The Synthesis And Spectroscopic Study Of Yag:Ce, Bi(Sm) Phosphor

With the advent of the world's energy crisis and the degradation of global environment, the development of modern science and technology are closely related to energy saving as well as environmental protection. In the early 90s of last century, "green lighting" plan was proposed. With the development of LED chip technology and the progress made in the phosphor research, white LED is the most promising lighting technology at present. It ushers in a fourth-generation lighting era. The most mature method of realizing white LED at present is to excite phosphors YAG:Ce by means of Blue LED chips, which has been industrialized. However, it is not of high luminous efficiency. Besides, when lighting, this kind of phosphors lacks red light element and its color rendering is not good. There is still much room for improvement. Focusing on this point, this thesis aims to actively seek for the solution: mixing a small amount of Bi³⁺ or Sm³⁺into phosphors YAG:Ce, and characterizing the obtained samples, through which certain significant results are gained.In the first chapter, this thesis analyzes the history, principles, current situation and applications of the LED, lists and compares the methods of realizing white LED, exploring the structure and properties of YAG and the principles, features, and various kinds of synthesis methods of YAG:Ce phosphors light-emitting and expounds the background, evidence and research significance of this selected topic. Chapter two introduces the drugs, instruments, experimental methods and characterization techniques used in the experiment. Chapter three synthesizes YAG:Ce phosphors, through characterization finds the best doping ratio: 0.06 of Ce³⁺, on this basis adds Bi³⁺ with different concentrations, analyzes the effect of Bi³⁺ on the structure and luminescent properties of YAG:Ce phosphors, and finally finds as follows: without changing the excitation of the phosphors and the shape of emission spectra, the doping of Bi³⁺ increases the lighting brightness. Its optimum doping concentration was 0.04 and lighting brightness is increased 5 times, which is due to the fact that Bi³⁺ transfers the absorbed energy to Ce³⁺. Bi³⁺ doping does not change the YAG:Ce phosphor structure. The sample is a pure YAG phase, with no mesophase or impurity phase occurring. In the lattice, Bi3 + and Ce³⁺ occupies the Y_<sup>3+ position. Characterizing the YAG:Ce and YAG:Ce,Bi phosphors under the different calcinations temperatures, we can find that the higher calcination temperature is, the stronger lighting brightness becomes. Meanwhile, particles clustering is more serious and its size larger and the simple particles more even. Chapter Four prepares the YAG:Ce,Sm phosphors with different Sm³⁺ doping concentrations and different calcination temperatures. Through the simple analysis, we can find that Sm³⁺ doping does not change the YAG:Ce phosphor structure. The sample is a pure YAG phase, with no mesophase or impurity phase occurring. Sm³⁺ doping improves the lighting brightness of the sample. Meanwhile, as the characteristics emission spectrum of Sm³⁺ is in the red light zone, YAG:Ce, Sm phosphors in the red zone have emission peaks. Energy transfer of Sm³⁺ and Ce³⁺ in YAG:Ce, Sm phosphors is a bi-directional transmission, and the excitation and emission spectra of the sample possess the characteristic spectra of both Ce³⁺ and Sm³⁺, but the characteristic spectrum of Ce³⁺ is dominant, so in energy transfer, largely, Sm³⁺ transfers energy to Ce³⁺. The effects of temperature on YAG:Ce,Sm phosphors and YAG:Ce, Bi phosphors are true of the same law: the higher calcination temperature is, the stronger lighting brightness of the phosphors becomes. Meanwhile, particles clustering is more serious and its size larger. Later, we can study energy transfer laws between Bi³⁺, Sm³⁺ and Ce³⁺ in other substrates. Besides, we can also find more sensitizers to enhance luminous efficiency and color quality of the YAG:Ce phosphors.