Enhanced temperature sensing performance of Er${}^{3+}$, Yb${}^{3+}$: PLZT ceramic based on emissions of Stark sublevels

In this study, the temperature sensing behaviors of emissions of Stark sublevels in Er${}^{3+}$/Yb${}^{3+}$ codoped lead lanthanum zirconate titanate (PLZT) transparent ceramic were examined. Based on the temperature-dependent upconversion fluorescence spectra excited by 980 nm, the emission intensities of the Stark sublevels ${}^2$H${}_{11/2(1,2)}$, ${}^4$S${}_{3/2(1,2)}$, and ${}^4$F${}_{9/2(1,2,3)}$ were obtained upon increasing the temperature from 160 to 320 K. All the transitions present strong temperature dependence under the competitive effects of thermal excitation and nonradiative relaxation. The optical temperature sensing properties of ${}^2$H${}_{11/2}$/${}^4$S${}_{3/2\left(1\right)}$, ${}^2$H${}_{11/2}$/${}^4$S${}_{3/2\left(2\right)}$, ${}^2$H${}_{11/2}$/${}^4$F${}_{9/2\left(1\right)}$, ${}^2$H${}_{11/2}$/${}^4$F${}_{9/2\left(2\right)}$, and ${}^2$H${}_{11/2}$/${}^4$F${}_{9/2\left(3\right)}$ were investigated using the fluorescence intensity ratio (FIR) technique. The largest absolute sensitivity S${}_a$ of 142.4 × 10${}^{-4}$ K${}^{-1}$ was obtained based on the FIRs of ${}^2$H${}_{11/2}$/${}^4$F${}_{9/2\left(1\right)}$ at 320 K, which is approximately 26 times larger than that of traditionally used thermal coupled levels ${}^2$H${}_{11/2}$/${}^4$S${}_{3/2}$ in the considered sample. In contrast, the maximum relative sensitivity S${}_r$ was 2.21% K${}^{-1}$ at 203 K. A comparison of these results with those of other Er${}^{3+}$/Yb${}^{3+}$ codoped materials reveals that Er${}^{3+}$/Yb${}^{3+}$: PLZT ceramics are a promising thermometer material at low temperatures. Applying FIRs based on the photoluminescence of Stark sublevels is a practical approach to achieving greater thermometric efficiency.