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Hydrogen passivation of Si nanocrystals is shown to result in a redshift of photoluminescence (PL) emission spectra, as well as the more commonly observed intensity increase. The shift is reversible, with spectra returning to their unpassivated values as hydrogen is removed from the samples by annealing. The magnitude of the redshift also depends on the implant fluence employed for nanocrystal synthesis, increasing with increasing fluence or particle size. These data are shown to be consistent with a model in which larger crystallites are assumed to contain a greater number of nonradiative defects, i.e., the number of nonradiative defects is assumed to scale with the surface area or volume of a nanocrystal. Hydrogen passivation then results in a disproportionate increase in emission from larger crystallites, giving rise to an apparent redshift in the composite PL emission spectrum.

The effect of hydrogen passivation on the photoluminescence from Si nanocrystals prepared in SiO2 by ion implantation and annealing is examined as a function of nanocrystal size (implant fluence). Passivation is shown to produce a significant increase in emission intensities as well as a redshift of spectra, both of which increase with increasing fluence. These results are shown to be consistent with a model in which larger nanocrystals are assumed to contain more nonradiative defects (i.e., the defect concentration is assumed to be proportional to the nanocrystal surface area or volume). Since this results in a smaller fraction of larger nanocrystals contributing to the initial luminescence, emission spectra are initially blueshifted relative to that that might be expected from the physical nanocrystal size distribution. The contribution from larger crystallites is then disproportionately increased by passivation resulting in the observed redshift.

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Efficient transmission of light through a metal layer has become a key issue for a variety of applications including light-emitting diodes and solar cells. We report here on a novel strategy where localized and extended surface plasmons are combined to maximize the fluorescence transmission through a metallic film. We show that the dispersion of an artificial material formed by an array of metal nanoparticles coupled to a flat metal layer can be engineered to make the metal film, in a specific direction, 100% transmissive.