-green-blue upconversion materials,the emissions can be precisely regulated.The upconversion emissions produced by 808 nm excitation realize a wider color gamut than the s RGB and printing CMY color space model.Finally,China zodiac patterns and complex images are printed through screen-printing technology.Under 808 nm excitation,they present polychromatic sequential toning visualization fluorescent patterns,while another succession of gradually changed versatile patterns are appeared under 980 nm excitation.As a proof of concept,a transparent polyvinyl chloride（PVC）self-adhesive label with patterns is attached to the bottle of wine package,which can achieve dual-model,full-color,and high-level fluorescent anti-counterfeiting for replacing the traditional single-mode security encoding.3.Fluorescence-responsive,self-healing elastomers of single-mode NaYF₄upconversion materials for Anti-counterfeiting application.Firstly,the as-obtained single-mode NaYF₄ upconversion materials are introduced into disulfide crosslinked polyurethane（DSPU）self-healing elastomers to prepare novel upconversion fluorescence-responsive DSPU（DSPU-UCCs）self-healing elastomers.The DSPU-UCCs films can present red,green,blue emissions as well as good mechanical properties（1037%stretchability）and self-healing ability（97.8%efficiency）.Surface scratch self-healing and rheological testing studies show that the disulfide bonds offer more efficient metathesis efficiency at higher temperatures.The healing time of surface scratch is 3 min at 90°C.In addition,DSPU elastomers can be reprocessed and reshaped,demonstrating recyclability and sustainable utility.Finally,Screen-printing technology is used for fabricating versatile patterns,which can replace the traditional patterning methods of relying on high cost mould or masks.Self-healing scratch electronic patterns and scratch electronic patterns indicate that DSPU-UCCs elastomers have wide application prospect in self-healing sensors,self-healing anti-counterfeiting labels fields.4.Fluorescence-responsive,transparent,self-healing elastomers based on dual-mode NaYF₄ upconversion materials for anti-counterfeiting application.Firstly,the transparent polyurethane（PU）self-healing elastomers with excellent mechanical properties are designed by regulating the percentage of hard segment and the molecular weight of soft segment polytetramethylene ether glycol（PTMEG）.The transparent PU elastomer possess high transparency（>92%）,superior toughness(87.7 MJ m^-3)and tensile strength（19.94 MPa）,which is 27.67 times better comparing with DSPU elastomers.The investigation of mechanical recovery performance verify that PU elastomer also has good restorability,which can recover large strain of 500%after relaxation at room temperature for 2 hours.Secondly,carbon quantum dots（CDs）are introduced into transparent PU self-healing elastomers to prepare fluorescence-responsive self-healing elastomers（PU-CDs）.PU-CDs can achieve blue fluorescence emission under UV excitation,and good mechanical self-healing properties（self-healing efficiency up to 95.57%）.Finally,the formulated dual-mode fluorescence inks based on core-shell structure NaYF₄ upconversion materials are screen-printed versatile patterns,in which the fluorescence intensity of core-shell structure upconversion materials is 2.5 times higher than that of single-mode particles.Under natural light,the patterns cannot be identified.Interestingly,the hidden patterns can perform multi-color emissions under 980 nm and 808 nm excitation,while blue fluorescence can be displayed under UV excitation.The researches of NaYF₄ upconversion materials and transparent PU self-healing elastomers open new avenues for the development of new self-healing optical materials and anti-counterfeiting device.