X-ray excited optical luminescence (XEOL) studies of CaF2 at the Ca L-3,L-2-edge

We report a study of the optical response of CaF2 specimens (crystal and po wder) with excitation photon energy tuned across the Ca L-3.2-edge. The lum inescence was in turn used to monitor the absorption across the Ca L-edge ( optical XAFS). It is found that the photoluminescence yield produces an inv erted spectrum. This observation is interpreted in terms of total absorptio n (thickness effect), the change in decay dynamics below and above the edge and the atomic origin of the luminescence. By comparing crystal and powder results, we find that the surface component of CaF2 exhibits a positive sh ift (similar to0.15 eV) relative to the bulk at the p-d resonance at the Ca L-3.2-edge. A DFT calculation has been carried out and it is in good accor d with the experiment. The implications of these results are discussed. (C) 2001 Elsevier Science BY All rights reserved.