Sensitivity Of Fluorescence Intensity Ratio Thermometry At High Temperature Based On Luminescence Of Eu³⁺/Tb³⁺/Cr³⁺

Temperature is an important thermodynamic parameter,and it is an indispensable monitoring parameter in industrial production,scientific research,infrastructure construction,and biology.Fluorescence Intensity Ratio(FIR)temperature sensor based on the rare earth doped materials shows advantages of high temperature measurement sensitivity and high spatial resolution,which makes FIR technique a research hotspot.FIR temperature sensing technology has the characteristics of non-contact temperature measurement,which can achieve high-precision temperature measurement and imaging of plasma,cells/biological tissues.Therefore,the development of the mechanism and performance of FIR temperature measurement methods for non-contact temperature measurement technique are of great significance.However,the relative sensitivity(S_r)of the FIR temperature measurement method based on the thermal coupling mechanism decreases sharply with increasing temperature,and it is difficult to maintain a stable and high S_r value in the high temperature range.In addition,during the process of increasing S_r,the temperature measurement uncertainty(?T)tends to increase.Therefore,how to break the thermal coupling relationship between the emitting centers based on the thermal coupling temperature measurement mechanism has become a research challenge,new FIR temperature measurement method needs to be proposed to obtain a highly sensitive and accurate FIR temperature measurement method.The purpose of this dissertation is to study the Eu³⁺based FIR temperature measurement method based on the new temperature measurement mechanism,to improve the temperature measurement sensitivity(S_r),to reduce the temperature measurement uncertainty(?T),and to expand the temperature measurement range.In this dissertation,a double absorption-single channel fluorescence signal detection FIR temperature measurement method based on the ground state and the excited state absorptions is designed.By monitoring the ⁵D₄?⁷F₅ single-wavelength fluorescence intensity of CaWO₄:Tb³⁺and the broadband fluorescence intensity emitted by the ⁵D₀ transition of CaWO₄:Eu³⁺,variable temperature excitation spectra are measured.The FIR temperature characteristics of the single-wavelength fluorescence peak and broadband fluorescence are analyzed,and the energy level properties between the ground state and the first excited state are studied.Compare the S_r performance of CaWO₄:Tb³⁺and CaWO₄:Eu³⁺with the FIR temperature measurement method based on single excitation-double fluorescence detection,the contribution of thermal coupling relationship to increase sensitivity is studied and the advantages of single-channel fluorescence signal detection is discussed.The transitions of the ⁵D₀ to ⁷F₂ Stark splitting levels is studied,and the origin of temperature sensitive characteristics of the valley formed by the overlap of the two fluorescence bands at 611.5 nm and 614.5 nm is analyzed.The valley-to-peak ratio(VPR)thermometry is developed based on the broadening mechanism of spectral line.Through the method of the fluorescence spectroscopy,the temperature characteristics of the VPR value are studied.Then the characteristics of signal-to-noise ratio of the VPR temperature measurement method and the prominent effect on increasing S_r in the high temperature range are analyzed,which guides the improvement of?T.The FIR temperature measurement method based on GdVO₄:Eu³⁺/Al₂O₃:Cr³⁺mixed materials is studied.By measuring the fluorescence spectroscopy,the non-thermal coupling correlation effect between Eu³⁺and Cr³⁺luminescence centers in the mixed material is analyzed,and the FIR and S_r temperature characteristic curves of the mixed material are characterized.The physical model of the temperature measurement method based on mixed materials is established,and the physical law between the S_r of the mixed material and the mono-sensitivity?of the two materials constituting the mixed material is explained.It shows that the internal non-thermal coupling mechanism of the GdVO₄:Eu³⁺/Al₂O₃:Cr³⁺mixed material can increase the high temperature S_r(633 K,1.4%K^-1).The temperature measurement method based on excitation wavelength modulation sensitivity is studied.Through the excitation spectra of GdVO₄:Eu³⁺and CaWO₄:Eu³⁺,the influence factors of the mono-sensitivity of Eu³⁺is studied,and the key role of red shift and broadening of the GdVO₄ charge transfer band in the wavelength modulation-S_r is analyzed.The temperature characteristics of S_r in the temperature range of 303–753 K of the GdVO₄:Eu³⁺/Al₂O₃:Cr³⁺mixed material and the?T of the FIR temperature measurement method are characterized.The advantages of the FIR temperature measurement method with wavelength modulation sensitivity are discussed,then the optimization method of the S_r of the mixed material-based FIR thermometry is proposed,which guiding the near constant value breakthrough of high S_r(2.4%K^-1)in the temperature range of 303–753 K.