0000000000246310
AUTHOR
V. Korsaks
Nitrogen vacancy type defect luminescence of AlN nanopowder
Abstract Native luminescent defects were investigated in AlN nanopowder (NP) using spectral characterization methods. Photoluminescence and its excitation spectra were studied within a wide temperature range from 8K up to room temperature. It was found that in AlN NP a broad luminescence band appears within a blue spectral region consisting of at least two sub-bands at 415 nm and 390 nm, which can be related to presence of two different but in the same time similar defect types. These luminescent defects are located either inside the bulk material or on the material surface. Interaction of the surface defects with environmental oxygen was found resulting in quenching of the blue luminescenc…
Defect-induced blue luminescence of hexagonal boron nitride
Abstract Native defect-induced photoluminescence around 400 nm (blue luminescence - BL) was studied in hBN materials with different size and various origins. The following spectral characterizations were used: spectra of luminescence and its excitation, luminescence dependence on temperature, luminescence kinetics, optically stimulated luminescence and infrared absorption. It was found, that the BL is characteristic for all these materials, which were studied. The BL forms a wide, asymmetric and phonon-assisted emission band at 380 nm. This luminescence can be excited either through the exciton processes, or with light from two defect-induced excitation bands at 340 nm and 265 nm. It was fo…
Photo-electrical and transport properties of hydrothermal ZnO
We performed the studies of optical, photoelectric, and transport properties of a hydrothermal bulk n-type ZnO crystal by using the contactless optical techniques: photoluminescence, light-induced transient grating, and differential reflectivity. Optical studies revealed bound exciton and defect-related transitions between the donor states (at ∼60 meV and ∼240 meV below the conduction band) and the deep acceptor states (at 0.52 eV above the valence band). The acceptor state was ascribed to VZn, and its thermal activation energy of 0.43 eV was determined. A low value of carrier diffusion coefficient (∼0.1 cm2/s) at low excitations and temperatures up to 800 K was attributed to impact the rec…
Hexagonal boron nitride luminescence dependent on vacuum level and surrounding gases
Abstract Gas sensing properties of hBN powder bulk and nanosize were studied. It was demonstrated that for hBN powders with grain sizes of 70 nm, 1 μm and 5 μm the native defect-induced luminescence observed at 400 nm under 265 nm light excitation and room temperature is sensitive to oxygen gas reducing luminescence intensity. The highest value of luminescence intensity is reached when sample is in vacuum. Results obtained allow conclusion that the hBN powder is prospective for sensing of oxygen gas. Some material properties such as dependence of luminescence intensity on vacuum level and pumping time, ratio of luminescence intensity when sample is in vacuum and gas, its dependence on mater…
Anisotropic photoluminescence of nonpolar ZnO epilayers and ZnO/Zn1 −xMgxO multiple quantum wells grown on LiGaO2 substrate
Ministry of Science and Technology, Taiwan (104-2221-E-110-012-MY3, 107-2221-E-110-004-MY3); National Natural Science Foundation of China (51602309, U1605245).
Spectral characterization of bulk and nanostructured aluminum nitride
Spectral characteristics including photoluminescence (PL) spectra and its excitation spectra for different AlN materials (AlN ceramics, macro size powder and nanostructured forms such as nanopowder, nanorods and nanotips) were investigated at room temperature. Besides the well known UV-blue (around 400 nm) and red (600 nm) luminescence, the 480 nm band was also observed as an asymmetric long-wavelength shoulder of the UV-blue PL band. This band can be related to the luminescence of some kind of surface defects, probably also including the oxygen-related defects. The mechanisms of recombination luminescence and excitation of the UV-blue luminescence caused by the oxygen-related defects were …
Photocatalytic activity of non-stoichiometric ZnFe2O4under visible light irradiation
Nanostructured zinc ferrites with different excess iron contents (ZnFe2+zO4, where z = 0.00, 0.05, 0.10 and 0.15) have been synthesized using the sol–gel auto-combustion method. The effect of excess iron on the structural, optical and visible light photocatalytic activity of zinc ferrite samples has been investigated. X-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), x-ray magnetic circular dichroism (XMCD), Brunauer–Emmett–Teller theory, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (UV–Vis) and photoluminescence spectroscopy were used to characterize the synthesized non-stoichiometric ZnFe2O4 powders. The XRD patterns demonstrated that the samples con…
Luminescence properties of LiGaO2 crystal
The study was supported by the Latvia-Lithuania-Taiwan research project “Nonpolar ZnO thin films: growth-related structural and optical properties” (Latvia: LV-LT-TW/2016/5 , Lithuania: TAP LLT 02/2014 , Taiwan: MOST 103-2923-M-110-001-MY3 ).
Optical properties of lithium gallium oxide
Abstract The optical dielectric function tensor of orthorhombic single-crystal LiGaO 2 was determined for polarizations along a , b , and c crystal-axis in the photon energy range from 0.04 eV to 6.5 eV by the generalized spectroscopic ellipsometry. In the far-infrared spectral range from 12.4 meV to 40 meV, the dielectric function was determined from conventional polarized transmittance and polarized reflectance measurements. Lineshape analysis of the dielectric function tensor major components allowed for a determination of the long-wavelength optical phonon characteristics, refractive indices dispersion, and parameters of interband and excitonic optical transitions.
Influence of vinyltriethoxysilane concentration on structural and luminescent characteristics of cerium doped yttrium based silicate phosphors
Abstract Cerium doped yttrium silicates phosphors (YSO:Ce) were prepared by gel combustion using vinyltriethoxysilane (VTEOS) as silicon sources along with aspartic acid as fuel and yttrium-cerium nitrate as oxidizer. The study presents the influence of VTEOS amount in the synthesis mixture on the structural and luminescent characteristics of silicate phosphors. The understanding of precursor׳s decomposition was achieved on the basis of thermal analysis in association with gas evolved analysis. XRD, FTIR and XPS were used to reveal the structural changes that occur with VTEOS molar amount variation from 1 to 3 mol. It was found that the main crystalline phase was X2-Y 2 SiO 5 . The luminesc…
Spectral and kinetic characteristics of pyroelectric luminescence in LiGaO2
Abstract Pyroelectric luminescence was observed in noncentrosymmetrical crystal LiGaO2 with the direct band gap around 6 eV. For the first time spectral and kinetic characteristics of pyroelectric luminescence were obtained. The temporal structure of the PEL signal was determined as a sequence of pulses with duration not longer than several nanoseconds. This allowed proposing of the luminescence mechanism: in vacuum conditions in LiGaO2 crystal pyroelectric luminescence occurs inside the sample due to radiative recombination of electrons with the positively charged intrinsic luminescence centres.