Difference values of spontaneous emission rate of a single-impurity molecule of pentacene in biaxial p-terphenyl crystal

The spontaneous emission rate of a single-impurity molecule in a birefringent host crystal depends on the angles between the transition dipole moment and the principal axes of the dielectric (permittivity) tensor as well as on the main dielectric constants of a host crystal. The transition dipole moment of a single pentacene impurity in p-terphenyl crystal may have four different orientations depending on the spectroscopic sites O1 to O4. Here the orientation of the transition dipole moment is defined by the angle Ω between the projection of the transition dipole moment to the image-plane of the crystal and the b′-axis. The relative spontaneous emission rate is calculated for these four spectroscopic sites in dependence on unknown component of the transition dipole moment, which is normal to the image-plane. Possible differences in the spontaneous emission rate of the electric dipole transition of pentacene in p-terphenyl crystal are up to 24%.