FE-3+ AS NEAR-INFRARED LUMINESCENCE CENTER IN ZNS

A richly structured luminescence is observed in the 1.2-m spectral region in pure and Fe-doped ZnS crystals for the first time. By means of emission, excitation, and magneto-optical measurements an unambiguous assignment to the 4T1(G)-6A1(S) transition of isolated Fe3+ on Zn2+ lattice sites becomes possible. Basic arguments are the sixfold degeneracy of the ground state with an isotropic g factor of 2.0260.010, the long decay time of about 4 ms, and the influence of additional iron doping. The excitation mechanism can be described by an energy transfer via free holes from Cu2+ to Fe2+ centers and a charge-transfer process Fe3+long->hFe2++hVB (VB denotes valence band). A comparison with the well-known isoelectronic Mn2+ centers reveals striking similarities. The numerous zero-phonon lines at T=1.8 K are due to the polytypic structure of the investigated crystals, offering several different Zn2+ lattice sites. The observed fine structures of the 4T1(G) terms and their behavior in a magnetic field indicate a strong Jahn-Teller coupling to E modes as is known for the Mn2+ centers. © 1990 The American Physical Society.