The luminescence behavior of 10 homometallic (Os2+) and heterometallic (Os2+/Ru2+) polynuclear metal complexes containing 2,3-dpp and/or 2,5-dpp as bridging ligands and bpy and/or biq as terminal ligands has been investigated (dpp = bis(2-pyridyl)pyrazine; bpy = 2,2’-bipyridine; biq = 2,2’-biquinoline). The nuclearity of the investigated compounds varies from 2 to 10. Each compound may be considered as a supramolecular species constituted by an assembly of distinct mononuclear components. All the examined compounds exhibit a luminescence band in the 850-1000-nm spectral region (rigid matrix, 90 K), which can be assigned to "triplet" metal-to-ligand charge-transfer levels localized on Os-containing components. Correlations among energies of the emission bands, oxidation potentials, compositions of the metal-based components, and their positions in the supramolecular array allow an unequivocal identification of the components responsible for the observed luminescence. For the Ru2+/Os2+ mixed-metal compounds, only an Os-based luminescence is observed. Exoergonic electronic energy transfer along a row of components arranged in an ’energy cascade’ pattern is 100% efficient. The results obtained elucidate the role played by intercomponent energy transfer in polynuclear metal complexes and may help in designing supramolecular structures where the pattern of energy migration is synthetically controlled.