Number 131 (Story #3), June 3, 1993 by Phillip F. Schewe and Ben Stein LUMINESCENCE IN POROUS SILICON is probably due to quantum-confinement effects. Although silicon does not readily emit light---certainly a drawback when it comes to optoelectronic applications---several years ago scientists noticed that silicon that had been bathed in acid, forming a sort of mangrove swamp of silicon filaments, did emit light, even into the visible range. Several explanations of this phenomenon, including the idea that the light is emitted by a residue (siloxene) left on the silicon surface, now seem to be ruled out by new experiments conducted by a Western Ontario-Wisconsin-Argonne-NRC (Ottawa) collaboration. The observed dependence of the luminescence wavelengths on porosity supports the notion that the narrowness of the filaments (some only a few nm wide) changes the band structure of silicon enough to permit light emission. (T.K. Sham et al., Nature, 27 May 1993.)