Research On Temperature Sensing Properties Of Yb³⁺/Er³⁺ Codoped Up-Conversion Luminescent Materials

As the most basic and core thermodynamic parameter,temperature plays a very important role in many scenarios such as modern life and production,biomedicine,and electronic manufacturing.Therefore,it is of great significance to realize its accurate and rapid measurement.The continuous progress of society and the flourishing of science and technology have put forward higher requirements for temperature measurement.Constrained by the characteristics of contact,traditional temperature sensors cannot provide fast-response dynamic measurement,nor can they meet the application requirements of some special scenarios（especially in nano-scale biological systems）.Non-contact optical temperature sensors based on rare earth doped up-conversion（UC）luminescent materials have the advantages of fast response,high spatial resolution and sensitivity,which provides a good solution to the above problems.Among numerous non-contact optical temperature sensing techniques,fluorescence intensity ratio（FIR）technology stands out as one of the mainstream technologies for research and application.This is mainly due to the fact that it can well resist the adverse effects caused by external fluctuations such as excitation power fluctuation and fluorescence loss,that is,it has strong anti-interference ability.In recent years,achieving sensitivity optimization and enhancement has been a hot research topic.The host largely affects the luminescence characteristics and optical temperature sensitivity of UC luminescent materials,so finding the ideal host material is an effective way to improve and optimize the sensitivity.In this paper,Gd₂（WO₄）₃and Y₆O₅F₈,which have low phonon energy and excellent stability,were used as hosts and Yb³⁺/Er³⁺as doped ion pair.Their phases,morphological characteristics and up-conversion luminescence properties were investigated.At the same time,their optical temperature sensing properties were evaluated based on FIR technique.The two main parts of the work carried out are as follows:（1）The Yb³⁺/Er³⁺co-doped Gd₂（WO₄）₃optical temperature sensing materials were prepared by co-precipitation with subsequent calcination.The phase,crystal structure and morphology were characterized and analyzed.Under 980 nm NIR excitation,the emission spectra are mainly composed of two strong green emission peaks centered at530 nm and 551 nm,respectively.And,Gd₂（WO₄）₃:10%Yb³⁺/2%Er³⁺exhibits the strongest emission.The UC luminescence process based on the two-photon process was studied by combining the analysis of the pump excitation power dependence of emission intensity and fluorescence decay process of Gd₂（WO₄）₃:10%Yb³⁺/2%Er³⁺.Based on the FIR technique,the absolute and relative sensitivities of optical temperature sensing for Gd₂（WO₄）₃:10%Yb³⁺/2%Er³⁺can reach the maximum values of 0.0139 K^-1（518 K）and 1.18%K^-1（293 K）,respectively.Therefore,Gd₂（WO₄）₃:Yb³⁺/Er³⁺have great potential for application in non-contact optical temperature sensors.（2）A two-step synthetic route[Y（OH）CO₃→Y（OH）_1.63F_1.37→Y₆O₅F₈]was designed to successfully synthesize the Y₆O₅F₈:Yb³⁺/Er³⁺optical temperature sensing materials.The phases and morphologies of the samples at every stage of the synthetic route were investigated,and the formation mechanism of Y（OH）_1.63F_1.37was proposed based on the time-dependent experiment.Under 980 nm excitation,the emission spectra consist of two faint green emission bands and one strong red emission band,and Y₆O₅F₈:10%Yb³⁺/1%Er³⁺exhibits the strongest UC emission.The possible absorption and emission processes of photons in Y₆O₅F₈:10%Yb³⁺/1%Er³⁺were elucidated in detail based on the UC luminescence two-photon process mechanism.Among them,the efficient energy transfer（ET）process from Yb³⁺to Er³⁺plays a very critical role,which was also confirmed by the decay curves.In addition,the optical temperature sensing performance of Y₆O₅F₈:10%Yb³⁺/1%Er³⁺was investigated and evaluated based on the temperature-dependent spectra in the tested temperature range,and its absolute and relative sensitivities were determined to be 0.0074 K^-1（518 K）and 1.39%K^-1（293 K）,respectively.The results indicate that Y₆O₅F₈:Yb³⁺/Er³⁺have important potential applications in non-contact optical temperature sensors.