Study On Preparation And Optical Performance Of Phosphors For White LED

White light emitting diodes （LED） is a kind of new products in lighting market. White LED is a key way to achieve semiconductor lighting. There are certain advantages in WLED such as high-efficiency, energy-saving, long life time, easy power supply, compact structure, fine controllability, high speed of response, pure and changeable lighting color and so on. Developing of white LED is still at an early stage currently. The synthesis of phosphors is a critical step to achieve white LED. Therefore, developing high quality phosphors is an important process to prepare the white LED with high lighting intensity, efficiency and high color-rendering index.In this thesis, a series of luminescent phosphors with different color were synthesized by different methods and the main contents are as follows:1. CaMoO₄:Eu₃+and CaMoO₄:Eu3+, yBi³+phosphors were prepared by microemulsion-hydrothermal method. XRD results showed that as-prepared samples were tetragonal crystal structure. SEM images indicate that the samples were basically flake in shape whose average size was1.5-2.5μm.The critical molar concentration of activator （Eu3+） in CaMoO₄Eu³+was0.05. The photoluminescent color can be tuned from orange-yellow （0.514,0.537） to white （0.339,0.333） by adjusting the doping concentrations of Eu3+ions. When Bi³+was doped into CaMoO₄:Eu³+, the intensity of emission peak located at616nm of Eu³+was enhanced and when the concentration of Bi³+was0.03, luminescent intensity was maximum.The chromaticity coordinates （CIE） varied from orange （0.497,0.347） to red （0.585,0.349） with increasing the content of Bi3+. These phosphors had absorption in the UV and blue region, and therefore they can be used as phosphors for converted white LEDs.2. CaMoO₄:Eu₃+, Tb₃+phosphor was synthesized via microemulsion-hydrothermal method. Energy transfer process between Eu₃+and Tb₃+was studied by adjusting the relative ratio of Eu³+and Tb³+. The as-obtained Eu³+and Tb³+-doped CaMoO₄showed strong characteristic red（616nm） and green（544nm） emissions under277nm UV light excitation. Luminescent colors of CaMoO₄:Eu³+, Tb³+samples can be tuned from green to red by simply adjusting the relative doping concentrations of Eu3+and Tb3+. The phosphor CaMoO₄. Eu³+, Tb³+could be considered as one of double emission phosphors for n-UV excited white light emitting diodes.3. Tb³+doped Mg₅（BO₃）3F phosphors were synthesized by low temperature combustion method. Phase structure of Mgs（BO₃）₃F:Tb³+phosphor was orthorhombic. The particle size of obtained sample was about1to2μm. When samples were sintered at800℃and molar concentration of Tb³+was0.05, the strongest emission peak located at543nm and the decay time of2.71ms was achieved. When the sintering temperature increased to900℃, the optimum doping molar concentration and decay time decreased to0.03and2.24ms. By adjusting the concentration of Tb³+, light color was varied from blue-green to green and adjustable luminescent color was achieved. Broad excitation band of Mgs（BO₃）₃F:Tb³+phosphor was in the range of200-400nm which can be matched with ultraviolet LED chips. This phosphor might be promising for application in W-LEDs.