Color centers oxygen vacancies

The Fs+ color center in the surface of an MgO crystal is an oxygen vacancy plus ... 

It should be noted that oxygen vacancies at oxide surfaces are of major importance for the physical and chemical behavior of these systems, apart from consequences for catalytic reactivity. As examples we mention point defects at silicon dioxide [130] or the existence of color centers at MgO surfaces which are due to localized electron states at oxygen vacancy sites and have been discussed extensively in the literature [131]. 

Radiation sources including X-rays, y-rays, and ultraviolet produce preferential light absorption at color centers in glass by formation of free electrons and holes. These are trapped at a defect such a vacancy, an interstitial atom, a multivalent impurity, or a nonbridging oxygen T The types of color center induced in siliea, soda-lime-silica, borate, and phosphate glasses are elucidated by optical and electron spin resonance studies of irradiated samples. Table 1 summarizes composition variables and reaction types that induce damage. 

F center (FC) Color center defect sites (oxygen vacancies) existing on oxide surfaces. 

F centers in alkali halides, which result from heating in alkali vapor. An F center in metal halides consists of a halide ion vacancy that has trapped an electron. This process creates additional energy levels between the valence band and the conduction band. A similar situation is found in MgO heated in Mg vapor the F center consists of two electrons trapped at an oxygen vacancy. F centers are one example of so-called color centers. There are other types of possible color centers in ionic materials involving electrons and holes. (See Section 11.9 F is Farben.)... 

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