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=7.2K) time-resolved VUV-spectroscopy technique. The intrinsic PL emission band at 340–350nm has been identified as due to radiative recombination of self-trapped excitons. The electronic structure parameters were determined: bandgap Eg≈12.5eV, energy threshold for creation of unrelaxed excitons 11.8eV<En<12.5eV. The PL emission bands at 320–325 and 450nm 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>13.5eV), as well as in the energy range of core transitions at 130eV. We have revealed UV–VUV PL emission bands at 170 and 208nm due to defects. A reasonable assumptions about the origin of the UV–VUV bands were discussed.
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