Study On Optical Temperature Sensing Properties Of Ho³⁺ Doped And Ho³⁺,Eu³⁺ Co-doped NaY（MoO₄）₂ Phosphors

Temperature plays an important role in daily life and production process,so accurate temperature measurement has become a popular direction in biological detection,aerospace,electronic production and other research fields.The traditional contact temperature measurement method cannot accurately monitor the temperature in extreme environments such as high temperature and high pressure,airtight,toxic and cell interior,so the selection of temperature measurement environment has great limitations.Among non-contact temperature measurement methods,fluorescence intensity ratio optical temperature sensing materials based on rare earth ion doping can be applied to most extreme environments,so fluorescence intensity ratio temperature measurement technology has become a hot direction of scientific research.Most optical temperature sensing materials choose rare earth ion Er³⁺as the activation ion,Er³⁺through the fluorescence intensity ratio of thermal coupling energy levels（TCL）to achieve the purpose of temperature measurement.The distance between the two thermal coupling energy levels is difficult to further increase,and the relative sensitivity of temperature measurement is low.Moreover,the luminescence colors of the two energy levels are similar and difficult to distinguish,resulting in low temperature measurement accuracy.In order to further improve the relative sensitivity of temperature sensing materials,non-thermal coupling energy levels（NTCL）fluorescence intensity ratio temperature sensing materials have gradually become the main direction of scientific research.Therefore,Ho³⁺doped NaY（MoO₄）₂phosphors were synthesized in this paper,and the fluorescence intensity ratio of NTCL was used to monitor the temperature.On the basis of this study,Ho³⁺,Eu³⁺co-doped NaY（MoO₄）₂phosphors were synthesized to further improve the temperature measurement performance of temperature sensing materials.The main content of this paper is as follows:（1）NaY（MoO₄）₂:5%Ho³⁺phosphors were successfully synthesized by hydrothermal method.The morphologies of the samples were changed by changing the amount of sodium citrate（Na₃C₆H₅O₇,Na₃Cit）as the chelating agent.Characterization of the microstructures and morphology of the synthesized samples by X-ray diffraction（XRD）and field emission scanning electron microscopy（FE-SEM）.The XRD patterns indicated that samples were synthesized as tetragonal scheelite structure,without diffraction peaks corresponding to impurities,and the synthesized samples were pure phase.The FE-SEM images showed that there was a clear relationship between the size of the samples and the ratio of sodium citrate to rare earths.It showed that the addition of sodium citrate as chelating agent would affect the morphology growth of phosphors.（2）The temperature-dependent emission spectra of the NaY（MoO₄）₂:5%Ho³⁺phosphors were measured in the range of 293-563 K.It can be seen that Ho³⁺had luminescent of different energy levels（~5F₄/~5S₂-~5I₈,~5F₅-~5I₈and ~5F₄/~5S₂-~5I₇）in the visible range,and the luminescent from different energy levels had different thermal quenching trends.Therefore,the two groups of fluorescence intensity ratios could be used for temperature monitoring.The two groups of fluorescence intensity ratios of the samples could be verified with each other,which made the temperature measurement of the samples self-calibrating.So the accuracy of samples temperature measurement could be improved to a large extent.It was found that when Cit^3-/Re³⁺=2,the sample had the maximum relative sensitivity at 485 K,and the maximum relative sensitivity were0.312%K^-1and 0.316%K^-1.（3）In this study,5%Ho³⁺and 0.2%Eu³⁺co-doped NaY（MoO₄）₂phosphors were successfully prepared by hydrothermal method.The phosphors with different morphologies were obtained by changing the molar ratio of sodium citrate to rare earth ions(Cit^3-/Re³⁺=0,0.5,1,2).The structure and morphology of the samples were characterized by XRD and FE-SEM.It can be seen from XRD that the samples were scheelite structure with tetragonal phase.As can be seen from the FE-SEM images,the size of the samples was related to the amount of sodium citrate.（4）The optical temperature-dependent emission spectra of 5%Ho³⁺and 0.2%Eu³⁺co-doped NaY（MoO₄）₂materials were measured.It can be found that the emission intensity from both Ho³⁺（~5F₄/~5S₂-~5I₈）and Eu³⁺（~5D₀-~7F₂）decreased as the temperature increased,but the emission intensity of Eu³⁺decreased faster than that of Ho³⁺.So the fluorescence intensity ratio of Ho³⁺to Eu³⁺could be used to monitor the temperature.The relative sensitivity of the sample(Cit^3-/Re³⁺=2)was found to have a maximum value of 0.95%K^-1at 524 K.The relative sensitivity was improved relative to the single doped materials.The results of this study showed that both Ho³⁺doped and Ho³⁺,Eu³⁺co-doped NaY（MoO₄）₂phosphors had good temperature measurement performance.By adding the chelating agent sodium citrate,the morphology of the samples could be altered.And the temperature sensing performance of the samples would be improved with amounts of sodium citrate increased.The study provided reference for the innovation and performance improvement of temperature measuring materials in this field.