Due to the shortage of energy, the development and replacement of energy-saving products around the world has become the trend of future industrial development, and the lighting and display devices in daily life occupy a large share of power consumption, so LED (photodiode) semiconductor lighting technology has been Become the focus of competing development around the world. The conventional phosphors used in white LEDs are mainly inorganic compound materials such as silicates and aluminate groups, and currently another type of high performance oxynitride/nitride phosphors have color rendering index, luminous efficiency, color temperature, lifetime, It has outstanding advantages in performance indexes such as chemical stability and thermal stability, and thus has gradually become an important class of phosphor material systems for white LEDs, and has been widely used in LED illumination and LED backlight display devices.
At present, the main method for preparing the oxynitride/nitride phosphor powder is the gas pressure synthesis method, which has high requirements on equipment, large power consumption, and correspondingly increased maintenance cost. On the product quality, the powder is relatively easy to agglomerate after calcination at high temperature (above 1700 °C), and the subsequent pulverization causes damage to the surface of the particles, resulting in the generation of a large number of surface defects, which directly affects the luminescence properties. In addition, the distribution of the particle size is not uniform, so that the bulk density of the powder is small, the scattering coefficient is increased, and the luminous efficiency is lowered. Metal or metal nitride raw materials required for the synthesis of nitride phosphors are not only expensive but also extremely unstable in air, resulting in complicated preparation processes and high production costs of these nitride phosphors. At present, only a few companies in Japan and the United States can provide such phosphors stably. Therefore, China urgently needs to develop green, reliable and low-cost synthesis technology to prepare high-quality oxynitride/nitride phosphor powder. 
Fig.1 Physical illumination of Ca-α-SiAlON:Eu2+ yellow phosphor synthesized by microwave method
At present, Dr. Liu Lihong and Dr. Huang Qing from the Institute of Structural and Functional Integrated Ceramics of the Institute of Materials Technology and Engineering of the Chinese Academy of Sciences have cooperated with Dr. Jie Rongjun from Zhejiang Qianren Plan to successfully prepare high quality nitrogen under low temperature and normal pressure by microwave method. Phosphors. The basic heating principle is to use the coupling of the raw material molecules and the electromagnetic field to convert the microwave energy into heat energy to heat the object. Therefore, the conventional air pressure synthesis method can achieve uniform zero-gradient heating in a large area of ​​the material, and the heating rate is fast and the sintering time is short. It is advantageous to obtain a powder having a uniform particle size distribution. For example, a high quality white LED Ca-α-SiAlON:Eu2+ phosphor was successfully synthesized at a pressure of 1550 ° C. The synthesis temperature was reduced by 150 ° C compared with the conventional air pressure method (1700 °, 0.5 MPa nitrogen protection). And compared with the luminescent properties of the powder synthesized by the pneumatic method under the same temperature conditions, it has a significant improvement in luminous intensity, quantum efficiency and thermal stability. The external quantum efficiency of the unoptimized phosphor tested at 450 nm excitation is up to 48%, which is expected to reach or exceed the luminous efficiency of commercial powders after sieving and purification. Fig. 1 is a physical luminescence picture of a Ca-α-SiAlON:Eu2+ phosphor synthesized by microwave method; Fig. 2 is a physical luminescence picture of a SrSi2O2N2:Eu2+ green phosphor synthesized by microwave method.
Fig. 2 Microwave synthesis of SrSi2O2N2: Eu2+ green phosphor
The successful development of the low-cost technology of nitride phosphor powder will greatly reduce the cost reduction of high-power LED lighting devices and backlight display, and will accelerate the process of promoting semiconductor lighting technology in China on a large scale. At present, the technology has applied for Chinese invention patent (201110152682.4) and PCT patent protection, and is promoting pilot production.
The project was supported by the “Team Action†talent fund of Ningbo Materials Institute, the “Hundred Talents Program†of the Chinese Academy of Sciences and the National Natural Science Foundation.
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