Generation and EPR characterization of color centers at the surface of ionic oxides

The activation of the surface of high surface area alkali-earth oxides to form surface color centers is described in detail. Two methods (the radiative coloring and the additive coloring by means of vapors of low ionization energy metals) have been adopted to form surface electron excess centers of various complexity. The EPR technique is essential to describe the nature and the structural features of the paramagnetic centers. The electron rich surface quickly reacts with a variety of adsorbed molecules forming adsorbed anions and radical anions. Two examples of such reactivity are illustrated in the final part of the paper.