High-precision Temperature Sensor Research Based On The Fluorescence Intensity Ratio Technology

In the past decades,rare earth ion doped nano-fluorescent materials have a wide range of mature applications by virtue of unique fluorescent properties,such as fluorescent anti-counterfeiting,biomedicine,temperature sensing,LED lighting,etc.Rare earth ions may create many different hues of light-emitting bands because they have a large number of energy levels.Ho³⁺,Er³⁺,Dy³⁺,Nd³⁺,and other rare earth ions are frequently utilized as luminescence centers.However,only by the rare earth ions themselves absorbing near-infrared pumping to produce photon efficiency is very low,luminescence is weak,the urgent need to address is to improve the efficiency of the activator ions on the conversion and temperature sensitivity.In this paper,we continue to introduce other metal ions while doping the sensitizer Yb³⁺,and measure and compare the changes of fluorescence intensity in each of its emission bands.On this basis,the thermometric performance of the samples is evaluated from the perspective of thermally coupled and non-thermally coupled energy levels,respectively.The main studies are as follows:（1）A series of up-conversion phosphor samples with different concentrations of Ho³⁺/Yb³⁺and Ho³⁺/Yb³⁺/Gd³⁺co-doped with BaWO₄were synthesized by the high-temperature solid phase method,respectively.After X-ray diffraction analysis and scanning electron microscopy experiments,the effects of introducing Gd³⁺ions on the physical phase structure and particle size of the materials were investigated.The emission spectra of the samples were measured under near-infrared pump excitation,and the optimal doping concentration of Gd³⁺ions was 35 mol%.The fluorescence intensity of the blue（465 nm,489 nm）,green（541 nm）and red（665 nm）emission peaks of the phosphors at this concentration were increased by 20.59,9.83,7.37 and27.59 times.On this basis,the sensitivity of the doping of Gd³⁺ions to the temperature of the thermally coupled energy levels and the non-thermally coupled energy levels was investigated separately using the fluorescence intensity ratio approach.At 403 K,the thermally coupled energy levels had an absolute sensitivity of19.58*10^-3K^-1.The relative sensitivity was 1.95%K^-1at 303 K.The absolute sensitivity of the non-thermally coupled energy levels was 12.0*10^-3K^-1,which was obtained at 573 K.（2）In order to create BaWO₄:Ho³⁺/Yb³⁺/Bi³⁺phosphors,a high-temperature solid phase technique was used.The produced samples were identified as pure phases using X-ray diffraction analysis,and the reduction in grain size following Bi³⁺doping was shown through scanning electron microscopy examination.The fluorescence intensity of the blue（465 nm,489 nm）,green（541 nm）and red（660 nm）emission peaks of the phosphor was enhanced by 2.07,3.28,34.08 and 20.49 times after doping with 20mol%Bi³⁺under the excitation of NIR pumping light source.The temperature dependence of the fluorescence intensity of Ho³⁺ions（660/541 nm）over⁵F₄/⁵S₂→⁵I₈/⁵F₅→⁵I₈was investigated.The absolute sensitivity of the non-thermally coupled energy level of the phosphor reaches a maximum value of 13.0*10^-3K^-1at563 K,and the relative sensitivity achieves a maximum value of 0.89%K^-1at 463 K.（3）BaWO₄:Ho³⁺/Yb³⁺/Ca²⁺phosphors with different concentrations were prepared based on the high-temperature solid phase method.The strongest luminescence was obtained for the concentration of 20 mol%Ca²⁺under the excitation of NIR pump light source,and the fluorescence intensity of the phosphor blue（465 nm,489 nm）,green（541 nm）and red（660 nm）emission peaks were increased by 9.57,3.8,2.87and 54.38 times,respectively.The fluorescence intensity ratios of the thermally coupled energy levels of Ho³⁺for ⁵F₁/⁵G₆and ⁵F_2,3/³K₈and the non-thermally coupled energy levels for ⁵F₄/⁵S₂and ⁵F₅were investigated in relation to the temperature,and the thermally coupled energy levels’absolute sensitivity peaked at 3.21*10^-3K^-1at563 K,whereas their relative sensitivity peaked at 0.29%K^-1at the same temperature;The absolute sensitivity of the non-thermally coupled energy levels reached a maximum value of 28.3*10^-3K^-1at 523 K.The relative sensitivity achieved a maximum value of 1.05%K^-1at 323 K.