Energy transfer by exciton-polarons in RbMnF3

Energy transfer in RbMnF3 was studied by time-resolved spectroscopy of the 4T1g-exciton luminescence. The threefold orbital degeneracy of the 4T1g-state is lifted by a Jahn-Teller coupling to eg-modes. The JT-effect leaves an orientational degeneracy of distorted MnF6-octahedra, which is lifted by application of uniaxial stress. The dynamics of exciton and trap luminescence after pulse excitation was investigated with and without stress. It was found that stress reduces the excitonic transfer rate considerably. The most striking effect was obtained with [110]-stress which produced a very slow nonexponential decay of the exciton luminescence. This behavior was interpreted as evidence for [110]-stress induced 2-dimensional energy transfer.