An efficient white-light LED

(Light-emitting diode) has been designed and built with very stable, environmentally friendly nitride compounds. Compared to incandescent or fluorescent lighting, solid-state devices for general illumination hold much promise for reducing costs and energy use, but many technical challenges remain. (See Physics Today, December 2001, page 42) One scheme being explored is the phosphor-conversion approach, in which light from a short-wavelength LED excites luminescent materials that then emit at longer wavelengths; the combined emissions produce white light. A team of scientists led by Wolfgang Schnick (University of Munich) used europium to dope two new phosphors—of a type called nitridosilicates—that are chemically and thermally stable and emit red and green light when excited by a blue-light LED. The resulting white light is of excellent quality and renders the colors of illuminated objects more faithfully than does a fluorescent lamp. In addition, at 25 lumens per watt, the new device’s efficiency...