The impurity core valence luminescence (CVL) of Rb0.82Cs0.18Cl mixed crystals was monitored at the Cl K- and Rb L3-absorption edges using X-ray excited optical luminescence (XEOL) technique. It is found that XEOL spectrum at the chlorine K-edge is identical with the Cl K-absorption spectrum of pure RbCl. It is demonstrated that investigation of the XEOL yield spectra of impurity CVL can deliver essential site sensitive information about the structure of the CVL emission centre.