Design,Preparation And Optical Properties Of Rare-Earth Doped Fluorescent Temperature Sensitive Materials

Temperature is a basic thermodynamic parameter.Its measurement and control play a very important role in daily life,chemistry,medicine,agriculture and other fields.Temperature sensors are made according to a variety of different measurement principles.Glass thermometers,thermocouple thermometers and gas thermometers are some common thermometers.However,these thermometers need to make full and direct contact with the object being measured.Under some complicated and extreme conditions,such as in a corrosive environment or when measuring objects with irregular surfaces,these thermometers will show their inherent defect.Therefore,fluorescent temperature-sensitive materials using optical thermometry that can solve the above problems have received widespread attention.Many fluorescent materials?eg: quantum dots,metal-organic frame material?can be used for temperature measurement,and rare earth ion-doped fluorescent materials have become popular materials due to their rich emission spectrum and other advantages.However,there are still some problems in the stability,sensitivity and fluorescence temperature sensitive mechanism of rare earth ion-doped fluorescent temperature sensitive materials.Thence,this thesis researches three parts to solve these problems.The following are the work content and results of the three aspects of this article:Firstly,the temperature sensing characteristics of Er³⁺-doped Li₃Y?VO₄?₂ fluorescent materials based on the thermal coupling level fluorescence intensity ratio temperature measurement strategy has been studied in Chapter 3.A series of samples with different concentrations of Er³⁺-doped Li₃Y?VO₄?₂ were successfully synthesized by high temperature solid phase method.In these samples,VO₄^3-effectively transfers energy to Er³⁺ ions,which excites their thermal coupling energy levels,resulting in ²H11/2 ?⁴I15/2 and ⁴S3/2 ?⁴I15/2 radiative transitions of Er³⁺.When the doping concentration of Er³⁺ is increased from 2% to 10%,the energy transfer efficiency of VO₄^3-to Er³⁺ is increased from 44.5% to 55.2%.Using the thermal coupling level fluorescence intensity ratio temperature measurement method,the emission spectrum of the sample in the temperature range of 298-573 K was detected.The relationship between the fluorescence intensity ratio at 524 nm and 552 nm and the temperature was well fitted with an exponential function,and the maximum relative sensitivity was 0.93% K^-1@298 K.Thermal cycling tests were performed at three temperature points: 303 K,438 K,and 573 K.The results showed excellent repeatability of the material.It shows that Li₃Y_1-x?VO₄?₂: xEr³⁺ has potential application prospects in the field of temperature sensing.Secondly,Eu³⁺-doped LuVO₄ fluorescent temperature-sensitive materials based on anomalous thermal quenching of the excitation band edge has been studied in Chapter 4.A series of samples with different concentrations of Eu³⁺ doped LuVO₄ were synthesized by high temperature solid phase method.When examining the sample's temperature-varying excitation spectrum in the range of 298-448 K,it was found that the V-O charge transfer band appears red-shifted and an abnormal thermal quenching occurs at the edge of the excitation band.This is due to the thermal population of vibronic sublevels of the ground electronic energy level.This phenomenon causes the opposite thermal response of the excitation broadband long-wavelength edge?about 350 nm?and the center of the excitation band?about 319 nm?and the characteristic emission of Eu³⁺?eg: 392 nm and 463 nm?.Taking advantage of this diversity change of thermal response,a novel temperature measurement strategy was proposed.Finally,the maximum relative sensitivity is 3.48% K-1@298 K? The thermal cycle diagram also shows the excellent repeatability of the material,indicating that Lu1-xVO4: xEu³⁺ has potential for high-performance optical temperature measurement applications.Finally,the temperature sensing characteristics of perovskite La₂MgTiO₆ doped with Nd³⁺,Ho³⁺,Pr³⁺ fluorescent temperature-sensitive materials in the near infrared region have been studied in Chapter 5.La_1.98MgTiO₆: 0.02Ln³⁺?Ln=Nd,Ho,Pr?samples were synthesized by high temperature solid-phase method.The samples have good luminescence in the near-infrared region.The temperature-sensitivity study using the fluorescence intensity ratio method has obtained the maximum relative sensitivity of 0.117% K^-1@298 K,0.52% K^-1@298 K,and 0.56% K^-1@448 K.This part of the research makes preliminary exploration for the application of this series of materials in the field of fluorescence temperature sensing in the near infrared region.