Er-doped and Er, Yb co-doped oxyfluoride glasses and glass-ceramics, structural and optical properties

The selected glasses and glass-ceramics pertinent to following chemical composition in mol%:48%SiO₂-11%Al₂O₃-7%Na ₂O-10%CaO-10%PbO-11%PbF₂-3%ErF₃ and 48%SiO ₂-11%Al₂O₃-7%Na₂O-10%CaO-10%PbO- 10%PbF₂-1%ErF₃-3%YbF₃ have been manufactured from high purity components (Aldrich) at 1450 °C in normal atmosphere. Glass optical fibers were successfully drawn. Subsequently they were subject to the heat-treatment at 700 °C in various time periods. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. It has been observed that the controlled heat-treatment of oxyfluoride glass fibers results in the creation of Pb₅Al₃F₁₉, Er ₄F₂O₁₁Si₃ and Er₃FO ₁₀Si₃ crystalline phases. The identified phases were characterized by X-ray powder diffraction (XRD) and confirmed by selected area electron diffraction (SAED). The fibers consist of mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. Their morphology was investigated applying high-resolution transmission electron microscopy. Optical properties and excited state relaxation dynamics of optically active ions (Er³⁺, Yb³⁺) in glass and glass-ceramics have been studied. Based on absorption spectra the Judd-Ofelt analysis was carried out. The main attention was directed to NIR luminescence at. 1.6 μm related to ⁴I_13/2 → ⁴I_15/2 Er³⁺ and less effective emission associated with ⁴I_11/2 → ⁴I_15/2 Er³⁺ and ²F_5/2 → ²F _7/2 Yb³⁺ transitions. The dissimilar spectroscopic properties have been revealed for glasses and glass-ceramic samples, respectively. The reduction of emission linewidth at 1.6 and 1.0 μm combined with substantial increase of ⁴I_13/2 lifetimes of erbium in glass-ceramics appear to be evidences that Er³⁺ ions are accommodated in crystalline phases. The structural and optical characteristics of oxyfluoride glass-ceramic fibers indicate that these optical systems may be considered as promising materials for Er-doped optical amplifiers operating within third telecommunication window.