Triplet exciton spins non-equilibrium polarisation due to their mutual annihilation

The effect of triplet excitons non-equilibrium polarization due to their mutual annihilation was predicted and experimentally observed in molecular crystals in 2004. In this paper we obtain kinetic equation for density matrix of exciton ensemble. This equation takes into account mutual diffusion of excitons. The model is studied numerically. Despite of large dimension of the problem (about 104 order), the choosed numerical algorithm makes possible not to use cluster for calculations. At some values of magnetic-resonance and molecular kinetic parameters time dependences of dipole and quadrupole electron spins polarisations of triplet excitons were obtained. It was shown, that mutual annihilation is effective mechanism for non-equilibrim quadrupolar spin polarization of triplets.