Volume 18, No. 1 - Spring 2009
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The Future of Lighting

Scientists Create

White

Light

That is Eco-friendly, Affordable

By Sarah Bahari

Mohammad Omary with viles of vivid luminescent liquids.

Mohammad Omary directs a UNT team that is pioneering research in the field of organic light-emitting diodes, an emerging technology that scientists say could revolutionize lighting.

Photo by: Mike Woodruff

In a quiet laboratory tucked into the third floor of the chemistry building, a dozen or so vials of colorful liquid clutter a table.

Mohammad Omary, an associate professor of chemistry at the University of North Texas, gestures to the trays of test tubes.

"This," Omary says, "is where we do the dirty work."

Here, UNT researchers from chemistry and materials science and engineering are rethinking a 130-year-old standby of modern technology — the light bulb. Their goal: design new lighting sources that are eco-friendly yet affordable, long-lasting and safe, simple in structure yet brilliant white in color.

Led by Omary, the team of faculty and student researchers is pioneering innovative research in the field of organic light-emitting diodes, or OLEDs, an emerging technology that scientists say could revolutionize lighting.

OLEDs on the Horizon

Often made on paper-thin flexible plastic bases, OLEDs could be a reality in homes and businesses across the country within the next decade.

The slim structure could lend itself to a variety of applications. Bedrooms could be wallpapered in light-emitting sheets. Football quarterbacks could receive play calls on tiny screens sewn into their uniforms. Television and computer screens undoubtedly will be flatter than ever before.

The technology's importance is clear. Lighting consumes nearly one-quarter of all electricity produced in the United States. OLEDs require far less energy to produce and operate than incandescent lights, which would lead to billions of dollars in savings and enormous reduction in carbon emissions.

Obstacles do remain, however. UNT scientists are attempting to determine which materials best create the perfect white light and how to improve the lifetime of devices.

With nearly $2.3 million from the U.S. Department of Energy, Omary and his fellow researchers are addressing — and solving — those problems.

"This is a very different, very new way of thinking about lighting," says Oussama Elbjeirami, a post-doctoral student at UNT who works with Omary. "The future of lighting is changing."

Energy Efficiency

Light bulbs, long the staple source for light in most homes, are inexpensive and relatively long-lasting. They work by forcing electricity through a metal filament into a vacuum.

Drug delivery and solar energy

Organic light-emitting diodes are not the only application for luminescent materials. Mohammad Omary received a $527,000 grant from the National Science Foundation to explore how light particles interact with the molecules designed and made by his research group. Understanding that interaction will help identify ways the materials can be beneficial.

For example, Omary's lab is working with several other professors to create water-soluble metal nanoparticles that could travel through the body, find cancerous cells and attack them when hit by a beam of light.

"This is very difficult," Omary says. "You want to make certain the particles will know only to attack the cancerous cells and leave the healthy ones alone."

Luminescent materials also are finding applications in solar energy. With a $210,000 grant from the Welch Foundation, Omary is working on chemicals that would absorb more solar energy and convert that light into electricity. He says his research group and collaborators already have made great strides in the field.

"This would be a tremendous scientific breakthrough," Omary says. "It would save, literally, billions of dollars in electricity costs."

But consider this, Omary says. An incandescent bulb gives off 10 percent light; the rest of its energy is useless heat.

"The efficiency is really bad," Omary says. "Ninety percent of its energy is wasted."

Beginning in 2012, the United States plans to phase out incandescent lamps.

Compact fluorescent lights, or CFLs, have been touted as a way to reduce energy and cut greenhouse gases. Fluorescent lamps use only about a quarter of the power of incandescent lamps and last 10 times longer, according to the U.S. Department of Energy.

But CFLs contain a small amount of mercury in the glass tubing, which makes them potentially harmful to dispose of and requires a careful cleanup if one breaks.

Organic light-emitting diodes could be the solution, UNT scientists say.

Developed by Kodak more than 30 years ago, the technology has gained traction in recent years because of the relatively low amount of energy required to produce and power it. An OLED is essentially a wafer-thin carbon-based film sandwiched between two conductors. When electrical voltage is applied, the organic material glows.

The U.S. Department of Energy has invested about $100 million during the last five to six years in solid-state lighting, light that is emitted from a solid object rather than from a vacuum or gas tube. The DOE hopes to have OLEDs ready for residential use by 2015.

"Organic light-emitting diodes are one of the most promising lighting technologies envisioned by the DOE to replace today's less efficient light sources," says Joel Chaddock, a project manager at the DOE.

Synthesizing and Engineering

To meet the goal, Omary and fellow researchers synthesize new metal-organic materials by mixing organic materials (containing carbon, hydrogen and nitrogen) with precursors of metals like gold, platinum or copper. The solid materials are capable of producing bright phosphorescence, or long-lived light emission.

Omary's group then sends those materials to Nigel Shepherd, an assistant professor of materials science and engineering at UNT, whose group is in charge of the design and construction of the light-emitting devices.

Nigel Shepherd and Minghang Li

Nigel Shepherd's group in materials science and engineering, including doctoral candidate Minghang Li, right, designs the new light-emitting devices.

Photo by: Mike Woodruff

Shepherd's group uses equipment at UNT's Center for Advanced Research and Technology — a $15 million federally funded facility with high-powered microscopes and other materials characterization tools — for some of the production work.

Specifically, they use a custom-designed, computer-controlled thermal evaporator, in which the organic molecules are gently heated and condensed into thin films. The films then fuse to a base, which is often made of plastic.

While the UNT team is focused primarily on white lights — those used for standard room lighting — the technology has applications in display lighting, such as television and computer screens, cell phones and alarm clocks. The biggest advantage of OLEDs is that, unlike liquid crystal display (LCD) televisions, they do not require a backlight to function. Removing that backlight would allow manufacturers to make televisions thinner than ever before.

Sony already has introduced a super-thin, high-priced television based on the technology that drew rave reviews for its crisp picture.

UNT is only halfway finished with the three-year DOE contract, but the research group already has surpassed its goals for the first two years and now is working on third-year objectives.

"Our team, with the hard work of the students, has made a great deal of progress. There are, of course, still many technical problems we're working through," Shepherd says. "But OLEDs show a lot of promise to replace incandescent and fluorescent lamps."

One White Light

The most significant questions have been how to achieve white light and extend the lifetime so OLEDs are competitive with fluorescent lamps. Most OLEDs combine red, green and blue emitters to create white light. That's problematic, however, because emitters age at different rates, Omary says. If the blue emitter fails first, which usually occurs, the lamp may give off a yellow light.

UNT's approach? Simplify the structure by creating one material that can produce white light on its own. This has been a major challenge in OLED technology.

The latest breakthrough by UNT demonstrated its potential, with a material made by Joyce Chen and Chi Yang in Omary's group, and devices made by Minghang Li and Ming-Te Lin in Shepherd's group. Work to improve the efficiency and color of the material continues, but Chaddock, with the DOE, says UNT's data suggest promise for a new material.

Chen, a graduate student in chemistry, says the research has been fascinating because they are addressing a real and serious problem.

"Often, chemists just focus on the chemistry and nothing else," Chen says. "But we're looking at real-life applications and ways these materials can save energy."

That, Omary says, is the end goal.

"We know we are in a global energy crisis," Omary says. "Getting rid of old light bulbs and adopting alternative sources of light is one of the most significant ways we can reduce our energy consumption."

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