Silicon Nanoparticles and Interstellar Extinction

To examine a recently proposed hypothesis that silicon nanoparticles are the source of extended red emission (ERE) in the interstellar medium, we performed a detailed modeling of the mean Galactic extinction in the presence of silicon nanoparticles. For this goal, we used the appropriate optical constants of nano-sized Si, which are essentially different from those of bulk Si because of quantum confinement. It was found that a dust mixture of silicon nanoparticles, bare graphite grains, silicate core-organic refractory mantle grains, and three-layer silicate-water ice-organic refractory grains works well in explaining the extinction and, in addition, results in the acceptable fractions of UV/visible photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions barely agree with the fraction of UV/visible photons needed to excite the observed ERE, we conclude that the intrinsic photon conversion efficiency of the photoluminescence by silicon nanoparticles must be near 100%, if they are the source of the ERE.