Radiation products and tunneling process in ionic glasses. 1. Radiation products and recombination in undoped nitrate and acetate glasses

Ionizing radiation acts on 3:2 KNO₃-Ca(NO₃)₂ glasses to produce a simple hole center, the NO₃ radical, and an excess electron center, which is probably the NO₃^2- radical. At 297 K, 10^-6 s after a 4-ns pulse of radiation a yield of 3.2 ± 0.2 ion pairs is found per 100 eV of absorbed energy. The ion pairs recombine, as observed by following the red absorption of NO₃ (λ_max 615 nm), from 10^-6 to 10² s. Diffusion of the reacting species is involved above the glass transition temperature (T_g = 341 K), while electron tunneling seems to be the main mechanism below T_g. The reaction is weakly temperature dependent (E_A ≃ 3 kcal) from 77 to 260 K, but E_A jumps to ≈ 18 kcal above 260 K. These results are discussed in terms of modern electron-transfer theories, which predict such a transition from weak to strong activation. Acetate glasses showed no detectable radiation coloration in the visible, and only a small, decaying absorption in the near UV.