Nm In Spectrum Research Articles

Luminescence of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms

We observed the appearance of a broad feature at 360 nm in spectra obtained during the destruction of ensembles of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen and deuterium atoms. We attribute this broad feature with a maximum at 360 nm to the N4 polynitrogen molecules which are the product of the neutralization reaction of ions with electrons in solid N2.

Identification of S VIII through S XIV emission lines between 17.5 and 50 nm in a magnetically confined plasma

43 spectral emission lines from F-like to Li-like sulphur ions have been identified in the wavelength range from 17.5 to 50 nm in spectra obtained following tracer injection into plasmas created in a magnetically confined plasma device, the stellarator TJ-II. Plasmas created and maintained in this heliac device with electron cyclotron resonance heating achieve central electron temperatures and densities up to 1.5 keV and 8 × 1018 m−3, respectively. Tracer injections were performed with ≤6 × 1016 atoms of sulphur contained within ∼300 μm diameter polystyrene capsules, termed tracer encapsulated solid pellets, using a gas propulsion system to achieve velocities between 250 and 450 m s−1. Once ablation of the exterior polystyrene shell by plasma particles is completed, the sulphur is deposited in the plasma core where it is ionized up to S+13 and transported about the plasma. In order to aid line identification, which is made using a number of atomic line emission databases, spectra are collected before and after injection using a 1 m focal length normal incidence spectrometer equipped with a CCD camera. This work is motivated by the need to clearly identify sulphur emission lines in the vacuum ultraviolet range of magnetically confined plasmas, as sulphur x-ray emission lines are regularly observed in both tokamak and stellarator plasmas.

Research of color characteristics of sugar production intermediates

It is known that in a sugar production, only about 80% of sucrose, extracted from the beet, is output as a commercial product. The rest is lost during the processing or remains in intermediates. The color of white sugar is mainly determined by the color of the returned to the first stage of crystallization of the brown sugars melt. An effective way to improve the quality of melt is affination of brown sugars. Coloring substances are preferably present in the film on the surface of sugar crystals. To improve the efficiency of affination experiments were carried out by layer-by-layer processing of the normalized crystal size with the saturated solution of white sugar. To evaluate the numerical characteristics of the color of the samples studied scanerometrical method followed by computer processing of images in RGB color mode was used. The studies suggest that the solution of the starting yellow sugar having visual yellow color intensively absorbs 450–480 nm of spectrum, so there is no blue component in the graphs. During the affination removing of coloring substances from the surface of crystals takes place changing the light absorption intensity. There is a bleaching of the samples at affination duration up to 3 minutes. Further 5–10 min treatment is accompanied by partial diffusion of colorants from mother liquor to the surface of crystals and improved chromaticity. Prolonged affination results in crystals abrasion; it is accompanied by unproductive energy consumption on the mixing process. The results obtained indicate that the effective removal of coloring substances occurs within 1–3 minutes of affination. In this case brown sugar chromaticity decreases from 625 to 130–230 units of optical density and mother liquor chromaticity is increased from 20 to 900–1600 units of optical density. The studies suggest that most of the coloring substances determining the chromaticity of yellow sugars is found in the film on the crystal surface and is easily removed by 3 min long affination. Method of determining of objects color characteristics in RGB system describes adequately the intermediates coloring of sugar production and can be used in research.

67.9 W high-power white supercontinuum all-fiber laser source.

We present a high-power white supercontinuum (SC) all-fiber laser source with average power of 67.9 W, spectrum ranging from 500 to 1700 nm, and spectral width exceeding 1000 nm for spectrum with flatness below 10 dB (except pump wavelength). Also, the visible waveband power (below 850 nm) occupies about 21% of the total SC power. A 145 W high-power picosecond pulse fiber laser is specially designed with high repetition frequency of 656 MHz to reduce nonlinear effects. Meanwhile, a homemade high-power mode field adaptor that can operate stably at hundreds of watts of pulse power has high coupling efficiency of 82%. To our knowledge, the 67.9 W white SC fiber laser source we achieved is the highest reported with such a wide and flat optical spectrum.

Optical Properties of Polyimide Films Implanted with Ni+ Ions

Transmission and refl ection spectra of polyimide fi lms 40-μm thick implanted with 40-keV Ni+ ions at fl uences 2.5·1016–1.5·1017 cm–2 and ion-beam current density 4, 8, and 12 μA/cm2 were studied in the range 200–1100 nm. It was shown that the optical transmission coeffi cient decreased smoothly after implantation as a result of light absorption and scattering in the modifi ed polymer layer containing nano-sized inclusions of C and Ni. The appearance of a broad refl ection band in the range 700–1100 nm in spectra from the implanted polymer and the reverse side of the polymer was due to a high Ni content in the implanted layer. The refractive index of the modifi ed implanted polymer layer that varied in the range 1.25–2.32 at 620 nm depending on the fl uence was determined by modeling the passage of light through the bilayer modifi ed layer/polymer matrix taking into account multiple refl ections at the interfaces.

Effects of metal cations on betanin stability in aqueous-organic solutions

An effect of metal cations on betanin stability was investigated in aqueous and organic-aqueous solutions. The presence of organic solvents (methanol, ethanol, and acetonitrile) affects substantially the pigments decomposition in acidic media induced by metal cations whose degrading action in such media is significantly higher than in aqueous solutions. The influence of Cu2+ on the stability was studied by spectrophotometry in more detailed manner, because of its ability to form complexes with betanin. The possibility of a complex formation between betanin and Ni2+ was also stated at pH 7–8; its relatively high stability in aqueous samples was observed. A presence of numerous products of betanin decomposition was detected in the wavelength range 380–500 nm in spectra obtained for most of metal cations investigated, especially for higher concentrations of the organic solvents.

Synthesis of Sr<sub>2</sub>Si<sub>5</sub>N<sub>8</sub>:Eu<sup>2</sup><sup>+</sup> Phosphor for Enhanced Red Emission

For removing impurities to improve luminescence properties, Eu2+- activated Sr2Si5N8 red phosphor for white light-emitting diodes (LEDs) was prepared by multiple heat-treatment synthesis which includes carbothermal reduction and nitridation. The X-ray diffraction (XRD) patterns were showed the standard single phase of Sr2Si5N8. With an optimized amount of Eu2+ (2 at. %) dopant, the broad excitation band of Sr2Si5N8:Eu2+ indicated that the phosphor was suitable for application of white LEDs with UV or blue chip, and red emission peak at 628 nm in spectra originating from the 4f65d1→4f7 transition of Eu2+ ion. After third heating process, luminescence properties of the obtained phosphor were improved obviously and higher than commercial YAG:Ce3+ phosphor.

Visible and near‐infrared nightglow of molecular oxygen in the atmosphere of Venus

The Herzberg II system of O2 has been a known feature of Venus' nightglow since the Venera 9 and 10 orbiters detected its c(0)–X(v″) progression more than 3 decades ago. We search for its emission at 400 nm–700 nm in spectra obtained with the VIRTIS instrument on Venus Express. Despite the weakness of the signal, integration over a few hours of limb observations of the planet's upper atmosphere reveals the unambiguous pattern of the progression. The selected data sample mainly the northern latitudes within a few hours of local midnight. The emission is ubiquitous on the nightside of Venus and can be discerned at tangent altitudes from 80 km to 110 km. The average emission vertical profiles of the c(0)–X(v″) progression and the O2a(0)–X(0) band, the latter from simultaneous near‐infrared spectra, are quite similar, with their respective peaks occurring within ±1 km of each other. We conclude that the net yield for production of the c(0) state is low, ∼1%–2% of the oxygen recombination rate, and that O(3P) and CO2 are the two likely quenchers of the Herzberg II nightglow, although CO cannot be ruled out. We also derive a value of 2.45 × 10−16 cm3 s−1 for the rate constant at which CO2 collisionally quenches the c(0) state. Our VIRTIS spectra show hints of O2A′(0)–a(v″) emission but no traces of the O (1S–1D) green line at 557.7 nm.

Optical spectra of anionic boron cluster compounds and their utilization for photometric detection

The article presents first collection of UV–vis absorption spectra of purely synthetic boron cluster compounds. Single-cage compounds have at least 11 cluster atoms; cobaltadicarboranes consists of 2 substituted 11-vertex bis(dicarbollide) clusters sandwiching the central cobalt atom. Spectrum of any of 18 investigated compounds has absorption maximum between 200 and 210 nm; its molar extinction coefficient is of the order of 10 3–10 4 L/mol cm. Second maximum exists in a spectrum of a single-cage compound if its exo-skeletal substituent absorbs UV-light above 200 nm. Spectra of cobaltadicarbaboranes both bridged and unbridged have pronounced second maxima between 270 and 300 nm. Their molar extinction coefficients range from 10 4 to 10 5 L/mol cm. First light absorption minimum is close to 254 nm in spectra with two and more absorption maxima. Several correlations are derived between structure of investigated compounds and their UV–vis absorption spectra.

Rheofluorescence studies of poly(p-phenylenevinylene) derivatives in simple shear flow

Common manufacturing approaches for polymer displays expose light emitting polymer solutions (LEPs) to high shear rates during film deposition. Little is yet known about the effects of shear on LEP conformation and alignment; the ability to manipulate these polymers in flow may prove critical for enhanced device performance. A novel spectroscopic approach that employs an optically accessible Couette cell has been developed to investigate the effects of a uniform shear field on LEP luminescence. Orientation and deformation in polymer solutions are observed as shear-dependent changes in fluorescence emission. We report the influence of simple shear flow on steady state fluorescence emission from MEH-PPV and two other poly(p-phenylenevinylene) derivatives, in dilute solution and a polystyrene matrix. Rheochromism, a shear-induced red shift of 4–6 nm in spectra recorded at shear rates of 100–1000 s −1, indicates a small extension of conjugated polymer coils. Changes in fluorescence emission intensity as a function of shear rate and observation geometry are attributed to alignment of prolate polymer coils in the flow field.

Photoinduced self-organization of donor–acceptor complex intended for oxidative splitting of water

The ground and excited states of complexes combined on the base of associated forms of meso-tetra( p-aminophenyl)porphine (TAPP) and donor–acceptor complex formed between triethylamine and manganese(II), in which manganese(II) moiety of the complex possessing Δ H pp=70 mT was preliminary transformed into the EPR-silent form, are investigated by absorption and luminescence spectroscopy. According to absorption and fluorescence spectra dramatic photoinduced transformation of the combined complex in the presence of NaHCO 3 is found under illumination with a non-stop change of exciting light wavelength from red to ultraviolet. Absorption spectrum (before the transformation) had a broad Soret band with the maximum at 433 nm, where the associated state of the porphyrin is preliminary estimated as a trimer. The complex obtained after the transformation has the components of monomeric porphyrin with the maximum of Soret band at 418 nm in the spectrum and porphyrin dimer coordinated with the manganese ions. The dimer has a broad Soret band with λ max=467 nm and a broad red band with the maximum at ca. 780 nm in the absorption spectrum, although none of these bands are observed in the spectrum before the illumination. Selective excitation into these Soret bands and the intermediate region, reveals well-known fluorescence of monomeric porphyrin, which is similar to that of tetraphenylporphine, and a strong IR emission with the maximum at 875–880 nm. The relationship between the fluorescence of the monomeric porphyrin and the IR emission depends on the wavelength of excitation. The results of the study of the combined complexes allow to conclude that the photoprocess of water oxidation takes place in the combined complex formed between associates of TAPP and EPR-silent manganese–triethylamine complex.

Dynamic wavelength equalizer in silica using the single-filtered-arm interferometer

A dynamic wavelength equalizer that can control attenuation at 22 points across 35 nm of spectrum in a smooth manner is presented. It achieves low loss (4.7 dB), because it consists of a Mach-Zehnder interferometer with a wavelength-dependent element in only one arm. Additional development is needed to reduce the polarization sensitivity.

Diode-pumped environmentally stable stretched-pulse fiber laser

We present results obtained with a stretched-pulse polarization additive pulse mode-locked (P-APM) fiber laser using an environmentally stable cavity design. With 980-nm diode-pumping levels of 200-mW 1.2-nJ pulses with 50 nm of spectrum are obtained. These pulses can be externally compressed to sub-100 fs. The effects of high output coupling (>80%) and pumping configuration on output performance an d intracavity pulse dynamics are studied.

Circular dichroism of the guanyloribonuclease Sa and its complex with guanosine 3′-phosphate

Extracellular guanyloribonuclease isolated from Streptomyces aureofaciens (RNAase Sa) exhibits a complex negative circular dichroism (CD) around 280 nm with a clear fine structure, and a positive Cotton effect at 235 nm. It contains about 42% of α-helix, 28% of β-structure and 33% of random coil as was determined by computation from the molar ellipticity in the region 240-210 nm. The circular dichroism at 280 nm is mainly due to the immobilization of 1–2 tyrosine residue(s) inside the enzyme molecule. On the other hand, the CD band at 285 nm might be due to an exciton coupling between near ultraviolet transitions of two tyrosine residues. The negative Cotton effect at 290 nm in a circular dichroism difference spectrum of the complex of RNAase Sa with a competitive inhibitor guanosine 3′-monophosphate ( Guo-3′-P ) is probably caused by the immobilization of two other tyrosine residues in the enzyme binding site which interact with the guanine base. A positive Cotton effect at 270 nm in this spectrum was attributed to an exciton interaction of one binding tyrosine residue with the guanine base, and the positive Cotton effect at 255 nm is induced most probably by the second binding tyrosine which might interact by hydrogen bonding between the phenolic hydrogen and O-6 of the pyrimidine ring.

Further studies on the composition and spectral properties of the photochemical reaction centers of bacteriochlorophyll b-containing bacteria

1. 1. There are no basic differences in the biochemical composition of photochemical reaction centers between bacteriochlorophyll a- and bacteriochlorophyll b-containing purple bacteria. Both types have the same stoichiometric ratios of bacteriochlorophyll/bacteriopheophytin/special pair (i.e., 4 : 2 : 1) and of carotenoid/bacteriochlorophyll (i.e., 1 : 4), and the molecular weight equivalencies of the polypeptide subunits of the reaction center are basically similar. 2. 2. The isolated reaction center of Rhodopseudomonas viridis contains polypeptide subunits of 38, 35, 28 and 24 kilodaltons. The latter two are aggregated by heat. Of the two c-type cytochromes present in the isolated material, c-553 (and possibly c-558) is coincident with the 38 kilodalton component. It is concluded that the 35, 28 and 24 kilodalton polypeptides correspond to the so-called H, M and L subunits of bacteriochlorophyll a-containing reaction centers. 3. 3. The isolated reaction center contains carotenoid which can apparently be removed from the reaction center by 4% (w/v) lauryldimethylamine oxide. 1′,2′-dihydroneurosporene (50–70%) and 1′,2′-dihydrolycopene (30–40%) constitute the bulk of the reaction center carotenoid. There is no specificity of carotenoid type inserted into the reaction center. 4. 4. The spectral forms of the chromophores in the 830-nm band of room and 77 K absorption spectra of reaction centers of Rps. viridis have been studied via fourth derivatives of the spectra. Four forms with maxima at 787, 812–813, 834–835 and ∼850 nm are present. We attribute the forms to bacteriopheophytin b (787 nm), two ‘voyeur’ bacteriochlorophyll b molecules (one at 812–813 nm and one at 834–835 nm), and a spectral component of P-960 (∼850 nm). Each spectral form in the 830-nm band occurs at the same wavelength maximum and in the same relative proportions in both intact photosynthetic membranes and isolated reaction centers. We thus conclude that each form, in particular the bacteriopheophytin and 812–813 nm bacteriochlorophyll components, is present in the intact photosynthetic membrane, and that they are not generated by treatment of the membranes with detergents; furthermore, we believe that the absorption bands between 780 and 860 nm in spectra of whole cells of Rps. viridis and Thiocapsa pfennigii are due to the absorbance of reaction center chromophores.