Fluorescence characteristics of 5-aminoquinoline in acetonitrile: Water

Photophysical and spectral properties of 5-aminoquinoline (5-AQ) in acetonitrile: water binary mixture have been studied to understand the excited state relaxation processes occurring in the excited state. Fluorescence of 5-AQ has been found to be quite sensitive to the hydrogen bond donating ability of the solvent mixture and is quenched in the presence of water. Hydrogen bonding in the excited state appears to be responsible for the quenching.     

SrTiO3：Cr^3＋晶体荧光光谱及荧光寿命的热效应

测量了SrTiO~3:Cr(3+)晶体5～200K的荧光光谱和寿命。并用单声子吸收与发射过程相关的电子振动跃迁理论较好地解释了150K以下荧光寿命随温度变化的规律。     

Temporal characteristics of the fluorescence of the anionic form of 3-hydroxyflavone

The spectral and temporal characteristics of the fluorescence of the anionic form of 3-hydroxyflavone in acetonitrile are studied. This form can be selected upon excitation in the region from 380 to 440 nm with the maximum near 420 nm. The fluorescence spectrum of this form has the shape of a wide structureless band peaked at about 470 nm. The lifetimes of the fluorescence of the anionic form in the region from 460 to 530 nm are measured; the average lifetimes do not depend on the recording wavelength in the entire region and are equal to 3.7 ± 0.2 ns. Addition of water to the solution leads to a gradual quenching of the fluorescence and its complete vanishing at a concentration of 10 M. This is a static quenching or quenching of the first kind according to Vavilov’s classification; i.e., it occurs in the ground state.     

Influence of deformations of a polymer matrix on the characteristics of dual fluorescence of 3-hydroxyflavone

The possibility of considerably changing the conditions for the proton transfer reaction in 3-hydroxyflavone molecules in polyvinyl alcohol (PVA) polymer matrices by stretching deformations is demonstrated. Samples of this kind are traditionally used to obtain ensembles of fluorophore molecules oriented along a chosen axis and for polarization measurements. The fluorescence spectrum of 3-hydroxyflavone in PVA has two characteristic bands in the violet and green spectral regions, which indicates excited-state proton transfer. Stretching leads to a strong reduction in the violet band, whose contribution in undeformed samples is comparable to the contribution of green fluorescence. Even twofold stretching of PVA films strongly decreases the violet band intensity, which is more pronounced in the case of sixfold stretching. In the latter case, the fluorescence spectrum behavior is very close to the pattern observed in nonpolar and aprotic solvents, in which the violet fluorescence intensity is very low. The data obtained indicate that mechanical stretching allows one to eliminate the main intermolecular factors that slow down the proton transfer between the active groups in PVA.     

Polymer microenvironmental effects on the photophysics of cinchonine dication

Photophysical properties of cinchonine dication (C⁺⁺) have been studied in protic and aprotic polymers by monitoring steady state and time resolved measurements. It is found to be sensitive towards the microenvironment of polymers. Edge excitation red shifted emission (EERS) is observed in all polymeric matrices. However, the magnitude of EERS is relatively high in protic as compared to aprotic polymer. Isobestic point in excitation spectra and three decay components in time resolved measurements indicate more than two trapped chemical species in the heterogeneous environment of the polymer. Solute-polymer interactions are found to produce the third decay channel, unlike in solution phase and may be useful to understand the polymer microenvironment.     

Polymer effects on small- and large-scale two-dimensional turbulence

We investigate the effect of dilute polymers on driven two-dimensional turbulence in a soap film. Transitions from strong to weak turbulence are identified by independently varying the polymer concentration phi and the energy injection rate epsilon(inj) . Studies of velocity structures in small scales reveal that strong saddles are suppressed, whereas weak ones become more populated. Interestingly, this redistribution of saddle points in turbulent flows strongly correlates with the quenching of velocity fluctuations on large scales, suggesting that this hydrodynamic structure may play a role in transferring energy from scale to scale.     

Magnetic field effects on the fluorescence of Cr3+ in GdAlO3

The fluorescence spectrum of Cr³⁺ in GdAlO₃ has been examined at 4.2 K as a function of magnetic field up to 60 kG. The resulting splitting of the ²E → ⁴A₂ emission lines are explained in terms of a modified molecular field approximation, which incorporates the effect of the spin fluctuations. The exchange constant in the relaxed excited state is found to be 1.2 cm^-1, which differs from that reported from absorption data. It is suggested that the difference may be related to the Frank-Condon effect.     

Polymer dynamics, fluorescence correlation spectroscopy, and the limits of optical resolution

In recent years, fluorescence correlation spectroscopy has been increasingly applied for the study of polymer dynamics on the nanometer scale. The core idea is to extract, from a measured autocorrelation curve, an effective mean-square displacement function that contains information about the underlying conformational dynamics. This Letter presents a fundamental study of the applicability of fluorescence correlation spectroscopy for the investigation of nanoscale conformational and diffusional dynamics. We find that fluorescence correlation spectroscopy cannot reliably elucidate processes on length scales much smaller than the resolution limit of the optics used and that its improper use can yield spurious results for the observed dynamics.     

Luminescence characteristics of the Pr3+ ion in SrAlF5

The paper reports on a study of luminescence and excitation spectra of SrAlF₅:Pr³⁺ (0.5 mol %) polycrystals performed at 10 and 300 K with synchrotron radiation in the range from 5 to 25 eV. The Pr³⁺ ions in SrAlF₅ were shown to emit successively two photons in transitions from the ¹ S ₀ and ³ P ₀ levels. The main energy characteristics of the compound, namely, the position of the 4f → 5d excitation band (5.95–8.0 eV), the energy separation between the ¹ S ₀, 4f and the lowest 5d levels (～0.15 eV), and the SrAlF₅ band gap width (～12 eV), were determined. SrAlF₅:Pr³⁺ was found to possess a number of features not found in other Pr³⁺-activated fluorides.     

Pressure effects on 2p5 3p - 2p5 3d transitions in neon

The collisional broadening and shift of four spectral lines of neon (747.2, 748.8, 753.5, 754.4 nm) arising from 2p⁵ 3p - 2p⁵ 3d transitions, emitted from a low-pressure glow discharge in pure neon and neon-helium mixtures have been measured using a Fabry-Perot interferometer. The values of pressure broadening and shift coefficients are determined and analyzed in terms of the impact theory.     

甲醇和乙醇的三维荧光光谱特性研究

为阐明甲醇和乙醇的光谱学特性,建立两者快速的辨析方法。采用三维荧光光谱,对甲醇和乙醇的荧光特性进行了研究。分析结果显示,甲醇的三维荧光光谱中出现了两个特征荧光峰,其荧光强度在甲醇体积浓度小于15%时与其浓度成正相关,乙醇的三维荧光光谱中出现了一个完整的特征荧光峰,其荧光强度在乙醇体积分数小于50%时与乙醇浓度成相关,甲醇比乙醇具有更高的荧光效率,以甲醇为有机溶剂研究化合物的荧光特性时,需要考虑甲醇的本底荧光。甲醇和乙醇的特征荧光峰位置差别较大,前者特征荧光峰出现在225/35 0nm和250/375nm处,而后者特征荧光峰位于240/310nm,据此可以有效辨析两种醇。     

Polymer and surface roughness effects on the drag crisis for falling spheres

We make time resolved velocity measurements of steel spheres in free fall through liquid using a continuous ultrasound technique. We explore two different ways to induce large changes in drag on the spheres: 1) a small quantity of viscoelastic polymer added to water and 2) altering the surface of the sphere. Low concentration polymer solutions and/or a pattern of grooves in the sphere surface induce an early drag crisis, which may reduce drag by more than 50% compared to smooth spheres in pure water. On the other hand, random surface roughness and/or high concentration polymer solutions reduce drag progressively and suppress the drag crisis. We also present a qualititative argument which ties the drag reduction observed in low concentration polymer solutions to the Weissenberg number and normal stress difference.     

Mechanochemical effects on the precursor formation and microwave dielectric characteristics of MgTiO3

Mechanochemical effects on the formation of Mg---O---Ti complex and microwave dielectric properties of MgTiO₃ oxides were studied using several different starting materials. Single phase MgTiO₃ powder was obtained after heating (900 °C, 2 h) the mechanically activated precursor from a mixture of two unitary powders, magnesium hydroxide and anatase (MP). Formation of MgTiO₃ on subsequent thermal treatment was significantly accelerated by incipient mechanochemical interaction. The Q value of the ceramics sintered at 1350 °C for 2 h from MP was higher than those of three other ceramics due to the uniformity of the microstructure and phase.     

The fluorescence and thermoluminescence characteristics of α-Al2O3:C ceramics

This paper reports that polycrystalline α-Al₂O₃:C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence (TL) and optical stimulated luminescence (OSL) of α-Al₂O₃:C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F⁺ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610K. The attenuation constant of exponentially decaying fast component (τ₁) and slow component(τ₂) of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al₂O₃:C crystal.     

The effect of relaxation and core–hole decay on the M5O3 X-ray fluorescence spectrum of La metal

In the M₅O₃ X-ray emission spectroscopy (XES) spectrum of La metal the spectral intensity ratio of the satellite to the diagram line is very large, as compared to that of the shakedown satellite to the main line in the M₅ X-ray photoelectron spectroscopy (XPS) spectrum. The large spectral intensity ratio is due to the X-ray fluorescence of the shakedown satellite via the relaxation of the M₅ main-line state to the shakedown satellite state on the time scale of M₅–hole decay. We attribute the large line width of the M₅ main-line state of La metal as compared to that of Ba metal, to the relaxation on the time scale of M₅–hole decay.     

垃圾渗滤液中溶解性有机物组分的三维荧光特性

运用三维荧光光谱技术研究了垃圾渗滤液中六种DOM组分的荧光特性。结果表明:类富里酸、类色氨酸和腐殖酸类物质是垃圾渗滤液DOM的主要组成,其中大量紫外区类富里酸物质的存在,是导致其可生化性差的主要原因。HOA含有较多紫外区类富里酸和较少可见区类富里酸,HIA正好相反;HIN组分主要包括紫外区和可见区类富里酸;HOB、HIB和HIN三种组分在各区域荧光信号都较强,包括HON组分在内,这四种组分荧光峰位置主要集中在类腐殖酸、紫外区类富里酸及可见区类富里酸三个区域;但不同组分的荧光强度差别较大,HOB和HIB在紫外区类富里酸有较强荧光强度,HIN在紫外区类富里酸、可见区类富里酸区域均有较强荧光强度;与这三者相比,HON在各位置的荧光信号中等;而HOA和HIA的荧光强度相对较弱,说明有机酸类物质的荧光特性较差。     

Micellar effects on the molecular aggregation and fluorescence properties of benzazole-derived push-pull butadienes

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in dioxane-water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties (such as polarity and CMC) have been determined using both dienes as probes.