Upconversion Luminescence Temperature Characteristics Of Rare Earth Ion-doped Barium Strontium Titanate Based Materials

The energy level system of rare earth ions is extremely rich.Through optics,temperature and power control,it has a wide range of applications in imaging display,non-contact temperature measurement,bioluminescence labeling and anti-counterfeiting.Therefore,rare earth ions have become the research focus of the scientific community.Among them,the luminescence properties of rare earth ions have attracted much attention.The luminescent properties of rare earth ions are due to the occurrence of energy level transitions,which are divided into radiative transitions and non-radiative transitions,both of which are equally important.During the energy level transition,some ions transition from the ground state to the excited state,and then return to the ground state.In this process,energy is released and accompanied by the generation of photons,which is called radiative transition.Heat is generated which reduces the luminous intensity of rare earth ions.In recent years,optical materials doped with rare earth ions have the advantages of high precision,high sensitivity,and fast response time,so they have received great attention in the practical application of optical temperature sensing.The research contents of this paper are as follows:（1）Ba_0.60Sr_0.40TiO₃（BST:x%Er（x=1,2,4,6,8））powders doped with different concentrations（molar percentages）of rare earth ions Er³⁺were prepared by the sol-gel method and systematically tested under the excitation of a 980 nm laser,the temperature dependence of the upconversion luminescence of different BST:x%Er³⁺in the temperature range 303 K-543 K was tested systematically.Based on the fact that the rare-earth ion Er³⁺has a pair of thermally coupled energy levels ²H_11/2 and⁴S_3/2,a corresponding change in its green light emission intensity is observed with increasing temperature.By measuring the fluorescence intensity ratio（FIR）of the green emission peak of the rare-earth ion Er³⁺,it can be used as a probe to measure the ambient temperature at which Er³⁺is inserted.The sensitivity of BST:x%Er³⁺material increases and then decreases as the concentration of rare-earth ion Er³⁺increases,and the fluorescence temperature sensitivity is maximum when the Er³⁺concentration is 2%,and the maximum values of relative fluorescence temperature sensitivity and absolute fluorescence temperature sensitivity are 0.42%K^-1 and 1.54%K^-1,respectively.And compared with different sintering temperature on its sensitivity,the study shows that the sintering temperature has a small effect on the sensitivity,which is because although the sintering process,the surrounding crystal field changes,resulting in changes in luminescence intensity,but FIR technology is used to fit the intensity ratio of the luminescence peak,so the change in the luminescence peak ratio is not affected by changes in the surrounding crystal field,which further illustrates that FIR technology can accept the test of harsh environments.（2）The Er³⁺/Yb³⁺co-doped BST phosphors were synthesized by hydrothermal and solvothermal methods,respectively,and the upconversion luminescence properties and fluorescence temperature characteristics of the powders were compared under the two synthesis environments.Under the excitation of 980 nm nanolaser,²H_11/2→⁴I_15/2,⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 jumps were observed at 526 nm,548 nm and 655 nm,and the difference was found that the dominant luminescence peaks were different for the samples prepared in two different media environments,where the dominant luminescence peak with ethylene glycol as the solvent was a green The dominant luminescence peak of ethylene glycol as the solvent is green,while the dominant luminescence peak of water as the solvent is red.The relative sensitivity Sr of fluorescence temperature of BST:2%Er³⁺/16%Yb³⁺co-doped with ethylene glycol as solvent decreased with increasing temperature and reached the optimum value of 0.83%K^-1 at 303 K.The relative sensitivity Sr of BST:2%Er³⁺/16%Yb³⁺co-doped with water as solvent increased with increasing temperature and reached the maximum value of 0.46%K^-1 at 543 K.The results show clearly that the powders synthesized under two different media conditions present high sensitivity near room temperature and high temperature,respectively,and exhibit different luminescent colors,which have promising applications in the field of optical temperature sensing.（3）The introduction of BST oxides on the fluoride base modifies and modifies its luminescence,and modulates the luminescence by changing the environment of its crystal field.From the microscopic point of view,the doping of barium strontium titanate changes the microstructure of fluoride;the luminescence spectra under 980nm laser excitation show that the doping of barium strontium titanate oxide in fluoride substrate material can change the luminescence color of NaYF₄:Yb/Er nanoparticles from yellow to green by adjusting the amount of BST.