Electron paramagnetic resonance and photoluminescence investigation of europium local structure in oxyfluoride glass ceramics containing SrF2 nanocrystals

Different compositions of europium doped aluminosilicate oxyfluoride glass ceramics prepared in air atmosphere have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy methods. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements show presence of homogenously distributed SrF₂ nanocrystals after the heat treatment of the precursor glass. Efficient Eu³⁺ incorporation in the high symmetry environment of glass ceramics is observed from the photoluminescence spectra. EPR spectra indicate Eu³⁺ → Eu²⁺ reduction upon precipitation of crystalline phases in the glass matrix. For composition abundant with Eu²⁺ in the glassy state such behaviour is not detected. Local structure around europium ions is discussed based on differences in chemical compositions.