Photoluminescence and the Nature of Surface Sites

Coordination Ciihmistry and STArai.iZATioN of Surfacf, Anions and Cations in no Cast oi- Unsupportf.d Atkaunf, Earth and Zirconium Oxidfs 

There is strong evidence that ions in positions of low coordination (LC) at oxide surfaces have unusual electron donor properties. At this point it is useful to define what is meant by ions of low coordination. 

A typical coordination of the ion in the bulk lattice can be defined by the number of nearest neighbor ions of the opposite sign for the octahedrally coordinated alkaline earth oxides this number is 6. Ions of lower coordination are designated by the subscript LC to denote a low coordination. For 

The results characterizing MgO can be summarized as follows Adsorption of electron-acceptor molecules such as NB in vacuo onto a MgO powder prepared by thermal outgassing in vacuo exhibited an EPR signal that could be assigned to NB or the corresponding negative radical ions A. The concentration of the radicals was monitored as a function of the outgassing temperature of MgO in vacuo. Twm maxima were found in the 

Measurements of the spin concentration indicate that relatively high concentrations of A (equivalent to about 0.5% of the surface oxide ions) can be formed. Other sources of electrons such as TMI impurities may be ruled out because of their low concentrations. The formation of NB radical ions was also found to be much greater on MgO smoke that had been etched by water vapor than on normal MgO smoke (65, 72). Etching of the regular cubic particles composing MgO smoke led to a considerable increase in the lowest coordination surface oxide ions, i.c., O c- 

---