Negative thermal expansion triggered anomalous thermal upconversion luminescence behaviors in Er3+/Yb3+-codoped Y2Mo3O12 microparticles for highly sensitive thermometry

For the sake of overcoming the challenges of optical thermometers with high sensitivity, we designed Er3+/Yb3+-codoped Y2Mo3O12 microparticles with thermally enhanced upconversion (UC) emission. Excited at 980 nm, the impact of the Yb3+ ion content on the UC emission properties of the prepared samples is studied. It is found that the optimal doping content for Yb3+ ions in the Y2Mo3O12 host is 13 mol% and the involved UC mechanism pertains to the two-photon excitation process. As the temperature increases from 303 to 583 K, an enhancement in the UC emission intensity is seen triggered by the NTE effect. Furthermore, via use of the fluorescence intensity rate, the thermometric behaviors of the Y2Mo3O12:Er3+/0.22Yb(3+) microparticles are explored, in which their maximum absolute and relative sensitivities are 6.79% K-1 and 0.79% K-1, respectively. Additionally, in comparison with those of the Y2Mo3O12:Er3+/0.22Yb(3+) microparticles, Y2Mo3O12:Er3+/0.22Yb(3+)@BiOF:Tm3+/Yb3+ composites exhibit superior thermometric properties with high absolute and relative sensitivities of 16.89% K-1 and 1.09% K-1, respectively. As Y2Mo3O12 compounds have NTE properties and high thermal stability, our findings may inspire new insight into developing thermally enhanced upconversion materials for highly sensitive thermometry.