Fluorescent Behavior of Solutions Containing More than One Solvent

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Abstract
Fluorescent emission of organic solutions in combinations of solvents is investigated in order to determine the reasons for the suitability or unsuitability of solvents for high-energy induced fluorescence, particularly where these solvents do not influence the emission under ultraviolet irradiation. Basically two types of behavior under high-energy radiation are found in these combined solvent solutions. In type I a considerable drop in emitted intensity occurs only when the amount of the ``poor'' solvent greatly exceeds that of the ``effective'' solvent, whereas in type II small amounts of added ``poor'' solvent produce large decreases in emitted intensity. The fluorescence depends upon the concentration of solute, larger concentrations giving greater light outputs. The results obtained are explained by assuming that energy transfer occurs from the ``poor'' solvent to the ``effective'' one. At the same time a decrease in actual lifetime of excitation in the ``effective'' solvent occurs which is induced by the presence of the ``poor'' solvent molecules. This shows up as a quenching of the gamma-ray induced fluorescence in solutions even with solutes which are scarcely quenched at all under ultraviolet light excitation. For type I behavior this quenching is small while for type II it is considerable.