In this work, stabilized f-ZrO2 ceramic samples with the compositions of (Zr0.82Y0.09Eu0.09)O1.91, (Zr0.82Y0.09Tb0.09)O1.91 and (Zr0.82Y0.09Eu0.045Tb0.045)O1.91 were studied. The elemental composition was studied by electron probe microanalysis, and the luminescent properties were studied by local cathodoluminescence (CL). An analysis of the Eu3+ CL spectra confirmed the stabilization of the cubic phase in ceramics at room temperature. The study of the obtained CL spectra, the 5D4-7F5Tb3+ band luminescence decay kinetics, CL images and excitation spectra showed europium sensitization by terbium in (Zr0.82Y0.09Eu0.045Tb0.045)O1.91. Keywords: f-ZrO2, Eu3+, Tb3+, Ceramics, Sensitization, Cathodoluminescence

Series of gadolinium tantalum niobates activated with Eu3+ and Tb3+ ((Gd1-y-zEuyTbz)NbxTa1-xO4 (x = 0, 0.3, 1; y = 0.6; z = 0.06; 0.15; 0.3)) were obtained for the first time. The formation of substitutional solid solutions was demonstrated. The obtained ceramic solid solutions had a monoclinic structure with I2/a space group. Electron probe microanalysis, photoluminescence (PL) and cathodoluminescence (CL) were used for studies of gadolinium tantalates and tantalum niobates series activated with Eu3++Tb3+. CL and PL spectra, concentration dependences of CL intensity and decay times, as well as excitation spectra for 5D0-7F2 Eu3+ and 5D4-7F5 Tb3+ bands were analyzed. It was shown for the first time that both energy transfer from Tb3+ to Eu3+ ions, and a reverse process - energy transfer from Eu3+ to Tb3+ ions are observed. This reverse process led to a decrease in CL intensity and decay times of europium bands in the presence of terbium 3+ in these materials. Presumably this phenomenon is influenced by anti-Stokes luminescence. This is confirmed by the dependences of anti-Stokes luminescence probability on temperature and excitation density.

For the first time, terbium-activated gadolinium tantalo-niobates were synthesized ((Gd1-xTbx)NbyTa1-yO4). The synthesis was carried out by the liquid-phase method. All studied materials had the main crystalline modification M GdNbO4. The content of impurity phases did not exceed 2-5%. The photo- and cathodoluminescence spectra were studied. Concentration quenching of the terbium ion luminescence for a series of solid solutions containing tantalum ((Gd1-xTbx)Nb0.9Ta0.1O4) occurs earlier than for pure gadolinium niobates ((Gd1-xTbx)NbO4). The obtained materials are promising for use as scintillators. Keywords: gadolinium tantalum-niobates, liquid-phase synthesis, Tb3+, luminescence, cathodoluminescence.

Series of ceramics based on Gd1-xEuxNbyTa1-yO4 (x = 0.01; 0.02; 0.06; 0.1; 0.2; 0.4) solid solutions with different Nb\Ta ratio were obtained for the first time. A detailed study of the structural and cathodoluminescent (CL) properties of the obtained materials was carried out. All samples had a monoclinic structure with I2/a space group (M-polytype). The content of phase impurities in some samples did not exceed 3-10 rel.%. CL bands attributed to transitions from 5D0, 5D1, 5D2, 5D3 levels to the 7Fj (j = 0-5) Eu3+ levels were observed in the CL spectra in the range of 350-750 nm. Concentration quenching of Eu3+ ions CL intensity occurred at concentrations from 0.1 to 0.2 form. un. of Eu3+. The Eu3+ CL intensity did not evidently depend on the Nb/Ta ratio for most of the samples. 5D0-7F2 Eu3+ transition decay kinetics was approximated with the sum of two exponentials. The presence of shorter decay time was associated with Eu3+ luminescence centers with an increased probability of nonradiative recombination located near extended defects and ceramic grain boundaries.

Впервые были синтезированы тантало-ниобаты гадолиния, активированные тербием ((Gd1-xTbx)NbyTa1-yO4 ). Синтез проводился жидкофазным методом. Все исследованные материалы имели основную кристаллическую модификацию М GdNbO4. Содержание примесных фаз не превышало 2-5%. Проведено исследование спектров фото- и катодолюминесценции. Концентрационное тушение люминесценции иона тербия для серии твердых растворов, содержащих тантал ((Gd1-xTbx)Nb0.9Ta0.1O4 ), наступает раньше, чем для чистых ниобатов гадолиния ((Gd1-xTbx)NbO4 ). Полученные материалы перспективны для использования в качестве сцинтилляторов. Ключевые слова: тантало-ниобаты гадолиния, жидкофазный синтез, Tb3+, люминесценция, катодолюминесценция.

In this work, stabilized f-ZrO2 ceramic samples with the compositions of (Zr0.82Y0.09Eu0.09)O1.91), (Zr0.82Y0.09Tb0.09)O1.91) and (Zr0.82Y0.09Eu0.045Tb0.045)O1.91 were studied. The elemental composition was studied by electron probe microanalysis, and the luminescent properties were studied by local cathodoluminescence (CL). An analysis of the Eu3+ CL spectra confirmed the stabilization of the cubic phase in ceramics at room temperature. The study of the obtained CL spectra, the 5D4-7F5 Tb3+ band luminescence decay kinetics, CL images and excitation spectra showed europium sensitization by terbium in (Zr0.82Y0.09Eu0.045Tb0.045)O1.91.

For the first time, a series of ceramic solid solutions of gadolinium tantalum niobates activated by europium was synthesized. A detailed interpretation of the obtained ceramics luminescence spectra was performed in the range of 580-630 nm for photoluminescence and 390-720 nm for cathodoluminescence. The transitions from 5D0, 5D1, 5D2 and 5D3 radiative levels of Eu3+ were observed in cathodoluminescence spectra of the samples. The main structural phase of the samples corresponded to the monoclinic structure with I2/a space group. The dependence of the europium luminescence bands Stark splitting on the Nb/Ta ratio in the material was studied for various radiative transitions. It was demonstrated that the distance between Eu3+ luminescence bands splitting increased in the solid solution series from GdNbO4 to GdTaO4. It can be due to an increase in the local field action on the Eu3+ ions.

We have developed a technological scheme for the preparation of europium-activated gadolinium niobates and tantalates and related solid solutions by a sol–gel process. It has been shown that, during synthesis of crystalline powders, raising the calcination temperature from 1200 to 1400°C leads to a decrease in the concentration of impurity phases from 10–15 to 4–10 wt %. The GdxEu1 –xTaO4 samples have been shown to have different structural polytypes at these temperatures. The synthesized materials exhibit bright red luminescence under photoexcitation.

This work is devoted to the study of self-glowing crystals containing alpha-radionuclides based on YPO4: Eu3+,238Pu, ZrSiO4:Tb3+,238Pu and ceramics based on cubic ZrO2:Eu3+,238Pu obtained in 2006, 2011, and 2017, respectively. The decay of a radionuclide causes radioluminescence of emission centers in the crystal causing its self-glowing. The paper presents the results of theoretical calculations of the energy conversion of alpha particles formed as a result of the radioactive decay of 238Pu, investigates the effect of radioactive decay on the luminescent properties of crystals, and proposes a method for estimating the power density of luminescence excitation during alpha decay. As a result of this work, the main ways of increasing the light yield for self-glowing crystals are proposed.

The paper is devoted to the study of the excitation capture efficiency of rare-earth ions emission levels upon electron-beam irradiation in well-known scintillation materials. The method is based on cathodoluminescent rise rate dependence on the electron beam current. Electron probe microanalysis was used to determine the composition of the samples. The technique allowed us to quantify the excitation capture efficiency for three emitting levels of rare-earth ions in Y2SiO5:Ce3+,Tb3+, to determine the energy transfer between high energy levels in Tm3+ and Cr3+ ions in Y3Al5O12 matrix, and to study the effect of crystalline matrix perfection on the excitation capture efficiency of Eu3+ energy levels in Y3Al5O12:Eu3+. It was shown that the excitation capture efficiency coefficient may differ in orders of magnitude for various energy levels of one ion.

The main purpose of this work was to carry out a low-temperature synthesis of glass ceramics containing YNbO4:Eu3+ crystallites and to study the structural and luminescent properties of the obtained samples. Within the framework of this work, the inclusions that crystallized under the conditions of low-temperature synthesis in the systems of SiO2-Na2O-K2O-Y2O3-Nb2O5-Eu2O3 (SiNaK) and B2O5-Na2O-Y2O3-Nb2O5-Eu2O3 (BNa) were investigated for the first time. It was shown that YNbO4: Eu3+ crystallized in both considered systems. In the SiNaK system the crystallization of SiO2 also occurred (quartz, crisstabolite, and tridymite) under the selected conditions. The BNa system proved to be the most promising for the synthesis of activated glass-ceramics with YNbO4, since the required crystallites crystallized only in ithis system. The luminescent properties of crystalline inclusions were investigated using the local cathodoluminescence technique. The composition and structure of glass ceramics were studied by electron-probe microanalysis and X-ray diffraction phase analysis.

In this work, the powder and ceramic samples of gadolinium tantalum niobate (Gd(Nb x Ta 1-x )O 4 ) grown by the liquid-phase method were studied. Phase homogeneity and composition were determined by x-ray diffraction analysis and electron probe microanalysis. Luminescent properties were studied by local cathodoluminescence technique. All samples obtained a high phase homogeneity. It was found that the dependence of the monoclinic lattice parameters on the niobium content in the niobium-tantalum pair has monotonic character. The solid solutions were formed at synthesis temperatures from 1180 to 1400°C. The sample of pure gadolinium niobate (GdNbO 4 ) showed the maximal cathodoluminescence intensity.

The work was aimed at development of glasses for encapsulation of self-glowing crystals, doped with alpha radionuclides. Bismuth borosilicate-based glass systems doped with Eu3+, B2O3-SiO2-Al2O3-Bi2O3-MO (where M = Ba, Sr and Zn) (Si-Bi -x), with various concentrations of activator were studied. The optimal synthesis conditions were selected, the composition of the obtained glasses was investigated using electron-probe microanalysis technique. Optical properties of glasses were investigated using the following methods - cathodoluminescence, photoluminescence and absorption. The range of the optimal activator concentration was determined.

Luminescent properties of yttrium-aluminum garnet activated by different amount of europium (YAG:Eu3+) single crystals were studied by local cathodoluminescence (CL) technique. Samples were grown by flux method. CL spectra were obtained in the range from 400 to 800 nm with spectral resolution of 0.1 nm. The rise and decay kinetics of various CL bands were investigated. The concentration dependencies of CL intensity and decay times of transitions were plotted. The concentration quenching for D-5(1)-F-7(2) Eu3+ transition was observed at about 3.5 at.% of Eu by Y, and for D-5(2)-F-7(1) and D-5(3)-F-7(3) transitions - at about 2.5-3 at.% of Eu by Y. For transition D-5(0)-F-7(1) no concentration quenching was observed. The high-energy excitation capture efficiency by different energy levels of Eu3+ in YAG was estimated based on the dependence of the CL rise rate of these levels on the electron beam current density. It was found that D-5(1) energy level excitation capture efficiency is about three times higher than that of the D-5(0), D-5(2) and D-5(3) energy levels.

The work is dedicated to the study of the phase stability of (Zr, Hf, Y, Eu)O-x ceramics with the calculated formula Zr0.41Hf0.41Y0.09Eu0.09O1.91 synthesized by the co-precipitation method and subjected to detonation in spherical shock waves and vacuum annealing at 1700 degrees C. The phase composition of the starting precursor and ceramic samples was investigated by X-ray diffraction analysis. To analyze the local structure of samples, the method of rare-earth ion spectroscopy was applied with the use of the local cathodoluminescence technique. It was demonstrated that detonation in spherical shock waves leads to a decrease of residual monoclinic phase in ceramics, and vacuum annealing leads to its complete disappearance. The significant changes in the phase composition of ceramics after the impact of high temperature in vacuum and high pressure under spherical shock waves are not observed. Such materials can be used as stable matrices for actinide immobilization or advanced luminescence materials to be applied under extreme conditions. (C) 2019 Elsevier B.V. All rights reserved.

The feasibility of synthesizing gadolinium tantalum niobates by the liquid-phase method was demonstrated. The methods of X-ray diffraction, electron probe microanalysis, local cathodoluminescence, and photoluminescence were applied to study the samples. It was shown that under the selected synthesis conditions (T ~ 1400°C for 3 hours), no solid solution of niobium-tantalum was formed in the powder samples. When obtaining ceramic samples, it was possible to obtain a solid solution and to study the dependence of the luminescence intensity on the niobium content upon excitation of the samples by an electron beam. The maximum luminescence intensity was observed in the sample with the composition of GdNb0.9Ta0.1O4. It was shown that the inhomogeneity of luminescence is not related to fluctuations in composition, but is related to the inhomogeneous distribution of vacancy centers, which are luminescence centers.

Lasing in MBE-grown impulsively pumped quantum cascade lasers of 9.6 μm at 140 K has been demonstrated. The active area is based on three-phonon resonance scattering of electrons. An In0.53Ga0.47As/Al0.48In0.52As solid alloy heteropair was used to form periods of quantum cascade lasers. The upper In0.52Al0.48As cladding of the waveguide was made thick. Alloyed and unalloyed lower metallization systems were studied. The threshold current density for a ridge laser 1 mm long and 27 μm wide has been found to roughly equal 3 kA/cm2 at 87 K. The optical output power has been estimated at a level of 20–35 mW.

Simulation of the structure of multijunction photodiodes has been performed on the assumption that an equal of the number of photons is absorbed in them, and PV characteristics have been stadied AlxGa1-xAs/GaAs photodiodes fabricated by the molecular-beam epitaxy technique. According to the performed measurements and analysis of the results, it has been shown that the efficiency of single-junction photodiodes in converting monochromatic optical radiation at a wavelength of 810 nm reaches 50%. The relationship between the "saturation" currents calculated from the dark I - V characteristic for the diffusion current flow (Shockley) in the space charge region of a photodiode p-n junction and the obtained values for the efficiency of converting optical radiation in the wavelength range of 700 - 900 nm has been shown. When the "saturation" current flow for the diffusion mechanism rises by an order of magnitude, the efficiency value at excitation by monochromatic radiation at 810 nm and 780 nm drops by 25% and 11%, respectively.

Генерация квантово-каскадных лазеров на длине волны излучения 9.6 µm