Search results for "purity"
showing 10 items of 356 documents
Quasiclassical free energy of superconductors : Disorder-driven first-order phase transition in superconductor/ferromagnetic-insulator bilayers
2020
In the seminal work by G. Eilenberger, Z. Phys. 214, 195 (1968), a closed-form expression for the free energy of inhomogeneous spin-singlet superconductor in terms of quasiclassical propagators has been suggested. However, deriving this expression and generalizing it for superconductors or superfluids with general matrix structure, e.g., spin-triplet correlations, has remained problematic. Starting from the Luttinger-Ward formulation, we discuss here the general solution. Besides ordinary superconductors with various scattering mechanisms, the obtained free-energy functional can be used for systems, such as superfluid $^{3}\mathrm{He}$ and superconducting systems with spatially inhomogeneou…
Photoluminescence of Al2O3 nanopowders of different phases
2012
Abstract Photoluminescence was studied in six samples of Al2O3 nanopowders produced from the same initial material by calcination in the 800–1400 °C temperature range. At temperature around 1200 °C phase transition in aluminum oxide lattice occurs; the samples produced at temperatures up to 1200 °C contain mainly δ phase, while those obtained at 1400 °C contain pure α phase. In all studied samples of nominally pure aluminum oxide nanopowders photoluminescence is determined by trace level concentrations of uncontrolled impurities. It was found that phase transition is accompanied with modification of the emission spectrum: a broad band centered around 750 nm presumably ascribed to emission o…
Quantum chemical modelling of perovskite solid solutions
2000
In line with our previous study (Eglitis R I et al 1998 J. Phys.: Condens. Matter 10 6271) for a single Nb impurity and Nb clusters in KTaO3 we present here the results of calculations for a series of perovskite KNbx Ta 1−x O3 (KTN) solid solutions (x = 0, 0.125, 0.25, 0.75, and 1). The quantum chemical method of the intermediate neglect of the differential overlap (INDO) combined with the large unit cell (LUC) periodic model is used. According to the INDO calculations, Nb impurity becomes off-centre in KTaO3 already at the lowest studied Nb concentration. Its off-centre displacement is in a good agreement with XAFS measurements. We compare our results with previous FP-LMTO calculations. Pe…
Comparison of the electrochemical properties of hematite thin films prepared by spray pyrolysis and electrodeposition
2015
Abstract This manuscript reports differences between the photoelectrochemical (PEC) activity of hematite (α-Fe 2 O 3 ) photoanodes produced by cathodic electrodeposition (ED) and spray pyrolysis (SP) methods. Both methods yield nanostructured polycrystalline α-Fe 2 O 3 thin films without additional impurity phases. However, α-Fe 2 O 3 produced by ED is characterised to have better crystallinity and higher porosity, which was confirmed by XRD and SEM analysis. Owing to this, α-Fe 2 O 3 obtained by ED generates a photocurrent that is 2.5 times higher than α-Fe 2 O 3 thin films prepared by SP. Furthermore, the influence of the thickness of the α-Fe 2 O 3 thin films on the flat-band potential p…
Energy transport in silica to oxygen-deficient luminescence centers. Comparison with other luminescence centers in silica and α-quartz
2004
Abstract The transport of energy absorbed by silica glass to oxygen-deficient luminescence centers in was studied in the range of intrinsic absorption from 8.2 up to 35 eV. The low efficiency of exciting those luminescence centers by transport of energy could not be ascribed merely to carrier scattering by the disordered structure. Other centers (Cu + , for example) could be excited in such process with sufficiently high efficiency, albeit lower than that in crystals. The low efficiency of interaction of oxygen deficient centers with quasi-particles is attributed to isolation of these centers in clusters and the non-radiative annihilation of the quasi-particles on the boundaries of these cl…
Excitation and emission spectra of LaInO3-based solid solutions doped with Sm3+, Sb3+
2017
Abstract X-ray analysis showed that all the ceramic samples of La 1- x Sm x InO 3 (0.010≤ x ≤0.025) solid solutions were single-phased but the samples of nominal composition of LaIn 0.98 Sb 0.02 O 3 , La 0.98 Sm 0.02 In 0.98 Sb 0.02 O 3 contained a small amount of impurity phase of LaSbO 3 -based solid solutions. It was established that La 0.98 Sm 0.02 InO 3 solid solution under the excitation of 275 nm and 320 nm exhibits the strongest photoluminescence among La 1- x Sm x InO 3 solid solutions with 0.010≤ x ≤0.025. Photoluminescence bands located in wavelength ranges of 550–580 nm, 585–625 nm and 630–680 nm exhibit 2–3 clear maxima each. According to the locations of these maxima we calcul…
Optically detected magnetic resonance investigation of a luminescent oxygen–vacancy complex in Mn-doped LiBaF3
2006
The structure of an oxygen-related luminescence centre in manganese-doped LiBaF 3 was investigated by means of photoluminescence (PL) and PL-detected electron paramagnetic resonance. At 20 K an oxygen-related complex shows two luminescence bands peaking at about 430 and 475 nm, when excited at 220 nm. These bands can be attributed to an excited triplet state (S = 1) of an oxygen-vacancy complex with the z axis of the fine structure tensor parallel to the (110) direction. This complex is believed to be next to a Mn 2+ impurity on a Ba 2+ site and can be described as an oxygen on a fluorine lattice site with a nearest fluorine vacancy along the (110) direction.
Photosensitivity of silica glass with germanium studied by photoinduced of thermally stimulated luminescence with vacuum ultraviolet radiation
2003
Photosensitivity of the germanium-doped silica was studied through kinetics of recombination of the created defects in isothermal and thermally stimulated luminescence (TSL) regimes. The main observed luminescence contains bands mainly due to Ge oxygen deficient center. The maximum of photosensitivity corresponds to the high-energy part of the 7.6 eV band. The growth of TSL intensity is almost linear for the case of excitation through monochromatic light and growth with saturation in the case of excitation with white light. The efficiency of formation of TSL peaks increases with an increase of the temperature. The result was explained as multi-step process of photochemical dissociation and …
Luminescence and Raman Detection of Molecular Cl2 and ClClO Molecules in Amorphous SiO2 Matrix
2017
The support from the Latvian Research Program project IMIS 2 (L.S., K.S.) and Latvian Science Council Grant 302/2012 (A.S.) is acknowledged. K.K. was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology. H.H. was supported by the MEXT Element Strategy Initiative to form research cores.
Temperature and impurity concentration effects on upconversion luminescence in LaInO3 doped with Er3+
2016
In this paper a novel method for synthesis of LaInO3:Er3+ is reported and upconversion luminescence properties of the synthesized material at different temperatures (9–300 K) are studied. The samples were prepared by co-precipitation and subsequent heat treatment of lanthanum, indium and erbium hydroxides. It is shown that the excitation at 980 nm leads to a strong green upconversion luminescence in the material. At the concentrations above 0.1 mol. % of Er3+ the energy transfer upconversion mechanism of the luminescence becomes evident. Further increase of Er3+ content in the material leads to higher red-to-green upconversion luminescence intensity ratio. The mechanisms responsible for the…