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

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-1D:Eu) is transformed into soluble methacrylate (-OMc) coordinated [Bi38O45(OMc)24(dmso)4]:Eu·4dmso·4H2O (C-2D:Eu) and [Bi38O45(OMc)24(EtOH)10]:Eu·4EtOH (C-2E:Eu) by ligand exchange and without changing the amount of Eu3+ doping (ω ≈ 1%). Based on SC XRD analysis of C-1D:Eu and C-2E: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-2D:Eu) to 65 % (C-1D:Eu). The solubility of C-2E: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-2E:Eu, showing distinct photoluminescence characteristics even with a low Eu3+ content of 2.7·10-5 mol%.