Red Spectral Region Research Articles

Spectral examination of a multiple-flame photometric detector for use in chromatography

An examination of the emission spectra produced in a novel multiple-flame photometric detector (mFPD) was performed and directly compared to spectra obtained from a conventional single-flame FPD mode. Through monitoring a broad spectral range from 250 to 850 nm, it was found that the mFPD produces sulfur emission predominantly as S2*, but HSO* can also be isolated in the red spectral region. Further, phosphorus emission in the mFPD was found to stem from HPO*, while carbon emission was attributed to CH* and C2*. Finally, background emission in the mFPD was determined to be from OH*. Qualitatively, these finding agree very well with the species found in a conventional single-flame FPD. However, quantitatively, the mFPD spectra consistently produced analyte emission bands that were relatively more intense, by as much as a factor of 3. In contrast with this, hydrocarbon spectra in the mFPD yielded significantly reduced relative intensities, owing to decreased C2* emission. As well, aromatic and aliphatic hydrocarbons produced much more similar distributions of CH* and C2* emission in the mFPD than in the conventional single-flame FPD mode. The results indicate that a relative reduction of C2 radical and an increase of oxidized carbon in the analytical flame of the mFPD could play a central role in the observed quenching-resistant behavior of this detector.

Effect of deuterium substitution for hydrogen in surface functionalisation of hydrophilic nanosilicon particles on their spectral and dynamic properties

Broadband femtosecond spectroscopy has been used to study two types of hydrophilic silicon nanoparticles: (1) photoluminescent, passivated with deuterium and oxidised in fully deuterated dimethyl sulphoxide, and (2) nonluminescent (control samples having a similar crystalline core), passivated with hydrogen and oxidised in dimethyl sulphoxide. We have found significant differences in ultrafast spectral – temporal induced absorption dynamics between the two types of nanoparticles in the energy range corresponding to their calculated band gap. The observed distinction is due to the considerably higher oxidation rate of silicon on the surface of the deuterated samples in comparison with the undeuterated ones and with the associated increase in the number of photoluminescence centres on the surface of the nanoparticles. In the samples containing self-trapped exciton (STE) energy states responsible for the photoluminescence in the red spectral region, carrier capture at these levels and carrier relaxation to the ground state have characteristic times in the femtosecond range. In the samples free of STE states, excited carriers relax to the conduction band bottom in a characteristic time of several picoseconds.

Modeling of the influence of light quality on the growth of microalgae in a laboratory scale photo-bio-reactor irradiated by arrangements of blue and red LEDs

Knowing the distribution of the density of radiant energy within a photo-bio-reactor and its impact on the growth of microalgae through the local rate of absorption of radiant energy is essential for the analysis, modeling and design of photo-bio-reactors. In this work we develop a physical model and a computer simulation algorithm, in order to accurately predict the rate of absorption of photons in microalgal cultures at each point of a reactor irradiated with a light source made of different arrangements of LEDs emitting in blue and red spectral regions. Results showed that the average absorption rates in the culture irradiated with blue LEDs were higher than that irradiated with red LEDs. However, the radiation emitted by red LEDs rendered greater energy efficiency for biomass production compared to that emitted by blue LEDs. The development of a computational model based on a Monte Carlo method allowed the determination of the local volumetric rate of photon absorption at each point inside the PBR at different culture times. The information obtained with this tool allowed a detailed assessment of the effect of different radiation conditions on growth of microalgae, regardless of the PBR and the light source used.

Influence of annealing in Zn vapor on the luminescence of MgZnO ceramics

AbstractZnO‐based compounds that exhibit a number of strongly overlapping emission bands in visible spectral region are promising materials for white‐light emitters with continuous emission spectrum. Defect‐related emission in doped with different impurities ZnO, however, spreads from green to red spectral region, so its shift toward shorter wavelengths is required. We supposed that this problem can be solved due to broadening of ZnO band gap by alloying ZnO with MgO. The enhancement of visible emission brightness is also an important problem. In this work, MgxZn1‐xO ceramics with x =0 and x=0.2 were sintered both in air and Zn vapor at 950 oC. Emission and Raman scattering spectra were measured at 300 K using 325 nm line of He‐Cd laser as excitation source. In samples sintered in air, bright UV emission and weak visible one took place, adding MgO to ZnO resulting in blue‐shift of the latter. Sintering in Zn vapor was found to weaken UV emission and to increase drastically the brightness of visible one especially in blue‐green spectral region. As a result, bright blue radiation was observed from MgZnO ceramics under excitation by considerably week UV light. Obtained effects were accounted for by the shift of “green” centers energetic level with respect to involved band edge as a result of band‐gap broadening and by the increase of this center density due to annealing in Zn vapor. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Far-Red Spectrum of Second Emerson Effect: A Study Using Dual-Wavelength Pulse Amplitude Modulation Fluorometry

Non-additive enhancement of the photosynthesis excited by simultaneous illumination with far-red light and light of shorter wavelengths is called as "second Emerson effect". Its action spectra are well-known as a photosynthetic yield's dependence on light wavelength in red (630-690 nm) spectral region at a constant-wavelength far-red illumination near 700-715 nm. However, the opposite dependence of the photosynthetic yield's of shorter constant-wavelength light (red or blue) on light wavelength in far-red (690-760 nm) spectral region was never studied. In this study the action spectrum of second Emerson effect was studied using a fast-Fourier dual-wavelength Pulse Amplitude Modulation (PAM) fluorometry. Chlorophyll fluorescence in ailanthus (Ailanthus altissima Mill.) leaves was excited with blue modulated light. Far-red induced decrease of fluorescence (fluorescence shift-FRIFS) was studied in response to illumination of leaves with a background light from 690 to 760 nm (10 nm step), calculating FRIFS = (F0-Fs)/F0, where F0-fluorescence measured without and Fs-with far-red light. Maximum FRIFS was observed at 720 nm (11.8%), but it still remained considerable at 740, 750 nm and a low FRIFS values were revealed at 690 and even at 760 nm. Measurements carried out with blue saturating flashes during and after far-red illumination showed the increase of quantum yield of Photosystem II (PSII), calculated as Fv/Fm at 720 nm background light. FRIFS had lower values under excitation with red modulating light. It is concluded that FRIFS is a result of a photochemical quenching caused by an additional selective far-red excitation of PSI in conditions when PSII is preferably excited by blue light thus leading the PSI to limit non-cyclic electron flow. The contradiction between the known absorption spectra of PSI-light harvesting complex I and the observed action spectrum of second Emerson effect (FRIFS spectrum) is discussed.

Luminescence spectroscopy and electronic structure of the PbMoO4 and Pb2MoO5 single crystals

Intrinsic photoluminescence (PL) and electronic structure of Pb2MoO5 single crystal are first described and compared with corresponding properties of PbMoO4 crystal. The PL properties of PbMoO4 and Pb2MoO5 crystals grown by Czochralski method are studied under the VUV synchrotron radiation excitations (3.7–14eV region of excitation photon energies) at T=8K. The electronic band structures of perfect PbMoO4 and Pb2MoO5 are calculated by the Full-Potential Linear Augmented Plane Wave method. The Pb2MoO5 crystals reveal intensive PL band in the yellow–red spectral region peaking at ∼600nm. All studied PbMoO4 samples reveal intensive PL band in the green spectral region and this band is accompanied by additional fast-decaying (τ≈3.5ns) component in the violet when the samples are grown with 30° orientation of seed with respect to the c axis. The excitation spectra of the violet component of PbMoO4 reveal complex excitation band with main peak at 6.2eV. It is assumed that the violet PL component of PbMoO4 is generated by intra-center excitations from the ground to singlet excited states 1A1–1T1,2 of the MoO42− molybdate groups located near point defects in subsurface layer of the crystal. Strong anisotropy of reflectivity spectra of PbMoO4 below 6eV is a consequence of peculiarities of the electronic structure of the crystal and reflectivity bands at ∼3.6 and ∼4.3eV are formed by band-to-band electronic transitions.

Four emission bands from a mixed-ligand iridium complex IrQ(ppy)2 at room temperature

Four photoluminescence bands are observed from iridium complex in UV, violet, green, and red spectral regions at room temperature. Such a multiple emission is found from a mixed-ligand iridium(III) complex, (8-quinolinolato) bis(2-phenylpyridyl) iridium IrQ(ppy)2, which consists of IrQ and Ir(ppy)2 components (Q: 8-quinolinolato, ppy: phenylpyridyl). Of the four emission bands, the UV emission band with maximum at about 330nm and the red emission band are attributed to the ligand-centered (1LC) 1nπ* and metal-to-ligand charge transfer (3MLCT) 3(ππ*) states from IrQ, respectively, while the violet emission band with maximum at about 400nm and the green emission band at about 513nm are attributed to the 1LC 1(nπ*) and 3MLCT 3ππ* states from Ir(ppy). It is suggested that (1) IrQ and Ir(ppy) generate their own emissions by the inefficient Förster energy transfer between IrQ and Ir(ppy) due to the orientation factor of nearly zero, and (2) each of IrQ and Ir(ppy) gives rise to two emissions from the singlet and triplet states by the inefficient intersystem crossing.

Cold-induced gene expression and ω3 fatty acid unsaturation is controlled by red light in Synechocystis

The expression of cold-induced genes, which are controlled by the cold sensor histidine kinase Hik33, and the formation of ω3 polyunsaturated fatty acids are controlled by light in the cyanobacterium Synechocystis sp. PCC 6803. Cold-induced Hik33-dependent gene expression is initiated by red light (∼700nm), but not by blue or green light. Red light also turns on the ω3 fatty acid desaturation. Different combinations of other wavelengths in red spectral region (635 and 726nm) had no effect on the red-light-activated cold-induced transcription or fatty acid desaturation. Therefore, the involvement of phytochrome-like photoreceptor(s), similar to phytochromes of higher plants, in this regulation was not confirmed. The absence of light-dependence of gene expression in the mutant cells deficient in Hik33 suggests the involvement of this histidine kinase in direct or mediated with red light regulation of cold responses in Synechocystis.

On the application of thin films of silicon nanoparticles for increasing solar cell efficiency

The effect of thin films of silicon nanoparticles (nc-Si), deposited onto the front surface of single-crystal silicon solar cells, on their conversion efficiency is studied. The thin films are grown using non-luminescent silicon nanoparticles with an average diameter of 12 nm with SiO x (0 ≤ x ≤ 2) shells and silicon nanoparticles 2 nm in diameter with organic shells of octadecene, which exhibit photoluminescence in the red spectral region. It was found that nc-Si film deposition increases the solar-cell conversion efficiency by 12% with respect to the initial value. An analysis of the current-voltage characteristics and reflectance spectra of solar cells allows the conclusion that the increase in the conversion efficiency is controlled by the passivation of defects on the front surface of the solar cell by nanoparticles and a decrease in the light reflectance of this surface.

Characterization of the solar light field within the ocean mesopelagic zone based on radiative transfer simulations

The solar light field within the ocean from the sea surface to the bottom of the mesopelagic zone was simulated with a radiative transfer model that accounts for the presence of inelastic radiative processes associated with Raman scattering by water molecules, fluorescence of colored dissolved organic matter (CDOM), and fluorescence of chlorophyll-a contained in phytoplankton. The simulation results provide a comprehensive characterization of the ambient light field and apparent optical properties (AOPs) across the entire visible spectral range within the depth range 200–1000m of the entire mesopelagic zone for varying chlorophyll-a concentration and seawater optical properties in the mixed surface layer of the ocean. With increasing depth in the mesopelagic zone, the solar irradiance is reduced by ~9–10 orders of magnitude and exhibits a major spectral maximum in the blue, typically centered around a light wavelength of 475nm. In the green and red spectral regions, the light levels are significantly lower but still important owing to local generation of photons via inelastic processes, mostly Raman scattering and to a lesser extent CDOM fluorescence. The Raman scattering produces a distinct secondary maximum in irradiance spectra centered around 565nm. Comparisons of our results with light produced by the radioactive decay of the unstable potassium isotope contained in sea salt (40K) indicates that the solar irradiance dominates over the 40K-produced irradiance within the majority of the mesopelagic zone for most scenarios considered in our simulations. The angular distribution of radiance indicates the dominance of downward propagation of light in the blue and approach to uniform distribution in the red throughout the mesopelagic zone. Below the approximate depth range 400–500m, the shape of the angular distribution is nearly invariant with increasing depth in the green and red and varies weakly in the blue. The AOPs at any light wavelength also assume nearly constant values within the deeper portion of the mesopelagic zone. These results indicate that the mesopelagic light field reaches a nearly-asymptotic regime at depths exceeding ~400–500m.

ChemInform Abstract: Recent Advances in Phthalocyanine‐Based Sensitizers for Dye‐Sensitized Solar Cells.

AbstractReview: 104 refs.

Europium superluminescence in optically transparent photonic crystals

Repeatedly filling the octahedral and tetrahedral pores in the quasicrystalline structure of three-dimensional opal matrices with europium-doped silica sols, we obtained two types of nanocomposites, depending on heat treatment conditions: opal photonic crystals filled with mesoporous glass and optically transparent, ordered quantum-dot photonic crystals. According to elemental analysis data, the nanocomposites were identical in europium concentration: within 10–30 ppm. The luminescence spectra of the nanocomposites were analyzed, and their photoluminescence was shown to depend on the morphological and microstructural characteristics of the quasicrystalline materials and the spectral position of the band gap of the ordered photonic crystals. The Eu3+ photoluminescence intensity increases considerably when the spectral position of the 5 D 0 → 7 F 2 transition approaches the band gap edge of the transparent photonic crystal. We present analysis of the feasibility of using europium-doped opaline and transparent photonic crystals as gain media for lasing in the red spectral region.

Variability in the light absorption coefficients of phytoplankton, non-algal particles, and colored dissolved organic matter in a subtropical bay (Brazil)

This study characterized the variability in magnitudes and spectral shapes of the absorption coefficients of phytoplankton, detritus, and colored dissolved organic matter (CDOM) in a dynamic bay (Santos Bay) in southeastern Brazil in response to the contributions of the main estuarine channel and large tide variations, therefore in different time scales. Two strategies were adopted: (1) monthly year-round sampling in the estuarine channel and Santos Bay and (2) sampling in Santos Bay during spring/neap tides and cold/warm months. Chlorophyll-a concentration and CDOM absorption were higher during warm (wet) months, while the relative contribution of organic and inorganic particles was driven by neap/spring tide cycles. Salinity partially accounted for changes in optical variables, especially for CDOM absorption and total suspended matter (TSM) during cold months and neap tides, respectively. The spectral shapes of detritus and CDOM absorption showed relatively little variability for the entire dataset and were not considered feasible for monitoring purposes. The spectral shape of phytoplankton absorption (index of cell size) varied broadly, with no remarkable dependence on the sampling conditions. Comparison of absorption coefficients measured by the Quantitative Filter Technique (QFT) and Transmittance Reflectance (TR) method showed higher phytoplankton coefficients toward longer visible wavelengths (flatter spectra) and shallower slopes of detritus absorption yielded by the TR method. Our results also suggest that measurements at the near red spectral region result from not only scattering signals but also non-algal particle absorption.

Sensing drought- and salinity-imposed stresses on tomato leaves by means of fluorescence techniques

In our study, we investigated whether multiple fluorescence indices may be used to sense physiological changes in tomato plants (Solanum lycopersicum L.) caused by salinity and water deficit as single or combined stresses. The fluorescence intensity in the blue (B), red (R) and far-red (FR) spectral regions and the pulse-amplitude-modulated (PAM) chlorophyll fluorescence, were recorded on a weekly basis in the scope of a long-term experiment. The results indicate the coefficient of photochemical quenching (qL), the B to FR fluorescence ratio and the logarithm of the FR fluorescence ratio after R and UV-light excitation as appropriate parameters to sense the response of plants to the imposed stress. The qL revealed the impact of water deficiency, whereas the two multispectral ratios revealed the influence of combined salinity and water shortage. Despite minor changes in the chlorophyll concentration, salinity and water deficit, when combined, had an additive impact on the chlorophyll fluorescence. Overall, the fluorescence signals of ‘Rio Grande’ were more affected by the induced stresses compared to ‘Harzfeuer’. The multiparametric fluorescence technique, confirming the trends obtained with the PAM-method, reveals promising perspectives for the ‘in situ’ evaluation of the physiological status of horticultural crops.

Rare Earth Doped Lanthanum Calcium Borate Polycrystalline Red Phosphors

Single-phased Sm3+doped lanthanum calcium borate (SmxLa2−xCaB10O19, SLCB,x=0.06) polycrystalline red phosphor was prepared by solid-state reaction method. The phosphor has two main excitation peaks located at 398.5 nm and 469.0 nm, which are nicely in accordance with the emitting wavelengths of commercial near-UV and blue light emitting diode chips. Under the excitation of 398.0 nm, the dominant red emission of Sm3+in SLCB phosphor is centered at 598.0 nm corresponding to the transition of4G5/2 → 6H7/2. The Eu3+fluorescence in the red spectral region is applied as a spectroscopic probe to reveal the local site symmetry in the host lattice and, hence, Judd-Ofelt parametersΩt (t=2, 4)of Eu3+in the phosphor matrix are derived to be3.62×10-20and1.97×10-20 cm2, indicating a high asymmetrical and strong covalent environment around rare earth luminescence centers. Herein, the red phosphors are promising good candidates employed in white light emitting diodes (LEDs) illumination.

Phytoplankton absorption and the chlorophyll a-specific absorption coefficient in dynamic Onondaga Lake

Phytoplankton absorption and its dependence on the concentration of chlorophyll a(Chl-a), as represented by the Chl-a–specific absorption coefficient (a*φ(λ)), is important to support models of growth and for bio-optical remote sensing algorithms to retrieve Chl-a. The dynamics of the phytoplankton absorption coefficient (aφ(λ)) and a*φ(λ), and their dependencies on Chl-a, are described for Onondaga Lake, New York, over a 6-year period for which major changes in trophic state, Chl-a, and community composition occurred. Strong positive dependencies of aφ(λ) on Chl-aare reported for absorption peaks in both the blue and red spectral regions that are qualitatively similar to relationships for ocean waters but differ quantitatively. Average values of a*φ at wavelengths of 440 and 676 nm were 0.0347 and 0.0171 m2 mg−1, respectively, with coefficients of variation of 37 and 31%. Significant negative relationships between a*φ and Chl-a were observed for blue and green wavelengths that were qualitatively consistent with the influences of pigment packaging and the contribution of accessory pigments to absorption. The operation of these influences is demonstrated through various forms of data analysis that resolved the following significant relationships: (1) negative dependence of the ratio aφ(440):aφ(676) on Chl-a; (2) flattening of aφ spectra in the blue and increases at the red maximum, with increases in Chl-a; and (3) negative dependence of aφ(490):aφ(676) on Chl-a. Values of a*φ(440) and a*φ(676) obtained for Onondaga Lake are considered in the context of the limited population reported for other inland waters and selected marine systems.

Synthesis and properties of tetra- and octacationicmeso-tetrakis(3-pyridyl)bacteriochlorin derivatives

The synthesis and properties of new water-soluble tetra- and octacationic derivatives of meso-tetrakis(3-pyridyl)bacteriochlorin are reported. Tetracationic salt was synthesized by quaternization of the pyridine groups of starting bacteriochlorin with 1,4-dibromobutane. Octacationic salts were obtained by treating of tetracationic salt with excess of pyridine or N,N-dimethylaminoethanol. Zinc complexes of water-soluble bacteriochlorin derivatives were prepared by direct metalation of corresponding non-metal compounds with zinc acetylacetonate, unlike to neutral bacteriochlorin which forms zinc complex only by transmetalation of the corresponding cadmium complex. The new bacteriochlorins have strong absorption in red and NIR spectral region. Free-base BCs possess good stability in aqueous solutions as compared to their zinc complexes and efficiently generate singlet oxygen.

Structural Parameters Controlling the Fluorescence Properties of Phytochromes

Phytochromes constitute a class of photoreceptors that can be photoconverted between two stable states. The tetrapyrrole chromophore absorbs in the red spectral region and displays fluorescence maxima above 700 nm, albeit with low quantum yields. Because this wavelength region is particularly advantageous for fluorescence-based deep tissue imaging, there is a strong interest to engineer phytochrome variants with increased fluorescence yields. Such targeted design efforts would substantially benefit from a deeper understanding of those structural parameters that control the photophysical properties of the protein-bound chromophore. Here we have employed resonance Raman (RR) spectroscopy and molecular dynamics simulations for elucidating the chromophore structural changes in a fluorescence-optimized mutant (iRFP) derived from the PAS-GAF domain of the bacteriophytochrome RpBphP2 from Rhodopseudomas palustris . Both methods consistently reveal the structural consequences of the amino acid substitutions in the vicinity of the biliverdin chromophore that may account for lowering the propability of nonradiative excited state decays. First, compared to the wild-type protein, the tilt angle of the terminal ring D with respect to ring C is increased in iRFP, accompanied by the loss of hydrogen bond interactions of the ring D carbonyl function and the reduction of the number of water molecules in that part of the chromophore pocket. Second, the overall flexibility of the chromophore is significantly reduced, particularly in the region of rings D and A, thereby reducing the conformational heterogeneity of the methine bridge between rings A and B and the ring A carbonyl group, as concluded from the RR spectra of the wild-type proteins.

Properties of a novel linear sulfur response mode in a multiple flame photometric detector

A new linear sulfur response mode was established in the multiple flame photometric detector (mFPD) by monitoring HSO* emission in the red spectral region above 600nm. Optimal conditions for this mode were found by using a 750nm interference filter and oxygen flows to the worker flames of this device that were about 10mL/min larger than those used for monitoring quadratic S2* emission. By employing these parameters, this mode provided a linear response over about 4 orders of magnitude, with a detection limit near 5.8×10−11gS/s and a selectivity of sulfur over carbon of about 3.5×103. Specifically, the minimum detectable masses for 10 different sulfur analytes investigated ranged from 0.4 to 3.6ng for peak half-widths spanning 4–6s. The response toward ten different sulfur compounds was examined and produced an average reproducibility of 1.7% RSD (n=10) and an average equimolarity value of 1.0±0.1. In contrast to this, a conventional single flame S2* mode comparatively yielded respective values of 6.7% RSD (n=10) and 1.1±0.4. HSO* emission in the mFPD was also found to be relatively much less affected by response quenching due to hydrocarbons compared to a conventional single flame S2* emission mode. Results indicate that this new alternative linear mFPD response mode could be beneficial for sulfur monitoring applications.

THEORETICAL CALCULATIONS OF AN OSMIUM MOLECULAR SWITCH

ABSTRACT We have investigated the molecular, electronic and optical properties of the [Os(tpy-py) 2 ] 2+ complex (tpy-py = 4’-(4-pyridyl)-2,2’:6’,2’’-terpyridine) and its protonated derivative [Os(tpy-pyH) 2 ] 4+ through Density Functional Relativistic calculations including Scalar and Spin Orbit corrections. The molecular geometry of the parent complex is not strongly modified by the protonation at the basic nitrogen atoms of the pyridine moieties of the terpyridine ligands in the complex. On the other hand, the optical properties of these complexes can be controlled by a change in the chemical acid-base environment, converting them into suitable materials to act as molecular switches or pH sensor devices. e-mail: dmacleod@unab.cl INTRODUCTION The innovative designs and creative thinking of numerous scientists led to artificial molecular mechanisms being used in device applications. [1] In this sense, molecular Switches comprise an interesting class of artificial molecular machines and can be defined as molecules that can be switched between two or more different states. In a particular case, Photochemical switches are molecular or supramolecular species in which properties or functions can be switched on and off by light. [1,2]In this context, recently [3,4] the photoluminescence in the far red spectral region and photosensitised generation of singlet oxygen, with associated near-IR emission, of the [Os(tpy-py)