Novel high-sensitivity optical thermometry based on fluorescence intensity ratio of <inline-formula><tex-math id="Z-20240425115725">\begin{document}${\text{VO}}_4^{3 - } $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_Z-20240425115725.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_Z-20240425115725.png"/></alternatives></inline-formula> to Pr<sup>3+</sup>
Authors: Yan Yong-Biao , Li Shuang , Ding Shuang-Shuang , Zhang Bing-Xue , Sun Hao , Ju Quan-Hao , Yao Lu ,   School of Physics, Changchun University of Science and Technology, Changchun 130022, China,   Nanophotonics and Biophotonics Key Laboratory of Jilin Province, International Joint Research Center for Nanophotonics and Biophotonics, Changchun University of Science and Technology, Changchun 130022, China
Published: March 2024

It is noteworthy that since 2010, the number of published and cited scientific papers on optical thermometry has increased exponentially. Optical thermometry technology is about to make a significant process in sensing, therapy, diagnosis, and imaging. The current research mainly focuses on optical thermometry that is developing towards high-sensitivity thermometry. In this work, a new thermometry strategy is proposed based on the different temperature-dependent behaviors between the host ions and the doped ions. Firstly, YVO<sub>4</sub>:<i>x</i>Pr<sup>3+</sup>(<i>x</i> = 0%–1.5%) phosphors are successfully synthesized by the solid-state method. Then, the structure and luminescence properties of the samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and fluorescence spectrophotometer. The XRD results show that Pr<sup>3+</sup> ions are successfully incorporated into the YVO<sub>4</sub> host, and the sample has a tetragonal phase crystal structure with space group <i>I</i>41/<i>amd</i>. The SEM results show that the samples are rectangular-shaped micron particles with smooth surfaces, and the average grain size is about 2.1 μm. Under the excitation of 320 nm, the sample mainly exhibits broadband blue emission around 440 nm and red emission at 606 nm, which are attributed to the charge transfer transition of <inline-formula><tex-math id="M2">\begin{document}${\text{VO}}_4^{3 - }$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M2.png"/></alternatives></inline-formula> and the <sup>1</sup>D<sub>2</sub>→<sup>3</sup>H<sub>4</sub> transition of Pr<sup>3+</sup>, respectively. The relationship between the luminescence of the sample and the concentration of Pr<sup>3+</sup> is studied. It is found that the optimal doping concentration of Pr<sup>3+</sup> is 0.5%, and a higher doping concentration will cause concentration to be quenched. The reason for quenching concentration is the electric dipole-quadrupole interaction. The luminescence peak position of the temperature-dependent spectrum of YVO<sub>4</sub>:0.5%Pr<sup>3+</sup> is consistent with that at room temperature. As the temperature increases, the total luminescence intensity gradually decreases, which is caused by thermal quenching, and the mechanism of thermal quenching is analyzed. Since the temperature-dependent behaviors of luminescence of <inline-formula><tex-math id="M3">\begin{document}${\text{VO}}_4^{3 - }$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M3.png"/></alternatives></inline-formula> and Pr<sup>3+</sup> are significantly different from each other, a new fluorescence intensity ratio thermometry strategy is realized. Temperatures range is 303–353 K, and the maximum absolute sensitivity and relative sensitivity are 0.651 K<sup>–1</sup> and 3.112×10<sup>–2</sup> K<sup>–1</sup> at 353 K, respectively, much higher than the traditional thermally coupled level thermometry strategy. In addition, there is no obvious overlap between the emission peaks of <inline-formula><tex-math id="M4">\begin{document}${\text{VO}}_4^{3 - }$\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240012_M4.png"/></alternatives></inline-formula> and Pr<sup>3+</sup>, which provides a good discrimination capability for signal detection. The above results show that this work provides a promising path for designing self-reference optical thermometry materials with excellent temperature sensitivity and signal discrimination.