The phenomenon of self-trapping of excitons is established mechanism of transformation of absorbe... more The phenomenon of self-trapping of excitons is established mechanism of transformation of absorbed energy in wide-gap crystals. Model objects for wide-bandgap oxides (Eg> 9 eV) with lowered crystal symmetry are binary oxides BeO, α-Al2O3, and α-SiO2, which are of considerable importance for both fundamental and applied physics. Self-trapped excitons (STEs) were discovered and investigated in all mentioned crystals. STEs we discovered in complex oxides Al2BeO4, Be2SiO4 and Be3Al2Si6O18 too [1]. The crystal lattices of the complex oxides Al2BeO4, Be2SiO4 exhibit motifs (weakly distorted BeO4 and SiO4 tetrahedra and AlO6 octahedra) that are typical of the parent crystal-forming compounds, namely, beryllium, aluminum, and silicon oxides. As a result, the scenarios of formation and the structure of the relaxed electronic excitations (associated with local lattice fragments) may turn out to be similar for binary and complex oxides. At the same time, structural units of Be3Al2Si6O18 are...
Praseodymium-ions doped luminescent materials are recently being actively investigated due to dem... more Praseodymium-ions doped luminescent materials are recently being actively investigated due to demonstration of fast interconfigurational 5d-4f optical transitions. These transitions appear, when a sufficiently strong crystal field shifts the lowest 4f 1 5d 1 excited state below the 1 S 0 level. Perfect timing and rather high emission output make researches of praseodymium impurity luminescence relevant. In this report we examine spectroscopic luminescent properties of some samples under excitation of X-ray synchrotron radiation.
We report experimental study of luminescent properties of modern scintillation material SrI 2 :Eu... more We report experimental study of luminescent properties of modern scintillation material SrI 2 :Eu 2+ carried out over the temperature range from 9 to 450 K by the means of the ultraviolet and vacuum ultraviolet spectroscopy with a time resolution. Photoluminescence of the Eu 2+ ions at 2.85 eV was studied under both the intracenter and interband excitations, including an X-ray excitation. The bandgap of the SrI 2 crystal has been estimated on the basis of the obtained results. In the temperature range below 100 K the intrinsic luminescence at 3.4 eV was revealed and this emission band was assigned by its properties to the luminescence of selftrapped anionic excitons in SrI 2. The pronounced manifestation of the effect of multiplication of electronic excitations was revealed in the energy range above 2E g .
We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO singl... more We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO single crystals with incident photon energies in the vicinity of the Be 1s absorption edge. The x-ray emission spectra show that at the Be 1s photoabsorption edge the lattice relaxation processes in the excitation site take place already on the timescale of the radiative decay of the core excitation. Comparison of the x-ray emission and the luminescence spectra indicates that the maximum energy loss of the process of lattice relaxation during the decay of inner-shell holes is similar to the loss that occurs in the self-trapping process of valence excitons. The possible decay channels of core excitations have been discussed and the mechanism for the creation of 5.2 eV luminescence at the photoabsorption resonances has been suggested.
h i g h l i g h t s < During crystal growth of Pr-doped LiBaAlF 6 , Ba 3 Al 2 F 12 was formed as ... more h i g h l i g h t s < During crystal growth of Pr-doped LiBaAlF 6 , Ba 3 Al 2 F 12 was formed as a by-product. < Microspectroscopy techniques allowed to study the two crystal phases separately. < The Pr 3þ concentration was found to be much higher in Ba 3 Al 2 F 12. < The possible reasons of Ba 3 Al 2 F 12 formation while growth of Pr 3þ :LiBaAlF 6 are discussed.
IOP Conference Series: Materials Science and Engineering, 2010
The experimental study of relaxation of anion and cation excitons at the selective VUV-(valence) ... more The experimental study of relaxation of anion and cation excitons at the selective VUV-(valence) and soft X-ray (inner-shell) excitations for binary BeO crystal and multicomponent oxide crystals Be 2 SiO 4 , Al 2 Be 3 Si 6 O 18 and Y 2 SiO 5 is presented. Results show that the relaxation during the timescale of decay of short-living anion and cation excitations leads to creation of self-trapped excitons at the corresponding low-symmetry (tetrahedral) local structural units of crystalline lattice. This can be caused by increase of dynamical instability of such a local structural units (in comparison with high symmetry ones), which facilitates selftrapping processes in these systems.
This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF ... more This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF 5 single crystals belonging to the I 4 1 /a space group. The presence of four non-equivalent Sr 2+ sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce 3+ luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O 2− impurity ion substituting for the F − ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF 5 ; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce 3+ 5d states. This method allows 'regular' unperturbed Ce 3+ centers with selected Sr 2+ sites to be assigned.
The phenomenon of self-trapping of excitons is established mechanism of transformation of absorbe... more The phenomenon of self-trapping of excitons is established mechanism of transformation of absorbed energy in wide-gap crystals. Model objects for wide-bandgap oxides (Eg> 9 eV) with lowered crystal symmetry are binary oxides BeO, α-Al2O3, and α-SiO2, which are of considerable importance for both fundamental and applied physics. Self-trapped excitons (STEs) were discovered and investigated in all mentioned crystals. STEs we discovered in complex oxides Al2BeO4, Be2SiO4 and Be3Al2Si6O18 too [1]. The crystal lattices of the complex oxides Al2BeO4, Be2SiO4 exhibit motifs (weakly distorted BeO4 and SiO4 tetrahedra and AlO6 octahedra) that are typical of the parent crystal-forming compounds, namely, beryllium, aluminum, and silicon oxides. As a result, the scenarios of formation and the structure of the relaxed electronic excitations (associated with local lattice fragments) may turn out to be similar for binary and complex oxides. At the same time, structural units of Be3Al2Si6O18 are...
Praseodymium-ions doped luminescent materials are recently being actively investigated due to dem... more Praseodymium-ions doped luminescent materials are recently being actively investigated due to demonstration of fast interconfigurational 5d-4f optical transitions. These transitions appear, when a sufficiently strong crystal field shifts the lowest 4f 1 5d 1 excited state below the 1 S 0 level. Perfect timing and rather high emission output make researches of praseodymium impurity luminescence relevant. In this report we examine spectroscopic luminescent properties of some samples under excitation of X-ray synchrotron radiation.
We report experimental study of luminescent properties of modern scintillation material SrI 2 :Eu... more We report experimental study of luminescent properties of modern scintillation material SrI 2 :Eu 2+ carried out over the temperature range from 9 to 450 K by the means of the ultraviolet and vacuum ultraviolet spectroscopy with a time resolution. Photoluminescence of the Eu 2+ ions at 2.85 eV was studied under both the intracenter and interband excitations, including an X-ray excitation. The bandgap of the SrI 2 crystal has been estimated on the basis of the obtained results. In the temperature range below 100 K the intrinsic luminescence at 3.4 eV was revealed and this emission band was assigned by its properties to the luminescence of selftrapped anionic excitons in SrI 2. The pronounced manifestation of the effect of multiplication of electronic excitations was revealed in the energy range above 2E g .
We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO singl... more We carried out a combined study of UV-VUV luminescence and resonant x-ray emission from BeO single crystals with incident photon energies in the vicinity of the Be 1s absorption edge. The x-ray emission spectra show that at the Be 1s photoabsorption edge the lattice relaxation processes in the excitation site take place already on the timescale of the radiative decay of the core excitation. Comparison of the x-ray emission and the luminescence spectra indicates that the maximum energy loss of the process of lattice relaxation during the decay of inner-shell holes is similar to the loss that occurs in the self-trapping process of valence excitons. The possible decay channels of core excitations have been discussed and the mechanism for the creation of 5.2 eV luminescence at the photoabsorption resonances has been suggested.
h i g h l i g h t s < During crystal growth of Pr-doped LiBaAlF 6 , Ba 3 Al 2 F 12 was formed as ... more h i g h l i g h t s < During crystal growth of Pr-doped LiBaAlF 6 , Ba 3 Al 2 F 12 was formed as a by-product. < Microspectroscopy techniques allowed to study the two crystal phases separately. < The Pr 3þ concentration was found to be much higher in Ba 3 Al 2 F 12. < The possible reasons of Ba 3 Al 2 F 12 formation while growth of Pr 3þ :LiBaAlF 6 are discussed.
IOP Conference Series: Materials Science and Engineering, 2010
The experimental study of relaxation of anion and cation excitons at the selective VUV-(valence) ... more The experimental study of relaxation of anion and cation excitons at the selective VUV-(valence) and soft X-ray (inner-shell) excitations for binary BeO crystal and multicomponent oxide crystals Be 2 SiO 4 , Al 2 Be 3 Si 6 O 18 and Y 2 SiO 5 is presented. Results show that the relaxation during the timescale of decay of short-living anion and cation excitations leads to creation of self-trapped excitons at the corresponding low-symmetry (tetrahedral) local structural units of crystalline lattice. This can be caused by increase of dynamical instability of such a local structural units (in comparison with high symmetry ones), which facilitates selftrapping processes in these systems.
This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF ... more This research is focused on the 4f-5d transitions in Ce 3+ centers doped into tetragonal β-SrAlF 5 single crystals belonging to the I 4 1 /a space group. The presence of four non-equivalent Sr 2+ sites in this compound leads to the appearance of three spectroscopically non-equivalent Ce 3+ luminescence centers, which can be well distinguished using a time-resolved laser spectroscopy technique. All 4f-5d transitions have slightly varying excitation and emission energies with characteristic probabilities resulting in several decay times that can be determined experimentally. One of these centers experiences strong perturbation due to a defect nearby, probably the O 2− impurity ion substituting for the F − ion and acting as a charge compensator as well. Identification of these photoluminescence centers is performed using crystal field calculations. The crystal field parameters are calculated for two identified centers using the structural data for SrAlF 5 ; diagonalization of the crystal field Hamiltonian results in obtaining the splitting of the Ce 3+ 5d states. This method allows 'regular' unperturbed Ce 3+ centers with selected Sr 2+ sites to be assigned.
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Papers by V. Pustovarov