CW laser discoloration of X-ray irradiated silver doped silicate glasses

Discoloration of X-ray irradiated silver doped silicate glass has been studied under thermal annealing and illumination by a focused CW laser beam (λ = 488.5 nm). We suggest that color centers in the Ag-doped glasses are produced mainly due to excitation of electrons in the O-Ag+ bonds and formation of neutral silver, and hole centers with non-bridging oxygen. At constant temperature the decay kinetics follows a second order reaction, in which the decrease of the number of centers is proportional to the square of their quantity. The activation energy of the thermal decay is found to be 0.52 ± 0.07 eV. Under CW laser irradiation the centers decay locally near the beam position forming micro holes with a radius, which grows with time and laser power. Thus light transmission through the holes increases as they are formed. Assuming that discoloration occurs due to transformation of the light energy into heat we calculate the temperature distribution around the focused laser beam as function of time and coordinates and from this we estimate the expected transmission as function of time. We find good agreement between the calculations and the experimental results.