Photochemical kinetics of ultrasmall semiconductor particles in solution: effect of size on the quantum yield of electron transfer

Abstract

The quantum yield ({Upsilon}) of photoinduced electron transfer from ultrasmall CdS and In{sub 2}S{sub 3} semiconductor particles to surface-adsorbed viologen molecules was measured as a function of the density of adsorbed photons in the particles. At a lower photon density, {Upsilon} tends to become constant, and, in the case of In{sub 2}S{sub 3}, the smaller particles show a lower {Upsilon}. In order to explain these observations, a kinetic model of a two-dimensional ladder was proposed. The ratio of the rate constant for electron-hole pair recombination (k{sub r}) to that for photoinduced electron transfer (k{sub e}) was estimated together with the radius of the particles by adopting the model. The ratio k{sub e}/k{sub r} for CdS was found to decrease by less than a tenth with the change in the particle radii from 2 to 4 nm.