Trivalent titanium ions (Ti3+) are known for their broadband emission in the visible and near-IR. Zinc aluminate spinel, or gahnite (ZnAl2O4) is known as a host matrix for transition-metal ions. We report on the structure and spectroscopic properties of transparent zinc aluminosilicate glass-ceramics (GCs) nucleated by TiO2 and based on Ti3+-doped ZnAl2O4 nanocrystals. The initial glasses were melted under different redox conditions. After heat-treatments at the temperatures in the range of 720 to 1100 °C, transparent GCs were obtained. The materials were studied by the DSC method, XRD analysis, Raman, absorption and luminescence spectroscopy. The main crystalline phase in GCs is ZnAl2O4 with a cubic structure. The crystals are 5 - 21 nm in size. Their unit cell parameters vary with the heat-treatment temperature due to the titanium ions entering the gahnite nanocrystals. The volume fraction of gahnite nanophase increases with the heat treatment temperature. At 1000 – 1100 °C, TiO2 (rutile) crystals with a size of 11 - 37 nm also appear. In GCs obtained from glasses melted under reducing conditions, broadband absorption is observed in the visible and near IR due to the Ti3+ ions in Oh positions in ZnAl2O4 crystals, the absorption of Ti3+ - Ti4+ pairs and the appearance of Ti3+ self-doped rutile. By changing the redox conditions of the glass synthesis, one can control the content of titanium ions in various oxidation states and the spectral properties of GCs.
We report on fabrication, structure, spectroscopic and nonlinear properties of a new functional optical material – transparent glass-ceramics (GCs) based on Co2+,Ga3+-codoped ZnO (Co2+:GZO) nanocrystals. The introduction of Ga3+ cations that are smaller than Zn2+ ones and have a different valence state, is expected to modify the crystal field around the Co2+ ions leading to broadband absorption at the 4A2(4F) → 4T1(4F) transition. The glass of the ZnO – K2O – Al2O3 – SiO2 system was doped with 3 mol% Ga2O3 and 0.05 mol% CoO. Transparent GCs were produced by secondary heattreatments at 680 – 860 °C. They contained one crystalline phase - nanosized (8 – 26 nm) hexagonal GZO crystals, Ga3+ ions being distributed between the ZnO nanocrystals and the residual glass. The absorption spectra of GCs contained an intense band at 1.3-1.65 μm related to the 4A2(4F) → 4T1(4F) Co2+ transition in Td sites. A rise of IR losses due to the free charge carrier scattering in GZO was observed. Absorption saturation of transparent GCs was studied at ~1.54 μm. They exhibited low saturation fluence, 0.7–1.3 ± 0.2 J/cm2, and high laser-induced damage threshold, ~25 J/cm2. Co2+,Ga3+- codoped ZnO-based transparent GCs are promising for passive Q-switching of eye-safe erbium lasers emitting at ~1.5- 1.7 μm.
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