Energy Transfer by Means of Collision in Liquid Organic Solutions under High Energy and Ultraviolet Excitations

Abstract

Experiments are described which show that energy transfer by means of "collisions" occurs when a liquid organic solution is excited by ultraviolet light as well by high-energy radiation. With light excitation the possibility of any transfer by ionization and/or by hidden radiation could be completely eliminated. It was found that energy transfer by way of collision between various molecules under excitation by light is of the same magnitude as with high-energy radiation excitation. Energy transfer by way of absorption and subsequent re-emission occurs only in complex solutions containing at least two kinds of efficient fluorescent molecules. Basically the technique of the experiments with light consisted of irradiating different solutions with various wavelengths, thereby selectively exciting various components of the solutions, and of observing the corresponding effects on the fluorescent light output. The solutions measured in this investigation used xylene and cyclohexane as solvents; anthracene, $p$-terphenyl, and 9,10-diphenylanthracene as fluorescent solutes; and additional naphthalene which in some respects behaves like a solvent when present in large concentrations. In complete agreement with results under gamma-ray excitation, energy transfer under light excitation takes place from naphthalene to anthracene and diphenylanthracene, and from xylene to terphenyl, while none occurs from naphthalene to terphenyl.