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Because of its energy saving, environmental protection and long life, white LED has become the next generation of lighting. Currently, commercialized white LED mainly uses blue chips to excite YAG:Ce3+ yellow phosphor. The blue light emitted from the wafer is mixed with the yellow light emitted from phosphor to form white light. However, due to the lack of red light in the emission spectrum of YAG:Ce3+ phosphors, the use of single YAG:Ce3+ phosphors can not get warm white light with low correlation color temperature (CCT <4500 K) and high color rendering index (CRI >80), thus limiting its application to indoor general lighting.

In order to solve this problem, we should add appropriate red phosphors to the components to supplement the red light components, so as to prepare the warm white LED with low color temperature and high color rendering index. At present, the commercialized red phosphors with better performance are mainly rare earth doped nitrogen (oxygen) compounds. However, such phosphors have limitations such as wide emission bandwidth and high pressure of preparation, resulting in low lumen efficiency and high price. Therefore, developing low-cost, narrow-band emitting red phosphors, especially rare earth luminescent materials, which can be effectively stimulated by blue chips, has become the focus of attention. This is also the key to improve the lumen efficiency of LED.

K2TiF4:Mn4+ red phosphor synthesized by wet chemical method and high efficiency white light emitting diodes

Chen Xueyuan, Professor of Fujian Institute of Chinese Academy of Sciences and Professor Liu Ruxi of the Department of chemistry of National Taiwan University and research team led by postdoctoral Lin Qunzhe, have successfully prepared Mn4+ doped K2TiF6, K2SiF6, NaYF4 and NaGdF4 Red Phosphors by high efficiency ion exchange method. The phosphors have strong absorption band (~460) in ~460 nm. 50 nm), which is very suitable for the excitation of Blu ray chip, and the emission is ~630 nm's sharp line red emission, which has higher lumen efficiency than the red phosphor of nitrogen oxide.

The absolute quantum efficiency of K2TiF6:Mn4+ phosphors at room temperature reaches 98%, which is better than most of the existing red phosphors. The phosphor has good fluorescence thermal stability, and its luminous intensity reaches 150 at room temperature at 150 degrees. The white light LED packaged with the red phosphor and YAG:Ce3+ yellow phosphor has a lumen efficiency of 116 lm/W at 60 mA driving current, color temperature 3556 K, and chromogenic index (Ra) 81. The ion exchange method developed by the research team is simple, can be prepared at room temperature and atmospheric pressure, and the raw material is cheap, so it has good market application prospects.

In addition, the team also studied the spectral characteristics of Mn4+ ions in fluoride matrix. The electronic energy level structure was revealed by low temperature and high resolution laser spectroscopy, and its anomalous intensity dependence of temperature was explained. The material provides reliable theoretical basis. The above research results were published in the full text form on the 8 day of July 2014 on Nature. Commun. 2014 (DOI: 10.1038/ncomms5312).

In recent years, the research team led by Professor Liu Ruxi has paid attention to the basic and practical applications of inorganic luminescent materials. Besides the important international journals such as Angew. Chem. It. Edit., J. Am. Chem. Soc., Chem. Mater, and other important works, 4 of them were published as high citation papers. More than 60 patents have been obtained.

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