A neoteric approach to achieve CaF2:Eu2+/3+ one-dimensional nanostructures with direct white light emission and color-tuned photoluminescence
2021
Abstract CaF2:Eu2+/3+ one-dimensional nanostructures including nanofibers, hollow nanofibers and nanobelts are respectively constructed via a newly-proposed technique of high-efficient combination of electrospinning with bi-crucible fluorinating technique. The diameters of CaF2:Eu2+/3+ nanofibers and hollow nanofibers are respectively 328 ± 2 nm and 290 ± 5 nm, and the width and thickness of nanobelts are 1.07 ± 0.013 μm and 150 nm, respectively. Under the excitation of 276-nm or 320-nm ultraviolet light, CaF2:Eu2+/3+ nanostructures exhibit characteristic emission peaks at 385 nm (purple) and 615 nm (red) assigned to 4f65 d1 (t2g)→8S7/2 energy levels transition of Eu2+ ions and 5D0→7F2 energy levels transitions of Eu3+ ions, respectively. XPS data further confirm the coexistence and proportion of Eu2+ and Eu3+ in the samples. CaF2:9%Eu2+/3+ nanofibers possess the highest luminescent intensity. White-emitting and color-tunable photoluminescence performance of CaF2:Eu2+/3+ nanostructures are realized by regulating the proportion of Eu2+ to Eu3+ ions, and luminescence mechanism is also proposed. Further, it is satisfactorily found that the proportion of Eu2+ to Eu3+ ions can be modulated by adjusting the Eu-doped concentration and calcination temperature. The detailed formation mechanisms of CaF2:Eu2+/3+ one-dimensional nanostructures are advanced, and the neoteric fabrication technique is successfully established. This design conception and construction strategy can provide some guidance for fabricating other one-dimensional nanostructures.
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