Engineers at the University of California San Diego have used computational algorithms and data mining to discover a new, less expensive and easy-to-make phosphor combination that can produce LEDs with a color rendering index of greater than 90. Phosphors are powdered materials that emit light and are commonly used in LEDs to convert blue or UV lighting into white light.
The process to devise phosphors used in LEDs has mostly gone through trial and error. While one firm, Intematix previously used computational methods to look at potential phosphors combinations for LEDs before testing them in the lab (Ref. press release), the new research is the first ever to look at compounds made up of oxygen, aluminum, lithium, and strontium.
Not all phosphors are the same. Some are less efficient at emitting and converting light from one part of the spectrum to emit light in other parts of the spectrum. And also the cost of producing such materials is a key consideration. And finally, the quality of light that they produce in terms of color rendering index varies depending upon the phosphor mixture.
The team utilized a systematic, broad computational approach devised in the lab of Shyue Ping Ong, a nanoengineering professor at the UC San Diego Jacobs School of Engineering and the study’s lead investigator. For the study, Ong’s team first gathered a list of the most frequently occurring elements in known phosphors. Surprisingly, they found no known phosphor materials containing a combination of strontium, lithium, aluminum and oxygen, four common phosphor elements. They looked at all the possible combinations of strontium, lithium, aluminum, and oxygen. Out of the 918 combinations of materials, Sr2LiAlO4 or simply SLAO was the top contender.
Scientists in the lab of Joanna McKittrick, a materials science professor at the Jacobs School of Engineering, figured out the recipe to make the new phosphor, and they proved and demonstrated the phosphor’s predicted light absorption and emission in lab tests.
Finally, a team led by materials science professor Won Bin Im at Chonnam National University in Korea optimized the phosphor recipe for industrial manufacturing and created white LED prototypes with the new phosphor and a UV emitter. They evaluated the quality of light from the LEDs using the Color Rendering Index (CRI), a scale that rates from 0 to 100 how accurate colors appear under a light source. While many commercial LEDs have CRIs of about 80, LEDs with the new phosphor resulted in CRI values greater than 90.
So, not only was the new material made mostly of abundant and somewhat inexpensive elements, but it was also easy to make.
Researchers published details about the new phosphor on Feb. 19 in the journal Joule.
Wang, Z.; Ha, J.; Kim, Y. H.; Im, W. B.; Mckittrick, J.; Ong, S. P., “Mining Unexplored Chemistries for Phosphors for High-Color-Quality White-Light-Emitting Diodes,” Joule, February 19, 2018. https://doi.org/10.1016/j.joule.2018.01.015