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.

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.

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.

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.

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.

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.

Solid solutions Gd2(1-x)TbxEuxO3, where x = 1 and 2.5 mol%, were obtained in an atmosphere of air and hydrogen by the sol-gel method followed by annealing at 700-1200 °C. It was found by XRD and IR spectroscopy that, during annealing, the solutions undergo chemical and phase transformations of the cubic modification into the monoclinic one and change the degree of crystallinity. Under some annealing conditions, the solid solution contains microinclusions of the Tb7O12:Eu3+ phase, which is not formed in a hydrogen atmosphere or at a high activator concentration of 2.5 mol% at 1200 oC. In accordance with these transformations, a redistribution of the photoluminescence activators Tb3+ and Eu3+ occurs over the centrosymmetric C3i, noncentrosymmetric C2 positions of the crystal lattice, and the surface states of Cs. As a result of these rearrangements, the parameters of the photoluminescence spectra change, which are associated with a change in the ways of transferring the excitation energy of the main radiative transitions of the photoluminescence activators Tb3+ and Eu3+.

•C-(GdxY1-x)2O3:Eu phosphors efficiency depends on short –range lattice order.•Short-range order was controlled by cations radii and Tamman's loosening.•Symmetry of Eu3+cation surrounding gives chromacity of the luminophors.•Anneling of samples at Tamman's temperature reduces a local symmetry of the lattice.•Optimal compositions are at xGd = 0.75–0.80 and 14 mol% of Eu3+.

Sol-gel synthesis of the (GdxY1–x)2O3: Eu3+ solid solutions (3.5 mol %) allows for the increase in the energy efficiency of emission of the red luminophor. The study of distribution of the luminescence activator Eu3+ has revealed that these ions substitute the Gd3+ ones in the cationic sublattice of ternary solid solution. The Eu3+ ions are predominantly localized in the noncentrosymmetrical position C2 at x < 0.50 and in centrosymmetrical position C3i at x > 0.50. The increase in the Eu3+ ions concentration in the C3i position stabilizes the cubic high-temperature structure of the solid solution in comparison with the monoclinic phase. The solid solution with x = 0.75 has been found to be the most efficient luminophor.

Evolution of the mother liquor pH in the course of the sol-gel precipitation of hydrogels of yttrium and europium oxohydroxides has been studied at different acidity of the system and the precipitant (NaOH) concentration. The optimal pH and components concentrations have been determined; the specific surface area of 210 m2/g (yttrium hydroxide) and of 100 m2/g (europium hydroxide) has been attained under these conditions.

The sol-gel method of the formation of the nanostructured luminophor based on Y 2 O 3 doped by Eu 3+ and Bi 3+ was studied. The mechanism of the dehydration and dehydroxylation of gels and xerogels of the mixed hydroxides, particle sizes, structure, and luminescent properties of the synthesized products based on Y 2 O 3 depend on the chemical nature of a precipitating agent (NaOH or NH 4 OH) and a washing agent (water and alcohol).

The process of dehydration of Gd(OH) 3 · n H 2 O obtained by the sol-gel method from a solution of Gd(NO 3 ) 3 , to Gd 2 O 3 in the temperature range of 50–700°C was explored. The hydrogel and Gd 2 O 3 structurization is shown to depend on the additives (AF-12 and 2-propanol). The final average particle size of Gd 2 O 3 after annealing at 700°C is 20±2 nm, depending on the conditions of the synthesis. The resulting oxide particles are larger than the particles of yttrium oxide Y 2 O 3 (17±2) obtained under the same conditions of the process due to the higher basicity of gadolinium and its higher coordination number with respect to the OH groups. This promotes the formation of crystalline phases of Gd(OH) 3 at lower temperature, 50–250°C, while maintaining a favorable structural short-range order in passing through an amorphous state to a crystalline Gd 2 O 3 .

A processes of formation of nanostructured powders of nickel oxide by annealing in the temperature range of 200–700°C of the nickel hydroxide obtained by the sol-gel method at 80°C from solutions of nickel nitrate by precipitation with alkali in the presence of surfactant AF-12 (polyethylene oxide alkylphenyl ether) was investigated. The formation of nanostructured powders of nickel oxide in the presence of a surfactant reduces the size of nanoparticles to 20–25 nm, which is 1.5 times smaller than the particles obtained without a surfactant. The effective influence of surfactant on the particle size begins in the temperature range of its decomposition and evaporation equal 350–400°C.

The process of formation of nickel oxide nanostructured powders by annealing nickel hydroxide in the temperature range 200–700°C was studied. Nickel hydroxide was prepared by precipitation with alkali from nickel nitrate solutions. The annealing process was shown to be multi-step. In the first stage the hydrogel Ni (OH) 2 · n H 2 O decomposes and partial dehydration of hydroxide occurs. Sizes of the formed particles decrease. At the temperatures above 230°C, further hydrogel decomposition and coalescence of NiO particles proceed. In view of the structural rearrangement of powder at the high temperatures 400–700°C, dehydration process is monitored by the decrease of NiO particles surface area at their coalescence. According to the change in the dehydration mechanism, the hierarchically nanostructured material forms, whose particle sizes are in the range 4–5, 9–12, and 18–40 nm.