Synthesis of Ge nanocrystals in SiO2films is carried out by precipitation from a supersaturated solid solution of Ge in SiO2made by Ge ion implantation. The films exhibit strong room‐temperature visible photoluminescence. The measured photoluminescence peak energy and lifetimes show poor correlations with nanocrystal size compared to calculations involving radiative recombination of quantum‐confined excitons in Ge quantum dots. In addition, the photoluminescence spectra and lifetime measurements show only a weak temperature dependence. These observations strongly suggest that the observed visible luminescence in our samples is not due to the radiative recombination of quantum‐confined excitons in Ge nanocrystals. Instead, observations of similar luminescence in Xe+‐implanted samples and reversible PL quenching by hydrogen or deuterium suggest that radiative defect centers in the SiO2matrix are responsible for the observed luminescence. ©1996 American Institute of Physics.