X-ray excited optical luminescence (XEOL) studies of CaF2 at the Ca L3,2-edge

In this article we review correlation effects in solids derived from electron energy-loss spectroscopic studies of valence band excitations carried out in transmission. In particular, we focus on `simpleʹ alkali metals, quasi one-dimensional metals [(TaSe4)2I], low-dimensional undoped model cuprates (Li2CuO2, Sr2CuO3, SrCuO2 and Sr2CuO2Cl2), high-TC superconductors (Bi2Sr2CaCu2O8) and the vanadate ladder compounds (V2O5 and NaV2O5).