Emission decay measurements under various excitation intensities and time-resolved absorption spectroscopy were applied to investigate the bimolecular reactions of the triplet lowest excited metal-to-ligand charge-transfer state ((MLCT)-M-3) in the neat crystals or doped crystals with energy acceptor. The rate of hopping to the nearest-neighbor site in the energy migration of (MLCT)-M-3 in [Ru(bpy)(3)](PF6)(2) was determined to be (3.5 +/- 0.5) x 10(8) s(-1) from the dependence of emission decay rates on the doping concentration of Os2+ and the rate constant of triplet-triplet (T-T) annihilation in the emission decay for the single-crystal or transparent mixed-crystal ground with KCI. The rate constants of hopping to the nearest-neighbor sites obtained for the crystals of [Ru(bpy)(3)]X-2 (X = Cl-, ClO4-, and PF6-) showed a distance dependence. The diffusion constants of triplet exciton in the crystals were also estimated. Time-resolved absorption spectroscopy revealed that T-T annihilation produced the one-electron transferred products. The rate of electron transfer between (MLCT)-M-3 in the crystal of [Ru(bpy)(3)](PF6)(2) was estimated to be greater than or equal to 5 x 10(10) s(-1) by time-resolved absorption spectroscopy.