The 3.8 eV absorption band constitutes a characteristic feature of silica glass with excess oxygen. Since 1.5 eV PL band is formed in the presence of a 3.8 eV absorption band, we studied features of the PL near 1.5 eV to further understand the origin of 3.8 eV absorption band. The 1.5 eV PL band was found to have unique characteristics such as: (1) being the highest intensity PL band observed for an oxygen surplus sample with a 3.8 eV absorption band present, (2) having a long lifetime of several ms and (3) having a PL spectrum with hyperfine structure. We also studied the relationship between 1.5 eV PL band and 3.8 eV absorption band. Two types of inter-related behaviors were observed in the intensity of 1.5 eV PL band and the amplitude of 3.8 eV absorption band. Using a thermal heat treatment experiment, we found a linear correlation between 1.5 eV PL band and 3.8 eV absorption band. Also, by comparing the effect of irradiation time on 3.8 eV absorption and 1.5 eV PL bands at 20 K, we found that an increase in the irradiation time caused a decrease in the amplitude of both 3.8 and 1.5 eV bands. Similarities were also observed in the spatial distribution of the two bands. The results obtained suggest that 3.8 eV absorption band plays a role in the formation of 1.5 eV PL band. (C) 2000 Elsevier Science B.V. All rights reserved.