By Greg Lavine
The Salt Lake Tribune

In the shadow of California's energy crisis, University of Utah physicists have some bright ideas on how to make tomorrowÕs light sources more energy efficient. Anyone who ever changed a light bulb after it was burning knows how hot it can become. Most of the electricity flowing through the bulb goes toward heat, not illumination. Valy Vardeny, chairman of the U.'s physics department, is investigating how to make a better light bulbÑusing what may be the next generation of bulbs, light-emitting diodes, or LED's. An article in today's issue of the journal Nature discusses a test Vardeny helped devise to evaluate materials used to make LED's. VardenyÕs team examined the light-producing abilities of 10 materials, including polymers that conduct electricity and oligomers. "People think that maybe light-emitting diodes will be the lamp of the future," Vardeny said. LED's already are popping up in traffic signals, computers, stereo systems and vehicle brake lights. Traditional bulbs are changed about every 1,000 hours; while LEDÕs could one day pump out light for up to 100,000 hours, Vardeny said. Today, 30 percent of all electricity goes toward lighting, he said. More efficient bulbs would need less energy to produce light. Conventional LED's, which have been around for about 35 years, usually are made with a gallium base. Scientists have long held that, at best, 25 percent of the electricity through these LEDÕs could be put toward making light, Vardeny said. The remaining 75 percent comes off as heat. In 1990, British researchers used organic materials to create the first so-called plastic LED's. Originally, researchers assumed that these LED's would also max out at a 25 percent efficiency rating. Vardeny said he and some colleagues, including U. post-doctoral physicist Markus Wohlgenannt, decided to challenge that notion. An earlier study indicated that at room temperature, some plastic LED's were using more than a quarter of their energy to produce light. Some researchers, including Vardeny, were at first skeptical about those results. Materials were placed in an environment cooled with liquid helium to 4 degrees Celsius above absolute zero. A laser beam was fired at each material to see how much of the energy would come out as light, Vardeny said. Wohlgenannt said that each material tested contained electrons, which have negative charges, and Òholes,Ó which have positive charges. The laser aimed at the material excites the electrons and Òholes,Ó setting them into motion. Light is produced when an electron pairs up with a "hole" under certain circumstances. Physical laws maintain that at best, one out of four pairs create light. "How can we fool this quantum mechanics law?" he said his group asked. Vardeny and his colleagues decided to add microwaves to their experimental set-up to change how the electrons and ÒholesÓ spin. If the spins on the electrons and "holes" do not match up, the pairs will not produce light. The microwaves altering the spins appear to create more proper light-producing pairs. If more than 25 percent of electron-"hole" pairings are properly aligned, less energy would be needed to produce light. Vardeny's data found efficiencies of up to 63 percent. Wohlgenannt said, "It seems, in principle, there is no upper limit." Microwaves may not be the only way to impact the spin on electrons and "holes." Vardeny said he is working on patent for a process to put impurities into plastic LEDÕs that will affect the spin of particles. Other authors of the nature study included Sumit Mazumdar, with the University of Arizona, in Tucson, as well as S. Ramashesha and Kunj Tandon, of the Indian Institute of Science, in Bangalore, India. Originally published January 25, 2001, in The Salt Lake Tribune.