High-pressure and optical properties of lanthanum magnesium hexa-aluminate doped with Mn (LMA:Mn) laser material

The effect of hydrostatic pressure on the emission spectra and fluorescence lifetime (τ) of Mn²⁺ in LaMgAl₁₁O₁₉ (LMA) crystals up to 101 kbar has been studied at room temperature. From the position of the peak (⁴T₁ → ⁶A₁ transition) in the emission spectra, we estimated that the pressure induced red-shift. A variation, slowly decreasing, in the fluorescence lifetime (τ) values for ⁴T₁ → ⁶A₁ transition was observed. The pressure-induced red-shift and lifetime variation could be described by simple models. In the considered pressure range (0-101 kbar), a good agreement between the experimental values and theoretically predicted values was obtained.     

Effect of hydrostatic pressure on the Raman spectrum of anatase (TiO2)

Raman spectra of anatase have been investigated under pressures up to 60 kbar and at room temperature. A pressure-induced phase transition is observed at pressures above 25.6 kbar. The 197 cm^-1 mode (at 1 atm.) of six Raman active modes exhibits anomalous pressure dependence in which the frequency decreases with increasing pressure. This mode may be significant in the phase transition. The remaining modes show usual behavior.     

Photophysics, Photochemistry and Energetics of UV Light Induced Disulphide Bridge Disruption in apo-α-Lactalbumin

Continuous 295 nm excitation of whey protein bovine apo-α-lactalbumin (apo-bLA) results in an increase of tryptophan fluorescence emission intensity, in a progressive red-shift of tryptophan fluorescence emission, and breakage of disulphide bridges (SS), yielding free thiol groups. The increase in fluorescence emission intensity upon continuous UV-excitation is correlated with the increase in concentration of free thiol groups in apo-bLA. UV-excitation and consequent SS breakage induce conformational changes on apo-bLA molecules, which after prolonged illumination display molten globule spectral features. The rate of tryptophan fluorescence emission intensity increase at 340 nm with excitation time increases with temperature in the interval 9.3–29.9°C. The temperature-dependent 340 nm emission kinetic traces were fitted by a 1st order reaction model. Native apo-bLA molecules with intact SS bonds and low tryptophan emission intensity are gradually converted upon excitation into apo-bLA molecules with disrupted SS, molten-globule-like conformation, high tryptophan emission intensity and red-shifted tryptophan emission. Experimental Ahrrenius activation energy was 21.8 ± 2.3 kJ.mol⁻¹. Data suggests that tryptophan photoionization from the S₁ state is the likely pathway leading to photolysis of SS in apo-bLA. Photoionization mechanism(s) of tryptophan in proteins and in solution and the activation energy of tryptophan photoionization from S₁ leading to SS disruption in proteins are discussed. The observations present in this paper raise concern regarding UV-light pasteurization of milk products. Though UV-light pasteurization is a faster and cheaper method than traditional thermal denaturation, it may also lead to loss of structure and functionality of milk proteins.     

二硼酸锂晶体的压致非晶化研究

二硼酸锂晶体的压致非晶化研究李玉栋，扈士芬，蓝国祥（南开大学物理系天津３０００７１）Ｐｒｅｓｓｕｒｅ－ＩｎｄｕｃｅｄＡｍｏｒｐｈｉｓａｔｉｏｎｏｆＬｉｔｈｉｕｍＤｉｂｏｒｉｔｅ￥ＹｕｄｏｎｇＬｉ；ＳｈｉｆｅｎＨｕａｎｄＧｕｏｘｉａｎｇＬａｎ（Ｄｅｐａ...     

Pressure-induced delocalization of photoexcited states in a semiconducting polymer

We present broadband transient absorption spectroscopy on the fluorescent copolymer poly(9,9-dioctylfluorene-co-benzothiadiazole) under hydrostatic pressure of up to 75?kbar. We observe a strong reduction of the stimulated emission intensity under pressure, coupled with slower decay kinetics and reduced fluorescence intensity. These observations indicate increased delocalization of photogenerated singlet excitons, facilitated by an increased dielectric constant at high pressure. Spin triplet excitons, generated via an iridium complex-F8BT oligomer, show reduced lifetimes under pressure.     

Raman spectroscopy of solid nitrogen up to 374 kbar

We measured the Raman spectrum of room-temperature solid nitrogen in a diamond cell at pressures up to 374 kbar. Only the molecular stretching mode was observed. The frequency of this mode appears to increase smoothly from 2340 cm^-1 at 39 kbar to 2394 cm^-1 at 374 kbar. Between about 50 and 120 kbar, the Raman line is split into a second, higher-frequency peak, which may be associated with molecular ordering in the solid. Measurements of broadening and splitting in fluorescence lines from the ruby pressure gauge indicate that solid nitrogen is reasonably plastic up to 130 kbar. We suggest that nitrogen might serve as a useful pressure medium.     

用高压显微光谱系统研究(Zn0.85Cd0.15)S:Cu,Al磷光体在流体静压力下施主-受主对的发光

用金刚石对顶砧高压显微光谱系统在室温和1bar—66kbar的流体静压力范围内研究了(Zn_0.85Cd_0.15)S:Cu,Al磷光体的发光峰位置和相对发光强度随压力而变化的规律。随着压力的增加,发射峰值波长迅速移向短波方向,而发射峰值对应的光子能量随压力增加的速率为4.7meV/kbar(38cm^-1/kbar)。这个值比该材料的吸收边随压力增加的速率要小。随着压力的增加,该磷光体的发光峰值相对强度急骤下降,当压力从常压升到66kbar时,发光峰值相对强度下降到原值的6％。这些结果可以用Al³⁺-Cu⁺的施主-受主对模型来解释。本文还估计施主(Al³⁺)和受主(Cu⁺)的激活能之和随压力增加的速率为3.7meV/kbar(30cm^-1/kbar)。 关键词：     

Pressure and temperature dependence of the emission in BaF2:Eu and SrF2:Eu

The 4f⁶5d¹(e)→4f⁷ emission (normal) of Eu²⁺ in SrF₂ and normal and anomalous emissions of Eu²⁺ in BaF₂ are studied as a function of pressure and temperature. Although in BaF₂ both emissions (anomalous and normal) shift with pressure in the same spectral direction (a red shift), the anomalous emission converts to the normal emission when the pressure increases to 33 kbar. Considering the dependence of BaF₂:Eu²⁺ luminescence on the pressure and temperature we have found that spectral transformation takes place due to a smooth pressure-induced level crossing at approximately the same pressure as the phase transition.     

相变及空位缺陷对SrF2在高压下光学性质的影响

本文采用第一性原理方法, 计算了SrF2的理想晶体和含锶、氟空位点缺陷晶体在100 GPa压力范围内的光学性质. 吸收谱数据表明, 压力因素引起的两个结构相变对SrF2的吸收谱均有影响: 第一个相变将导致其吸收边蓝移, 第二个相变将导致其吸收边红移. 空位点缺陷的存在将使得SrF2的吸收边红移, 其中氟空位点缺陷引起的红移行为更显著. 尽管如此, 这些红移并未使得SrF2晶体在可见光区出现光吸收的现象(是透明的). 波长在532 nm处的折射率数据指明, 在SrF2的三个结构相区, 其折射率均随压力的增加而增大, 且SrF2的高压结构相变也使得其折射率增大. 锶空位点缺陷将导致SrF2的折射率降低, 但氟空位点缺陷的存在对其基本没有影响. 分析表明, SrF2晶体有成为冲击窗口材料的可能.     

Optoacoustic study of laser-induced near-critical states of thin aluminum films

The results of the optoacoustic study of aluminum states within a temperature range of 3–14 kK and a pressure range of 0.1–4 kbar were considered. These high-energy states were achieved by heating a submicron metal film confined by a transparent dielectric via nanosecond laser pulses with a fluence of up to 11 J/cm². The dynamics of the temperature, pressure, and reflectivity of aluminum was studied at a nanosecond time resolution.     

Calibration of the R ruby fluorescence lines in the pressure range [0-1 GPa] and the temperature range [250-300 K]

Abstract

The pressure range [&1 GPa] and the temperature range [250–300 K] are commonly used in many science fields like biology, agro-chemistry, pharmacology, or geology. In this paper, the calibration of the ruby R lines of fluorescence is performed in these pressure and temperature ranges, using the melting curve of pure water. The linear shifts of ruby peaks are equal to ?0.140cm^?1/K and ?0.768cm^?1/kbar with R₁, and to ?0.137cm^?1/K and ?0.779 cm^?1/kbar with R₂. The accuracy of pressure measurements can be as good as ± 10MPa if the temperature is known with ±0.5 K. Such a precision is achieved if: (1) the position of each peak is determined using an inversion method; (2) daily shifts of the spectrometer are corrected before each acquisition; (3) peak positions of each ruby are known at ambient pressure and temperature.     

Fluorescence properties of Ag nanoparticles in water, methanol and hexane

Ag nanoparticles, synthesized employing the electro-exploding wire technique, are reported. Absorption in the UV-visible region by these particles is characterized by the features reported in the literature, namely, a possible plasmon peak at ∼404 nm. For Ag nanoparticles dispersed in water, photo-excitation in the ranges 210-235 and 255-280 nm produces similar fluorescence emission at ∼300 nm, whose corresponding resonant absorption takes place at 215 and 270 nm in the excitation spectra. Further, we study the effect of the surrounding medium (solvent effect) on fluorescence from these nanoparticles by comparing fluorescence emission in methanol and hexane for photo-excitation in the same range. Compared to water, fluorescence emission in methanol is observed red-shifted at ∼310 nm, which further red-shifts to ∼325 nm in hexane. The corresponding resonant absorptions in methanol are at 225 and 275 nm. Consequence of this red-shift in a less polar solvent is discussed.     

Raman spectroscopy and magnetic properties of KMCr(CN)6 under pressure

We study the effect of pressure on Raman spectra as well on magnetic properties of molecule-based magnets KNiCr(CN)₆ and KMnCr(CN)₆. The effect of pressure on the ν[C≡N] vibration band which is located in the 2100–2200?cm^?1 spectral range is relatively weak. Hydrostatic pressure has small almost a negligible effect on the Curie temperature of ferromagnetic KNiCr(CN)₆ while leads to a pronounced reversible Curie temperature increase occurrence of new magnetic phase under pressure in the case of KMnCr(CN)₆. Applied pressure affects magnetization curves only marginally. All pressure-induced changes are reversible.     

Pressure-induced phase transition in LiLuF4:Pr3+ investigated by an optical technique

The luminescence and luminescence kinetics of LiLuF(4) doped with 1.5 at.% of Pr(3+) obtained at high hydrostatic pressure changing from ambient to 220 kbar applied in a diamond anvil cell are presented. It has been shown that pressure causes shift of the emission lines toward the red with rates of the order of single cm(-1) kbar(-1). The pressure-induced phase transition from tetragonal to fergusonite structure for pressure above 100 kbar was observed. The crystal field calculations performed showed that this phase transition reduces the point symmetry of the Pr(3+) site from the S(4) to the C(2) point group.     

High Pressure Spectroscopy of Ce Doped Yag Crystal

Electronic structure and optical properties of the Ce^3? in YAG has been investigated by standard spectroscopy (photoluminescence, absorption and excitation spectra) and high pressure spectroscopy. The bandshape of the emission spectrum for different pressures has been analyzed and influence of pressure on energy of the 5d¹ states and the electron-lattice coupling have been determined. The significant red shift of the peak of the emission band (the respective pressure coefficient has been equal to—12cm^?1/kbar) has been obtained. The shift has been understood by taking into account pressure induced increase of the 5d¹ level splitting and increase of the electron-lattice coupling strength.     

Dark energy interacting with neutrinos and dark matter: a phenomenological theory

A model for a flat homogeneous and isotropic Universe composed of dark energy, dark matter, neutrinos, radiation and baryons is analyzed. The fields of dark matter and neutrinos are supposed to interact with the dark energy. The dark energy is considered to obey either the van der Waals or the Chaplygin equations of state. The ratio between the pressure and the energy density of the neutrinos varies with the red-shift simulating massive and non-relativistic neutrinos at small red-shifts and non-massive relativistic neutrinos at high red-shifts. The model can reproduce the expected red-shift behaviors of the deceleration parameter and of the density parameters of each constituent. Dedicated to Professor Ingo Müller on the occasion of his seventieth birthday.     

相变及空位缺陷对高压下GeO_2光学性质的影响

本文采用第一性原理方法,在100 GPa的压力范围内,计算了GeO_2理想晶体和含锗、氧空位点缺陷晶体的光学性质.吸收谱数据表明,压力诱导的三个结构相变对GeO_2晶体的吸收谱均有影响:第一个相变将导致其吸收边蓝移,而第二和第三相变将使得其吸收边红移.锗和氧空位点缺陷的存在将导致GeO_2的吸收边红移,但氧空位点缺陷引起的红移更明显.尽管如此,分析发现,在100 GPa的压力范围内,压力、相变以及空位点缺陷等因素都不会导致GeO_2晶体在可见光区出现光吸收现象(是透明的).波长在532 nm处的折射率数据显示,在GeO_2的四个相区,其折射率均随压力增加而降低;而且,GeO_2的三个结构相变以及锗、氧空位点缺陷都会导致其折射率有所增大.本文预测,GeO_2有成为冲击光学窗口材料的可能.     

Effect of hydrostatic pressure on the phase transition of ferroelectric PbTiO3

The effect of hydrostatic pressure on the dielectric constant of the Nb-doped lead titanate ceramics was measured up to 60 kbar at room temperature. From the previously observed pressure dependence of lattice parameters and the present results, it is concluded that the tetragonality decreases linearly with a slope of ?7.6×10^?4/kbar and that the pressure dependence of the tetragonal-cubic transition temperature is ?8.4K/kbar.     

Conformational Transitions of the Catalytic Domain of Heme-Regulated Eukaryotic Initiation Factor 2α Kinase, a Key Translational Regulatory Molecule

In mammalian cells, the heme-regulated inhibitor (HRI) plays a critical role in the regulation of protein synthesis at the initiation step through phosphorylation of α-subunit of the eukaryotic initiation factor 2 (eIF2). In this study we have cloned and performed biophysical characterization of the kinase catalytic domain (KD) of rabbit HRI. The KD described here comprises kinase 1, the kinase insertion domain (KI) and kinase 2. We report here the existence of an active and stable monomer of HRI (KD). The HRI (KD) containing three tryptophan residues was examined for its conformational transitions occurring under various denaturing conditions using steady-state and time-resolved tryptophan fluorescence, circular dichroism (CD) and hydrophobic dye binding. The parameter A and phase diagram analysis revealed multi-state unfolding and existence of three stable intermediates during guanidine hydrochloride (Gdn-HCl) induced unfolding of HRI (KD). The protein treated with 6 M Gdn-HCl showed collisional and static mechanism of acrylamide quenching and the constants (K _sv  = 3.08 M⁻¹and K _s   = 5.62 M⁻¹) were resolved using time resolved fluorescence titration. Based on pH, guanidine hydrochloride and temperature mediated transitions, HRI (KD) appears to exemplify a rigid molten globule-like intermediate with compact secondary structure, altered tertiary structure and exposed hydrophobic patches at pH 3.0. The results indicate the inherent structural stability of HRI (KD), a member of the class of stress response proteins.