F-center

English thumb|220px|F-center in an NaCl crystal Etymology F (from German Farbe, from Farbzentrum) + center. Noun en crystallography A type of point defect in crystals where an anion (negative ion) vacancy in the lattice traps one or more electrons, creating a localized site that absorbs specific wavelengths of light, thereby coloring the typically transparent material (e.g. the yellowing of NaCl due to trapped electrons in missing chloride sites); defects that form due to irradiation (e.g. X-rays), heat, or alkali metal vapor treatment and can be removed by annealing. en Farbe center color center. en point defect