Hydrothermal Synthesis Of Silicate Phosphors

Green fluorescent zinc silicate (doped with Mn²⁺), red fluorescent zinc silicate (doped with Eu³⁺), and red fluorescent yttrium silicate (doped with Eu³⁺) were prepared hydrothermally at low temperature in this work. The effects of reaction parameters on their formation, crystallite structure, morphology, size and luminescence were investigated and discussed. A possible formation mechanism was brought forward. Experimental base and academic gist were provided for preparation of silicate.We had developed a hydrothermal method to prepare Zn₂SiO₄ nanocrystallines. Orbicular or virgulate Zn₂SiO₄ had been attained by the reaction of zinc acetate and tetraethyl orthosilicate (TEOS) or sodium silicate. On the basis of the above experimental results, if TEOS was used as silicon source to synthesize Zn₂SiO₄ at the present of ammonia, the sample particles would tend towards the formation of nanorod with the increasing of base concentration. Moreover, when TEOS was used as silicon source to synthesize Zn₂SiO₄ in different solvent systems with different solvent ratios, pure-phase Zn₂SiO₄ can be obtained under the condition of different lowest reaction temperature. Furthermore, strong green and red fluorescence property was obtained by the Mn²⁺ or Eu³⁺ doping in Zn₂SiO₄, respectively, Further research is being carried out on the mechanism of morphology forming and the smaller particles' preparation. Presently, blue luminescent film Zn₂SiO₄:Ce³⁺ had been prepared by sol-gel method, we will try to make blue luminescent powder by hydrothermal method, then white-light powder with the same host material maybe prepared in the future.The mixture of ethanol and oleic acid was used as solvent to prepare Zn₂SiO₄ with solvothermal method. In order to control the size and morphology, we change solvent ratio of ethanol-oleic acid (v/v). We prolong the time of beating up mixture. When the ratio of ethanol-oleic acid (v/v) is 1/1.5, we found that the size of sample was smaller. We also had tried to prepare Zn₂SiO₄ using SiO₂ as silicon source. First, little size, uniform and well dispersed round SiO₂ particles was prepared with the hydrolysis of TEOS. And then, tried to synthesize Zn₂SiO₄ using SiO₂ as silicon source. Because of the low reactive activity of SiO₂, when without enough ammonia in the reactive mixture, the product is ZnO; and when large quantity ammonia was put in the reactive mixture, the product is pure-phase Zn₂SiO₄. The intensities of Zn₂SiO₄ peaks in XRD picture increase with the increasing ammonia content in the mixed solvent system. Too much ammonia in the mixed solvent system led to the formation of big rod particles.It is very difficult to prepare yttrium silicate with hydrothermal method or solvothermal method at low temperature, nowadays, it was developed certainly, the mixture of some yttrium silicate had been synthesized. In this method, different silicon source and different yttrium source did not influence formation of final product, and the best condition of reaction is 230℃, 12h, and with a certain quantity NaOH as mineralizing agent activator. Moreover, the yttrium silicate is very steady at high temperature; its morphology is bundle of rods and blossom; and it displays strong red fluorescence when excited by ultraviolet light...