Zero field optically detected magnetic resonance of multiple localized states in 1,4-dibromonaphthalene crystals

A systematic study of the localized states of 1,4-dibromonaphthalene was made, both as a dilute guest in a host crystal and as a trap site in the neat crystal, utilizing zero field magnetic resonance techniques. The kinetic parameters associated with the various ’’localized’’ triplet states have been determined. These include the relative intersystem crossing rates, the relative radiative rates from the spin states to the electronic and vibronic origins, and the total depletion rates from the individual spin sublevels. The results of these studies indicate that the correlation of the magnetic structure of trap states and the energy difference between traps and a host band is not straightforward, even for one-dimensional systems. Moreover, these results imply that spin exchange and equilibrium between traps and band states can severely influence the dynamics of energy migration and must be incorporated into any temperature dependent line shape analysis of the exciton transitions, particularly for 1,4-dibromonaphthalene because of the similarity in trap and exciton EPR frequencies.