Optical emission and excitation spectra of [Rh(bpy-h 8 ) 3 ] 3 + , [Rh(bpy-h 8 ) 2 (bpy-d 8 )] 3 + , [Rh(bpy-d 8 ) 3 ] 3 + , [Pt(bpy-h 8 ) 2 ] 2 + , [Pt(bpy-h 8 )(bpy-d 8 )] 2 + , [Pt(bpy-d 8 ) 2 ] 2 + , [Ru(bpy-h 8 ) 3 ] 2 + , [Ru(bpy-h 8 ) 2 (bpy-d 8 )] 2 + , and [Ru(bpy-d 8 ) 3 ] 2 + are discussed. A series of trends--also including [Os(bpy) 3 ] 2 + --is uncovered. These trends, which are connected with an increase in metal-d or MLCT character in the lowest triplet states, can for instance be seen in transition energies, emission lifetimes, zero-field splittings, rates of spin-lattice relaxation, vibronic satellite structures, and changes of nuclear equilibrium positions on excitation. Moreover, the compounds investigated are also appropriate for consideration of the concept of dual emission , the relation between MLCT character and covalency, as well as the current models of localization/delocalization. In particular, a comparison of the properties of [Rh(bpy) 3 ] 3 + - and [Ru(bpy) 3 ] 2 + -doped [Zn(bpy) 3 ](ClO 4 ) 2 provides illustrative and very strong evidence for covalent delocalization in the lowest excited states of [Ru(bpy) 3 ] 2 + , while ligand-centered localization is found in the states of [Rh(bpy) 3 ] 3 + . Misinterpretations might occur if the aggregation effects of the chromophores are not taken into account.