Optical absorption measurements of the 2.0‐eV band and photoluminescence measurements of the 1.9‐eV emission, excited by various excitation bands, were carried out on high‐purity silica glasses subjected to &ggr;‐ray irradiation. Two, and possibly three, different forms of nonbridging oxygen hole centers were deconvoluted from the results of the isochronal annealing experiments. The difference in the peak wavelength of the 2.0‐eV absorption and 1.9‐eV luminescence bands among various forms of nonbridging oxygen hole centers is reported.