Synthesis Of Tungstate And Molybdate Nano-particles And Study On Their Luminescence Properties

Nanoparticles and nanocluster materials are a new class of advanced materials exhibiting unique chemical and physical properties compared to those bulk materials. Tungstates and molybdates are two important families of inorganic materials which have high potential applications in various fields, such as in photoluminescence, microwave applications, optical fibers, scintillator materials, humidity sensors, magnetic properties, and catalysis. Tungstates and molybdates have been prepared by different routs, such as Czochralski method, solid state reaction, heating of RO film with WO3 vapor, sol-gel reaction. However, these methods have some disadvantages, e.g. high temperature and prolonged reaction time being needed, larger particles in size and irregular in morphology, and inhomogeneous chemical composition. On the contrary, molten salt method and hydrothermal method are of simple instrumentations, low temperature, short holding time and available to a large scale production. Therefore, in this thesis, we have prepared tungstates and molybdates powders by a molten salt method and hydrothermal method.1. Na2WO4 and Zn(NO3)2 were used as the starting materials, and ZnWO4 nanoparticles were successfully synthesized by a molten salt method with LiNO3 salt. The powders obtained were characterized by using X-ray diffractometer (XRD), a transmission electron microscope (TEM) and photoluminescence spectra (PL), respectively. The morphology and dimension of the ZnWO4 nanorods were affected by such conditions as calcining time and the weight ratio of the salt to ZnWO4 precursor. The improved PL properties of the ZnWO4 nanorods can be obtained with the decease to nanometer scale in particle size.2. SrWO4 nano-particles with a scheelite structure were successfully prepared by a molten salt method, Na2WO4 and SrCl2 as the starting materials. SrWO4 nano-particles were characterized by XRD, SEM, TEM and PL, respectively. The results showed that we could get SrWO4 powders by a direct precipitation in the room temperature, which were larger and inhomogeneous. However, SrWO4 nano-particles could be obtained by a molten salt method at a low temperature. The particle size, morphology, and crystallinity of SrWO4 nanoparticles are strongly relied on such experimental parameters as holding time and weight ratio of LiNO3 salt to SrWO4 precursor. The formation and development of SrWO4 crystallites should be based on a dissolution-recrystallization process. The improved PL properties of SrWO4 crystallites strongly relied on their particle size and crystallinity. The better crystallinity, the higher PL emission peak is.3. CdMoO4 nano-particles were successfully synthesized by a hydrothermal process at a low temperature, and the powders were characterized in detail by XRD, SEM, TEM and PL, respectively. CdMoO4 particles could be obtained under the hydrothermal condition from micrometer to nanometer sizes by varying their precursors. The PL spectra results showed that the optical properties of CdMoO4 crystallites obviously relied on their particle sizes. The improved PL properties of CdMoO4 crystallites can be obtained by decreasing the particle size to a nanometer scale.4. CdMoO4 precursor was synthesized by a microemulsion method with Na2MoO4 and Cd(NO3)2 as the starting materials, and CdMoO4 nano-particles were successfully synthesized by a molten salt method. The powders were characterized in detail by XRD, SEM, TEM and PL, respectively. The results showed that with a proper weight ratio of the salt, prolonging the holding time can affect the CdMoO4 crystallinity and particle size a lot. However, with a definite holding time, changing the weight ratios of the salt has little influence on the CdMoO4 crystalinity and particle size. The improved PL properties of CdMoO4 crystallites strongly relied on their particle size and crystallinity. The better crystallinity, the higher PL emission peak is.