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Research on Tungsten, Molybdate Fluorescent Material by Molten Salt Synthesis Method

Author: ZhouShengPing
Tutor: WangJiaGuo
School: Wenzhou University
Course: Physical and chemical
Keywords: Molten salt method Fluorescence Crystal growth Morphology
CLC: TB34
Type: Master's thesis
Year: 2011
Downloads: 114
Quote: 0
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Abstract


Rare earth doped fluorescent materials are widely used in lighting, display devices, sensors, high-energy physics, biomedical and other fields. The red phosphors AMoO4:Eu3+, Li+（A=Ca, Sr）, EuLiM2O8（W =Mo, W）, Y2O3:Eu3+ and the yellow white LED phosphor Y3Al5O12:Ce3+（YAG:Ce） synthesized by molten salt method can be effectively excited by ultraviolet light or blue light and emit fluorescence with high intensity.. The growth of fluorescent material crystals in molten salt can be controlled by adjusting the type and the amount of molten salts, reaction temperature and reaction time. The influence of experimental conditions on composition, morphology and luminescence properties of samples has been investigated by XRD, SEM, excitation and emission spectra. Specific conclusions are as follows:1. In molten salt environment, octahedral particles AMoO4:Eu3+, Li+（A=Ca, Sr） and EuLiM2O8（W=Mo, W）, fibrous SrMoO4:Eu3+, Li+, rod EuLiM2O8（W=Mo, W）, spherical Y2O3:Eu3+ and spherical YAG phosphors have been successfully synthesized.2. Octahedral shape of phosphor crystals have been obtained in NaCl at 800°C, fibrous and rod-like phosphor crystals have been prepared in KCl respectively at 900°C and 800°C. Spherical Y2O3:Eu3+ particles have been fabricated in Li2SO4 at 1100°C. Globular YAG:Ce3+ crystals have been obtained in KCl with K3PO4 as a additive at 1200°C. With the temperature and molten salt content increasing, the morphology of tungsten molybdate phosphors has changed to be irregular flakes. 3. It is observed that the fluorescence intensity of CaMoO4:Eu3+, Li+ decreases with the increase of the reaction temperature. It is supposed that it is difficult for Eu3+ to enter the lattice of host CaMoO4 at high temperature. Therefore, the characteristic emission of Eu3+ decreases whereas the intrinsic emission of molybdate calcium increases. In EuLiM2O8 phosphor system, the luminous intensity of rod-shaped samples is higher than that of octahedral samples. In Y2O3:Eu3+ system, the brightness of the samples obtained in sulfate is higher than that in chloride. The sample Y2O3:Eu3+ synthesized in Li2SO4 shows the highest brightness compared to those synthesized in other molten salts. As for the YAG:Ce phosphor, the sample with homogeneous morphology obtained in the complex molten salt of NaCl and KCl has higher brightness than that synthesized in single molten salt.

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