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Synthesis and Luminescent Properties of Rare Earth Doped Molybdate Phosphors Materials for Light Emitting Diodes

Author: LiQiuXia
Tutor: ChenDongHua
School: Central South University for Nationalities
Course: Physical and chemical
Keywords: Luminescence LEDs Solid-state reaction Molybdate Charge compensation Energy transfer
CLC: TN312.8
Type: Master's thesis
Year: 2011
Downloads: 83
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Abstract


With many obvious advantages as green lighting, the White LEDs has attracted more and more attention by the people, and has been focused on in the LEDs research filed.At present, the routine for fabrication of WLEDs is the phosphor-convened LEDs（pc-LEDs）in which a single blue or near ultraviolet LED chip is combined with multi-color phosphors. In phosphor-converted light-emitting diodes devices, the red/green/blue tricolor phosphors are pumped by UV-InGaN chips （400 nm） or blue GaN chips （460 nm） and generate white light. However, the efficiency of the Y2O2S: Eu3+ is instable due to the release of sulfide gas, and is much lower than that of the blue and green phosphors. Based on blue LED plus yellow phosphor, there exists at least two drawbacks, such as lower color-rendering index, lower luminous efficiency. So that red-emitting phosphor is introduced to improve the CRI and increase the light conversion efficiency. Hence, in order to improve the efficiency of the phosphor, it is urgent to research and develop new, high efficiency and stable families of red-emitting phosphors with high absorption in the UV or blue wavelengths.This paper we start from synthesizing researching novel red phosphors materials for Light Emitting Diodes as a starting point. By solid-state reactions, Molybdate as matrix, rare earth ions of Pr3+, Eu3+ as primarily activators, and appropriate auxiliary added, in the paper, the synthesis and photo luminescent characteristics of the four series of red-emitting materials were investigated in details, which can be excited efficiently by UV （397 nm） or blue （466 nm） light:The series of phosphor KxSr1-2xMoO4: xPr3+（0.00≤x≤0.04） was synthesized, and luminescent properties were studied. The crystallization , particle sizes of samples and the excitation and emission spectra were investigated by powder X-ray diffraction（XRD）, transmission electron-microscopy（TEM） and LS-55 luminescence spectrophotometer, respectively. TEM images were in good agreement with the theoretical calculation data from the XRD patterns. The doping concentration of rare earth ions and the sintered temperature were optimized. As a dispersant, the influence of the PEG on the luminescent properties and morphological characterization of the phosphors were investigated.The series of phosphor （BaSr）MoO4: Pr3+, RX（R = Li/Na/K, X = F/Cl/Br） was synthesized, and luminescent properties were studied. Their crystal structures, photo luminescent characteristics were investigated, respectively. The conditions for synthesis of these phosphors are also optimized, including the sintering temperature and concentration of Pr3+ ions. Influence of the replacement way on the properties of phosphor was investigated. The effects of auxiliary reagent on the crystal structure, luminescence properties such as luminescence intensity and morphology of particles were investigated, and the best auxiliary reagent was determine.The series of phosphor Y2（Mo/WO4）3: Eu3+was synthesized, and luminescent properties were studied. Using the Eu3+ as activators, polyethylene glycol （PEG） as dispersant, Y2（MoO4）3: Eu3+were synthesized by solid-state reactions, and their crystal structures, morphology of particles and photo luminescent characteristics were investigated, respectively. Through experimentation, MoO42- was partially substituted by WO42-, the phosphor of Y2（Mo/WO4）3: Eu3+ were synthesized and studied.The series of phosphor K2Ba（MoO4）2: Eu3+/Sm3+, X-（X = F/Cl/Br） was synthesized, and luminescent properties were studied. The concentration of Pr3+ ions and sintering temperature were optimized by XRD diffraction and spectral characteristics, and the critical transfer distance （Rc） among Eu3+ ions is calculated. Sm3+ ion and a monovalent anion X-（X = F/Cl/Br） can be usedto enhance the light emission of Eu3+-activated phosphors, as an efficient sensitizer as charge compensation, respectively. Further, the possible emission mechanism was discussed about the charge transfer mechanism from Sm3+ to Eu3+. A monovalent anion charge compensation influence on the luminescent intensity of phosphors is investigated.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Semiconductor technology > Semiconductor diode > Diodes: structure and performance > Light-emitting diodes
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