Crystal structures and luminescence properties of La3Zr4F25 and α-LaZr3F15

Abstract

During a study of the LaF₃–ZrF₄ system, both La₃Zr₄F₂₅ and α-LaZr₃F₁₅ compounds have been evidenced. Their crystal structures have been determined from single-crystal X-ray diffraction data. La₃Zr₄F₂₅ crystallises in the cubic system with a=12.384 Å and I3d space group (no. 220). Its crystal structure is built up of (ZrF₆)^2– octahedra and (LaF₈)^5– dodecahedra sharing corners. The low temperature form, α , of LaZr₃F₁₅ is orthorhombic (space group Pmmn, no. 59) with a=15.721 Å, b=16.299 Å, c=8.438 Å. Its structure is built of corner-sharing tricaped trigonal prisms surrounding the La³⁺ ions and both octahedra and monocapped trigonal prisms encompassing the Zr⁴⁺ ions. This structure is characterised by dynamically disordered (ZrF₆)^2– complex anions.

The Eu³⁺ luminescence properties of these phases have been investigated and are discussed in relationship with their crystal structures.