Preparation And Characterization Of Phosphors Activated By Eu(Ⅱ) Or Eu(Ⅲ) And Their Application In Light-emitting Diodes

Since the first white-light emitting diode (WLED) came into being in 1996, more and more interests have been focused on them because they have a lot of advantages on long lifetime, lower consumption, and eco-friendly etc. However, the current tri-color phosphors for NUV LEDs are mainly some traditional phosphors. These phosphors show lower excitation efficiency in NUV region. Furthermore, the green and red phosphors show low stabilities and cause some environmental problems both in preparation and in LED application as they contain sulfur element, which would release toxic sulfur oxides in use. All the above reasons cause the difficulties to improve luminescence efficiency and operation lifetime of white LEDs. Hence it is academic interesting and shows application potential to improve traditional phosphors or search for new phosphors applied in near UV LEDs. The purpose of this thesis is to search for novel phosphors which have high luminescence efficiency and stability for NUV LEDs. To overcome the defects and shortages of the currently used phosphors, Eu(Ⅱ/Ⅲ) doped complex oxides were synthesized in the NUV WLEDs in this thesis. The structure and morphology of the phosphors were characterized by X-ray diffraction(XRD), their photoluminescent properties were investigated. Finally, LEDs were fabricated by coating the chosen phosphors onto the NUV-emitting InGaN chips. The thesis consists of the following six chapters.In the first chapter, the development of WLEDs illumination was briefly introduced. The development of white LEDs and the current phosphors for near UV LEDs were reviewed. At last, the research subject and content of thesis were designed.In the second chapter, a series of Eu³⁺ doped Y_1-xEux(PO₃)₃ (0≤x≤1) phosphors were prepared by solid state reactions. The XRD and photo-luminescent properties of the phosphors were investigated. The results show that, the obtained phosphors were pure-phase when the sample Y_1-xEux(PO₃)₃ calcinated at the temperature range between 600 and 900℃, then we studied the photoluminescent properties of the samples calcinated at 800℃in detail, and the samples have a best photoluminescent properties can be obtained when x=1.In the third chapter,a series of Eu³⁺ doped BaCa_1-x(PO₃)₄:xEu³⁺ phosphors were prepared by solid state reactions, a series of Li+ and Eu³⁺ codoped BaCa(PO₃)₄ were prepared in the following time. The XRD and photo-luminescent properties of the phosphors were investigated. The results show that, the emission intensity of BaCa_0.9(PO₃)₄:0.1Eu³⁺ among the BaCa_1-x(PO₃)₄:xEu³⁺ is the highest, the photo-luminescence intensity of BaCa_0.75Eu_0.1Li_0.15(PO₃)₄ is the highest in BaCa_0.9-xEu_0.1Li_x(PO₃)₄ , the results show that the photo-luminescence can be enhanced by doping Li⁺ ions. Furthermore, the test results of BaCa_0.9-xEu_0.1Li_x(PO₃)₄ phosphors show that the doping of Li+ ions under some concentration can obviously enhance the photo-luminescence intensity, with the compensation for charge.In the fourth chapter, a series of phosphors Ba_1-xEu_xCa(PO₃)₄ ,Ba_0.85Eu_0.15Ca_1-xMnx(PO₃)₄ were prepared in CO ambience at 700℃and their photoluminescent properties were studied. With the increase of the doped Eu²⁺ concentration, the resultsindicate that the excitation spectra of the phosphors have no obvious change, but the photoluminescent intensity continually enhanced. It began to decreased when x=0.15. With the increase in Mn²⁺, energy transfer can be observed in Ba0.85Eu0.15Ca_1-xMnx(PO₃)₄. In the fifth chapter, in order to investigate the application of the synthesized phosphors in NUV-InGaN-based white LED, red LEDs were fabricated by coating the phosphors Eu(PO₃)₃ , BaCa_0.9(PO₃)₄:0.1Eu³⁺ , BaCa_0.75Eu_0.1Li_0.15(PO₃)₄ onto the NUV-emitting InGaN chips.,In the last of this thesis, the main research results were summarized and a brief prospect on the phosphors applied in NUV InGaN-based LED was made.