Construction And Performances Of Europium-doped Alkaline Earth Metal Fluoride Halides One-dimensional Nanostructures

Alkaline earth metal fluorohalide is a promising luminescent host material due to its low phonon energy.Eu^2+/3+ ion is one of the important rare earth luminescent ions,and Eu^2+/3+ doped nanosized luminescent materials have been extensively studied.At present,Eu^2+/3+-doped alkaline earth metal fluoride halides zero-dimensional nanomaterials have been prepared by hydrothermal method,precipitation method,hot-press sintering method and ionothermal synthesis technique.However,no reports on Eu^2+/3+-doped alkaline earth metal fluoride halides one-dimensional nanostructures are found in references.Electrospinning technology is recognized as one of the effective methods for the preparation of one-dimensional nanomaterials due to its simple equipment,easy implementation,high repeatability,and product diversification.Therefore,it is an important and valuable subject of research to fabricate Eu^2+/3+-doped alkaline earth metal fluoride halides one-dimensional nanostructures and to study their characteristics in depth.In this dissertation,Eu^2+/3+ doped alkaline earth metal fluorohalide one-dimensional nanostructures including nanofibers,hollow nanofibers,nanobelts,novel nanowire-in-nanotube structured nanofibers and nanoribbon-in-nanoribbon structured nanobelts were constructed via a novel technique of high-efficient combination of electrospinning with bi-crucible fluorohalogenation technique.The samples were characterized by XRD,SEM,XPS and PL,and some meaningful results were obtained.The details are as follows:1.Cubic phase CaF₂:Eu^2+/3+ nanofibers,hollow nanofibers and nanobelts were manufactured via electrospinning technology combined with bi-crucible fluorination technology.Under the excitation of 276 nm and 320 nm ultraviolet light,the CaF₂:Eu^2+/3+ nanostructures exhibit a strong purple emission at 385 nm attributed to the 4f⁶5d¹→⁸S_7/2 energy level transition of Eu²⁺ and a strong red emission at 615 nm assigned to the ⁵D₀→⁷F₂ energy level transition of Eu³⁺.White-emitting and color-tunable photoluminescence of CaF₂:Eu^2+/3+ one-dimensional nanostructures are realized by adjusting the concentration of europium ions and the calcination temperature.2.Tetragonal-phase CaFCl:Eu^2+/3+ nanofibers,hollow nanofibers and nanobelts were synthesized by electrospinning technology in combination with bi-crucible fluorochlorination technology.The structure,morphologies,luminescence properties of the CaFCl:Eu^2+/3+ nanostructures have been studied.Both Eu²⁺ and Eu³⁺ coexist in CaFCl:Eu^2+/3+ one-dimensional nanostructures.White-emitting and color-tunable photoluminescence of CaFCl:Eu^2+/3+ one-dimensional nanostructures are achieved by modulating europium concentration.3.Neoteric CaF₂:Eu^2+/3+@void@SiO₂ and CaFCl:Eu^2+/3+@void@SiO₂ nanowire-in-nanotube structured nanofibers were successfully prepared through electrospinning technology connected with bi-crucible fluorohalogenation technology for the first time.The structure,morphologies and luminescence properties have been characterized.Nanowire-in-nanotube structured nanofibers possess large length-diameter ratio,and have potential applications in sensors,biomedicine and catalysis,etc.4.Novel CaF₂:Eu^2+/3+@void@SiO₂ and CaFCl:Eu^2+/3+@void@SiO₂ nanoribbon-in-nanoribbon structured nanobelts were successfully constructed via electrospinning technology combined with bi-crucible fluorohalogenation technology for the first time.This preparation technique has the advantages of low cost,simple operation,and without introducing organics.The new findings have important guidance for the preparation of other one-dimensional nanomaterials with special structures.