Complexes of the type [Ru(X)(R)(CO)(2)(alpha-diimine)], where X = halide or Mn(CO)(5), R = alkyl, and alpha-diimine = 2,2’-bipyridine (bpy), pyridine-2-carbaldehyde N-isopropylimine (iPr-PyCa), and N,N’-diisopropyl-1,4-diaza-1,3-butadiene (iPr-DAB), were found to be emissive in 2-MeTHF glass at 77 K. The emission quantum yields are in the 1.3 x 10(-2) to 7 x 10(-5) range, whereas the lifetimes vary between 15 and 0.3 mu s, depending on the ligands. The room temperature emission in fluid solution was investigated for the photostable [Ru(X)(R)(CO)(2)(alpha-diimine)] complexes (X = halide; R = Me, Et). Emission quantum yields and lifetimes were found to vary in the ranges 1.8 x 10(-3) - 10(-5) and 177-40 ns, respectively, according to the nature of X and R. The solution emission of [Ru(I)(Me) (CO)(2)(iPr-DAB)I is quenched either by energy transfer (anthracene) or by electron transfer with both electron accepters (N,N’-dimethyl-4,4’-bpy cation or N-methyl-4,4’-bpy cation) or donors (amines). Emission properties of this complex are only slightly solvent dependent. In 2-MeTHF solution, both emission quantum yield and lifetime increase with decreasing temperature. Importantly, the nature of the emission (i.e., energy, lifetime, quantum yield, rate constants of both radiative and nonradiative decays) was found to be strongly dependent on the alpha-diimine ligand used and, especially, on the coligands X and R. However, the nonradiative rate constant does not regularly increase with decreasing emission energy as predicted by the "energy-gap law". Instead, the emission properties were found to reflect the character of the emissive excited state that changes from metal-to-alpha-diimine charge transfer (MLCT) for X = Cl to halide to alpha-diimine charge transfer (XLCT) for X = I and sigma-bonding to alpha-diimine (sigma(b) pi*) for X = Mn(CO)(5).