Complexation between variable-valency uranium and organic ligands in solutions,their photostability and spectral identification

We discuss possible directions for searching for prospective materials based on low-valency uranium (III–V) as detection media for hard electromagnetic radiation. We have studied the processes of formation of tetravalent and pentavalent uranium complexes from UO₂(NO₃)₃·6H₂O and UO₂Cl₂·H₂O in DMF and with addition of CCl₄, including when the systems are exposed to radiation in the visible range (400–450 nm). In the first case (UO₂(NO₃)₃·6H₂O solutions in DMF), upon irradiation we observe stable complexes of pentavalent uranium, and when CCl₄ is added to the solution we observe complexes of tetravalent uranium. In the system UO₂Cl₂·3H₂O in DMF, we do not observe the appearance of new forms of uranium; but when CCl₄ is added, then complexes of tetravalent uranium are formed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 184–187, March–April, 2007.     

Preparation of CdO nanoparticles by mechanochemical reaction

CdO nanoparticles of 43 nm in crystal size were successfully synthesized by the mechanochemical reaction (CdCl₂ + Na₂CO₃) with NaCl as a diluent and subsequent thermal treatment at 700°C for 2 h. The samples were characterized by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Effect of calcination temperature on the crystal size of CdO nanoparticles was primarily investigated. The apparent activation energy of CdO nanoparticle formation during thermal treatment was calculated to be 12.2 kJ/mol.     

Electronic spectra of uranium tetrachloride clusters with electron-donor ligands

Electronic absorption spectra of nanoclusters of uranium tetrachloride are obtained experimentally and analyzed over a wide spectral range, from the visible to the IR. The structure of the long wavelength electronic absorption spectra is discussed in terms of the structure and electron-donor number of the attached ligand. Molecules of dimethyl sulfoxide (DMSO), hexamethyl phosphotriamide (HMPT), and water were used as ligands. The effect of the symmetry of the surroundings of the U⁴⁺ ion on the structure of the electronic spectrum is examined. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 182–187, March–April 2009.     

Spectra and structure of hexavalent uranium nanoclusters with mixed acido ligands in the coordination sphere

We have obtained and spectroscopically studied mixed acido ligand (Cl, I) uranyl complexes. We used IR absorption spectra to analyze the nature of incorporation of neutral molecules (in particular, dimethylsulfoxide) into the inner coordination sphere of uranium that that do not completely exhaust the coordination capacity of the central uranium atom. We have observed a good correlation between the frequencies of the totally symmetric stretching vibration of the ion in the IR absorption and luminescence. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 100–103, January–February, 2009.     

Influence of mechanochemical activation in various media on structure of porous and non-porous silicas

Influence of mechanochemical activation on porous structure and surface properties of porous and non-porous silicas in air, water and ethanol has been studied. Milled samples have been investigated with help of nitrogen adsorption-desorption, mercury porometry, thermogravimetric analysis, FTIR and ESR spectroscopy. It has been revealed that destruction of porous structure of silicagel at dry milling and, on the contrary, formation of porous silica from non-porous powders (aerosils) during treatment in liquid media occurs.     

Dynamics of formation of the composition,structure, and spectral characteristics of uranium complexes

We have examined general rules for the change of frequency of stretching vibrations of UO ₂ ²⁺ (uranyl) as a function of U-O and uranium-ligand interatomic distances. We analyzed the behavior of these frequencies as a function of donor number (DN) of the organic ligand by studying IR absorption and visible luminescence spectra. A linear correlation was found. We proposed spectroscopic methods for determining the DN of ligands, which are difficult to estimate by other methods, and the composition and structure of uranium complexes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 433–438, July–August, 2007.     

贫铀球壳中D-T中子诱发的铀反应率的测量与分析

为校验次临界能源堆的概念设计,在R19.4/30.0 cm的贫铀球壳装置上采用活化法开展14 MeV中子学积分实验.布放6片贫铀活化片于球壳中与入射D离子束90°方向上的不同位置处活化,用HPGe探测器测量238U(n,γ)反应、238U(n,f)及235U(n,f)反应和238U(n,2n)各反应产物发射的特征γ射线,得到了相应的反应率.238U(n,γ)反应率的不确定度为3.6％-3.7％,238U(n,D和235U(n,f)反应率的不确定度为5.1％-5.9％,238U(n,2n)反应率的不确定为4.3％-4.7％.用MCNP5程序在ENDF66c数据库下进行模拟计算,238U(n,γ)反应率的计算值/实验值(C/E)为0.972-1.034,238U(n,f)和235U(n,f)反应率的C/E为0.983-1.058,238U(n,2n)反应率的C/E为0.979-1.019.     

Characterization of uranium tetrafluoride (UF4) with Raman spectroscopy

The Raman spectrum of uranium tetrafluoride (UF₄) is unambiguously characterized with multiple Raman excitation laser sources for the first time. Across different laser excitation wavelengths, UF₄ demonstrates 16 distinct Raman bands within the 50–400 cm⁻¹ region. The observed Raman bands are representative of various F–F vibrational modes. UF₄ also shows intense fluorescent bands in the 325–750 nm spectral region. Comparison of the UF₄ spectrum with the ZrF₄ spectrum, its crystalline analog, demonstrates a similar Raman band structure consistent with group theory predictions for expected Raman bands. Additionally, a demonstration of combined scanning electron microscopy and in situ Raman spectroscopy microanalytical measurements of UF₄ particulates shows that despite the inherent weak intensity of Raman bands, identification and characterization are possible for micron‐sized particulates with modern instrumentation. The published well‐characterized UF₄ spectrum is extremely relevant to nuclear materials and nuclear safeguard applications. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd.     

Catalytic activation of hydrogen peroxide by Cr2AlC MAX phase under ultrasound waves for a treatment of water contaminated with organic pollutants

This study aims to investigate the sonocatalytic activation of hydrogen peroxide (H₂O₂) using Cr₂AlC MAX phase prepared by the reactive sintering process. The hexagonal structure of the crystalline MAX phase was confirmed by X-ray diffraction. Moreover, the compacted layered structure of the MAX phase was observed via scanning electron microscopy and high-resolution transmission electron microscopy. Under the desired operating conditions, Cr₂AlC MAX phase (0.75 g/L) showed suitable potential to activate H₂O₂ (1 mmol/L) under sonication, thereby allowing a considerable removal efficiency for various organic pollutants, including dimethyl phthalate (69.1%), rifampin (94.5%), hydroxychloroquine (100%), and acid blue 7 (91.5%) with initial concentration of 15 mg/L within 120 min of treatment. Kinetic analysis proved that the degradation reaction followed pseudo-first-order kinetics. Scavenging tests demonstrated that hydroxyl radicals and singlet oxygen were effective species during degradation. Furthermore, a probable mechanism for dimethyl phthalate degradation was suggested according to gas chromatography-mass spectroscopy and nuclear magnetic resonance analyses. The obtained results confirmed the capability of the triple Cr₂AlC/H₂O₂/US process as a promising method for treating contaminated water.     

高能重离子辐照的低活化钢硬化效应

为了探讨聚变堆候选低活化钢的抗辐照性能,在兰州重离子加速器国家实验室HIRFL的材料辐照终端,利用63 MeV的~(14)N离子和336 MeV的~(56)Fe离子在-50?C下对一种国产低活化钢进行辐照实验.借助离子梯度减能装置,使入射离子能量在0.22—6.17 MeV/u之间变化,从而在样品表面至24μm深度范围内产生0.05—0.20 dpa的原子离位损伤坪区.利用纳米压痕仪测试样品辐照前后的显微硬度,通过连续刚度测量(constant stiffness measurement)得到低活化钢硬度的深度剖面信息.使用Nix-Gao模型很好地描述了纳米压痕硬度随深度递减的现象(压痕尺寸效应,indentation size effect),从而有效避免了低能离子辐照的软基体效应(softer substrate effect).正电子湮灭寿命谱显示低活化钢在辐照之后长寿命成分增加,说明样品中产生了大量缺陷形成空位团,从而导致了材料力学性能的变化,在离子辐照剂量增加至0.2 dpa时,平均寿命τ_m增加量逐渐变慢,材料中辐照产生的缺陷趋于饱和.     

Determination of the activation energy by stochastic analyses of molecular dynamics simulations of dislocation processes

An investigation is reported of the probability and the probability density of thermal activation of stress-driven dislocation processes, as simulated using molecular dynamics (MD). Stochastic analyses of the survival probability are found to lead to simple relationships between the loading history and the distribution of the interaction time and strength. It is shown that the determination of the activation energy associated to a thermally activated event can be achieved by a reduction of the stochastic process to a process obeying the Poisson's distribution, preserving the activation probability at the survival time. The method is applied to the kink-pair mechanism for screw dislocations in iron. Predictions are compared with experimental results and with other methods reported in the literature, which allows the difference in the approximations and in the assumptions considered in these models to be underlined.     

Use of micro‐Raman spectrometry coupled with scanning electron microscopy to determine the chemical form of uranium compounds in micrometer‐size particles

In the frame of nuclear safeguards, knowledge of the chemical form (stoichiometry) of the uranium compounds present in the micrometric particulate material sampled by wiping surfaces in an inspected nuclear facility may point out the industrial process implemented in the installation. Micro‐Raman spectroscopy (MRS) coupled with scanning electron microscopy (SEM) has been used for the first time to analyze micrometer‐size particles of various uranium oxides [UO₂, U₃O₈, UO₃, and UO₄ · 4(H₂O)] deposited on carbon disks. Uranium particles are detected by means of SEM, and Raman analysis is then directly carried out inside the SEM measurement chamber without moving the carbon disk from SEM to MRS. When particles are deposited on appropriate carbon disks (sticky carbon tapes), despite a loss of signal‐to‐noise ratio of about an order of magnitude with regard to the stand‐alone MRS, all uranium oxides are successfully identified in particles by in‐SEM Raman analysis, obtaining similar characteristic bands as the ones obtained with the stand‐alone MRS. Moreover, with the SEM–MRS coupling, particles as small as 1 µm can be analyzed, whereas, without the SEM–MRS coupling, only particles larger than ~5 µm are efficiently analyzed, after localization inside the SEM, transfer of the sample holder into the MRS, and relocation of the particles inside the MRS. Copyright © 2013 John Wiley & Sons, Ltd.     

An anomalous change in the frequency of plasmon resonances of island metal films upon their contact with some polar organic media

We have examined the changes in the extinction of island metal films that occur as a result of their contact with a liquid crystal or polymethylmethacrylate. The morphology of surface nanostructures has been investigated. We have revealed that, upon immersion of an island metal film into a liquid medium molecules of which are polar, the shift of the plasmon resonance in the extinction spectrum and the increase in the extinction at the frequency of this resonance can substantially differ from the shift and the extinction increase theoretically calculated for an isotropic surrounding substance. We have shown that the reason for these differences is the local anisotropy of the refractive index of the medium in the immediate vicinity of metal particles, which is determined both by the shape of particles and by the degree of occupation of the substrate surface.     

有机层厚度变化的有机电致发光器件与微腔器件光谱分析

设计中心波长为520nm,改变有机层厚度,即空穴传输层NPB和发光层Alq3的厚度,分别由10nm逐渐增加至100nm,器件的总体厚度也随着改变,分别计算模拟出有机电致发光器件(OLED)和微腔有机电致发光器件(MOLED)的电致发光谱(EL),并对光谱的积分强度、峰值强度、半峰全宽、峰值位置的三维分布图进行比较分析。综合考虑光谱的峰值位置(中心波长)、最大的峰值强度和积分强度(与亮度、效率相关)、最小半峰全宽(色纯度高)进行合理的设计,可以找到最佳厚度。发现:NPB和Alq3的厚度分别为70和62nm时,器件性能最佳,并且微腔器件的结果尤为明显。结果表明,通过模拟计算,可以深入探索MOLED和OLED发光特性,设计出合理的器件结构。     

Study of isotopes of carbon,thorium, and uranium in travertine and thermal spring samples: implications for effects of changes in geochemical environment and processes

Data on modern radiocarbon activity in the old travertine formations of the Pymvashor hydrothermal system were used, in combination with ²³⁰Th/U dating of the travertine, to estimate the ¹⁴C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine (¹⁴C_calc). With the known values of ¹⁴C_calc and average age of the thermal water, and under the assumption that the residence time of the water in aquifer was constant over the last 13.9?±?1.5 ka, the initial ¹⁴C contents (¹⁴C₀) in the ancient thermal water were estimated. The findings in this study are that (1) both ¹⁴C₀ and δ¹³С have decreased in young waters compared to the ancient waters; (2) although atmospheric ¹⁴C activity (¹⁴C_atm) has also decreased in the same time, the decrease in ¹⁴C₀ is faster than the decrease in ¹⁴C_atm. Under certain assumptions, one could link changes in ¹⁴C₀ and δ¹³C to climate change. Decrease in δ¹³С of soil CO₂ and decrease in ¹⁴C₀ was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in ¹⁴C_atm. There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO₂, caused by thawing permafrost.     

Photophysical properties of a series of high luminescent europium complexes with fluorinated ligands

A series of high luminescent europium complexes have been synthesized, such as Eu(TFNB)₃phen (1), Eu(PFNP)₃phen (2), Eu(HFNH)₃phen (3) and Eu(PFND)₃phen (4), which have β-diketone ligands containing fluorinated alkyl chains with different lengths and conjugated naphthyl groups, i.e., 4,4,4-trifluoro-1-(2-naphthyl)butane-1,3-dione (TFNB); 4,4,5,5,5-pentafluoro-1-(2-naphthyl)pentane-1,3-dione (PFNP); 4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)hexane-1,3-dione (HFNH) and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-pentadecafluoro-1-(2-naphthyl)decane-1,3-dione (PFND). And 10-phenanthroline (phen) is coordinated as the neutral second ligand in 1-4. The crystal structures of 1 and 2 have been studied, which are typical and similar to that of 3. The results of TGA-DTA suggest that these Eu complexes have good thermal stabilities. By means of absorption and (time resolved) emission spectroscopy including determination of luminescence quantum yields, energy transfer dynamics and so on, the following results have been obtained: first, these Eu complexes show characteristic pure red color photoluminescence emission with high quantum efficiencies from the central Eu³⁺ ions through the excitation of the ligands; secondly, photophysical properties of 1, 2, 3 and 4, especially the lifetimes of excited states ⁵D₀ of Eu³⁺ ions and quantum efficiencies are influenced by the different lengths of fluorinated alkyl chains, though the singlets (S₁) and triplets (T₁) of the fluorinated ligands are almost the same.     

Synthesis, structure and luminescence properties of zinc (II) complexes with terpyridine derivatives as ligands

Five zinc (II) complexes (1-5) with 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) derivatives as ligands have been synthesized and fully characterized. The para-position of phenyl in ptpy is substituted by the group (R), i.e. tert-butyl (t-Bu), hexyloxy (OHex), carbazole-9-yl (Cz), naphthalen-1-yl-phenyl-amine-N-yl (NPA) and diphenyl amine-N-yl (DPA), with different electron-donating ability. With increasing donor ability of the R, the emission color of the complexes in film was modulated from violet (392 nm) to reddish orange (604 nm). The photoexcited luminescence exhibits significant solvatochromism because the emission of the complexes involves the intra-ligand charge transfer (ILCT) excited state. The electrochemical investigations show that the complexes with stronger electro-donating substituent have lower oxidation potential and then higher HOMO level. The electroluminescence (EL) properties of these zinc (II) complexes were studied with the device structure of ITO/PEDOT/Zn (II) complex: PBD:PMMA/BCP/AlQ/LiF/Al. Complexes 3, 4 and 5 exhibit EL wavelength at 552, 600 and 609 nm with maximum current efficiency of 5.28, 2.83 and 2.00 cd/A, respectively.     

Spectroscopic studies on the luminescence properties of ternary europium complexes with different ligands

In this paper, ligand effect of several bi-dental oxygen (O) and nitrogen (N) ligands on the red luminescence properties of europium ion (Eu³⁺) was studied comprehensively. Absorption, emission, and excitation spectral properties of ternary europium complexes with different combinations of ligands including thenoyl trifluoroacetone (TTA), naphthyl trifluoroacetone (NTA), 2,2′-bipyridyl (bpy) and phenanthroline (Phen) were investigated. Efficient Eu³⁺ red emission was observed with all the combinations of the above mentioned ligands. The most intense emission was found with the all nitrogen coordinated complex Eu(bpy)₂(Phen)₂ while the longest wavelength excitation band was recorded with oxygen-nitrogen mixed NTA-bpy complex Eu(NTA)₁(bpy)₃. With change of the ligands combination and ratio, the Eu³⁺ emission peak changes slightly from 612 to 618 nm. The absorption and excitation spectra of the europium complexes were compared and analyzed referring to the individual absorption spectral properties of the ligands. The relation between ligand-to-metal charge transfer states and luminescence intensities for different complexes was studied.