Enhanced luminescence of Eu3+ doped β-PbF2 oxyfluoride glass ceramics for a new optical thermometry by charge compensation and local lattice symmetry breaking

Abstract

Eu3+ doped β-PbF2 oxyfluoride glass ceramics (GCs) were synthesized via conventional melt-quenching method. The micro-morphology and luminescence properties of the fabricated GCs were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectra. A new temperature sensing mechanism based on fluorescence intensity ratio (FIR) between 5D0 → 7FJ (1, 2, 3, 4) and 5D0 → 7F0 transitions of Eu3+ ion was proposed. Such new mechanism is due to strong thermal coupling of 7FJ (J = 0, 1, 2, 3, 4) states because of their small energy gap. With the increase of temperature, more and more population reaches high states 7FJ (J = 1, 2, 3, 4) from 7F0 state through thermalization process leading to different temperature-dependent transitions of 5D0 → 7FJ (J = 0, 1, 2, 3, 4). Furthermore, lattice distortion around Eu3+ ions caused by co-doped K+ ions resulting in distinct enhancement of emission of Eu3+ ion and violent splitting of 7FJ (J = 2, 3, 4) states. Meanwhile, narrowing of energy gap between 7FJ (J = 0, 1, 2, 3, 4) states resulting from the violent splitting of 7FJ (J = 2, 3, 4) states facilitated thermalization process between 7FJ (J = 0, 1, 2, 3, 4) states and then enhanced sensitivity of temperature measurement was obtained. We believe that this preliminary study will provide an important advance in exploring other innovative optical thermometry.