| White light-emitting diodes (W-LEDs) are considered as the fourth generation of solid-state lighting sources due to their energy savings, environmental friendliness, high energy efficiency and long persistence characteristics. Currently, white light is mainly achieved by phosphor converted LEDs. Therefore, the research and development of excellent phosphor is the precondition of a high quality W-LEDs. Because of its deficient red emission, commercial white light, which is formed by a blue InGaN LED chip and Y3Al5O12:Ce3+(YAG:Ce) Garnet phosphor, has high color temperature and low color rendering index. So the researchers suggested mixing red phosphors with YAG:Ce to improve this problem. In addition, white light can also be produced by using an ultraviolet (UV) LED chip coated with three emitting blue, green and red phosphors, which attracted significant attentions for its better color rendering index. As an important member of tricolor phosphor, the development of red emission phosphor is considered as an ignored subject in the field of optical materials. But the white light mixed from multiple phosphors has the new problems of re-absorption of emission colors and ratio regulation for each phosphor. On the basis of red phosphors research, a single-phased full color emitting phosphor for long-UV pumped white LED has been achieved in this thesis.Based on high physical and chemical stability, aluminates CaYAl3O7are selected to be the ideal host material in our work. Considering the traditional solid state method has high sintering temperature and clusters product. Combustion method is used in CaYAl3O7samples preparation to meet purpose of depressing sintering temperature and gaining uniformity products. The main work of this thesis is as follows.(1) CaYAl3O7:RE3+(RE=Eu, Sm, Ce, Tb) samples are synthesized by combustion method. Not only the influence of the reaction temperature, solution pH value and amount of fuel on CaYAl3O7single phase synthesis, but also the crystal structure of CaYAl3O7matrix is discussed in detail.(2) Red emission of Eu3+at617nm is obtained in CaYAl3O7:Eu3+samples under near393nm excitation. The red emission intensity of CaYAl3o7:Eu3+phosphor is improved by introducing charge compensation and sensitizer ions. Firstly, the influence of charge compensation ions Li+, Na+and K+ions on the red emission intensity of CaYAl3O7:Eu3+is studied. Take Li+as example, we focuse on the luminescence properties of CaYAl3O7:Eu3+, Li phosphor. When the concentration of Li+is at10mol%, the red emission intensity of Cao.8oYAl307:0.10Eu3+,0.10Li+at617nm is increased by25%compared with Ca0.9oYAl307:0.10Eu3+. Secondly, Sm3+ions are co-doped into CaYAl3O7:Eu3+phosphors as sensitizer. And an energy transfer channel, Sm3+→Eu3+, is built to raise the red emission intensity of CaYAl3O7:Eu3+samples. When the concentration of Sm3+is at4mol%, the red emission intensity of CaYAl3O7:0.04Eu3+,0.04Sm3+at617nm is increased by50%compared with CaYAl3O7:0.04Eu3+. Thirdly, the green typical emission of Tb3+ions is co-doped with CaYAl3CO7:0.04Eu3+,0.04Sm3+samples as the green component. The light-emitting color of CaYAl3O7:0.01Eu3+,0.04Sm3+, xTb3+can be tuned form the red light area (0.472,0.285) to the white light area (0.405,0.373) continuously by the adjustment of Tb3+concentration.(3) Red emission of Sm3+at600nm is obtained in CaYAl3O7:Sm3+samples under near402nm excitation. In consideration of the f-f absorption transitions of Sm3+ions which exhibits narrow band in the excitation spectrum. So the Ce3+→Tb3+→Sm3+energy transfer mechanism system is put forward to realize indirect sensitization effect of Ce3+on Sm3+and extend the excitation wavelength of Sm3+ion. In the meantime, the light-emitting color of CaYAl3O7:0.01Eu3+,0.04Sm3+, xTb3+is tuned form the blue light area to the white light area by the adjustment of Tb3+concentration. When the concentration of Tb3+is at60mol%, a single phase white LED phosphor is obtained with perfect CIE=(0.33,0.35). The Most important is that this Ce3+→Tb3+→Sm3+energy transfer scheme can provide a feasible route to build sensitization relationship between rare earth ion pairs almost no providing energy transfer effect. |
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