romikgosai/squad_modified_2 huggingface dataset:
The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994 and was based on InGaN. In parallel, Isamu Akasaki and Hiroshi Amano in Nagoya were working on developing the important GaN nucleation on sapphire substrates and the demonstration of p-type doping of GaN. Nakamura, Akasaki and Amano were awarded the 2014 Nobel prize in physics for their work. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using indium tin oxide (ITO) on (AlGaInP/GaAs).

Q1: What color LED was demonstrated in 1994?
A1: blue
Q2: Who demonstrated the first blue LED?
A2: Shuji Nakamura
Q3: What did Nakamura, Akasaki, and Amano receive for their work?
A3: 2014 Nobel prize in physics
Q4: Who investigated the efficiency of high-brightness LED at Cardiff University in 1995?
A4: Alberto Barbieri
Q5: What substance did Barbieri use in his work with high-brightness LED?
A5: indium tin oxide
The attainment of high efficiency in blue LEDs was quickly followed by the development of the first white LED. In this device a Y
3Al
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12:Ce (known as "YAG") phosphor coating on the emitter absorbs some of the blue emission and produces yellow light through fluorescence. The combination of that yellow with remaining blue light appears white to the eye. However using different phosphors (fluorescent materials) it also became possible to instead produce green and red light through fluorescence. The resulting mixture of red, green and blue is not only perceived by humans as white light but is superior for illumination in terms of color rendering, whereas one cannot appreciate the color of red or green objects illuminated only by the yellow (and remaining blue) wavelengths from the YAG phosphor.

Q1: What LED quickly followed the blue LEDs?
A1: white
Q2: What does the YAG phosphor coating produce?
A2: yellow light
A P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called electroluminescence, which can be defined as the emission of light from a semi-conductor under the influence of an electric field. The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region. Free electrons are in the conduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes will be lesser than the energy levels of the electrons. Some portion of the energy must be dissipated in order to recombine the electrons and the holes. This energy is emitted in the form of heat and light.

Q1: What converts absorbed light energy into an electric current?
A1: P-N junction
Q2: What is the phenomenon where a P-N junction emits light when an electrical current is applied to it?
A2: electroluminescence
Q3: Where are the free electrons located in the production of electroluminescence?
A3: the conduction band
Q4: Whose energy levels are lower than the electrons in the electroluminescence process?
A4: holes existing in the P-region
Q5: Why is some energy in the electroluminescence process emitted as heat and light?
A5: to recombine the electrons and the holes
In September 2003, a new type of blue LED was demonstrated by Cree that consumes 24 mW at 20 milliamperes (mA). This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006, they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Nichia Corporation has developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA. Cree's XLamp XM-L LEDs, commercially available in 2011, produce 100 lm/W at their full power of 10 W, and up to 160 lm/W at around 2 W input power. In 2012, Cree announced a white LED giving 254 lm/W, and 303 lm/W in March 2014. Practical general lighting needs high-power LEDs, of one watt or more. Typical operating currents for such devices begin at 350 mA.

Q1: In what year was a new type of blue LED produced?
A1: 2003
Q2: Who demonstrated in 2003 the new type of blue LED?
A2: Cree
Q3: How much more efficient as standard incandescents was the white LED commercially available in 2003?
A3: four times
Q4: What is the typical operating current for high-power LEDs?
A4: 350 mA
The most common symptom of LED (and diode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can also occur. Early red LEDs were notable for their short service life. With the development of high-power LEDs the devices are subjected to higher junction temperatures and higher current densities than traditional devices. This causes stress on the material and may cause early light-output degradation. To quantitatively classify useful lifetime in a standardized manner it has been suggested to use L70 or L50, which are the runtimes (typically given in thousands of hours) at which a given LED reaches 70% and 50% of initial light output, respectively.

Q1: What is a symptom of LED failure?
A1: loss of efficiency
Q2: What is rare in LED lighting?
A2: Sudden failures
Q3: What was notable in early red LEDs?
A3: their short service life
Q4: What could cause early light-output degradation in LEDs?
A4: higher junction temperatures
Q5: What is a classification used in LED lighting to describe how much usefulness it will receive?
A5: L70 or L50
Since LED efficacy is inversely proportional to operating temperature, LED technology is well suited for supermarket freezer lighting. Because LEDs produce less waste heat than incandescent lamps, their use in freezers can save on refrigeration costs as well. However, they may be more susceptible to frost and snow buildup than incandescent lamps, so some LED lighting systems have been designed with an added heating circuit. Additionally, research has developed heat sink technologies that will transfer heat produced within the junction to appropriate areas of the light fixture.

Q1: LED efficacy is inversely proportional to what?
A1: operating temperature
Q2: Where is LED lighting very well suited?
A2: supermarket freezer
Q3: LEDs produce less waste heat than what other device?
A3: incandescent lamps
Q4: What is LED lighting more susceptible to than incandescent light?
A4: frost
The first blue-violet LED using magnesium-doped gallium nitride was made at Stanford University in 1972 by Herb Maruska and Wally Rhines, doctoral students in materials science and engineering. At the time Maruska was on leave from RCA Laboratories, where he collaborated with Jacques Pankove on related work. In 1971, the year after Maruska left for Stanford, his RCA colleagues Pankove and Ed Miller demonstrated the first blue electroluminescence from zinc-doped gallium nitride, though the subsequent device Pankove and Miller built, the first actual gallium nitride light-emitting diode, emitted green light. In 1974 the U.S. Patent Office awarded Maruska, Rhines and Stanford professor David Stevenson a patent for their work in 1972 (U.S. Patent US3819974 A) and today magnesium-doping of gallium nitride continues to be the basis for all commercial blue LEDs and laser diodes. These devices built in the early 1970s had too little light output to be of practical use and research into gallium nitride devices slowed. In August 1989, Cree introduced the first commercially available blue LED based on the indirect bandgap semiconductor, silicon carbide (SiC). SiC LEDs had very low efficiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum.[citation needed]

Q1: What students developed the first blue-violet LED?
A1: Herb Maruska and Wally Rhines
Q2: The first blue-violet LED was developed at what University?
A2: Stanford
Q3: When was the first blue-violet LED developed?
A3: 1972
Q4: What substance helped demonstrate the first blue electroluminescence?
A4: zinc-doped gallium nitride
In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, Dr. Moustakas at Boston University patented a method for producing high-brightness blue LEDs using a new two-step process. Two years later, in 1993, high-brightness blue LEDs were demonstrated again by Shuji Nakamura of Nichia Corporation using a gallium nitride growth process similar to Dr. Moustakas's. Both Dr. Moustakas and Mr. Nakamura were issued separate patents, which confused the issue of who was the original inventor (partly because although Dr. Moustakas invented his first, Dr. Nakamura filed first).[citation needed] This new development revolutionized LED lighting, making high-power blue light sources practical, leading to the development of technologies like BlueRay, as well as allowing the bright high resolution screens of modern tablets and phones.[citation needed]

Q1: In what decade were breakthroughs made that brought in the modern era of GaN-based optoelectronic devices?
A1: 1980s
Q2: Who first patented a method to produce high-brightness blue LEDs?
A2: Shuji Nakamura
Q3: Who first invented a method to produce high-brightness blue LEDs?
A3: Dr. Moustakas
Q4: What technology was made possible by high-power blue light sources?
A4: BlueRay
Q5: What is one modern gadget that benefits from high-power blue LED lighting?
A5: tablets
Nakamura was awarded the 2006 Millennium Technology Prize for his invention. Nakamura, Hiroshi Amano and Isamu Akasaki were awarded the Nobel Prize in Physics in 2014 for the invention of the blue LED. In 2015, a US court ruled that three companies (i.e. the litigants who had not previously settled out of court) that had licensed Mr. Nakamura's patents for production in the United States had infringed Dr. Moustakas's prior patent, and order them to pay licensing fees of not less than 13 million USD.

Q1: What Nobel Prize did Nakamura, Amano, and Akasaki receive in 2014?
A1: Physics
Q2: What award did Nakamura receive in 2006 for his invention?
A2: Millennium Technology Prize
Q3: How many companies did a judge say infringed on Dr. Moustakas's prior blue light patent in 2015?
A3: three
Q4: What was the fine given to the three companies?
A4: not less than 13 million USD
By the late 1990s, blue LEDs became widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative In/Ga fraction in the InGaN quantum wells, the light emission can in theory be varied from violet to amber. Aluminium gallium nitride (AlGaN) of varying Al/Ga fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of InGaN/GaN blue/green devices. If un-alloyed GaN is used in this case to form the active quantum well layers, the device will emit near-ultraviolet light with a peak wavelength centred around 365 nm. Green LEDs manufactured from the InGaN/GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems, but practical devices still exhibit efficiency too low for high-brightness applications.[citation needed]

Q1: What are cladding layers?
A1: active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN
Q2: How can light emission be varied from violet to amber?
A2: By varying the relative In/Ga fraction in the InGaN quantum wells
Q3: What does AlGaN stand for?
A3: Aluminium gallium nitride
Q4: What LEDs are more efficient when produced from the InGaN/GaN systems than without?
A4: Green
With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies. Shorter-wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 240 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LED emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices. Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices. UV-C wavelengths were obtained in laboratories using aluminium nitride (210 nm), boron nitride (215 nm) and diamond (235 nm).

Q1: What substance does nitrides contain?
A1: aluminium
Q2: What sort of LEDs are becoming more available on the market?
A2: Ultraviolet
Q3: What is the range of wavelengths for cheap UV LEDs?
A3: 375–395 nm
Q4: Shorter wavelength diodes provide wavelengths as low as what?
A4: 240 nm
Q5: What UV wavelengths are found in sterilization devices?
A5: 250–270 nm
White light can be formed by mixing differently colored lights; the most common method is to use red, green, and blue (RGB). Hence the method is called multi-color white LEDs (sometimes referred to as RGB LEDs). Because these need electronic circuits to control the blending and diffusion of different colors, and because the individual color LEDs typically have slightly different emission patterns (leading to variation of the color depending on direction) even if they are made as a single unit, these are seldom used to produce white lighting. Nonetheless, this method has many applications because of the flexibility of mixing different colors, and in principle, this mechanism also has higher quantum efficiency in producing white light.[citation needed]

Q1: What colors are used to form white light?
A1: red, green, and blue
Q2: What is the method called that mixes red, green, and blue colors to form white light?
A2: multi-color white LEDs
Q3: What does the multi-color white LED method need to produce the end result?
A3: electronic circuits
Q4: What is another name to reference the multi-color white LED method?
A4: RGB LEDs
There are several types of multi-color white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different methods, include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency will mean lower color rendering, presenting a trade-off between the luminous efficacy and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.

Q1: What is a factor that may be different in the various types of multi-color white LEDs?
A1: luminous efficacy
Q2: Higher efficiency in multi-color white LEDs may mean what?
A2: lower color rendering
Q3: What is one type of multi-color white LED?
A3: tetrachromatic
Q4: What type has the best luminous efficacy?
A4: dichromatic white LEDs
Q5: What luminous efficacy does trichromatic white LEDs have?
A5: >70 lm/W
Multi-color LEDs offer not merely another means to form white light but a new means to form light of different colors. Most perceivable colors can be formed by mixing different amounts of three primary colors. This allows precise dynamic color control. As more effort is devoted to investigating this method, multi-color LEDs should have profound influence on the fundamental method that we use to produce and control light color. However, before this type of LED can play a role on the market, several technical problems must be solved. These include that this type of LED's emission power decays exponentially with rising temperature, resulting in a substantial change in color stability. Such problems inhibit and may preclude industrial use. Thus, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists.

Q1: Multi-color LEDs offer what else besides the formation of white light?
A1: to form light of different colors
Q2: What problem must be solved before multi-color LEDs can play a role in the market?
A2: power decays exponentially with rising temperature
Q3: What problem results when rising temperatures decays power?
A3: substantial change in color stability
This method involves coating LEDs of one color (mostly blue LEDs made of InGaN) with phosphors of different colors to form white light; the resultant LEDs are called phosphor-based or phosphor-converted white LEDs (pcLEDs). A fraction of the blue light undergoes the Stokes shift being transformed from shorter wavelengths to longer. Depending on the color of the original LED, phosphors of different colors can be employed. If several phosphor layers of distinct colors are applied, the emitted spectrum is broadened, effectively raising the color rendering index (CRI) value of a given LED.

Q1: What method involves coating LEDs of one color with phosphors of different colors?
A1: phosphor-converted white LEDs (pcLEDs)
Q2: In pcLEDs method, a fraction of what light is used?
A2: blue
Q3: What shift does blue light undergo in the pcLEDs method?
A3: Stokes
Q4: The different colors of phosphors that can be used is based on what?
A4: the color of the original LED
Q5: What broadens the emitted spectrum in a pcLEDs method?
A5: If several phosphor layers of distinct colors are applied
Phosphor-based LED efficiency losses are due to the heat loss from the Stokes shift and also other phosphor-related degradation issues. Their luminous efficacies compared to normal LEDs depend on the spectral distribution of the resultant light output and the original wavelength of the LED itself. For example, the luminous efficacy of a typical YAG yellow phosphor based white LED ranges from 3 to 5 times the luminous efficacy of the original blue LED because of the human eye's greater sensitivity to yellow than to blue (as modeled in the luminosity function). Due to the simplicity of manufacturing the phosphor method is still the most popular method for making high-intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high-intensity white LEDs presently on the market are manufactured using phosphor light conversion.

Q1: What do phosphor-based LEDs luminous efficacies depend on?
A1: the spectral distribution of the resultant light output
Q2: What is the most popular method for making high-intensity white LEDs?
A2: phosphor method
Q3: Why is efficiency sometimes lost in phosphor-based LEDs?
A3: heat loss from the Stokes shift
Q4: What are some of the luminous efficacies of yellow phosphor based white LED compared to blue?
A4: 3 to 5 times the luminous efficacy
Q5: What type of emitter is used in phosphor-based white LED methods?
A5: monochrome
Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stoke shift loss. Losses attributable to internal optical losses due to re-absorption in the LED chip and in the LED packaging itself account typically for another 10% to 30% of efficiency loss. Currently, in the area of phosphor LED development, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor. Conformal coating process is frequently used to address the issue of varying phosphor thickness.

Q1: What can improve the efficiency of LED-based white light?
A1: more efficient phosphors
Q2: What is the most efficient yellow phosphor?
A2: YAG phosphor
Q3: What is the percentage of stoke shift loss in YAG phosphor?
A3: less than 10%
Q4: What area are scientists looking into regarding phosphor LED development?
A4: higher operation temperatures
Q5: What is one method that can raise the efficiency of phosphor-based LEDs?
A5: adapting better package design
White LEDs can also be made by coating near-ultraviolet (NUV) LEDs with a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness. A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.

Q1: White LEDs can be made by coating what?
A1: near-ultraviolet (NUV) LEDs
Q2: What are near-ultraviolet LEDs coated with to create white LED?
A2: copper and aluminium-doped zinc sulfide (ZnS:Cu, Al)
Q3: What device also works in a similar way as NUV LEDs?
A3: fluorescent lamps
Q4: The method of coating NUVs less efficient than what other LEDs?
A4: blue
Q5: What light can harm human eyes or skin?
A5: UV light
A new style of wafers composed of gallium-nitride-on-silicon (GaN-on-Si) is being used to produce white LEDs using 200-mm silicon wafers. This avoids the typical costly sapphire substrate in relatively small 100- or 150-mm wafer sizes. The sapphire apparatus must be coupled with a mirror-like collector to reflect light that would otherwise be wasted. It is predicted that by 2020, 40% of all GaN LEDs will be made with GaN-on-Si. Manufacturing large sapphire material is difficult, while large silicon material is cheaper and more abundant. LED companies shifting from using sapphire to silicon should be a minimal investment.

Q1: What is being used to produce white LEDs?
A1: wafers composed of gallium-nitride-on-silicon
Q2: What size are the wafers used to create white LEDs?
A2: 200-mm
Q3: By using silicon wafers, what is being avoided?
A3: costly sapphire substrate
Q4: What needs to be used to reflect light that would otherwise be wasted?
A4: mirror-like collector
Q5: By what year will% of all GaN LEDs be made with gallium-nitride-on-silicon wafers?
A5: 2020
Quantum dots (QD) are semiconductor nanocrystals that possess unique optical properties. Their emission color can be tuned from the visible throughout the infrared spectrum. This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering than white LEDs since the emission spectrum is much narrower, characteristic of quantum confined states. There are two types of schemes for QD excitation. One uses photo excitation with a primary light source LED (typically blue or UV LEDs are used). The other is direct electrical excitation first demonstrated by Alivisatos et al.

Q1: What nanocrystals possess unique optical properties?
A1: Quantum dots
Q2: Quantum Dot LEDs can do what special skill?
A2: create almost any color on the CIE diagram
Q3: The narrowing of the emission spectrum in Quantum Dot LEDs allows them to do what?
A3: better color rendering
Q4: How many types of schemes are there in Quantum Dot LED excitation?
A4: two