Now that several research groups around the world have confirmed the provocative discovery that ultra-fine silicon wires and particles glow when stimulated with ultraviolet light, people are dreaming out loud of radically faster communication devices based in part upon silicon's special luminescent properties. But researchers are still struggling to explain why silicon emits light. Work by UC Davis researchers Subhash H. Risbud, director of the Materials Research Center and mechanical engineering professor, and Li-chi Liu, his doctoral student, supports the prevailing theory that assumes the light-emitting properties of silicon particles are directly related to their tiny size. Risbud and Liu recently created three-dimensional silicon dots sealed in glass. Silicon may gain its ability to glow when the particles become so small that the electrons are forced into different and discrete energy levels compared to the normal energy band the electrons occupy in bulk silicon semiconductor wafers; the size of the silicon particle dictates the wavelength of light emitted. This principle is called "quantum confinement." Risbud and other researchers foresee a time when optical devices based upon this principle will one day communicate signals along a specific light wavelength (or color) in much the same way television broadcasts occur at certain frequencies. At the recent Materials Research Society meeting in San Francisco this spring, however, a German researcher proposed that the glowing silicon phenomenon was better explained by a chemical alteration of the silicon, not by the size of the tiny silicon structures. In late July, Risbud will join a host of international researchers for another round of vigorous debate about new experimental results and the competing theories at a special workshop on light-emitting silicon to be held in Germany.