What is color center of alkali halides?

Color centers in alkali halides are defects in the crystal lattice that result from the absence of an alkali metal atom or halide ion, leading to the creation of an electron trap or vacancy. These defects can absorb specific wavelengths of light, resulting in the coloration of the material. Common examples include the F-center, which forms when an electron occupies a vacancy left by a halide ion, imparting a characteristic color to the crystal. The presence and type of color centers can significantly influence the optical properties of the alkali halide.