Silica glass doped with Nd and Al prepared by sol-gel method. Change in the state of aluminium in the formation process

To determine the effect of Al₂O₃ on the homogeneous dispersion of neodymium in a silica glass doped with Al³⁺ and Nd³⁺ ions, the coordination states of Al³⁺ and Nd³⁺ ions were investigated by UV-VIS absorption spectroscopy and ²⁷Al NMR (solution and solid). In the formation process of a silica glass (2Nd₂O₃6Al₂O₃92SiO₂), the states of Al³⁺ and Nd³⁺ ions varied continuously. A local structure of Nd³⁺ ions in the silica glass was stabilized when the dried gel was heated to 300 °C. The symmetry of aluminium tetrahedra was strongly affected by a Nd³⁺ ion through a bond between neodymium and aluminium. Distortion of the aluminium tetrahedra became large with increase in temperature of heat treatment for the dried gel. It was concluded that the isolation of Nd³⁺ ions may be stabilized by distortion of the aluminium tetrahedra.