Jahn-Teller effect and the luminescence spectra of ${\mathrm{V}}^{2+}$ in ZnS and ZnSe

A dynamical Jahn-Teller effect has been proposed to interpret the fine structure of the luminescence spectra of ${\mathrm{V}}^{2+}$ impurities in ZnS and ZnSe. The ground ${}^{4}F$ 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 ${}^4{T}_1$ multiplet and on the excited ${}^4{T}_2$ 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 $\mathrm{ZnSe}:{\mathrm{V}}^{2+}$ and $\mathrm{ZnS}:{\mathrm{V}}^{2+}.$ In the latter, the temperature effects present in the spectra are also accounted for by the resulting energy-level scheme.