Infrared absorption spectra of hydrogen complexes in type I diamonds

The 3107 cm^?1 peak has been observed in the infrared absorption spectra of all but one of some 50 type I diamonds examined. Evidence is presented which strongly supports the interpretation of this peak as being due to a carbon-hydrogen bond stretching mode. Reasons are given for believing that the hydrogen responsible for this, and the associated 1405 cm^?1 line, is present as a constituent of the vinylidene group( > C = CH₂).Several new peaks, of fairly general occurrence, are reported in the wavenumber range 3400 cm ^?1 to 2750 cm ^?1. Some of these lines, seen only when the specimens exhibit at least partial type Ib character, are almost certainly due to nitrogen-hydrogen bond stretching. Others, found in type Ia and/or partially type Ib specimens may be due to C-H or N-H stretching in different local environments. Our observations show that hydrogen is as ubiquitous an impurity in diamond as nitrogen.Possible sites within the crystals for these hydrogenous groups are discussed.     

On the possible origins of natural diamonds

A brief survey of the current theories of formation of diamonds in nature leads to the hypothesis which suggests the possibility of natural diamonds having formed metastably—a hypothesis which has not been enjoying much experimental support in its favour. The authors present briefly some aspects of the investigations which have resulted in demonstrating a new process whereby the dissolution and metastable autoepitaxial (re)crystallization of diamond occurs at atmospheric pressure. A comparison of certain reported growth characteristics of natural (terrestrial) and synthetic (high pressure, solvent-catalyst) diamonds with those of the metastable diamond overgrowths reveal many striking similarities. These results therefore serve as evidence to support the metastable origin hypothesis.     

Luminescence bands in natural brown diamonds

We report on new luminescence bands exhibited by natural brown/mauve diamonds. We describe detailed absorption and luminescence measurements in the visible spectral region. The structured bands with ZPL at 2.424 eV, 2.114 eV, 1.819 eV and 1.707 eV, and a broad band with a maximum at 1.8 eV are shown to be the main components of the visible luminescence. Bands with ZPL at 2.114 eV, 1.819 eV and 1.707 eV are shown to correspond to forbidden transitions with lifetimes of the order of msec. Energy absorbed by the 2.424 eV centre is transferred into the 1.819 eV centre.     

Optical absorption and energy-loss spectra of aligned carbon nanotubes

Optical-absorption cross-sections and energy-loss spectra of aligned multishell carbon nanotubes are investigated, on the basis of photonic band-structure calculations. A local graphite-like dielectric tensor is assigned to every point of the tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations in media with tensor-like dielectric functions. A Maxwell-Garnett-like approach appropriate to the case of infinitely long anisotropic tubules is also developed. Our full calculations indicate that the experimentally measured macroscopic dielectric function of carbon nanotube materials is the result of a strong electromagnetic coupling between the tubes. An analysis of the electric-field pattern associated with this coupling is presented, showing that in the close-packed regime the incident radiation excites a very localized tangential surface plasmon. Received 18 January 2001     

Effect of annealing on the optical absorption spectra of single-walled carbon nanotubes

The thermal stability of initial and purified samples of single-walled carbon nanotubes prepared through gas-phase disproportionation of carbon monoxide CO in the presence of iron particles under high pressure (the HiPCO method) is investigated using optical absorption spectroscopy and thermogravimetry. An analysis of the optical absorption spectra demonstrates that thermal oxidation of the initial material proceeds rather rapidly and uniformly owing to the catalytic effect caused by the presence of iron particles in the sample. The destruction of the carbon nanotubes contained in the as-prepared and purified samples begins at temperatures of ～250 and ～300°C, respectively. It is shown that single-walled metallic nanotubes undergo faster oxidation as compared to the single-walled semiconducting nanotubes.     

Excitonic absorption spectra and ultrafast dephasing dynamics in arbitrary carbon nanotubes

We illustrate the potential of the density matrix theory for investigation of optical properties of arbitrary single‐walled carbon nanotubes (CNTs). We have performed microscopic calculations of excitonic absorption spectra for CNTs of different chiral angles and diameters. The obtained results are in good agreement with experiments, in particular the excitonic binding energies match well both experiments and ab initio calculations. Furthermore, we show the strength of our approach by presenting calculations of the ultrafast Coulomb driven non‐equilibrium dynamics in CNTs. We find excitation induced dephasing on the picosecond time scale depending on the excitation strength. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impurity centers in synthetic and natural diamonds with a system of electron-vibronic Lines at 418 nm in luminescence spectra

Physics of the Solid State - Analysis of the spectra of IR absorption, ESR, and luminescence of natural and synthetic diamonds with a system of electron-vibronic lines at 418 nm in the luminescence...     

Bulk femtosecond laser marking of natural diamonds

Point-by-point multi-shot femtosecond laser writing of micro-scale linear damage tracks and symbolic logo information was performed inside single-crystal natural diamonds in transversal writing geometry at variable basic operational parameters (numerical aperture of focusing optics, depth of focusing inside samples and peak laser pulse powers). The filamentary character of femtosecond laser writing of buried damage tracks in this material at the supercritical peak laser powers was revealed.     

Broadening of vibrational spectra of carbon dioxide upon absorption and condensation in nanopores

Coherent anti-Stokes Raman Spectroscopy (CARS) has been used to study the vibrational Q-branch with the frequency of 1388 cm^?1 of the ν₁ mode of carbon dioxide molecules filling a sample made of nanopore glass at room temperature (20.5°C). The measurements were carried out in a gas cell at pressures approaching saturation P _sat. When pressure was increased above 0.8 P _sat, in addition to the spectral component due to the gaseous phase molecules, the CARS spectra featured a component due to the molecules adsorbed on the pore walls. Simulation of spectra taking the interference of these two contributions into account enabled the estimation of the broadening of the vibrational molecular spectra in the adsorbed layer. The spectral width of the component due to the adsorbed molecules was nearly a factor of two times larger than that of molecules in the bulk liquid phase. At pressures above 0.94 P _sat, the spectral width of the component due to the adsorbed molecules decreased to values close to those measured in the bulk liquid phase, which corresponds to the condensation of molecules in nanopores.     

Cathodoluminescence spectra of diamonds in UHP rocks from the Kokchetav Massif, Kazakhstan

We propose to investigate the diamonds from the Kokchetav Massif, northern Kazakhstan, which is the best example of diamond-eclogite facies metamorphism, using cathodoluminescence (CL) techniques. CL spectra measurements of diamonds from garnet-pyroxene-quartz rocks and dolomitic marbles, made at 80 K, revealed peaks at 2.156, 2.463, and 3.188 eV and a broad band at 2.72-2.80 eV. Panchromatic and monochromatic diamond images analysed by CL reveal concentric zones of variable luminescence. This indicates that the diamond crystals grow during several metamorphic stages under ultra high pressure (UHP) metamorphism conditions. The inhomogeneous broadening and lower 2.156 eV ZPL peak suggests the presence of a higher concentration of defects and stresses in the rim compared to the core.     

香荆芥酚的荧光光谱和吸收光谱研究

研究了中药活性成分香荆芥酚(Carvacrol)的荧光光谱和吸收光谱,依据光谱数据测量了香荆芥酚的电离常数和荧光量子产率.在pH＜2.0时,香荆芥酚的荧光随溶液pH增大而增强;在pH2.0～8.0范围内,香荆芥酚有稳定的强荧光,最大激发波长为278 nm,最大发射波长为306 nm; pH＞8.0时荧光强度随pH的增大...     

X-ray computer tomography of natural fibrous diamonds and ballas

The results of investigation of natural fibrous diamonds by laboratory X-ray computer tomography using monochromatic radiation are presented. The existence of numerous heterophase microinclusions in fibrous crystals is established. Spatial distribution of inclusions can be connected both with morphological features of crystals, and with growth conditions. It is established that the ballas practically does not contain inclusions of extraneous phases.     

Measurement of energy spectra of charged particles emitted after the absorption of stopped negative pions in carbon

Energy spectra of charged particles (protons, deuterons, tritons, ³He, ⁴He and lithium nuclei) emitted after the absorption of stopped negative pions in a thin polyethylene target of 20 mg/cm² have been measured with high accuracy from the experimental threshold energy (of about 0.5 MeV) up to the kinematical limit of about 100 MeV.     

多壁碳纳米管束储氢机理的X射线吸收谱研究

采用X射线吸收精细结构光谱探索性地研究了多壁碳纳米管束.在多壁碳纳米管束不同入射角的X射线吸收精细结构光谱中，观察到C—H σ^*共振峰强度随入射角的变化而发生变化.在常温常压下出现C—H键可能与多壁碳纳米管束中存在缺陷有关，缺陷数量越大C—H σ^*共振峰的强度越大.光谱中C—C π^*和C—C σ^*共振峰强度的变化趋势都不同于C—H σ^*共振峰，这有力地证明了在常温常压条件下氢原子是吸附在多壁碳纳米 关键词： X射线吸收精细结构光谱 碳纳米管 储氢 化学吸附     

Effect of pressure on the Raman spectra of synthetic diamonds with boron impurity

The raman scattering technique is used for studying diamonds with a 0.04–0.1 at % boron impurity under a pressure up to 3 GPa in a chamber with sapphire anvils. The Raman frequency increases linearly with pressure for all samples with pressure coefficients of 2.947 cm^?1/GPa for pure diamond and 3.01 cm^?1/GPa for boron-doped samples. The Raman linewidths remain unchanged for pure diamond and for diamond with a boron concentration of about 0.04 at % and decrease linearly upon an increase in pressure for samples with a boron concentration of about 0.1 at %. The Raman spectra with a line profile corresponding to the Fano resonance do not change qualitatively up to a pressure of 3 GPa. In diamond samples with a boron impurity exceeding 0.1 at %, the boron concentration in the surface layer can be substantially higher than at the center of the sample.