Observation of the time variation of the magnetic-field-induced polarization of triplet exciton emission in GaSe

The magnetic-field-induced linear polarization of the triplet bound-exciton emission has been studied by means of time-resolved spectroscopy in uniaxial GaSe crystals under unpolarized pumping conditions. It is found that the magnetic-field dependence of the linear-polarization degree of the exciton luminescence varies during the ifetime of the excited state. The degree of polarization significantly increases with increasing the delay of the emission measurement. For delay times $T\ge 1\,\mu$s, the exciton emission in the applied magnetic field is virtually completely polarized. A theoretical description is proposed for the observed time variation of the magnetic-field-induced polarization of the triplet bound-exciton emission.