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Preparation And Properties Of Rare Earth Oxides Luminescent Materials Via Electrospinning Process

Posted on:2010-08-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Y HouFull Text:PDF
GTID:1101330332960512Subject:Materials science
Abstract/Summary:PDF Full Text Request
Rare earth luminescent materials have been widely used in the fields of lighting and display, such as fluorescent lamps, cathode-ray tubes, field emission displays and plasma display panels, and other functional materials based on their outstanding physical and chemical properties arising from their 4f electrons. It is worth noting that porous materials functionalized with photoluminescence via doping rare earth ions have potential applications in the fields of drug delivery and disease diagnosis and therapy. In this dissertation, valuable explorations have been carried out on a combinative synthetic method of electrospinning and sol-gel process to rare earth oxides luminescent materials and luminescence functional porous materials, as well as their preparation, structure, morphologies, photoluminescent, cathodoluminescent and drug delivery properties.A series of rare earth oxides luminescent materials with different morphologies (fiber-like, belt-like and tube-like) and sizes have been prepared. Due to the efficient energy transfer from the VO43- group to the lanthanide ions (Ln3+), the Ln3+ show their characteristic strong emissions in the YVO4 nanofibers and microbelts under ultraviolet excitation. With PO43- ions partial replacement of the VO43- ions, multicolor tuning emissions of the YPo.8Vo.204:Ln nanofibers can be achieved by changing the doping concentration of Ln3+. Under ultraviolet excitation Ce3+ or Tb3+ doped LaPO4 nanofibers and microbelts show their characteristic emission, i.e. Ce3+ 5d-4f and Tb3+5D4-7FJ (J= 6,5,4,3) transitions, respectively. Excitation into the Ce+ band yields both the weak emission of Ce3+ and the strong emission of Tb3+(5D4-7FJ, J= 3,4,5,6) in Ce3+and Tb3+codoped LaPO4. This indicates that an energy transfer from Ce3+ to Tb3+occurs in the nanofibers and microbelts of LaPO4.As self-activating phosphors, calcium tungstate (CaW04) and calcium molybdate (CaMoO4) with the scheelite structure, can exhibit blue and blue-green emission, respectively. The excitation spectrum of CaWO4:Tb3+ nanofibers or nanotubes consist of a broad band due to charge transfer absorption from the oxygen ligands to the central tungsten atom within the WO42- groups. The presence of the excitation peak of WO42- groups in the excitation spectrum of Tb3+indicates that there is an energy transfer from the WO42- groups to Tb3+ ions in the CaWO4:Tb3+nanofibers and nanotubes. Excitation into the WO42- group yields the emissions spectrum corresponding to the f-f transitions of Tb3+, which is dominated by the green emission 5D4-7F5 transition. Compared with the emission of Tb3+, the intrinsic blue emission from WO42- groups is very weak, suggesting that an efficient energy transfer from WO42- groups to Tb3+ has occurred. The energy transfer process also occurs between MoO42-and Ln3+in CaMoO4:Ln (Ln= Eu3+, Tb3+, Dy3+), the corresponding luminescence color can be tuned from blue-green to green, yellow, orange-red by changing the doping ion (Ln3+) and the doping concentrations of Ln3+ion in CaMoO4 nanofibers. Excitation into the host band of Gd2MoO6:Eu3+ nanofibers or nanobelts yields the emission spectrum corresponding to f-f transitions of Eu3+, which is dominated by the hypersensitive red emission 5Do-7F2 transition. The presence of the strong host band in the excitation spectrum of Eu3+ indicates that there exists an energy transfer from Gd2MoO6 host to the doped Eu3+Under ultraviolet excitation and low-voltage electron beam excitation, the doped rare earth ions show their characteristic emission in the obtained rare earth luminescent materials. The belt-like and tube-like phosphors have higher luminescence intensity than fiber-like phosphors due to lower defect concentration in the former. These studies indicate that electrospinning is a facile route for the development luminescent materials that are useful in many types of color display fields. Luminescent, porous and bioactive europium-doped hydroxyapatite (HAp:Eu3+) nanofibers and microbelts have been prepared by a combination method of sol-gel and electrospinning process using cationic surfactant as template. The obtained multifunctional hydroxyapatite nanofibers or microbelts, which possess porous structure and red luminescence property, can be performed as a drug delivery host carrier to investigate the drug storage/release properties using ibuprofen (IBU) as a model drug. In addition, the emission intensity of Eu3+ in the drug carrier system varies with the released amount of IBU, thus making the drug release be easily tracked and monitored by the change of the luminescence intensity. This material, which combines the porous structure and the strong red luminescent property, can be served as a novel functional drug delivery system, demonstrating a great potential in the drug delivery and disease therapy field.
Keywords/Search Tags:rare earth luminescent material, electrospinning, luminescent properties, energy transfer, drug delivery
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