Schematic representation

Schematic combination of the new coordination polymer (centre) from the local environments of the typical matrix materials (oxides (right) and fluorides (left)) for the doping of lanthanides

Source: BAM, division Biophotonics

Lanthanoid compounds are important for various applications such as analytical sensors and non-linear optics. Here, the material class of coordination polymers plays a decisive role because of its modularized structure system. The modularized structure makes it possible to adapt and optimize the crystal structures to the desired application quickly and easily. However, main group oxides and fluorides are preferred matrix materials for Ln3+-doped materials because of their low phonon energy and large band gap (high ionic character). More recently, however, fluorine-containing coordination polymers have increasingly become the focus of research. These allow the combination of the local environment of the main group oxides and fluorides in a coordination polymer. In this article, firstly, lanthanide-doped coordination polymers (CPs) with different bonding motifs, which were synthesized mechanochemically, are discussed and, secondly, the influence of the different fluorine positions in the structure on the decay time τ of the excited states is investigated. Fluorine can be integrated into the network via a fluorinated organic linker, here barium tetrafluorooterephthalate Ba(p-BDC-F4)2, or directly via a metal-fluorine bond (barium terephthalate fluoride BaF(p-BDC)0.5). The CP with a metal-fluorine bond shows the highest lifetime of the excited states of the lanthanides (Eu3+, Tb3+ or Eu3+&Tb3+). The excitation of the lanthanides can be done directly via the excitation wavelength typical for lanthanides and via the excitation wavelength of the linker. This allows the simultaneous excitation of Eu3+ and Tb3+ in one CP. In the emission spectra (λem=393 nm) of the mixed doped CPs (Eu3+ and Tb3+), the bands of both lanthanides can be observed. The incorporation into the crystal lattice and the homogeneous distribution of the lanthanides in the CPs are shown by X-ray diffraction, TEM, STEM-EDS measurements and the long decay times. Thus, this article connects to one classical matrix materials with the nine fluorinated coordination polymers.

Luminescent properties of Eu3+/Tb3+ doped fluorine containing coordination polymers
S. Zänker, G.Scholz, T. Krahl, C. Prinz, F. Emmerling, E. Kemnitz
published in Science Direct, Vol. 117, July 2021, page 106614
BAM, division Biophotonik and division Structure Analysis