Molecular electronic model and vibronic coupling to ɛ-vibrational modes of the fluorescent level4T1ofd5ions in II-VI and III-V compounds

Abstract

Complete electronic and vibronic models including the second-order molecular spin-orbit (MSO) interaction are proposed to analyze the fine structure of the orbital triplet levels ${}^{4}{T}_{1}(G)$ of ${d}^{5}$ ions in tetrahedral symmetry. First, a molecular model which has been used to calculate the first-order MSO interaction is extended to the calculation of the second-order MSO interaction. Then Ham's model for the vibronic coupling to \ensuremath{\varepsilon}-vibrational modes of the first- and second-order MSO interactions is used to describe the fine structure patterns and, in particular, the energy-level ordering in terms of the Huang-Rhys factor S. Third, these models are applied to the calculation of the electronic and vibronic structures of the fluorescent level ${}^{4}{T}_{1}(G)$ of ${\mathrm{Mn}}^{2+}$ in cubic ZnS and in ZnSe. For the level ${}^{4}{T}_{1}(G)$ of ${\mathrm{Mn}}^{2+}$ in cubic ZnS, the second-order MSO interaction becomes preponderant because the first-order MSO interaction due to the cation can be completely compensated for by the first-order MSO interaction due to the ligands. For the level ${}^{4}{T}_{1}(G)$ of ${\mathrm{Mn}}^{2+}$ in ZnSe, the first-order MSO interaction is primarily controlled by the ligands. It is shown that the experimental fine structures can be correctly accounted for by the molecular model. Finally, a qualitative model is proposed for the fine structure of the fluorescent level of ${\mathrm{Fe}}^{3+}$ in InP and GaAs.