America’s future light source

http://news.ufl.edu/2011/08/31/quantum-dot-based-leds/

Manufacturing method paves way for commercially viable quantum dot-based LEDs

Filed under Engineering, Research, Technology on Wednesday, August 31, 2011.

GAINESVILLE, Fla. — University of Florida researchers may help resolve the public debate over America’s future light source of choice: Edison’s incandescent bulb or the more energy efficient compact fluorescent lamp.

It could be neither.

Instead, America’s future lighting needs may be supplied by a new breed of light emitting diode, or LED, that conjures light from the invisible world of quantum dots. According to an article in the current online issue of the journal Nature Photonics, moving a QD LED from the lab to market is a step closer to reality thanks to a new manufacturing process pioneered by two research teams in UF’s department of materials science and engineering.

“Our work paves the way to manufacture efficient and stable quantum dot-based LEDs with really low cost, which is very important if we want to see wide-spread commercial use of these LEDs in large-area, full-color flat-panel displays or as solid-state lighting sources to replace the existing incandescent and fluorescent lights,” said Jiangeng Xue, the research leader and an associate professor of materials science and engineering “Manufacturing costs will be significantly reduced for these solution-processed devices, compared to the conventional way of making semiconductor LED devices.”

A significant part of the research carried out by Xue’s team focused on improving existing organic LEDs. These semiconductors are multilayered structures made up of paper thin organic materials, such as polymer plastics, used to light up display systems in computer monitors, television screens, as well as smaller devices such as MP3 players, mobile phones, watches, and other handheld electronic devices. OLEDs are also becoming more popular with manufacturers because they use less power and generate crisper, brighter images than those produced by conventional LCDs (liquid crystal displays). Ultra-thin OLED panels are also used as replacements for traditional light bulbs and may be the next big thing in 3-D imaging.

Complementing Xue’s team is another headed by Paul Holloway, distinguished professor of materials science and engineering at UF, which delved into quantum dots, or QDs. These nano-particles are tiny crystals just a few nanometers (billionths of a meter) wide, comprised of a combination of sulfur, zinc, selenium and cadmium atoms. When excited by electricity, QDs emit an array of colored light. The individual colors vary depending on the size of the dots. Tuning, or “adjusting,” the colors is achieved by controlling the size of the QDs during the synthetic process.

By integrating the work of both teams, researchers created a high-performance hybrid LED, comprised of both organic and QD-based layers. Until recently, however, engineers at UF and elsewhere have been vexed by a manufacturing problem that hindered commercial development. An industrial process known as vacuum deposition is the common way to put the necessary organic molecules in place to carry electricity into the QDs. However, a different manufacturing process called spin-coating, is used to create a very thin layer of QDs. Having to use two separate processes slows down production and drives up manufacturing costs.

According to the Nature Photonics article, UF researchers overcame this obstacle with a patented device structure that allows for depositing all the particles and molecules needed onto the LED entirely with spin-coating. Such a device structure also yields significantly improved device efficiency and lifetime compared to previously reported QD-based LED devices.

Spin-coating may not be the final manufacturing solution, however.

“In terms of actual product manufacturing, there are many other high through-put, continuous “roll-to-roll” printing or coating processes that we could use to fabricate large area displays or lighting devices,” Xue said. “That will remain as a future research and development topic for the university and a start-up company, NanoPhotonica, that has licensed the technology and is in the midst of a technology development program to capitalize on the manufacturing breakthrough.”

Other co-authors of this article are Lei Qian and Ying Zheng, two postdoctoral fellows who worked with the professors on this research. The UF research teams received funding from the Army Research Office, the U.S. Department of Energy, and the Florida Energy Systems Consortium.

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Credits

לוח דירות להשכרה, למכירה, דרושים, יד שניה - הומלס

לוח דירות להשכרה, למכירה, דרושים, יד שניה - הומלס

Light on the subject

THE FEDERAL GOVERNMENT OF GERMANY....has imposed a complete ban on the use of cool-white fluorescent tubes. This on the basis that their continued use was seen as harmful to the state of the nations health, particularly the workforce. Therefore today in Germany on a Federal level it is illegal to install the same cool-white fluorescent tubes we in Australia use as standard!

AMERICANS WITH DISABILITIES ACT.

• The Act recommends the exclusive use of full-spectrum lighting in the workplace.

Employers are required to provide:

• Illumination as needed to prevent fatigue. 
• Full-spectrum total room lighting. 
• Glare control.

SOME LIGHT ON THE SUBJECT - RESEARCH

Citing American Optometrists Association figures, Dr. Sheedy noted that eye related complaints are the "number one" problem cited by computer users. Eye irritation nightmare:- Other problems becoming apparent include eye irritations produced by glare. Some experts warn that eyesight damage could become an OH&S nightmare in the 1990's. A related study found that more than 10% of workers complained of sore eyes every day. More than 50% suffered sore eyes at least once a week. (OHM issue No. 93)

Research during the last ten years shows that the physiological and psychological effects of artificial lighting are very significant and quantifiable. The amount of light is important, but the composition of quality of light is perhaps the most important factor, affecting health, temperament, and the ability to see clearly. Physiological studies have also conclusively shown that, under full spectrum lamps versus cool white lamps, humans have increased oxygen intake, reduced heart rate, increased ability to absorb vitamin D and calcium and improved muscle utilisation. (Hughes,1986) (Neer,1984)

Recent reports conclude, "The results support the conclusion that artificial lighting simulating natural light (full spectrum lamps) is perceived as significantly more pleasant, natural, bright and stimulating. Subjects felt more relaxed, less fatigued and as having greater eye comfort under the simulated natural light Additionally, they rated their work as being more distinct, easier and satisfying. " (Hughes. 1986)

Initial experiments by Aston and Bell chambers were confirmed by the extensive research of the Naval Submarine Research laboratory. The experiments and research concludes that fluorescent lamps with superior colour rendering result in a visual clarity that is 40% greater than typical cool white lamps.

In 1973, Dr. Ott used four windowless, first grade classrooms in Sarasota, Florida to test the effectiveness of full spectrum lighting. Two classrooms received installations of full-spectrum lights while two classrooms kept the standard cool-white fluorescent lights. The results: the level of behaviour improved considerably in the classes with the full-spectrum lights while the overall academic level of the children in those classes rose considerably.

The use of cool-white fluorescent lights has been legally banned in Germany at a Federal level, largely due to the work of Drs. Ott and Hollwich.

Full-spectrum lighting provides many benefits that are of immediate relevance to our Occupational Health and Safety considerations. Human resource interests are being prioritized in progressive companies and business. These physiological and psychological advantages, combined with sustained quality performance, represent the future in work place illumination. 10/34 Marlborough Rd., Ph./Fax. (03)9876 0799

HEATHMONT 3135 Mob. 0418 334 127
Research during the last ten years shows that the physiological and psychological effects of artificial lighting are very significant and quantifiable. The amount of light is important but the composition, of quality of light, is perhaps the most important factor, affecting health, temperament, and the ability to see clearly. Sunlight is the most critical element of virtually all forms of life. The full spectrum lamps provided by United Energy are the closest approximation of sunlight available in fluorescent lamps. The studies and reports summarized here explain why it is so important to use natural sunlight type lighting wherever possible. All chemical, mineral and vitamin substances taken into the body have unique wavelength absorption characteristics. Wavelength energy penetrates the skin and interacts directly at the molecular level with chemicals and minerals in the blood supply, aiding in the substance breakdown for assimilation into the body of the desirable substances and excretion of the undesirable. Full spectrum lamps and sunlight produce wavelengths that kill numerous bacteria, molds, yeasts and viruses.

A most obvious example of this is that sunlight and full spectrum fluorescent light are used to treat jaundice. The short wavelengths of natural light interact with serum bilirubin, converting it to a nontoxic substance. (McDonagh, 1980)

A study by the Council of Educational Facility Planners compared cool white to full spectrum fluorescent lamps in a controlled scientific test in classrooms. Students had a 2.5 times better attendance record in rooms with full spectrum lamps. That is they were sick much less frequently. (Graves, 1985) (Hathaway, 1980)

Physiological studies have also conclusively shown that, under full spectrum lamps versus cool white lamps, humans have increased oxygen intake, reduced heart rate, increased ability to absorb vitamin D and calcium and improved muscle utilization. (Hughes, 1986) (Neer, 1984)

Natural sunlight makes people feel better than artificial light does. The more natural the light the more comfort and better performance. Statistically significant differences are proven for subjects in rooms lit by cool white lamps versus full spectrum lamps. Subjects brought from outdoors into cool white rooms tended to become less lively or lethargic. The subjects exhibited no change when brought from outdoors into full spectrum rooms. Visual accuracy and alertness were measurably better in the full spectrum rooms versus the cool white rooms. (Maas, 1974)

Recent reports conclude, "The results support the conclusion that artificial lighting simulating natural light (full spectrum lamps) is perceived as significantly more pleasant, natural, bright and stimulating. Subjects felt more relaxed, less fatigued and as having greater eye comfort under the simulated natural light. Additionally, they rated their work as being more distinct, easier and satisfying." (Hughes, 1986)

Being able to see clearly is typically attributed to the amount of light, however, clear color rendering is at least as important. The most obvious example of this is white appearing as white and black as black, instead of light yellow and dark brown. Enhanced black and white contrast makes written material easier to read and makes objects appear brighter.

Initial experiments by Aston and Bellchambers were confirmed by extensive research by the Naval Submarine Research Laboratory. The experiments and research concludes that fluorescent lamps with superior color rendering result in a visual clarity that is 40% greater than light from typical cool white lamps. The reason for this is that the red/green contrasts contribute to distinguish borders and the blue/yellow make little or no contribution to the distinctness of borders. Cool white lamps are strong in the blue/yellow contrasts and weak in the red/green. Full spectrum lamps have an appropriate balance of spectral contrast. (Worthy, 1985)

FOR MORE INFORMATION:
1. Birren, F.; Light, "Color and Environment"; 1969.
2. Boyce, P.R.; "Human Factors in Lighting"; 1981.
3. Graves, B.; "Shedding Light on Learning"; American School and University; Volume 36; March 1985.
4. Hollowich, F.; "The Influence of Ocular Light Perception on Metabolism in Man and Animals"; Springer Verlag; 1980.
5. Hughes, P. , Ph.D. ; "The Use of Simulated Natural Light in the Design of the Earth Sheltered Environment"; Conference on Earth Sheltered Environment/University of Minnesota; 1986.
6. Mass, J.; "Effects of Spectral Differences in Illumination on Fatigue"; Journal of Applied Psychology, Volume 59; 1974.
7. Ott, J.; "Light Radiation and You"; 1982.
8. Tiller, D.; "Toward a Deeper Understanding of Psychological Aspects of Lighting"; Journal of IES; Summer, 1990.
9. Worthey; "An Analytical Visual Clarity Experiment"; Journal of IES, Fall 1985.
10. Wurtman, R.; "Biological Implications of Artificial Illumination"; IES National Technical Conference; September 1968.

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