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

•Hexagonal NaGdF4 nanocrystals embedded bulk glass ceramics were fabricated.•The incorporation of Ln3+ dopants into the β-NaGdF4 lattice was demonstrated.•Upconversion luminescence was highly intensified after glass crystallization.•Such glass ceramics had possible application in the optical temperature sensors.

Lanthanide doped hexagonal β-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 β-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 β-NaGdF4 crystalline lattice with low phonon energy and high crystallinity after crystallization. Furthermore, the temperature-dependent green upconversion emissions assigned to 2H11/2 → 4I15/2 (520 nm) and 4S3/2 → 4I15/2 (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.

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