Ningbo Materials Institute breaks through green low-cost synthesis technology of nitride phosphors

Due to the shortage of energy, the development and replacement of energy-saving products worldwide have become the trend of future industrial development, and the lighting and display devices in daily life account for most of the share of electrical energy consumption, so LED (photodiode) semiconductor lighting technology has Become the focus of competing development around the world. The traditional phosphors used in white LEDs are mainly inorganic compound materials such as silicate and aluminate groups. At present, another type of high-performance oxynitride / nitride phosphors are in color rendering index, luminous efficiency, color temperature, life, It has outstanding advantages in performance indexes such as chemical stability and thermal stability, so it has gradually become an important type of phosphor material system used in white LEDs, and has been widely used in LED lighting and LED backlight display devices.

At present, the main method for preparing oxynitride / nitride phosphors is the air pressure synthesis method, which requires high equipment, large power consumption, and correspondingly increased maintenance costs. In terms of product quality, the powder is relatively easy to agglomerate after calcination at high temperature (above 1700 degrees). The subsequent crushing causes the destruction of the particle surface, resulting in the generation of a large number of surface defects, which directly affects the luminescence performance. In addition, the particle size distribution is not uniform, making the bulk density of the powder small and increasing the scattering coefficient, reducing the luminous efficiency. The metal or metal nitride raw materials required for the synthesis of nitride phosphors are not only expensive but also extremely unstable in the 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 steadily. Therefore, China urgently needs to develop green, reliable and low-cost synthesis technology to prepare high-quality oxynitride / nitride phosphors.

Currently, postdoctoral fellow Liu Lihong and researcher Huang Qing of the Structural and Functional Integrated Ceramics R & D team of Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences have cooperated with Dr. Xie Rongjun from the Zhejiang Thousand Talents Program to successfully produce high-quality nitrogen at low temperature and pressure using microwave Chemical phosphor. The basic heating principle is to use the coupling of raw material molecules and electromagnetic fields to convert microwave energy into thermal energy to heat objects. Therefore, it can achieve zero gradient uniform heating of large areas in the material compared with traditional pneumatic synthesis methods, and it has a fast heating rate and short sintering time. It is beneficial to obtain powder with uniform particle size distribution.

For example, the high-quality Ca-α-SiAlON: Eu² + phosphor for white LEDs was successfully synthesized under normal pressure at 1550 degrees Celsius, and the synthesis temperature was reduced by 150 degrees Celsius compared with the conventional air pressure method (1700 degrees, 0.5MPa nitrogen protection) Compared with the luminescence characteristics of the powder synthesized by the air pressure method under the same temperature conditions, it has significantly improved luminous intensity, quantum efficiency and thermal stability. The unoptimized external quantum efficiency of the phosphor tested at 450nm wavelength excitation can reach 48%, and the efficiency is expected to achieve or exceed the luminous efficiency of commercial powder after screening and purification. Figure 1 is the photo-luminescence of Ca-α-SiAlON: Eu² + phosphor synthesized by microwave; Figure 2 is the photo-luminescence of SrSi2O2N2: Eu² + green phosphor synthesized by microwave

The successful development of green low-cost technology of nitride phosphors will greatly promote the reduction of costs of high-power LED lighting devices and backlight display, and will accelerate the promotion of China's semiconductor lighting technology 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.

This project is supported by the Ningbo Institute of Materials '"Team Action" Talent Fund, the Chinese Academy of Sciences' "Hundred Talents Program" and the National Natural Science Foundation of China.

Fig.1 Photoluminescence picture of Ca-α-SiAlON: Eu² + yellow phosphor synthesized by microwave method

Figure 2 Microwave synthesis of SrSi2O2N2: Eu² + green phosphor powder

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