A Minireview of the Natures of Radiation-Induced Point Defects in Pure and Doped Silica Glasses and Their Visible/Near-IR Absorption Bands, with Emphasis on Self-Trapped Holes and How They Can Be Controlled
Figure 2
ESR-determined number densities (bold curves, relative units) and independently determined optical-band intensities (symbols, eV/cm) for X-ray-induced defect centers in separate samples of a Ge-doped-silica fiber-optic perform following irradiations to the same dose at 100 and 77 K, respectively, and subsequent 5-minute isochronal anneals to the higher temperatures. (The ESR data were also recorded at discrete temperatures but are displayed here as continuous curves as an aid to the eye). It is seen here that the self-trapped holes (STHs) and the Ge trapped-electron centers correlate well with optical absorption bands centered near 2.4 and 4.4 eV, respectively (and have identical oscillator strengths [5, 6]). The upshifted Ge number-density curve (dashed blue curve relating to Ge’s higher oscillator strength) strongly matches the 5.8 eV optical data below 300 K and is cryptically correlated with those data above 300 K. The diamonds, representing a 5.2-eV band not associated with any ESR-detectable defect, are shown here displaced upward by a factor of 2.4 from their originally recorded optical intensities in order to discover their perfect match with the red curve in the range 200–370 K, which comprises the sum of the changes of the Ge and Ge number densities in the range 200–370 K multiplied by negative 0.5. This figure—adapted from [5]—was recently published in [6], where full explanations of the meanings and implications of these data can be found.
