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Thursday, 31 October 2013 12:34

Materials Day: Performance metrics

From Edison’s incandescent bulb to current light emitting diodes, the pace of change in lighting has sped up. “The pace at which LEDs are being adopted in the marketplace is unprecedented, something we’ve never seen before,” said Dr. Vanita Mani, Technology Leader for Energy Storage and Conversion Materials at GE Global Research.

vanita mani
 VANITA MANI

Mani spoke at at the Materials Day Symposium, hosted by the Materials Processing Center Oct. 23, 2013. The daylong symposium was held in Little Kresge Auditorium on the MIT campus. Noting that people depended on controlling fire for light until the mid 1800s when incandescent light bulbs became commercially available, Mani said,  “We have solutions, we have multiple choices. Our fire control lasted for a quarter of a million of years, incandescent 130 years, fluorescent light bulbs 70 years. LEDs, who knows, a couple of decades? We don’t know, but the point is the speed at which things are required to be invented is unprecedented. We have to provide solutions at a pace and invent at a pace that we have not done before.”

LEDs are already more efficient than CFLs, she noted. “Efficiency and performance metrics are good but not sufficient; you’ve got to figure out how to make things practical.” Developing a new material has to consider three pillars simultaneously, performance, life and cost, according to Mani.

When a spike in rare earth element costs spurred GE’s core shell phosphor research, Mani’s group developed a process for creating a green phosphor for fluorescent lights. “For this particular case, (we) have an inert core and just the very surface has the active rare earth oxide. It turns out that through lab scale testing, this core shell phosphor is just as good as having the entire phosphor made out of doped material. It has the same quantum efficiency, with potentially the same reliability and with a lower material cost. But the technology is still in development because “manufacturing of these phosphors has to be scaled up big time. We have to figure out how to scale up efficiently to make the cost-benefit worthwhile. This is a case study of how some times the game changer is not about performance, the game changer is about reducing costs and maybe even keeping parity in reliability,” she said.

Mani’s group also developed a process for adding potassium fluorosilicate (PFS) doped with manganese as a red line emitter for LED lighting. “We saw some phenomenal results, excellent color, which we were going after, and also very, high efficiency, 140 lumens per watt. So fantastic.”

“We also came up with treatment of the phosphor so you can remove some of the surface manganese, which allows the phosphor to handle higher temperatures and higher humidity. It improved the quantum efficiency, and we improved the (high temperature, high humidity) degradation by a factor of seven. This is ongoing research. We’re working again on simultaneously figuring out performance (lumens per watt), color, reliability and cost,” she said.

“It’s not always that the biggest coolest challenges are based on performance parameters,” Mani suggested. “I’d love to see the day where a Ph.D. thesis is entitled, “Parity in Performance but 10-X improvement in reliability and 10-X improvement in cost.”

Related Materials Day articles

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Materials Day: Phosphorescent OLEDs

Materials Day: Advances in materials driving new technologies   

Massachusetts Institute of Technology
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