Luminescence centers in bismuth-containing oxytungstate ceramics

Abstract

We have studied the photoexcitation and luminescence spectra of Bi 2 WO 6 , Y 2 WO 6 and Y 2 WO 6 :Bi ceramics. We used the Alentsev-Fock method to decompose the spectra into elementary components. The emission bands with maximum at 2.93 eV in the luminescence spectrum of Bi 2 WO 6 , 3.02 eV in the luminescence spectrum of Y 2 WO 6 , and 2.95 eV in the luminescence spectrum of Y 2 WO 6 :Bi are assigned to luminescence of self-localized Frenkel excitons. The bands with maxima at 2.35 eV and 1.90 eV in the spectrum of Bi 2 WO 6 , 2.25 eV and 1.75 eV in the spectrum of Y 2 WO 6 , and 2.35 eV and 1.85 eV in the spectrum of Y 2 WO 6 :Bi are connected with oxygen vacancies.Introduction. The problems of personal, industrial, and reactor dosimetry and also the use of nuclear physics methods in geophysics, medicine, and other fields of science and technology are responsible for the increasingly rigorous and diverse demands made on solid-state scintillators. Recently studies of tungstate compounds have become significantly widespread [1,2]. Tungstates are among a group of inorganic crystal phosphors whose luminescence is generally connected with excitation of elements of the crystal lattice itself. Among tungstate systems, some interest has been stimulated in oxytungstate compounds of lanthanides and also Y and Bi [3,4]. The spectral properties and kinetics of tungstates are considerably affected by defects which arise both in the crystal lattice and also as a consequence of deviation of the crystal composition from stoichiometric [1]. Taking into account the fact that the nature of the optically active centers determining the luminescent properties of these phosphors mainly remains unclear, study of oxytungstate systems in different states, such as single crystalline, ceramic, and thin-film states, seems rather important. The aim of this work was to study the luminescence of the ceramics Bi 2 WO 6 , Y 2 WO 6 , and Y 2 WO 6 :Bi.Experimental Procedure. Ceramic samples of the oxytungstates Bi 2 WO 6 , Y 2 WO 6 and Y 2 WO 6 :Bi were obtained by solid-phase synthesis, by annealing in air a premixed and pressed mixture of oxides of stoichiometric composition. The annealing temperature of 1000 o C-1100 o C corresponded to a temperature for the formation of Me 2 WO 6 (Me = Bi) in the oxide system Me 2 O 3 -WO 3 [5,6]. The content of the activator Bi 3+ in the starting material was 0.5 mole %. The x-ray excitation source was an URS-55 apparatus (Russia) with a copper anticathode (40 kW, 2-12 µA). The luminescence with laser excitation was studied in pulsed excitation mode using an LGI-21 laser with wavelength of the exciting light equal to 337.1 nm (3.68 eV). The photoexcitation source was a DksEl-1000 lamp with a ZMR-3 monochromator. Luminescence of the samples was analyzed using an SF-4A monochromator and detected by an FÉU-51 photomultiplier, the signal from which was fed through an amplifier to a PDA-1 recorder (Ukraine). The luminescence spectra were corrected for the spectral selectivity of the photodetector.Results and Disc...