Luminescence and infrared absorption from laser excitation of trapped electrons in aqueous glasses

When samples of trapped electrons in 9.5M LiCl and 3.1M MgCl2 aqueous glasses at 77 K were bleached by single pulses of 694 nm light from a Q-switched ruby laser, infrared absorption was produced, and luminescence observed in the near ultraviolet and visible. The luminescence had a spectrum centered at 400–420 nm and its intensity was measured over eight decades of time (100 ns to 10 s) following the laser pulse. Over much of this period the luminescence intensity was inversely proportional to the time. No such effects were found for trapped electrons in NaOH or K2CO3 glasses nor in γ-irradiated LiCl or MgCl2 glasses when an electron scavenger was present. This suggests that optical excitation on the low energy side of the visible absorption band causes trapped electrons to be released from their traps, after which they may be temporarily caught in shallow traps from which they tunnel to radiation produced reaction partners, as has been observed during pulse radiolysis.