Breakthrough Makes LED Lighting Much More Efficient

In a breakthrough discovery, scientists at the University of California Santa Barbara have figured out how to make LEDs brighter and more efficient. So reports Phys.Org.

Scientists have been researching LED, or light-emitting diode lighting, for some time, given the benefits it provides over traditional incandescent or fluorescent lighting. LED technology is now used in televisions and street lights, for instance, because they last longer, give off less heat, use less energy and aren’t as damaging to the environment.

But to date, the creation of LED lighting has been done more by trial and error than by science, says Ram Seshadri, a professor in UC’s Solid State Lighting & Energy Center, where the breakthrough LED research took place. Seshadri says all major recent advances in solid-state lighting are based on gallium nitride LEDs, where phosphors are applied to an LED chip in such a way that photons from the blue gallium nitride LED can pass through the phosphor. The phosphor then converts and mixes the blue light into the green-yellow-orange range of light. When the green-yellow-orange light is combined just right with the blue light, the result is white light. But finding the right combination of phosphor materials requires finding crystal structures that act as hosts to activator ions, which convert the higher-energy blue light to lower-energy yellow/orange light. And until now, it’s been difficult to know which phosphors make good hosts and which do not. If the wrong phosphor is chosen, some of the photons are wasted as heat.

But waste isn’t the only problem. When LEDs are used for things like the front lights on vehicles, it’s essential that they are bright, and yet the brighter LEDs are made, the warmer they get, and at some point, that heat adversely impacts the phosphor’s properties.

Not many phosphor materials remain efficient at high temperatures, says Jakoah Brgoch, a postdoctoral associate researcher who was part of the breakthrough discovery.

“There is little understanding of how to choose the host structure for a given activator ion such that the phosphor is efficient, and such that the phosphor efficiency is retained at elevated temperatures,” he said.

But using calculations based on density functional theory — developed by UCSB professor and 1998 Nobel Laureate Walter Kohn – Seshadri, Brgoch and materials professor Steven DenBaars realized that the rigidity of the crystalline host structure is key to determining which phosphors are more efficient. That is, those with a more rigid structure make better hosts. But even better, they could use density functional theory to compute the indicators of structural rigidity. In that way, the phosphors could be screened before they are applied to an LED chip. So reports

DenBaars, who also is a professor of electrical and computer engineering, said the researchers want to achieve 90% efficiency, or 300 lumens per watt. That’s a drastic difference from ordinary incandescent bulbs, which are 5% efficient, and fluorescent lamps, which are about 20 efficient. The group has already achieved up to 60% efficiency in the laboratory, DenBaars said.

The breakthrough research, which will appear in The Journal of Physical Chemistry, has put solid-state lighting, and efforts to make it brighter and more efficient, on a fast track. Soon, incandescent and fluorescent bulbs, which are less efficient and require more energy to produce light, could become obsolete.

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