To determine if the only source of optical absorption between 5.8 and 5.9 eV is the E' center (absorbing at 5.85 eV) two separate suites of type III silica samples were implanted, one with Si and one with O. Several ion energies were used for implantation to produce layers 600 and 570 nm thick in the Si case and in the O case, respectively. Concentrations of implanted ions in the layers ranged from > 0.02 to < 2.1 at. %, with uncertainties in the concentrations less than +/- 5%. Optical absorption measurements were made from 2.0 to 6.5 eV and electron spin resonance (ESR) measurements were performed at similar to 20.3 and 33 GHz at temperatures in the 77-100 K range. Several ESR active defects were observed including the E'(gamma) center (O vacancy), the nonbridging oxygen hole center, the peroxy radical, a possibly oxygen related center, labeled OS, and a component around g = 2.0026. In the O-implantation case, by comparing the increasing optical absorption at 5.85 eV with the observed decrease in the ESR E' densities with increasing O concentration, we conclude that an oxygen related band is created and its intensity increases with increasing O concentration. In the silicon case, the optical absorption coefficient and the E'(gamma) density as a function of Si implantation dose have a correlation coefficient that is similar to 1, within reasonable errors. We conclude that in the O-implantation case the absorption between 5.8 and 5.9 eV is in part due to an O related defect state in addition to the E'(gamma) center while in the Si case it is mainly the E' center that is responsible for the 5.85 eV absorption band. (c) 2006 American Institute of Physics.