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 degrees C results in precipitation of nickel titanate-zirconate xNiO center dot yTiO(2 center dot)zZrO(2) nanocrystals with Ni2+ ions entering octahedral sites. Optical absorption of samples treated at 800-1100 degrees 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 T-3(2g)(3F) -> (3)A(2g)(F-3) transition of Ni-[6](2+) ions (FWHM more than 200 nm, centered at similar to 1.2 mu m) 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. (C) 2013 Elsevier B.V. All rights reserved.