Excellent temperature sensitivities based on the FIR technique of up-conversion luminescence in a novel NaLaTi2O6:Yb3+,Tm3+ material

Abstract

Fluorescent luminescence thermometers possessing high temperature sensitivities have drawn extensive interest with increasing demand in daily life and industrial fields. However, thermal quenching usually takes place with increasing temperature for rare earth ion doped up-conversion luminescence phosphors. In this work, screened NaLaTi₂O₆:Yb³⁺,Tm³⁺ materials were synthesized via a high-temperature solid-state reaction method. Strong blue and near-infrared up-conversion luminescence (UCL) emissions, as well as relatively weak red emissions, were observed under 980 nm laser excitation at room temperature. The emission bands of Tm^{3+ 1}G₄ → ³H₆ (blue), ¹G₄ → ³F₄ (red), and ³H₄ → ³H₆ (near infrared) transitions significantly decayed with increasing temperature owing to the general thermal quenching effect. However, attractively, a negative thermal expansion effect, thermally boosted luminescence, appeared for Tm^{3+ 3}F_2,3 → ³H₆ transition (deep red emission), which is likely to be derived from the phonon-assisted energy transfer effect. With the aid of high-contrast thermal-dependent characteristics of these transitions, extremely high maximal absolute and relative sensitivities of 4.29 K⁻¹ at 653 K and 36.2% K⁻¹ at 303 K, respectively, were achieved based on the proposed fluorescent intensity ratio (FIR) thermometry technique, which are one order of magnitude higher than previously reported results. These fascinating results indicate that the as-prepared materials could be excellent candidates for application in optical thermometry and encourage us to devise thermally boosted up-conversion and self-reference optical thermometers by utilizing Tm³⁺-activated luminescence phosphors.