Jahn-Teller coupling in the excited level of the F+centre in CaO: uniaxial stress effect

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Abstract
Linear dichroism has been measured in both the absorption and emission bands of the F+ centre in CaO under uniaxial stress. In order to analyse the emission results the method of moments is generalized to transitions taking place from an orbitally degenerate level. It is shown that this analysis allows a direct determination of the Ham reduction factors. It is verified that absorption and emission measurements lead to the same values for these factors K(E)=0.40, K(T2)=0.39. These values when compared with K(T1)=0.02 clearly show that the excited level is subject to the special kind of Jahn-Teller effect described by O'Brien (1971). Detailed analysis of the polarized spectra allows the determination of the symmetry of the modes of vibration giving rise to the vibronic structure and clearly shows that modes in a large range of energies are involved in the Jahn-Teller coupling.