Si+ implanted silica glass has been investigated by IR reflectance and
VIS-NIR transmittance spectroscopy. Spectra can be simulated with the
complex dielectric functions of SiO2 glass and amorphous silicon by m
eans of a simple effective medium theory and a multilayer model. It ca
n be derived from the evaluation of the spectra that modification of t
he glass structure is the preferred process for ion doses < 10(17) Si/cm(2). Higher ion doses lead to a formation of amorphous silicon prec
ipitates. Simulation of the spectra allows determination of that part
of implanted Si+ ions which is accumulated as elementary (metallic) si
licon in the host substrate. Furthermore the results indicate that qua
ntum confinement effects, which are known in the case of silicon nanoc
rystals, also occur in amorphous silicon colloids.