Structural and optical characterization of SiO2 under irradiation with swift heavy ions

SiO2 single crystals irradiated with 600 keV, 4 and 5 MeV Kr ions using the 320 kV High Voltage Experimental Platform (IMP, Lanzhou) were investigated with infrared, fluorescence spectroscopes and TEM. In the low-energy regime, single ion tracks are well separated and the damage process is dominated by the formation of simple color centers such as F+ and F2 centers. For the high energy ions, the energy density in ion tracks produced at a high stopping power is larger, and consequently the defect concentration increases significantly. At higher defect densities, the distance between single defects is smaller facilitating the aggregation of individual electron center to defect cluster and defect annihilation by recombination of hole and electron centers. The latter process determines the limited efficiency of color-center creation under heavy-ion irradiation. Using the unified thermal spike model, a combination of the elastic collision spike model and the inelastic thermal spike model based on electronic energy losses, it is possible to fully describe the experimental data, which clearly demonstrate a synergy between the nuclear energy loss and the electronic energy loss processes.