Novel Sol-Gel Route to Prepare Eu 3+ -Doped 80SiO 2 -20NaGdF 4 Oxyfluoride Glass-Ceramic for Photonic Device Applications.

Oxyfluoride glass-ceramics (OxGCs) with the molar composition 80SiO ₂ -20(1.5Eu ³⁺ : NaGdF ₄ ) were prepared with sol-gel following the "pre-crystallised nanoparticles route" with promising optical results. The preparation of 1.5 mol % Eu ³⁺ -doped NaGdF ₄ nanoparticles, named 1.5Eu ³⁺ : NaGdF ₄ , was optimised and characterised using XRD, FTIR and HRTEM. The structural characterisation of 80SiO ₂ -20(1.5Eu ³⁺ : NaGdF ₄ ) OxGCs prepared from these nanoparticles' suspension was performed by XRD and FTIR revealing the presence of hexagonal and orthorhombic NaGdF ₄ crystalline phases. The optical properties of both nanoparticles' phases and the related OxGCs were studied by measuring the emission and excitation spectra together with the lifetimes of the ⁵ D ₀ state. The emission spectra obtained by exciting the Eu ³⁺ -O ^2- charge transfer band showed similar features in both cases corresponding the higher emission intensity to the ⁵ D ₀ → ⁷ F ₂ transition that indicates a non-centrosymmetric site for Eu ³⁺ ions. Moreover, time-resolved fluorescence line-narrowed emission spectra were performed at a low temperature in OxGCs to obtain information about the site symmetry of Eu ³⁺ in this matrix. The results show that this processing method is promising for preparing transparent OxGCs coatings for photonic applications.