Isomorphous substitution and luminescence properties of haloapatites synthesized by the low-temperature method
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RYSTAL GROWTH
Isomorphous Substitution and Luminescence Properties of Haloapatites Synthesized by the Low-Temperature Method Yu. N. Savin, N. V. Babayevskaya, and A. V. Tolmachev Scientific Technical Center Institute for Single Crystals, National Academy of Sciences of Ukraine, Kharkiv, 61001 Ukraine e-mail: [email protected] Received November 3, 2006
Abstract—Single-phase polycrystalline fluorapatites of the Ca10 – xMex(PO4)6F2:Eu3+ (Me = Pb, Mg) composition are obtained by deposition from aqueous solutions. The effect of modifier ions (Pb2+, Mg2+) with significantly different ionic radii on the structure and spectral luminescence properties of the fluorapatites are studied. It is established that Pb2+ and Mg2+ ions affect the preferred location of Eu3+ ions in the structure of Ca10 – xMex(PO4)6F2 crystals. PACS numbers: 81.10.Dn DOI: 10.1134/S1063774508070274
INTRODUCTION Apatites and apatite-like structures (Me10(ZO4)6X2) activated by rare-earth element (REE) ions have a set of unique properties, making them promising for various physical and physicochemical applications. First, apatites allow a large variety of isomorphous and nonisomorphous substitutions. Second, owing to the presence of a strong intracrystalline field in REE-activated apatites, these materials exhibit a significant multiplet splitting. In addition, the presence of different nonequivalent sites in the apatite crystal lattice allows one to introduce activators with different ionic radii and charge states. Finally, REE ions in such structures have large absorption and luminescence cross sections; hence, they can be applied in design of lasers, plasma displays, and converters for light sources [1, 2]. Currently, despite the significant number of studies on the synthesis (mainly, by the conventional solid-phase method) and investigation of apatites, low-temperature methods (in particular, synthesis from aqueous solutions) are actively developed in view of the development of organic–inorganic composites Apatites (including haloapatites) activated with ions of different metals have been widely investigated [3–6]. However, the effect of physicochemical synthesis conditions on the processes of formation and growth of I II apatites of mixed composition Me 10 – x Me x (PO4)6F2 (MeI = Ca, MeII = Pb, Mg) from aqueous solutions and their phase composition, structure, and spectral luminescence properties have been inadequately studied. In this paper, we report the results of investigation of the effect of modifier ions (Pb2+, Mg2+) on the structure and spectral luminescence properties of calcium fluora-
patites (FAs) obtained by the low-temperature method from supersaturated aqueous solutions. EXPERIMENTAL The initial sample of apatites of mixed composition Ca10 – xMex(PO4)6F2:Eu3+ (Ca-FA:Eu3+) (Me = Pb, 0 ≤ x ≤ 10; Mg, 0 ≤ x ≤ 4) were obtained by deposition from mixed CaCl2, KH2PO4, and PbCl2 (MgCl2) aqueous solutions, containing KF in the presence of an acetate buffer. The solutions were mixed in a thermostated vessel at constant temperature a
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