Trapped Electron in the Irradiated Single Crystal of Ice Doped with Some Impurities: Its Formation and Photobleaching at 77°K

Publisher Website
Google Scholar
Abstract
It is found that single crystals of ice doped with 10−4–10−2M ammonium fluoride and alkali fluoride color considerably by gamma ray irradiation at 77°K. Their spectra all are the same as the one in the pure crystal (the peak is at 6400 Å), and the largest optical density is about 6 times as high as that in the pure crystal. These enhanced absorptions represent an increase of the concentration of the trapped electrons in the doped samples. D2O crystals doped with NH4F show a similar increase, having the same spectrum as that in pure D2O crystal (the maximum yield is about 10 times of that in the pure H2O crystal). The increased electrons are not due to those produced in the locally amorphous parts. Other samples doped with such impurities as NH4Cl, NH4OH, KCl, NaOH, etc., do not show such coloring. Trapping sites for these electrons are considered. Photobleaching of the pure and the doped crystal shows simple and uniform decays and the original spectrum is almost unchanged by the stimulation at any wavelength. The spectrum represents only one species trapped in one definite form of potential. The trapped electron in the pure and the doped crystal show a low bleaching efficiency for the wavelength corresponding to the peak of the spectrum. Wavelength dependence of the bleaching quantum efficiency shows a steep rise from roughly 5000 Å to the higher energy side. The peak of the optical absorption spectrum is a transition to the bound state. The asymmetrical tail in the high energy side of the spectrum corresponds to the transition to the higher excited levels, bound or in the continuum.