Low-temperature luminescence and thermoluminescence from BeO:Zn single crystals

Low-temperature luminescence and thermoluminescence (TL) of BeO:Zn single crystals have been studied in the temperature range of 6–380 K and energy ranges of 1.2–6.5 eV (emission spectra) and 3.7–20 eV (luminescence excitation and reflection spectra). The introduction of zinc impurity ions (0.05 at. %) into BeO host lattice leads to the creation of both the trapped electron and hole centers: Zn$^+$ and Zn$^{2+}$ O$^−$. These two new centers are responsible for two TL glow peaks at 307 and 145 K with activation energies of 0.96 and 0.40 eV, and two emission bands at 6.0 and 1.9–2.6 eV. The first emission band is attributed to radiative annihilation of the Zn-impurity bound excitons, and the second one is associated with the intracenter electronic transitions in the defect complex comprising zinc impurity ion. The 6.0 eV luminescence center can be excited at 9.6 eV, the low-energy tail of the BeO host absorption, but below the first excitonic maximum (10.45 eV). The 1.9–2.6 eV luminescence center can be excited at the BeO optical transparency band. Both emission bands in BeO:Zn appear in the X-ray induced luminescence spectra at T = 6 K. This indicates that not only these luminescence centers are excited during band-to-band transitions, but they participate in recombination processes as well. The low-temperature (T$_0$ = 6 K) TL study of BeO:Zn single crystals was made for the first time. Analysis of the low-temperature TL glow curves allowed us not only to experimentally determine the energy characteristics of the Zn impurity states in BeO:Zn, but reveal an extremely strong influence of the isovalent zinc impurity on fluctuation rearrangement of BeO host lattice. Note, the fluctuation rearrangement of BeO host lattice, which occurs in the temperature range of self-trapped exciton transformation (80–180 K), was previously known only for undoped BeO and BeO crystals with heterovalent impurities

Optical and luminescence spectroscopy studies of electronic structure of Li6GdB3O9Li_6GdB_3O_9 single crystals

This article presents the study of electronic structure of Li6GdB3O9 single crystals and radiative relaxation of electronic excitations in them. The investigation was performed by the means of low-temperature optical and luminescence far-ultraviolet spectroscopy upon excitation by synchrotron radiation. On the basis of the low-temperature (T = 10 and 30 K) spectra of the reflection, recorded in the present research and the dispersions of the complex optical functions of View the MathML sourceεˆ(E),nˆ(E) and μ(E)μ(E), calculated in the framework of the oscillator model, we have determined the parameters of the electronic structure of the Li6GdB3O9 crystals as follows. The value of the minimum energy for the interband transitions in the boron–oxygen framework is View the MathML sourceEg=9.42eV, the energy position of the first excitonic peak in the excitation spectra for anionic excitons is View the MathML sourceEn=1=7.46eV, the minimum threshold energy for excitation of excitons in linear chains of the Gd3+ cations is View the MathML sourceEc=6.80eV. The excitation spectra of an intrinsic luminescence of Li6GdB3O9 crystals, recorded at 10 K in the range of the optical charge-transfer transitions O–Gd have a band with the maximum at View the MathML sourceECT=6.57eV

Facile Synthesis of Pyrazole-and Benzotriazole-Containing Selenoethers

Azole-containing selenoethers, 1,5-bis(3,5-dimethylpyrazol-1-yl)-3-selena pentane and 1,3-bis(1,2,3-benzotriazol-1-yl)-2-selena propane were prepared by the reaction of corresponding tosylate or chloride with sodium selenide generated in situ from elemental selenium and sodium formaldehydesulfoxylate (rongalite)

A luminescence spectroscopy study of new Li2BaAl2F10\mathrm{Li_2BaAl_2F_{10}} single crystal

Large Li$_2$BaAl$_2$F$_{10}$ single crystals of optical quality were grown using the vertical Bridgman method. X-ray diffraction method was used to determine the crystal structure (orthorhombic symmetry Cmc2$_1$), lattice parameters, atomic coordinates. The luminescent properties were investigated using selective photoexcitation by synchrotron radiation (E = 3.7–21 eV, T = 8 K, time integrated and time-resolved spectra) as well as upon excitation with unfiltered X-ray beam (synchrotron radiation or X-ray tube). We revealed both the broadband luminescence at E$_m$ = 4.0 eV (E$_{ex}$=11.72 eV) attributed to the radiative annihilation of self-trapped excitons (STE) and the excitonic-type near-defect luminescence at E$_m$ = 3.0–3.2 eV (E$_{ex}$=11.25 eV) attributed to radiative relaxation of electronic excitations in nonequivalent structural units of the crystal lattice. The fast exponential component with lifetime of 5.6 ns, a low-intensity intermediate component with a lifetime of 75–100 ns, a constant level — pedestal (sum of the micro- and millisecond decay components) were revealed in luminescence decay kinetics. The electronic structure parameters (bandgap = 13.0 eV, low-energy onset of the intrinsic host absorption E$_c$ = 11.2 eV), the energy threshold for the excitation of STE-luminescence ( E$_{th}$ = 11.2 eV) are determined from spectroscopic data. Thermoluminescence (TL) has been studied (90–350 K) using spectral-integral regime. Four partially overlapping TL glow peaks were revealed, their deconvolution was done and thermal activation parameters were determined using TGCD method

Cracking of Heavy Oil at Presence of Zeolite Y Modified of Nickel Nanopowder

Изучен процесс термического и каталитического крекинга тяжелой нефти в присутствии цеолита Y, содержащего наноразмерный порошок никеля, при температуре 450 °С, давлении 0,5…0,7 МПа и продолжительности реакции 60 и 120 мин. Установлено, что наибольший выход фракций, выкипающих до 350 °С, наблюдается при крекинге нефти с добавкой 5,0 % мас. катализатора 2,0 % Ni/HY в течение 60 мин и составляет 67,1 %. Приводятся данные спектрометрии ЯМР 1Н, группового и вещественного состава продуктов термического и каталитического крекинга тяжелой нефти. Показано, что в жидком продукте каталитического крекинга нефти с добавкой 2,0 % Ni/HY содержится меньше смол и асфальтенов и больше масел по сравнению с жидкими продуктами термического и каталитического крекинга в присутствии HY.Process of thermal and catalytic cracking of heavy oil at presence of zeolite Y containing nickel nanopowder is studied at temperature 450 °С, pressure 0,5 … 0,7 МПа and durations of reaction 60 and 120 minutes It is shown, that the greatest yield of the distillate fractions boiling up to 350 °С is obtained via crude oil catalytic cracking by an addition of 5 % mas. catalyst 2,0 % Ni/HY during of experiment of 60 min, it is 67,1 %. Data of spectrometry of a nuclear magnetic resonance Н1, group and material constitution of products of thermal and catalytic cracking of heavy oil are cited. It is shown, that liquid product of catalytic cracking of heavy oil with the additive of 2,0 % Ni/HY contained the least quantity of resins and asphaltenes and grater quantity of oils in comparison with liquid products of thermal and catalytic cracking by addition catalyst HY

Cracking of Heavy Oil at Presence of Zeolite Y Modified of Nickel Nanopowder

Изучен процесс термического и каталитического крекинга тяжелой нефти в присутствии цеолита Y, содержащего наноразмерный порошок никеля, при температуре 450 °С, давлении 0,5…0,7 МПа и продолжительности реакции 60 и 120 мин. Установлено, что наибольший выход фракций, выкипающих до 350 °С, наблюдается при крекинге нефти с добавкой 5,0 % мас. катализатора 2,0 % Ni/HY в течение 60 мин и составляет 67,1 %. Приводятся данные спектрометрии ЯМР 1Н, группового и вещественного состава продуктов термического и каталитического крекинга тяжелой нефти. Показано, что в жидком продукте каталитического крекинга нефти с добавкой 2,0 % Ni/HY содержится меньше смол и асфальтенов и больше масел по сравнению с жидкими продуктами термического и каталитического крекинга в присутствии HY.Process of thermal and catalytic cracking of heavy oil at presence of zeolite Y containing nickel nanopowder is studied at temperature 450 °С, pressure 0,5 … 0,7 МПа and durations of reaction 60 and 120 minutes It is shown, that the greatest yield of the distillate fractions boiling up to 350 °С is obtained via crude oil catalytic cracking by an addition of 5 % mas. catalyst 2,0 % Ni/HY during of experiment of 60 min, it is 67,1 %. Data of spectrometry of a nuclear magnetic resonance Н1, group and material constitution of products of thermal and catalytic cracking of heavy oil are cited. It is shown, that liquid product of catalytic cracking of heavy oil with the additive of 2,0 % Ni/HY contained the least quantity of resins and asphaltenes and grater quantity of oils in comparison with liquid products of thermal and catalytic cracking by addition catalyst HY