Influence of Cobalt Doping on the Photogenerated Holes in ZnO Nanoparticles

The efficient cobalt doping of zinc oxide nanoparticles grown by chemical method, with Co 2+ substituting the Zn 2+ cations, is proved by electron spin resonance spectroscopy for cobalt concentration from 0.01% to 1.00%. The gradual killing of the usual core‐defect signal ( g ≈ 1.96) as the Co concentration is increased prevents its ionization by optical excitation from X 0 to X − , thus inhibiting the corresponding hole releasing. Consequently, the methyl radical is no longer generated on the nanoparticles surface by the photo‐Kolbe reaction . It is thus confirmed that the hole involved in the dissociation of surface acetate actually comes from the optically excited core‐defect g = 1.96, and that the number of these defects can be tuned by some very small amount of cobalt impurities.