Structural and optical properties of ZnO–Al2O3–SiO2 system glass–ceramics containing Ni2+-doped nanocrystals

Transparent glass–ceramics were prepared from Ni2+-doped ZnO–Al2O3–SiO2 (ZAS) system glasses by annealing. The color of the glasses drastically changed from brownish yellow to green by annealing. The crystalline phase being precipitated by annealing was identified as solid solutions of spinel compounds. The crystalline sizes estimated by transmission electron microscope observation in Ni2+-doped post-annealed glasses were about 10–15 nm in diameter, while that in non-doped post-annealed glasses were 5–10 nm. This suggests that Ni2+ ions in ZAS glass were incorporated into the crystalline phases as nucleation agents of crystallization. It was confirmed from optical absorption measurements that Ni2+ ions occupied fivefold sites in the as-cast glass, while Ni2+ ions occupied octahedral sites in the post-annealed glass. The Ni2+-doped post-annealed glasses exhibited near-infrared emission. It is thought that the crystals containing Ni2+ ions act as emission centers.