PHOTOCHEMICAL KINETICS OF ULTRASMALL SEMICONDUCTOR PARTICLES IN SOLUTION - EFFECT OF SIZE ON THE QUANTUM YIELD OF ELECTRON-TRANSFER

The quantum yield (Φ) of photoinduced electron transfer from ultrasmall CdS and In2S3 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, Φ tends to become constant, and, in the case of In2S3, the smaller particles show a lower Φ. 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 (kr) to that for photoinduced electron transfer (ke) was estimated together with the radius of the particles by adopting the model. The ratio ke/kr for CdS was found to decrease by less than a tenth with the change in the particle radii from 2 to 4 nm. © 1990 American Chemical Society.