7 - The Physics and Chemistry of Color: the 15 Mechanisms

Abstract

Color is perceived when the wavelengths constituting white light are absorbed, reflected, refracted, scattered, or diffracted by matter on their way to our eyes; alternatively, a non-white distribution of light may be emitted by some system. Fifteen causes of color originating in a variety of physical and chemical mechanisms can be sorted into five groups. Vibrations and simple excitations produce the colors of incandescence; gas excitations, vibrations, and rotations; ligand field effects produce color in transition metal compounds and as impurities in otherwise colorless substances; molecular orbital effects produce the colors of organic compounds, and of charge transfer compounds; energy band effects give the colors seen in metals and alloys, in semiconductors, in doped semiconductors, and in color centers; geometrical and physical optic effects produce colors from dispersive refraction, scattering, interference, and diffraction. In these 15 mechanisms, it is the interaction of light with the electrons in matter that produces color.