Crystal absorption spectra

Crystal absorption spectra

The wavelength or energy dependence of the attenuation of electromagnetic radiation as it passes through a crystal, due to its conversion to other forms of energy in the crystal. When atoms are grouped into an ordered array to form a crystal, their interaction with electromagnetic radiation is greatly modified. Free atoms absorb electromagnetic radiation by transitions between a few electronic states of well-defined energies, leading to absorption spectra consisting of sharp lines. In a crystal, these states are broadened into bands, and the cores of the atoms are constrained to vibrate about equilibrium positions. The ability of electromagnetic radiation to transfer energy to bands and ionic vibrations leads to broad absorption spectra that bear little resemblance to those of the free parent atoms. See Absorption of electromagnetic radiation, Atomic structure and spectra, Band theory of solids, Lattice vibrations