FLUORESCENCE LIFETIME STUDIES OF CRUDE OILS

The fluorescence lifetimes of a series of crude oils at various concen trations have been measured for UV-visible excitation and emission wav elengths. The lifetime results are compared with fluorescence spectra and quantum yields for these solutions. The concentration effects of e nergy transfer and quenching are large and result in a significant dec rease in fluorescence lifetimes for high concentrations and for heavy crude oils. Thus, radiationless processes dominate in energy transfer. At high concentrations, energy transfer produces large red shifts in fluorescence emission spectra, while quenching produces a large reduct ion in quantum yields. Stern-Volmer analyses of lifetime and quenching data show a linear dependence of energy transfer and quenching rates on concentration. The rate constants are consistent with collisions wh ich are very efficient at energy transfer and quenching, and the rates of these two processes are comparable.