We present results on the photoluminescence ͑PL͒ properties of silicon nanocrystals as a function of their size. The nanocrystals are synthesized by laser pyrolysis of silane in a gas flow reactor and deposited at low energy on a substrate after a mechanical velocity and size selection. Both the photoluminescence spectroscopy and yield have been studied as well as the effect of aging of the samples in air. The measurements show that the PL of the silicon nanocrystallites follows the quantum confinement model very closely. The apparent PL yields are rather high ͑up to 18%͒. From evaluation of the size distribution obtained by atomic force microscopy it is concluded that the intrinsic PL yield of the nanocrystals can reach almost 100%. These results enabled us to develop a simple theoretical model to describe the PL of silicon nanocrystals. This model can also explain the changes of PL with aging of the sample, just by invoking a decrease of the size of the crystalline core as a result of oxidation.

In this article, we show how the well-known one-phonon confinement model can be improved to determine the diameter of silicon nanocrystalline spheres from the optical phonon wave-number shift, even using a physical-meaning weighting function. We show that the fundamental parameter is the knowledge of the phonon dispersion. The accuracy of our approach is supported by experimental data obtained by selective UV Raman scattering on nanocrystalline silicon thin films produced by size-selected silicon cluster beam deposition.