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.