Several classification methods of LED

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The three major white LED phosphor technologies are in a stalemate. The following content requires a reply to be seen. Author: Chen Dengming. The rapid development of LED lighting commercialization is expected to increase the market demand for white LED phosphors. With the continuous investment in phosphor research and development, the three major white LED phosphors that have been developed are expected to meet the requirements of performance diversity and severity in response to different applications. In order to control global greenhouse gas emissions and save the earth's limited energy resources, in recent years, countries have formulated energy policies and have all proposed "energy conservation and carbon reduction" plans. Among them, incandescent lamps have been announced to be eliminated by Australia, the European Union, and California, USA. Light-emitting diodes (LEDs) have the advantages of low heat generation, low power consumption, long life, fast response speed, and small size. At present, the global white LED lighting industry continues to flourish, especially in the application of mobile phone panel backlight, lighting and automotive industries. There is unlimited potential. In recent years, many panel manufacturers at home and abroad have introduced white LEDs as the backlight source of notebook computer LCD displays, replacing traditional cold cathode fluorescent lamps that use mercury. From the perspective of solving environmental and energy problems, incandescent bulbs have always had low energy efficiency and heating problems; as for mercury-containing fluorescent lamps, there is the disadvantage of mercury pollution. For this reason, LED lighting will undoubtedly become the goal of global lighting manufacturers to go all out. Although there are still many problems to be solved in the use of white light LEDs for people's livelihood lighting, in the foreseeable future, with the gradual reduction of manufacturing costs and the continuous development of lighting application fields, white light LEDs are expected to become a lighting product with great potential in the next 10 years. Since 1993, when Nichia Chemical of Japan successfully developed the world's first commercial blue and purple light LEDs made of indium gallium nitride (InGaN), the advent of a new generation of lighting with white light LEDs has been accelerated. Nichia Chemical also published a single-chip white light LED with InGaN/Y3Al5O12:Ce3+ (abbreviated as YAG:Ce) phosphor in 1996. Since then, the world has been competing fiercely for the research and development of white light LED related technologies. Nichia Chemical has already started mass production of white light LEDs with a luminous efficiency of 150 lumens per watt in 2007. The company also said that in the first phase, it will start with mass production of products with a forward current of 20 mA. This LED luminous efficiency is currently the highest record in the global industry. At present, the white light LED production technology in the market is mainly divided into two mainstreams. The first is to use phosphors to convert the blue light or ultraviolet light generated by blue light LED or ultraviolet UV-LED into dual-wavelength (Dichromatic) or triple-wavelength (Trichromatic) white light. This technology is called phosphor converted white light LED (Phosphor Converted-LED); the second type is multi-chip white light LED, which forms white light by combining two (or more) LEDs of different colors. At present, the most common white light LED products on the market are blue light LED chips with yellow light phosphors, which are mainly used in automotive lighting and mobile phone panels. According to the current white light LED product market analysis, phosphor converted white light LED can be said to be the mainstream method. The performance of the three major white light LED phosphors has its own advantages. Since Nichia Chemical published a single-chip white light LED with InGaN/Y3Al5O12: Ce3+ (abbreviated as YAG: Ce) phosphor in 1996, phosphor converted white light LED technology has become the mainstream of the market. The development of phosphors has evolved from relatively unstable sulfides and halides to aluminates, silicates, nitrides, and oxynitrides, which have better chemical and high-temperature stability. Recently, nitrides and oxynitrides are the most popular (Table 1). It is understood that the combination that is recognized by the industry as the most efficient in producing white light is still Nichia Chemical's use of blue LED chips with YAG:Ce yellow phosphors. In addition, the yellow phosphor TAG developed by Osram Opto Semiconductors performs relatively poorly. In addition, the use of blue LED chips with green and red sulfide or oxide phosphors is another feasible option. Generally, the industry recognizes that high-quality phosphors for white light LEDs must have strong absorption of the LED chip emission wavelength and high light-to-light conversion efficiency; stable physical and chemical properties and non-toxicity, anti-oxidation, moisture resistance, no reaction with packaging resins, chips and metal wires; excellent temperature fluorescence quenching characteristics (at least above 120°C); light-emitting characteristics (emission wavelength and chromaticity) that match LEDs; and moderate particle size with a narrow distribution range and good dispersion. If it is too coarse or too fine, it will lead to poor light efficiency. Summarizing the characteristics of bandwidth, quantum efficiency, thermal stability, chemical stability, and whether the emission wavelength can be adjusted, the performance of the three most popular types of phosphors in the market is compared. ? Garnet-type oxide phosphors The patent disclosed by Nichia Chemical of Japan covers a wide range of chemical compositions of garnet-type oxide phosphors, especially in the systematic adjustment of the yttrium aluminum garnet yellow phosphor component Y3Al5O12:Ce3+, where Y3+ is replaced by Tb3+ or Gd3+ or Al3+ is replaced by Ga3+ to derive multiple series of (Y,Gd,Sm)3 (Al,Ga)5O12:Ce3+ yellow-orange phosphors that can be matched with chips of different blue wavelengths (440-480 nanometers). In addition, in order to improve the color rendering of white light LEDs made using YAG:Ce series phosphors, which cannot be compared with traditional white light sources, or the color temperature needs to be adjusted, if necessary, the red phosphors listed in Table 1 can be added to the phosphor formula to effectively improve it. On the other hand, Philips-Lumileds once used 460 nanometer blue light LEDs with green light SrGa2S4:Eu2+ and red light SrS:Eu2+ phosphors to produce white light LEDs with a color rendering index (Ra) of 82-87 and a color temperature of 3,000-6,000K. This is an example of a packaging method. In recent years, as the technology of near-ultraviolet (390-410 nanometers) and ultraviolet (365-385 nanometers) LED chips has gradually matured and has been successfully mass-produced, the production of white light LEDs has gradually matured. In particular, global optoelectronics giants such as Germany's Osram Optoelectronics, Japan's Nichia Chemical and Toyota Gosei (Toyada-Gosei), the United States Philips-Lumileds and Cree, and many other companies have actively invested in it. It is worth noting that Cree in the United States has produced 50 milliwatt 385-405 nanometer ultraviolet LEDs; Nichia has mass-produced 365, 375 and 385 nanometer wavelength LEDs and the Ra value of its white light LEDs is ≥90. The era of white light LED lighting with high efficiency, high Ra value and multiple color temperatures is just around the corner. ? Silicate phosphor The development of silicate phosphor originated from Zn2SiO4:Mn2+ of General Electric (GE) in the United States in the early 1940s. It has gone through the development of various materials such as (Sr, Ba,Mg)3Si2O7:Pb2+(1949), BaSi2O5:Pb2+ (1960), Sr4Si3O8Cl4:Eu2+(1967), BaSi2O5:Pb2+(1960), and in 1998 (Ba,After the discovery of Si)2SiO4:Eu2+, the application of silicate phosphors in white light LEDs has progressed rapidly. Now there are many materials that can be used for white light LEDs. Table 3 lists and compares the spectral characteristics of common silicate phosphors. At present, the important patents of silicate phosphors are still owned by Toyota Gosei, Nichia Chemical, Osram Opto Semiconductors and Intematix of the United States. In the production of phosphor-converted white light LEDs, silicate is another important new choice because the material has significant absorption of ultraviolet, near-ultraviolet and blue light; it has the highest brightness value among all yellow light phosphors; the output quantum efficiency is higher than 90%, and there is still room for improvement; the mass production cost is low; when used in ultraviolet LEDs, it has high temperature stability (at least above 120℃); it has physical (such as high-intensity radiation) and chemical stability, anti-oxidation, anti-moisture, and no reaction with packaging resin; and it can be matched with ultraviolet/blue light chips to provide conditions for the production of white light LEDs of various color temperatures. Thermal quenching of luminescence or temperature stability of phosphors has always been valued by high-power white LEDs that are troubled by heat dissipation issues. Nitride and oxynitride phosphors In the 1980s, metal nitrides (oxynitrides) were mostly used as structural or functional ceramics. Their application in white light LEDs has only begun to be noticed in recent years. Currently, the world's leading nitride and oxynitride phosphors are mainly the Technical University of Eindhoven in the Netherlands and the National Institute for Materials Science and Engineering in Japan. Science (NIMS), Mitsubishi Chemical Corporation, Ube Industries, Japan, and OSRAM Opto Semiconductors, etc., although the process of nitride or nitrogen oxide phosphors usually requires high temperature and high pressure conditions, this phosphor has many characteristics that can show the potential for white light LED applications, including diverse crystal structures and chemical compositions, adjustable emission wavelengths; considerable physical and chemical stability; can be excited by ultraviolet, near-ultraviolet or blue light; the fluorescence emission spectrum has a large wavelength red shift; extremely small temperature fluorescence quenching effect (at least > 120°C); highly covalent bonding (narrow energy gap), showing strong electron cloud diffusion effect and crystal field splitting effect; and highly condensed anion network crystal structure, weakening the temperature effect on fluorescence quenching, etc. Because LED lighting components require high color rendering and stability, nitrides and nitrogen oxides have stronger electron cloud diffusion (Nephelauxetic) effects derived from covalent structures than oxides, so this series of white light LED phosphors are gradually valued. As early as 1999, Osram Opto Semiconductors of Germany applied for patents related to red-yellow (Ca, Sr, Ba) xSiyNz: Eu nitride phosphors at the European Patent Office of the European Union. Among them, SrzSi5N8: Eu and SrSi7N10: Eu, which can be applied to blue and ultraviolet LEDs, belong to this category. In 2001, the National Institute for Materials Science (NIMS) of Japan applied for patents for Cax(Eu, Tb, Yb, Er) y(Si, Al) 12(O, N) 16, a nitride phosphor with high luminous efficiency, which can produce multiple colors of light. This material includes orange-yellow Ca-α-SiAlON doped with various rare earth ions (such as Eu2+, Ce3+, Dy3+, Eu3+ and Mn2+) and green-light MSi2N2O2: Eu2+ and other fluorescent materials. In addition to the currently more popular nitrides CaAlSiN3 and nitrogen oxides SrSi2O2N2:, recently several researchers from Mitsubishi Chemical Corporation in Japan suggested that orange light (Sr,Ca)AlSiN3:Eu2+ nitrides can be used in combination with green light CaSc2O4:Ce3+ or Ca3(Sc,Mg)2Si3O12:Ce3+ for general lighting; and the company's new green light nitrogen oxide Ba3Si6O12N2:Eu can replace CaSc2O4:Ce3+ oxide and be combined with orange light CaAlSiN3:Eu2+ nitride silicon for use in liquid crystal panel backlight sources. The principle of the above suggestion is to use high brightness and high color rendering as the biggest difference between lighting and display. Among them, the novel nitrogen oxide Ba3Si6O12N2:Eu composition that can be excited by ultraviolet and blue light has a complex crystal structure and difficult synthesis conditions. It is characterized by a smaller half-maximum full width (FWHM) (~68 nanometers) at a wavelength of 525 nanometers. It is worth mentioning that Japanese NIMS researchers have tried to produce white light LEDs composed of red (CaAlSiN3:Eu2+), yellow (α-SiAlON:Eu2+), and green (β-SiAlON:Eu2+) phosphors with blue LED chips (Figure 5). Among them, CaAlSiN3:Eu2+ can make the chip 460 Nano blue light is converted into 650 nano red light, β-SiAlON:Eu2+ can convert it into 540 nano green light, and α-SiAlON:Eu2+ yellow light can be added to adjust the proportion of red, green and blue light to produce a light source that meets the color characteristics of the color filter. NIMS researchers pointed out that when the above white light LED is used as a backlight source for liquid crystal panels, the color gamut range simulation value NTSC is 91%, which is richer than the 72% of the current white light LED using YAG phosphor. This shows the infinite potential of making white light LEDs with red, green, blue and yellow nitrogen oxides. The technological progress of converting white light LEDs into three popular types of phosphors, namely yttrium aluminum garnet, silicate and nitride (oxy) compounds, is closely related to the use and development of novel phosphors. Although the international industry-university research and development of white light LED phosphors has not stagnated, its momentum has approached saturation, and the patent layout of global optoelectronics manufacturers related to white light LED phosphors is more complete than expected. As the industrial development speed and progress of white light LED lighting far exceeds expectations, the demand for phosphors will increase day by day and become more urgent. The domestic industry and academia will undoubtedly face critical pressure and limitations in the research and development of phosphors. How to break through the current situation and further strengthen the global competitiveness of the domestic white light LED industry depends on closer cooperation and incentives between industry and academia to create a bright future for the LED industry.Ca)AlSiN3:Eu2+ nitride can be used with green light CaSc2O4:Ce3+ or Ca3(Sc,Mg)2Si3O12:Ce3+ for general lighting; and the company's new green light nitrogen oxide Ba3Si6O12N2:Eu can replace CaSc2O4:Ce3+ oxide and be used with orange light CaAlSiN3:Eu2+ nitride silicon for liquid crystal panel backlight. The principle of the above suggestion is to use high brightness and high color rendering as the biggest difference between lighting and display. Among them, the novel nitrogen oxide Ba3Si6O12N2:Eu composition that can be excited by ultraviolet and blue light has a complex crystal structure and difficult synthesis conditions. It is characterized by a smaller half-maximum full width (FWHM) (~68 nanometers) at a wavelength of 525 nanometers. It is worth mentioning that Japanese NIMS researchers have tried to produce white light LEDs composed of red (CaAlSiN3:Eu2+), yellow (α-SiAlON:Eu2+), and green (β-SiAlON:Eu2+) phosphors with blue LED chips (Figure 5). Among them, CaAlSiN3:Eu2+ can make the chip 460 Nano blue light is converted into 650 nano red light, β-SiAlON:Eu2+ can convert it into 540 nano green light, and α-SiAlON:Eu2+ yellow light can be added to adjust the proportion of red, green and blue light to produce a light source that meets the color characteristics of the color filter. NIMS researchers pointed out that when the above white light LED is used as a backlight source for liquid crystal panels, the color gamut range simulation value NTSC is 91%, which is richer than the 72% of the current white light LED using YAG phosphor. This shows the infinite potential of making white light LEDs with red, green, blue and yellow nitrogen oxides. The technological progress of converting white light LEDs into three popular types of phosphors, namely yttrium aluminum garnet, silicate and nitride (oxy) compounds, is closely related to the use and development of novel phosphors. Although the international industry-university research and development of white light LED phosphors has not stagnated, its momentum has approached saturation, and the patent layout of global optoelectronics manufacturers related to white light LED phosphors is more complete than expected. As the industrial development speed and progress of white light LED lighting far exceeds expectations, the demand for phosphors will increase day by day and become more urgent. The domestic industry and academia will undoubtedly face critical pressure and limitations in the research and development of phosphors. How to break through the current situation and further strengthen the global competitiveness of the domestic white light LED industry depends on closer cooperation and incentives between industry and academia to create a bright future for the LED industry.Ca)AlSiN3:Eu2+ nitride can be used with green light CaSc2O4:Ce3+ or Ca3(Sc,Mg)2Si3O12:Ce3+ for general lighting; and the company's new green light nitrogen oxide Ba3Si6O12N2:Eu can replace CaSc2O4:Ce3+ oxide and be used with orange light CaAlSiN3:Eu2+ nitride silicon for liquid crystal panel backlight. The principle of the above suggestion is to use high brightness and high color rendering as the biggest difference between lighting and display. Among them, the novel nitrogen oxide Ba3Si6O12N2:Eu composition that can be excited by ultraviolet and blue light has a complex crystal structure and difficult synthesis conditions. It is characterized by a smaller half-maximum full width (FWHM) (~68 nanometers) at a wavelength of 525 nanometers. It is worth mentioning that Japanese NIMS researchers have tried to produce white light LEDs composed of red (CaAlSiN3:Eu2+), yellow (α-SiAlON:Eu2+), and green (β-SiAlON:Eu2+) phosphors with blue LED chips (Figure 5). Among them, CaAlSiN3:Eu2+ can make the chip 460 Nano blue light is converted into 650 nano red light, β-SiAlON:Eu2+ can convert it into 540 nano green light, and α-SiAlON:Eu2+ yellow light can be added to adjust the proportion of red, green and blue light to produce a light source that meets the color characteristics of the color filter. NIMS researchers pointed out that when the above white light LED is used as a backlight source for liquid crystal panels, the color gamut range simulation value NTSC is 91%, which is richer than the 72% of the current white light LED using YAG phosphor. This shows the infinite potential of making white light LEDs with red, green, blue and yellow nitrogen oxides. The technological progress of converting white light LEDs into three popular types of phosphors, namely yttrium aluminum garnet, silicate and nitride (oxy) compounds, is closely related to the use and development of novel phosphors. Although the international industry-university research and development of white light LED phosphors has not stagnated, its momentum has approached saturation, and the patent layout of global optoelectronics manufacturers related to white light LED phosphors is more complete than expected. As the industrial development speed and progress of white light LED lighting far exceeds expectations, the demand for phosphors will increase day by day and become more urgent. The domestic industry and academia will undoubtedly face critical pressure and limitations in the research and development of phosphors. How to break through the current situation and further strengthen the global competitiveness of the domestic white light LED industry depends on closer cooperation and incentives between industry and academia to create a bright future for the LED industry.