Synthesis And Characteristic Of Y₃Al₅O₁₂:Eu³⁺ Red Phosphor By Coprecipitation Method

White LED hailed as 4th generation light source will overtake incandescent, fluorescent and high intensity discharge lamps. It has a good prospect of application and maybe replace traditional lighting. At this stage, the overall trend of the development of White LED is determined by the high color-rendering index, low color-temperature, high power, which is influenced by red phosphor performance.However, the red phosphors applied to white LED have low conversion efficiency, unstable nature and badly luminous decay to become an barrier on LED development. So the study on high conversion efficiency and good luminous red phosphor to LED become hotspot of research by large companies both at home and abroad and research organizations.Chemical coprecipitation is a widely applicable method of wet chemical synthesis, which raw materials' composition can be mixed on the molecule or atom size. It is helpful to control the doping amount accurately, raise the activity of reacting, reduces the firing temperature notably. Therefore, the coprecipitation method is very hopeful to substitute solid state reaction and apply to the industrialization production of the phosphors.In this paper, Y₃Al₅O₁₂:Eu³⁺ red phosphors were synthesized by coprecipitation method with mixed precipitating agent and tow step calcination. The main points of the thesis are as following:â‘ The research significance and status of white LED and rare earth materials was overviewed. The working principle of white light LED and light-emitting mechanism of rare earth materials was introduced. Advantages and disadvantages of various phosphors synthetic technologies of Y₃Al₅O₁₂:Eu³⁺ red phosphors were discussed briefly.â‘¡The optimal conditions for synthesis of Y₃Al₅O₁₂:Eu³⁺ red phosphor by coprecipitation method was studied.The results showed that the photoluminescence intensity of Y₃Al₅O₁₂:Eu³⁺ red phosphor influnced on metallic solution, precipitant, molar ratio between NH3·H2O and NH4HCO3, reaction temperature,reaction time and so on. When the metallic solution content reached 0.4mol/L,the precipitant content reached 4mol/L, the molar ratio between NH3·H2O and NH4HCO3 reached 4:1, reaction temperature reached 25℃(at room temperature), reaction time reached 60min, drop speed is 3mL/min, mixing speed is 300rpm, Eu3+ content reached 0.06, PEG content reached 4%(quality score), the photoluminescence intensity of Y₃Al₅O₁₂:Eu³⁺ red phosphor reached highest. â‘¢The study of calcination process to crystal structures, luminescence and particle size distribution properties of the Y₃Al₅O₁₂:Eu³⁺ red phosphors was investigated. The result shows that the chemical coprecipitation synthesis of the Y₃Al₅O₁₂:Eu³⁺ red phosphors were precisely of a suit with the high-temperature solid-phase method in spectral properties. The excitation wavelength was 395nm and the emission wavelength was 591-635nm; The pure YAG crystal phase has been formed when the calcination temperature is 1000℃. Compared with high temperature solid-state method, the synthesis temperature reduces 500℃nearly. Adding the flux NaF, photoluminescence peak intensity of Y₃Al₅O₁₂:Eu³⁺ red phosphor powders strengthens, but decreases by excessive flux NaF content and the optimal flux NaF content is 4%.â‘£Bi3+ droped (Y,Bi)AG:Eu3+ red phosphor powders with good photoluminescence performance were synthesized by chemical co-precipitation method. The factors of Bi3+ to crystal structures, luminescence and surface morphology properties of the Y₃Al₅O₁₂:Eu³⁺ red phosphors were investigated. The result shows that The photoluminescence intensity of Y₃Al₅O₁₂:Eu³⁺ red phosphor strengthens with increasing Bi3+ content due to the sensitizing of Bi3+ to Eu3+,but decreases by excessive Bi3+ ions. When the Bi3+ content reaches x=0.0010, the photoluminescence intensity is highest. Adding Bi3+ cannot change the crystal structure of Y₃Al₅O₁₂:Eu³⁺ phosphor, which is garnet with a little different lattice parameter. The particles of (Y,Bi)AG:Eu3+ red phosphor are spherical-like shapes, narrow size distributions with non-aggregation.