Local Environment-Modulated\nf–f Transition\nin Unit-Cell-Sized Lanthanide Ultrathin Nanostructures

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