High-sensitive upconversion optical thermometers derived of Y(Nb_0.5Ti_0.5)₂O₆:Er³⁺/Yb³⁺ phosphors under 808 nm and 980 nm excitation

Y(Nb_0.5Ti_0.5)₂O₆:Er³⁺/Yb³⁺ phosphors were obtained through the solid state reaction method, where the temperature dependence of up-conversion luminescence properties under 980 nm and 808 nm excitation and the potential application as optical temperature sensor were evaluated. Measurements of X-ray diffraction the formation of a single phase in all the samples analyzed. Phosphors synthetized were excited at 980 nm and 808 nm, where was observed green and red emissions correlated to transitions from Er³⁺ ions. The power-dependent study demonstrated that filling the levels referring to the green and red emissions involves two-photon processes for both excitations evaluated. Moreover, possible mechanistic proposals for the YNT: Er³⁺/Yb³⁺ system at 980 nm and 808 nm were elaborated based on the up-conversion (UC) emission dependence on pump power. Optical temperature-sensing properties were evaluated through fluorescence intensity ratio (FIR) technique, where relative (S_R) and absolute (S_abs) sensitivities were obtained employing thermally coupled levels (TCL) and non-thermally coupled levels (NTCL) from Er³⁺ ions. S_abs and S_R values were compared with the other sensors based on ceramics and demonstrated that YNT: Er³⁺/Yb³⁺ system presented sensitivities values near or greater than these phosphors, indicating that the YNT: Er/Yb phosphors could be employing as optical temperature sensors in the high-temperature region.