Luminescence, structure and antiferroelectric-type phase transition in Ca8ZnEu(P04)7

Photoluminescence excitation and emission spectra of new phosphate CasZnEu(P0(4))(7) have been investigated. The influence of the composition on the luminescence intensity has been shown. The substitution of Zn2+ for Ca2 + in Ca9Eu(P0(4))(7) with the formation of Ca8ZnEu(P0(4))(7) leads to the increased emission intensity D-5(0) -> F-7(2) by about 1.5 times and to decreased number of bands from three to one in the range of D-5(0) -> F-7(0) transition. Conditions of preparation do not influence the luminescent properties and distribution of Eu3+ cations in the structure. DSC, SHG data and dielectric spectroscopy reveal that Ca8ZnEu(P0(4))(7) belongs to antiferroelectrics (T-c = 836 K). The first-order antiferroelectric/paraelectric transformations are accompanied by a changing symmetry (R3c to R3m). The structure of Ca8ZnEu(P0(4))(7) (sp. gr. R3c) was refined by the Rietveld method. The Zn2+ cations occupy the M5 site. The Eu3+ and Ca2+ ions are located in the Ml and M3 sites of beta-Ca-3(P0(4))(2)-type structure.