A NOVEL TRAPPED ELECTRON CENTER ON SODIUM VAPOR DOPED MAGNESIUM-OXIDE

When thermally activated MgO is exposed to low levels of Na metal vapors, surface F-s(+) color centers are generated. For higher amounts of added metal a paramagnetic species is formed whose electron paramagnetic resonance spectrum is characterized by a quartet of lines which have different line widths and intensities. This spectrum has been assigned to a novel center constituted by the association of a partially ionized sodium atom and a suitable electron trap at the solid surface. This species can be written as Na delta(+)(trap)(delta-) where the total spin density on the Na is about 0.26. The peculiar spectral features have been interpreted in terms of both surface heterogeneity and g and A anisotropy.