Electrospinning preparation and luminescence properties of Eu(TTA)₃phen/polystyrene composite nanofibers

Efficient luminescent composite nanofibers, composed of polystyrene (PS, M_w=250000) and europium complex Eu(TTA)₃phen (TTA=2-thenoyltrifluoroacetone, phen=1,10-phenanthroline) with diameters ranging from 350 nm to 700 nm, were prepared by electrospinning and characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), fluorescence spectroscopy, and thermogravimetric analysis (TG). The room-temperature fluorescence spectra of the composite nanofibers were composed of the typical Eu³⁺ ion red emission, assigned to the transitions between the first excited state (⁵D₀) and the multiplet (⁷F_0-4). Owing to the incorporation of the europium complex into the PS fiber matrix and the subsequent distortion of the symmetry around the lanthanide ions by the capping PS, the polarization of the Eu³⁺ ions was enhanced, which increased the probability for electronic dipole allowed transitions. The monochromaticity (⁵D₀→⁷F₂/⁵D₀→⁷F₁) around the Eu³⁺ ions was also efficiently improved. Judd-Ofelt intensity parameters (Ω₂ and Ω₄) were determined from the emission spectra based on the ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄ electronic transitions, respectively. The results showed that the Ω₂ values of the composite nanofibers were apparently higher than that of the pure complex, indicating an increased covalency degree in the europium first coordination shell due to the modification of PS matrix. The modification of the polymer matrix also resulted in much higher thermal stability of the composite fibers than that of the pure complex.