Study On The Preparation,Luminescent Mechanism And Multifunctional Application Of Rare Earth Doped Multi-modal Composite Materials

In recent years,data security has become a global issue facing various industries.In order to improve the security of information coding,more and more attention has been paid to the development of an anti-counterfeiting technology with simple preparation process,low cost and environment-friendly.Traditional single-mode fluorescence methods such as watermarks and bar codes are easily copied and pirated,so the accuracy is not high.Organic phosphorescent materials are not suitable for long-term storage of information due to their poor thermal and light stability.Multi-color anti-counterfeiting patterns have unique advantages,such as spatially resolvable colors at characteristic excitation wavelengths,multi-level data encryption and difficult to copy.In addition,non-contact fluorescence temperature measurement has broad application prospects in the field of temperature measurement and control.If we can synthesize a multifunctional material that integrates temperature measurement and anti-counterfeiting,it will greatly facilitate our lives.The selection and design of multifunctional materials depend on the characteristics of good physical and chemical properties,wide sources,environmental friendliness,and simple production processes.We have noticed that inorganic rare earth doped nano-luminescent materials have a lot of advantages such as rich energy level structure,wide emission wavelength,and long energy level life.In particular,rare earth doped oxides have the advantages of good stability and simple synthesis.Carbon dots,as a new type of luminescent nanomaterial,have the advantages of low toxicity,high luminous efficiency,strong biocompatibility,etc.,and have potential application value in the field of imaging and sensing.How to composite materials in a simple way,design the location of the luminous center and the way of energy transfer are the focus of our research.Most of the research focuses on the design and optimization of fluoride core-shell structure to achieve the purpose of multi-modal light emission.Considering the simplicity and feasibility of synthesis and large-scale preparation,we choose stable and inexpensive oxides as the matrix to design the composite materials in this paper.In this paper,the preparation of rare earth-doped YVO₄/YPO₄ oxide nano-composites and YVO₄/carbon quantum dots?CDs?composites are studied.The energy transfer mechanism,the effect on temperature and its application in the field of anti-counterfeiting are discussed.The specific discussions and results are as follows:?1?YVO₄:Er³⁺,Yb³⁺@YPO₄:Eu³⁺core-shell nanoparticles were successfully synthesized by a simple hydrothermal method,and the growth between oxides was achieved.The optimal pH value of YVO₄ core and the optimal doping concentration of Er³⁺and Yb³⁺rare earth ions were found through experiments.When the YPO₄:Eu³⁺shell grows further,not only the luminescence of Er³⁺in the core is enhanced,but also VO₄^3-in the core can efficiently transfer energy to Eu³⁺in the shell.Based on Er³⁺high-intensity up-conversion luminescence under 980 nm excitation and Eu³⁺bright down-conversion luminescence under 320 nm excitation,the core-shell structure is conducive to achieving the purpose of multi-color light emission under variable power?fixed xenon lamp current is unchanged,changing the power density of the 980 nm laser?.In addition,the design of this core-shell structure can achieve the purpose of dual-mode temperature measurement,it is a multifunctional nano-particle that integrates security and temperature measurement.?2?CDs are currently the most popular luminescent materials due to their excellent light emitting characteristics,high stability,good biocompatibility,and environmental friendliness.Considering the simplicity of the synthesis,a stable blue light carbon dot with green afterglow?The afterglow time reaches 5s?was successfully prepared by high temperature liquid phase cracking synthesis method.At the same time,YVO₄:Eu³⁺nanoparticles were synthesized by hydrothermal method.The morphology,crystal phase,absorption spectrum,excitation and emission spectra of the samples were characterized respectively.Considering the differences in the excitation spectra of the two materials,a binary temperature probe was prepared by physically mixing the two materials at a ratio of 1:1 and a cyclic,high-sensitivity temperature measurement was achieved using a non-thermally coupled form.The mixture was further dispersed in a polyacrylic acid?PAA?cross-linking agent to prepare an anti-counterfeit ink.The color-adjustable luminescence under UV lamps?254 nm and 365 nm?was achieved successfully by this composite method.The ultra-long afterglow?10 s?green phosphorescence can be seen by turning off the 365 nm light source,which realizes the advanced anti-counterfeit mode of four-modal imaging for easy operation.In addition,experiments show that the luminescence of CDs has good stability,and the anti-counterfeiting pattern remains stable after being stored for a long time.Therefore,this composite material can stably preserve the anti-counterfeiting information for a long time.