Hyperfine versus relaxation mechanisms of the magnetic field effect on recombination fluorescence of geminate pairs

Magnetic field effects on the recombination luminescence of geminate pairs were observed in several X-irradiated systems. In decane solution of pyrene, the magnetic field dependence was sharp, i.e. it saturates at a relatively low magnetic field. In squalane solution, on the other hand, the magnetic field dependence is dull, and the fluorescence continues to increase even at 300 mT. In the case of pyrene-doped ethylene-propylene rubber (EP rubber), the magnetic field dependence becomes sharp again through the viscosity of the medium is much higher than that of squalane. In the presence of a quencher, the magnetic field dependence for squalane solution become sharp, and is similar to that for decane solution without a quencher. These observations were analyzed theoretically with the aid of calculations for simple model systems. It has been shown that the time profile of recombination as well as the initial spin state of the geminate pair can be obtained through curve fitting of the observed magnetic field dependence of the fluorescence.