Light-emitting diodes (LEDs) that produce white light can be made by coating a blue LED with phosphor or by mixing differently colored LEDs, which requires electronic circuits to control the blending of the colors. Phosphor-based LEDs are less efficient and degrade faster than other LEDs.
Zhiyuan Xie, Lixiang Wang, and co-workers, Chinese Academy of Sciences, have developed a star-shaped polymer that could be used in white LEDs. They incorporate six polyfluorene arms around a donor-acceptor type core. The simultaneous blue emission from the arms and orange emission from the core resulted in white electroluminescence with the highest efficiency reported for a single-polymer white LED. Core aggregation, and subsequent quenching, was prevented by the branched arms which makes the new polymers more effective than previous linear and star-shaped single-polymers.
Polymer-based white LEDs could overcome the efficiency problems seen with other LEDs and lead to their use in flat-panel displays or as low energy light sources.
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