Synthesis, crystal structures and spectroscopic properties of pure YSb2O4Br and YSb2O4Cl as well as Eu3+- and Tb3+-doped samples

Abstract

The quaternary halide-containing yttrium(III) oxidoantimonates(III) YSb₂O₄Cl and YSb₂O₄Br were synthesised through solid-state reactions from the binary components (Y₂O₃, Sb₂O₃ and YX₃, X = Cl and Br) at 750 °C in evacuated fused silica ampoules with eutectic mixtures of NaX and CsX (X = Cl and Br) as fluxing agents. YSb₂O₄Cl crystallizes tetragonally in the non-centrosymmetric space group P42₁2 with unit-cell parameters of a = 773.56(4) pm and c = 878.91(6) pm, whereas YSb₂O₄Br is monoclinic (space group: P2₁/c) with a = 896.54(6) pm, b = 780.23(5) pm, c = 779.61(5) pm and β = 91.398(3)°, both for Z = 4. The two new YSb₂O₄X compounds contain [YO₈]¹³⁻ polyhedra, which are connected via four common edges to form layers (d(Y³⁺–O²⁻) = 225–254 pm) without any Y³⁺⋯X⁻ bonds (d(Y³⁺⋯X⁻) > 400 pm). Moreover, all oxygen atoms belong to ψ¹-tetrahedral [SbO₃]³⁻ units, which are either connected to four-membered rings [Sb₄O₈]⁴⁻ in the chloride (Y₂[Sb₄O₈]Cl₂ for Z = 2) or endless chains in the bromide (Y_1/2(SbO₂)Br_1/2 for Z = 8) by common vertices. With distances of 307 pm in YSb₂O₄Cl and 326 pm in YSb₂O₄Br there are not even substantial bonding Sb³⁺⋯X⁻ (X = Cl and Br) interactions at work. Luminescence spectroscopy on samples doped with trivalent europium and terbium showed an energy transfer from the oxidoantimonate(III) moieties as the sensitizer in the host structure onto the lanthanoid activators.