Hydrothermal Synthesis And Morphology Control Of Titanates

The physical or chemical properties of titanates,such as mechanical,photoelectric,magnetic and catalytic properties,depend on the crystal shape,grain size,morphology and surface state of the material itself.The evolution of grain size and morphology are of great significance to the development of material science to realize various functions of titanate and broaden the application field.Calcium titanate is a cubic system and a typical representative of perovskite structure.Due to its many existing and potential applications,the preparation and performance optimization of calcium titanate has become a hot topic.Among the common preparation methods of calcium titanate,the morphology and size of the samples prepared by hydrothermal method are controllable,the chemical purity is high,and the phase is uniform.In this paper,three kinds of CaTi03:Pr3+phosphors with different morphologies were synthesized using three different morphologies of precursors by hydrothermal doping Pr3+.The effects of hydrothermal temperature,hydrothermal time and concentration of NaOH on its composition,morphology and luminescence properties were studied.The samples were characterized by X-ray diffraction,scanning electron microscope,transmission electron microscope and fluorescence spectrometer.The results show that:(1)CaTi03:Pr3+ red phosphors were prepared by hydrothermal method using titanium dioxide hydrate nanowires as precursors.When the hydrothermal temperature is 200 ? and the hydrothermal time is 6 h,hollow cube CaTi03 prepared is not only of high purity,but also has a good shape of hollow cube with a diameter of about 1?m?1.5 ?m.The optimum concentration of NaOH was determined to be 2 mol/L by changing the concentration of NaOH.It is inferred from the SEM diagram that the hollow cube is due to the directional growth of nanowires and Oswald ripening effect.In addition,the fluorescence measurement results show that hollow cube CaTiO3:Pr3+phosphors have good luminescence performance.(2)CaTi03:Pr3+ red phosphors were prepared by hydrothermal method using micron spheres as precursor.When the hydrothermal temperature is 200 ? and the hydrothermal time is 1 h,the layered CaTi03 not only has high purity,but also exhibits uniform and complete layered morphology.The pore on the surface of the crystal is due to the formation of bubbles in the decomposition of organic matter in the process of microspheres dissolution and reprecipitation.In addition,the fluorescence results show that the strongest excitation peak of the product is at 330 nm and the strongest emission peak is at 612 nm.(3)CaTi03:Pr3+ red phosphors were prepared by hydrothermal method using K2Ti4O9 whiskers as precursor.When the hydrothermal temperature is 180? and the hydrothermal time is 16 h,the cubic CaTiO3 is not only of high purity but also of good dispersion.In the preparation process,the hydrothermal conditions need to be strictly controlled,because the excessive temperature of hydrothermal or the prolongation of hydrothermal time will lead to crystal agglomeration.(4)The morphology and luminescence intensity of CaTi03:Pr3+phosphors with three different morphologies synthesized by hydrothermal synthesis were compared.The results show that layer-like shape CaTiO3:Pr3+ phosphor prepared by using micronspheres as precursor has the strongest luminescence,but the cubic CaTiO3:Pr3+ phosphor prepared with potassium tetratitanate whiskers as precursor has the longest afterglow life.