Pressure dependence of the refractive index and electronic polarizability of LiF, MgF2 and CaF2

The pressure dependence of the refractive index of LIF, MgF2 and CaF2 was measured up to 8 GPa using an interferometric method with the diamond anvil cell. Despite the different crystalline structures, a similar increasing behavior of n(P) for the three compounds under consideration was observed, indicating that the fluorine ion should have an important role in the volume dependence of the optical properties of these materials. The respective variations of the electronic polarizabilities were determined by the Lorentz-Lorenz approach and they are represented by the following Mueller parameters: for LiF, Lambda(0) = 0.65, for MgF2, Lambda 0 = 0.71 and for CaF2, Lambda(0) = 0.55. Some empirical models found in the literature relating to the electronic polarizability and the interatomic distance, were examined but one of them adequately describe the observed behavior.