Crystal structures and luminescence properties of novel compounds K 4 M 2 [Al 2 Si 8 O 24 ] ( M = Ce, Gd)
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CTURE OF INORGANIC COMPOUNDS On the 70th Anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences
Crystal Structures and Luminescence Properties of Novel Compounds K4M2[Al2Si8O24] (M = Ce, Gd) S. M. Aksenova, V. A. Rassulovb, R. K. Rastsvetaevaa, and V. K. Taroevc a
Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia email: [email protected] b Fedorovsky AllRussian Research Institute of Mineral Resources, Russian Academy of Sciences, Moscow, 119017 Russia c Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033 Russia Received February 6, 2013
Abstract—Two novel potassium rare earth silicates, obtained by hydrothermal synthesis, have been investi gated by Xray diffraction and described by the general formula K4M2[Al2Si8O24] (M = Ce, Gd). The param eters of the monoclinic K4Ce2[Al2Si8O24] and K4Gd2[Al2Si8O24] cells are, respectively, as follows: a = 26.867(1), 26.6520(2) Å; b = 7.4150(2), 7.2854(1) Å; c = 14.910(1), 14.8182(1) Å; β = 123.52(1)°, 123.46(1)°; and sp. gr. P21/n. The structures are solved by the charge flipping method and refined in the anisotropic approximation of thermal vibrations for atoms to R = 5.2 and 2.5%, respectively. The compounds under study are crystallized into a new structural type, which is based on twolevel [Al2Si8O24] layers, com bined into a threedimensional framework by columns of edgesharing sevenvertex REE polyhedra. Potas sium atoms are located in the framework channels. The spectral luminescence characteristics are determined. The luminescence bands are typical of Gd3+ and Ce3+ ions. Upon excitation by light with λexc = 246 nm, a band due to the 2D → 8F5/2 transition with λmax = 430 nm is observed in the spectrum of K4Ce2[Al2Si8O24] and a band related to the 6P7/2 → 8S7/2 transition with λmax = 311 nm is observed in the spectrum of K4Gd2[Al2Si8O24]. DOI: 10.1134/S1063774513060023
INTRODUCTION Currently, the interest in alkaline microporous rare earth silicates is caused by their photoluminescence and ionexchange properties. This study continues the systematic investigations of the hydrothermal synthe sis and structure of alkaline rare earth silicates to establish the conditions for incorporating lanthanides into solid phases. Previously, europiumcontaining compounds were synthesized and studied. Eu3+containing phases were synthesized in Cu containers under oxidative condi tions corresponding to the Cu–Cu2O buffer associa tion. Their structures have layered [Si6O15] and ribbon [Si6O17] and [Si8O21] motifs [1]. The europiumcon taining phase, synthesized under reducing conditions (corresponding to the Ni–NiO buffer pair), is charac terized by a framework structure composed of silicon– oxygen nanotubulenes [2]. In this study, we obtained K4Ce2[Al2Si8O24] and two novel phases, K4Gd2[Al2Si8O24], by hydrothermal synthesis and studied their crystal structures and luminescence properties. SYNTHESIS AND ANALYSIS OF SAMPLES
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