F-centre
Quick Summary
A color center is a defect in a solid where an atom is missing from its regular position, and an electron is associated with this empty space. This defect absorbs specific colors of light, giving the solid its characteristic hue.1
The F-center, derived from the German word for "color," is a well-understood type of color center. It forms when a negatively charged ion is absent from an ionic solid, and an electron occupies this vacancy. This trapped electron can only absorb certain colors of light. For instance, F-centers in sodium chloride absorb blue light, resulting in a yellow-orange color. Solids without color centers can still be colored if impurity atoms or other light-absorbing structures are present.1
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