The samples of the C-Y2O3 compounds doped with photoluminescence activators Tb3+ and Eu3+ with the concentration of 3 and 3.5 mol

Samples of Gd2O3:Tb(3 mol%) phosphor were obtained by sol-gel method followed by annealing at 800oC and 1200oC in air. At high annealing temperature, the intensities of the main emission bands 484 and 541 nm increase, but the ratio of the intensities of these emission bands to their satellites 493 and 549 nm respectively decreases. Based on the analysis of X-ray diffractometry, radiation spectra, far-infrared and Raman spectroscopy, as well as diffuse reflectance spectroscopy, we established: the increase in the crystallinity of the samples with a significant reduction of the lattice strain stress at elevated annealing temperatures, changes in the structure of the bandgap with degenerated acceptor and donor zones of impurities Tb4+ and Tb3+ respectively. The diffuse reflection spectra of the sample after annealing at 800oC under optical excitation showed a direct charge transition through the bandgap with Eg = 2.56 eV. After elevated annealing temperature the concentration of Tb4+ ions decreases due to reduction to Tb3+. As a result, at low excitation energies the degeneracy of the acceptor zone is still preserved and there is a direct transition of charges through the bandgap with Eg = 2.55 eV. At high excitation energies the degeneracy of the acceptor zone is removed and there is a direct transition through the bandgap with Eg = 3.39 eV. These effects are accompanied by a relatively large increase in the emission intensity of the satellites, especially at the 549 nm.

The Y2O3@SmS composite with a core-shell nanostructure was synthesized using the polyol sol-gel method. For the first time the oxide powder Y2O3@Sm2O3 precursor was obtained from Y2O3 and Sm(acac)(3) solutions in diatomic alcohol ethylene glycol C2H4(OH)(2) by the precipitation of urea (NH2)(2)CO. Next, the precursor was heated to 633 K in the sulfidation atmosphere and annealed at 1423 K to obtain the final Y2O3@SmS composite. It was found that Y2O3@SmS compound contains a small amount of Sm2S3 impurity phase due to the diffusion process of the sulfur atoms of SmS2 phase to the sample surface, followed by a transition of SmS2 to Sm2S3 phase. The short-range order was analyzed using both Raman and XPS spectroscopy. The obtained data showed that Y2O3@SmS composite has a core-shell structure. Y2O3 phase was considered as a core, and the SmS phase - as the shell. Using the SEM and HRTEM data it was found that synthesized sample contained a significant amount of the core-shell nanoparticles with the average size of similar to 200 nm. The Seebeck coefficient was of -40 mu V/K at 430 K. The obtained value was two times greater compared to SmS@Y2O2S and (YO2S)-O-2@SmS core-shell compounds studied previously.

— We report the preparation of SmS@Y 2 O 2 S and Y 2 O 2 S@SmS ceramics with a core–shell nanostructure via 1123-K sulfidation of rare-earth oxides prepared by the sol–gel method, involving precipitation from starting metal nitrate solutions with NH 4 OH as a precipitant, followed by annealing of the resultant sulfide phases in an induction furnace at 1473 K. Using X-ray diffraction and scanning electron microscopy data, we have evaluated the average crystallite size in the materials and examined the morphology of the constituent phases in them. In addition, the short-range order in the coexisting nanostructures has been analyzed in detail using Raman spectroscopy and X-ray photoelectron spectroscopy data.

The lattice disorder of different architecture and dimensions influence on the thermoelectric properties (Seebeck coefficient S, resistivity rho, total thermal conductivity kappa tot ,, power factor S 2 /rho, figure of merit ZT) of the polycrystalline ternary sulfides MTS 3 was studied. The high-temperature misfit layered compounds (MS) z NbS 2 (MS is Gd x Dy 1-x S solid solutions) were chosen as objects of the study. The variation of gadolinium concentration along the series x=0.0, 0.1, 0.2, 0.5, 1.0 allowed one to alter the short-range and the long-range order of the crystal lattice and to study their effect on thermoelectric parameters of (Gd x Dy 1-x S) z NbS 2 . At low concentration of x=0.1 the crystallite size increases, cause the deformation stresses decrease and, thereby, leads to an abnormal changes of S, rho, kappa tot values and ZT decrease. An increase of the gadolinium concentration (x=0.2-0.5) alters the electronic structure and the interatomic bonding character of the incommensurate subsystems [Gd x Dy 1-x S] and [NbS 2 ]. In this case, S and rho values remains practically unaffected, while the thermal conductivity value decreases by 40% and ZT increases by 2 times. The nature of this phenomenon and the anisotropy of the thermoelectric properties were discussed. Keywords:: misfit layers compounds, thermoelectric properties, lattice disorder, solid solution, crystallite boundaries.

Samples of Gd 2 O 3 : Tb(3 mol%) phosphor were obtained by sol-gel method followed by annealing at 800 o C and 1200 o C in air. At high annealing temperature, the intensities of the main emission bands 484 and 541 nm increase, but the ratio of the intensities of these emission bands to their satellites 493 and 549 nm respectively decreases. Based on the analysis of X-ray diffractometry, emission spectra, far-infrared and Raman spectroscopy, as well as diffuse reflectance spectroscopy, we established: the increase in the crystallinity of the samples with a significant reduction of the lattice strain stress at elevated annealing temperatures, changes in the structure of the bandgap with degenerated acceptor and donor zones of impurities Tb 4+ and Tb 3+ respectively. The diffuse reflection spectra of the sample after annealing at 800 o C under optical excitation showed a direct charge transition through the bandgap with E g =2.56 eV. After elevated annealing temperature the concentration of Tb 4+ ions decreases due to reduction to Tb 3+ . As a result, at low excitation energies the degeneracy of the acceptor zone is still preserved and there is a direct transition of charges through the bandgap with E g =2.55 eV. At high excitation energies the degeneracy of the acceptor zone is removed and there is a direct transition through the bandgap with E g =3.39 eV. These effects are accompanied by a relatively large increase in the emission intensity of the satellites, especially at the 549 nm. Keywords: Gd oxide, Tb 3+ + photoluminescence spectra, far infrared and Raman spectroscopy spectra, structure of the bandgape, distribution of Tb 3+ and Tb 4+ in cation sublattice.

Samples of Gd2O3:Tb(3 mol%) phosphor were obtained by sol-gel method followed by annealing at 800oC and 1200oC in air. At high annealing temperature, the intensities of the main emission bands 484 and 541 nm increase, but the ratio of the intensities of these emission bands to their satellites 493 and 549 nm respectively decreases. Based on the analysis of X-ray diffractometry, radiation spectra, far-infrared and Raman spectroscopy, as well as diffuse reflectance spectroscopy, we established: the increase in the crystallinity of the samples with a significant reduction of the lattice strain stress at elevated annealing temperatures, changes in the structure of the bandgap with degenerated acceptor and donor zones of impurities Tb4+ and Tb3+ respectively. The diffuse reflection spectra of the sample after annealing at 800oC under optical excitation showed a direct charge transition through the bandgap with Eg = 2.56 eV. After elevated annealing temperature the concentration of Tb4+ ions decreases due to reduction to Tb3+. As a result, at low excitation energies the degeneracy of the acceptor zone is still preserved and there is a direct transition of charges through the bandgap with Eg = 2.55 eV. At high excitation energies the degeneracy of the acceptor zone is removed and there is a direct transition through the bandgap with Eg = 3.39 eV. These effects are accompanied by a relatively large increase in the emission intensity of the satellites, especially at the 549 nm.

The lattice disorder of different architecture and dimensions influence on the thermoelectric properties (Seebeck coefficient S, resistivity , total thermal conductivity κtot, power factor S2/, figure of merit ZT) of the polycrystalline ternary sulfides MTS3 was studied. The high-temperature misfit layered compounds (MS)zNbS2 (MS is GdxDy1-xS solid solutions) were chosen as objects of the study. The variation of gadolinium concentration along the series x = 0.0, 0.1, 0.2, 0.5, 1.0 allowed one to alter the short-range and the long-range order of the crystal lattice and to study their effect on thermoelectric parameters of (GdxDy1-xS)zNbS2. At low concentration of x = 0.1 the crystallite size increases, cause the deformation stresses decrease and, thereby, leads to an abnormal changes of S, , κtot values and ZT decrease. An increase of the gadolinium concentration (x = 0.2–0.5) alters the electronic structure and the interatomic bonding character of the incommensurate subsystems (GdxDy1-xS) and NbS2. In this case, S and  values remains practically unaffected, while the thermal conductivity value decreases by 40% and ZT increases by 2 times. The nature of this phenomenon and the anisotropy of the thermoelectric properties were discussed.

Luminophores Gd2O2S : Tb(3-7 mol.%), obtained through the stage of sol-gel formation of Gd2O3 : Tb precursors with their subsequent sulfidation in sulfur vapor with LiF flux at 700oC, showed high luminescence efficiency. The characterization of the obtained samples by a set of physicochemical methods established that an increase in the concentration of the Tb3+ activator leads to its specific distribution: over gadolinium vacancies (VGd)''', by replacing Gd3+ ions and concentrating it at the boundaries of crystallites. It is noted that in this case, the morphology of crystallites changes, the short-range order of the structural unit of the lattice (Gd2O2) changes with the introduction of S2- ions into oxygen vacancies [VO]oo or the substitution of O2- anions, as a result of which the long-range order of the anionic sublattice is violated and the band gap decreases. At high concentrations of the photoluminescence activator Tb3+ 7 mol.%, radiation quenching does not occur due to the presence of the GdOF and TbOF phases. Variations of these effects with an increase in the Tb3+ concentration lead to an increase in the intensity of the emission in the green region of the 5D4->7Fj transitions and a decrease in the intensity of the emission in the blue region of the 5D3->7Fj transitions. Keywords: phosphor Gd2O2S : Tb(3-7 mol.%), real lattice structure, photoluminescence activator distribution, far infrared spectroscopy, Raman spectroscopy, XPS spectroscopy.

The Seebeck coefficient, the electrical resistivity, the total thermal conductivity and the thermoelectric figure of merit of Y2O2S@SmS and SmS@Y2O2S ceramic samples with core-shell nanostructure within the temperature range from 300 to 770 K was studied. It was found that the samples studied demonstrate a promising thermoelectric property in high temperature region (T >= 773 K). The thermoelectric parameters for SmS@Y2O2S of S = -30 mu V/K, rho = 0.53 mu f center dot m and ctot = 2.60 W/m center dot K at T = 773 K were measured. These values result in increased ZT value of 0.48 at T = 773 K in comparison with those for lanthanide-based thermoelectric materials.

Люминофоры Gd2O2S : Tb(3-7 mol.%), полученные через стадию золь-гель формирования прекурсоров Gd2O3 : Tb с последующим их сульфидированием в парах серы с плавнем LiF при 700oC, показали высокую эффективность свечения. Характеризацией полученных образцов набором физико-химических методов установлено, что увеличение концентрации активатора Tb3+ приводит к его специфическому распределению: по вакансиям гадолиния (VGd)''', замещением ионов Gd3+ и концентрированием его на границах кристаллитов. Отмечено, что при этом изменяется морфология кристаллитов, изменяется ближний порядок структурной единицы решетки (Gd2O2) c внедрением ионов S2- в вакансии кислорода [VO]oo или замещением анионов O2-, в результате чего нарушается дальний порядок анионной подрешетки и уменьшается ширина запрещенной зоны. При этом, образующиеся примесные фазы GdOF : Tb и TbOF способствуют повышению эффективности фотолюминесценции. Вариации этих эффектов при росте концентрации Tb3+ приводят к росту интенсивности полос излучения зеленой области переходов 5D4->7Fj и снижению интенсивности полос излучения синей области переходов 5D3->7Fj. Ключевые слова: люминофор Gd2O2S : Tb(3-7 mol.%), реальная структура решетки, распределение активатора фотолюминесценции, дальняя инфракрасная спектроскопия, рамановская спектроскопия, РФЭС-спектроскопия.

In this work, we investigated the features of the photoluminescence of C-Gd 2(1-x) Tb x Eu x O 3 luminophores at x=1.0 and 2.5 mol%, which are associated with the distribution of Tb 3+ and Eu 3+ activator ions over the centrosymmetric C 3i and noncentrosymmetric C 2 positions of cations in the bixbyite lattice, as well as in the positions at the boundaries crystallites C S . We studied the phase transformations of the samples, changes in the morphology of crystallites, photoluminescence spectra, and spectra of the far infrared region 50-600 cm -1 with changes in the annealing modes of the initial products of the sol-gel synthesis Gd 2(1-x) Tb x Eu x (OH) y (CO 3 ) z · n(H 2 O) at temperatures of 900 and 1200 o C in air and hydrogen. Correlations have been established between changes in the characteristics of the samples and the parameters of their annealing. Based on the analysis of these correlations, the redistribution of activators over the indicated cation positions was determined, and a model was proposed for identifying infrared absorption bands in accordance with the localization of activators along the cationic sublattices C 3i and C 2 . Keywords: Gd oxide, luminescence activators Tb 3+ and Eu 3+ , annealing in air and in hydrogen, correlation of photoluminescence and far infrared spectra, distribution of activators in the lattice.

Федеральное государственное бюджетное учреждение наукиИнститут неорганической химии им.А. В. Николаева Сибирского отделения Российской академии наук

Solid solutions Gd2(1 – x)TbxEuxO3 (where x = 1 and 2.5 mol %) are prepared by the sol–gel method with subsequent annealing at 700–1200°C in air and hydrogen atmospheres. It is found by XRD and IR spectroscopy that the solutions undergo the chemical and phase transformations from the cubic modification to the monoclinic one in the annealing process and change the degree of crystallinity. Microinclusions of the Tb7O12:Eu3+ phase are present in a solid solution under certain annealing conditions, which are not formed in a hydrogen atmosphere or with a high activator concentration of 2.5 mol % at 1200°C. In accordance with these transformations, the Tb3+ and Eu3+ photoluminescence activators are redistributed over the C3i centrosymmetric and C2 noncentrosymmetric crystal lattice sites and the Cs surface states. These rearrangements give rise to changes in the parameters of the photoluminescence spectra, which are associated with a change in the ways of transferring the excitation energy of the main radiative transitions of the Tb3+ and Eu3+ photoluminescence activators.

The decomposition mechanisms of hydrated hydroxides of rare-earth metals Sm(OH)3·(H2O)gel·nH2O and Y(OH)3·(H2O)gel·nH2O, and also compound [Sm(OH)3·(H2O)gel·nH2O]q@[Y(OH)3·(H2O)gel·nH2O]p with a core–shell nanostructure were studied. In the course of the thermal treatment of hydroxides in the range of 25–900°C, stages of successive phase transformations were observed. The Avraami-Erofeev model of topochemical reactions describes the formation of phases in the systems under study with the highest correlation coefficient. The kinetics of successive dehydration and dehydroxylation of the above compounds was studied, kinetic equations of the topochemical reactions were presented, and apparent activation energies and the preexponents of the reactions were calculated. The activation energy for polycondensation of the compound with a core-shell nanostructure is lower than that of individual hydrates of samarium and yttrium hydroxides.

In this work, we investigated the features of the photoluminescence of C-Gd2(1-x)TbxEuxO3 luminophores at x = 1.0 and 2.5 mol%, which are associated with the distribution of Tb3+ and Eu3+ activator ions over the centrosymmetric C3i and noncentrosymmetric C2 positions of cations in the bixbyite lattice, as well as in the positions at the boundaries crystallites CS. We studied the phase transformations of the samples, changes in the morphology of crystallites, photoluminescence spectra, and spectra of the far infrared region 50–600 cm–1 with changes in the annealing modes of the initial products of the sol – gel synthesis Gd2(1 – x)TbxEux(OH)y(CO3)z · n(H2O) at temperatures of 900 and 1200oC in air and hydrogen. Correlations have been established between changes in the characteristics of the samples and the parameters of their annealing. Based on the analysis of these correlations, the redistribution of activators over the indicated cation positions was determined, and a model was proposed for identifying infrared absorption bands in accordance with the localization of activators along the cationic sublattices C3i and C2.

The temperature dependences of Seebeck coefficient, electrical conductivity (Т=300–873K), thermal conductivity and figure of merit (Т=300–770K) of polycrystalline samples of solid solutions based on gadolinium and dysprosium sulfides with γ-GdxDy1-xS1.49 (x=0.1, 0.2, 0.3, 0.4) composition were studied. It was established that samples morphological features, namely, the specific surface area of crystallites causing a change in the number of deformation centers determines the thermal conductivity of -GdxDy1-xS1.49, and it was found that there is an anomalous decrease in thermal conductivity for composition with х = 0.2. For this composition the lowest values of Seebeck coefficient -371 mkV/K at 873K, electrical resistivity 880 mkΩ∙m at 873K and thermal conductivity 0.68 ± 0.03 W/m·K at 770K were obtained, in this case the thermoelectric figure of merit reaches ZT = 0.23.

The work is devoted to the study of temperature dependences of thermal conductivity ( T = 300–770 K) of polycrystallic samples of solid solutions based on gadolinium and dysprosium sulfides of the compositions: γ -Gd x Dy 1− x S 1.49 ( x = 0.1, 0.2, 0.3, 0.4). It has been found that the morphological features of samples, namely, the specific surface area of crystallites, which causes a change in the number of deformation centers, determines the value of the thermal conductivity of γ-Gd x Dy 1− x S 1.49 solid solutions. The presence of an abnormal decrease in thermal conductivity for the composition of x = 0.2 has been established. When the temperature increases to 770 K, this anomaly decreases slightly. The minimum value of the thermal conductivity coefficient of 0.68 ± 0.03 W/(m·K) is reached for the composition under consideration at 770 K.