Preparation Of Luminescent Materials For Fiber By Fluxing Method And Study On Red Luminescence Properties

Luminous fiber is a functional fiber that can keep glowing in the darkness.It is spun from rare earth long-lasting luminescent materials and fiber-forming polymers.Its luminescence performance mainly depends on the long-lasting luminescent materials activated by rare earth ions.The blue and green light luminous fibers have been industrialized due to the good afterglow properties of silicate and aluminate luminescent materials.Limited by the afterglow performance of red long-lasting phosphor,the research of red luminous fiber has encountered a bottleneck.In this research,a composite luminescence method is adopted by using a phosphor with good afterglow performance as the secondary light source,and the red organic fluorescent material Rhodamine B is used as the light conversion agent to absorb the short-wavelength secondary light source and convert it into red fluorescence.So the the red long afterglow effect of the luminous fiber is realized by this method.In this paper,the luminescence mechanism and ion doping rules of Eu²⁺/Eu³⁺activated luminescent materials were studied.It was found that the phosphors with good luminous properties are mainly SrAl₂O₄,Sr₂Mg Si₂O₇ and Y₂O₂S.In order to make phosphor meet meet requirements of fiber,the fluxing process and fluxing mechanism are studied.Then the SrAl₂O₄ phosphor with high specific surface area prepared by the fluxing method is combined with rhodamine B through a coupling agent,and the bonding process and composite structure were researched.Nextly,the SrAl₂O₄/rhodamine B composite phosphor was subjected to spinning experiments,and the luminous properties of fibers prepared by melt and wet spinning were studied.In order to solve the problem of the low red fluorescent purity,the coaxial wet spinning method was used to distribute the long afterglow material and Rhodamine B in the inner and outer layer of the fiber respectively,and then the luminous performance was analyzed.The main research work and results are summarized as follows:(1)The research work was carried out from three aspects:the luminescence mechanism of activated ions and co-dopants,the influence of the host on the properties of phosphors,and the influence of doping concentration on the luminous performance.The long afterglow mechanism of europium ions activated phosphors,and the doping rule of activating and co-doped ions were explored through the analysis of the florescent spectrum and afterglow properties.It was found that Eu²⁺/Eu³⁺not only serves as the luminous center for electronic transition in the crystal structure,but also has intrinsic electron trap energy levels,meanwhile,co-doped ions can provide a richer electron transition trap energy level for the electron transition.The matrix affects the luminescence spectrum and afterglow performance of Eu²⁺/Eu³⁺luminous center.When the host ion and activating ion have similar valence state and ion radius,higher afterglow performance can be obtained.In SrAl₂O₄,Sr₂Mg Si₂O₇ and Y₂O₂S phosphors,when the concentration of co-doped ions is higher than that of activating ions,better afterglow performance can be obtained.(2)To solve the problems of uneven reaction,grain agglomeration,and difficulty in product grinding caused in the high-temperature solid-phase reaction process,a series of fluxes were used to prepare the SrAl₂O₄,Sr₂Mg Si₂O₇ and Y₂O₂S phosphors applied in the luminous fibers.It was found that the flux combination of Li₂B₄O₇ and Li F has a good fluxing effect on the preparation of SrAl₂O₄ phosphor.Li₂B₄O₇ and Li F can reduce the melting point of the reactants and increase the fluidity of the melt,so that the reaction was carried out completely.The F^-can block the agglomeration between the crystal grains to reduce the density of the product,so that the phosphor obtained by grinding has a higher afterglow brightness and specific surface area.Besides,the Li Cl can replace Li F to play a fluxing effect.The raw material has high reactivity during the preparation of Sr₂Mg Si₂O₇ phosphor,H₃BO₃ has obvious fluxing effect in the reaction.The addition of H₃BO₃ can improve the fluidity of the melt during the reaction,meantime,Li Cl can improve the fluxing effect by reducing the surface tension of the melt.The study found that the Li₃PO₄,Li₂CO₃ and Li Cl flux combination has a good fluxing effect on the preparation of Y₂O₂S phosphor.Since the main component of the reactant is transition metal oxide,the reaction activity is relatively low,consequently,the content of flux required is relatively high.(3)In order to prepare composite red long-lasting luminescent material,the SrAl₂O₄phosphor with high afterglow brightness and large specific surface area prepared by the fluxing method was used as the secondary light source,and the silane coupling agent was used to combine the SrAl₂O₄ and rhodamine B.As the concentration of rhodamine B increases,the fluorescence color of the composite phosphor has a red shift,while the afterglow brightness was reduced.The lammps simulation software was used to study the molecular dynamics of the interface structure of the material,the interface structure SrAl₂O₄-coupling agent-Rhodamine B was first constructed,and then mechanically poprperty was tested by means of molecular dynamics.It was found that the chemical bonds of interface structure break when subjected to external stretching or shearing force,and the broken chemical bonds is related to the interface area under external force,and the Si-C bond in the silane coupling agent is weaker and prone to breakage relatively.(4)The SrAl₂O₄/Rhodamine B composite phosphor was used to prepare PP luminous fibers and PAN luminous fibers through melt and wet spinning,and the luminous properties were measured.Based on the mechanical test result of molecular dynamics simulation,the analysis shows that the Rhodamine B coated on the surface of SrAl₂O₄ will be separated from it due to the high temperature and screw extrusion in the melt spinning,while the composite structure is relatively stable during the wet spinning.Therefore,the two componenets are not separated easily,and the luminous fiber prepared by wet spinning appear better red fluorescent effect.To improve the purity of the red fluorescence,the PAN red luminous fiber was prepared by the coaxial wet spinning method,and the long afterglow phosphor and rhodamine B were distributed in the inner and outer layer of fiber respectively,which avoided the drop of color purity caused by the separation of SrAl₂O₄ and Rhodamine B.Compared with the blend spinning method,the fluorescence light emitted by the coaxial luminous fiber has higher red light purity.