White LED Formed From A Bulk Material

Energy-efficient light-emitting diodes that produce white light have potential as a next-generation technology for general lighting applications. But current methods to make white LEDs require that they be built up from multiple components. For example, white LEDs can be made by combining red, blue, and green LEDs or by coating blue or near-ultraviolet LEDs with a phosphor material. Wooseok Ki and Jing Li at Rutgers University now report the first bulk semiconductor material that directly generates white light and potentially could be used to make single-component white LEDs (J. Am. Chem. Soc., DOI: 10.1021/ja801601y). The researchers designed a crystalline hybrid material composed of cadmium sulfide double layers bonded by alkyl amine groups. They initially tested the material's light-emitting properties by coating it on a commercially available blue LED; the structure emits white light. Ki and Li then discovered that doping the CdS layers with manganese ions enhances the illumination. The structure of the material and thus its light-emitting properties can be tuned by swapping out amine groups and by changing the thickness of the semiconductor layer, the researchers note.