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Description
Pale yellow crystals of $Ln$Sb$_2$O$_4$Br ($Ln$ = 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 $P2_1/c$. In contrast to hitherto reported quaternary lanthanoid(III) halide oxoantimonates(III) [1], in $Ln$Sb$_2$O$_4$Br the lanthanoid(III) cations are exclusively coordinated by oxygen atoms in the shape of square hemiprisms. These [$Ln$O$_8]^{13−}$ polyhedra form layers parallel to the (100) plane by sharing common edges as shown in Figure 1. All antimony(III) cations are coordinated by three oxygen atoms forming ψ$^1$-tetrahedral [SbO$_3]^{3−}$ units, which have oxygen atoms in common building up meandering strands along [001] (Figure 2) according to 1D-{[SbO$^v_{2/2}$O$^t_{1/1}]^–$} (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 $Ln^{3+}$ cations. Since Sb$^{3+}$ is known to be an efficient sensitizer for $Ln^{3+}$ emission, photoluminescence studies were carried out to characterize the optical properties and assess their suitability as light phosphors. Indeed, for both, GdSb$_2$O$_4$Br and TbSb$_2$O$_4$Br doped with about 1.0 – 1.5 at-% Eu$^{3+}$ efficient sensitization of the Eu$^{3+}$ emission could be detected. The resulting luminescence properties of both doped and undoped GdSb$_2$O$_4$Br and TbSb$_2$O$_4$Br are summarized in Figure 3. For TbSb$_2$O$_4$Br, in addition, a remarkably high energy transfer from Tb$^{3+}$ to Eu$^{3+}$ could be detected that leads to a substantially increased Eu$^{3+}$ emission intensity, rendering it an efficient red light emitting material [2].
References
[1] F. C. Goerigk, Th. Schleid, Z. Anorg. Allg. Chem. 2019, 645, 1079–1084.
[2] F. C. Goerigk, V. Paterlini, K. V. Dorn, A.-V. Mudring, Th. Schleid, Crystals 2020, 10, 1089–1111.
