Photoluminescence of monoclinic Li3AlF6 crystals under vacuum ultraviolet and soft X-ray excitations

Abstract

Using Bridgman technique we have grown monoclinic β-LiAF crystals suitable for optical studies, performed XRD-identification and Rietveld refinement of the crystal structure and carried out a photoluminescence study upon vacuum ultraviolet (VUV) and extreme ultraviolet (XUV)-excitations, using the low-temperature (T = 7.2 K) time-resolved VUV-spectroscopy technique. The intrinsic PL emission band at 340-350 nm has been identified as due to radiative recombination of self-trapped excitons. The electronic structure parameters were determined: bandgap Eg≈12.5 eV, energy threshold for creation of unrelaxed excitons 11.8eV<En<12.5eV. The PL emission bands at 320-325 and 450 nm were attributed to luminescence caused by lattice defects. We have discovered an efficient excitation of PL emission bands in the energy range of interband transitions (Eex>13.5 eV), as well as in the energy range of core transitions at 130 eV. We have revealed UV-VUV PL emission bands at 170 and 208 nm due to defects. A reasonable assumptions about the origin of the UV-VUV bands were discussed. © 2015 Elsevier B.V. All rights reserved.