Effects of anisotropy and the proximity to the surface on the spontaneous emission rate of pentacene in p-terphenyl crystal

Due to the anisotropy of a birefringent host crystal, the spontaneous emission rate of a single-impurity molecule depends on the orientation of the transition dipole moment relative to the host crystal. In p-terphenyl crystal, the transition dipole moment of a single pentacene impurity can have four different orientations. Here the relative spontaneous emission rate of the electric quadrupole transition is calculated depending on the unknown component of the transition dipole moment normal to the a′/b′-plane. Maximum difference in the spontaneous emission rate of the electric quadrupole transition is up to 9%. For comparison, the effects caused by the proximity to the plane surface of the crystal are calculated.