A strategy towards MF2:Yb3+, Er3+/SiO2 (M=Ba, Sr, Ca) yolk-shell nanofibers and yolk-shell nanobelts with up-conversion fluorescence

A simple and universal technique of the combination of uniaxial electrospinning with subsequent peculiar dual-crucible fluorination technology is innovatively designed and used to construct metallic fluorides yolk-shell nanofibers (YSNFs) and yolk-shell nanobelts (YSNBs) directly for the first time. As a case study, Yb 3+ /Er 3+ co-doped alkaline earth metal fluoride (BaF 2 , SrF 2 and CaF 2 ) as core layer and SiO 2 as shell layer are applied to construct the yolk-shell one-dimensional nanostructures . Under the optimum calcination temperature (600 °C) and time (5 h), the obtained MF 2 :Yb 3+ , Er 3+ /SiO 2 (M=Ba, Sr, Ca) samples are of pure cubic phase, and display the yolk-shell nanofibers and yolk-shell nanobelts with good size uniformity and green up-converting fluorescence. By HF acid treatment of the samples, it is not only proved that the shell layer is SiO 2 , but also independent core-layer MF 2 :Yb 3+ , Er 3+ (M=Ba, Sr, Ca) nanofibers and nanobelts with good size uniformity and excellent up-conversion luminescence are obtained. Especially, only fluorination process among the halogenation can form such exceptive YSNFs and YSNBs one-dimensional nanostructures , and the formation mechanisms of YSNFs and YSNBs are proposed and verified, and further the novel technique is established. The new technique possesses the merits of simple device and easy operation, large output, well-defined morphology and high preparative success rate of yolk-shell nanofiber and yolk-shell nanobelt, universality to metallic fluorides. The design philosophy and the construction technique for the exceptional yolk-shell one-dimensional nanostructures afford a facile approach for the fabrication of other functional metal fluorides yolk-shell one-dimensional nanostructures.