| Since white LEDs (light emission diodes) exhibit many advantages over conventional lighting devices such as low electric consumption, high brightness, long lifetime, good reliability, fast response and environment-friendly characters, they are called the next-generation solid-state light. Of the methods available for creating white light with LEDs, the phosphor-converted (PC) emission method is the common way. In this way, one method is combining tricolor phosphors with n-UV LED chips for white light, another method is combining yellow phosphor (or green and red phosphors) with blue LED chips to gerenrate white light. The former method has the following advantages:the reliable stability of n-UV LED chip, uniform color, tunable color temperature, high color rendering index. The presently used red phosphor for n-UV LED chips is commercially still limited to Y2O2S:Eu3+. However, the sulflde-based phosphors are chemically unstable and the efficiency of the currently applied red phosphor Y2O2S:Eu3+is much lower than that of common blue phosphor BaMgAl10O17:Eu2+. Therefore, the disadvantage of this method is lacking of red phosphor with high efficiency and stability. As for the latter method, the advantages include low cost and mature technology. However, the disadvantage is also abvious. On one hand, color shifting occurs in the light device due to the disadvantage of the brightness decay in blue LED chips. On another hand, the white LEDs by the combination of blue LED chips with yellow phosphor (YAG:Ce3+) exhibits a problem of undesirable color balance due to the lack of red region. Therefore, no matter in one way by combining tricolor phosphors with n-UV LED chips, or another way by combining yellow phosphor (or green and red phosphors) with blue LED chips, red phosphor and green phosphor with high efficiency and stability are necessary for white light. To develop high efficient and stable phosphors for n-UV LED chips or blue LED chips, in this thesis, two stable host lattices are selected as the candidate for red and green phosphors synthesis, and the photoluminescence properties and mechanism of them are discussed.This thesis contains two major works.1) By solid state reaction, red phosphors Eu3+doped Sr3MoO6were synthesized.With increasing Eu3+concentration, red emission intensity climb up and reach the maximum at x=0.4, then decline. After further research, we disscuss the mechanism of the strengthening and declining of red emission intensity. In addition, enhanced emission intensities are observed in the phosphors co-doped with charge compensator, and the influence of different charge compensation on the phosphors is investigated.2) By solid state reaction, green phosphors Ba2SiO4:Eu2+were synthesized. By introducing Al, green emission intensity of samples can be greatly improved. The experimental results show introducing Al can strengthen the light absorption of Eu2+. Then, we used flux to further enhance green emission intensity. In addition, the emission peak of the sample can be tuned by introducing Sr.To sum up, in the thesis, for red phosphor Sr3MoO6:Eu3+, two factors of strengthening the red emission are the increase of excited level population and the increase of5D0â†'7F2transition probability, and two factors of declining the red emission are concentration quenching and impurity phase SrMoO4. K+performs the best charge compensation effect. For green phosphor Ba2SiO4:Eu2+, green emission intensity of can be greatly improved by introducing Al. |
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