Synthesis and Crystal Structure Analysis of Multinary Germanates and Stanates Containing Rare-earth Elements

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New compounds CaY_2Ge_3O_<10>, CaY_2Ge_4O_<12>, Ca_<0.8>Y_<2.4>Sn_<0.8>O_6, Ca_<1.5>Eu_3Sn_<0.5>O_7 were synthesized in the systems of rare-earth-Ca-Ge/Sn-O by solid state reaction at 1000 - 1500℃ in air. Single crystals of these compounds were obtained by annealing or by slow cooling of partially melted samples. The crystal structures of these new compounds were analyzed by the single crystal X-ray diffraction method. CaY_2Ge_4O_<12> is isotypic with SrNa_2P_4O_<12>, CaY_2Ge_3O_<10> crystallizes in a novel structure where Ca and Y atoms are situated disorderly in three 7-fold coordination sites between isolate germinate groups of triple GeO4 tetrahedra, Ca_<0.8>Y_<2.4>Sn_<0.8>O_6 is isotypic with Mg_3TeO_6, and Ca_<1.5>Eu_3Sn_<0.5>O_7 crystallizes in a novel structure which is related to the structure of B-form Eu_2O_3.Ca_<0.8>(Y_<1-x>Eu_x)_<2.4>Sn_<0.8>O_6 (0.0〓x<0.3) Ca_<0.8>Y_<2.4>Sn_<0.8-y>Ti_yO_6 (0.0〓y〓0.24) and Ca_<0.8>(Y_<0.9>)Eu_<0.1>)_<2.4>Sn_<0.8-y>Ti_yO_6(0.0〓y〓0.16) were prepared and investigated their luminescence properties. Under ultraviolet light irradiation of 250-264 nm, Ca_<0.8>(Y_<0.9>)Eu_<0.1>)_<2.4>Sn_<0.72>Ti_<0.08>O_6 and Ca_<0.8>(Y_<0.9>Eu_<0.1>)_<2.4>Sn_<0.8>O_6 showed bright red emission of 614 nm due to the ^5Do^<-7>F_2 transition of Eu^<3+>. A broad emission peak of Ti^<4+> centered at 450 nm was observed for Ca_<0.8>Y_<2.4>Sn_<0.72>Ti_<0.08>O_6, suggesting the possibility of energy transfer from Ti^<4+> to Eu^<3+>.