In this work, sodium tetrahydroxoborate (NaB(OH)4) that is the main product of the hydrolysis reaction of NaBH4 with a relatively small excess of water is studied in the reaction with sodium borohydride in the presence of a catalyst and without it. It was found, that mixtures consisting of NaB(OH)4 and NaBH4 begin to melt at 70 degrees C with the formation of a liquid phase without destroying the close coordination environment for both types of boron atoms. When a cobalt -based catalyst is added to mixtures, significant hydrogen evolution is observed. The resulting products are hydrogen and amorphous borates with a gross composition close to [NaBO2 & sdot;0.75H2O]. Carrying out the catalytic hydrolysis of borohydride in the system of initial composition H2O:NaBH4:catalyst under the conditions same to that the catalytic reaction of NaBH4 and NaB(OH)4 was observed is a promising way to produce H2 since it provides a high yield of hydrogen at small amounts of catalyst and atmospheric pressure. Catalytic hydrolysis carried out in the temperature range 80-120 degrees C with initial molar ratios H2O:NaBH4 = 3 and 2.7, and atmospheric pressure demonstrates a hydrogen yield of 8.3 wt% and NaBH4 conversion of 96 % at only 2.3 wt% of CoCl2 as catalyst. Since the resulting final composition of borates is close to [NaBO2 & sdot;0.66H2O], the potential mass yield of hydrogen in this process can reach 9.3 wt%.

In this work sodium tetrahydroxoborate (NaB(OH)4) that is the main product of NaBH4 hydrolysis reaction if water excess is relatively small has been examined in reaction with sodium borohydride with and without a catalyst. It was found that mixtures consist of NaB(OH)4 and NaBH4 start to melt at 70°C producing liquid phase with no destruction of close coordination environment for both types of boron atoms. But if Co-based catalyst is added to the mixtures the significant hydrogen evolution is observed. Obtained products are hydrogen and amorphous borates with gross-composition close to [NaBO2×0.75H2O].Carrying out catalytic hydrolysis with molar ratios 3≥H2O:NaBH4≥2 during which liquid water is used instead of the tetrahydroxoborate is a promising way for H2 production with high mass yield at mild temperature, small quantities of a catalyst, and atmospheric pressure. The catalytic hydrolysis caring out at the temperature range 80-120ºC, initial molar ratios H2O:NaBH4=3 and 2.7 and atmospheric pressure demonstrates hydrogen yield 8.2Wt% and 97% of NaBH4 conversion at only 2.3Wt% of a Co-based catalyst. Taking into account that the obtained final borate gross composition is close to [NaBO2×0.66H2O], the potential mass yield of hydrogen in this process could reach 9.3Wt% for all the reactants including the catalyst.

Lasing efficiency of neodymium-doped yttrium-aluminium garnet (YAG) ceramic samples, which were fabricated at the Fryazino Branch of the Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences and the SLPG 'Raduga' in 2016-2017, is studied under the conditions of end-and side-pumping. The efficiency of lasers based on this ceramics was 64 % in the case of end-pumping and 68 %-70 % upon side-pumping. The laser level lifetimes are measured in ceramics with neodymium concentrations of 1, 2, 3, and 4 at %. The measured lifetimes well agree with the literature data. The dependences of the lasing threshold on the cavity length under the conditions of transverse mode locking and diode end-pumping are studied for different samples of laser ceramics in a semiconfocal cavity. In sum, the performed investigations showed that the quality of the first industrial samples of Russian laser ceramics are highly competitive in quality with the ceramics produced by Konoshima Chem. Corp., Ltd., which is considered by the laser community as an etalon.

To produce Yb-doped yttrium lanthanum oxide (Yb3+:(LaxY1−x)2O3) thin disc ceramics from laser synthesized nanopowders, two colloidal methods were used: slip casting and electrophoretic deposition. Sintering of the compacts in vacuum (3×10−4Pa at 1625°C for 12h) led to high transparency of the ceramics. Ceramic discs with relative densities higher than 99.99% and grain sizes of about 25μm were fabricated. The in-line transmittance of 0.5mm thick Yb0.17La0.19Y1.64O3 ceramics amounted to 80.5% at 1150nm wavelength. The materials obtained promise to be good gain media for ytterbium high power pulse disc lasers.

SiO2, ZrO2, B2O3 and MgO oxides and their combinations were used as sintering aids for preparation of yttrium aluminum garnet (YAG) ceramics doped by Nd2O3, Er2O3, Ho2O3, Tm2O3 and Yb2O3. The influence of these additives on optimal sintering temperature, grain growth, volume of residual pores and optical quality of the ceramics were investigated. The best combination of the sintering additives was found and high quality samples of YAG:Nd (1 at.%) ceramics were obtained. The original method of laser optical quality characterization of ceramics was developed and tested. The main laser parameters of YAG:Nd (1 at.%) ceramics samples are measured and compared with the best well known laser ceramics. The samples of YAG:RE (RE- Er2O3, Ho2O3, Tm2O3 and Yb2O3) ceramics are obtained, and their optical transmittance spectra are measured. Composite structures of YAG:Yb (5 at.%) - YAG were obtained by the simplest method of successive joint compaction of different composition layers.

The effect of sintering aids of SiO2, ZrO2, B2O3, and MgO oxides on the optimum sintering temperature, ceramics grain growth, total volume of residual pores, and optical quality of obtained ceramics is studied. The best combinations of sintering aids are found; as a result, YAG:Nd (1 at%) samples of ceramics of high optical quality are obtained. An original method for characterizing laser properties of ceramics is developed. Comparative measurements of main laser characteristics of the obtained ceramics and ceramics of the Konoshima Chemical Corp. Ltd wellknown in the world practice, are performed.

Neodymium doped yttrium aluminum garnet (1-4 at.%) Nd3+:Y3Al5O12 laser ceramics were obtained by the reactive sintering method using commercial alpha-Al2O3, Y2O3, and Nd2O3 powders as starting materials, and SiO2, ZrO2 as a complex sintering aid. Phase composition and microstructure of Nd3+:Y3Al5O12 substitutional solid solutions were studied by XRD, SEM, XPS and UV-vis spectrophotometry methods. The regularities for entering of iso- (Nd3+) and heterovalent (Si4+, Zr4+) impurities into the garnet structure were revealed based on an assumption of formation of substitutional solid solutions. The influence of impurity point defects on optical properties of Nd3+:Y3Al5O12 laser ceramics was studied. (C) 2016 Elsevier B.V. All rights reserved.

The properties of the highly-doped Nd3+ (1-4 at. %):YAG optical ceramics obtained by reactive sintering procedure are reported. Absorption spectra of the various Nd3+ concentration samples were measured in the wide spectral range of 250–1200nm. At least 11 lines of various intensities were found in the range 780–820nm where absorption transitions from ground state to 4F9/2 and 4F5/2 occur. Luminescence spectra were measured in 800-1200nm wavelength range where main lasing radiation transitions took place. It was found that lasing properties manifest the optical efficiency 16, 18 and 9% for the samples with Nd3+ concentration of 1, 2 and 4 at. %, respectively.

This paper describes the fabrication and investigation of highly transparent Yb-doped yttrium lanthanum oxide ceramics. For sintering of the ceramics we used a technology, which consists of several consecutive steps: (a) synthesis of weakly agglomerated nanopowder by laser ablation, (b) compacting of the green body with cold isostatic pressing (CIP), and (c) sintering in vacuum. After calcinations of the synthesized nanopowder at 1200 degrees C, a pure single-phase solid solution Yb3+:(La5Y1-x)(2)O-3 was formed. The lanthanum ions proved to be a good aid to sinter yttria ceramics doped with Yb3+ at comparatively moderate temperatures of about 1650 degrees C. The ceramics have a relative density higher than 99.99% and grain sizes around 40 mu m. The absorption coefficient of 3.2 mm thick Yb0.12La0.27Y1.61O3 ceramics is 0.01 cm(-1) at 1150 nm. Laser oscillation at a wavelength of 1033 nm is demonstrated. (C) 2015 Elsevier B.V. All rights reserved.

The influence of the size of Y2O3 powder particles on the structure formation and densification of Nd3+:Y3Al5O12 laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd3+:Y3Al5O12 phase. Bulk swelling of pressed samples during sintering of 2.94Y2O3-0.06Nd2O3-5Al2O3 powders with the size ratio of the initial particles R(Al2O3/Y2O3) ∼ 5 is observed. The application of different-sized powders (R ∼ 2.5) provides quantitative ratios between phases in the 3Y2O3-5Al2O3 system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd3+:Y3Al5O12 have been obtained by the solid-phase sintering of oxide powders (R ∼ 2.5). The slope efficiency for 1 at % Nd3+:Y3Al5O12 laser ceramics is found to be 33%.

To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 °C a pure single-phase solid solution Yb3+:(LaxY1−x)2O3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb3+ at moderate temperatures about 1650 °C. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb0.11La0.23Y1.66O3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers.

Processes of phase formation and densification during reactive sintering of YAG:Nd3+ laser ceramics have been studied through the 2.88Y2O3–0.12Nd2O3–5Al2O3 model powder system with a bimodal yttria particle size distribution. It has been found that utilization of submicron yttria powders can provide a competitive advantage of shrinkage over swelling processes by changing the kinetics of YAG phase formation. Excluding the swelling effect during densification allows one to produce YAG:Nd3+ (4 at%) laser ceramics by reactive sintering with in-line optical transmission of about 80% at λ=650 for a 1mm thick sample.

The lasing characteristics of 1% Nd:YAG and 0.8% Nd:YAG laser ceramics synthesised, respectively, at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences and at the Institute of Radio Engineering and Electronics, Fryazino Branch, Russian Academy of Sciences are studied. Lasing was obtained in all the samples with a slope efficiency from 7% to 25% and a maximum output power exceeding 4 W. Intrinsic absorption and scattering losses in the ceramics are estimated.

Чистые и легированные ионами Nd и Yb керамики иттрий-алюминиевого граната и (Y,La)2O3 лазерного качества с оптическим пропусканием в области лазерной генерации около 1 мкм более 80% получены методом твердофазного синтеза с использованием неагломерированных нанопорошков Y2O3 и Al2O3. Нанопорошки Y2O3 получены методом лазерного испарения и химического осаждения в растворах мочевины, а также путем помола промышленного Y2O3 в специально сконструированном лабораторном аттриторе со скоростью вращения мешалки до 1500 об./мин. Для синтеза керамики ИАГ был использован промышленный Al2O3. Все нанопорошки после помола имели размер частиц порядка сотни нанометров. Спекание в вакуумной печи при 1615–1750°C компактов, полученных из этих нанопорошков, дало высокопрозрачные образцы керамики.

Undoped and Nd- or Yb-doped laser-grade yttrium aluminum garnet and (Y,La)2O3 ceramics with a transmittance above 80% in the 1-μm lasing region have been prepared by solid-state reactions using nonagglomerated Y2O3 and Al2O3 nanopowders. The Y2O3 nanopowders were prepared via laser evaporation, chemical precipitation from urea solutions, and grinding of commercially available Y2O3 in a purposedesigned laboratory-scale attritor at stirrer rotation rates of up to 1500 rpm. The YAG ceramics were prepared using commercially available Al2O3. After grinding, all of the powders had a particle size on the order of a hundred nanometers. Green compacts produced from the nanopowders were sintered in a vacuum furnace between 1615 and 1750°C to give highly transparent ceramic samples.

Density, morphology, optical transmittance and luminescence of undoped and europium-doped Lu2O3 ceramics have been studied. It has been revealed that europium ions in concentration of 5 at.% act as a solid-state sintering aids in Lu2O3 ceramics promoting its densification. Lu2O3:Eu3+ optical ceramics with relative density of 98 +/- 2%, with an average grain size of 50 mu m and in-line transmittance of 41% in the visible wavelength range has been produced by vacuum sintering at T = 1850 degrees C. The scintillation characteristics of Lu2O3:Eu3+ ceramics under excitation with alpha-particles (Pu-238 source, E = 5.46 MeV) have been determined for the first time (S = 500 +/- 50 photons/MeV, R = 26.5%). (C) 2012 Published by Elsevier B.V.