2. Optical concepts relating to the transparency of ceramics

2.1 Notion of optical transparency window

The range or "window" of optical transparency of a given material depends essentially on its composition, crystal structure and the nature of the defects (structural or microstructural) it contains. The lower limit, generally located in the near-UV range, is determined by the energy jump or "gap" (noted ΔE _G ) between the atomic orbitals of the conduction and valence bands of a given material. Electromagnetic radiation whose wavelength is less than this gap (E _photon > ΔE _G ) is absorbed by electrons that are excited towards the conduction band levels. The high limit in the infrared is determined by the...