The study of organic anions by a deferred luminescence technique: “Stimulation spectra”

Abstract

A technique is described for obtaining “stimulation spectra” of negative species trapped during γ- or U.V.-irradiation of organic solids. These spectra correspond to the absorption spectra of the negative species and are due to the liberation of electrons (from traps or from anions) and to their recombination with cations, leading to an emission of light. The spectra thus obtained are not perturbed by the absorption spectra of the positive species present. Depending on the concentration of aromatic solutes, the relative amounts of trapped electrons and anions detected give information on the distance to which free electrons can migrate in the matrix (120 Å in glassy MCH, 320 Å in polycrystalline MCH). Electrons can be transferred reversibly between physical traps and solute molecules by illumination in the respective absorption bands. The solids studied were: solutions of biphenyl in glassy and polycrystalline MCH, 3 MP, cyclohexane and benzene; solutions of styrene, pyrene, naphthalene, durene in glassy MCH or 3 MP, and pure polycrystalline acetone. In ethanol, boric acid and carbon tetrachloride no stimulation spectra were obtained.