Optical and magnetic properties of Fe2+ and Cr2+ in II–VI semiconductors: the Jahn-Teller effect

Abstract

The 5 D terms of Fe 2+ and Cr 2+ in the tetrahedral potential at cation sites in II-VI compounds split into orbital doublet and triplet states. While in Cr 2+ the orbital triplet has lower energy than the doublet, the opposite is the case in Fe 2+ . Both ions have singlet ground states after the spin-orbit interaction is taken into account and, hence, both are Van Vleck paramagnets. The optical absorption spectra of Fe and Cr based materials differ and are explained on the basis of a dynamic Jahn-Teller effect in the former and a static one in the latter. These considerations permit us to explain the optical as well as the magnetic properties observed in these materials.

High-magnetic-field EPR of Cr-based diluted magnetic semiconductors

“…For the Jahn-Teller energies three different parameters are necessary, in agreement with Vallin et al 27 In Vallins case the Jahn-Teller energy is larger, the Cr 2ϩ displacement in the host lattice will be larger, and to obtain the same energy level scheme the spin-orbit interaction parameters must increase as well to account for the smaller overlap between the Cr 2ϩ 3d wave functions and the ligand wave 24 we used slightly higher crystal field parameters, but neglected the spin-spin interaction term in the Hamiltonian and diversified the spin-orbit parameter, where Colignon used a too general approach, using the free ion spin-orbit parameter value. They also find a large difference in the Jahn-Teller energy values over the three compounds, while we used approximately the same values for all three host lattices.…”

“…where, instead of using one free ion spin-orbit coupling parameter, 24 we used three different parameters. This reflects the fact that the strength of the spin-orbit coupling may depend on admixture between the Cr 3d wave functions and the ligand wave functions, which is different for the 5 E and 5 T 2 states.…”

Dynamic Jahn-Teller effect in crystals doped with 3d ions

“…The importance of the JT effect on the specific heat and magnetic properties of these systems was acknowledged and some possible coupling mechanisms and competing distortions have been subsequently suggested [82]. More recently, higher resolution luminescence spectra and well resolved absorption experiments were added to information of the infrared properties of Cr 2+ in semiconductors [83][84][85].…”

Electronic Levels Of Cr2+ Ion Doped In II-VI Compounds Of ZnS – Crystal Field Treatment

“…II-VI compounds are frequently studied materials because of their multiple applications [1], but it remains still to research the detailed nature of the electronic properties associated with the transition-metal ions doped in such host materials. Most studies [2][3][4][5][6][7][8][9][10][11][12] reveals that these properties can be better explained if were taken into account beside the electrostatic interactions, the Jahn-Teller effect, spin-orbit, spin-spin interactions and Tress correction between the nd electrons of the transition-metal ions doped in semiconductors and between the ions and the ligands. The tetrahedral site symmetry of the impurity Cr 2+ ion doped in ZnS host matrix decrees, due to the static Jahn-Teller effect [2-6], from tetrahedral (T d ) to tetragonal (D 2d ) symmetry, and gives the degeneracy of the energy levels [7,8].…”

“…Most studies [2][3][4][5][6][7][8][9][10][11][12] reveals that these properties can be better explained if were taken into account beside the electrostatic interactions, the Jahn-Teller effect, spin-orbit, spin-spin interactions and Tress correction between the nd electrons of the transition-metal ions doped in semiconductors and between the ions and the ligands. The tetrahedral site symmetry of the impurity Cr 2+ ion doped in ZnS host matrix decrees, due to the static Jahn-Teller effect [2-6], from tetrahedral (T d ) to tetragonal (D 2d ) symmetry, and gives the degeneracy of the energy levels [7,8]. The spin-orbit, spin-spin interactions and Tress correction also influence the optical and magnetic properties of the Cr 2+ :ZnS system.…”