The application of yellow phosphors on blue LED chips is currently the most important way to prepare white LEDs. The disadvantage of white LEDs prepared in this manner is that color rendering is not good enough, and it is difficult to prepare white LEDs with low color temperature (<4000K). In order to improve the color rendering index of white LEDs and to prepare white LEDs with low color temperature, the most effective and convenient way is to simultaneously apply yellow (or green) phosphors and red phosphors on the blue LED chips. However, the existing red phosphor suitable for blue light excitation is not too low in luminous efficiency or too in stable, and is difficult to be applied to the preparation of high color rendering white LEDs. To this end, Rare Earth New Materials Co., Ltd. (National Engineering Research Center for Rare Earth Materials) has developed two types of high-efficiency low-light fading red phosphors through nearly three years of efforts, and both types of phosphors have been successfully applied. The preparation of white LEDs with high color rendering and low color temperature. (Ca,Sr)S: The Eu2+ red phosphor has a high and wide effective excitation band in the 410-500 nm range, so the phosphor is suitable for blue LED chip excitation. However, the performance of the phosphor is not stable enough, the light decay is large, and the escape of sulfur causes damage to the chip. In the preparation process of the phosphor, the rare earth has effectively reduced the deliquescence, oxidation and sulfur precipitation of the powder through the addition and surface treatment of the auxiliary powder, so that the stability of the powder is greatly improved. The application results in Xingu Optoelectronics Co., Ltd. and other units show that white phosphor LEDs with color rendering index above 90 and color temperature below 3000K can be prepared by using the phosphor, and the color coordinates of white LEDs are less than 10 within 1000 hours. %, with high stability. While improving the sulfide red phosphor, a new type of alkaline earth and transition metal composite oxide red phosphor was successfully developed. This series of phosphors uses trivalent europium as an activator and can be effectively excited by UV, violet or blue LEDs. This series of phosphors is significantly superior to traditional red phosphors in terms of stability and luminous efficiency. The national invention patent has been declared. The above two kinds of red phosphors have formed products and are sold to many LED packaging manufacturers in the United States, South Korea, Taiwan and the Mainland, resulting in better social and economic benefits.
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