The addition of small amounts of low ionization energy metals to the surface of the oxide was studied by means of electron paramagnetic resonance spectroscopy. The metals which were investigated were Mg, and the alkali metals from Li to Rb. Under the experimental conditions which were used, the added metal atoms were ionized and the electrons were trapped at the surface in the form of both 1-electron (Fs+) and 2-electron (Fs) color centers. The Fs+ paramagnetic centers which were formed were similar to those which were obtained by -irradiation or ultra-violet irradiation. The line-width and saturation properties of the electron paramagnetic resonance spectra depended upon the nature of the added metal, even though the nature of the interaction between the released electron and parent cation was unclear. A less intense line which was present in all of the spectra was attributed to sub-surface F+ centers.

E.Giamello, D.Murphy, L.Ravera, S.Coluccia, A.Zecchina: Journal of the Chemical Society - Faraday Transactions, 1994, 90[20], 3167-74