Nanosecond dynamics of destruction of the surface layer of a heterogeneous nanocrystalline solid (sandstone) under the friction

It has been found that the friction of a heterogeneous material, namely, sandstone, leads to the appearance of triboluminescence. The phenomenon of triboluminescence corresponds to luminescence of ≡Si–O free radicals and Fe³⁺ ions. These radicals and ions are formed as a result of the breaking of Si–O–Si bonds in nanocrystals of quartz and feldspar entering into the composition of the sandstone. The time dependence of the triboluminescence intensity represents a set of flashes, each having the duration of a few nanoseconds. It has been assumed that triboluminescence flashes correspond to the appearances of cracks in the material. Сrack opening is found to be approximately 180 nm. The size distribution of the cracks is exponential.     

The kinetics of the triboluminescence of zinc sulphide I

The paper proposes a two-stage model of the time dependence of triboluminescence as a function of the magnitude of the applied exciting pressure; it is confirmed by the results of measuring the time dependence of triboluminescence. The decay of triboluminescence excited by a blow and by friction is measured. The spectral dependence of triboluminescence in ZnS-Mn was found. It has the same form as in photoluminescence and in addition contains maxima corresponding to the electric discharge in air.     

Periodic triboluminescence of zinc sulphide

Powdered ZnS-Mn (Cu, Ag) was scattered in the form of a suspension in different solids. The mechanical excitation of triboluminescence was periodic with a frequency of 50 Hz. The resultant triboluminescence is also periodic if the exciting pressure does not exceed 700 kg/cm². The creation of triboluminescence does not depend on the kind of surrounding medium.     

The intensity of triboluminescence

The first values of the absolute triboluminescence intensity, in units of photons/mol, are reported for molecular crystals and salts. The values range from 5 × 10¹⁶ photons/mol for cholesteryl salicylate to 6.2 × 10¹⁰ photons/mol for magnesium sulfate. The mechanical yield of triboluminescence is defined and the lower limit is determined.     

Synthesis and characterization of highly triboluminescent doped europium tetrakis compounds

One of the most intriguing properties involving crystals is their ability to emit light when fractured. While this property was discovered over 200 years ago, no one has ever been able to come up with a complete theory that can predict the physical principles associated with triboluminescence. However, this has not stopped scientists from coming up with various uses for these materials. One such application is to use these materials as the active element for smart impact sensors that can warn of catastrophic impacts. If these sensors are to become a reality however, the material must emit a bright light when fractured. One of the brightest triboluminescent materials found thus far is europium dibenzoylmethide triethylammonium (EuD₄TEA). This material was discovered by Hurt in 1966 and is bright enough to be seen in daylight. In 2011, the authors discovered that synthesizing EuD₄TEA using europium nitrate instead of chloride significantly increased the triboluminescence yield and made the synthesis much easier and more consistent. However, to date, there are few investigations into the effects of dopants on the triboluminescence of EuD₄TEA. This paper reports the investigation of the effects of various dopants on: (1) The triboluminescent light yield, (2) Crystal size and structure, (3) Synthesis time, and (4) Prompt decay time. Results show that inclusion of dopants during synthesis increases the triboluminescence emission of EuD₄TEA by 55%, significantly reduces the synthesis time, and controls the decay time. All of these properties can be useful for constructing the first prototype of a customized impact sensor.     

Light emitted from a liquid that flows in a narrow channel as triboluminescence

The flow of a liquid through a narrow channel under a high pressure (on the order of tens of atmospheres) can be accompanied by emission of light, which has been termed hydroluminescence. We have shown that this light emission takes place both from the gas and from the liquid phase, with each type of emission being characterized by its own radiation spectrum. The spectra of hydroluminescence are similar to the spectra of photoluminescence obtained upon UV irradiation of a liquid under study. Therefore, the hydroluminescence of a liquid is not a light emission of a specific type; the flow through the narrow channel is only one of the ways of excitation of the light emission, which, in this case, is caused by friction. In other words, hydrodynamic luminescence can be referred to a wider class of phenomena—triboluminescence.     

EPR and UV spectrometry investigation of sucrose irradiated with carbon particles

Solid state/EPR (SS/EPR) dosimeters of carbon ions irradiated sucrose are studied with EPR, and their water solutions – with UV spectroscopy. Doses between 20 and 200 Gy are used with linear energy transfer (LET) values for carbon ions of 63, 77, 96 and 230 keV μm^?1. After irradiation all samples show typical for irradiated sucrose EPR and UV spectra. The obtained data are compared with those previously reported for nitrogen particles and gamma rays irradiated sucrose. The identical shape of both the EPR and UV spectra of irradiated with various type radiation samples suggests that generated free radicals are not influenced by the nature of radiation. The lack of difference in the line width of the separate lines or the whole EPR spectrum, obtained for gamma and heavy particles irradiation, suggests negligible spin–spin interaction among the radiation-generated free radicals in the samples. The linear dependence of the EPR response on the absorbed dose radiation is found to be higher when generated by gamma rays, than by the same absorbed dose of heavy particles. In addition, the EPR response for carbon ions is higher than that for nitrogen ions. Water solutions of irradiated sucrose exhibit UV spectrum with absorption maximum at 267 nm, attributed to the recombination products of free radicals. The UV band intensity depends on the absorbed dose radiation. The UV spectra obtained for carbon, nitrogen and gamma rays irradiated sucrose are also compared.     

Do triboluminescence spectra really show a spectral shift relative to photoluminescence spectra?

There are many reports in the literature of a spectral difference between the triboluminescence (TL) spectrum and the solid-state photoluminescence (PL) spectrum of the same compound. Numerous reasons have been suggested for this difference including pressure-induced changes to Franck-Condon factors during the lifetime of the TL light emission; self-absorption of the TL emission and fracture-induced symmetry changes perturbing the local field of the TL emitting species. However, in a number of cases, the luminescent spectra were recorded on different equipment with different spectral responses, with the resolution of either luminescent spectrum rarely quoted. To avoid artificial spectral differences, care must be taken to account for the response of each equipment over the wavelength range studied, as well as any resolution difference. We have therefore measured the TL and solid-state PL spectra of sixteen TL compounds on the same spectrometer at an identical resolution. Furthermore, the solid-state photoluminescent lifetime has been determined for all samples and the implication that these values have for observing pressure-induced (Franck-Condon) luminescent spectral changes discussed. Finally, in all cases where a significant difference was observed between TL and PL spectra, either self-absorption of the TL emission or fracture-induced perturbations of the local field have been evoked to explain the difference.     

可见-近红外透射光谱检测活体甘蔗蔗糖分的方法

蔗糖分是衡量甘蔗品质的重要指标,基于光谱学原理的活体甘蔗蔗糖分无损检测的方法具有重要意义。探究了不同光谱测量方式对预测结果的影响,改进了特征提取方法,建立了甘蔗蔗糖分预测模型。采用自行搭建的甘蔗透射光谱采集平台,在光源与探测器夹角为120°,150°和180°的条件下,按照甘蔗表皮蜡质去除与否,获取了123个甘蔗样本在6类不同采集方式下的甘蔗透射光谱数据集。首先采用了偏最小二乘回归（PLS）的建模精度评价了Savitzky-Golay平滑处理（S-G平滑）、标准正态变化（SNV）、多元散射校正（MSC）、一阶微分（FD）等多种光谱预处理方法对模型性能的影响,选取了综合效果最好的SNV进行预处理。接着分析了不同光谱测量方式对蔗糖分建模的影响。结果发现：(1) 对于蜡质覆盖的影响而言,去蜡后的光谱透过率更高、单样本不同采集位点的光谱差异更低、与蔗糖分的相关性也更高;(2) 对于光谱采集角度的影响而言,在一定范围内光谱透过率随角度的增大而降低;(3) 在获取的6类数据集中,去蜡且采集角度为120°的测量方式下获取的透射光谱建模效果最好,预测集相关系数为0.790 6,预测集均方根误差为0.898 6。最后,使用了间隔偏最小二乘法（i-PLS）、遗传算法（GA）、蚁群算法（ACO）和提出的基于全波段PLS建模回归系数的改进蚁群算法（VRC-ACO）筛选特征波长。VRC-ACO挑选得到的特征波长数量最少（10个）,且建模效果最好,预测集相关系数达到0.861 6,比全波段建模结果提高9.0%,预测均方根误差降低到0.746 6,比全波段建模结果降低20.0%。该研究为甘蔗蔗糖分无损检测及相应传感器的研发提供了理论支持。     

Evidence for Potassium-Sucrose Interaction in Biological Mid-Infrared Spectra by Multidimensional Analysis

Complex-formation between carbohydrates and cations could have important biological implications.

In this work, Mid-Infrared spectra of pure sucrose solutions and of biological solutions containing sucrose and potassium ions (K+) were investigated by Principal Component Analysis (PGA).

By direct examination of the Mid-Infrared spectra of the biological solutions containing K⁺ ions, no interactions between the cations and sucrose molecules could be observed. However, when the spectral pattern obtained by PCA and which is associated with sucrose, was examined, splitting and shifts in the characteristic absorption bands were observed owing to interactions between sucrose molecules and K⁺ ions. The 997 cm-1 peak which had a visible shoulder at 991 cm-1 and that is observed in pure solutions, was decomposed in the biological solutions into 3 distinct peaks at 1004, 996 and 990 cm-1. The two peaks centered at 1053 cm-1 were split into 3 peaks: 1060, 1051, 1045 cm-1. Hence by PCA, shoulders were characterized in biological solutions and more distinct peaks could be observed. These split and shift phenomena are similar to those obtained when crystalline sugar salts were investigated. This type of interaction, involving potassium ions and sucrose molecules, would be responsible for the storage of this cation which role is essential in plant metabolism.     

Microcrack dynamics in a polymer composite material during friction

The dynamics of microcracks in the surface layers of a polymer and a polymer composite during friction is studied by triboluminescence (TL). The samples are prepared from poly(phenylene sulfide) (PPS) and a composite consisting of PPS reinforced by carbon fibers. An analysis of the spectra shows that TL appears during the relaxation of the electron excitation of the free radicals that form upon the breakage of chemical bonds in carbon fibers and PPS molecules. TL consists of bursts corresponding to microcrack nucleation, and the burst intensity corresponds to the microcrack surface area. Microcracks form in time intervals of several tens of microseconds rather than continuously. Within these intervals, microcracks form in series sequentially, one by one, at a time step of 3?C4 ??s. Each series consists of several (up to 30) microcracks that also form sequentially, in 20-ns intervals. The sequential nucleation of microcracks and microcrack series is explained by stress redistribution in fracture zones in PPS and the composite.     

ZnS:Mn摩擦发光特性的研究

本文报道了ZnS:Mn具有良好摩擦发光性能。研究了ZnS:Mn发光中心Mn^2 及其含量以及样品的灼烧温度、灼烧时间等条件对样品发光特性的影响。优化浓度配比和制备条件制备出了较高摩抢擦发光效率的ZnS:Mn摩擦发光材料。摩擦发光机理可能是由于机械能使ZnS:Mn的电子从基态激发到激发态所致,而具有较高的摩擦发光效率可能来源于ZnS:Mn具有较宽的激发能量范围。     

桂林西瓜霜系列产品的红外光谱分析

采用红外光谱法、二阶导数红外光谱法和二维相关红外光谱法,对桂林西瓜霜系列产品进行了快速无损比对分析研究。结果表明,同一生产厂家不同品种的西瓜霜在红外光谱上差异较显著,所添加辅料的类型和含量有所不同。在一维红外谱图上,西瓜霜喷剂﹑西瓜霜胶囊在638和616 cm-1处有明显的硫酸钠的特征峰;西瓜霜清咽含片﹑西瓜霜喉宝含片和西瓜霜润喉片的红外光谱中,能明显地看到蔗糖、糊精等辅料的特征峰,其中西瓜霜润喉片的红外谱图与蔗糖的红外谱图非常相似,说明西瓜霜润喉片中所添加的蔗糖较多。而在二维红外谱图上,由于五种西瓜霜的自动峰及相关峰峰簇的位置和数量和峰的相对强度的不同,其差别体现得更为明显和直观。应用红外光谱、二阶导数红外光谱和二维相关红外光谱技术,不仅可以提供西瓜霜系列产品主要化学成分的相关信息,还可以对各产品所添加的辅料类型和含量进行分析和指认。因此,红外光谱法是考察中药资源的一种简便、快速、直观、有效的方法。     

Progress in triboluminescence-based smart optical sensor system

Extensive research work has been done in recent times to apply the triboluminescence (TL) phenomenon for damage detection in engineering structures. Of particular note are the various attempts to apply it in the detection of impact damages in composites and aerospace structures. This is because TL-based sensor systems have a great potential for wireless, in-situ and distributed (WID) structural health monitoring when fully developed. This review article highlights development and the current state-of-the-art in the application of TL-based sensor systems. The underlying mechanisms believed to be responsible for triboluminescence, particularly in zinc sulfide manganese, a highly triboluminescent material, are discussed. The challenges militating against the full exploitation and field application of TL sensor systems are also identified. Finally, viable solutions and approaches to address these challenges are enumerated.     

Façade noise abatement prediction: New spectrum adaptation terms measured in field in different road and railway traffic conditions

The Façade Acoustic Insulation Index is one of the most disputed parameters for residential and non-residential buildings. The real performance of the façades does not often agree with the calculated one during the design stage. The field measurement sessions are usually carried out using pink noise spectra, as suggested by the International Standards ISO 717-1. In the present paper six mean spectra derived from in field measurements were proposed: urban toads, traffic lights, roundabouts, freeways, Highways, very high speed trains, high speed trains, and low speed trains. The proposed spectra were equalized against acoustic distortion and were used to measure the noise abatements in a terraced house and in a classroom façade. The highest abatements result for spectra with high levels at high frequencies, better absorbed than low ones by façade elements and frames. The spectrum adaptation terms were also calculated both for the standard and the proposed spectra and were used to predict the façade abatements in compliance with EN ISO 12354-3: the values C_j calculated from the proposed spectra provided more reliable results than the terms C and C_tr (ISO 717-1) and represent a useful tool to predict the noise façade abatements.     

Site selective optical spectra of free base porphin in anthracene

The low temperature optical spectra of free base porphin in crystalline anthracene have been observed in the visible region of the spectrum. Quasilines and broad components were observed in the region of the forbidden Q bands. Site selection techniques were used to separate the spectra of inequivalent site species, and vibronic frequencies were assigned in the ground state and excited Q states. The relative strengths of the broad and quasiline components of the spectra in the Q_x and Q_y states indicated that the host lattice may affect the relative transition strengths of Q_x and Q_y. These results indicated that the strength of the transition to Q_x is greater than that of Q_y for a free porphin molecule.     

Sum rules and figures-of-merit on the microwave permeability of nanocrystalline microwires

The microwave permeability spectra of three nanocrystalline microwires were investigated, and dynamic magnetization M_μ(F) was determined from these spectra. An experimental verification of the theoretical prediction that this quantity was lower than the saturation magnetization was carried out, and it was further shown that the theoretical result provided straightforward guidelines for the conception of high-permeability materials, including successful tradeoffs between a higher resistivity and an increased saturation magnetization. M_μ(F) was determined to be an appropriate figure-of-merit for several applications, including high-frequency noise suppressors.     

Evaluation of intramolecular energy transfer process in the lanthanide(III) bis- and tris-(TTA) complexes: Photoluminescent and triboluminescent behavior

This work reports the energy transfer mechanism process of [Eu(TTA)₂(NO₃)(TPPO)₂] (bis-TTA complex) and [Eu(TTA)₃(TPPO)₂] (tris-TTA complex) based on experimental and theoretical spectroscopic properties, where TTA=2-thienoyltrifluoroacetone and TPPO=triphenylphosphine oxide. These complexes were synthesized and characterized by elemental analyses, infrared spectroscopy and thermogravimetric analysis. The theoretical complexes geometry data by using Sparkle model for the calculation of lanthanide complexes (SMLC) is in agreement with the crystalline structure determined by single-crystal X-ray diffraction analysis. The emission spectra for [Gd(TTA)₃(TPPO)₂] and [Gd(TTA)₂(NO₃)(TPPO)₂] complexes are associated to T→S₀ transitions centered on coordinated TTA ligands. Experimental luminescent properties of the bis-TTA complex have been quantified through emission intensity parameters Ω_λ (λ=2 and 4), spontaneous emission rates (A_rad), luminescence lifetime (τ), emission quantum efficiency (η) and emission quantum yield (q), which were compared with those for tris-TTA complex. The experimental data showed that the intensity parameter value for bis-TTA complex is twice smaller than the one for tris-TTA complex, indicating the less polarizable chemical environment in the system containing nitrate ion. A good agreement between the theoretical and experimental quantum yields for both Eu(III) complexes was obtained. The triboluminescence (TL) of the [Eu(TTA)₂(NO₃)(TPPO)₂] complexes are discussed in terms of ligand-to-metal energy transfer.     

Strong Coulomb correlation effects in ZnO

The electronic structure, band parameters, and optical spectra of wurtzite-type ZnO were studied by first-principles calculations within different approximations of the density functional theory. The local-density approximation underestimates the band gap, the energy levels of the Zn-3d states, the band dispersion, the crystal-field splitting, the spin-orbit interaction, and location of peaks in the optical spectra. The generalized-gradient approximation slightly corrects the discrepancies with the experimental findings and it shows good agreement for the optical spectra with experimental data at energies 10-20 eV for E⊥c. Studies within the local-density approximation with the multiorbital mean-field Hubbard potential show that strong Coulomb correlations are in operation. From effective mass calculations it is found that holes are much heavier and more anisotropic than the conduction-band electrons in ZnO.     

Quenching of tribo- and photoluminescence in a Tb2(SO4)3 · 8H2O + NaNO2 crystalline mixture

It is found that the addition of NaNO₂ to Tb₂(SO₄)₃ · 8H₂O crystals quenches tribo- and photo-luminescence from the latter. In the case of triboluminescence, the glow of both Tb³⁺* ions (solid component of triboluminescence) and N ₂ ^* molecules (gas component) is quenched. The NO ₂ ^? ion is known to be an efficient quencher of Tb³⁺ ion luminescence by the mechanism of radiationless energy transfer in solutions. That quenching takes place when a crystalline quencher is in contact with a crystalline phosphor and also with a gaseous (molecular) phosphor seems to indicate that the excitation energy is transferred not only within individual crystals but also between contacting surfaces of the phosphor and quencher and at the gas-solid interface.