The effects of neutron ([inverted lazy s]300 K) and ion bombardment ([inverted lazy s]85 K), and subsequent isochronal annealing, on the near‐infrared transmittance of SixGe1-x alloys (x=0.24, 0.44, and 0.73) have been investigated and compared to those for similarly bombarded Si and Ge. Defect absorption bands are observed in all three alloy compositions and can be separated into Ge‐like and Si‐like centers. Energy positions for the bands increase linearly with Si fraction. Damage‐induced near‐edge absorption is also observed in all three alloy compositions. Results for the Ge‐like center are consistent with the previous assignment of a 2.4‐μm band in Ge to divacancies. Growth of the Si‐like center between 200 and 300 K is consistent with Si stabilization of divacancies formed from vacancies initially trapped by Ge. Annealing loss of the Si‐like center is also consistent with the thermal stability expected for SiSi bonding through a divacancy. The formation rate for Si‐like centers by bombardment near 300 K can be explained by SiSi bonding through divacancies in a random alloy when two Si atoms are in the same plane as the divacancy and are nearest neighbors to the divacancy. Neutron‐induced hole‐removal rates approaching those for p‐type Si are indicated by free‐carrier absorption measurements on the x = 0.44 and 0.73 alloys.