Vacancies and Electron Deficient Surface Anions on the Surface of MgO Nanoparticles

In the course of surface defect characterization on MgO nanoparticles three different types of O - species were observed by electron paramagnetic resonance (EPR) spectroscopy. They are a result of UV excitation under high-vacuum conditions/in O 2 atmosphere or of surface color center bleaching by N 2 O, respectively. On the other hand, the O - species induce homolytic H 2 splitting which was evidenced for the first time by infrared (IR) spectroscopy. The resulting products are a so far unknown IR active OH group and an uncharged surface mobile H atom. The latter one acts as a reducing agent for either one of two types of anion vacancies which are transformed into EPR active surface color centers F S + . They are fundamentally different from the classical F S + (H) center obtained in predominant abundance by UV irradiation of MgO in H 2 atmosphere. One of the above-mentioned O - species is created by bleaching of F S + (H) by N 2 O. The respective EPR signal is exactly the same as that obtained by thermal decomposition of a surface ozonide species which was produced by UV induced O 2 chemisorption at a single cation vacancy. Thus, one may conclude that the classical F S + (H) center has to be related to a cation−anion divacancy.