Fabrication And Optical Properties Research Of Anti-Counterfeit Fabrics Based On Rare Earth Fluorescent Materials

The world economy is rapidly evolving and the economic market is ever-expanding,leading to the widespread presence of counterfeit and substandard products.Hence,the development of highly reliable anti-counterfeiting measures is of paramount importance.Infrared up-conversion phosphors have attracted widespread attention for their unique infrared light excitation-visible light emission characteristics.Although infrared up-conversion luminescent materials have always had good application prospects in the field of anti-counterfeiting,the current stage of up-conversion anti-counterfeiting applications are more embodied in anti-counterfeiting inks and other technologies,and research in the field of up-conversion fluorescent anti-counterfeiting fibers still faces many challenges:（1）Luminescent powder requires a complex and challenging large-scale chemical procedure to prepare it.Anti-counterfeiting ink with powder often utilizes hydrothermal synthesis method,pyrolytic method,etc.to fulfill the particle size criteria,but these processes have low yield and are complicated,so that it is challenging to achieve the continuous fiber production.（2）The luminous intensity of luminous powder varies greatly,and the colour is monotonous.Even on the current stage,the synthesis of green,blue,and red up-conversion luminescent powder is more mature,but green and blue luminescent powders mainly aim at the wavelength excitation of 980 nm,red luminescent powder is more for the wavelength excitation of 808 nm.Plus,their brightness varies irregularly,which is hard to meet the colour requirements.（3）The wavelength of infrared excitation is monotonous.At present,most of the infrared up-conversion luminescent materials are excited at fixed wavelength,such as 808 nm,980 nm,etc.,which can only be excited with a laser of fixed wavelength.（4）The fluorescent anti-counterfeiting fibers are difficult to spin continuously.Majority of the fluorescent fibers are mainly fabricated via electrospinning,which is discontinuous.Melt spinning has high requirements on the particle size and dispersion of up-conversion phosphor,the traditional synthesis method is difficult to meet the requirements of phosphor particle size.Based on the issues mentioned above,it is challenging to develop the fluorescent anti-counterfeiting fibers that have multiple anti-counterfeiting,high light intensity,and highly environmental stability.This thesis proposed that using high-temperature co-precipitation to synthesize lanthanide ion-doped NaYF₄up-conversion phosphors powders,and further with the improvement on the large-scale preparation of up-conversion phosphors powders and the regulation of melt spinning process,developing high-quality multicolor and multifunctional fluorescent anti-counterfeiting fibers.The works that have been carried out are mainly comprised of four aspects as follows:（1）The traditional synthesis process was improved to prepare highly efficient green up-conversion luminescent powder（NaYF₄:0.2Yb,x Er）,and investigate the variation of the luminescence intensity of the powder under different Er doping concentrations.The blue up-conversion powder（NaYF₄:Yb,Tm）and the red up-conversion powder（Y₂O₃:Yb,Er）were prepared,and their luminescence performances with excitation light of 980 nm were analyzed.（2）The prepared tricolor phosphor with required particle size was used for color mixing first,and the mechanism on color adjustment was explored.The colorful letters and QR codes on the fabrics were obtained via screen-printing the up-conversion luminescent powders,and the QR codes could be read by mobilphone.（3）By pelletizing the multicolor up-conversion luminescent powder and UV luminescent powder mixed with PA6,the multicolor and dual-wavelength fluorescent anti-counterfeit fibers with 10 wt.%luminescent powder were prepared by melt spinning.The luminescent effect and the resistance performances on temperature,acid,alkali and ultraviolet of fibers were studied.（4）The up-conversion phosphor with broadband band Sr S:Eu,Sm was prepared,which covering the range of infrared cameras.It can be luminous under the excitation of infrared cameras,so that achieving the function of anti-peeping,then,it is printed with NaYF₄:Yb,Er to obtain multiple anti-counterfeiting and anti-piracy fluorescent security fabrics.