Research Of The YAG Phosphor For White LED Preparation Process

In recent years, energy policys have been formulated in many countries in order to control the global greenhouse gas emissions and save energy. At the some time, the "energy saving and carbon reduction" programs have been put forward competitively. Incandescent lamps have been eliminated as lighting facilities in some of these countries one after another, such as Australia, European Union and California(USA). With the development of semiconductor lighting technology, LED has been widely used in lighting, display and other fields because of it’s significant advantages such as high efficiency, energy saving, environmental protection. This is very important to the energy saving and emission reduction, sustainable development.There are many ways to make white light LED, in terms of current technical level and manufacturing costs, the most widely used method is coating a layer of cerium doped yttrium aluminum garnet phosphor(YAG:Ce) over a blue LED chip, blue and yellow light are mixed to obtain white light.The phosphor is one of the key link to produce white light LEDs, as one of the key material of semiconductor lighting technology, it directly affects the quality of white LED’s brightness, luminous efficiency, color rendering index, color temperature, lighting decay and lifespan, and other properties.There are the several main production methods of YAG:Ce for white LEDs: high temperature solid phase sintering,liquid phase chemical co-precipitation, hydro-thermal, sol-gel, pechini colloid, microemulsion, combustion, microwave, etc.This thesis summarizes the advantages and disadvantages these preparation methods, and mainly studies the liquid phase chemical co-precipitation method. In this thesis, influence of various process conditions on the properties of phosphor in the liquid phase precipitation are studied in detail. The effect of rare earth doping on the structure and luminescence properties of the phosphors is also been discussed. And we conducted experiments of coating the phosphor powders. The main research contents are as follows:(1) Summarized the types and preparation methods of phosphor for white LED. Analyzed the advantages and disadvantages of these types and methods.(2) Prepared qualified precursor by liquid phase chemical co-precipitation method, including selection of raw materials,precipitating agent, surface active agent, calibration solution concentration, condition of precipitating and ageing, etc.(3) The first sintering: Selection of sintering temperature, selection of sintering time, selection of fluxing agents,the best concentration of cerium doping.(4) The second reducing: Reduce the Ce4+ ions in the crystal to Ce3+ ions using the reduction of hydrogen,in order to improve the luminous efficiency of phosphor.(5) The coating treatment: To form a layer of silica coating on the surface of phosphor crystals, in order to improve the luminescent properties and service life of the product.(6) Packaging experiment: Produce 1W white light LEDs by packaging YAG:Ce phosphor that we prepared in this experiment and blue LEDs, and then assemble into LED ball-type bulbs, in order to test comprehensively the performance index of phosphor.In this research, YAG:Ce phosphor was prepared by using liquid phase chemical co-precipitation method, research and experiments are meaningful and provide a theoretical basis for further research.