Influence of NiO on phase transformations and optical properties of ZnO-Al2O3-SiO2 glass-ceramics nucleated by TiO2 and ZrO2. Part II. Optical absorption and luminescence

Absorption and luminescence of nickel-containing ZnO-Al2O3-SiO2 glasses and glass-ceramics nucleated by TiO2 and ZrO2 were investigated for variable NiO content and heat-treatment conditions. Ni2 + ions in the as-cast glasses are predominately five-fold coordinated. Heat-treatment of glasses containing 1-3 mol.% NiO at 730-800 °C results in precipitation of nickel titanate-zirconate xNiO·yTiO2·zZrO2 nanocrystals with Ni2 + ions entering octahedral sites. Optical absorption of samples treated at 800-1100 °C is determined by precipitation of gahnite nanophase with Ni2 + ions entering both octahedral and tetrahedral sites and minor fraction of ions remaining in the residual glass phase. These samples are characterized by strong near-IR luminescence associated with 3T2g(3F) → 3A2g(3F) transition of [6]Ni2 + ions (FWHM more than 200 nm, centered at ~ 1.2 μm) in gahnite nanocrystals. Luminescence intensity increases substantially with the increase of heat-treatment temperature due to increase of volume fraction of gahnite nanophase and size of gahnite nanocrystals (which in turn causes decrease of relative fraction of Ni2 + ions located near the nanocrystal surface and suppresses the non-radiative relaxation path), the second factor is the dominant one. Concentration of NiO has dramatic effect on the luminescence efficiency of glass-ceramics due to a strong temperature and concentration quenching.