The article describes the studied features of formation of nanocrystalline powders of erbium oxide with the addition of lanthanum oxide by the method of thermochemical synthesis (combustion), intended for obtaining high-density ceramics. The sources for synthesis were nitrate salts of erbium and lanthanum, and polyvinyl alco-hol was used as a dispersing agent for separating agglomerates. The alloying and sintering additive – lantha-num oxide La2O3 – was introduced into the initial composition in the form of lanthanum nitrate. Studies of the morphological and structural characteristics of the powders using scanning electron microscopy and X-ray phase analysis showed that the Er2О3 : La powder samples calcined at 850 °C have a quasi-spherical particle shape with sizes of 21–28 nm, and heat treatment of the powders at 1100 °C in an air atmosphere promotes par-ticle growth to 76–103 nm and their agglomeration. It is shown that nanostructured Er2O3 : La powders obtained by thermochemical reactions and calcined at 850 ºC luminesce intensely in the IR-area centered at 1533.6 nm upon excitation at 519 nm, and the lumines-cence spectrum has a shape typical for a crystalline matrix

The relationship between the chemical composition, phase structure, grain size, electrical resistance, and Seebeck coefficient in composite ceramics (ZnO)z[(TM)xOy]1 – z (TM = Fe, Co (transition metals); 0 ≤ x ≤ 3, 1 ≤ y ≤ 4, 0.5 ≤ z ≤ 50 wt %), obtained using one- and two-stage technology has been examined. Experimental data on the electrical conductivity, Hall effect, and thermoelectric parameters of doped and undoped ceramics are presented. In the wurtzite phase of the studied ceramics, two levels were found: a shallow level with ionization energy ΔE1 ≈ 0.04–0.05 eV and a deep level with ΔE2 ≈ 0.24–0.37 eV. The relationship between the phase composition, electrical conductivity, and thermoelectric power in the studied ceramics has been established. Doping of zinc oxide with iron is shown to be promising for increasing the Seebeck effect.

Разработан метод синтеза дегидроксилированных ультрадисперсных порошков граната, легированного ионами церия (желтого люминофора), низкотемпературной термохимической реакцией. Установлено, что размеры, структура, морфология частиц полученных порошков иттрийалюминиевого граната, активированного ионами церия (YAG:Ce), в значительной степени зависят от состава горючей смеси и режима последующей термической обработки. Средние размеры кристаллических частиц, рассчитанные по данным удельной поверхности порошков, находятся в области от 0,9 мкм до 1,6 мкм в зависимости от температуры обжига (от 650 до 1200°С), а диаметр первичных частиц YAG:Ce (средний размер области когерентного рассеяния) составляет 45 нм при температуре обжига 650°С. Порошки на основе YAG:Cе, синтезированные термохимическим методом с использованием смеси нитратов иттрия, алюминия, церия и смешанного горючего (карбамид и гексаметилентетрамин), при возбуждении синим светом люминесцируют в широкой полосе в диапазоне 470–750 нм с центром у 550 нм (желтое излучение). Установлено, что при получении YAG:Cе термохимическим методом в карбамиде и гексаметилентетрмине развивается температура, достаточная для образования соединения Y3Al5O12 и вхождения ионов церия в структуру граната. Газовая восстановительная среда, образующаяся при термохимической реакции, способствует формированию ионов Се3+.

This article describes a new method of thermochemical synthesis of luminescent nanostructured powders of Y2O3:Eu3+ and Y2O3:Bi3+, Eu3+ based on the burning of nitrate salts in the presence of a complex organic fuel consisting of a mixture of carbamide and hexamethylenetetramine (HMTA). It is established that using a combined fuel - a mixture of carbamide and HMTA - in a thermochemical reaction followed by calcination of the precursor at 650oC gives more friable powders than the reaction with pure carbamide as a fuel, with a large amount of cavities. It is shown that when preparing Y2O3:Eu3+powders, complex compounds of anhydrous nitrates Y(NО3)3∙3СO(NH2)2 and Eu(NO3)3∙6CO(NH2)2 with urea are formed at the gel stage. They are decomposed at a higher temperature (about 1200oС) resulting from the combustion process. As a result, corresponding crystalline oxides are formed. The europium ions replace a part of the yttrium ions in the structure of Y2O3 favouring the formation of a luminescent powder. X-ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy have been used to characterize these powders. The powders synthesized in this manner (calcination at 650oC) show a sharp peak in the X-ray diffraction picture at 2θ = 28.94° corresponding to crystalline Y2O3 particles with average particle size 62.3 nm. However, when treatment temperature is increased to 1200oC, and the process duration is 1 h, the average particle size increases to 0.25 microns. Measurement of photoluminescence spectra of the samples revealed a maximum in the red region (λ=612 nm) when exciting at a wavelength of 395 nm (violet radiation). Luminescence intensity increases by 15% when introducing bismuth ions into the Y2O3 matrix and decreases by 30% when calcinating the Y2O3:Eu3+ powders at 1100oС. The nanostructured Y2O3:Bi3+, Eu3+ powders obtained by the burning method can be applied in systems for protecting valuable security and industrial products, because these powders have special luminescent characteristics allowing to make visual observation of texts and tags under the radiation of LED sources without application of UV-lamps.

A new approach to the synthesis of nanostructured yttrium oxide powders doped with europium ions by the method of combustionis is described. Carbohydrates (fructose, sucrose) and acetic acid were used as a fuel and hexamethylenetetramine – as additional fuel for ignition of the mixture. Based on the study of specific surface area, microstructure and morphology of the obtained powders, as well as after precursor calcination at 700, 900 and 1100 °C , it was found that specific surface area decreases with the increase of calcination temperature. This is due to the removal of weakly bound impurity groups (ОН, NO, СО2) from the surface of aggregates, compaction of the crystalline structure of the matrix particles and larger particle formation. In case of calcination at 700 °C, nanostructured particles with a size ranging from 39 nm (combustion in acetic acid) to 53 nm (burning in sucrose) are formed. Larger aggregates with particle sizes from 0.6 µm (in presence of sucrose) to 0.23 microns (in presence of acetic acid) are formed at 1100 °C. The powders obtained in such a way exhibit efficient luminescence properties in the red region of the spectrum upon excitation in the UV range (wavelength 250 nm).

Powders were synthesized in the yttrium oxide + zinc oxide system doped with europium oxide by the method of redox combustion of a mixture of yttrium, zinc, and europium nitrates in the presence of saccharose (fuel). The structure and the physicochemical and luminescent properties of the particles being formed and of a ceramic on their basis were examined.

Y 3 Al 5 O 12 :Ce 3+ ceramics additionally doped with chromium from the gas phase were synthesized by a colloidchemical method. It was established that its luminescence spectrum included a broad poorly resolved band with a barycenter at 570 nm due to Ce 3+ and narrow bands in the region 670–750 nm due to Cr 3+ in Y 3 Al 5 O 12 and YAlO 3 . The structure of Cr 3+ optical centers in both subsystems, the kinetic properties of their luminescence, and the transfer between them of electron excitations were considered.

Материалы XV Междунар. науч.-техн. конф. студентов, аспирантов и молодых ученых, Гомель, 23–24 апр. 2015 г.