A so far unique technique for a size-controlled synthesis of Silicon nanocrystals is introduced in this thesis. The synthesis technique is based on the phase separation of nanometer thick SiOx layers arranged in an SiOx/SiO2 superlattice structure. By this way, both a control of the nanocrystal size by the SiOx layer thickness, and over the inter-crystal distance by the stoichiometry x (within the layers) is possible. This independent control of crystal size and distance makes a separation of excitonic confinement and migration effects possible. A characterization of these effects was carried out by temperature- and time-dependent photoluminescence spectroscopy. The appearance of the momentum-conserving silicon phonons within the resonant photoluminescence signal played a major role in the clarification of the origin of the luminescence signal. Additionally, the energy transfer from excitonic states in the silicon nanocrystals to Er3+ ions, which were subsequently introduced by ion implantation, was investigated. The resonant character of this transfer process has been proven and transfer efficiencies up to 100% were measured. These very high transfer efficiencies have their origins in the high densities of quasi monodisperse nanocrystals with a band gap energy adjustable to the higher absorbing states of the Er3+ ions. Consequently, it could be shown that by the independent size and distance control introduced in this synthesis technique a detailed characterization of basic physical problems is possible and a basic requirement for the application of this material system for optical emitter and amplifiers or nonvolatile memories is fulfilled.