Silicon Nanoparticles and Interstellar Extinction

To examine a recently proposed hypothesis that silicon nanoparticles are thesource of extended red emission (ERE) in the interstellar medium, we performeda detailed modeling of the mean Galactic extinction in the presence of siliconnanoparticles. For this goal we used the appropriate optical constants ofnanosized Si, essentially different from those of bulk Si due to quantumconfinement. It was found that a dust mixture of silicon nanoparticles, baregraphite grains, silicate core-organic refractory mantle grains and three-layersilicate-water ice-organic refractory grains works well in explaining theextinction and, in addition, results in the acceptable fractions of UV/visiblephotons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractionsbarely agree with the fraction of UV/visible photons needed to excite theobserved ERE, we conclude that the intrinsic photon conversion efficiency ofthe photoluminescence by silicon nanoparticles must be near 100%, if they arethe source of the ERE.