Synthesis and Crystal Structure of the Short Ln Sb 2 O 4 Br Series (Ln = Eu–Tb) and Luminescence Properties of Eu 3+ -Doped Samples.

Pale yellow crystals of LnSb₂O₄Br (Ln = Eu–Tb) were synthesized via high temperature solid-state reactions from antimony sesquioxide, the respective lanthanoid sesquioxides and tribromides. Single-crystal X-ray diffraction studies revealed a layered structure in the monoclinic space group P2₁/c. In contrast to hitherto reported quaternary lanthanoid(III) halide oxoantimonates(III), in LnSb₂O₄Br the lanthanoid(III) cations are exclusively coordinated by oxygen atoms in the form of square hemiprisms. These [LnO₈]¹³⁻ polyhedra form layers parallel to (100) by sharing common edges. All antimony(III) cations are coordinated by three oxygen atoms forming ψ¹-tetrahedral [SbO₃]³⁻ units, which have oxygen atoms in common building up meandering strands along [001] according to { [ SbO 2 / 2 v O 1 / 1 t ] – } ∞ 1 (v = vertex-sharing, t = terminal). The bromide anions are located between two layers of these parallel running oxoantimonate(III) strands and have no bonding contacts with the Ln³⁺ cations. Since Sb³⁺ is known to be an efficient sensitizer for Ln³⁺ emission, photoluminescence studies were carried out to characterize the optical properties and assess their suitability as light phosphors. Indeed, for both, GdSb₂O₄Br and TbSb₂O₄Br doped with about 1.0–1.5 at-% Eu³⁺ efficient sensitization of the Eu³⁺ emission could be detected. For TbSb₂O₄Br, in addition, a remarkably high energy transfer from Tb³⁺ to Eu³⁺ could be detected that leads to a substantially increased Eu³⁺ emission intensity, rendering it an efficient red light emitting material. [ABSTRACT FROM AUTHOR]