Jahn-Teller effect and the luminescence spectra of V²⁺ in ZnS and ZnSe

A dynamical Jahn-Teller effect has been proposed to interpret the fine structure of the luminescence spectra of V²⁺ impurities in ZnS and ZnSe. The ground ⁴F term of the impurity is split by the crystal field into three multiplets. The spin-orbit and the spin-spin interactions are taken into account as well as a linear Jahn-Teller coupling with a trigonal phonon mode, both on the ground ⁴T₁ multiplet and on the excited ⁴T₂ multiplet. The Lanczos-recursion procedure with a proper choice of the initial state is followed to calculate the vibronic states. A comparison with experimental energies and intensities indicates that a dynamical Jahn-Teller effect plays an important role to explain the fine structure of the luminescence spectra of ZnSe:V²⁺ and ZnS:V²⁺. In the latter, the temperature effects present in the spectra are also accounted for by the resulting energy-level scheme.