Research On Optical Temperature Sensing Performance Of Rare Earth Ions Doped ZrO₂ Nanoparticles

Temperature is one of the most basic physical parameters,and its accurate detection is vital to industrial,military,medical,energy and other fields.Compared with traditional temperature measurement methods,optical temperature measurement technology has the characteristics of fast response,convenient operation and wide application.Among them,the fluorescence intensity ratio（FIR）temperature measurement technology has attracted much attention because it can effectively reduce the temperature measurement errors caused by fluorescence loss and electromagnetic field interference.The temperature measurement technology is mainly based on the fluorescence intensity ratio of the rare earth ion(RE³⁺)level transition to characterize temperature.At present,FIR temperature measurement technology has achieved good development,but there are still many problems,such as low temperature measurement sensitivity and resolution,and low luminous efficiency.Therefore,there is an urgent need to systematically study the optical temperature measurement performance from various aspects.In our study,different rare earth ion-doped ZrO₂ nanoparticles were prepared by gel combustion method,and their optical temperature measurement performance was investigated in detail.The main three aspects are as follows:First,the luminescence properties of rare earth ions with up-conversion luminescence in ZrO₂ nanoparticles were studied.Then we use the temperature measurement scheme of defect luminescence to improve the sensitivity.The third is a temperature measurement technology based on the valley-to-peak intensity ratio（VPR）between adjacent fluorescence peaks,and combined with the fluorescence lifetime measurement technology to achieve dual-mode temperature measurement.The specific research content is as follows:（1）Nitrate is used as a raw material.We first investigate the process of preparing ZrO₂ nanoparticles by gel combustion method to obtain the optimal preparation process conditions.The results determined that the optimal titration p H of the nitrate solution should be controlled to 7,the optimal calcination temperature was 800°C,and the holding time was 2h.Based on suitable processes,the rare earth ion-doped ZrO₂ nanoparticle materials with up-conversion luminescence were separately designed,and the up-conversion luminescence performance of Ho³⁺/Yb³⁺co-doped ZrO₂ nanoparticles was studied.The optical temperature measurement performance was studied by using FIR temperature measurement technology.（2）Gd³⁺-doped ZrO₂ nanoparticles were prepared by the gel-free combustion method.It was found that changes in the concentration of Gd³⁺would affect the intensity of defect luminescence in ZrO₂ nanoparticles.When 275 nm ultraviolet light was used as the excitation light source,the ultraviolet emission of Gd³⁺and defect-related luminescence can be excited simultaneously.We analyzed the defect types of ZrO₂ and found that the matrix luminescence in ZrO₂ may be caused by the combined luminescence of oxygen and carbon defects.Moreover,we revealed that there was a certain energy transfer relationship between oxygen and carbon defects during optical temperature measurement through EPR and TL spectra at different temperatures.In addition,when using FIR temperature measurement technology for optical temperature measurement based on defect emission and Gd³⁺ion emission,high absolute temperature sensitivity(S_ɑ-max=6.408 K^-1)and relative sensitivity(S_r-max=3.452%K^-1)were obtained.The result was far better than that of most rare earth doped luminescent materials.（3）We prepared x%Eu³⁺:ZrO₂ nanoparticles with smaller grain size（about 10nm）,and studied the effect of Eu³⁺doping concentration on the phase,structure and down-conversion luminescence properties of ZrO₂.The optical temperature measurement performance of 10%Eu³⁺:ZrO₂ nanoparticles was studied by a new VPR temperature measurement technology.As a result,the highest relative sensitivity was 1.8%K^-1 at 293 K.In addition,by characterizing parameters such as temperature repeatability and temperature error,it was found that VPR optical temperature measurement had excellent stability,and the minimum value of temperature uncertainty evaluation was～0.27 K.When using fluorescence lifetime temperature measurement,the best relative sensitivity was 0.33%K^-1.（4）Based on the study of VPR temperature measurement technology,in order to achieve excellent performance in three biological windows（NIR-Ι:～650-950 nm;NIR-ΙΙ:～1000-1350 nm;NIR-ΙΙΙ:～1500-1850 nm）,we designed Er³⁺/Yb³⁺:ZrO₂nanoparticles.We first studied the effect of different doping concentrations of Yb³⁺on the luminescence properties of Er³⁺/Yb³⁺:ZrO₂ nanoparticles,and found that the best luminescence properties were obtained when the doping concentrations of Er³⁺and Yb³⁺were 1.5 mol%and 6 mol%,respectively.Combined with VPR temperature measurement technology,we found that the nanoparticle can monitor the temperature in three biological windows at the same time.For VPR-1,VPR-2,and VPR-3,the maximum values of S_r obtained at 293 K were 0.75%,1.1%,and 1.3%K^-1,respectively.In addition,the optical temperature measurement behavior of the emission from the two Stark transitions of ⁴I_13/2→⁴I_15/2 was studied using FIR temperature measurement technology in NIR-III.The highest relative sensitivity obtained was 0.61%K^-1,which was significantly lower than the relative sensitivity obtained by VPR temperature measurement technology.