Europium doped transparent glass ceramics containing CaF2 micron-sized crystals: structural and optical characterization

Abstract

Transparent glass ceramics containing CaF₂ micron-sized crystals were prepared using a modified liquid-phase sintering route. The morphology and microstructural evolution of the CaF₂ crystals before and after liquid-phase sintering were examined using X-ray diffraction, field-emission scanning electron microscopy and transmission microscopy. After sintering at 800 °C for 10 min, the CaF₂ crystals were approximately 20 μm in size and were uniformly distributed throughout a precursor glass prepared using melt-quenching method. The glass ceramic containing CaF₂ micron-sized crystals prepared using liquid-phase sintering achieved the highest in-line transmittance of 76% in the visible region and 92% in the near-IR region. High near-IR transmittance of glass ceramics was attributed to the matching of the refractive index of the precursor glass with that of CaF₂ in the near-IR region. The luminescence properties and local environment of Eu³⁺ in the precursor glass and glass ceramic were investigated using photoluminescence spectra, photoluminescence lifetimes and phonon sideband spectroscopy, and the results determined that some of the Eu³⁺ ions in the precursor glass incorporate into CaF₂ micron-sized crystals after sintering and enter C_4v site symmetry.