Abstract This study aims to learn more about the structure of densified silica with focus on the metamict-like silica phase (density = 2.26 g/cm 3 ) by examining the formation of E’ point defects and interstitial molecular oxygen O 2 by 2.5 MeV electron irradiation. High-dose (11 GGy) irradiation creates a metamict-like phase and a large amount of interstitial O 2 , which is destroyed upon subsequent additional lower-dose electron irradiation. The O 2 cathodoluminescence (CL) data indicate that the formation of O 2 from peroxy linkages Si–O–O–Si in silica network is strongly dependent on the intertetrahedral void sizes. The position and shape of the O 2 emission line support the idea that the configuration of these voids in metamict phase is close to that of non-densified silica. Moreover, data support the strong correlation between the formation of 3-membered rings of Si–O bonds and E’-centers when silica density increases from 2.20 to 2.26 g/cm 3 .