Analysis of R and N₁ Center Absorption Structures in NaF

Abstract

The shape of the optical absorption structure caused by an electronic transition of a color center depends on the strength of the electron-phonon coupling parameter S. S can be interpreted as the most probable number of phonons involved in the transition. In the case of weak coupling (S « 1) only a sharp zero-phonon line occurs, whereas for strong coupling (S > 8) only a broad and smooth multiphonon band is observed. Intermediate coupling gives rise to both a zero-phonon line and a detailed multiphonon structure [l] as it can be seen in figure 2.