Novel open-framework europium silicates prepared under high-temperature and high-pressure conditions
Two new europium silicates, Na15Eu3Si12O36 (denoted as 1) and K2EuSi4O10F (denoted as 2), were successfully synthesized under high-temperature and high-pressure conditions, and structurally characterized by single-crystal and powder X-ray diffraction (XRD). The single-crystal XRD analysis of 1 reveals that its structure is based on [Si6O18]n12n− cyclosilicate anions that are built from six SiO4 tetrahedra sharing two of their four O corners with each other. Such [Si6O18]n12n− cyclosilicate anions are linked via EuO6 octahedra to form a three-dimensional (3D) framework containing 6-membered ring channels delimited by the SiO4 tetrahedra and EuO6 octahedra along the  direction. The structure of 2 consists of infinite tubular chains of corner-sharing SiO4 tetrahedra, which are further linked together via corner sharing O atoms by infinite chains of EuO4F2 octahedra forming a 3-D framework that contains 8-ring and 6-ring channels along the  direction. The photoluminescence properties of 1 and 2 were also investigated.