Up-conversion Luminescence And Temperature Sensing Properties Of Rare Earth Doped Vanadate

In rare earth doped materials,up-conversion,also known as Anti Stokes,is the process of absorbing low energy photons at long wavelengths and emitting high energy photons at short wavelengths.It has the advantages of high color purity,high absorption capacity,high conversion efficiency,fluorescence lifetimes from nanoseconds to milliseconds,stable properties,and various types of emission spectra.It has been used in infrared light detection,short-wave laser,optical temperature sensor,photovoltaic cell,bio-fluorescence labeling,medical diagnosis and so on.Vanadate has excellent luminescent properties,strong stability,and significant advantages in lighting,solid state lasers,and display host materials.Up-conversion Luminescence properties and temperature sensing properties of Na₃La（VO₄）₂ is reported rarely.In this thesis,Na₃La（VO₄）₂:Er³⁺/Yb³⁺/Zn²⁺,Na₃Lu（VO₄）₂:Er³⁺/Yb³⁺,and BaV₂O₆:Er³⁺/Yb³⁺/Zn²⁺have been prepared to investigate their up-conversion luminescence and temperature sensing properties including doping concentration,the spectra and pump dependence,energy transfer mechanism and temperature measurement based on fluorescence intensity ratio.The main work is as follows:（1）The series of Na₃La（VO₄）₂:x Er³⁺/y Yb³⁺samples were prepared.The emission spectra of the samples included stronger green light and weaker red light.The XRD patterns of the samples were compared with the standard XRD patterns.According to the valence state and ion radius,the doped rare earth ions replaced La³⁺in the Matrix.When the doping concentration of Er³⁺and Yb³⁺was changed,the emission spectra changed,the optimum doping concentration of Er³⁺and Yb³⁺is 0.04 and 0.15,respectively.The up-conversion luminescence of Na₃La（VO₄）₂:Er³⁺/Yb³⁺is a two-photon process.Based on the fluorescence intensity ratio technique,the temperature sensing function of the material is FIR=9.08×exp（-1055.34/T）,and the fitting degree is 99.97%.The absolute sensitivity of temperature measurement is 0.0425 K^-1 at 553 K and the relative sensitivity is 0.1040 K^-1 at 303 K.Considering to the analysis of valence state and ion radius,Zn²⁺occupies the lattice position of La³⁺after doping Zn²⁺in Na₃La（VO₄）₂.When the concentration of Zn²⁺was 0.12,the luminescence intensity are obviously enhanced,and the green emission can be enhanced by 1.33 times.The temperature sensing function of the material is FIR=6.31×exp（-987.61/T）and the fitted degree of Zn²⁺doped samples were higher than 99.9%.For Na₃La（VO₄）₂:Er³⁺/Yb³⁺/Zn²⁺The absolute sensitivity of temperature measurement is 0.0220 K^-1 at 493 K and the relative sensitivity is 0.0640 K^-1at 313 K,which is lower than samples without Zn²⁺.（2）The series of Na₃Lu（VO₄）₂:x Er³⁺/y Yb³⁺samples were prepared.The emission spectra of the samples included stronger green light and weaker red light.The valence state of Lu³⁺is equal to that of Er³⁺,and the ionic radius of Lu³⁺is smaller than that of Er³⁺.Therefore,rare earth ions replace Lu³⁺in the Matrix.By changing the doping concentration of Er³⁺and Yb³⁺.The optimum doping concentration of Er³⁺and Yb³⁺were0.02 and 0.30,respectively.According to the dependence of pump power and emission spectra,the up-conversion luminescence of Na₃Lu（VO₄）₂:Er³⁺/Yb³⁺is a two-photon process.The results show that the temperature sensing function of the material is FIR=14.10×exp（-733.24/T）,and the fitting degree is 99.8%.When the temperature is313 k,the absolute sensitivity reaches a maximum of 0.0152 K^-1.The up-conversion luminescence of Na₃La_zLu_1-z（VO₄）₂:0.02Er³⁺,0.1Yb³⁺（z=0,0.2,0.4,0.6,0.8,1.0）were a two-photon process.（3）The series of BaV₂O₆:x Er³⁺/y Yb³⁺samples were prepared.Considerding the valence state and ion radius analysis,the doped rare earth ions replaced Ba²⁺in the Matrix.By changing the doping concentration of Er³⁺and Yb³⁺,the optimum doping concentration of Er³⁺and Yb³⁺was 0.03 and 0.30 respectively.According to the dependence emission spectrum data on the pump power,the slope n value is1.13,1.40,1.28 with the error 0.03,0.05,0.04.So the up-conversion luminescence of rare earth doped BaV₂O₆ material is a two-photon process.Based on the fluorescence intensity ratio,the temperature sensing function of the sample is FIR=31.62×exp（-1240.27/T）,and the maximum absolute sensitivity is 0.0200 K^-1.Zn²⁺codoping in BaV₂O₆:Er³⁺/Yb³⁺is also studied.When the concentration of Zn²⁺is 0.04,the luminescence intensity of the sample increases remarkably.The green emission intensity increases by 6 times and the red emission intensity increases by 2 times.The green emission intensity is still much higher than the red emission intensity.The reason is that the radius of Zn²⁺is smaller than that of Ba²⁺,so the local crystal field will change when Zn²⁺is added.Moreover,the addition of Zn²⁺ions can adjust the symmetry of the crystal field of the luminescent center to break the 4f electric dipole parity forbidden and strengthen the electric dipole transition and enhance the emission intensity.The temperature sensing function of the material is FIR=6.85×exp（-741.26/T）and the fitted degree of Zn²⁺doped samples are higher than 99.9%.For BaV₂O₆:Er³⁺/Yb³⁺/Zn²⁺the absolute sensitivity of temperature measurement is 0.0360 K^-1 at 473 K and the relative sensitivity is 0.0520 K^-1 at 313 K.