Synthesis And Luminescent Properties Of The Green Phosphor Ca₃Sc₂Si₃O₁₂:Ce

In order to get high quality light in white LED, green phosphor is usually needed to improve green emitting of the device. Although there are a series of green phosphors, such as silicates, aluminates and oxynitrides, they had their disadvantages, and cannot feed the needs in actual application. A new high efficiency green scandium silicate phosphor-Ca3Sc2Si3O12:Ce was invented by Mitsubishi Chemical, however, its preparation and application are still being developed.In this thesis, the green phosphor Ca3Sc2Si3O12:Ce was synthesized by high temperature solid state method, the firing temperature, time and atmosphere of the synthesis process were investigated. Results show that this synthesis method usually leads to Sc2O3of impurity, which causes bad influence on luminous efficiency, stability and production cost. The matrix changes and positive ion substitution were revealed to have important influence on the structure and luminescence properties of the green phosphor Ca3Sc2Si3O12:Ce. These changes could reduce Sc2O3impurity, but they did not completely eliminate it, and the luminescence intensities of the as-prepared samples decrease by doping with other ions.The reaction mechanism of the phosphor synthesized by high temperature solid state method was investigated by means of thermogravimetry-differential thermal analysis (TG-DTA) and X-ray diffraction (XRD) analysis. Results show that the synthesis process mainly exhibits two steps:the first step is the metathesis reaction of CaC03and SiO2for producing CaSiO3and CO2; the second step is the reaction of CaSiO3and SC2O3for forming the target phosphor. The second step is the rate limiting one of total reaction, which is controlled by the diffusion of Sc2O3. The effect of firing conditions on the second step was analysed by means of The Gentling Equation. Results show that increasing of firing temperature and time is favorable for the reaction, while the reaction is impossibly completed by only changing reaction condition.In order to obtain pure Ca3Sc2Si3O12phase, a new synthesis route is proposed based on high temperature solid state method. Firstly, an intermediate compound Sc2Si2O7was synthesized by SC2O3and SiO2. Then Sc2Si2O7was fired, with other raw materials for producing the green phosphor Ca3Sc2Si3O12:Ce with pure phase and higher brightness. With this route, the reaction activity of Sc2O3was improved, and the reaction was finally completed with no Sc2O3impurity in the product.