Er^sup 3+^ doped BaYF^sub 5^ nanofibers: facile construction technique, structure and upconversion luminescence

Er^sup 3+^ doped BaYF^sub 5^ 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(CH^sub 3^COO)^sub 2^ + Y(NO3)^sub 3^ + Er(NO3)^sub 3^] composite nanofibers via electrospinning, the next step is calcining the composite nanofibers into mixed oxide nanofibers in air, and finally BaYF^sub 5^:Er^sup 3+^ nanofibers are successfully synthesized by fluorination of the as-prepared mixed oxide nanofibers used as precursor via a double-crucible method applying NH^sub 4^HF^sub 2^ as fluorinating agent. X-ray diffractometry analysis reveals that BaYF^sub 5^:Er^sup 3+^ nanofibers are pure tetragonal phase with space group of P/421m. The diameter of BaYF^sub 5^:Er^sup 3+^ nanofibers is 109.9 ± 10.9 nm under the 95 % confidence level. Upconversion emission spectra analysis manifests that BaYF^sub 5^:Er^sup 3+^ nanofibers emit strong green and weak red upconversion emissions centering at 522 (^sup 2^H^sub 11/2^ [arrow right] ^sup 4^I^sub 15/2^), 540 (^sup 4^S^sub 3/2^ [arrow right] ^sup 4^I^sub 15/2^) and 651 (^sup 4^F^sub 9/2^ [arrow right] ^sup 4^I^sub 15/2^) nm, respectively. Moreover, the emitting colors of BaYF^sub 5^:Er^sup 3+^ nanofibers are located in the green region in CIE chromaticity coordinates diagram. The optimum doping molar concentration of Er^sup 3+^ ions is found to be 5 %. The formation mechanism of the BaYF^sub 5^:Er^sup 3+^ nanofibers is also studied. This preparation technique can be applied to fabricate other rare earth fluoride nanofibers.