Preparation And Application Of Near-infrared Rare Earth Doped Upconversion Luminescent Materials

With the rapid development of science and technology in recent years,more and more researchers have begun to pay attention to the preparation and properties of upconversion luminescent materials.Its unique anti-Stokes shift luminescence mechanism makes it have unique advantages:wide emission spectral bandwidth,stable properties,stable luminescence and infrared excitation,and it also has the advantages of low biological toxicity and weak fluorescence background.It is often used in anti-counterfeiting identification,biological detection analysis and medical treatment.In this paper,Tm³⁺,Yb³⁺double-doped NaErF4 was prepared by solvothermal method using NaErF₄ and LiLu(MoO₄)₂as host materials,and then wrapped with Si O₂ to improve the luminescence properties.Er³⁺,Tm³⁺,Yb³⁺tri-doped LiLu(MoO₄)₂ was prepared by using LiLu(MoO₄)₂ as host material by high temperature solid-phase method,which improved its low luminous efficiency due to low-concentration doping caused by concentration quenching theory.,and its luminescence mechanism,energy transfer and external morphology were studied and the following results were obtained:(1)The stable and efficient preparation system of NaErF₄ doped Tm³⁺,Yb³⁺up-conversion luminescent material was realized,and its luminescence principle was expounded.Using erbium oxide,hydrochloric acid,sodium hydroxide and ammonium fluoride as raw materials,1-octadecene as the reaction matrix and complexing with oleic acid to prepare NaErF₄.Its chemical properties are stable and the particle size is uniform.When the doping ratio of Tm³⁺is0.5%,its red light intensity is the strongest and the ratio of red light to green light intensity increases from 0.7 of pure NaErF₄ to24.4.Continue to increase the doping ratio to find that the red-green ratio decreases,and the concentration quenching occurs to reduce the red light intensity.Obviously,compared with pure NaErF₄,Tm³⁺,Yb³⁺double-doped NaErF₄ not only has a qualitative improvement in luminous intensity,but also can adjust the ratio of red light to green light intensity by changing its doping ratio,so that it can be used in anti-counterfeiting detection.And other fields have broader application prospects.(2)The use of silica to modify the external morphology enhances the luminous efficiency and service life of the Tm³⁺,Yb³⁺doped NaErF₄ up-conversion light-emitting system,making it more practical.Taking polyvinylpyrrolidone dissolved in n-amyl alcohol as the host material,adding ammonia water and ethyl orthosilicate as the reaction material,in the acidic environment provided by sodium citrate,a layer of Si O₂ is wrapped around the NaErF₄:Tm³⁺/Yb³⁺rare earth luminescent material,so that the luminescence of NaErF₄:Tm³⁺/Yb³⁺rare earth materials is further enhanced.Its red light intensity is enhanced 3.39 times.(3)The Er³⁺,Tm³⁺,Yb³⁺triple-doped system with LiLu(MoO₄)₂ as the host material was studied for the fluorescence intensity and lifetime of thermally coupled energy levels,thus realizing more accurate temperature sensing applications.LiLu(MoO₄)₂solid powder materials doped with Er³⁺,Tm³⁺,Yb³⁺were synthesized by high temperature solid-state method,and their external morphology was characterized by XRD.A 980nm infrared light generator was used to excite LiLu(MoO₄)₂:0.5%Er³⁺,1%Tm³⁺,7%Yb³⁺powder samples,the upconversion emission spectra were measured at the temperature range from 303K to 563K,and the thermal coupling energy of Er³⁺was analyzed The change of the fluorescence intensity ratio of the grades(~2H_11/2,~4S_3/2)with the change of temperature.The thermal quenching effect was studied by measuring different fluorescence intensity ratios by changing the test temperature.When the temperature is 303K,its thermal coupling energy level peak ratio is 0.95×10-3K^-1,and when it is heated to 563K,its thermal coupling energy level peak ratio becomes 4.47×10^-3K^-1,which is then sorted by linear fitting.The function relationship of peak ratio with temperature is obtained,and accurate fluorescence temperature sensing is realized.This characteristic makes it have important applications in the fields of fluorescent anti-counterfeiting,non-contact fluorescent temperature measurement,and biomedical inspection.