Splitting of vibronic levels in Cs2SiF6:Mn4+

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Abstract
An account is given of structure in the prominent vibronic transitions within the 4A2g to 2Eg absorption and emission bands of Mn4+ in Cs2SiF6. The emission lines associated with the nu 3(t1u), nu 4(t1u) and nu 6(t2u) vibrations of the MnF62- octahedron all give symmetrical line shapes. On the other hand, the high resolution absorption spectrum reveals that the lines associated with the nu 3(t1u) and nu 6(t2u) vibrations are composed of two and four lines respectively with overall separations of approximately 5 cm-1. Low-temperature, high-field Zeeman measurements are used to show that this structure arises from the splitting of the vibronic levels due to the electron-odd-vibration interaction. For both cases a very good account of the splittings and the intensities including the Zeeman measurements are given in terms of two vibronic coupling and two intensity parameters. This is the first time a vibronic splitting associated with a Gamma 8 electronic state has been conclusively demonstrated.