Study On Temperature Sensing Performance Of Rare Earth Double Doped Luminescent Materials Based On Fluorescence Intensity Ratio Technology

As an important physical parameter,temperature plays a vital role in daily life,industrial production and medical treatment.At present,there are many temperature measurement methods,such as radiation temperature measurement method,laser interference temperature measurement method,ultrasonic acoustic temperature measurement method.However,the temperature measurement method based on fluorescence intensity ratio is widely concerned because of its advantages such as non-contact temperature measurement,anti-electromagnetic interference and high sensing accuracy.Its principle is that the ratio of fluorescence intensity between two thermal coupling energy levels of rare earth ions changes regularly with temperature.The 4f5d energy level of rare earth ions is isolated by the stable 6s energy level,and there are abundant electron energy levels,so many rare earth ions have thermal coupling energy levels suitable for temperature measurement,such as²F_7/2and ²F_5/2energy levels of Nd³⁺,²H_11/2and ⁴S_3/2energy levels of Er³⁺ions.If Yb³⁺is added as sensitizer,the luminescence efficiency can be improved,the required pump power can be lower,so that the application is more extensive.Based on fluorescence intensity ratio technique,the temperature sensing properties of Yb³⁺/Nd³⁺and Yb³⁺/Er³⁺co-doped phosphors were studied in this article.The research contents are as follows:（1）Yb³⁺/Nd³⁺co-doped Ca Ti O₃phosphors were prepared by high-temperature solid-phase method,different compositions were designed,and the optimal doping concentration of Yb³⁺/Nd³⁺was explored.The spectrum shows that the best composition is Ca_0.987Ti O₃:0.7%Yb³⁺,0.6%Nd³⁺.The spectrum,and luminescence principle of luminescence principle were analyzed.The ²F_7/2and ²F_5/2energy levels of Nd³⁺are used as the thermal coupling energy level pair to analyze the temperature.The results show that in the temperature range of 323-563 K,the emission light of the material increases with the increase of temperature,the relative sensitivity can reach1.52%K^-1.Multiple experiments show that this material has good repeatability,and the temperature uncertainty is less than 0.45 K.This material can be combined with a Y-type fiber optic probe to build a temperature measurement system.（2）Y₂WO₆:Yb³⁺/Er³⁺phosphors were prepared by high temperature solid state method.The optimum doping concentration of Yb³⁺/Er³⁺was determined as8mol%/1mol%through experiments.The materials were characterized from three aspects:phase analysis,morphology analysis and spectral analysis.The chromaticity coordinate diagram shows that the emission light obtained under different excitation sources has different colors,which can be used for multi-mode anti-counterfeiting.In terms of temperature measurement applications,upconversion variable temperature spectroscopy,down-conversion variable temperature spectroscopy,and variable temperature fluorescence decay lifetime can be used for temperature sensing analysis.The results show that the material has good repeatability in the range of 303-573 K,and the relative sensitivity can reach 1.25%K^-1and the temperature uncertainty is less than 0.82 K.Therefore,Y₂WO₆:Yb³⁺/Er³⁺is a multifunctional material that can be applied to multi-mode anti-counterfeiting and multi-mode temperature measurement.（3）NaYF₄:Yb³⁺/Er³⁺@NaYF₄core-shell structure materials were prepared by co-precipitation method.Transmission electron microscopy analysis shows that the core of this material is about 17.5 nm,and the size of the shell after cladding is about22.5 nm.The synthesized core-shell material was modified to change its hydrophobicity and confirmed by Fourier transform infrared spectroscopy.The temperature sensing analysis of this nanomaterial was performed within 296-373 K.Under the excitation of 980 nm with a power density of 0.4 W/cm²,the temperature dependent spectra of the material were obtained.After analysis by FIR technology,it is concluded that the relative sensitivity of this material can reach 1.23%K^-1.The temperature measurement accuracy is less than 0.13 K.And the material has good repeatability,so it can be applied to fields such as biological nanothermometers.