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 N2O, 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 N2O. 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.