Computational models are being used to identify combinations of materials that could help reduce the costs of manufacturing white LEDs. Experiments by Rutgers University researchers suggest materials and processes for phosphor-converted white LEDs (PC-WLEDs) that could be up to 90 percent cheaper than current methods that rely on rare-earth elements. The team created a PC-WLED by immobilizing a preselected molecular chromophore into a rigid coordination framework. This shifts the chromophore's emissions further into the yellow region and enables a quantum yield similar to that of a commercially available phosphor doped with the rare-earth element cerium (YAG:Ce3+). An LED coated with a yellow phosphor is shown turned off (top) and on (bottom). This "green" LED is inexpensive and provides warm white light. Courtesy of Zhichao Hu. "One of challenges we had to overcome was to figure out the right conditions to synthesize the compound," said Rutgers University postdoctoral associate Zhichao Hu. "Like cooking, the synthesis requires a recipe. It's often not the case that one can simply mix the starting materials together and get the desired product. We optimized the reaction conditions — temperature and the addition of a solvent — and developed an easy procedure to make the compound with high yield." To achieve the soft white light that consumers expect, LEDs typically use a single semiconductor chip to produce blue light and a yellow-emitting phosphor coating. Materials like cerium used in these coatings are expensive and in limited supply because they are primarily available from mining operations outside the U.S. Led by professor Jing Li, the Rutgers team develops hybrid phosphor-based technologies that are more sustainable, efficient and lower in cost. They combine common metals with organic luminescent molecules to produce phosphors that emit a controllable white light from LEDs. By varying the metal and organic components, the researchers can systematically tune the color of the phosphors to regions of the visible light spectrum that are most acceptable to the human eye. Because many material combinations are possible, the researchers use a computational approach to sort through the possibilities and predict what colors the various combinations will emit. They then test the best combinations experimentally. The research was presented at the 250th National Meeting & Exposition of the American Chemical Society in Boston. Funding came from the National Science Foundation.