In [Ru(bpy)3][NaCr(ox)3], ox = C2O42-, bpy = 2,2'-bipyridine, three different mechanisms for energy migration within the 2E state of [Cr(ox)3]3- were distinguished: a phonon assisted process at T > 4.2 K, and resonant and quasi resonant processes at 1.5 K. In NaMg[Al1-xCrx(ox)3]·9(H2O/D2O), persistent spectral holes could not only be burnt by direct irradiation into the 3A2→2E spin-flip transition but also via resonant energy transfer. In [Rh1 xCrx(bpy)3][NaMIII1-yCry(ox)3]ClO4, M = Rh, Al, the energy transfer from [Cr(ox)3]3- to [Cr(bpy)3]3+ has two contributions, due to super-exchange and electric dipole-dipole interactions, respectively. External pressure affects the two contributions differently, demonstrating the power of pressure experiments for elucidating the mechanisms of excitation energy transfer processes. In the mixed crystal series [Zn1-xRux(bpy)3][NaCr(ox)3], five distinct sites are created for each Cr3+ ion according to the binomial distribution of the four closest M2+ positions around a given Cr3+ ion. These were evidenced by high-resolution absorption spectroscopy.