Study On Preparation And Luminescence Properties Of Metal Chalcogenides Nanomaterials

Metal chalcogenides are important functional materials with wide applications in the optical,electronic and optoelectronic field.The nanomaterials of metal chalcogenides are even the hot subject of the material researches.The properties of the nanomaterials depend on their process history,size,morphology and distribution.Thus the preparation method and the morphology controlling become the key parts of the nanomaterial researches.In Chapter 2 and 3 of this thesis,we took one ternary sulfide and a series of binary selenide/sulfides/tellurides as the objects of study,developed several handy and environment-friendly methods to synthesize these chalcogenides,and investigated the formation process and the control of the products and their morphology.The polyoxides, as one kind of the chalcogenides,are the most useful luminescence host materials,and phosphors with better luminescent property can be developed by choosing and modifying the host materials.In Chapter 4,we chose the stable zirconates as the object, and carried out a research on the preparation,rare earth ions-doping and luminescence property of them.In Chapter 1,we introduced the conception,preparation method of nanomaterials,the theory of luminescence and the luminescent materials,and presented the current research status of the metal chalcogenide nanomaterials preparation.In Chapter 2,CuInS₂ hollow nanospheres were prepared through a surfactantassisted glycol-reflux method.The hollow spheres have an average diameter of 80-100 nm,and the shells of the hollow spheres are composed of CuInS₂ nanoparticles of about 10 nm in size.A vesicle-template mechanism was proposed to explain the formation process of the hollow structure,during which amorphous hollow structures are first formed on the surfactant template and then crystallize in the refluxing process. Furthermore,in the reaction,glycol acted not only as a good solvent but also as a reducer reducing Cu²⁺ to Cu⁺.The trace water in the raw materials was also required for the formation of CuInS₂. Considering the problems existing in the present synthesis methods of selenide nanomaterials,such as the toxic reagents and rigorous reaction condition,we introduced in Chapter 3 two methods to prepare nanoscaled metal slenides(sulfides or tellurides). Both of the methods are featured with easy operation,low toxicity,low cost and high controlling.Phase-and morphology-controllable synthesis of the various chalcogenide materials were researched through the two methods,the structure and morphology of the products were characterized,and several mechanisms were proposed to explain the formation of the different phase and morphology.Firstly,it is the Acetate-Paraffin method,by which we synthesized a series of selenides/sulfides/tellurides.The products showed various morphologies.Mechanisms were proposed to explain the formation of the different chalcogenides and their nanostructures.Paraffin liquid instead of TOP was used to dissolve Se(S/Te) powder.Oleic acid can react with each metal acetate to form the soluble M-OA complex,promising the thorough reaction between metal cations and Se(S/Te)/paraffin solution,and thus this method is suitable for the preparation of many metal chalcogenides.The morphologies of the chalcogenides are mainly affected by two factors,the crystal structure and the action of oleic acid on the crystal faces.To examine the phase and morphology control of the products from the Acetae-Paraffin method,we carried out an in-depth study on copper selenide,which show complexity of composition and structure.CuSe or Cu_2-δSe was selectively synthesized by adjusting the reaction parameters.The formation of the different phases of copper selenide is determined by two elements—the redox and stability.Theδvalue of Cu_2-δSe can also be adjusted by changing the oleic acid amount.The products showed two morphologies, nanoflakes,or the mixture of nanoflakes and nanowires.A concentration-limited growth mechanism was proposed to explain the various morphologies of Cu_2-δSe and CuSe forming at the different condition.The SDBS-modified CuSe nanoflakes exhibited good dispersivity in water.The other method is based on ethylene glycol.PbSe nanoparticles and Se micro/nanorods can be selectively synthesized in the same reaction system by this glycol method.It is a kinetic competition process.PbSe nanocrystals would form when the reaction temperature was controlled at a high level,while the low temperature favored the formation of Se rods.The products showed more regular morphology when ionic surfactants was used.The PbSe phase was easier to form when the surfactant was cationic.This method can be used in the other metal cation/surfactant system,resulting in Se micro/nanorods and other selenide nanocrystals.The research emphasis in Chapter 4 switched to the luminescence property.Pure and doped metal zirconates—perovskite-structured SrZrO₃ and pyrochlore-structured RE₂Zr₂O₇ nanocrystals were prepared through a facile sol-gel-combustion method.The products were characterized by the crystal structure and luminescence property,and some new luminescence properties and relationship between structure and luminescence were discovered.Firstly,SrZrO₃ nanocrystalline flakes were prepared through a combustion reaction ignited at a temperature as low as 300℃.The further calcination at 700℃removed the organic residues and improved the crystallinity of the products.For the first time,we detected a luminescence at 400nm,which might originate from the defect centers in the nanocrystals.The intensity of this luminescence was dramatically enhanced after the further calcination,due to the removal of organic residues which has a deleterious effect on the luminescence.Porous and Eu³⁺-doped SrZrO₃ nanopowders were prepared by combustion at 700℃.Eu³⁺-doped SrZrO₃ emitted strong red light under UV excitation.The structure details of the nanocrystals can be revealed by exciting the products with light of different wavelength.The Eu³⁺-doped SrZrO₃ phosphor showed a high stability of luminescence.Secondly,a series of RE₂Zr₂O₇ (RE=La,Nd,Eu,Y) powders were prepared through the combustion reaction ignited at 600℃.The products showed crystal structure of pyrochlore or defected fluorite,and morphology of aggregated nanocrystals.Except the characteristic luminescence emission of Eu³⁺ for Eu₂Zr₂O₇,all the samples showed luminescence originating from the intrinsic oxygen Frenkel defect of the crystals.The intensity of this emission can be increased by the doping of Pb²⁺.The amplitude of the increase varies widely for different RE₂Zr₂O₇.Analyzing the crystal structure and luminescence property of RE₂Zr₂O₇,we found that the luminescence intensity of RE₂Zr₂O₇ is intimately related to the ordering degree of their crystal structure.So we proposed a method to judge the disordering degree of RE₂Zr₂O₇(from pyrochlore structure to defected fuorite structure) according to the luminescence intensity of them.Considering the luminescence intensity is relative,the disordering degree can be estimated by the increase amplitude of the luminescence after the doping of Pb²⁺.The increase amplitude is larger,the ordering degree is higher,and the increase amplitude is smaller,the ordering degree is lower. La₂Zr₂O₇ and Y₂Zr₂O₇ nanocrystals were doped with rare earth ions.Eu³⁺-doped La₂Zr₂O₇ and Y₂Zr₂O₇ nanocrystals showed orange-red emission from the characteristic transition of Eu³⁺.The luminescence intensity increased with the Eu³⁺ concentration. Dy³⁺-doped La₂Zr₂O₇ nanocrystals emited yellow and blue light at 575nm and 480nm respectively.The luminescence intensity first increased and then decreased with the Dy³⁺ concentration because of the luminescence concentration quenching,and 2.0mol% is the best doping concentration of Dy³⁺.Eu³⁺,Dy³⁺-codoped La₂Zr₂O₇ nanocrystals only showed the characteristic luminescence of Eu³⁺.The luminescence intensity of Eu³⁺,Dy³⁺-codoped La₂Zr₂O₇ nanocrystals is much higher than that of the samples only doped with Eu³⁺,due to the energy transfer from Dy³⁺ to Eu³⁺ in the codoped sample. There was a change in the fine structure of the emission spectra when the excitation wavelength or Eu³⁺ concentration was altered,which can disclose the structure feature of La₂Zr₂O₇ and Y₂Zr₂O₇ nanocrystals.In Chapter 5,a concise summary of the contents was given.