Lighting Up Two-Dimensional Lanthanide Phosphonates: Tunable Structure–Property Relationships toward Visible and Near-Infrared Emitters

Abstract

We report the solvothermal synthesis and characterization of the structure, morphology, and photoluminescence properties of a series of unprecedented layered, organic–inorganic lanthanide (LnIII) phosphonates based on tert-butyl- (Bu t ), 1-naphthalene (Naph)- and 4-biphenyl (Biphen)-phosphonic acid. Through systematic variation of the ligand and the LnIII, we discuss the key structure–property relationships that must be managed for the design of Ln-phosphonates with tailored functionality. Single crystal and X-ray powder diffraction studies revealed that the size and shape of the employed ligand affects the type of layered material that forms. In agreement with their molecular structures, two distinct crystal morphologies are observed, 1D nanorods and 2D platelets, demonstrating that the anisotropy in the crystal structure and the variable coordination behavior of the ligands is directly translated to the crystal growth. Judicious selection of the ligand enables us to switch-on Ln-centered photoluminescence in both the visible (EuIII, TbIII) and near-infrared (NdIII and YbIII) spectral regions. Notably, the presented Yb-phosphonates are rare examples of phosphonate-based near-infrared emitters. Furthermore, the EuIII spectral fingerprint provided unique insight into the coordination environment of the metal center, facilitating structural characterization where X-ray diffraction analysis was limited.