Luminescent Analysis of Eu³⁺ and Tb³⁺ Flufenamate Complexes Doped in PMMA Polymer: Unexpected Terbium Green Emission under Sunlight Exposure

The design of efficient luminescent lanthanide materials with a wide range of different excitation wavelengths in the UVA, UVB, and UVC regions, as well as under sunlight exposure, is highly desirable for application as molecular light-converting devices. In this work, [Ln(fluf)3(L)] complexes (Ln3+: Eu, Gd, and Tb) and doped PMMA:(1%)Tb(fluf)3(L) films, where fluf stands for the flufenamate ligand and L is H2O, phen, tppo, topo, and dpso, were successfully prepared by a facile one-pot method, and their photophysical properties were also investigated. The Ln3+ compounds were characterized by elemental analysis, Fourier transform infrared absorption spectroscopy, thermogravimetric analysis, X-ray powder diffraction, and diffuse reflectance spectroscopy techniques. The Eu3+ complexes present very weak emission intensities at 300 K temperature, showing very low intrinsic quantum yield (QEuEu) values due to a highly operative luminescence quenching by a low-lying ligand to metal charge transfer state. However, these values are significantly increased when obtained at low temperature (77 K). For Tb3+ complexes and the doped PMMA, polymeric films revealed an unprecedented bright emission under excitation at UVA, UVB, and UVC radiation. In addition, the doped polymers under sunlight exposure show the characteristic 5D4 → 7F6–0 transitions of the Tb3+ ion, exhibiting green emission color. These luminescent doped polymeric materials act as efficient energy harvesters and converters. Hence, the optical results show that the PMMA:(1%)Tb(fluf)3(L) photonic materials are highly versatile and desirable, presenting suitable application as efficient light-converting molecular devices and as luminescent solar concentrators.