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Preparation, Spectral Properties And Energy Transfer Of Calcium Magnesium Chlrosilicate Phosphor

Posted on:2005-11-26Degree:MasterType:Thesis
Country:ChinaCandidate:Y FangFull Text:PDF
GTID:2121360122486848Subject:Physical chemistry
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Calcium magnesium chlorosilicate(Ca8Mg(SiO4)4Cl2) phosphor activated by divalent europium ions (Eu2+), known as CMSC, can be used as a high efficient green phosphor for white light emitting diode (w-LED). In recent years, w-LED has got much progress, and how to improve the luminescent efficiency of the phosphor becomes very important. In this thesis, the samples of CMSC doped with Eu2+ ion and other activators were studied. The efficiency of the phosphor can be improved greatly by adjusting the concentrations of the activators in the proper range and the compositions of the host. The luminescent mechanism of the phosphor and the energy transfer between the activators were discussed.The experiments reveal that the luminescent efficiency of the CMSC:Eu2+ samples greatly depends on the concentration of Eu2+, and the luminescent intensities of the samples are obviously affected by the excess CaCl2 in the reaction. The best luminescence can be gained by doping Eu2+ ion at the concentration of 0.1 atom percent. The emission intensity of the sample of CMSC:Eu2+ synthesized with excess CaCl2 is stronger than that of the sample synthesized without excess CaCl2, as the excess CaCl2 acts as flux and ensures enough chlorine and calcium in reaction.The spectral properties of CMSC:Eu2+, Mn2+and CMSC:Ce3+, Eu2+ were studied and the energy transfers between Eu2+-Mn2+ and Ce3+-Eu2+ are discussed. There exists energy transfer from Eu2+ to Mn2+ in CMSC:Eu2+,Mn2+, and the energy transfer type is probably resonance transfer. However, the energy transfer is limited. Eu2+ ion can be well sensitized by Ce3+ ion in the system of CMSC:Ce3+,Eu2+, and there is energy transfer between them. CMSC:Eu2+doped with Ce3+ ion could improve the intensity of luminescence when Eu2+ is in low concentration.CMSC:Eu2+,Dy3+, which is a new type and high efficient green phosphor for w-LED, was synthesized for the first time. The emission intensity of CMSC:Eu2+, Dy3+ is obviously stronger than that of CMSC:Eu2+. This indicates that there is energy transfer in the system of CMSC:Eu2+,Dy3+. The emission of sensitizer can hardly be observed in the system, so the energy may not be re-absorption and resonance transfer. And the exclusive energy transfer may be exciton transfer. CMSC:Eu2+ is doped with transition element Zn, or alkaline earth elements Ba or Sr, and the effects of the doped elements on luminescent properties are investigated. When CMSC:Eu2+ doped with Zn2+, Zn2+ ion occupies the site of Mg2+ , the position of the emission peak of the phosphor is nearly no change. The emission intensity is slightly improved when Zn2+ is in low concentration. However, when the system is doped with Ba2+ or Sr2+, they replace Ca2+ site. The dopants would change the intensity of crystal field of the host and the emission peak moves to shorter wavelength. The emission peaks move to 464nm and 450nm when the samples are doped with Sr2+ and Ba2+, respectively.
Keywords/Search Tags:calcium magnesium chlorosilicate, phosphor, LED, energy transfer, rare earth
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