A model for spectral diffusion induced by resonant energy migration applied to the 4A2→2E transition of Cr3+ in [Cr(ox)3]3− (ox=C2O42−)

In the 3D oxalate networks [NaCr(ox)3][Rh(bpy)3]ClO4 and [NaCr(ox)3][Ru(bpy)3] (ox=oxalate, bpy=2,2′-bipyridine) three different types of energy migration within the 4A2→2E transition can be identified. One is a resonant process between spectral members spaced by the ground-state zero-field splitting (ZFS). This leads to the sequential appearance of additional sharp lines spaced by the ground-state ZFS in the fluorescence line narrowing spectrum across the inhomogeneous line. The second one is a quasi-resonant process between spectral neighbours and manifests itself by rapid spectral diffusion. The third one is the well-known phonon-assisted process setting in at higher temperature.