Optimizing the Eu³⁺ Concentration in Novel Eu-Doped Thermoplastic Polyurethane Films for the Development of Highly Emissive Red Flexible Material

New flexible red-emitting materials are prepared based on the thermoplastic polyurethane (TPU) and Eu(TTA)₃bipy (Eu), as doping europium(III) species. The films are achieved by slow evaporation of the mixture of the complex species and TPU in dichloromethane/dimethylformamide (DCM/DMF), and are characterized by Fourier transform infrared, thermogravimetric analysis (TGA), powder X-ray diffraction, scanning electron miscroscopy coupled to an energy dispersive X-ray spectroscopy detector (SEM-EDS), and atomic force microscopy (AFM). Considering the whole characterization dataset, it is possible to identify the main interactions of the complex with the polymeric host, which are responsible for the properties of the obtained film. When excited at 394 nm, a quantum yield (QY) of 17.2% is obtained for a 1% concentration of europium(III) ion, which is an excellent performance considering the high dilution of Eu in the matrix. Furthermore, the material retains a transparency comparable to that of pristine TPU. The QY values for films with higher concentration, such as 4% and 10%, are close to those of the pristine Eu (36–41% using 394 nm excitation source), and also preserve a well-resolved Stark splitting for all transitions (⁵D₀ → ⁷F_0-4). Therefore, this work highlights a new flexible material with a low content of europium(III) ions with excellent emissive properties.