Organic solutions with poor high-energy-induced fluorescence can often be made much more efficient by introducing large concentrations of substances such as naphthalene and some related compounds. The naphthalene can be considered as an intermediate solvent; the energy originally mainly absorbed in the less effective solvent goes over to the naphthalene from which it then proceeds to the fluorescent solute. Naphlene is considerably more effective as such an intermediate solvent than any other of the known efficient solvents, e.g., xylene. It is shown that the particular effectiveness of naphthalene stems from two causes: first, the energy transfer from the "poor" solvent to naphthalene is faster than to other substances; secondly, the excited naphthalene molecule is often quenched less than, e.g., xylene by quenching atoms present in the solution. These results are applied to the enhancement of the high-energy-induced fluorescence of solutions containing various elements even as heavy as bismuth.

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