The Influence of Excimer Formation on Solvent-Solute Energy Transfer in Organic Liquid Scintillators

Excimer (excited dimer) formation occurs in all the aromatic hydrocarbon solvents used in liquid scintillators. The influence of this process on solvent-solute energy transfer has been studied for a model system: 9, 10-diphenyl anthracene (DPA) in 1, 6-dimethyl naphthalene (DMN), diluted by n-heptane (Hp). Data on the fluorescence lifetimes, spectra and quantum yields and the viscosity of DMN in Hp are used to analyze the results. It is found that the energy transfer rate parameters of the excited monomer and excimer differ, but that they are independent of Hp dilution. The influence of diffusion and solvent energy migration on solvent-solute energy transfer are discussed, and a migration mechanism involving excimer formation and dissociation is proposed.