Electron-vibration effects in Cs2SiF6 : Mn4+

Abstract

We report a study of the 4 A 2g →2 T 1g absorption band of Mn4+ in Cs2SiF6. The band shows several lines or groups of lines associated with transitions from the 4 A 2g ground state to the spin-orbit components (2 T 1g )Γ8 and (2 T 1g )Γ6 coupled to the three odd-parity vibrations v 6(t 2u ), v 4(t 1u ) and v 3(t 1u ). The absorptions associated with the (2 T 1g )Γ8 electronic state have structure whereas those associated with the (2 T 1g )Γ6 do not. It is shown that the structure is a consequence of splitting of the Γ8 × v vibronic multiplets by electron-vibration interaction. The intensity of the 4 A 2g →(2 T 1g )Γ i + vj vibronic transitions are expressed in terms of a small number of parameters; two parameters for v(t 1u ) modes and three for v(t 2u ) modes. Plausible but not good fits to the low temperature Zeeman data and vibronic splitting patterns are obtained. The excitation spectrum of the Cs2SiF6 : Mn4+ in the region of the 4 A 2g →2 Eg and 4 A 2g →2 T 1g is recorded using a c.w. dye laser. This reveals numerous weaker lines involving combinational modes and even-parity modes v5 (t 2g ), v 2(eg ) and v 1(a 1g ). Several interesting electron-vibrational effects are observed. These are illustrated and discussed qualitatively.