New Lanthanide Silicates Based on Anionic Silicate Chain, Layer, and Framework Prepared under High-Temperature and High-Pressure Conditions

Three new lanthanide silicates K1.25Gd1.25Si2.5O7.5 (denoted as GdSiO-CJ7), Cs3TbSi8O19·2H2O (denoted as TbSiO-CJ8), and Cs3DySi6O15 (denoted as DySiO-CJ9) were synthesized by using a high-temperature and high-pressure hydrothermal method. Their structures determined by single-crystal X-ray diffraction revealed anionic silicate chain, layer and framework, which are further connected with LnOn polyhedra to form novel lanthanide silicate frameworks. The structure of GdSiO-CJ7 consists of unbranched silicate chains [Si5O15]10- extending along the b axis, which are linked together by edge-sharing linked GdO6 and GdO8 chains along the c axis to form a 3-D framework with two types of 10-ring channels along the [010] and [001] directions, respectively. The structure of TbSiO-CJ8 consists of double 4,8-net sheets [Si8O19]6- built up from SiO4 tetrahedra, which are linked together via TbO6 octahedra to form a 3-D framework with 8-ring channels along the [100] and [010] directions. The structure of DySiO-CJ9 is based on a 3-D silicate framework [Si6O15]6- with 6-rings, where DyO6 octahedra are located between two adjacent 6-rings and connected with six Si atoms via O atoms. The photoluminescence photoluminescence properties of TbSiO-CJ8 and EuSiO-CJ8 were investigated.