Low-temperature luminescence of ScF3 single crystals under excitation by VUV synchrotron radiation

The work was supported by the Latvian Science Council grant LZP-2018/2-0358. The research leading to this result has also been supported by the project CALIPSO plus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. The author is grateful to K. Chernenko (MAX IV Laboratory, Lund University) for his assistance during beamtime experiments and to A. I. Popov for the fruitful discussions. V.P. also acknowledges Valsts pētījumu programma “Augstas enerģijas fizika un paātrinātāju tehnoloģijas” (Projekta Nr. VPP-IZM-CERN-2020/1-0002). REFERENCESPhotoluminescence and excitation spectra of ScF3 single crystals have been measured under vacuum ultraviolet excitations utilizing undulator synchrotron radiation from 1.5 GeV storage ring of MAX IV synchrotron. The emission peak at 280 nm is explained as emission band of self-trapped excitons in ScF3. This emission is quenched at 50 K and activation energy of thermal quenching was obtained. The excitation spectrum in vacuum ultraviolet spectral range exhibits that the luminescence of self-trapped excitons effectively occurs under direct excitation in the excitonic absorption band, whereas under higher energies this excitation is strongly suppressed, however, multiplication of electronic excitation processes have been successfully identified. ---- / / / ---- This is the preprint version of the following article: V. Pankratova, J. Purans, V. Pankratov, Low-temperature luminescence of ScF3 single crystals under excitation by VUV synchrotron radiation, Low Temperature Physics, 46, 1196 (2020), DOI https://doi.org/10.1063/10.0002473, which has been published in final form at https://aip.scitation.org/doi/10.1063/10.0002473. This article may be used for non-commercial purposes in accordance with American Institute of Physics terms and conditions for sharing and self-archiving.Latvian Science Council grant LZP-2018/2-0358; CALIPSO plus under the Grant Agreement 730872; Projekta Nr. VPP-IZM-CERN-2020/1-0002; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

Study of phase composition, photocatalytic activity, and photoluminescence of TiO2 with Eu additive produced by the extraction-pyrolytic method

The Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2. The work was also partially supported by the LZP grant 2020/2-0074. R. Burve has been supported by the project “Synthesis of nanostructured materials based on titanium dioxide and tin dioxide and investigation of their physicochemical properties” Nr. MP-2019/7, for strengthening scientific personnel capacity 2019/2020 at the Riga Technical University. Authors are grateful to Dr. K. Šmits for the microscopic measurements and SEM images.Due to the unique properties and wide array of applications of nanocrystalline materials based on titanium dioxide, the study of new synthesis approaches remains relevant. In this study, within the framework of the extraction-pyrolytic method (EPM), we suggest using the mixtures of Ti- and Eu-containing organic extracts based on valeric acid as precursors for fabrication of nanocrystalline TiO2-based powders with different Eu content: 0.5 mol%, 5 mol%, and 50 mol%. The thermal behavior of individual metal-containing extracts and their mixture was studied by thermogravimetric analysis and differential scanning calorimetry (TGA–DSC). To characterize phase composition and morphology of produced materials, the X-ray diffraction (XRD) method and scanning electron microscopy (SEM) were used. Photoluminescence properties of Eu3+ ions in TiO2 nanocrystals have been studied. Photocatalytic activity of produced materials was tested in the reaction of methylene blue (MB) oxidation under UV-VIS irradiation. Correlation between synthesis parameters (Eu content and pyrolysis temperature) and properties of produced materials (phase composition, photoluminescence and photocatalytic properties) has been studied. It was demonstrated that the presence of a Eu-containing extract in the precursor mixture increases the anatase-to-rutile phase transformation temperature. The highest efficiency (degradation degree of MB 96%) was shown by TiO2 powder consisting of mixed polymorphs, anatase (main phase) and rutile, with 0.5 mol% Eu additive. It was shown that anatase-to-rutile phase transformation in TiO2:Eu3+ nanoparticles manifests in a degradation of Eu3+ luminescence intensity.--//-- Published under CC BY-NC-ND 4.0 licence.The Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2; LZP grant 2020/2-0074; R. Burve has been supported by the project “Synthesis of nanostructured materials based on titanium dioxide and tin dioxide and investigation of their physicochemical properties” Nr. MP-2019/7, for strengthening scientific personnel capacity 2019/2020 at the Riga Technical University

Evolution of free volumes in polycrystalline baga2o4 ceramics doped with eu3+ ions

H.K. and Y.K. would like to thank A. Ingram for assistance in PAL experiments. The authors thank E.A. Kotomin and M. Brik for the many useful discussions. The research was (partly) performed in the Institute of Solid State Physics, University of Latvia ISSP UL. ISSP UL as the Center of Excellence is supported through the Framework Program for European universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project.BaGa2O4 ceramics doped with Eu3+ ions (1, 3 and 4 mol.%) were obtained by solid-phase sintering. The phase composition and microstructural features of ceramics were investigated using X-ray diffraction and scanning electron microscopy in comparison with energy-dispersive methods. Here, it is shown that undoped and Eu3+-doped BaGa2O4 ceramics are characterized by a developed structure of grains, grain boundaries and pores. Additional phases are mainly localized near grain boundaries creating additional defects. The evolution of defect-related extended free volumes in BaGa2O4 ceramics due to the increase in the content of Eu3+ ions was studied using the positron annihilation lifetime spectroscopy technique. It is established that the increase in the number of Eu3+ ions in the basic BaGa2O4 matrix leads to the agglomeration of free-volume defects with their subsequent fragmentation. The presence of Eu3+ ions results in the expansion of nanosized pores and an increase in their number with their future fragmentation. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Published under the CC BY 4.0 license.This work was supported by the Ministry of Education and Science of Ukraine (project for young researchers No. 0119U100435) for H.K and Y.K.; the National Research Foundation of Ukraine (project 2020.02/0217) for I.K. and H.K. as well as by the Latvian research council via the Latvian National Research Program under the topic “High-Energy Physics and Accelerator Technologies”, Agreement No: VPP-IZM-CERN-2020/1-0002, for V.P. and A.I.P; ISSP UL as the Center of Excellence is supported through the Framework Program for European universities Union Horizon 2020, H2020-WIDESPREAD-01–2016–2017-TeamingPhase2 under Grant Agreement No. 739508, CAMART2 project

Luminescence properties and time-resolved spectroscopy of rare-earth doped SrMoO4 single crystals

The work of V. Pankratova was supported by the financial support of Scientific Research Project for Students and Young Researchers (SJZ/2020/05) realized at Institute of Solid State Physics, University of Latvia. The Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.Luminescence properties of nominally pure and doped with Eu3+ and Pr3+ ions SrMoO4 single crystals grown by the Czochralski method have been studied. Thermal quenching of intrinsic emission of pure and doped SrMoO4 single crystals has been observed, as well as a correlation of thermal quenching activation energies with rare-earth ion concentration has been observed. Tunable laser was used to study time-resolved luminescence in a range from 10 K to room temperature. The effect of dopant nature and concentration on intrinsic emission and decay kinetics has been elucidated. --//-- Viktorija Pankratova, Elizaveta E. Dunaeva, Irina S. Voronina, Anna P. Kozlova, Roman Shendrik, Vladimir Pankratov, Luminescence properties and time-resolved spectroscopy of rare-earth doped SrMoO4 single crystals, Optical Materials: X, Volume 15, 2022, 100169, ISSN 2590-1478, https://doi.org/10.1016/j.omx.2022.100169. Article published under the CC BY-NC-ND licence.Scientific Research Project for Students and Young Researchers (SJZ/2020/05); the Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Study of luminescence properties of co-doped Gd3(Ga,Al)5O12:Ce crystals

Darbā tika pētītas Gd3Ga3Al2O12:Ce un ar divvērtīgajiem (Mg2+, Ca2+) un četrvērtīgajiem (Zr4+, Ti4+) metālu joniem koaktivēto Gd3Ga3Al2O12:Ce absorbcijas un luminiscences īpašības, ka arī tika izmērītas luminiscences dzišanas kinētikas un to temperatūras atkarības. Darbā tika piedāvāti Gd3Ga3Al2O12:Ce luminiscences mehānismi pētāmajos ierosinājumos.Absorption and luminescence properties of Gd3Ga3Al2O12:Ce and co-doped with divalent (Mg2+, Ca2+) and tetravalent (Zr4+, Ti4+) ions Gd3Ga3Al2O12:Ce crystals have been studied as well as time-resolved luminescence and its temperature dependence. In this study luminescence mechanisms of Gd3Ga3Al2O12:Ce have been proposed

Luminescence and Vacuum Ultraviolet Excitation Spectroscopy of Nanophosphors under Synchrotron Irradiation

Vacuum ultraviolet (VUV) excitation spectroscopy under synchrotron irradiation is a powerful tool for the investigation of luminescence properties of wide bandgap nanocrystalline phosphor materials. The advantages of selective excitation in a wide spectral range present the possibility to explore the different aspects of luminescence processes in nanophosphors separately. It is shown that direct excitations of emission centers in wide bandgap materials need excitations in VUV spectral range and such excitations provide valuable information about f–f, f–d transitions, defects, and excitonic transitions in wide bandgap nanophosphors. It is also demonstrated that size-dependent luminescence properties of nanophosphors are significant if the electron thermalization length becomes larger than the size of the nanoparticles. In this case, multiplication of electronic excitations processes well-known in bulk materials are suppressed strongly in nanophosphors

Crystal Growth and Spectroscopy of Yb²⁺-Doped CsI Single Crystal

The single crystals of CsI-Yb2+ were grown, and their spectroscopic studies were conducted. The observed luminescence in CsI-Yb2+ is due to 5d–4f transitions in Yb2+ ions. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were found. The excitation spectra of Yb2+ luminescence bands were obtained in the range of 3–45 eV. The mechanism of charge compensation of Yb2+ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity–vacancy complexes in two different positions. The charge compensation of Yb2+ occurs via cation vacancies in the nearest-neighbor and next-nearest-neighbor positions.The Yb2+ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors

Time-resolved luminescence and excitation spectroscopy of Co-doped Gd3Ga3Al2O12 scintillating crystals

The work of Viktorija Pankratova was supported by the Latvian Science Council grant LZP-2018/2-0358. Vladimir Pankratov gratefully acknowledges the financial support from the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST «MISiS» (Grant No. К3-2018-021). The research leading to this result has also been supported by the project CALIPSO plus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART 2. The optical absorption spectrum at low temperature reported in this paper were measured on the equipment of the Central of Collective Use “Isotope-geochemical studies” of the Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences. Authors are grateful to A.I. Popov for the fruitful discussions.Cerium doped Gd3Ga3Al2O12 (GGAG) single crystals as well as GGAG:Ce single crystals co-doped by divalent (Mg2+, Ca2+) and tetravalent (Zr4+, Ti4+) ions have been studied by means of time-resolved luminescence as well as the excitation luminescence spectroscopy in vacuum ultraviolet (VUV) and soft X-ray (XUV) spectral range. Tunable laser excitation was applied for time-resolved experiments in order to obtain luminescence decay curves under excitations in Ce3+, Gd3+ and excitonic absorption bands. The influence of the co-dopant ions on the Ce3+ luminescence decay kinetics is elucidated. The fastest luminescence decay was observed for the Mg2+ co-doped crystals under any excitation below bandgap energy indicating the perturbation of the 5d states of Ce3+ by Mg2+ ions. Synchrotron radiation was utilized for the luminescence excitation in the energy range from 4.5 to 800 eV. Special attention was paid to the analysis of Ce3+ excitation spectra in VUV and XUV spectral range where multiplication of electronic excitation (MEE) processes occur. Our results demonstrated that GGAG:Ce single crystals co-doped by Mg2+ ions as well as the GGAG:Ce crystal annealed in vacuum reveal the most efficient excitation of Ce3+ emission in VUV-XUV excitation range. The role of intrinsic defects in MEE processes in the co-doped as well as in the annealed GGAG:Ce single crystals is discussed.Horizon 2020 Framework Programme CALIPSO Plus under the Grant Agreement 730872; Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement 739508; Science Council of Latvia LZP-2018/2-0358; Horizon 2020 Framework Programme project CAMART², Ministry of Science and Higher Education of the Russian Federation К3-2018-021

Unveiling the role of carbonate in nickel-based plasmonic core@shell hybrid nanostructure for photocatalytic water splitting

Abstract Though carbonates are known for several decades, their role in sun-light driven photocatalysis is still hidden. Herein, carbonate boosted solar water splitting in nickel-based plasmonic hybrid nanostructures is disclosed for the first time via in-situ experiments and density-functional theory (DFT)-based calculations. Ni@NiO/NiCO₃ core@shell (shell consisting of crystalline NiO and amorphous NiCO₃) nanostructure with varying size and compositions are studied for hydrogen production. The visible light absorption at ∼470 nm excludes the possibility of NiO as an active photocatalyst, emphasizing plasmon driven H₂ evolution. Under white light irradiation, higher hydrogen yield of ∼80 µmol/g/h for vacuum annealed sample over pristine (∼50 µmol/g/h) complements the spectroscopic data and DFT results, uncovering amorphous NiCO₃ as an active site for H₂ absorption due to its unique electronic structure. This conclusion also supports the time-resolved photoluminescence results, indicating that the plasmonic electrons originating from Ni are transferred to NiCO₃ via NiO. The H₂ evolution rate can further be enhanced and tuned by the incorporation of NiO between Ni and NiCO₃