Magnetic effects on delayed fluorescence in naphthalene crystals at low and high triplet exciton densities

Abstract

We have measured the magnetic effects on the triplet exciton annihilation in naphthalene crystals at low and at high exciton densities. At high triplet densities the magnetic effects on delayed fluorescence intensity cannot be explained by the current theories on triplet exciton interactions in molecular solids. From the magnetic field anisotropy of the delayed fluorescence intensity at low triplet densities we conclude that in naphthalene the influence of spin-lattice relaxation on the kinematics of triplet exciton annihilation is not negligible. This implies that the exciton diffusion in this material is almost two dimensional, with the anisotropy of more than 1000 to 1.