A neoteric approach to achieve CaF2:Eu2+/3+ one-dimensional nanostructures with direct white light emission and color-tuned photoluminescence

Highlights: • A novel strategy is used to synthesize CaF₂:Eu^2+/3+ one-dimensional nanostructures. • CaF₂:Eu^2+/3+ nanofibers, hollow nanofibers and nanobelts are firstly synthesized. • Tunable multicolor luminescence can be achieved via tuning contents of Eu²⁺ and Eu³⁺. • White light emission is realized by doping single europium element in a single matrix. • Ratio of Eu²⁺ to Eu³⁺ can be easily modulated via regulating Eu-doped concentration. -- Abstract: CaF₂:Eu^2+/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:Eu^2+/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:Eu^2+/3+ nanostructures exhibit characteristic emission peaks at 385 nm (purple) and 615 nm (red) assigned to 4f⁶5 d¹ (t_2g)→⁸S_7/2 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%Eu^2+/3+ nanofibers possess the highest luminescent intensity. White-emitting and color-tunable photoluminescence performance of CaF₂:Eu^2+/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:Eu^2+/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.