Dissertation > Excellent graduate degree dissertation topics show

Synthesis,Phase Composition and Luminescence Property of Rare Earth Molybdate Red Phosphors

Author: RaoYang
Tutor: LiYongXiu
School: Nanchang University
Course: Inorganic Chemistry
Keywords: Co-precipitation Zinc molybdate red phosphors rare earths phasecomposition
CLC: O611.4
Type: Master's thesis
Year: 2012
Downloads: 114
Quote: 0
Read: Download Dissertation

Abstract


Red phosphors are key materials for the improvement of color rendering index of LED lighting, and play an important role in white LED energy-efficient lighting devices. Among them, rare earth doped molybdate red phosphors have attracted widespread attention due to their high stability and high luminescence efficiency. However, the phase composition of molybdate is changeable with synthesis conditions, which leads to a significant impact on their luminescent properties. The aim of this study was focused on the exploitation of red phosphors with high luminescence efficiency by tuning the phase composition through the synthesis condition optimizing.Firstly, a series of zinc europium molybdate red phosphors have been prepared using a simple chemical co-precipitation method, and their structure, photo luminescent (PL), particle size and morphology were characterized. It was found that the excitation spectra of as-synthesized phosphors are attributed to the charge transfer absorption band of molybdate and the f-f characteristic emission of Eu3+at395nm and466nm, and the emission spectra of Eu3+display the transition of5D0-7Fj with main peak at613nm. The as-synthesized samples are composed of two phases, one is the fine crystalline Zn5Mo2O11.5H2O, another is an unknown phase with poor crystal. Strengthening stirring or prolonging aging time can reduce the phase content Zn5Mo2O11.5H2O and decrease the fluorescence intensity as well as the particle size, indicating that Zn5Mo2O11.5H2O has more significant contribution on the fluorescence intensity and can transfer to the unknown phase during the aging process. The optimal synthesis conditions regarding to the fluorescence intensity were determined to be pH value7.0-8.0, Eu3+doping concentration25%, reaction temperature35℃. Charge compensation can effectively improve the luminous intensity of phosphors and Li+is found to be the best one. SEM results showed that the morphology of samples prepared by co-precipitation is irregular shape, however, the particles prepared under the existing of PVP is hexagonal sheet with particle size ranging from2to4μm, illustrating that the addition of dispersants can influence on the morphology of phosphors.Zn0.5MoO4:Eu0.25Li0.25red phosphor synthesized by high temperature solid state can be effective excited by395nm near-ultraviolet and466nm blue-ray, and emit the pure red color at615nm. However, it is difficult to obtain phosphor with pure phase and the doped concentration of europium is high. So a series of Bi3+, Sm3+, Y3+and Gd3+co-doped phosphor were synthesized by high temperature solid-phase method to investigate the influence of partial replacement of Eu3+by Bi3+, Sm3+, Y3+or Gd3+and charge compensation replacement of2Zn2+with Gd3++Li+on the phase composition, luminescence intensity. The results demonstrated that partial replacement of Eu3+by Bi3+, Y3+or Gd3+does not lower the fluorescence intensity, which is beneficial for the synthesis of phosphors with high efficiency and low Eu3+doping concentration. The optimal percentage of Bi3+for replacing Eu3+is8%. At the same time, a remarkable red shift was observed in the emission spectrum of sample with co-doping of Y3+. On contract, co-doping with Sm3+resulted in the fluorescence intensity decreasing. With the replacement percentage of2Zn2+with Gd3++Li+increasing, the fluorescence intensity of zinc molybdate was increased first and then decreased, correspondingly, the phase composition varied from multiphase to single phase. This fact illustrated that the existing of few of zinc molybdate phase shows contribution to the luminescence emission, because the emission of samples with pure calcium molybdate phase is lower than that with multiphase. Therefore, it is an effective method for exploiting high efficiency luminescence materials and optimizing synthesis condition through the tuning of phase composition.

Related Dissertations

  1. Studies on Synthesis, Characterization and Properties of Fe-V Co-doped TiO2 Catalyst,O614.411
  2. The Study of TWC Catalytic Removal NOx from Waste Incineration Flue Gas,O643.36
  3. Arsenic and antimony chalcogenides Solvothermal Synthesis and Characterization,O641.4
  4. IVA metal chalcogenides Solvothermal Synthesis and Structure,O611.4
  5. Al Doped Zno Transparent and Heat Insulation Coatings,TB383.1
  6. Synthesis and Properties of Rare Earth Red-emitting Phosphors for White LED,O482.31
  7. The Research on Preparation Technology and Sintering Behavior of Rare Earth Aluminates (Dy3Al5O12、 NdAlO3、LaAl11O18),TB383.3
  8. Preparation and Research Electrochemical Properties of LiFePO4 for Cathode Material of Lithium-ion Batteries,TM912
  9. Study on Synthesis and Magnetism of Flake Shaped BaFe12O19,TB383.1
  10. La 0.5 Sr 0.5 Preparation and Characterization MnO 3 perovskite -type oxides,O611.4
  11. Lithium- ion battery cathode material lithium iron phosphate synthesis and modification,TM912
  12. Study on the Synthesis and Optical Properties of New Inorganic Luminescent Materials Co-doped with Rare Earth Ions,O611.4
  13. New multi- color fluorescent nano- biological materials and research,TB383.1
  14. Fabrication and Properties of Nano-sized Powders and Transparent Ceramics of Lutetium Compounds,TQ174.1
  15. Preparation and Property Investigation of Fe3O4 and Fe3O4 @ Gd2O3:Eu Labeling Nanoparticles,TB383.1
  16. Preparation and Properties of LiFePO4/C as a Cathode Material for Lithium-ion Batteries,TM912
  17. The Search of Potential Binding Sites of Serum Response Factor (SRF) and Research of the Profile of the Binding Sites of SRF in Human Genome,Q75
  18. Synthesis and Luminescent Properties of Rare Earth Doped YAB Green Phosphor,O482.31
  19. Preparation and thermodynamic study of copper indium oxide nanopowder,TB383.1
  20. The Preparation of the Hydrogen Carrier Methylcyclohexane’s Dehydrogenation Catalyst Ni-Cu/γ-Al2O3 and Its Reaction Performance,TQ203.2
  21. Study on Preparation and Luminescent Properties of γ-LiAlO2 Based Luminescent Materials,O611.4

CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Chemical elements and inorganic compounds > Inorganic synthetic chemistry
© 2012 www.DissertationTopic.Net  Mobile