Elsevier Science 1 Journal logo A comparative study of photoemission and cross luminescence from BaF 2 V.N. Makhov a,* , M.A. Terekhin a , M. Kirm b , S.L. Molodtsov c , D.V. Vyalikh d a Lebedev Physical Institute, 119991 Moscow, Russia b Institut für Experimentalphysik der Universität Hamburg, 22761 Hamburg, Germany c Institut für Oberflächen- und Mikrostrukturphysik, TU Dresden, 01062 Dresden, Germany d Institut für Experimentalphysik, Freie Universität Berlin, 14195 Berlin, Germany Available online 25 August 2004 Abstract The photoelectron spectra of the well known fast scintillator material BaF 2 have been recorded and compared with luminescence spectra measured earlier. A comparison of cross luminescence and photoelectron spectra for BaF 2 has allowed to estimate the relaxation energy of the core (Ba 5p 3/2 ) hole during its radiative lifetime with respect to cross luminescence transition being equal to ~1.3 eV. The photoelectron spectra obtained at low temperature favors the model of the F 2p –Ba 5p 1/2 electron transition for the recently found emission band of BaF 2 at 7.6 eV. Keywords: Cross luminescence; Photoemission; Phonon broadening; Core hole relaxation; Scintillators; * Corresponding author. Tel.: +7 095 1326575; fax: +7 095 9382251; e-mail: makhov@sci.lebedev.ru 1. Introduction The nature of luminescence (so-called cross- luminescence – CL) from the well-known fast scintillator material BaF 2 is still under discussion. In accordance with simple model [1], CL in BaF 2 is due to radiative transitions of the holes from the uppermost core Ba 5p band into the valence F 2p band. It is observed after complete electronic and lattice relaxation occurring near the long-lived (τ ~ 10 -9 s) core hole. However, the processes of core hole relaxation are not yet well understood. Since the spectra of photoelectrons reflect the electronic structure of the crystal before core hole relaxation, the comparison of luminescence data with that of photoemission measurements can help to clarify the influence of relaxation effects on optical and electronic properties of the crystals. Up to now low-temperature photoemission data have been scarcely reported for most insulating ionic crystals. Due to difficulties of such measurements (e.g., surface charging effects) and moderate performance of experimental equipment formerly used, mainly data recorded at room temperature with