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A ligand-field model is used to compute the spin–lattice coupling coefficient C11 to strains of symmetry EΘ of the fundamental state 6A1 of Mn in cubic ZnS and ZnSe. It is shown that the proposed ligand-field model in which C11 is given by a second-order perturbation scheme involving the molecular spin–orbit interaction between the fundamental state 6A1 and the three orbital triplet states 4T1 at lower energy gives theoretical values which correctly account for the experimental results. A detailed study is made of the strain-induced variations of the crystal electrostatic field, the metal–ligand, and ligand–ligand group overlap integrals and the molecular spin–orbit interaction. It is shown that in ZnS the strain-induced variation of the crystal electrostatic field is almost completely compensated by the strain-induced variations of the group overlap integrals and the molecular spin–orbit interaction thus explaining the small experimental value for C11 in this compound. In ZnSe the contributions of the strain-induced variation of the group overlaps and of the molecular spin–orbit interaction are preponderant. [ABSTRACT FROM AUTHOR]

A theoretical determination of the Jahn–Teller coupling constants of d5 ions in tetrahedral clusters is performed in the framework of the angular overlap model and the quasimolecular approximation. It is shown that the angular model correctly predicts the trend of the preponderant coupling of the 4T1(G) and 4T2(G) levels of Mn2+ in MnS4 and MnSe4 to the E-vibrational effective mode. Finally, the limitations of this model are discussed. In particular, it is shown that more elaborated covalent models are needed to interpret the Jahn–Teller coupling coefficients of the 4E and 4A1 levels of d5 configurations and to determine the influence of the crystal on the clusters. [ABSTRACT FROM AUTHOR]

A molecular orbital model has been elaborated to determine the orbit–lattice coupling coefficients to strains of symmetry E of the orbital triplet states of d5 ions in tetrahedral symmetry. The wave functions and energies of the monoelectronic molecular orbitals have been determined for a tetrahedral molecule MnX4 in a crystal and for a slightly distorted molecule of symmetry D2d corresponding to a strain Eθ. It is shown that in D2d symmetry, the splitting of the monoelectronic molecular orbitals e and t2 is due to the variations of the group overlap integrals and the variation of the crystal electrostatic field with respect to their values in cubic symmetry. The orbit–lattice coupling coefficients which are independent of the spin–orbit interactions, are obtained by diagonalizing the Tanabe–Sugano matrices for the orbital triplet states and then using the molecular orbitals in D2d symmetry as zero-order wave functions in a first-order perturbation scheme. The proposed model for the orbit–lattice coupling coefficients of the orbital triplet states 4T1 and 4T2 at lower energy for Mn2+ in ZnS and ZnSe gives theoretical values which differ at most by 30% from the experimental values. It is shown that three fifths of the theoretical values for the orbit–lattice coupling coefficients are due to the variations of the group-overlap integrals, the remaining part of the theoretical values being due to the variations of the crystal electrostatic field describing the Coulomb’s interaction in the molecular model. [ABSTRACT FROM AUTHOR]

A very detailed analysis of the fine structure of the 4E(G) state of Mn2+ in cubic and nearly cubic clusters is presented to account for the unusual fine structure observed in ZnSe:Mn. First, experimental results are reported which show that the spin-orbit interaction in the 4E(G) state of Mn2+ in ZnSe is about one half of that previously observed in cubic or nearly cubic clusters as MnS4, MnBr4, and MnCl4 and that the state Γ8 is neatly shifted with respect to the Kramers doublets Γ6 and Γ7. Second, a model is elaborated which shows that second-order spin-orbit interactions reduced by a Jahn–Teller coupling to E vibrational modes accounts well for the observed overall splitting of the 4E(G) state in the studied clusters and that fourth-order spin-orbit interactions correctly describe the shifts of the Γ8 state. The validity of the perturbation schemes is discussed and the results are compared to those obtained from a complete diagonalization in the d5 configuration. [ABSTRACT FROM AUTHOR]

The electronic fine structure of the orbital triplet levels 4T2(G) of d5 ions in tetrahedral II–VI compounds is determined from an extended molecular model involving the first- and second-order molecular spin–orbit (MSO) interaction. For the levels 4T2(G) of Mn2+ in cubic ZnS, it is shown that the first-order MSO interaction is almost identical to that predicted by the crystal-field (CF) model. For the levels 4T2(G) of Mn2+ in cubic ZnSe, the splittings of the fine structure lines due to the first-order MSO interaction is much larger than the splitting predicted by the CF-model. Concerning the second-order (MSO) interaction, it is shown that the splitting of the levels Γ8(5/2) and Γ6 at lower energy drastically depends on the spin–orbit coupling constants of the electrons p of the ligands. Finally, an analysis is made of the coupling to ϵ-vibrational modes from Ham''s model, and the selective intensity transfer observed on the fine structure lines of the level 4T2(G) of Mn2+ in ZnS and ZnSe is analyzed in detail. [Copyright &y& Elsevier]

The electronic and vibronic structures of Mn2+ in near cubic fluorescent centers in ZnS due to stacking faults are compared to the structure of the cubic centers. First, for one of the near cubic center, a phenomenological vibronic model of the fluorescent level is elaborated from the analysis of the uniaxial stress effect and of the relative dipole strengths of the four well defined fundamental vibronic lines (FVL). Second, it is shown that the electronic structure of the near cubic center due to the spin–orbit and spin–spin interactions is almost identical to that of the cubic centers. Third, it is shown that a previous model for the very unexpected electronic structure of the cubic centers is clearly confirmed from an analysis of the vibronic structure in near cubic centers. [Copyright &y& Elsevier]