Luminescence following laser excitation of trapped electrons in mixed-solute aqueous glasses

Abstract

Based on measurements of the luminescence produced when infrared-absorbing electron states (e^–_ir) at 77 K decay, it is contended that this electron state is normally to be expected in irradiated aqueous media and is not anomalous to those few specific solutes in whose glasses it has been found. Rather, it is destroyed, or its formation is inhibited, by the majority of solutes which are commonly used to make aqueous glasses. This conclusion comes from studies of mixed-solute glasses, specifically using MgCl₂ glasses with CaCl₂, Mg(ClO₄)₂ or ethylene glycol added as second solutes. Though all three second solutes inhibit the luminescence from the MgCl₂ glass, quite different mechanisms seem to be involved in each case, as shown by the time-dependence of the luminescence intensity. It is suggested that e^–_ir converts spontaneously to e^–_ir when ethylene glycol (or 2-propanol) is present because it inhibits the luminescent process without destroying e^–_ir. These species were produced in the experiments by photoexcitation at 694 nm of stable trapped electrons formed by γ-radiolysis at 77 K.