Scintillation Efficiencies at High Solute Concentrations: Possible Energy Transfer from S3 States of Excited Aromatic Solvents

At normal solute concentrations (3–10 g/liter) the relative scintillation efficiency of a solution is dependent upon the particular solvent; 1,2,4-trimethylbenzene>p-xylene>toluene>benzene. The relative scintillation yields seem to follow the same general trend as the efficiency of internal conversion of S3 → S1 of the aromatic solvent. At high solute concentrations (>150 g/liter) the relative scintillation efficiency of these solutions was independent of the particular aromatic solvent. It was assumed that the fluorescence was produced by a process which involved energy transfer before the S3 → S1 internal conversion. A possible mechanism involves the transfer of energy from the S3 state of the solvent to an excited state of the solute, F3. The relative scintillation efficiency of concentrated solutions would then be dependent upon the internal conversion efficiency for the process F3 → F1.