@bourdillon] in the fundamental absorption region and in the core-level excitation range. In the same decade reflection spectra of $CdF_{2}$ have been determined in comparison with those of $SrF_{2}$,[@bourdillon] while UPS and XPS spectra of $CdF_{2}$ and $SrF_{2}$ have appeared in the literature in 1980.[@raisin] Also $\beta$-$PbF_{2}$ and $CdF_{2}$ mixed crystals absorption coefficients have been reported by spectrophotometry measurements.[@kosacki]

Various theoretical methods have been applied to study either the ground state or the excited states of the fluorite compounds. The energy bands and reflectance spectra of $CaF_{2}$ and $CdF_{2}$ have been determined within a combined tight-binding and pseudopotential method.[@albert] Mixed crystals of $CaF_{2}$, $SrF_{2}$, $CdF_{2}$, $\beta $-$PbF_{2}$ have been studied with respect to their electronic energy bands and density of states (DOS) within the linear muffin-in orbital (LMTO) method.[@kudrnovsky] Linear and non-linear optical properties of the cubic insulators $CaF_{2}$, $SrF_{2}$, $CdF_{2}$, $BaF_{2}$ and other compounds have been determined by first-principles orthogonalized linear combination of atomic orbitals (OLCAO).[@ching] Point defect studies in $CdF_{2}$ have been performed within the plane wave pseudopotential (PW-PP) method.[@mattila] With respect to one-particle and two-particle electronic properties and energy band gaps, state-of-the-art techniques have been applied until now only to $CaF_{2}$. In fact, electronic band structures of 