“The white LEDs using blue LEDs will disappear sooner or later.†Nakamura’s remarks during a speech at the “GaN Energy Revolution†seminar held on July 24 shocked the industry. Nakamura Shuji won the 2014 Nobel Prize in Physics for the development of high-efficiency blue LEDs. Now he has “overthrown†this result in one fell swoop. It is the blue LED itself that has obvious defects, or is it because of the new company’s Soraa pushes the purple LED. Promotion? Will the future blue LEDs withdraw from the historical stage? With these questions, I interviewed some experts in the industry and analyzed them one by one.
Nakamura’s remarks are for the benefit of participating companies?
LEDs are narrow-band light sources based on semiconductor components with wavelengths ranging from infrared to ultraviolet. The first LEDs have an illumination wavelength ranging from infrared to green. Blue LEDs need to study the growth technology of high-quality crystals and the p-doping control technology of wide-bandgap semiconductors, which were only realized on GaN systems in the late 1980s. In addition, the development of high-efficiency blue LEDs also requires the preparation of GaN-based alloys with different compositions, and needs to be integrated into a multilayer structure of heterojunctions and quantum wells.
The fluorescent material is excited by the blue LED, and emits green and red spectrum light. When combined with the blue light, it looks white light. In addition, several LEDs with different complementary colors (red/green/blue) can also be used to form white light. Both of these technologies are used in today's high-efficiency electroluminescent white light sources to achieve significant energy savings.
However, Nakamura Shuji now pointed out that on the one hand, a combination of a blue LED chip and a yellow phosphor forms a white LED, the wavelength of the light is not balanced, and there is a problem that the peak intensity of the blue light is high and the sleep disorder is easily caused, that is, "blue light." problem".
On the other hand, a conventional white LED composed of a blue LED and a fluorescent material does not contain ultraviolet rays. Therefore, there are sometimes differences in the colors presented compared to other light sources that contain sunlight and ultraviolet light.
As a result, Nakamura Shuji sentenced that “white LEDs using blue LEDs will disappear sooner or later†and pointed out that “the white LEDs sold by American Soraa Company are the solution.â€
It is understood that Soraa is an LED venture company established by Nakamura as a co-founder. It mainly sells whites that use red (R), green (G), and blue (B) phosphors on a purple LED chip. LED. This is reminiscent of his remarks because of his own shareholding company's own interests?
In this regard, most LED industry experts said that the possibility is higher.
WhichLEDs, from the perspective of business and traders, believes that Nakamura has the possibility to promote its shareholding companies. "The things that I invented are seen by myself. It is actually very interesting. From the point of view of the number of casualties in World War II, if Mr. Nobel is alive, he should hate himself for inventing TNT."
Wang Haibo, vice chairman of the China Lighting Association and director of the Institute of Electrical Light Source Materials of Nanjing University of Technology, also said that this is not surprising. "Nakamura said that the background of this passage is naturally thought to be for commercial purposes."
"It should be reversed, because he saw the prospect of purple LED, will invest in such a company based on purple LED research and development. It is not known whether this speech is out of the company's interests." China Rare Earth Society expert group Experts, Secretary General of the China Rare Earth Association Optical Function Materials Branch and Wu Hong, director of the Shanghai Lighting Society, suggested using retrospective thinking to look at this matter.
Liang Chao, deputy general manager of Jiangsu Borui Optoelectronics Co., Ltd., believes that Nakamura Shuji is not for the benefit of the company. "As a scientist who won the Nobel Prize, it should have a high moral standard and professional ethics. The view of blue LED is theoretically supported and certainly reasonable."
Chen Zhen, vice president of Jingneng Optoelectronics, agrees with this view. "I believe his judgment should be based on his understanding and starting point."
Purple LED has obvious advantages?
Whether Nakamura’s remarks are really out of the company’s interests, we can’t make a conclusion, but whether the purple LEDs that it is now admired will really replace the blue LEDs, which can be objectively analyzed.
Wu Hong has a positive attitude towards the development prospect of purple LED. "Purple light conversion white light is more efficient, the spectral distribution is balanced, and the color rendering index is relatively good. It is of great significance for energy saving, emission reduction and light quality improvement. The high impact has not yet been popularized, but the advantages are obvious."
Specifically, what are the advantages of white LEDs obtained through purple LEDs?
1. The color rendering index is high.
Such a white LED obtains blue light by exciting a phosphor with a purple LED, and the peak intensity of the blue light is not too high. Moreover, it can also output all the light in the visible light wavelength range, so the color rendering index is relatively high, and the ideal white color like sunlight can be realized. Moreover, its red color rendering index "R9" is particularly high, and the average color rendering index "Ra" is also as high as 95.
2. High luminous efficiency.
(1) Since a purple LED is fabricated using a GaN substrate, a GaN-based semiconductor is stacked on a GaN substrate to produce a purple LED chip, which belongs to a "GaN on GaN" type LED, and a GaN-based semiconductor layer has a relatively high crystal quality, so that the purple LED luminous efficiency is high. High, and the efficiency is improved fast.
(2) The purple LED chip is triangular, and the shape of the ordinary LED chip is a quadrangle. In contrast, the light emitted from the light-emitting layer of the triangular LED chip is emitted to the chip with higher efficiency (light extraction efficiency). Since the crystal quality and light extraction efficiency of the purple LED are high, the "WPE (wall-plug efficiency)" obtained by dividing the light output by the input power can reach 84%. The WPE of ordinary blue LEDs is only 50-60%.
(3) Ordinary blue LED chips are fabricated on sapphire substrates. Since the lattice constants of GaN-based semiconductors and sapphire are different, crystal defects called "dislocations" are apt to occur. However, there is almost no difference in lattice constant between the GaN substrates, and thus crystal defects are hard to occur. The dislocation density can be reduced to about 1/1000 compared to products using sapphire substrates.
(4) Another feature of the purple LED chip is that it is less prone to "droop" problems. The decrease in luminous efficiency is a phenomenon in which the luminous efficiency is lowered when the driving current density is increased in order to increase the luminous intensity, and is also a major problem in improving the luminance. The GaN on GaN type has higher crystal quality, and is less prone to light degradation than sapphire substrate type products. Therefore, the GaN substrate type product can increase the current density by 5 to 10 times compared with the sapphire substrate type product.
Will the blue LED be squeezed out of the historical arena?
The use of violet or ultraviolet LED to excite RGB three-color phosphors to obtain high-color white LED technology has gained more and more favor in the industry when the current chip efficiency has been increased to a new level. So, will the blue LED finally withdraw from the historical stage?
WhichLEDs indicate that purple plus red, green and blue primary color phosphors have been mass-produced on traditional fluorescent lamps. Only the purple LED was developed to replace the high-voltage arc in the traditional fluorescent lamp to break through the mercury vapor to form ultraviolet light, but the white light formed by the ultraviolet LED does not have an overwhelming advantage. As a kind of three primary colors, blue light is a necessary condition for the formation of white light and will not withdraw from the historical stage.
"The white light source produced by blue LED has its drawbacks and advantages. Among them, blue peak and point light source are the most prominent problems. At present, the technology of phosphor can reduce the intensity of blue light and improve the color rendering of the light source. To improve the impact of glare, Wang Haibo agrees with the huge application prospects of Ziguang, but also said that the quality of Blu-ray can be continuously optimized. "The researchers of Blu-ray LEDs continue to improve the quality of light sources, and believe that Blu-ray will be more competitive in the market. ".
Relying on cost advantage and technical advantage, the comparison between blue LED and violet LED is not clear. Wang Haibo likens the relationship between “LCD TV and plasma TVâ€, that is, for the same purpose, adopting different technical paths, real competition. As a result, it is still not possible to "knot a conclusion". He said, "Who can win in the market is like the college entrance examination. It depends on the scores of the examinations, and it depends on the quality of others' examinations. In the end, it depends on the comparative advantages of the two."
Chen Zhen believes that white LEDs based on blue LEDs are still the mainstream of lighting, while white LEDs based on purple LEDs can be used for high-end lighting. "Whether a product will be replaced, technical reasons only account for a small part. Product cost, use Habits and the choice of mainstream manufacturers are important reasons for affecting the market share of a product."
From the overall perspective, Liang Chao said, “Is it true that Ziguang LED can lead the mainstream of the market in the future, and then force the blue LED to exit the market? At least it is difficult to make a clear judgment at present. Relevant supporting materials, equipment, supporting level of the industrial chain, etc. Etc., all affect the development process of the industry."
White LED technology is a flash in the pan?
Some netizens believe that whether the white light source produced by blue LED or purple LED is very close to natural light, its glare and blue light radiation still exist, which is not healthy for the human eye. Also, from the point of view of color reproduction and softness of illumination, there may be an alternative light source that is superior to LEDs. So is this white LED technology closer to natural light a short-lived or a big development trend?
WhichLEDs analyzes that the generation of glare is not unique to LEDs. All light sources with high brightness may produce glare. The higher the energy of light, the greater the damage to human skin and eye cells, so it will not be a drawback of LEDs. Through reasonable lighting design and control of glare. Controlling the intensity of blue light in the spectral components in future white light can reasonably control the blue radiation problem.
Similarly, traceability to UV LEDs may be more radiant, which will be a major difficulty in the promotion of UV LEDs. At present, PHILIPS promotes Cirsp White's COB product with a 410nm wavelength purple LED, which can excite the fluorescent component in the fiber to form white. However, such a luminaire cannot be used as a main lighting, and can only be used as a clothing store or a partial studio. In such an environment for a long time, it will cause greater damage to the skin.
"In terms of color reproduction, it is not the strength of LED. It cannot exclude the generation of other technologies to achieve very high color reproduction and softer illumination. The alternative to lighting has different occasions, although LED is not the best alternative for all occasions. But it may be the best alternative to local occasions, as long as this part of the replacement market is ready, after all, a technology can not meet all the needs." WhichLEDs further analyzed.
"In terms of existing technologies and products, the light source that can truly achieve the best alternative must be LED." Chen Zhen believes that LED's own advantages are unparalleled. “Color reproduction and illumination softness are all parameters that can be adjusted. As long as the sacrifice of brightness and cost can be done well in this respect. There are two technologies that have an impact on the overall light source status of LEDs. These two technologies are OLEDs. And LEP. But these two technologies are far from the status of replacing LEDs. It can only be said that these two technologies have advantages in some sub-segments, and may be a supplement to LED light sources."
From incandescent lamps to LED lamps, the development of lighting has experienced the development of thermal radiation sources, gas discharge sources and solid-state light sources. Each revolution is a revolution in the field of artificial lighting. Wang Haibo said, "The field of solid-state lighting will continue to generate new light sources, including UV LEDs, OLEDs, quantum dot technology, laser lighting, etc., but any kind of light source is a stop for the development of lighting technology. The end of development."
Wu Hong also believes that LED can not be regarded as the best light source at present, but LED still has a lot of potential advantages that have not been fully exploited. As for the hot-spot QLED, OLED and other light source technologies are developing, but the concept The hype is obvious, and the practitioners still have to be down-to-earth.
"In fact, the replacement process of the light source is happening." Liang Chao said frankly. For the development of white LEDs, he believes that it should first be measured by the needs of the general consumer. "At present, companies are constantly releasing products with higher color rendering or higher levels of other indicators, often based on pure technical indicators. The purpose of these indicators, whether it is really improving the consumer experience, may not be known."
WhichLEDs has expressed some opinions on the development trend of white LEDs. White LEDs mainly focus on lighting, and the development trend can also be discussed from the level of meeting lighting requirements: 1. Must have high efficiency. High efficiency can save energy, and about 12% of the world's energy is spent on lighting. 2. Has a high color rendering index. The high color rendering index and high color saturation are more capable of color reproduction and can restore the color of sunlight. 3. High color saturation. In the future, white LEDs will develop to full-spectrum light sources. Of course, the full spectrum is not only the result of LED efforts, but also must match the phosphors of different excitation wavelengths.
Conclusion :
"Science is by no means a permanent book. Every major achievement will bring new problems. Any development will face new problems over time, and we must constantly solve it." Einstein once said that science, blue LED and purple LED are the same, will not be full of LED technology development, but will certainly become a milestone in the application of LED technology.
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