Crystal structure of sodium rare earth oxyborates Na2Ln2(BO3)2O (Ln = Sm, Eu, and Gd) and optical analysis of Na2Gd2(BO3)2O:Eu3+

A new structural family of rare earth oxyborates Na(2)Ln(2)(BO3)(2)O (Ln = Sm, Eu and Gd) is evidenced, The structure, determined by single crystal X-ray diffraction, is monoclinic, space group P2(1)/c, Z=4, with a 10.695(6) Angstrom, b = 6.320(4) Angstrom, c = 10.328(6) Angstrom, beta = 117.80(4)degrees, V = 617.5(9)Angstrom(3), R-1 = 0.039, wR(2) = 0.101 for Na2Gd2(BO3)(2)O. The three-dimensional network is built up from infinite sheets of LnO(8) polyhedra in the (b,c) plane, which are separated by sodium ions. The luminescence of trivalent europium in polycrystalline Na2Gd2(BO3)(2)O: Eu3+ is analysed at 77K, The low symmetry of the rare earth sites, deduced from the X-ray diffraction study, is confirmed, The crystal field strength is high for both europium sites. (C) 1999 Academic Press.