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

Three new lanthanide silicates K(1.25)Gd(1.25)Si(2.5)O(7.5) (denoted as GdSiO-CJ7), Cs(3)TbSi(8)O(19)·2H(2)O (denoted as TbSiO-CJ8), and Cs(3)DySi(6)O(15) (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 LnO(n) polyhedra to form novel lanthanide silicate frameworks. The structure of GdSiO-CJ7 consists of unbranched silicate chains [Si(5)O(15)](10-) extending along the b axis, which are linked together by edge-sharing linked GdO(6) and GdO(8) 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 [Si(8)O(19)](6-) built up from SiO(4) tetrahedra, which are linked together via TbO(6) 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 [Si(6)O(15)](6-) with 6-rings, where DyO(6) 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.