The fusion temperature (T&fgr;), the oxygen partial pressure (PO2) during melting and the quenching rate fromT&fgr;all influence the optical absorption in the 5.06‐eV (245‐nm) region. These observations are consistent with the assumption that the defect responsible for the optical absorption is an oxygen vacancy or complex of vacancies. The activation energy for the formation of the defect in GeO2glasses which is repsonsible for the optical absorption is 2.3 eV which is larger than the activation energy for oxygen diffusion (∼1 eV).