MODEL FOR THE ELECTRONIC AND VIBRONIC STRUCTURE OF T-4(1) LEVELS OF D(5) IONS COUPLED TO E VIBRATIONAL-MODES - CASE OF THE FLUORESCENT LEVEL OF MN2+ IN ZNS

The four fundamental vibronic lines of a T-4(1) level of a d(5) ion co upled to E vibrational modes in cubic symmetry have been observed, An analysis of the four fine-structure lines of the fluorescent level T-4 (1) of Mn2+ in cubic ZnS, which have been observed at high resolution in pure cubic ZnS crystals, shows that the relative energies and dipol e strengths (RDS) of the quasidegenerate levels are not those predicte d by previous electronic and vibronic models. A model is elaborated in three steps. First, from Ham's model fur the coupling of orbital trip let states to E modes, a phenomenological operator describing the firs t-order and second-order spin-orbit interaction aad the spin-spin inte raction in terms of three parameters is proposed to account for the en ergy lei els and tlx RDS`s. Two phenomenological descriptions deduced from an analysis of the RDS are proposed for the studied state, Second , a detailed analysis of the spin-orbit and spin-spin interactions in terms of the Huang-Rhys factor and of the energy of the effective phon ons shows that the electronic spin-orbit interaction in l . S is oi op posite sign to that predicted by the model restricted to the d(5) conf iguration. Finally, a covalent model involving the molecular spin-orbi t interaction defined by Misetich and Buch is developed to account for the first-order spin-orbit splitting of the orbital triplet states of Mn2+ in II-VI compounds.