A comprehensive study of X-ray stimulated luminescence was carried out on 4 types of high-purity amorphous silica. High-OH and low-OH, as well as O-excess and O-deficient, materials were studied. The room-temperature visible X-ray luminescence was measured continuously as a function of X-ray doses ranging from 0 to 400Mrad. Electron paramagnetic resonance was used to determine the concentrations of 2 key radiation-induced defects: the E center and the non-bridging O hole center. The X-ray luminescence spectra were deconvoluted into 4 Gaussian components, with centers at 1.9, 2.2, 2.6 and 2.75eV. The same centers and widths could be used to describe the spectra in all 4 types of sample; only the intensities varied. The 2.6 and 2.75eV lines were strongly dose-dependent, and rose from near-zero intensity at zero dose in all of the materials. These 2 lines were strongly related to each other, and exhibited essentially the same dependence upon dose and sample type. This correlation suggested that the 2 lines were due to the same radiation-induced defect, or to closely related defects. The dose dependence and sample-to-sample variation of the 2 lines exhibited some similarity to the E' concentration. Unlike the 2.6 and 2.75eV lines, the 1.9eV line had a high intensity at the lowest doses that were measurable. A simple phenomenological model was proposed in order to describe the 1.9eV line. This model involved 2 populations of defects. One population was present at zero dose, and was assumed to be dose-independent, while the second population was dose-dependent. Evidence was presented to show that the dose-dependent defect was the non-bridging O hole center. The X-ray luminescence due to the dose-independent population was thought to be associated with a transient response to X-rays, or to a metastable defect. This population was not expected to be observable in post-irradiation investigations which involved electron paramagnetic resonance or conventional photoluminescence techniques. Similarly to the 1.9eV line, the 2.2eV line also had a relatively high intensity at the lowest measurable X-ray dose. The behavior of this line was in general agreement with the self-trapped exciton model.

X-Ray Induced Luminescence of High-Purity Amorphous Silicon Dioxide. A.J.Miller, R.G.Leisure, W.R.Austin: Journal of Applied Physics, 1999, 86[4], 2042-50