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Zeitschriftendaten
Format
Zeitschrift
eISSN
2255-8896
Erstveröffentlichung
18 Mar 2008
Erscheinungsweise
6 Hefte pro Jahr
Sprachen
Englisch

Suche

Volumen 55 (2018): Heft 6 (December 2018)

Zeitschriftendaten
Format
Zeitschrift
eISSN
2255-8896
Erstveröffentlichung
18 Mar 2008
Erscheinungsweise
6 Hefte pro Jahr
Sprachen
Englisch

Suche

7 Artikel
Open Access

Comparison of Luminescence in LiGaO2, Al2O3-Ga and Al2O3-Li Crystals

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 4 - 12

Zusammenfassung

Abstract

We have studied luminescence of LiGaO2, Al2O3-Ga and Al2O3-Li crystals in order to reveal the nature of luminescence centres and mechanisms in these crystals. In Al2O3-Ga presence of Ga impurities determines occurrence of the 280 nm emission band, which demonstrates intra-centre character in photoluminescence and recombination character under X-ray irradiation. In Al2O3-Li crystal lithium induced luminescence is presented with the 326 nm band, which has a recombination character. Basing on spectral similarity of the main luminescence bands in pure LiGaO2 crystal with the dopant-induced emission bands in Al2O3, and on peculiarities of the X-ray induced thermoluminescence, the adjustment of the previous luminescence interpretation is done. It is proposed that the donor-acceptor pairs with random separation distribution responsible for the 280 nm emission are represented with gallium Ga (plus an electron) and O (plus a hole) pairs, while the donor-acceptor pairs, producing the 330 nm emission band contain a lithium ion, presumably in the interstitial position Lii0, and a neighbouring oxygen ion with a caught hole.

Schlüsselwörter

  • alumina
  • donor-acceptor pairs
  • exciton
  • lithium metagallate
  • luminescence
Open Access

Influence of Pressure and Temperature on X-Ray Induced Photoreduction of Nanocrystalline CuO

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 13 - 19

Zusammenfassung

Abstract

X-ray absorption spectroscopy at the Cu K-edge is used to study X-ray induced photoreduction of copper oxide to metallic copper. Although no photoreduction has been observed in microcrystalline copper oxide, we have found that the photoreduction kinetics of nanocrystalline CuO depends on the crystallite size, temperature and pressure. The rate of photoreduction increases for smaller nanoparticles but decreases at low temperature and higher pressure.

Schlüsselwörter

  • copper oxide
  • high-pressure
  • nanocrystalline
  • radiolysis
  • x-ray absorption spectroscopy
Open Access

First-Principles Calculations of Oxygen Diffusion in Ti-Al Alloys

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 20 - 29

Zusammenfassung

Abstract

The projector augmented-wave method within the density functional theory is applied to investigate the oxygen diffusion in the intermetallic Ti-Al alloys. It is shown that the highest oxygen absorption energies in Ti-Al alloys correspond to the octahedral Ti-rich sites but the presence of aluminium in the nearest neighbours leads to a substantial decrease in the oxygen absorption energy in the alloys. The migration barriers for the oxygen diffusion between various interstices in the crystal lattice of the Ti-Al alloys are estimated. The preferred migration paths along a and c axes and limiting barriers of the oxygen diffusion in the alloys are determined. The dependence of the oxygen diffusion coefficient on Ti-Al alloy composition is discussed.

Schlüsselwörter

  • atomic diffusion
  • electronic structure
  • oxygen
  • Ti-Al alloys
Open Access

AB Initio Calculations of CUN@Graphene (0001) Nanostructures for Electrocatalytic Applications

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 30 - 34

Zusammenfassung

Abstract

Substitution of fossil-based chemical processes by the combination of electrochemical reactions driven by sources of renewable energy and parallel use of H2O and CO2 to produce carbon and hydrogen, respectively, can serve as direct synthesis of bulk chemicals and fuels. We plan to design and develop a prototype of electrochemical reactor combining cathodic CO2-reduction to ethylene and anodic H2O oxidation to hydrogen peroxide. We perform ab initio calculations on the atomistic 2D graphene-based models with attached Cu atoms foreseen for dissociation of CO2 and H2O containing complexes, electronic properties of which are described taking into account elemental electrocatalytical reaction steps. The applicability of the model nanostructures for computer simulation on electrical conductivity of charged Cun/graphene (0001) surface is also reported.

Schlüsselwörter

  • Cu-decorated graphene
  • DFT
  • electronic properties
  • ESM
Open Access

Effect of in Doping on the ZnO Powders Morphology and Microstructure Evolution of ZnO:In Ceramics as a Material for Scintillators

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 35 - 42

Zusammenfassung

Abstract

Transparent ZnO ceramics are of interest for use as material for high-efficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered cera-mics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:In ceramics microstructure is characterised by the trans-crystalline mode of fracture, faceted GBs with places of zig-zag forms and predominant distribution of In at the GBs. Such indium induced modifications of GBs promote removal of point defects and reduce PL parameter α = Idef/Iexc in comparison with the undoped ceramics. Results characterise ZnO:In cera-mics with improved GBs properties as a prospective material for scintillators.

Schlüsselwörter

  • grain boundaries
  • hot pressing sintering
  • In doped ZnO ceramics
  • photoluminescence
  • ZnO powders
Open Access

Luminescence Properties and Decay Kinetics of Mn2+ and Eu3+ Co-Dopant Ions In MgGa2O4 Ceramics

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 43 - 51

Zusammenfassung

Abstract

The MgGa2O4 ceramics co-doped with Mn2+ and Eu3+ ions were synthesized via a high-temperature solid-state reaction technique. The samples with various Eu3+ concentrations were characterised using high-resolution photoluminescence (PL) spectroscopy. The PL spectra show weak matrix emission in a blue spectral region with dominant excitation band around 380 nm. Manganese ions are highly excited deeply in UV region and exhibit emission band peaked at 502 nm. The Eu3+ ions show characteristic f-f excitation and emission lines. The energy transfer between host defects and activator ions was observed. Luminescence decay curves of Mn2+ and Eu3+ emission showed complex kinetics with both Eu3+-ion concentration and excitation wavelength changes.

Schlüsselwörter

  • energy transfer
  • europium (Eu) and manganese (Mn) ions
  • decay kinetics
  • magnesium gallate MgGaO
  • photoluminescence
Open Access

Introduction Of Energy Saving Principles: Technologies And Awareness, Latvian Experience

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 52 - 62

Zusammenfassung

Abstract

The article presents an overview of the current situation of awareness of the Latvian citizens in the field of state-of-the-art energy-saving technologies. The authors present a wide range of data obtained as a result of a survey on the attitude of residents to new technologies and readiness to follow the development trends of a smart city.

The article contains the analysis and recommendations for improving the efficiency of introducing new energy-saving and energy-efficient technologies into each household in order to create the most favourable conditions for the implementation of long-term plans for the development of smart cities in Latvia.

Schlüsselwörter

  • citizen awareness
  • efficient energy use
  • energy consumption
  • energy control and management
  • energy saving technologies
  • smart city
  • survey
7 Artikel
Open Access

Comparison of Luminescence in LiGaO2, Al2O3-Ga and Al2O3-Li Crystals

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 4 - 12

Zusammenfassung

Abstract

We have studied luminescence of LiGaO2, Al2O3-Ga and Al2O3-Li crystals in order to reveal the nature of luminescence centres and mechanisms in these crystals. In Al2O3-Ga presence of Ga impurities determines occurrence of the 280 nm emission band, which demonstrates intra-centre character in photoluminescence and recombination character under X-ray irradiation. In Al2O3-Li crystal lithium induced luminescence is presented with the 326 nm band, which has a recombination character. Basing on spectral similarity of the main luminescence bands in pure LiGaO2 crystal with the dopant-induced emission bands in Al2O3, and on peculiarities of the X-ray induced thermoluminescence, the adjustment of the previous luminescence interpretation is done. It is proposed that the donor-acceptor pairs with random separation distribution responsible for the 280 nm emission are represented with gallium Ga (plus an electron) and O (plus a hole) pairs, while the donor-acceptor pairs, producing the 330 nm emission band contain a lithium ion, presumably in the interstitial position Lii0, and a neighbouring oxygen ion with a caught hole.

Schlüsselwörter

  • alumina
  • donor-acceptor pairs
  • exciton
  • lithium metagallate
  • luminescence
Open Access

Influence of Pressure and Temperature on X-Ray Induced Photoreduction of Nanocrystalline CuO

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 13 - 19

Zusammenfassung

Abstract

X-ray absorption spectroscopy at the Cu K-edge is used to study X-ray induced photoreduction of copper oxide to metallic copper. Although no photoreduction has been observed in microcrystalline copper oxide, we have found that the photoreduction kinetics of nanocrystalline CuO depends on the crystallite size, temperature and pressure. The rate of photoreduction increases for smaller nanoparticles but decreases at low temperature and higher pressure.

Schlüsselwörter

  • copper oxide
  • high-pressure
  • nanocrystalline
  • radiolysis
  • x-ray absorption spectroscopy
Open Access

First-Principles Calculations of Oxygen Diffusion in Ti-Al Alloys

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 20 - 29

Zusammenfassung

Abstract

The projector augmented-wave method within the density functional theory is applied to investigate the oxygen diffusion in the intermetallic Ti-Al alloys. It is shown that the highest oxygen absorption energies in Ti-Al alloys correspond to the octahedral Ti-rich sites but the presence of aluminium in the nearest neighbours leads to a substantial decrease in the oxygen absorption energy in the alloys. The migration barriers for the oxygen diffusion between various interstices in the crystal lattice of the Ti-Al alloys are estimated. The preferred migration paths along a and c axes and limiting barriers of the oxygen diffusion in the alloys are determined. The dependence of the oxygen diffusion coefficient on Ti-Al alloy composition is discussed.

Schlüsselwörter

  • atomic diffusion
  • electronic structure
  • oxygen
  • Ti-Al alloys
Open Access

AB Initio Calculations of CUN@Graphene (0001) Nanostructures for Electrocatalytic Applications

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 30 - 34

Zusammenfassung

Abstract

Substitution of fossil-based chemical processes by the combination of electrochemical reactions driven by sources of renewable energy and parallel use of H2O and CO2 to produce carbon and hydrogen, respectively, can serve as direct synthesis of bulk chemicals and fuels. We plan to design and develop a prototype of electrochemical reactor combining cathodic CO2-reduction to ethylene and anodic H2O oxidation to hydrogen peroxide. We perform ab initio calculations on the atomistic 2D graphene-based models with attached Cu atoms foreseen for dissociation of CO2 and H2O containing complexes, electronic properties of which are described taking into account elemental electrocatalytical reaction steps. The applicability of the model nanostructures for computer simulation on electrical conductivity of charged Cun/graphene (0001) surface is also reported.

Schlüsselwörter

  • Cu-decorated graphene
  • DFT
  • electronic properties
  • ESM
Open Access

Effect of in Doping on the ZnO Powders Morphology and Microstructure Evolution of ZnO:In Ceramics as a Material for Scintillators

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 35 - 42

Zusammenfassung

Abstract

Transparent ZnO ceramics are of interest for use as material for high-efficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered cera-mics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:In ceramics microstructure is characterised by the trans-crystalline mode of fracture, faceted GBs with places of zig-zag forms and predominant distribution of In at the GBs. Such indium induced modifications of GBs promote removal of point defects and reduce PL parameter α = Idef/Iexc in comparison with the undoped ceramics. Results characterise ZnO:In cera-mics with improved GBs properties as a prospective material for scintillators.

Schlüsselwörter

  • grain boundaries
  • hot pressing sintering
  • In doped ZnO ceramics
  • photoluminescence
  • ZnO powders
Open Access

Luminescence Properties and Decay Kinetics of Mn2+ and Eu3+ Co-Dopant Ions In MgGa2O4 Ceramics

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 43 - 51

Zusammenfassung

Abstract

The MgGa2O4 ceramics co-doped with Mn2+ and Eu3+ ions were synthesized via a high-temperature solid-state reaction technique. The samples with various Eu3+ concentrations were characterised using high-resolution photoluminescence (PL) spectroscopy. The PL spectra show weak matrix emission in a blue spectral region with dominant excitation band around 380 nm. Manganese ions are highly excited deeply in UV region and exhibit emission band peaked at 502 nm. The Eu3+ ions show characteristic f-f excitation and emission lines. The energy transfer between host defects and activator ions was observed. Luminescence decay curves of Mn2+ and Eu3+ emission showed complex kinetics with both Eu3+-ion concentration and excitation wavelength changes.

Schlüsselwörter

  • energy transfer
  • europium (Eu) and manganese (Mn) ions
  • decay kinetics
  • magnesium gallate MgGaO
  • photoluminescence
Open Access

Introduction Of Energy Saving Principles: Technologies And Awareness, Latvian Experience

Online veröffentlicht: 25 Jan 2019
Seitenbereich: 52 - 62

Zusammenfassung

Abstract

The article presents an overview of the current situation of awareness of the Latvian citizens in the field of state-of-the-art energy-saving technologies. The authors present a wide range of data obtained as a result of a survey on the attitude of residents to new technologies and readiness to follow the development trends of a smart city.

The article contains the analysis and recommendations for improving the efficiency of introducing new energy-saving and energy-efficient technologies into each household in order to create the most favourable conditions for the implementation of long-term plans for the development of smart cities in Latvia.

Schlüsselwörter

  • citizen awareness
  • efficient energy use
  • energy consumption
  • energy control and management
  • energy saving technologies
  • smart city
  • survey

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