In the last few years, LEDs (light emitting diodes) have begun replacing incandescent and fluorescent lights in a number of niche applications. Although these solid-state lights have been used for decades in consumer electronics, recent technological advances have allowed them to spread into areas like architectural lighting, traffic lights, flashlights and reading lights. Although they are considerably more expensive than ordinary lights, they are capable of producing about twice as much light per watt as incandescent bulbs; they last up to 50,000 hours or 50 times as long as a 60-watt bulb; and, they are very tough and hard to break. Because they are made in a fashion similar to computer chips, the cost of LEDs has been dropping steadily.
While the future of electronics and other fields may revolve around nanotechnology, researchers and manufacturers are faced with fabricating large-scale components out of building blocks invisible to the naked eye. Creating hybrid optoelectronic devices depends on the precise positioning of functionally distinct materials. The researchers used organic molecules currently used in OLEDs as an organic semiconductor to deliver an electrical charge to the quantum dots. They used two parallel processes, which are already widely applicable in industry, to create separate but layered structures out of nanoscale materials.
Until now quantum dots have been known primarily for their ability to produce a dozen different distinct colors of light simply by varying the size of the individual nanocrystals: a capability particularly suited to fluorescent labeling in biomedical applications. Artificial atoms or quantum dots (QDs) constructed from semiconductors are expected to provide the basis for future generations of device technologies such as threshhold-less lasers and ultra-dense memories. The quantum dots can be induced by interface fluctuations (top of the figure) in a quantum well, self-assembled with the driving force being lattice mismatch (bottom) or formed with lithographic techniques.Recently the world have made a number of unexpected discoveries arising from the breakthrough of single quantum dot spectroscopy based on ultra high resolution techniques.
The small size results in new quantum phenomena that yield some extraordinary bonuses. Material properties change dramatically because quantum effects arise from the confinement of electrons and "holes" in the material (a hole is the absence of an electron; the hole behaves as though it were a positively charged particle). Size changes other material properties such as the electrical and nonlinear optical properties of a material, making them very different from those of the material's bulk form. If a dot is excited, the smaller the dot, the higher the energy and intensity of its emitted light. Hence, these very small, semiconducting quantum dots are gateways to an enormous array of possible applications and new technologies.
According to michael bowers who made the quantum dots and discovered their unusual properties, the white-light quantum dots, produce a smoother distribution of wavelengths in the visible spectrum with a slightly warmer, slightly more yellow tint. As a result, the light produced by the quantum dots looks more nearly like the “full spectrum” reading lights now on the market which produce a light spectrum closer to that of sunlight than normal fluorescent tubes or light bulbs. Of course, quantum dots, like white LEDs, have the advantage of not giving off large amounts of invisible infrared radiation unlike the light bulb. This invisible radiation produces large amounts of heat and largely accounts for the light bulb’s low energy efficiency.
The approach is based on encapsulating semiconductor quantum dots — nanoparticles approximately one billionth of a meter in size — and engineering their surfaces so they efficiently emit visible light when excited by near-ultraviolet (UV) light-emitting diodes (LEDs). The quantum dots strongly absorb light in the near UV range and re-emit visible light that has its color determined by both their size and surface chemistry.
Unlike traditional LCDs, which must be lit from behind, quantum dots generate their own light. Depending on their size, the dots can be "tuned" to emit any color in the rainbow. And the colors of light they produce are much more saturated than that of other sources.A latest Quantum dots LED, 'MIT QD-OLED' contains only a single layer of quantum dots sandwiched between two organic thin films.The researchers have demonstrated organized assemblies over a 1-square centimeter area and the same principle could be used to make bigger components.The latest MIT QD-OLED have a 25-fold improvement in luminescent power efficiency over previous QD-OLEDs. They are more efficient and achieve even higher color saturation.
Quantum-dot LEDs, particularly those that provide the hard-to-reach blue end of the spectrum, appear to be key to opening any number of exciting technological advances in the fields of full-color, flat-panel displays; ultrahigh-density optical memories and data storage; backlighting; and chemical and biological sensing."Highly efficient, low-cost quantum dot-based lighting would represent a revolution in lighting technology through nanoscience."
Thus hybridising an inorganic nanocrystal and a quantum dot lead to a quantum dot-organic light-emitting device (QD-OLED) a new kind of optoelectronic device that could lead to new types of flat panel displays to supersede liquid crystal displays in everything from mobile devices to TV sets.
While the future of electronics and other fields may revolve around nanotechnology, researchers and manufacturers are faced with fabricating large-scale components out of building blocks invisible to the naked eye. Creating hybrid optoelectronic devices depends on the precise positioning of functionally distinct materials. The researchers used organic molecules currently used in OLEDs as an organic semiconductor to deliver an electrical charge to the quantum dots. They used two parallel processes, which are already widely applicable in industry, to create separate but layered structures out of nanoscale materials.
Until now quantum dots have been known primarily for their ability to produce a dozen different distinct colors of light simply by varying the size of the individual nanocrystals: a capability particularly suited to fluorescent labeling in biomedical applications. Artificial atoms or quantum dots (QDs) constructed from semiconductors are expected to provide the basis for future generations of device technologies such as threshhold-less lasers and ultra-dense memories. The quantum dots can be induced by interface fluctuations (top of the figure) in a quantum well, self-assembled with the driving force being lattice mismatch (bottom) or formed with lithographic techniques.Recently the world have made a number of unexpected discoveries arising from the breakthrough of single quantum dot spectroscopy based on ultra high resolution techniques.
The small size results in new quantum phenomena that yield some extraordinary bonuses. Material properties change dramatically because quantum effects arise from the confinement of electrons and "holes" in the material (a hole is the absence of an electron; the hole behaves as though it were a positively charged particle). Size changes other material properties such as the electrical and nonlinear optical properties of a material, making them very different from those of the material's bulk form. If a dot is excited, the smaller the dot, the higher the energy and intensity of its emitted light. Hence, these very small, semiconducting quantum dots are gateways to an enormous array of possible applications and new technologies.
According to michael bowers who made the quantum dots and discovered their unusual properties, the white-light quantum dots, produce a smoother distribution of wavelengths in the visible spectrum with a slightly warmer, slightly more yellow tint. As a result, the light produced by the quantum dots looks more nearly like the “full spectrum” reading lights now on the market which produce a light spectrum closer to that of sunlight than normal fluorescent tubes or light bulbs. Of course, quantum dots, like white LEDs, have the advantage of not giving off large amounts of invisible infrared radiation unlike the light bulb. This invisible radiation produces large amounts of heat and largely accounts for the light bulb’s low energy efficiency.
The approach is based on encapsulating semiconductor quantum dots — nanoparticles approximately one billionth of a meter in size — and engineering their surfaces so they efficiently emit visible light when excited by near-ultraviolet (UV) light-emitting diodes (LEDs). The quantum dots strongly absorb light in the near UV range and re-emit visible light that has its color determined by both their size and surface chemistry.
Unlike traditional LCDs, which must be lit from behind, quantum dots generate their own light. Depending on their size, the dots can be "tuned" to emit any color in the rainbow. And the colors of light they produce are much more saturated than that of other sources.A latest Quantum dots LED, 'MIT QD-OLED' contains only a single layer of quantum dots sandwiched between two organic thin films.The researchers have demonstrated organized assemblies over a 1-square centimeter area and the same principle could be used to make bigger components.The latest MIT QD-OLED have a 25-fold improvement in luminescent power efficiency over previous QD-OLEDs. They are more efficient and achieve even higher color saturation.
Quantum-dot LEDs, particularly those that provide the hard-to-reach blue end of the spectrum, appear to be key to opening any number of exciting technological advances in the fields of full-color, flat-panel displays; ultrahigh-density optical memories and data storage; backlighting; and chemical and biological sensing."Highly efficient, low-cost quantum dot-based lighting would represent a revolution in lighting technology through nanoscience."
Thus hybridising an inorganic nanocrystal and a quantum dot lead to a quantum dot-organic light-emitting device (QD-OLED) a new kind of optoelectronic device that could lead to new types of flat panel displays to supersede liquid crystal displays in everything from mobile devices to TV sets.
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