Bulk glass ceramics containing Yb3+/Er3+:β-NaGdF4 nanocrystals: Phase-separation-controlled crystallization, optical spectroscopy and upconverted temperature sensing behavior

Lanthanide doped hexagonal beta-NaGdF4 nanocrystals embedded transparent bulk glass ceramics were successfully fabricated via a phase-separation-controlled crystallization route. Elemental mapping in the scanning transmission electron microscope and optical spectroscopy analysis demonstrated the partition of the active centers into the beta-NaGdF4 crystalline lattice. As a result, upconversion luminescence of the glass ceramic co-doped with Yb3+ and Er3+ is about 60 times as high as that of the precursor glass, attributing to the modification of Yb3+/Er3+ surrounding from phase-separated amorphous nanoparticle to b-NaGdF4 crystalline lattice with low phonon energy and high crystallinity after crystallization. Furthermore, the temperature-dependent green upconversion emissions assigned to H-2(11/2) -> I-4(15/2) (520 nm) and S-4(3/2) -> I-4(15/2) (540 nm) transitions were investigated, and the corresponding fluorescence intensity ratio of these two thermally coupled emitting-states greatly enhanced with increase of temperature. Using such fabricated glass ceramic as an optical thermometric medium, the maximum sensitivity reached as high as 0.0037 K-1 at 580 K. It is expected that the investigated Er3+/Yb3+ codoped glass ceramic might be a very promising candidate for accurate optical temperature sensors. (C) 2015 Elsevier B.V. All rights reserved.