Comparison of High-Energy and Ultraviolet-Radiation Induced Luminescence in Liquid Systems

Abstract

Luminescence induced by Co60-gamma excitation of some organic solvent-solute pairs has been compared with 2537 A excitation as to dependence of intensity on solute concentration and on concentration of an added quencher. The solutions studied were 1,6-diphenylhexatriene in benzene, p-terphenyl in benzene, and p-terphenyl in toluene. The quencher was bromobenzene. The energy-transfer parameter Q of the Kallmann-Furst theory and the quenching constant were obtained for each of the systems. Within an estimated experimental error of about 5%, Q was unaffected by change in source of excitation. The efficiency of quenching was found to be greater for Co60-gamma than for uv excitation for the two systems involving p-terphenyl. With diphenylhexatriene as solute, however, the quenching constant was unchanged. These results argue against a mechanism of energy exchange involving charge transfer. The high rates of transfer and quenching are consistent with a picture of the solvent involving the existence of small ordered regions within which exciton transfer can occur so that the entire region is viable to attack by a foreign molecule with resultant quenching or energy transfer.