The photosensitization of colloidal particles of antimony-doped SnO2 by electrostatically adsorbed Ru(bpy)(3)(2+) (bpy = 2,2’-bipyridine) produced Ru(bpy)(3)(3+) and a conduction band electron (e(cb)(-)) with a quantum efficiency close to 1. The influence of the injected electron population density on the dynamics of the subsequent recombination between Ru(bpy)(3)(3+) and e(cb)(-) was investigated by nanosecond laser flash photolysis. The initial average number of Ru(bpy)(3)(3+)/e(cb)(-) pairs per particle (N-e) created by the laser pulse was varied in the range 0.03-7. The rate of recombination (k(rec)) increased nonlinearly by a factor of 250 over this range in N-e. The nonlinear dependence of k(rec) on N-e was analyzed quantitatively using two different models : (1) an electrochemical model based on the Butler-Volmer equation and (2) a model based on the Auger recombination mechanism. Both models gave satisfactory fits to the data with parameters that are physically reasonable. The Butler-Volmer equation was used to relate the rate of recombination to the overpotential driving the reaction by making the assumption that the overpotential is linearly proportional to N-e. That analysis gave values of (2.1 +/- 0.7) x 10(6) s(-1) for the intrinsic rate constant and 0.59 +/- 0.11 for the transference number, with each excess electron contributing 22 +/- 6 mV to the overpotential. In the Auger-capture model, it was assumed that an equilibrium exists between Ru(bpy)(3)(3+) and the stannic hydroxyl radical, >SnO., and that e(cb)(-) recombines with >SnO. and not directly with Ru(bpy)(3)(3+). The values of n(0) and B-1 exp(Delta E degrees/k(B)T) were found to be (1.3 +/- 0.1) x 10(19) cm(-3) and (9 +/- 1) x 10(-34) cm(6) s(-1), respectively, where n(0) is the equilibrium concentration of free electrons, B-1 is the coefficient for the conduction band-to-trap Auger transition, and Delta E degrees is the difference in reduction potentials of Ru(bpy)(3)(3+) and >SnO.. Comparison of these data to those for colloidal particles of undoped SnO2 showed that the doping of SnO2 with antimony does not significantly affect the dynamics of electron recapture by Ru(bpy)(3)(3+).