Research On Upconversion/Downconversion Luminescence And Temperature Measurement Characteristics Of Rare Earth Doped Inorganic Materials

Non-contact optical thermometry,based on the rare earth doped inorganic materials,has received increasing attentions nowadays.It has a fast response,strong anti-interference and many other advantages.However,there are some weak points such as low sensitivity and insufficient fluorescence intensity Hinder its application.Therefore,in this work,the temperature sensitivity of Er³⁺is improved by selecting different TCLs,and the fluorescence intensity of Er³⁺is greatly enhanced through the doping of alkali metal ions.In addition,the host material Eu³⁺doped under down-conversion conditions is studied.The temperature measurement in multiple modes was studied,and higher relative sensitivity has been obtained.Simple high-temperature solid-state reaction was used to prepare Er³⁺/Yb³⁺-doped GdVO₄ phosphors.The effect of Er³⁺and Yb³⁺doping concentration on Er³⁺upconversion luminescence was investigated under 980 nm laser pumping.When the doping concentration of Er³⁺is 2 mol%,and the concentration of Yb³⁺is 10 mol%,the upconversion luminescence of Er³⁺is the best.Through the research of the luminescence characteristics of Er³⁺under different excitation powers,the experiment found that the population of Er³⁺⁴F_7/2,²H_11/2,and ⁴S_3/2 energy states are all two-photon processes.The relationship between the fluorescence intensity of each energy state of Er³⁺and the temperature was studied.The experiment found that the fluorescence intensity of the⁴F_7/2 energy state increases with the increase of temperature;the fluorescence intensity of the ²H_11/2 energy first increases and then decreases with the increase of temperature;the fluorescence intensity of the ⁴S_3/2 energy state decreases monotonously with the increase of temperature.We use the fluorescence intensity ratio of the ⁴F_7/2-⁴S_3/2 TCLs to achieve high-sensitivity temperature measurement.The maximum relative sensitivity obtained in the experiment is 2.3%K^-1,which is much greater than the traditional²H_11/2-⁴S_3/2 TCLs(maximum value is 0.9%K-1).In order to increase the luminous intensity of Er³⁺further,the host material is doped with alkali metal ions Li⁺,Na⁺,K⁺.The results indicate that optimal doped concentration of Li⁺,Na⁺,K⁺are 5 mol%,7mol%and 9 mol%respectively.The fluorescence intensity of Er³⁺enhances 4 times,6times and 3.5 times after alkali ions Li⁺,Na⁺,K⁺are added.Through the study of the fluorescence decay curve,we found that doping with alkali metal ions can reduce the non-radiative relaxation of rare earth ions,which enhances up-conversion luminescence and signal-to-noise ratio,and enhances the reliability of the temperature measurement.We have studied the down-conversion luminescence of Er³⁺.We did not find ⁴F_7/2 state luminescence due to the different pumping mechanism under down-conversion conditions.We studied the temperature measurement characteristics of Er³⁺under down-conversion conditions.The experiment found that the pumping mechanism of the 380nm laser is to directly excite Er³⁺,while the 330 nm laser first excites VO₄^3-,and then VO₄^3-transfers energy to Er3+.The heat effect caused by non-radiative relaxation will be generated during the transfer process,so the temperature measurement sensitivity when excited at 380 nm is higher than 330 nm.It can be concluded from the experiment that selecting the appropriate wavelength in the down-conversion temperature measurement process is also crucial for achieving high-sensitivity temperature measurement.The GdVO₄/YAG/YAM:Eu³⁺phosphors were synthesized via the simple high-temperature solid-state reaction,and the down-conversion luminescence characteristics of Eu³⁺in three different matrix materials and the law of fluorescence change with temperature was researched.The J-O parameters?₂ of Eu³⁺in GdVO₄,YAG,and YAM are calculated to be 5.31×10^-20 cm²,4.12×10^-20 cm²,2.69×10^-20 cm² respectively.It can be seen from the calculation results that GdVO₄ has the weakest lattice symmetry,and YAM has the strongest symmetry.The radiation transition rates of Eu³⁺in different materials are calculated.The radiation transition rates A₂ of Eu³⁺in GdVO₄,YAG,and YAM are 870.2s^-1,483.9 s^-1,and 316.4 s^-1 respectively.We can know from experiment that GdVO₄:Eu³⁺has the weakest symmetry and the strongest luminescence,so it is more suitable for temperature measurement.Measuring temperature via the fluorescence intensity ratio of Eu³⁺.The maximum S_rof different phosphors are 0.627%K^-1,0.429%K^-1and 0.458%K^-1respectively,so the Temperature measurement precision of these phosphors is GdVO₄>YAM>YAM.The fluorescence decay time was researched,the maximum time of these materials is 0.19 ms,3.78 ms and 1.34 ms when temperature is 573 K,323 k and 323 K separately.The relationship between displacement of the peak position of the Eu³⁺excitation spectrum as well as the half-height width of the spectrum and the temperature are studied.The experimental results show that the movement distance of the center peak position of the Eu³⁺and the half-width of the spectrum have linear relationship with temperature.The temperature measurement of Eu³⁺line displacement has high sensitivity,the maximum relative sensitivity at room temperature is 5.9%K^-1.which achieve high-sensitivity temperature measurement.