An absorption edge is a specific wavelength or energy level at which a material starts to absorb photons, leading to a significant increase in absorption coefficient. It typically occurs in materials such as semiconductors, insulators, and certain elemental or compound materials. The absorption edge is significant in various contexts: 1. **Semiconductors**: In semiconductors, the absorption edge corresponds to the energy gap (bandgap) between the valence band and the conduction band.
Articles by others on the same topic
An absorption edge is an abrupt change in photon absorption as incident photon energy crosses an electronic excitation threshold. For inner-shell photoionization, a new vacancy-production channel opens near the shell's binding energy. This threshold concerns incident energy; a Characteristic X-ray concerns a subsequent difference of atomic energies. They are different observations. Barkla's lecture explicitly treats characteristic emission as requiring a critical excitation condition, while discussing characteristic radiation separately from scattering.[ref]
Characteristic Röntgen Radiation by Charles Glover Barkla. Nobel Lectures, Physics 1901–1921; Barkla, Characteristic Röntgen radiation, printed p. 395, PDF p. 135: shorter-wavelength excitation and critical condition
In the stipulated X-ray fluorescence model, the K threshold is , whereas the K lines are and . An absorber made of a different material could have its own absorption edge between those line energies, preferentially removing the upper line. Actual near-edge structure and attenuation values require material data; the following deliberately chosen coefficients are not such data.