Controllable Synthesis And Study On The Properties Of Rare Earth Doped Molybdate And Phosphate Phosphors

The rare earth elements exhibit specific optical properties, due to its unfilled 4f orbits and elections. Molybdates and phosphates doped with rare earth ions have become important materials including light emitting diodes, because of their excellent features, such as high security, long lifetime, tunable emission light colors and so on. In this thesis, hydrothermal and solvothermal methods were used to prepare a series of optical molybdates and phosphates doped with different rare earth ions. And the relations of their composition-structure and morphology-optical property were studied carefully. The main achievements were obtained as follows.The NaRe(MoO4)2 materials (Re= La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er) were prepared by the hydrothermal method, and characterized by XRD, SEM and so on. Meanwhile, the influences of the hydrothermal treatment time, temperature, pH value of the synthesis solution and Re3+/MoO42- molar ratios on the morphologies of samples were studied. The crystallization evolution mechanism of NaRe(MoO4)2 was proposed. And the effects the morphology and crystal size on their luminescent property were investigated carefully. At last, the white light NaY(MoO4)2 phosphor was obtained by co-doping Tm3+/Dy3+/Eu3+ions, and its CIE Chromaticity Coordinate is (0.33,0.33).Bipyramid NaY(MoO4)2 was synthetized by the EDTA-assisted method. With the help of EDTA, NaY(MoO4)2 bipyramid was formed gradually through an evolution from 0D primary nano-particles to 2D nano-sheets and eventually 3D bipyramid. Through La3+ was introduced into the NaY(MoO4)2 hosts instead of Y3+, NaYxLa1-x(MoO4)2 crystals were synthesized. When the x value is 0.5, the shape of the product is quasi-spherical and the red luminescent intensity is strongest. Compared with NaY(Mo04)2 host, the concentration quenching of Eu3+was increased to 10%.Rare earth nitrates and phosphate ester were used as the raw materials to prepare RePO4 (Re= Y, La, Gd) by the solvothermal method. In the synthesis process, the effect of water/ethanol volume ratio on the structure and morphology of sample was studied. It was found that pure YPO4 could not be obtained in the ethanol solvent. To obtain perfect morphology, the feeding ratio of Re and P should be controlled strictly. For the preparation of YPO4, the appropriate molar ratio of Re/P was 2/2; for YPO4, Re/P was 2/4; for GdPO4, Re/P was 2/10. In the YPO4 host, the quenching concentration of Eu3+ and Tb3+ is 5%, respectively. When Eu3+ and Tb3+ were co-doped into the YPO4 host, the luminescent color could be changed from red to green, for instance,3%Eu-2%Tb and 2%Eu-3%Tb were added in the YPO4 host, their CIE Chromaticity Coordinates were (0.360,0.333) and (0.340,0.347), respectively, which are closed to white light emission.