Europium Doped Atomically Precise Bismuth Oxido Nanoclusters as Molecular Building Blocks for Photoluminescent Hybrid...

Structural and optical characterization of Eu³⁺ doped atomically precise bismuth oxido nanoclusters (BiO-NCs) of about 2 nm in size is reported. The BiO-NC [Bi₃₈O₄₅(NO₃)₂₄(dmso)₂₈]:Eu (C-1_D:Eu) is transformed into soluble methacrylate (^-OMc) coordinated [Bi₃₈O₄₅(OMc)₂₄(dmso)₄]:Eu·4dmso·4H₂O (C-2_D:Eu) and [Bi₃₈O₄₅(OMc)₂₄(EtOH)₁₀]:Eu·4EtOH (C-2_E:Eu) by ligand exchange and without changing the amount of Eu³⁺ doping (ω ≈ 1%). Based on SC XRD analysis of C-1_D:Eu and C-2_E:Eu partial substitution of the bismuth atoms with preference in the inner {Bi₆O₉} core of the {Bi₃₈O₄₅} cluster is suggested. Temperature dependent photoluminescence studies show bismuth- and europium-based dual emission at low temperatures, whereas only the latter is preserved at room temperature. As a result of the low-symmetry environment of Eu³⁺ a remarkable intensity of the ⁵D₀→⁷F₀ (electric dipole) transition is observed, accompanied by lifetimes of about 2 ms and quantum yields ranging from 53% (C-2_D:Eu) to 65 % (C-1_D:Eu). The solubility of C-2_E:Eu enables its use for the synthesis of organic-inorganic hybrid materials. Thus, transparent hybrid materials were prepared by radical copolymerization of methyl methacrylate, 2-hydroxyethyl methacrylate and C-2_E:Eu, showing distinct photoluminescence characteristics even with a low Eu³⁺ content of 2.7·10^-5 mol%.