Preparation, Upconversion Luminescence Properties And Temperature Sensing Characteristics Of Rare Earth Ion Doped Positive/negative Thermal Expansion Composite Material

Temperature is widely used in different fields of important physical parameters,accurate measurement of temperature for the normal operation of many industries and scientific research is of vital significance,therefore,accurate temperature measurement has always been the focus of scientific research.At present,optical temperature measurement technology using the fluorescence intensity ratio（FIR）of rare earth-doped materials has attracted widespread attention for its high precision and high reliability.However,FIR temperature measurement technology is limited by the difference between the energy level of the matrix and rare earth ions,and with the increase of temperature,the phenomenon of UCL thermal quenching is usually observed in most lanthanide ion-doped positive expansion materials,which greatly affects the performance of luminescence and the accuracy of detection.Doping rare earth ions into negative thermal expansion materials（NTE）is an effective method found to avoid thermal quenching of UCL,and with the increase of temperature,negative thermal expansion materials undergo lattice contraction due to the special arrangement and abnormal vibration of atoms and ions,thereby enhancing the energy transfer between rare earth ions.Therefore,based on the thermal enhancement and thermal quenching phenomena of UCL generated by the composite of positive and negative expansion materials,this paper studies and discusses the up-conversion luminescence properties and temperature sensing performance of materials.Negative thermal expansion material Sc₂W₃O₁₂:Yb³⁺,Er³⁺fluorescent powder and positive thermal expansion material La₂Mo₂O₉:Yb³⁺,Ho³⁺fluorescent powder was synthesized by high-temperature solid-phase method under air atmosphere.The positive/negative expansion composite fluorescent powder was prepared by mixing the two-phase fluorescent powder in a ratio of 1:1.Under 980 nm laser excitation,the relationship between the luminescence intensity of Sc₂W₃O₁₂:Yb³⁺,Er³⁺and La₂Mo₂O₉:Yb³⁺,Ho³⁺fluorescent powder and temperature was investigated,and it was demonstrated that the UCL thermal enhancement phenomenon of Sc₂W₃O₁₂:Yb³⁺,Er³⁺is attributed to the negative expansion property of the material.In the temperature range of 293 K to 573 K,the near-infrared fluorescence intensity ratio（FIR）(I₈₄₅/I₆₅₅)was studied,indicating that FIR increases with temperature.At 293 K,the maximum relative sensitivity（Sr）of near-infrared FIR(I₈₄₅/I₆₅₅)was 2.07%K^-1.The results showed that the mixed fluorescent powder has potential application value as a new type of temperature sensor.Positive expansion material TiO₂:Yb³⁺,Er³⁺three-dimensional ordered macroporous inverse opal photonic crystals were prepared by a template-assisted method,and Yb₂W₃O₁₂:Er³⁺precursor solution was filled into the TiO₂:Yb³⁺,Er³⁺three-dimensional ordered macroporous film.After secondary sintering,Yb₂W₃O₁₂:Er³⁺coated TiO₂:Yb³⁺,Er³⁺core-shell structure was formed.Under 980 nm excitation,as the measurement temperature increases,the green UCL of negative expansion Yb₂W₃O₁₂:Er³⁺shell increases,and the red UCL of positive expansion TiO₂:Yb³⁺,Er³⁺core layer decreases.The temperature sensing performance was characterized by monitoring the intensity ratio of UCL between 525 nm and 660 nm,and the temperature sensitivity（Sr）was approximately 1.12%K^-1.Therefore,the great potential of negative/positive expansion lattice film with core-shell structure as a new temperature sensing system.