Electronic, optical and luminescent properties of PbFCl single crystal

The first-principles calculation of energy band structure and density of states of the PbFCl crystal based on the plane waves and pseudopotential method in the frame of the generalized gradient approximation (GGA) were performed. Further, calculation with the GW approximation was used to correct the bandgap. The so-called GW approximation represents the lowest expansion of the self-energy, Sigma, equal to the Green function G times the screened Coulomb interaction W. The calculated result shows that the direct bandgap is located at the Z point in the Brillouin zone with the gap of 3.5 eV in the GGA frame and 5.0 eV after GW correction. X-ray photoemission spectroscopy for the valence band (VB-XPS) was carried out to compare with the calculated density of states in the valence band, suggesting that the calculated result is in agreement with the experimental result. The reflection, excitation and emission spectra were measured using a synchrotron radiation light source in the energy region of 4-9.5 eV. The absorption and emission of the cation exciton was observed at 5.0 and 3.8 eV, respectively. The components of Pb 6p states and Pb 6s states located at the bottom of the conduction band and the top of the valence band, respectively, prove the possibility of the cation exciton of Pb2+.Violet band emission peaking at 3.1 eV was also observed, which may be due to the self-trapped exciton or the Pb2+, ion close to the Schottky-like defect.