  The results of XPS core-level and valence band measurements,
photoluminescence spectra of a-SiO2 implanted by Zn-ions (E=30 keV, D=1*1017
cm^-2) and Density Functional Theory calculations of electronic structure as
well as formation energies of structural defects in silica glass induced by
Zn-ion implantation are presented. Both theory and experiment show that it is
energetically more favorable for implanted zinc ions to occupy the interstitial
positions instead of cation substitution. As a result, the Zn-ions embedded to
interstitials, form chemical bonds with the surrounding oxygen atoms, formation
ZnO-like nanoparticles and oxygen-deficient SiOx matrix. The subsequent thermal
annealing at 900 0C (1 hr) strongly reduces the amount of ZnO nanoparticles and
induces the formation of {\alpha}-Zn2SiO4 phase which markedly enhances the
green emission.
