Application status and Prospect of luminescent mat

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Application status and trend of luminescent materials for high-quality white LED light source

rare earth luminescent materials are one of the core materials of current lighting, display and information detection devices, and also the indispensable key materials for the development of new generation lighting and display technology in the future. At present, the R & D and production of rare earth luminescent materials are mainly concentrated in China, Japan, the United States, Germany and South Korea. China has become the largest producer and consumer of rare earth luminescent materials in the world. In the display field, wide color gamut, large-size and high-definition display are important development trends in this field in the future. At present, there are many ways to realize wide color gamut, such as LCD, qled, OLED and laser display technology. Among them, LCD technology has formed a very complete LCD technology and industrial chain, which has the greatest cost advantage and is also the focus of the development of display enterprises at home and abroad. In the field of lighting, full spectrum lighting similar to sunlight, as a more healthy lighting method, has become the focus of the industry. As an important development direction of future lighting, laser lighting has attracted more and more attention in recent years, and has taken the lead in the application of automotive headlamp lighting system, which can obtain much higher brightness and lower energy consumption than xenon headlamp or LED lamp. As an indispensable physical environment factor for plant growth and development, light environment can regulate and control plant morphology, promote plant growth, shorten the time for plants to bloom and bear fruit, and improve plant yield and productivity. It has become a global focus. It is urgent to develop high-performance luminescent materials suitable for plant growth and lighting. In the field of information detection, IOT and biometric (biometric authentication) technologies have a market prospect of trillions. The core components of both need near-infrared sensors using rare earth luminescent materials. With the upgrading of lighting and display devices, rare earth light-emitting materials, as their core materials, are also changing with each passing day. The current situation and development trend of light-emitting materials are detailed as follows

1. Luminescent materials for high-quality display technology

1.1 luminescent materials for LED backlight of wide color gamut liquid crystal display

in recent years, liquid crystal display (LCD) has the strongest development momentum in flat panel display and has become the leading technology in the field of flat panel display. Liquid crystal display based on white light emitting diode (LED) backlight has outstanding advantages such as good color reduction, low power consumption and long life. At present, the penetration rate in the field of liquid crystal display has exceeded 95%. In terms of the generation mode of white LED for liquid crystal display, by comprehensively considering its technology, performance and cost, the "blue LED chip + Phosphor" mode is still the mainstream mode of white LED generation due to its high technology maturity and relatively low cost. For LCD LED backlight, the white light generated by "blue LED chip + Phosphor" needs to generate pure red, blue and green light after filtering and splitting. Therefore, phosphor is the key factor to determine the color gamut of LED backlight LCD

at present, the phosphors commonly used in LED backlight liquid crystal display are y3al5o12:ce (yag:ce) phosphor system and sialon:eu green phosphor (some of which adopt silicate green powder) and nitride red phosphor combination system. Due to the wide spectral peaks and poor color purity of the former, the display gamut range of the display made by the former is about 70%ntsc, while the display gamut range of the latter technical scheme can only be increased to 80%ntsc, but the color coordinate y value of green powder and the color coordinate x value of red powder are low, so the display gamut range of the display is difficult to reach more than 85%ntsc, and the light efficiency is reduced by 40% compared with the previous technical scheme. Wide color gamut LCD LED display technology means that it has a display color gamut of more than 90%ntsc, which can accurately present images, enrich colors, and achieve stunning visual effects of restoring the real world. At present, the key implementation method of wide color gamut LED backlight display is the system of "blue chip + sialon:eu green powder + fluoride red powder". However, at present, the performance of the new high-efficiency fluoride phosphor for LED backlight of wide color gamut liquid crystal display developed by the State-owned Research Institute of rare earth is at the same level as the international level, especially the germanium fluoride phosphor, which is the only one in the industry that can be supplied in bulk. There is still a big gap between the performance of domestic sialon:eu green powder and that of foreign countries. Although domestic rare earths can realize the small batch preparation of high band sialon:eu green powder, their main markets are monopolized by foreign enterprises

at present, the industrialization level of LCD color gamut based on the new LED backlight has exceeded 90%ntsc. It is urgent to develop new phosphors and led backlights to further improve the LCD color gamut to 110%ntsc, which is comparable to OLED/qled technology. Fortunately, the development of narrow-band emission red powder with longer wavelength than the existing fluorinated phosphors and green powder with higher purity than sialon:eu green pink has begun, It is expected to reach the application level in the next 2-3 years, which will surely lay a very good material foundation for the efficient use of China's already established very complete LCD technology and industrial chain, seize the commanding height of the future wide color gamut LCD technology, and realize the breakthrough and catch-up of China's LCD technology

1.2 light emitting materials for other emerging display technologies

oleds have many advantages, such as active luminescence, high luminous efficiency, good luminous color purity, bright color, low power consumption, ultra light and thin devices, flexible, etc., which are conducive to full-color display. They have good development prospects in the display field and are favored by the industry. The application potential of OLED display technology in wearable devices such as TVs, terminals, VR, watches, and the gradual recognition of domestic OLED panels by the market will also provide explosive power for the OLED display industry. According to the market survey, among the 3000 US dollars of high-end market in the United States, OLED TV sets accounted for 65% of the market in the first quarter of 2017, and 55 inches could reach 100%. The situation in Europe is the same. Therefore, OLED display technology still has a good application prospect. Luminescent materials (red, blue and green) are important components of OLED display devices. They directly determine the performance and application of OLED devices. Luminescent materials that meet the application requirements must have good comprehensive properties, such as high luminescent brightness and quantum yield; It has large absorption cross section and wide excitation range under near ultraviolet or blue light excitation; Environmentally friendly; Good UV resistance; Good carrier transmission performance; Good thermal stability, film-forming property, etc. at present, the comprehensive properties of OLED display luminescent materials still need to be further improved

quantum dot materials have excellent light-emitting properties, such as high quantum efficiency, continuously adjustable light-emitting wavelength, narrow half peak width, etc. quantum dots are used to replace traditional phosphors, so that the color gamut of the display screen can be improved to 110%ntsc. However, there are still several bottlenecks to be overcome in the application of quantum dot luminescent materials

first of all, due to the small size and large specific surface area of nanocrystalline particles, nanocrystalline particles are prone to oxidation and decomposition under the action of light, heat and chemistry, resulting in a sharp decline in their optical properties. The problem of light decay at operating temperature has become a major obstacle to the improvement of luminous efficiency and life of quantum dot white LED

secondly, although quantum dots are easier to blend with packaging adhesive and other materials than traditional rare earth phosphors, due to the problem of interface compatibility, there are still some problems such as agglomeration and phase separation when blending nanocrystals with packaging media, which makes it difficult to further improve the luminous efficiency of LED products. The use of quantum dot luminescent materials is also an alternative technical way to prepare wide color gamut display devices. However, due to the high cost and complexity of components, and the quantum materials contain CD, it has a negative impact on the environment, and because of its cost, it has not been applied on a practical scale

the stability of quantum dot luminescent materials is the main factor that limits its marketization. Relevant researchers are carrying out a series of relevant research on this issue. With the improvement of material stability, it can be predicted that the half-life of quantum dot white LED will reach more than 10000 hours within three years, and the market will be established at the same time

the field of quantum dot display has been in a situation of tripartite confrontation among China, the United States and South Korea, with fierce competition. Fortunately, China has some first mover advantages in core materials, prototype devices and manufacturing processes. It is expected to provide a good opportunity for China's display industry to break through the patent blockade of foreign technology routes and realize "overtaking by changing lanes"

2. Luminescent materials for high-quality lighting technology, Even pursuing full spectrum lighting similar to sunlight, domestic and foreign packaging enterprises have accelerated the development of full spectrum LED products. At present, there are mainly two ways to realize full spectrum led: multi chip LED and single chip LED. Single chip LED has become the first choice for packaging enterprises because of its simple implementation, low cost and more continuous spectrum. The single chip implementation mode is divided into blue light chip technology (blue light chip + multi-color emitting phosphor) and UV/near UV chip technology (UV/near UV chip + multi-color emitting phosphor). In the blue-green chip technology, there is a serious lack of spectrum in the blue-green part of the device spectrum, which theoretically makes it difficult to achieve the needs of high-quality full spectrum healthy lighting. At present, the UV and near UV chip technology in the third generation semiconductor, which is the national key development, is becoming more and more mature, which makes the UV/near UV chip technology become the preferred technology for full spectrum lighting

the technology of various phosphors excited by blue light has become mature, but most of these phosphors can not be efficiently excited by purple light. At present, there are many researches on green, yellow and red phosphors for excitation of UV/near UV chips. However, the common problem is that the luminous efficiency is low, which is difficult to meet the practical application. The development of phosphors suitable for high-efficiency excitation of violet light, wide band emission and low mutual absorption among various phosphors has become the research focus of the industry, and it is also an important driving force for China to make a breakthrough in intellectual property in the future lighting field. Therefore, in the field of full spectrum lighting, it is an important opportunity to realize green and healthy lighting to grasp the development opportunities and trends of high-energy and short wave third-generation semiconductor technology and develop new supporting luminescent materials, especially new phosphors suitable for UV/near UV chips

2.2 luminescent materials for high-density energy excitation

led lighting has become an indisputable mainstream lighting technology. It is expected that by 2020, the semiconductor lighting field alone will form a trillion market scale. Compared with the first and second generation semiconductor materials, the third generation semiconductor has the advantages of high breakdown voltage, wide forbidden band, high thermal conductivity, high electron saturation rate, strong radiation resistance, etc. at the same time, it also has the characteristics of high luminous efficiency and high frequency. It can be widely used in many strategic emerging industries such as semiconductor lighting to promote and support the next generation industrial reform. Torsional strength of the third generation semiconductor -- when the material is used in the solid-state lighting field when the data is subject to the phenomenon of subordination, it can greatly improve the light efficiency and light color quality of the device. However, the important characteristics of the third generation semiconductor lighting source are the increase of current density and the shift of the light wavelength emitted by the chip to the direction of high-energy short wave. In view of the fact that the light-emitting material directly determines

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