Pyroelectric properties of lithium triborate in the temperature range from 4.2 to 300 K

Temperature dependences of pyroelectric coefficients γ^T and γ^S corresponding to the mechanically free (T) and clamped (S) states of a lithium triborate (LBO) sample are studied and found to be nonmonotonic. It is proposed that the anomalies are associated with an increase in anharmonism of the lithium sublattice of LBO long before its transition to the superionic state. The spontaneous polarization at T=200 K is estimated to be 0.25 C/m². In the structural motif, the mesotetrahedra responsible for the emergence of spontaneous polarization of LBO are singled out.     

The Contours of the Bands of the Structural Luminescence and Absorption Spectra of Solid Solutions and Crystals of Uranyl Compounds at Low Temperatures

Temperature evolution of the fine structure of the electronic spectra of uranyl nitrates and fluorides is considered. It is shown that for pure crystals at T = 4.2 K the contour is described by the Lorentz curve; for other cases a convolution of the type of the Voigt function is typical. Weak electron–phonon interaction leads to temperature broadening of spectra predominantly due to the Boltzmann change in the population of the initial electronic–vibrational states.     

Fine fluorescence and absorption spectra of hypericin in a polymer matrix at a temperature of 4.2 K

Monochromatic photoexcitation and selective registration in bands of purely electronic S₁↔S₀ transitions resulted in fine fluorescence and absorption (fluorescence excitation) spectra of hypericin in polyvinylbutyral at a temperature of 4.2 K. Vibration analysis of the spectra is done and conclusions are made about the form of many normal vibrations. It is found that the formation of intramolecular hydrogen bonds in the hypericin structure has a substantial effect on the relative position of the electronic vibrational levels of the pigment molecule. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina ave., Minsk 200072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 539–545, July–August, 1998.     

Methods for fine-tuning frequencies of absorption of actinide complexes to frequencies of laser generation lines

On the basis of analysis of relationships relating, among themselves, the positions of bands in the spectra of electron and IR absorption of uranyl complexes in solutions and the donor ability of neutral ligands, the possibility is shown for fine-tuning frequencies of absorption of complexes to frequencies of argon- and CO₂-laser generation lines and using them in the development of methods of control over chemical reactions involving actinides. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 420–422, May–June, 1999.     

Temperature dependence of photoluminescence and electroluminescence of ZnS:Mn crystals

By means of comprehensive analysis of the temperature dependences of the photoluminescence for ZnS:Mn crystals, we have observed persistent changes in the intensity, shape, and position of the maximum in the emission spectrum associated with changes in the immediate environment of the manganese luminescence centers. We have also observed inflection points on the voltage vs. brightness characteristics of the samples, the position of which depends on the frequency of the exciting voltage and the temperature. The observed dependences are explained using concepts describing the mechanisms of pre-breakdown luminescence. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 631–636, September–October, 2006.     

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.     

Luminescence and Energy Transfer in Frozen Solutions of Uranyl Sulfate in Selective Excitation

Luminescence spectra of vitrified solutions of uranyl sulfate in a concentrated sulfuric acid are investigated in the range 4.2–80 K in selective laser excitation. It is shown that the luminescence spectra are a superposition of two components — the component that is related to the resonance excitation of uranyl complexes and the component that is caused by the luminescence of uranyl complexes sensitized by the transfer of electron-excitation energy from the resonance-excited centers. The nonselective character is established for the spectral migration of electron-excitation energy with participation of the bending vibrations of the uranyl complex that ensure direct vibrational transitions between neighboring electronic energy levels. The temperature evolution of the luminescence spectra can be described within the framework of the model of configuration coordinates with allowance for only the linear terms of vibronic interaction.     

Mechanism of photoluminescence excitation of Mn<Superscript>2+</Superscript> ions in ZnS crystals

The mechanisms of photoluminescence excitation of Mn²⁺ ions in ZnS crystals have been investigated on the basis of complex analysis of the temperature dependences of the photoluminescence and photoluminescence-excitation spectra of ZnS:Mn crystals. The activation energy of a manganese luminescence center was estimated at E_a = 0.17 ± 0.05 eV. It is shown that E_a represents an energy band with a width ΔE_a = 0.1 eV, within which a manganese luminescence center can experience radiationless recombination. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 788–793, November–December, 2005.     

Measurements of near millimeter wave atmospheric attenuation in the temperature range 259K to 282K

Field measurements of absorption of near millimetre waves by the atmosphere at temperatures below 280°K have confirmed that there is an additional absorption component characterised by a much larger temperature exponent than can be attributed to water dimers in equilibrium.     

Anomalous states of the structure of (NH4)2SO4 crystals in the temperature range 4.2–300 K

Crystals of the (NH₄)₂SO₄ ammonium sulfate are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameters exhibits an anomalous behavior, namely, a global hysteresis, and an anomalous increase in the lattice parameter a and the unit cell volume at temperatures below the ferroelectric phase transition point (T _c=223 K). The series of superstructure reflections observed corresponds to an incommensurate composite structure. Analysis of the temperature behavior of the mismatch parameters for the matrix (host) and superstructure (guest) lattices demonstrates that the (NH₄)₂SO₄ compound undergoes a number of phase transitions, including a transition to a three-dimensionally incommensurate composite phase and transitions to commensurate (along one of the crystallographic directions) composite phases.     

采用短程飞行时间吸收谱测量冷原子温度时参数误差的影响

详细介绍了短程飞行时间吸收谱测量冷原子温度的基本模型和实验方法.在对铯原子磁光阱中冷原子温度测量的基础上,分析了初始时刻冷原子云中心到探测光束中心的垂直距离、冷原子云初始半径、探测光束半径三个参数的误差分别对于通过短程飞行时间吸收谱测量冷原子温度时所带来的影响,并比较了这些参数各自的影响程度. 关键词： 冷原子温度 飞行时间 短程飞行时间吸收谱     

Optical properties of CuInS2 nanoparticles in the region of the fundamental absorption edge

Glasses are obtained that contain CuInS₂ nanoparticles dispersed in a silicate matrix. The absorption and luminescence spectra of the glasses containing CuInS₂ nanocrystals with particle dimensions of 10–70 nm are studied. The possible reasons for the longwave shift of the fundamental absorption edge and inconsistency of the crystal structure of the CuInS₂ nanoparticles with a chalcopyrite lattice are discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 387–393, May–June, 1998.     

闪电通道温度诊断中观测距离的影响

利用无狭缝光栅摄谱仪获得了青海高原地区云对地闪电首次回击过程的光谱,运用比尔-朗伯定律,考虑传播过程中谱线强度的衰减,计算讨论了观测距离对通道温度诊断结果的影响.结果表明,不同观测距离下得到的光谱诊断放电通道温度,其结果有一定差异;远距离观测得到的温度小于近距离观测的结果;观测距离越远,所得温度的误差越大.因此,在远距离观测的情况下,修正更为重要.由计算结果,得到了温度修正的半经验公式,由此,可以扣除观测距离对闪电通道温度诊断结果的影响.     

Pyroelectric properties of β-BaB2O4 in the temperature range from 2.5 to 90 K

Results are presented of experimental studies of how the spontaneous polarization of β-BaB₂O₄ (BBO) varies with temperature in the range from 2.5 to 90 K. Values of the pyroelectric coefficient γ _s are calculated, and effective values of the Debye temperature (Θ=112 K) and the Einstein temperature (Θ_E=28 K) are estimated. It is shown that the dominant contribution to γ _s comes from acoustic lattice modes. A mechanism is proposed to explain why the temperature dependence of the pyroelectric effect in linear pyroelectric materials is different from that in ferroelectrics. Fiz. Tverd. Tela (St. Petersburg) 39, 1631–1633 (September 1997)     

非对称量子点中磁极化子性质的磁场和温度依赖性

采用Tokuda线性组合算符法和Lee-Low-Pines变换法,研究了温度和磁场对非对称抛物量子点中强耦合磁极化子性质的影响,简捷地得到了作为量子点的横向受限强度ω₁、纵向受限强度ω₂、电子-声子耦合强度α、外磁场的回旋频率ω_c和温度参数γ的函数的磁极化子的振动频率λ、基态能量E₀和有效质量m 关键词： 非对称量子点 强耦合磁极化子 磁场和温度依赖性     

不同组分的钒酸盐混晶Ybt:YxGd1-t-xVO4光谱与激光性质的比较研究

研究了三种掺Yb钒酸盐混晶Yb_0.005:Y_0.298Gd_0.697VO₄, Yb_0.007:Y_0.407Gd_0.586VO₄和Yb_0.009:Y_0.575Gd_0.416VO₄的室温偏振吸收谱和发射谱. 结果表明,最强的吸收和发射相应于π偏振,位 关键词： 掺Yb钒酸盐混晶 吸收谱和发射谱 激光振荡 偏振态     

Electronic Spectra and the Mechanism of Complexing of Uranyl Nitrate in Water–Acetone Solutions

Based on the analysis of electronic absorption and luminescence spectra, the processes of complexing in an aqueous solution of uranyl nitrate hexahydrate (UO₂(NO₃)₂·6H₂O) on gradual addition of small amounts of acetone have been investigated. In a pure aqueous solution, uranyl exists as the UO₂·5H₂O complex. It is shown that addition of acetone to the solution leads to displacement of some water molecules from the first coordination sphere of uranyl and formation of uranyl nitrate dihydrate complexes, UO₂(NO₃)₂·2H₂O. It has been established that the stability of these complexes is determined by the decrease in both the water activity and the degree of hydration of uranyl and nitrate. This is the result of the local increase in the concentration of the molecules of acetone (due to its hydrophobicity) in those regions of the solution in which there are uranyl and nitrate ions. The experimental facts supporting the proposed mechanism are given.