Synthesis And Luminescence Properties Of Rare Earth Doped Silica Nano And Micro Materials

Recently,rare earth doped nano/micron luminescent materials as a member of functional material have attracted extensive attentions due to their wide applications in the fields of display,lighting,biomarker and bioimaging.Silica is one of the most promising rare earth doped substrate material due to its unique optical property,high transparency and good thermal stability.Meanwhile,the unique three dimensional network structure of silica can further protect and stabilize the rare earth ions doped inside.Thus,the preparation of rare earth doped silica materials with excellent mechanical property,stable chemical property,good biocompatibility and remarkable luminescent performance is of great significance.In addition,large amounts of hydroxyl groups in the amorphous silica are beneficial to further functionalization,and expand their applications in different fields.Therefore,rare earth doped silica materials have attracted more and more attentions.However,it is well known that the chemical and physical properties of materials are closely related to the preparation methods and the morphology and size of the product.Therefore,the preparation of rare earth doped silica nano/micron materials with different morphologies by various methods to explore the luminescent materials with excellent properties and applicability has become a hot research topic.In this work,a series of rare earth doped silica luminescent materials with different sizes and morphologies were prepared by sol-gel template method,electrospinning method and microemusion method.The formation mechanism and effect factors of rare earth doped silica materials with different morphologies were systematically studied.The main contents of the research work are as follows:1.The Eu³⁺doped silica microrods were prepared by sol-gel method using citrate acid as template.The results showed that stirring,dropping speed of ammonia and gel time had effects on the morphology of the sample.The formation mechanism was discussed in detail.Under the excitation of 393 nm ultraviolet light,the samples exhibited the characteristic red emission of Eu³⁺ions.The strongest luminescent intensity was obtained in the composition of 9 mol%Eu³⁺.2.A series of Eu³⁺/Tb³⁺doped silica nanospheres with controllable size and adjustable color were prepared by sol-gel method using CTAB as template.The size of silica nanospheres is seriesly influedced by reaction temperature.The realitionship between size and luminescence is discussed.Under the excitation of 377 nm ultraviolet light,the energy transfer mechanism from Tb³⁺to Eu³⁺was explored by adjusting the doping ratio of Eu³⁺and Tb³⁺in silica nanospheres and the emission colors could change from green,yellow,orange,pink to red.3.One dimensional Eu³⁺doped silica solid fibers were prepared by monoaxial electrospinning method using PVP as template.The influences of PVP and water contents on the size and morphology of samples were discussed.The diameter of silica fibers gradually increased with the increase of Eu³⁺concentration.Under the excitation of 393 nm ultraviolet light,the Eu³⁺doped silica fibers exhibited obvious red emission of Eu³⁺,and the intensity and lifetime reached the maximum when the doping concentration of Eu³⁺was 16 mol%.4.One dimensional Eu³⁺/Tb³⁺doped silica hollow nanofibers were successfully prepared by coaxial electrospinning method using PMMA and PVP as templates.The effects of polymer,solvent and the spinning speed of core and shell solutions on the morphology of the sample were investigated.Under the excitation of ultraviolet light,the SiO₂:Eu³⁺fiber exhibited red emission,the SiO₂:Tb³⁺fiber exhibited green emission,and the SiO₂:Eu³⁺,Tb³⁺sample exhibited orange emission,which realized the multi-color luminescence property.5.The Eu³⁺doped silica twisted nanowires were successfully prepared by water-in-oil?W/O?microemulsion method.The influences of the amount of water and sodium citrate on the morphology of the product were investigated.FT-IR spectra showed that Eu³⁺mainly existed in the silica matrix in the form of Si-O-Eu bond.The formation process of Eu³⁺doped silica twisted nanowires was explained in detail according to a modified gas-liquid-solid mechanism.Under the excitation of 393 nm ultraviolet light,the SiO₂:Eu³⁺twisted nanowires exhibited red emission of Eu³⁺.The luminescence intensity reached the maximum when the Eu³⁺doping concentration was 20 mol%,and the intensity was obviously enhanced after calcination.6.A series of Eu³⁺/Tb³⁺doped silica nanoparticles were prepared by oil-in-water?O/W?microemulsion method,including flower-like nanospheres,flower-like nanodisks,circular nanodisks and sunken nanocapsules.With the same concentration of Eu³⁺/Tb³⁺ions,the luminescence intensity of the nanocapsules was strongest,while the flower-like nanospheres was weakest,which was related to the surface structure and the amount of defects.Meanwhile,by simply adjusting the doping concentration ratio of Eu³⁺and Tb³⁺in the silica nanocapsules,the emission colors changed from red,orange to green,realizing the multicolor emission.