Combustion Synthesis And Luminescent Properties Of Silicates,Aluminates Luminescent Materials For WLED

Because of petrifaction resources'lack,many countries have attached importance to worldwide energy sources crisis and bring lighting thrift techniques,especially white LEDs into national development stratagem. Compared with conventional lighting sources,white LEDs have many merits in energy saving,compact optics designs,cold sources,startup at low volt or electrical current,long life-span,rapid brightness and color changes,aseismatic,recvclable,unpolluted and so on,there's obvious benefits to economic and environment. More and more attentions are put to this novel region. White LEDs are believed to be the fourth generation of lamp-house after incandescent lamp,fluorescent lamp and discharge light and there are the future of illumination,which have huge market. Recently,the phosphor-conversion is one of main approaches for fabricating white LED. Study on phosphors which are used as converter is the most active currently in luminescent material field. So, the prepared phosphors have become one of the key techniques for fabricating white LEDs.The solid-state reaction process has been used intensively for white LEDs phosphors synthesis,but this process often results in poor homogeneity and requires high calcinating temperature. Furthermore,the grain size of phosphors powders are prepared through solid-state reaction method. Phosphors of small particles must be obtained by grinding the larger phosphor particles. Those processes easily introduce additional defects and greatly reduce luminescence efficiency. With the development of scientific technologies for white LEDs phosphors, several chemical synthesis technologies, such as sol—gel, co-precipitation, microwave and combustion synthesis methods have been applied to prepare the white LEDs phosphors. All of these methods were conducted in liquid phases so that each controlled and uniformly mixed. The combustion process to prepare the precursor powders, however, is very facile and only takes a few minutes, which has been extensively applied to the preparation of various oxide materials. This synthesis technique makes use of he heat energy liberated by the redox exothermic reaction at a relative low igniting temperature between metal nitrates and urea or other fuels. Furthermore, the process is also safe, instantaneous and energy saving.In this dissertation, Li₂MSiO₄: Eu²⁺( M: Ca, Ba) and MxSr_1-xAl₂O₄:Eu²⁺(M: Zn, Ca) phosphors were synthesized by combustion method. X-ray diffractometer (XRD), transmission electron microscope (TEM), luminescence spectrophotometer were used to analyze and measure the crystal structure, morphology, excitation and emission spectra were also discussed.The following is included:(1) The present status and prospect of white LEDs illumination industry are reviewed firstly. Then it analysises the light emitting principles,relization methods and key materials of white LEDs,and puts the emphasis on the preparation techniques of the phosphors for white LEDs.(2) Using urea as fuel and boric acid as flux material, Li2CaSiO4: Eu²⁺ phosphor material was prepared by the combustion method.(3) Li2 (Ba_0.99, Eu_0.01) SiO₄: B³⁺ with UV-LED phosphors were prepared at the first time by the combustion method at 600℃. The luminescent properties of luminescent materials have been studied systematically.(4) The boric acid was effective in improving the phosphor intensity of Li₂BaSiO₄:Eu²⁺ particles. The optimum molar ratio of boric acid to barium nitrate was about 0.06.(5) Eu²⁺ activated SrAl2O4 is a good compact fluorescent green UV-LED material. In this dissertation, SrAl₂O₄: Eu²⁺ phosphor was synthesized by combustion method.In order to enhance the phosphor intensity, the crystal lattice was found changing when substituting B3+, Zn²⁺ for Al³⁺ and Sr²⁺.(6) The SrAl2O4: Eu²⁺ is doped with Ca²⁺, they replace Sr²⁺ site. The dopants would change the intensity of crystal field of the host and emission peak moves to shorter wavelength. The excitation and emission spectra were measured and the emission peak changed with the host. Evident blue shift occurred when part or all of Al³⁺was substituted by Ca²⁺, which can match different need for wavelength.