Author: Yu Su
Due to its small size, low cost and simple control loop design, the blue chip + YAG aluminate yellow phosphor is the mainstream implementation of current white LEDs , and has become the way most LED packaging manufacturers in China follow. However, the white LED package patent for YAG yellow phosphor is owned by Nichia Chemical . The white LED products that Chinese manufacturers use this technology are bound to be blocked by their patents when they are exported, which drags down the market. Therefore, to avoid the international patent blockade of blue LED + yellow phosphor, a breakthrough in key materials is needed.
The principle of blue LED+YAG phosphor is to apply a layer of YAG phosphor on a 460nm blue light chip, and use a blue LED to excite the phosphor to produce a 555nm wavelength yellow light complementary to blue light, and to mix complementary yellow and blue light. White light. It is unrealistic to make breakthroughs in chip manufacturing/epitaxial materials in the short term. The industry generally agrees that new phosphor materials are an effective way to break through the international patent barriers of white LEDs. For example, Osram 's TAG aluminate yellow phosphor is a successful breakthrough in YAG phosphor patents (other major phosphor technologies for white LEDs, as well as Toyota Synthetic , Intermec and Tridonic silicate phosphors) . At present, the yellow powder on the Chinese market is almost all of the Japanese patented YAG aluminate phosphors. Therefore, in order to take the initiative in the white LED market , China needs its own white LED phosphor technology. Dr. Wang Haijun from Yuji Core Light Co., Ltd. said that the yellow phosphor of the nitride is expected to replace the YAG aluminate phosphor to avoid the patent barriers related to Nichia.
Phosphor is one of the key materials that affects the light efficiency, service life, color rendering index and color temperature of white LEDs. The uneven brightness of the color is mainly caused by the uneven coverage of the phosphor outside the luminescent layer of the chip. Therefore, how to make the phosphor evenly cover the outside of the luminescent layer of the chip is the focus of the white LED package, and the uniformity of the mixing of the phosphor and the encapsulating material is more. Will affect the consistency of the white light emitted by the LED. A disadvantage of the blue chip with YAG yellow phosphor is the poor brightness and chromaticity of the red spectrum. It is reported that Yuji Technology's nitride yellow phosphor won the 2010 Nanhai Cup National Semiconductor Lighting Product Innovation Award. The reason for the award is that the nitride yellow phosphor has higher color rendering than YAG aluminate and silicate phosphor. Sexuality and coverage of higher color gamut, suitable for occasions with rich colors. Wang Haiqi said that Yuji Technology's nitride yellow phosphor has applied for international patents. Due to the large red and blue domains of nitride phosphors, YAG and silicate are not available. Currently, its main application is YAG. The market where powder can't be done, such as the high-warm color and plant growth lamp that the company currently cooperates with the National Academy of Agricultural Sciences, belongs to this type. Because different plants have different spectral requirements, in order to achieve the corresponding blue and red spectrum, there is a certain proportion of photon number. If traditional red and blue chips are used, it is necessary to find relevant spectral points, which is easy to cause Even problem. The advantage of using phosphors is that red and blue light can be determined according to the amount of phosphor, even if the light emitted by 200 LEDs is the same.
The gamut is the sum of the color effects that the system can produce. We know that the wider the gamut that the backlight can achieve, the more vivid the color performance of the LCD. Wang Haijun said that the use of phosphors to solve the backlight packaging problem can solve the problem of uniformity of illuminating and brightening. The company's nitride phosphor covers the wavelength of 500nm to 660nm, and many LED backlights can not be achieved by YAG and silicate phosphors. Only nitride can be required. For example, nitride phosphors can achieve YAG and silicate can not achieve pink. In addition, the high-power LEDs of the Yuji core light are mainly used for high color rendering index applications such as photographic fill light and medical mechanical shadowless lamps. Because the infrared part of the traditional light source generates heat, it is unfavorable to the patient and its tissue, while the shadowless lamp with high color rendering LED only includes visible light and no heat. In high color rendering applications, product yields can be achieved through techniques such as color temperature control, which can be relatively inexpensive. For example, the high-power LED of the Yuji core light has a total deviation of 400k in the 5,800k attachment of the photo-filling positive white area, while the national standard allows the deviation to be in the range of 1,000k. The color temperature requirement is less than half of the national standard deviation, and the color temperature is solved. The drift problem has been shipped in large quantities.
Dr. Wang Haijun also admitted that the luminous efficacy of YAG phosphors has reached more than 80%, but the efficiency of nitride phosphors is currently relatively low, about 10%. However, because of the effect of light efficiency on brightness, general illumination will be more dependent. For example, for backlight applications, higher color rendering and stability are required, and high brightness is not required. As NOx phosphors have great potential as emerging phosphor technology, the development of YAG aluminate has reached its limit, so Wang Haijun believes that NOx phosphor technology will mature in the next 5-6 years. To the current level of YAG, first break through the monopoly of YAG phosphor patents.
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