Er³⁺ doped BaYF₅ nanofibers: facile construction technique, structure and upconversion luminescence

Er³⁺ doped BaYF₅ nanofibers have been successfully fabricated by electrospinning combined with a double-crucible fluorination method we recently proposed. For the fabrication process, the first step is to prepare PVP/[Ba(CH₃COO)₂ + Y(NO₃)₃ + Er(NO₃)₃] composite nanofibers via electrospinning, the next step is calcining the composite nanofibers into mixed oxide nanofibers in air, and finally BaYF₅:Er³⁺ nanofibers are successfully synthesized by fluorination of the as-prepared mixed oxide nanofibers used as precursor via a double-crucible method applying NH₄HF₂ as fluorinating agent. X-ray diffractometry analysis reveals that BaYF₅:Er³⁺ nanofibers are pure tetragonal phase with space group of P/421m. The diameter of BaYF₅:Er³⁺ nanofibers is 109.9 ± 10.9 nm under the 95 % confidence level. Upconversion emission spectra analysis manifests that BaYF₅:Er³⁺ nanofibers emit strong green and weak red upconversion emissions centering at 522 (²H_11/2 → ⁴I_15/2), 540 (⁴S_3/2 → ⁴I_15/2) and 651 (⁴F_9/2 → ⁴I_15/2) nm, respectively. Moreover, the emitting colors of BaYF₅:Er³⁺ nanofibers are located in the green region in CIE chromaticity coordinates diagram. The optimum doping molar concentration of Er³⁺ ions is found to be 5 %. The formation mechanism of the BaYF₅:Er³⁺ nanofibers is also studied. This preparation technique can be applied to fabricate other rare earth fluoride nanofibers.