We have investigated the formation of silicon nanocrystals (Si-nc) ex situ of the silicon dioxide host matrix as well as their structural and optical properties. Two different methods were used: Si-nc prepared by electrochemical etching as reference and Si-nc fabricated by ball milling. We show that both methods are able to prepare Si-nc with quantum confinement size (< 10 nm). The Si-nc fabrication ex situ of host matrix allows investigating additional properties in colloidal ethanol dispersion by light scattering. The identification of Si-nc in the ethanol-based colloids has been performed by Malvern autosizer experiments. We show the clustering effect of Si-nc and as well as declustering step by adding ammonia to ethanol-based colloids. Reached Si-nc sizes from light scattering experiment corresponds to that evaluated by other independent techniques. Furthermore, we have prepared spin on glass-based self-supporting samples with high Si-nc concentration layers which allowed PL analysis. In all cases visible photoluminescence at room temperature was detected. However, for Si-nc prepared by ball milling a weak PL was detected, which likely originates rather from surface states then quantum confinement size effect. (c) 2004 Elsevier B.V. All rights reserved.