Though this consumption represents a large drain on resources, it also presents a tremendous opportunity for savings. Improving the efficiency of commercially available light bulbs -- even a little -- could translate into dramatically lower energy usage if implemented widely.
In the latest issue of Journal of Applied Physics, published by the American Institute of Physics (AIP), a group of scientists at the Chinese Academy of Sciences is reporting an important step towards that goal with their development of a new type of light emitting diode (LED) made from inexpensive, plastic like organic materials. Designed with a simplified "tandem" structure, it can produce twice as much light as a normal LED -- including the white light desired for home and office lighting.
"This work is important because it is the realization of rather high efficiency white emission by a tandem structure," says Dongge Ma (firstname.lastname@example.org), who led the research with his colleagues at the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences.
Found in everything from brake lights to computer displays, LEDs are more environmentally friendly and much more efficient than other types of light bulbs. Incandescent bulbs produce light by sending electricity through a thin metal filament that glows red hot. Only about five percent of the energy is turned into light, however. The rest is wasted as heat. Compact fluorescent bulbs, which send electricity through a gas inside a tube, tend to do much better. They typically turn 20 percent or more of the electricity pumped through them into light. But compact fluorescents also contain small amounts of mercury vapor, an environmental toxin.
LEDs on the other hand, are made from thin wafers of material flanked by electrodes. When an electric current is sent through the wafers, it liberates electrons from the atoms therein, leaving behind vacancies or "holes." When some of the wandering electrons and holes recombine, they create a parcel of light, or photon. These photons emerge from the side of the wafer as visible light. This turns 20 to 50 percent, or even more, of the input energy into light. LEDs also concentrate a lot of light in a small space.
Producing LEDs that can compete with traditional light bulbs for cost and efficiency is one thing. Making LEDs that consumers want to use to light their homes is quite another. One of the main barriers to the widespread use of LED lights is the light itself. LEDs can easily be manufactured to produce light of a single color -- like red -- with applications such as traffic lights and auto brake lights. Indoor lighting though, requires "natural" white light. This quality is measured by the color-rendering index (CRI), which assigns a value based on the light source's ability to reproduce the true color of the object being lit. For reading light, a CRI value of 70 or more is optimal. LEDs can produce white light by combining a mixture of blue, green, and red light, or by sending colored light through a filter or a thin layer of phosphors -- chemicals that glow with several colors when excited. However, these solutions increase costs. To reach a larger market, scientists would like to make inexpensive LEDs that can produce white light on their own.
The authors of this paper report important advances towards this goal. First, they built LEDs from organic, carbon-based materials, like plastic, rather than from more expensive semiconducting materials such as gallium, which also require more complicated manufacturing processes. Second, they demonstrated, for the first time, an organic white-light LED operating within only a single active layer, rather than several sophisticated layers. Moreover, by putting two of these single-layer LEDs together in a tandem unit, even higher efficiency is achieved. The authors report that their LED was able to achieve a CRI rating of nearly 70 -- almost good enough to read by. Progress in this area promises further reduction in the price of organic LEDs.
The work of Dongge Ma and colleagues was funded by the Hundreds Talents program of Chinese Academy of Sciences, the National Science Fund for Distinguished Young Scholars of China, the Foundation of Jilin Research Council, Foundation of Changchun Research Council, Science Fund for Creative Research Groups of NSFC, and the Ministry of Science and Technology of China.
The article "A high-performance tandem white organic LED combining highly effective white units and their interconnection layer" by Qi Wang et al. was published online on April 6, 2009 [J. Appl. Phys. 105, 076101 (2009)]. The article is available at http://link.aip.org/link/?JAPIAU/105/076101/1. Journalists can obtain a free copy of the article by emailing email@example.com.
ABOUT THE JOURNAL
Journal of Applied Physics, published by the American Institute of Physics (AIP), is an archival journal presenting significant new results in applied physics. The journal publishes original and review articles that emphasize understanding of the physics underlying modern technology. See: http://jap.aip.org/.
The American Institute of Physics (AIP) is a not-for-profit membership corporation chartered in 1931 for the purpose of advancement and diffusion of the knowledge of physics and its application to human welfare. An umbrella organization for 10 Member Societies, AIP represents over 134,000 scientists, engineers and educators and is one of the world's largest publishers of physics journals. A total-solution provider of publishing services, AIP also publishes 12 journals of its own (many of which have the highest impact factors in their category), two magazines, and the AIP Conference Proceedings series. Its online publishing platform Scitation (registered trademark) hosts more than 1,000,000 articles from more than 175 scholarly journals, as well as conference proceedings, and other publications of 25 learned society publishers.
Jason Bardi | EurekAlert!
Further reports about: > AIP > Applied and Environmental Microbiology > CRI > LED > Light Emitting Diode > Photon > Physic > Science TV > color-rendering index > computer displays > environmental toxin > fluorescent bulbs > light bulbs > mercury vapor > organic material > plastic like organic materials > tandem structure > white light
SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University
Molecule flash mob
19.01.2017 | Technische Universität Wien
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences