In the 3D network [Rh(bpy)(3)][NaCr(ox)(3)]ClO4 (ox = oxalate, bpy = 2,2'-bipyridine) phonon-assisted as well as resonant energy migration within the R-1 line of the (4)A(2) -> E-2 transition of Cr3+ has been identified. The latter is dominant below 4.2 K, and in a fluorescence line narrowing spectrum, it manifests itself in a multiline C pattern across the inhomogeneous line width with spacings corresponding to the zero-field splitting of the (4)A(2) ground State (Milos, M. Kairouani, S.; Rabaste, S.; Hauser, A. Coord. Chem. Rev. 2008, 252, 2540). H. Riesen demonstrated efficient spectral hole burning within the R-1 line of Cr3+ doped at low concentrations into partially deuterated NaMg[Al(ox)(3)]center dot 9H(2)O (Riesen, H. Coord. Chem. Rev. 2006 250, 1737). Here we show that at higher Cr3+ concentrations in the same host, both phenomena call be observed simultaneously, the resonant energy migration thus creating in additional series of persistent side holes.