Exciton diffusion in solid solutions of luminescent lanthanide β-diketonates

Local Environment-Modulated f-f Transition in Unit-Cell-Sized Lanthanide Ultrathin Nanostructures

The regulation of the f-f transition is the basis of utilizing the abundant optical properties of lanthanide (Ln), of which the key is to modulate the local environment of Ln ions. Here, we constructed Eu(III)-based unit-cell-sized ultrathin nanowires (UCNWs) with red luminescence and polymer-like behavior, which appears as an ideal carrier for regulating f-f transition. The f-f transition of Eu(III) in UCNWs could be precisely regulated through various ligands. It is the unusual surface states that make the UCNWs exhibit greater electric dipole strength and better sensitivity to various ligands compared with the carefully constructed ultrathin nanosheets. In addition, the possibility of regulating f-f transition in UCNWs through energy transfer and a high entropy strategy was also revealed. Finally, a temperature-dependent universal fluorescent ink was prepared based on UCNWs, which provides ideas for intelligent flexible fluorescent materials.

Mechanochemical Syntheses of Ln(hfac)3(H2O)x (Ln = La-Sm, Tb): Isolation of 10-, 9-, and 8-Coordinate Ln(hfac)n Complexes

Volatile lanthanide coordination complexes are critical to the generation of new optical and magnetic materials. One of the most common precursors for preparing volatile lanthanide complexes is the hydrate with the general formula Ln(hfac)₃(H₂O)_x (x = 3 for La-Nd, x = 2 for Sm) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato). We have investigated the synthesis of Ln(hfac)₃(H₂O)_x using more environmentally sustainable mechanochemical approaches. Characterization of the products using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, elemental analysis, and powder X-ray diffraction shows substantial differences in product distribution between methods. The mechanochemical synthesis of the hydrate complexes leads to a variety of coordination compounds including the expected hydrate product, the known retro-Claisen impurity, and hydrated protonated Hhfac ligand depending on the technique employed. Surprisingly, 10-coordinate complexes of the form Na₂Ln(hfac)₅·3H₂O for Ln = La-Nd were also isolated from reactions using a mortar and pestle. The electrostatic bonding of lanthanide coordination complexes is a challenge for obtaining reproducible reactions and clean products. The reproducibility issues are most acute for the large, early lanthanides whereas for the mid to late lanthanides, reproducibility in terms of product distribution and yield is less of an issue because of their smaller size and greater charge to radius ratio. Ball milling increases reproducibility in terms of generating the desired Ln(hfac)₃(H₂O)_x along with hydrated Hhfac (tetraol) and free Hhfac products. The results illustrate the dynamic behavior of lanthanide complexes in solution and the solid state as well as the structural diversity available to the early lanthanides.

Mechanochemical reactions to prepare Ln(hfac)₃(H₂O)_x (Ln = La-Sm, Tb) complexes are used to illustrate the highly variable coordination chemistry of the early lanthanides compared to the mid-lanthanides. Using either a mortar and pestle or ball mill results in unexpected products and different product distributions. An open mortar and pestle can yield 10-coordinate pentakis-hfac complexes of La, Ce, Pr, and Nd, whereas ball milling consistently results in Ln(hfac)₃(H₂O)_x complexes with volatile Hhfac and hydrated Hhfac·2H₂O (tetraol) that can be removed by vacuum.