Crystal Structure and Fluorescence Properties of R₂Zr₂O₇ and (R_1-xEu_x)₂Zr₂O₇ Compounds

Abstract

R₂Zr₂O₇ and (R_1-xEu_x)₂Zr₂O₇ (R=La, Pr, Sm, Eu, Gd, Tb, Er, Y) were prepared at 1600°C in air and their fluorescence properties were studied. The crystal structures of these compounds were pyrochlorite-type for the light rare earths and CaF₂-type for the heavy rare earths, respectively. However, Gd₂Zr₂O₇ and Y₂Zr₂O₇ showed broad and small (111) X-ray diffraction peaks which were characteristic of the pyrochlorite-type structure. Further, annealing at 1500°C increased the intensity and the sharpness of the (111) peak of Gd₂Zr₂O₇. When the compounds were excited by the 254nm line, only the Eu-doped La₂Zr₂O₇, Gd₂Zr₂O₇ and Y₂Zr₂O₇ showed emission spectra due to Eu³⁺ ions. These spectra and X-ray diffraction, showed that in La₂Zr₂O₇ almost all rare earth ions occupy D_3d symmetry sites, but in Y₂Zr₂O₇ and Gd₂Zr₂O₇ most rare earth ions occupy most of the Oh symmetry sites and partially the D_3d sites.