Preparation And Spectroscopic Properties Of Rare Earth Doped Alkaline Earth Silicate Matrix Phosphors

Luminescent materials of silicate-matrix have good chemical and thermal stability, and thus scientists have focused lots of attention on researching and developing new silicate phosphors for a long time. From the viewpoint of development of materials and fundamental research, series of typical silicate phosphors are prepared and characterized for w-LEDs under the irradiation at near UV light. In summary, the main contents of this dissertation are as follows:In chapter 1, we illustrate the basic principles of PL materials and explain the PL properties of the transition metal Mn2+ions and some rare-earth ions, such as Eu3+, Dy3+, Sm3+and Eu2+ions. At last, the recent research progress based on silicate system used for w-LEDs is also presented.In chapter 2, series of red-emitting Ca2(l-x)Al2Si07:2xEu3+phosphors are prepared by the sol-gel method. The effects of annealing temperature and doping concentration on crystal structure and PL properties of phosphors are investigated. The results show that the optimal emission intensity is obtained when concentration and temperature are 14 mol% of Eu3+ions and 1100℃for these phosphors.In chapter 3, series of Ca2SiO4:Ln3+(Ln=Dy, Sm) phosphors are prepared by the high temperature solid-state reaction. The structure and PL properties excited by near UV light are investigated. The results show that a pure Ca2SiO4 phase is obtained when the samples are sintered at 1200℃for 4 h and the excitation spectra have good absorption in the range between 350 and 420 nm, indicating that these phosphors can be used for w-LEDs. The optimal concentration of Dy3+is 2 mol% and optimal concentration of Sm3+ is 2 mol%. Moreover, the effect of Na2CO3 on the PL properties of Ca2SiO4:Sm3+phosphor is also investigated, and the optimal concentration is 6 mol%.In chapter 4, a novel full-color Ca1.5Ba1.5MgSi2O8:Eu2+,Mn2+phosphor for w-LEDs is prepared by the high temperature solid-state reaction. The effects of the flux contents, concentration and calcination time on the PL properties are investigated. The results show that the novel phosphor can be obtained when the sample is sintered at 1000℃for 1.5 h with the existence of BaCl2 as flux and the main structure of the sample is a mixture which consists of the two phase of Ba1.31Ca0.69SiO4 and BaCa2Mg(SiO4)2. The best single-doped concentration of Eu2+ is 4 mol%. The phosphor exhibits a strong excitation band between 330 and 410 nm and the phosphor shows a broad-band emission peak centered at 456 nm which can be fitted to 446,468,493 and 531 nm by Gaussian fitting, due to 4f65d1�'4f7 transitions of Eu2+ions. Upon excitation at near UV light, the Eu2+-Mn2+ co-doped sample shows that there are two successive spectra with blue-green-emitting in the range from 430 to 550 nm and red-emitting in the range from 560 to 630 nm which are attributed to the 4f65d1-8S7/2 transitions of Eu2+and the 4T1-6A1 transition of Mn2+respectively and thus the two of them can contribute to white light.Furthermore, series of green-emitting 0.6ZnO-0.3SiO2-0.15B2O3:xMn2+phosphors are prepared by the sol-gel method in chapter 5. The effects of doping concentration on the structure and PL properties are investigated. The results show that proper contents of Mn2+ will affect the structure of the matrix. Although the concentration won't affect the position and shape of the emission spectra, yet significantly affect the intensity of emission spectra. The optimal concentration of Mn2+is 2 mol%.