Atomically Precise Bismuth Oxido Nanoclusters as Hosts for Ln$^{3+}$: Effects of Doping on Optical and Magnetic Properties of a Soluble Metal Oxide

A series of lanthanoid-doped bismuth oxido nanoclusters (BiO-NCs) of the type [Bi$_{38}$O$_{45}$(NO$_3$)$_{24}$(dmso)$_y$]:Ln (C-1:Ln; Ln$^{3+}$ = La – Lu, ≠ Pm; y = 26–28) including isostructural host and doped structures is reported. Successful doping with ≈1 ω% of the BiO-NCs was demonstrated by ICP-OES, ESI-MS, and exemplarily by SC XRD analysis for C-1:Gd and C-1:Dy. The dopants are statistically albeit nonuniformly distributed on the lattice position of Bi$^{3+}$ and change the optical and magnetic properties of the BiO-NC host material. Altered optical properties (UV–vis and PL) were demonstrated with special focus on C-1:Er, C-1:Yb, and C-2d:Dy showing dual Bi$^{3+}$ and the Ln$^{3+}$ specific PL emissions, resulting in characteristic emission combinations over a wide wavelength range from visible to the NIR region and lifetimes up to 0.5 ms. Starting from C-1:Gd and C-1:Dy the methacrylate-substituted BiO-NCs [Bi$_{38}$O$_{45}$(OMc)$_{24}$(EtOH)$_{14}$]:Gd (C-2$_E$:Gd) and [Bi$_{38}$O$_{45}$(OMc)$_{24}$(EtOH)$_{14}$]:Dy (C-2E:Dy) were synthesized to finally give solvate-free [Bi$_{38}$O$_{45}$(OMc)$_{24}$]:Ln (C-2$_d$:Gd, C-2$_d$:Dy) after drying. The introduction of paramagnetic behavior in the BiO-NC diamagnetic host structure was confirmed by SQUID measurements. We further investigated the suitability of Gd$^{3+}$ in C-2$_d$:Gd as a polarization agent for dynamic nuclear polarization (DNP)-enhanced MAS NMR experiments, which resulted in a proton enhancement factor of approximately 10.