August 19, 2015

New technology can expand LED lighting, cutting energy use and greenhouse gas emissions

An LED coated with a yellow “phosphor” is shown turned off (left) and then turned on (right).
This “green” LED is inexpensive and provides warm white light. Credit: Zhichao Hu, Ph.D.

(August 19, 2015)  Highly efficient, light-emitting diodes (LEDs) could slash the world’s electricity consumption. They are already sold in stores, but more widespread adoption of the technology has been hindered by high costs due to limited availability of raw materials and difficulties in achieving acceptable light quality. But researchers will report today that they have overcome these obstacles and have developed a less expensive, more sustainable white LED.

The scientists will discuss their research at the 250th National Meeting & Exposition of the American Chemical Society (ACS). ACS is the world’s largest scientific society. The national meeting, which takes place here through Thursday, features more than 9,000 presentations on a wide range of science topics.

“If more people in the U.S. used LEDs in their homes and businesses, the country’s electricity consumption could be cut in half,” says Zhichao Hu, Ph.D., a member of the Rutgers University team that performed the research under the direction of Jing Li, Ph.D. At that time, he was a graduate student. He is now a postdoc at Rutgers and is studying the recovery of rare-earth elements there. Zhichao adds that studies show substituting one LED light for a common incandescent light bulb in every American household could save the nation $700 million annually in energy costs.

To achieve the common, soft white light that consumers expect, current LED technologies typically use a single semiconductor chip to produce light, usually blue, and then rely on a yellow-emitting “phosphor” coating to shift the color to white. That’s because LEDs do not emit a white light. The phosphor is made from materials, such as cerium-doped yttrium aluminum garnet, that are composed of rare-earth elements. These elements are expensive and in limited supply, since they are primarily available only from mining operations outside the U.S. Additionally, the light output of these phosphors tends to be harsh, “cold” colors.

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