Temperature sensing properties of self-crystalized Ba2LaF7: Tb3+ glass ceramics

Abstract

Fluorescence intensity ratio (FIR) techniques for temperature sensing based on the thermally-coupled energy levels (TCELs) of two excited states of rare earth ions are widely investigated. However, their performance in lower temperature detection are poor because of thermal decoupling between two emitting levels with relatively large energy gap. On the other hand, most of luminescent thermometer materials so far reported are in powder form, which suffer from severe light scattering and high hygroscopicity. Fortunately, transparent glass ceramics offer an alternative to improve optical property as well as stability of luminescent materials. Hence, herein self-crystallized 20% Tb3+ doped transparent Ba2LaF7 glass ceramics were synthesized by traditional high-temperature melting method to examine its temperature sensing ability by employing the two low-lying states 7F5 and 7F6 of Tb3+, which are thermally coupled even at lower temperature. Under the resonance excitation of 7F5 → 5D4 transition at 543 nm, the emission intensity of 5D4 → 7F6 enhances with the temperature rising from 300 K to 630 K. The maximum relative sensitivity reaches 2.88% K−1 at 300 K, which is better than the previous results reported. Moreover, the repeatability of the integrated intensity of 5D4 emission of Tb3+ under eight consecutive heating-cooling cycles indicates that the sample has a good reliability and reusability. All results suggest that the 20% Tb3+ doped transparent Ba2LaF7 glass ceramics are one of the excellent candidate materials for optical thermometers.