Optical Temperature Behavior Of Rare Earth Doped Tungstate Upconverting Materials

Rare earth doped upconversion materials have some advantages in non-contact temperature measurement,such as rapid light-temperature response,strong resistance to environmental electromagnetic interference,and high spatial resolution of temperature measurement.The occupying abides by the Boltzmann distribution.The distribution of electrons changes with temperature.The response from different energy levels to temperature is different.The fluorescence intensity corresponding to each transition are also different.We use it to develop the tungstate upconverting materials and investigate the optical temperature behavior.The researchers have been working to broaden the temperature measurement range and to improve the sensitivity of upconversion luminescent materials in the temperature measurement process.Here,We explored some tungstate upconverting materials.?1?The upconversion luminescent materials Na_0.5Yb_0.5WO₄-Sc₂?WO₄?₃:Yb³⁺/Er³⁺with different doping ratios were synthesized by high temperature solid phase method.The structure of the samples was analyzed by X-ray diffraction?XRD?.The phase composition ratio of the sample was qualitatively analyzed.The 980 nm near-infrared laser was used as the excitation source to obtain the variable power excitation spectra of the samples.The peaks belong to the transitions of Er³⁺:²H_11/2?⁴I_15/2 and ⁴S_3/2?⁴I_15/2.According to the relationship between the intensity and the pump power,it is determined that the upconversion is a two-photon process.Based on the temperature-varying spectra,the fluorescence intensity ratios were calculated and the relationship between the fluorescence intensity ratio and the temperature was plotted.This material has been tested to have a range of 320 to 520 K and a sensitivity of 0.008 K^-1.?2?According to previous experimental results,NaLu?WO₄?₂:1%Yb³⁺/1%Er³⁺was synthesized at 1200°C.The spectra with different power were measured by a 980 nm laser.The luminescence peak belongs to the transitions of Er³⁺:²H_11/2,⁴S_3/2,⁴F_9/2 energy levels.Using the power of 0.5 W,the range of 313-573 K obtained from the temperature-varying spectra.The peaks 531/553 nm belonging to the ²H_11/2,⁴S_3/2 were selected and the fluorescence intensity ratio was calculated.It was found that the spectra changed at around480 K.The occurrence of this temperature turning point was explained by the dependence of the upconversion luminescence intensity on temperature.The temperature turning point is close to the upper limit of the range of 313⁵73 K.Below the temperature turning point,the sensitivity is up to 0.0079 K^-1.Above the temperature turning point,the sensitivity is as high as 0.0106 K^-1.So far,it is a high level among the similar materials reported.In this thesis,NaLu?WO₄?₂:1%Yb³⁺/1%Er³⁺upconversion materials were prepared and the upconversion luminescence mechanism was studied.The temperature variability spectra were detected.The NaLu?WO₄?₂:1%Yb³⁺/1%Er³⁺has better thermal stability and excellent optical temperature behavior compared with the traditional fluoride upconversion material.It can be used as a candidate material for non-contact optical temperature sensing.