Abstract
Spectra of photoluminescence (PL) in the region of 1.5–5.5 eV, PL excitation spectra (3–22 eV), PL decay kinetics and PL temperature dependence were measured for single crystals and ceramics K3WO3F3 as well as for ceramics K3WO3F3 irradiated by fast electrons. Synchrotron radiation was used for low temperature PL experiments with time resolution. Single crystals are transparent in microwave, visible and near UV range, inter-band transition energy is Eg = 4.3 eV. In K3WO3F3, the wide band luminescence in the region of 2.5 eV with the Stokes shift of 1.5 eV with the microsecond decay kinetics is connected with luminescence of triplet self-trapped excitons (STE). This luminescence is formed by electronic transitions in [WO3F3] octahedron. Different distortion of KWOF crystal lattice is manifested in the change of the Stokes shift of the STE luminescence band. The 3.2 eV emission band in low-temperature PL spectrum with decay times of 1.8 ns and 11 ns corresponds to singlet STE luminescence. A new 2.9 eV emission band is discovered in low-temperature PL spectrum in the samples irradiated by fast electrons (E = 10 MeV, D = 160 kGy). This emission band is excited not through the intracenter mechanism but through the creation of excitons bound on the defects. It is suggested that it is F-like centers of anionic sublattice induced by the mechanism of elastic collision.
Highlights
The group of crystals based on tungstates/molybdates have been of particular interest for over a hundred years
This luminescence is formed by electronic transitions in [WO3F3] octahedron
It is suggested that it is F-like centers of anionic sublattice induced by the mechanism of elastic collision
Summary
The group of crystals based on tungstates/molybdates have been of particular interest for over a hundred years They are widely used in a great range of tasks: in laser technology, as scintillation materials in radiation safety systems, for thermal neutrons detection, double β-decay, etc. The group of oxyfluorides with general formula A3MO3F3, where A can be rubidium, cesium, or potassium and M can be tungsten, titanium, niobium or molybdenum, are attractive compounds for developing new noncentrosymmetric crystals having ferroelectric and ferroelastic properties. This is achieved due to the strong distortion of metal-(O,F) polyhedra in the crystal lattice because of different ionicity of metal-O and metal- F bonds. The luminescence spectroscopy can be a sensitive method to study the character of lattice distortion of oxyfluorides
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