Research On Preparation And Printing Performance Of ZnO Quantum Dots Fluorescent Anti-counterfeiting Paper

With the rapid growth of the global economy,counterfeit and inferior goods emerge one after another.Research o n advanced anti-counterfeiting technology and material has become a hot spot worldwide.Fluorescent anti-counterfeiting technology is one of the most widely used high-level anti-counterfeiting technologies,which displays the fluorescent color different fr om the natural light under specific illumination conditions to realize the identification of the true and false.Metal oxide nanoparticles have good optical properties and have huge application potential in the field of anti-counterfeiting.Among them,zin c oxide quantum dots have excellent properties such as long life,narrow emission band,stable dispersion,good photosensitivity and environmental protection.They can replace traditional rare earth phosphors for anti-counterfeiting printing,which is green and environmentally friendly and meets the needs of sustainable development.In this paper,zinc acetate was used as the precursor,and KOH was used as the alkali source to prepare zinc oxide quantum dots with an average particle size of5.64 nm.It was observed that the ZnO quantum dots were regular spherical particles of good water solubility under transmission electron microscope.Under the excitation of 365 nm ultraviolet light,ZnO quantum dots emit ted visible light with a wavelength of 554 nm,namel y bright yellow fluorescence.The ZnO quantum dots were dissolved in deionized water and coated on the surface of paper by ultrasonic method to obtain photoluminescent paper.The photoluminescent paper was the same as ordinary paper under sunlight,but it could emit bright yellow light under ultraviolet light.The photoluminescence intensity of ultrasonic coated paper increased with the increase of the loading of ZnO quantum dots on its surface.The loading of ZnO quantum dots increase d as the concentration of the ultrasonic solution increased.This study found that when the concentration of ultrasonic solution was 1 mol·L^-1,the loading of ZnO quantum dots on the surface of ultrasonic coated paper increased to the maximum,and the photoluminescence intensit y also reached the maximum.Ultrasonic coated paper still retain ed high photoluminescence efficiency after 60 hours of continuous irradiation with ultraviolet lig ht,which means that the paper had excellent light stability.However,after the second ultrasonic cleaning,the loading of ZnO quantum dots and the photoluminescence efficiency of the ultrasonic coated paper decreased significantly,indicating that the coated paper could be recycled after ultrasonic cleaning,which was consistent with the sustainable development concept of resource recycling.In application,graphics could be printed on the ultrasonic coated paper.Under natural light,the graphics appeared the color of ink.While under ultraviolet light,the non-graphics part of the printed product appeared bright yellow.So,the authenticity could be verified by a simple ultraviolet lamp.Acetic acid was used as ink to write on the u ltrasonic coated paper.There was no change in the paper under natural light.However,bright yellow fluorescence of the graphics printed by acetic acid was quenched under ultraviolet light.The quenching traces left by acetic acid on the ultrasonic coated paper could not be copied,which could effectively prevent the copy of pictures and texts.Due to the different hiding power of different dot percentage inks on paper,the non-solid color block on the coated paper showed a completely different color effect under ultraviolet light than that under daylight.Color blocks with different percentages of dots were formed to a chieve the purpose of anti-counterfeiting.As human could hardly to distinguish the extremely small color difference,this paper combined the characteristic of human vision with the printing dots to hidden markers on printed matter,which realized the anti-counterfeiting application that could be clearly visible only under ultraviolet light.Zinc oxide quantum dot coated paper had excellent photoluminescen t properties.They could show fluorescent effect by simple ultraviolet light irradiation,which were easy to identify authenticity and low manufacturing cost.Besides,these paper were environmentally friendly and had the properties of antibacterial and anti-aging.Applying the ultrasonic coated paper in the field of packaging and printing anti-counterfeiting is of great significance to develop advanced anti-counterfeiting technology which is convenient to identify,high degree of anti-counterfeiting and environmental protection.