MAGNETOOPTICAL STUDY OF PARAEXCITONS IN NAI

Effects of an external magnetic field on the free-exciton luminescence (FEL) and the paraexciton resonance have been studied for NaI. The Ze eman splitting of the paraexciton is observed with use of the techniqu e of magnetic-electric dipole two-photon absorption, from which the ef fective g value is derived to be 1.15. It is also found that the field -induced redshift of the zero-phonon luminescence line from free excit ons follows exactly the Zeeman shift of the lowest level of the paraex citon. This fact provides clear evidence that the FEL of NaI originate s from the radiative annihilation of paraexcitons, and not of orthoexc itons, which were proposed in previous works.