4Ag↔2Eg transition of Mn4+ in Cs2TiF6

Abstract

We report and interpret the4A2g↔2Eg absorption, emission, linear dichroism, MCD and MCE of the MnF62- octahedra at sites of D3d symmetry in single crystals of Cs2TiF6. The spectra show many sharp features but a simplified calculation using cubic basis functions successfully accounts for all of the major features and much of the detailed structure. The electronic levels are not split by the trigonal field in first order but trigonal distortion splits the three-fold degenerate ve(t2u) vibration of the octahedron into a twofold degenerate v6(eu) and a non-degenerate v6(aiu) vibration and these two vibrational modes give rise to the features 213 cm-1 and 246 cm-1 from the zero-phonon line respectively. Similarly the v4(tiu) vibration is split into a V4(zu) + v2(eu) vibration and give the features at 313 cm-1 and 340 cm-1 respectively. Several transitions involving two or more quanta of vibration are clearly seen in the emission and MCE spectrum. At an energy shift of greater than 700 cm-1 from the zero-phonon transition these features are found to consist of progressions in the v1(a1g) breathing mode and the v2(eg) two-fold degenerate Jahn-Teller active mode. This structure can again be explained, with one exception, in terms of a calculation which assumes cubic basis functions. The exception is the reversal in sign of the MCE at a frequency V4(eu) + v2(eg) compared with that at v6(eu) which is not fully understood. Show more