The remarkable optomagnetic properties of the lanthanides (Ln) make Ln-based materials ideal for biomedical applications, including diagnostic and therapeutic approaches. This is due the unique electronic properties of the Ln (f-elements) allowing for upconversion and near-infrared emission under near-infrared excitation as well as high magnetic moments. Sodium lanthanide fluorides (NaLnF4) are our favorite materials, and we developed a fast and reliable microwave-assisted synthetic approach allowing crystalline phase and size control in the sub 20 nm realm. Having a fast and reliable synthetic route towards NaLnF4 NPs on hand, we now explore various nanoparticle architectures and compositions with the goal to optimize their optomagnetic properties, ultimately resulting in the design of biocompatible multimodal bioprobes. This includes MRI and CT contrast agents based on Gd- and Dy-containing NPs, and novel near-infrared emitters based on Ho or Pr for deep tissue optical bioimaging under near-infrared illumination, matching the biological transparency windows.