The Effect Of PH Value Of Reaction Solution On Upconversion Luminescence Properties Of NaYF₄:Yb³⁺/Er³⁺/Ca²⁺and NaYbF₄:Er³⁺

Since the end of the last century,anti-Stokes fluorescent materials have been widely used.Rare earth ion-doped upconversion（UC）luminescent materials are characterised by their stable photochemistry,low toxicity and long fluorescence lifetime.They have broad applications in bio-imaging,multi-dimensional displays,optical anti-counterfeiting,optical temperature sensors and solar cells.However,the luminescent properties of rare earth upconversion luminescent materials are easily affected by external factors such as p H,citrate ion(Cit^3-)content,Na F content,reaction time and temperature during the synthesis process.This paper focuses on the effect of p H of the reaction solution on the luminescence properties of Er³⁺ions,the details are as follows:（1）A series of Na YF₄:20 mol%Yb³⁺,2 mol%Er³⁺,x mol%Ca²⁺（x=0,15,20,25,30,35,40,45）microcrystals prepared by hydrothermal method at different p H value of the reaction solution.Through the analysis of scanning electron microscope,it is found that with the increase of the doping concentration of Ca²⁺ions,the quantity of surface defects on Na YF₄ crystals gradually decreases,and the longitudinal growth of the crystal finally forms tapers at both ends of the crystal.Comparing the upconversion spectra,it is found that the optical doping concentration of Ca²⁺is 30 mol%for Na YF₄:Yb³⁺/Er³⁺/x Ca²⁺microcrystal synthesized at p H=3 when the luminescence intensity of Er³⁺ion is maximum,while the optical doping concentration of Ca²⁺improve to 40 mol%（p H=10）.（2）Na Yb F₄:x mol%Er³⁺（x=0.1,0.5,1.0,2.0,3.0）microcrystals synthesized by hydrothermal method at p H=10 and F/Ln=6.The effects of Er³⁺ion doping concentration and excitation power on the red and green emission intensity of Er³⁺ions are mainly discussed.With the increase of Er³⁺ions concentration,the luminescence intensity and the intensity ratio of red to green of Er³⁺ions first increase and then decline.In addition,changing the excitation power can further improve the Er³⁺ions luminescence intensity and optimize the intensity ratio of red to green.