**22. Microwave synthesis**

Firing (sintering) is a necessary step for solid-state phosphor synthesis since activation energy must be supplied for the activators to go into the crystal structure of the host material. By solid-state reaction, conventional synthesis of phosphors takes many hours even with flux. Microwave processing is a relatively new technique and characterized by substantially accelerated reaction kinetics in the material systems if properly chosen. Using microwave processing, various phosphors have been synthesized. The high efficiency phosphors developed for field emission displays, plasma displays, and white light emitting diodes (LED) tend to be degraded by the operating environment and/or the devices' manufacturing conditions. Transparent oxide coating on phosphor powders is an effective approach to protecting phosphors from ageing, The coating can isolate the phosphor from the environment and could protect both the phosphor and the device. Microwave synthesis of some important phosphors and microwave processing of some phosphors coated with oxides are reported. In one study, microwave synthesis was carried out in a 2.45 GHz, 6 kW capability multimode microwave furnace with atmosphere controlled, although, only about 1 kW or less power was needed in the experiments. The powder sample (30-70 g each) was loaded in an alumina crucible, which was then placed in a properly insulated package with SiC as microwave susceptor. The insulation package was made of porous FiberFrax Duraboard 3000. The temperature of the sample was monitored with an optical pyrometer. The temperature was controlled by adjusting input power. During the microwave processing, the sample was rotating horizontally about the axis. The samples were microwave heated up and held at the designed temperatures for typically 10-20 min. The microwave-synthesized products were characterized for particle size, brightness, phase composition, morphology, luminescence emission, and color coordinates. Optimization of the parameters is required to achieve desired properties **[23].** 
