Dynamics of the magnetic-field-induced optical alignment of triplet bound excitons in GaSe under resonant excitation conditions

The dynamics of the transverse-magnetic-field-induced linear polarization of the radiation of triplet bound excitons in uniaxial crystals has been studied by time-resolved spectroscopy on an example of GaSe under resonant excitation by linearly polarized light. The linear polarization of the radiation arises due to the difference between the behaviors of its π- and σ-components in a magnetic field. It has been found that the magnetic-field dependences of the π- and σ-component intensities are functions of the pump light polarization and vary considerably with the lifetime t of the excited states. It has been revealed that the resonant excitation of excitons by light polarized with E‖B and E ⊥ B is accompanied by the magnetic-field-induced alignment of their dipole moments along the vector E of the pump light. In the case of excitation by light with E ⊥ B, the optical alignment of excitons is observed only in the initial period of their life, and the linear polarization of exciton radiation changes sign at a certain t>t ₀. A theoretical description of these effects is proposed.