Pulse radiolysis of sodium metaphosphate glasses

The effects of ionizing radiation on sodium metaphosphate glasses are investigated using pulse radiolysis techniques. In pure glasses the transient absorbance changes can be described by the consecutive exponential decays of three fractions exhibiting absorption maxima at 6900 A (fraction I, τ_1/2, = 3.2 μsec), 5600 Å (fraction II, τ_1/2 = 0.29 msec), and 5200 A (fraction III, τ_1/2 = 6.3 msec). After all decays a residual permanent absorption at 5000 Å (fraction IV) is left. The effects of doping the glass with various metal cations are analyzed. Characteristic electron scavengers (e.g., Ag⁺, Cd²⁺, Pb²⁺) are found to inhibit the formation of fraction I while hole scavengers (Ce³⁺, Ag⁺) prevent the formation of the other fractions. The effects are analyzed and attributed to reactions between the ions and the precursors of fraction I and fractions II-IV, the precursors being identified as very mobile electron-excess (e^-) and electron-deficiency (h⁺) centers, respectively. Accordingly, the decaying fraction I is tentatively attributed to solvated electrons (e_I^-) while fractions II-IV are assigned to various electron deficiency (hole) centers (h_II⁺, h_III⁺, h_IV⁺). In Ag⁺-doped glasses the very fast primary processes Ag⁺ + e^- → Ag° and Ag⁺ + h⁺ → Ag²⁺ are followed by slower reactions attributed to Ag° + Ag⁺ → Ag₂⁺ and h_IV⁺ + Ag⁺ → Ag²⁺. The feasibility of a third process Ag₂⁺ + Ag⁺ → Ag²⁺ + Ag₂ is considered.