Study On The Controllable Synthesis Of Rare Earth Doped Tungstate And Their Photoluminescence Performance

Micro-/nano-materials of metal tungstates have been received increasing interests in the field of catalytic oxidation and photoluminescence, because of their peculiar crystallographic structure and striking nano-effect. Therefore, it is not only full of great social and economic values but also a heat pot of present research area that controlled synthesis micro-/nano-materials of metal tungstates with various morphologies, to study the performance of material dependence on their structure,size and morphology, and to find their new applied fields. In this paper, a serious of micro-/nano-materials of metal tungstates materials with different crystalline structures and morphologies have been synthesized by a hydrothermal method. The as-prepared products and their properties were characterized by XRD?SEM?FTIR?PL and so on. The main details of research are summarized as follows:1 ? Under a mild heat of 170?, three-dimensional?3D? flower-like Bi₂WO₆ microspheres has been fabricated by a sodium nitrate assisted hydrothermal method using Na₂WO₄·2H₂O and Bi?NO₃?₃·5H₂O as precursors. It has found that sodium nitrate played an important role in directing growth and self-assembly flower-like Bi₂WO₆ microspheres by changing the concentration of the additives. On the basis of appropriate of additive concentration demonstrated that the changing pH value carries a great effect on the morphology and the phase composition of Bi₂WO₆ microspheres. The results indicate the product has always been the Bi₂WO₆ when the pH value is less than 10.8. While transforming the pH = 12.4, then the product was converted to Bi_3.84W_0.16O_6.24 and the BET of the obtained powder is 33.427m2g-1 at pH=1.2 and the 4M sodium nitrate solution.2 ? The NaLa?WO₄?₂ have been synthesized via a PEG-400 assisted hydrothermal method. The results indicate that the powders undergo a phase transformation from WO3?NaLa?WO₄?₂ with the increase of pH value from 1.0 to9.0. Highly uniform monodisperse distribution millefeuille-like microcrystalline with three dimensional structure were prepared under the condition of 180?,pH=9.0 and VPEG-400:VH20=1:1. Meanwhile, the emission spectrum excited by 393 nm shows that the transition 5D0?7F1 is much greater than the 5D0?7F2 when Eu³⁺ was doped, which indicates that Eu³⁺ ions occupy noninversion center sites in NaLa?WO₄?₂ crystal lattice. The as-prepared powders display strong redluminescence. Concentration quenching would be seen while continue to increase the doping content of Eu³⁺ to 20mol%.3 ? The red NaLa?WO₄?₂:Eu³⁺-Bi3 + phosphors have been synthesized via a PEG-400 assisted hydrothermal method. The powders have always been pure phase at the pH value from 7.0 to 10.0. Highly uniform monodisperse square shaped crystallites with the size ranged from 5-6?m were prepared under the condition of180?, pH=9.0, VPEG-400:VH20=1:1 and 5% Eu³⁺-doped. The formation of the products tend to have a spherical growth when the incorporation of Bi³⁺ increased;Meanwhile, the emission spectrum excited by ?ex=396nm shows that the powders display strong red luminescence and Eu³⁺ occupy noninversional central position in NaLa?WO₄?₂ crystal lattice. Well sensitization effect can be seen by the incorporation of a small quantity of Bi³⁺. The optimum amount of Bi³⁺ is 0.8mol% and the luminous intensity of Eu³⁺ increased nearly 4.2 times. To continue to increase the doping content of Bi³⁺ will lead to concentration quenching and the cascade energy transfer mechanism of the bismuth ion bridge: WO42-?Bi³⁺?Eu³⁺ is also studied.4?Different morphologies of NaLa?WO₄?₂ microcrystalline were synthesized via a simple NaNO₃ assisted hydrothermal method. The laminar structure,carambola-like structure and olive-like structure NaLa?WO₄?₂ microcrystalline could obtained by regulating the concentration of NaNO₃. Furthermore, NO3- played a key role in directing products growth and self-assemble into olive-like structure from laminar structure when the additives were changed to Na F and KNO3. When doped with Eu³⁺ and Tb³⁺ and the quenching concentration were 20mol% and 15mol%,respectively. The luminescence properties depends on micromorphology of the products strongly, the olive-like structure with length of 6?m in average and middle width of 3?m in average showed the best performance.