Optically active and highly coherent emitters in solids are a promising platform for building practical quantum computers and networks. Rare-earth atoms have several important properties for building practical quantum photonic devices, including record long coherence times and the ability to be hosted in a wide range of solid-state materials. We target particular materials (and choose particular rare-earth species and isotopes) that enable certain application-specific functionalities. I will present recent results from our lab on studying rare-earth atoms in different host materials and configurations. This includes characterizing new stoichiometric rare-earth crystals with narrow linewidths and record high emitter densities, as well as photonic integration of rare-earth doped materials in chip-scale platforms.