Synthesis, crystal structures and optical properties of open-framework gallium phosphates: NaGa3F4(PO4)(2)(H2O)(2) and AGa(2)P(2)O(7)(OH)(3)(H2O) (A = K, Rb)

Abstract

Three new alkali-metal gallium phosphates NaGa3(PO4)2F4(H2O)2 (1), KGa2P2O7(OH)3(H2O) (2), and RbGa2P2O7(OH)3(H2O) (3) were obtained using hydrothermal methods. Compound 1 crystallizes in the chiral space group P43212. The structure of 1 features a three-dimensional (3D) framework composed of 2D layers of corner-sharing GaO4F2 and GaO2F4 octahedra that are further bridged by PO4 tetrahedra with Na+ cations residing in the oxyfluorinated gallolayers. Compounds 2 and 3 are isostructural, both crystallizing in the centrosymmetric space group P21/c; their structures consist of novel 3D gallophosphate frameworks constructed from Ga4O20 tetramers interconnected by PO4 units with 8-membered ring channels along the b-axis, in which K+/Rb+ cations are located. The diffuse reflectance spectra show that the ultraviolet (UV) cut-off edges are about 292 ​nm (4.25 ​eV), 275 ​nm (4.51 ​eV) and 306 ​nm (4.05 ​eV) for 1-3, respectively. Luminescent studies suggest that 1-3 emit blue light under the excitation of near-ultraviolet light. Show more