Research On Fluorescence Intensity Ratio Temperature Measure Method Based On Rare Earth Ions Doped Micro And Nano Materials

Rare earth ions doped materials not only have a wide range of applications in the traditional metallurgical machinery,petrochemical industry and glass ceramics fields,but also have broad application prospects in the emerging fields of permanent magnet,magnetostriction,magnetic refrigeration,magneto-optic,magnetic bubble,fluorescence,hydrogen storage,catalysis,superconductivity,etc.Among them,Compared with other temperature measurement methods,the temperature sensing method based on the photo-luminescence fluorescence intensity ratio of rare earth ions has attracted considerable attention because of its advantages of fast response speed,high sensitivity,accurate measurement,and ability to overcome the influence of measurement environment changes.However,with the development of science and technology,the limitations of this temperature measurement method are gradually revealed,such as low fluorescence efficiency,poor temperature sensitivity and other factors,which restrict the development of this technology and need to be solved urgently.In addition,there are few systematic studies on the influencing factors of ratiometric temperature measurement at home and abroad,which also restricts the development of this technology to a certain extent.Therefore,the fluorescence characteristics and temperature sensitive characteristics of rare earth ion fluorescent materials are discussed,in this paper,to analyze and solve the above problems.The Yb³⁺-Er³⁺co-doped Ca Mo O₄phosphors were synthesized by high-temperature solid-phase method.At the pumping of 980 nm laser,the effects of laser power,laser pumping time,crystallinity,and temperature measurement range on the photo-thermal were systematically investigated by fluorescence intensity ratio method at the thermometric behavior of thermally coupled levels(²H_11/2and ⁴S_3/2)of Er³⁺ions.By optimizing and correcting the fitting equation of Boltzmann fluorescence intensity ratio,it is found that higher pumping power,longer pumping time,higher temperature measurement range,and lower crystallinity will enhance the photo-thermal effect and reduce the relative sensitivity of temperature measurement.According to the above research,this subject propose a method to reduce the photo-thermal effect by reducing the laser pumping power and improving the crystallinity of the phosphors to reduce the non radiative relaxation rate while using the pulsed laser pumping within the appropriate temperature range.A secondary sintered composite phosphors composed of NaY(WO₄)₂:Yb³⁺-Nd³⁺and Na(WO₄)₂:Er³⁺were prepared by high-temperature solid-state method,and a kind of luminescent material with good temperature measurement performance was designed.XRD,SEM and Raman were used to characterize the mixed phosphors before and after secondary sintering,and the effect of secondary sintering on the energy transfer between Nd³⁺and Er³⁺ions was also analyzed.Under the pumping of 980 nm laser,when the temperature is increased from 304 to 773 K,the near-infrared emission(710-920 nm)of Nd³⁺ions is effectively enhanced,while that of Er³⁺ions centered at 1536 nm is thermally quenched.Using two bands of fluorescence bands with significantly different dependence on temperature as the monitoring signal,the relationship between intensity ratio and temperature was researched,and the thermometry sensitivity was calculated.Meanwhile,by optimizing the doping concentrations of the three kinds of rare earth ions,it is found that when the doping concentrations of Yb³⁺,Nd³⁺and Er³⁺ions are 10,2 and 1.5 mol%,respectively,the thermometry sensitivity is largest at 304 K,and the maximum sensitivity is 5.14%K^-1with a measurement uncertainty of 0.1 K^-1.At this time,the fluorescence of the monitored band is 753 nm for Nd³⁺ions and 1536 nm for Er³⁺ions,respectively.The temperature measurement performance is better than the previously reported rare earth luminescence temperature sensors,indicating that this method lays the foundation for realizing the optical temperature measurement target with ideal performance.NaYF₄nanoparticles with single-doped Nd³⁺,Nd³⁺@Yb³⁺core-shell structure and Nd³⁺@Yb³⁺@Er³⁺doped core-shell structure were prepared by solvothermal method,and their fluorescence spectra and temperature measurement characteristics under 980 nm laser pumping were studied.When the near infrared fluorescence originated from Nd³⁺ion thermal coupling energy levels were used as the monitored fluorescent band,the temperature measurement performance of Nd³⁺@Yb³⁺core-shell structured nanoparticles is limited by the thermal coupling energy level difference,which limits the further improvement of thermometry sensitivity.For this reason,Er³⁺ions are introduced to design Nd³⁺@Yb³⁺@Er³⁺core-shell-shell and Nd³⁺-Yb³⁺-Er³⁺triple-doped nanoparticles.The ratio of 655 nm red fluorescence from Er³⁺ions and 805 nm near-infrared fluorescence from Nd³⁺ions are used to measure temperature.It is found that the temperature measurement using Nd³⁺@Yb³⁺@Er³⁺core-shell-shell nanoparticles can break the limitation of Nd³⁺ions thermal coupling energy level difference,avoid the influence of energy transfer between Nd³⁺and Er³⁺ions on temperature measurement,and improve the sensitivity of temperature measurement.At the same time,the Nd³⁺ions located in the central core layer are far away from the surface defect quenching center,which increases the fluorescence intensity with rise of temperature.In contrast,Er³⁺ions located in the outer shell are affected by the surface defects,and the fluorescence intensity is not enhanced.This different temperature dependence further enhances the sensitivity of temperature measurement,and achieves a high sensitivity of 2.06%K^-1at 303 K,which can be well applied to biomedical temperature measurement and other fields.In addition,by changing the pumping power of the laser,it is found that the pumping power also has a great influence on the temperature measurement of the nanoparticles,which is verified by establishing a steady-state rate equation to analyze the fluorescence mechanism of rare earth ions.