Study On The Photoluminescence Properties Of The Rare Earth Doped Oxide Phosphors Prepared By Hydrothermal Method

Due to the potential applications in the tricolor energy-saving lamps, cathode ray tube, field emission display and plasma display panel and so on, phosphors based on the rare earth elements (RE) doped materials have attracted enormous interests. However, the mainly used phosphors are the photoluminescence material based on the sulfide. Sulfide based phosphors have many disadvantages such as: poor thermal stability and generation of contamination gas. Even though the RE based phosphors have good photoluminescence properties, the cost is too high. Therefore, it is of great importance to reduce the environment pollution and lower the cost as well as to improve the photoluminescence properties of RE based phosphors.In the thesis, a novel synthesis route of Y₂O₃:Eu³⁺, Gd₂O₃:Eu³⁺ and Y₂O₃:Tb³⁺, Gd₂O₃:Tb³⁺ phosphor was proposed. By adjusting the experimental conditions, the optimum doping amount of activator ions (Eu³⁺ and Tb³⁺) was achieved. Furthermore, metals ions (Li⁺, Mg²⁺, Al³⁺) were co-doped into the phosphors to improve the photoluminescence properties of the as-prepared phosphors, make sure which the best doping ions and theirs the best doping amounts. The major results achieved in the thesis are given as follows:Firstly, red phosphors Y₂O₃:Eu³⁺and Gd₂O₃:Eu³⁺ were prepared by a simple hydrothermal process followed by a post-annealing process. Y₂O₃:Eu³⁺ phosphor achieves the strongest emission intensity as the molar ratio of Y³⁺ to Eu³⁺ is 20:1. Gd₂O₃:Eu³⁺ phosphor achieves the strongest emission intensity as the molar ratio of Gd³⁺ to Eu³⁺ is 30:1. In order to further enhance the emission intensity, metals ions (Li⁺, Mg²⁺, Al³⁺) were doped and red phosphors Y₂O₃:Eu³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) and Gd₂O₃:Eu³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) were prepared. The result showed that red phosphor Y₂O₃:Eu³⁺:Li⁺ achieves the strongest emission intensity as the molar ratio of Y³⁺:Eu³⁺:Li⁺ is 20:1:1, and the emission intensity is 1.06 times as high as that of the Y₂O₃:Eu³⁺ phosphor. Gd₂O₃:Eu³⁺:Li⁺ achieves the strongest emission intensity as the molar ratio of Gd³⁺:Eu³⁺:Li⁺ is 30:1:0.5, and the emission intensity is 2.42 times as high as that of the Gd₂O₃:Eu³⁺ phosphor. Gd₂O₃:Eu³⁺:Mg²⁺ achieves the strongest emission intensity as the molar ratio of Gd³⁺:Eu³⁺:Mg²⁺ is 30:1:1, and the emission intensity is 1.27 times as high as that of the Gd₂O₃:Eu³⁺ phosphor. For the phosphors doped with Al³⁺, the emission intensity of Y₂O₃:Eu³⁺ and Gd₂O₃:Eu³⁺ decreased. The result shows that Li⁺ ions are suitable dopants for the improvement of photoluminescence properties of Y₂O₃:Eu³⁺, while Li⁺ and Mg²⁺ ions are suitable dopants for the improvement of photoluminescence properties of Gd₂O₃:Eu³⁺.Secondly, green phosphors Y₂O₃:Tb³⁺and Gd₂O₃:Tb³⁺ were prepared by a simple hydrothermal process followed by a post-annealing process. Y₂O₃:Tb³⁺ phosphor achieves the strongest emission intensity as the molar ratio of Y³⁺ to Tb³⁺ is 20:1. Gd₂O₃:Tb³⁺ phosphor achieves the strongest emission intensity as the molar ratio of Gd³⁺ to Tb³⁺ is 30:1. In order to further enhance the emission intensity, metals ions (Li⁺, Mg²⁺, Al³⁺) were doped and green phosphors Y₂O₃:Tb³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) and Gd₂O₃:Tb³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) were prepared. The result showed that green phosphor Y₂O₃:Tb³⁺:Li⁺ achieves the strongest emission intensity as the molar ratio of Y³⁺:Tb³⁺:Li⁺ is 20:1:1, and the emission intensity is 1.16 times as high as that of the Y₂O₃:Tb³⁺ phosphor. Y₂O₃:Tb³⁺:Mg²⁺ achieves the strongest emission intensity as the molar ratio of Y³⁺:Tb³⁺:Mg²⁺ is 20:1:10, and emission intensity is 1.04 times as high as that of the Y₂O₃:Tb³⁺ phosphor. Gd₂O₃:Tb³⁺:Li⁺ achieves the strongest emission intensity as the molar ratio of Gd³⁺:Tb³⁺:Li⁺ is 30:1:1, and the emission intensity is 1.51 times as high as that of the Gd₂O₃:Tb³⁺ phosphor. Gd₂O₃:Tb³⁺:Mg²⁺ achieves the strongest emission intensity as molar ratio of Gd³⁺:Tb³⁺:Mg²⁺ is 30:1:5, and the emission intensity is 1.11 times as high as that of the Gd₂O₃:Tb³⁺ phosphor. For the phosphors doped with Al³⁺, the emission intensity of Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ decreased. The result shows that Li⁺ and Mg²⁺ ions are suitable dopants for the improvement of photoluminescence properties of Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺.Thirdly, red phosphors Y₂O₃:Eu³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) and Gd₂O₃:Eu³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) and green phosphors Y₂O₃:Tb³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) and Gd₂O₃:Tb³⁺:M (M=Li⁺, Mg²⁺, Al³⁺) were prepared by a hydrothermal process. The results of XRD showed that all prepared phosphors with a cubic crystal structure. Different doping ions or same doping ions with different doping amounts have great effect on the structural properties of the as-prepared phosphors.In conclusion, phosphors Y₂O₃:Eu³⁺and Gd₂O₃:Tb³⁺ were prepared by hydrothermal method. It is found that the doping metals ions (Li⁺, Mg²⁺, Al³⁺) may improve the photoluminescence properties and the thermal stability. Finally, the result shows that phosphors: Li⁺ doped red phosphors Y₂O₃:Eu³⁺ and Gd₂O₃:Eu³⁺, Mg²⁺ doped red phosphors Gd₂O₃:Eu³⁺; Li⁺ and Mg²⁺ doped Y₂O₃:Tb³⁺ and Gd₂O₃:Tb³⁺ show better photoluminescence properties.