Preparation Of Rare Earth Fluorides For Strong Upconversion Red Light Emission And Anti-counterfeiting Applications

Lanthanide doped upconversion luminous materials are helpful and vital for illumination,detection,anti-counterfeiting,and optical processing sensors due to their low toxicity,extended luminescent lifespan,and strong resistance to photobleaching.Our study is focused on the precise regulation of upconversion luminescence emission,with the problem being upconversion red light regulation.Current research on red upconversion luminescence is mostly focused on the conversion from green light,although its overall upconversion efficiency is modest.This thesis is divided into two parts that address the current issue of low up conversion red light efficiency:（1）The β-NaLuF₄:Er³⁺,Tm³⁺micron crystal precursors were produced using a simple hydrothermal approach,and their red upconversion luminescence was considerably increased by the synergistic impact of ion exchange and Tm³⁺doping up to75 times.XRD,Eu³⁺probe,ICP,and other testing methods revealed that the OH defects inside the lattice of the ion-exchanged sample were successfully removed,enhancing the capture and use of excitation energy and attaining a better upconversion efficiency.Tm³⁺doping as the energy capture center can enhance not only red emission but also excitation energy loss.The ion-exchangedβ-NaLuF₄:Er³⁺,Tm³⁺micron crystals display greater red upconversion emission thanβ-Na YF₄ andβ-Na Gd F₄.The fingerprint pictures with red upconversion emission were successfully taken in dark field environment by designing a simple mechanical device,and the color of the fingerprint pictures has extremely strong power stability,which will be suitable for more application scenarios while using,providing a reference for upconversion anti-counterfeiting.（2）Using one-step hydrothermal method,β-NaLuF₄:Er³⁺,Tm³⁺microcrystals were prepared by increasing the precursor concentration,and the red upconversion luminous efficiency could also be significantly improved.Although the ion exchange method can obtain efficient red upconversion luminescence,its experimental process requires a two-step hydrothermal method,and the experimental time is long.The one-step hydrothermal method by increasing the concentration of the precursor is more convenient.At the same time,XRD,Eu³⁺probe,ICP and other testing methods found that increasing the precursor concentration can effectively eliminate the OH^-defects in the lattice,thereby improving the red up-conversion efficiency.In addition,doping Er³⁺and Tm³⁺is beneficial to increase the emission intensity of up-conversion red light.The increase of Er³⁺concentration shortens the distance between ions and improves the energy transfer between ions.Doping Tm³⁺can prevent long-distance energy migration and maximize the luminescence quenching effect is reduced,and the red upconversion luminescence is enhanced.This high-concentration method for preparingβ-NaLuF₄:Er³⁺,Tm³⁺microcrystalline can not only improve its luminous efficiency,but also achieve a significant increase in its yield,which provides experimental basis and theoretical guidance for industrial production.