Fabrication and luminescence properties of YF3:Eu3+ hollow nanofibers via coaxial electrospinning combined with fluorination technique

Polyvinyl pyrrolidone (PVP)–PVP/Y(NO₃)₃ + Eu(NO₃)₃] core–sheath composite nanofibers were prepared by coaxial electrospinning, and then Y₂O₃:Eu³⁺ hollow nanofibers were synthesized by calcination of the as-prepared composite nanofibers. For the first time, YF₃:Eu³⁺ hollow nanofibers were successfully fabricated by fluorination of the Y₂O₃:Eu³⁺ hollow nanofibers via a double-crucible method using NH₄HF₂ as fluorinating agent. The morphology and properties of the products were investigated in detail by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM), and fluorescence spectrometer. YF₃:Eu³⁺ hollow nanofibers were pure orthorhombic phase with space group Pnma and were hollow-centered structure with the mean diameter of 211 ± 29 nm. Fluorescence emission peaks of Eu³⁺ in the YF₃:Eu³⁺ hollow nanofibers were observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₁ (587 and 593 nm), ⁵D₀ → ⁷F₂ (615 and 620 nm), and the ⁵D₀ → ⁷F₁ hypersensitive transition at 593 nm was the dominant emission peak. Moreover, the emitting colors of YF₃:Eu³⁺ hollow nanofibers were located in the red region in CIE chromaticity coordinates diagram. The luminescent intensity of YF₃:Eu³⁺ hollow nanofibers was increased remarkably with the increasing doping concentration of Eu³⁺ ions and reached a maximum at 7 mol% of Eu³⁺. This preparation technique could be applied to prepare other rare earth fluoride hollow nanofibers.