Optical Spectra of Exchange Coupled Mn++ Ion Pairs in ZnS:MnS

The optical spectra of several ZnS:MnS (1 to 10 mole%) mixed crystals were obtained at temperatures from 4.2° to 300°K. A concentration dependence was found which proved that certain bands were due to pairs of Mn++ ions in nearest-neighbor cation sites. Temperature—dependent absorption bands were found which were interpreted to give an interionic exchange integral in the ground state of —9 cm—1 in the spin—spin Hamiltonian H = —2JS1·S2. This agrees with the value obtained from the analysis of the susceptibility of pure MnS. The narrow bands due to transitions to the 4A1, 4E(G) states were shown to fit an isotropic spin—spin coupling law with J = +6 cm—1 for each state. The inversion of sign from the ground state is not fully understood. The selection rules for the transitions do not follow those for the total spin (ΔS = 0).