| White light emitting diodes (W-LEDs) are considered as the next-generation light source for general illumination due to the superior advantages such as high efficiency, high brightness, long lifetime, low power consumption, etc. Therefore, to research and development W-LEDs is meaningful and important no matter to market prospects, economic value or from the social benefits. Under this background, there is an urgent need to develop a new luminescent materials with stable, efficient and environment friendly properties with the rapid development of white LED devices. Tungstate is a kind of self-activated luminescent materials with good chemical stability and thermal stability, and we choose it as the object to study. Nowadays, the conventional solid-phase method (often higher than 1000K) was used as the key method to prepare luminescent-materials with drawbacks:high temperature, high energy consumption. In this paper, we used the hydrothermal method with optimizing the synthesis process parameters:such as temperature, time, pH, etc. to prepare europium-doped tungstate nanorods-phosphors and studied the luminescent properties.The first chapter introduces the development background, main categories and preparation methods of luminescent materials, mainly to the tungstate luminescent material and rare earth ions. CdW04 crystals has been widely used in the XCT detector for scintillation properties; CdWO4 ceramics is used to make filters, dielectric substrate and other microwave devices; CdWO4 nano-powder is used as photocatalysts for environmental protection to rhodamine B, methyl orange and other compositions. These applications have shown that CdW04 has good light emitting characteristics, and the properties can be improved with adding appropriate active ions, so we believe CdWO4 have potential application as a phosphor.The second chapter was used to introduce main instruments and reagents which was need to the preparation. Then, we also briefly introduce the characterization methods,In the third chapter, Eu3+-doped CdWCU phosphors with different doping concentrations were synthesized by a hydrothermal method. The as-prepared CdWO4:Eu3+phosphors showed strong red emission at 613 nm corresponding to the 5D0-7F2 transition of Eu3+under 464 nm blue light excitation. The optimized doping concentration of Eu3+was 0.5 mol% for the highest emission intensity at 613 nra, and the concentration quenching occured when the concentration of Eu3+was beyond 0.5 mol%. As the CdWO4.0.5%Eu3+phosphor was pumped by blue-light, high color purity and high luminous intensity red emission with chromaticity coordinates (0.6465,0.347) was achieved which was close to the NTSC(x= 0.670, y=0.33). This phosphor matched well with the output wavelength of commercial GaN-based blue light-emitting diodes (LEDs), and may have potential application in white light emission devices based on blue LEDs.In the fourth chapter, Eu3+€dWO4 single-phased phosphor for white-light-emitting diode (W-LED) was prepared by a hydrothermal method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as photo luminescence (PL) spectra. The main luminescence center changed between WO42" groups and Eu3+ions at different pH values, which led to different light-emitting properties of the samples. Under the excitation of 296 nm UV light, stable and independent white emission could be achieved when the pH value of the precurcor was 7. The CIE chromaticity coordinates of the Eu3+CdWO4 phosphor synthesized at pH=7 were jc=0.323 and j>=0.317, which were close to the values of standard chromaticity (x=0.33 and j=0.33) for NTSC system. The CIE chromaticity calculation demonstrated its potential application in white light emission devices based on UV chips.The last chapter summarized the innovation and some conclusions of this article. At same time, we describe the main research directions of the luminescent materials, then draft some plans. |
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