Materials Science

US and Korean researchers discover new phosphor material for white LEDs

Using computational tools and data mining, researchers have discovered a new type of phosphor material for white LEDs that is not only inexpensive but also easy to fabricate. A research team comprising collaborators from Chonnam National University in Korea and University of California San Diego used the new phosphor material to build prototype white LED light bulbs which displayed better color quality than many LEDs commercially available on the market today.

The team published the results of the new phosphor on 19th February 19 in the journal, Joule.1

Phosphors are substances that produce light. They are one of the main ingredients used for making white LEDs. However, the phosphors used in many commercially-available white LEDs are made of rare-earth elements, which are very costly, and some are also difficult to manufacture. Some also create LEDs with poor colour quality.

The researchers from the US and Korea created a new type of phosphor that circumvents these problems. The phosphor is called Sr2LiAlO4, or simply SLAO. It is mostly made of earth-abundant elements such as aluminum, oxygen, strontium, and lithium; it can be produced using industrial techniques, and it can produce LEDs that make colours that are more vivid and accurate.

The discovery of SLAO took only 3months, thanks to acomputational method developed by the US team, headed by Shyue Ping Ong, lead principal investigator of the study and a nanoengineering professor at the UC San Diego. This is a short time frame, compared with the decades of trial-and-error experiments it usually takes to find a novel material.

Ong’s research team first collected a list of elements that occur most often in known phosphor materials. S They then used a data mining algorithm to produce new phosphor candidates that contain all these four elements and carried out a set of first-principles calculations to estimate which would perform exceedingly well as a phosphor. Among the 918 candidates, SLAO was identified as the top material, predicted to be stable and show good  photoluminescence properties. The Korean team, headed by materials science professor Won Bin Im at Chonnam National University in Korea, improved the phosphor recipe for industrial manufacturing and developed prototypes of white LED using the new phosphor material.

The main limitation of phosphor is its less than ideal quantum efficiency (i.e. how efficiently it changes the incoming light to a different coloured light – of about 32%), but the team found that SLAO retains over 88% of its emission at typical operating temperatures. In the case of commercially-available LEDs, there is often a tradeoff with color quality, Ong noted. “But we want the best of both worlds. We have achieved excellent color quality. Now we are working on optimizing the material to improve quantum efficiency,” he said.

1 .Wang Z, Ha J, McKittrick J, Ong SP, Kim YJ, Im WB. Joules 2018;2:1-13. (DOI