Near-infrared Absorption Spectra Research Articles

Acridine orange base as a dopant for n doping of C60 thin films

We present a study on n doping of C60 thin films by acridine orange base [3,6-bis(dimethylamino)acridine(AOB)] combining conductivity, field effect, and Seebeck measurements. An increase of more than six orders of magnitude in conductivity is observed for a doping ratio of 6mol%, accompanied by a decrease in the activation energy from 0.64to0.15eV compared to the undoped C60. We observe a clear doping effect immediately after sample preparation, but also a further activation by annealing or illumination. The field effect and Seebeck measurements confirm n-type conduction of C60 thin films and show that deep donor states are formed in AOB-doped C60 thin films. A field effect mobility of 0.2cm2∕Vs is achieved for a doping level of 1.8mol%. Near Infrared (NIR) and Fourier transform infrared (FTIR) spectra demonstrate electron transfer from the dopant to the matrix: For C60 doped with AOB, C60− is present in NIR absorption and FTIR spectra. On the other hand, a peak corresponding to acridine orange [3,6-bis(dimethylamino)acridinium chloride (AOBH+)] is also observed in the FTIR spectrum of C60:AOB, where AOBH+ corresponds to AOB with one additional proton attached. Electrochemical data of AOB and AOBH+ in acetontrile suggest that the AOB radical cation is not stable, but is rapidly transformed into a compound with similar properties to AOBH+. Conductivities of C60 thin films doped with bis(ethylenedithio)-tetrathiafulvalene were also investigated to confirm that the doping effect of AOB in C60 does not result from a simple electron transfer from AOB to C60.

Uncertainty Analysis of Visible and Near-Infrared Data of Hydrocarbons

Measurement of physical and chemical properties of hydrocarbons plays an important role in the exploration and production of oil wells. In situ measurement of chemical properties of hydrocarbons makes use of visible and near-infrared (vis-NIR) absorption spectra of hydrocarbons. Uncertainty analysis of these fluid properties is central to developing a fundamental understanding of the distribution of hydrocarbons in the reservoir. In this manuscript, we describe an algorithm called the fluid comparison algorithm (FCA), which provides a statistical framework to quantify and compare hydrocarbon fluid properties and associated uncertainties derived from vis-NIR measurements. The inputs to FCA are the magnitude and uncertainty of vis-NIR spectroscopy data of two hydrocarbons. The output of FCA is a probability that two fluids are statistically different. FCA lays the foundations for subsequent optimization and capture of representative reservoir hydrocarbons. Furthermore, in some circumstances, it can also enable real-time decisions to identify reservoir compartmentalization and hydrocarbon composition gradients in natural oil reservoirs.

布地に含まれる水の近赤外吸収スペクトルと定量

Diffuse-reflection near-infrared absorption spectra of water adsorbed on various fabrics (cotton, linen, rayon, silk, wool, polyester, nylon, and polyacrylonitrile) were obtained by calculating difference spectra of the fabrics before and after drying with a thermostatic hot-air oven. Peak wavenumbers, widths, shapes, and intensities of the bands due to the water were found to depend on the kind of fabric. The dependence is presumably caused by the difference of the amount of water and of the interaction between the water and fiber molecules. Linear regres-sion lines were obtained for the relations between the amount of water measured as the weight and the peak intensity of the water band around 5140 cm-1. Quantitative analysis of water content of fabrics was found to be possible.

Improved near-infrared methane band models and k-distribution parameters from 2000 to 9500 cm −1 and implications for interpretation of outer planet spectra

The band model fits of Sihra [1998. Ph.D. Thesis. University of Oxford], subsequently reported by Irwin et al. [2005. Icarus 176, 255–271], to new measurements of low-temperature near-infrared self-broadened methane absorption spectra combined with earlier warmer, longer path measurements of both self- and hydrogen-broadened methane spectra measured by Strong et al. [1993. J. Quant. Spectrosc. Radiat. Transfer 50, 363–429], have been found to contain severe artefacts at wavelengths of very low methane absorption. Although spectra calculated from these new band data appear to be reliable for paths with low to medium absorption, transmissions calculated for long paths of high methane absorption, such as for Uranus, Neptune and Titan are severely compromised. The recorded laboratory transmission spectra of Sihra [1998. Ph.D. Thesis. University of Oxford] and Strong et al. [1993. J. Quant. Spectrosc. Radiat. Transfer 50, 363–429] have thus been refitted with a more robust model and new k-distribution data for both self- and hydrogen-broadened methane absorption derived. In addition, a new model of the temperature dependence of the absorption has been employed that improves the quality of the fit and should also provide more accurate extrapolations to low temperatures.

Optical absorption of Co2+ in gel-derived aluminosilicate glass-ceramics

Abstract Pure and Co2+-doped aluminosilicate gels were prepared by the sol–gel method from two different aluminum salts, aluminum-iso-propoxide and aluminum nitrate, and heat-treated at 40–1200 °C. Visible and near-infrared (NIR) absorption spectra of the heated samples were studied. When the heat-treatment temperature was 1100 °C, Co2+-doped aluminosilicate samples, obtained by using aluminum-iso-propoxide, crystallized to Al2O3 nanocrystals and exhibited a broad absorption band in the range of 1200–1600 nm, which is characteristic of tetrahedral Co2+ ions in crystals. The existence of the broad absorption band has allowed us to consider this kind of material as possible candidate for passive Q-switched materials in the NIR region. While the sample prepared from aluminum nitrate was amorphous when heated to 1200 °C.

Tunable near‐infrared optical properties based on poly(methyl methacrylate)–oxide waveguide materials

AbstractIn this study, two classes of low‐loss optical planar waveguides were prepared from trialkoxysilane‐capped poly(methyl methacrylate) (PMMA)–silica and PMMA–titania hybrid materials, respectively. The prepared hybrid films had very uniform structure and surface planarity. The incorporation of the silica or titania segments into the acrylic polymer matrix reduced the intermolecular interaction and thus induced an increase in anharmonicity of the C‐H bond in the acrylic segment. Therefore, the third harmonic stretching vibration absorption of the C‐H bond was red‐shifted and resulted in a tuning of near‐infrared (NIR) optical absorption. The optical loss of the studied waveguides was reduced from 0.65 dB/cm of the PMMA waveguide to 0.26 and 0.28 dB/cm with increasing the silica and titania content in the hybrid materials, respectively. The reduction of the C‐H number density and shifting of the NIR absorption spectra accounted for the relationship between the optical loss and the inorganic oxide content. The increased anharmonicity through the incorporation of the inorganic moiety in the hybrid materials provides another approach for tuning the NIR optical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1224–1228, 2005

Fluorinated polymer with high thermal stability for fabrication of 32-channel arrayed waveguide grating multiplexer on silicon

A cross-linkable fluorinated poly (ether ether ketone) (FPEEK) was synthesized for the fabrication of arrayed waveguide grating (AWG) multiplexer. The results of thermal gravimetric analysis (TGA) and near-infrared absorption spectrum show that the materials have high thermal stability and high optical transparency in the infrared communication region. The refractive index of FPEEK can be controlled easily by changing the fluorine content of the materials. The 32-channel AWG multiplexer is fabricated using the FPEEK and oxygen reactive ion etching technology. The AWG multiplexer exhibits that the insertion loss is from 12.8 to 17.8 dB and the channel crosstalk is less than −20 dB. The wavelength channel spacing and the center wavelength are 0.8 nm and 1 548 nm, respectively.

Dynamic Jahn-Teller Effects in IsolatedC60−Studied by Near-Infrared Spectroscopy in a Storage Ring

We have measured the near-infrared absorption spectrum for isolated C60- ions at room temperature. Two bands, at 9145 cm(-1) and 10460 cm(-1), have been identified in addition to the main absorption band at 9382 cm(-1), seen also at low temperature in a matrix. An interpretation based on the theory of dynamic Jahn-Teller effects is proposed.

Photobiomodulation Directly Benefits Primary Neurons Functionally Inactivated by Toxins: ROLE OF CYTOCHROME c OXIDASE

Far red and near infrared (NIR) light promotes wound healing, but the mechanism is poorly understood. Our previous studies using 670 nm light-emitting diode (LED) arrays suggest that cytochrome c oxidase, a photoacceptor in the NIR range, plays an important role in therapeutic photobiomodulation. If this is true, then an irreversible inhibitor of cytochrome c oxidase, potassium cyanide (KCN), should compete with LED and reduce its beneficial effects. This hypothesis was tested on primary cultured neurons. LED treatment partially restored enzyme activity blocked by 10-100 microm KCN. It significantly reduced neuronal cell death induced by 300 microm KCN from 83.6 to 43.5%. However, at 1-100 mm KCN, the protective effects of LED decreased, and neuronal deaths increased. LED significantly restored neuronal ATP content only at 10 microm KCN but not at higher concentrations of KCN tested. Pretreatment with LED enhanced efficacy of LED during exposure to 10 or 100 microm KCN but did not restore enzyme activity to control levels. In contrast, LED was able to completely reverse the detrimental effect of tetrodotoxin, which only indirectly down-regulated enzyme levels. Among the wavelengths tested (670, 728, 770, 830, and 880 nm), the most effective ones (830 nm, 670 nm) paralleled the NIR absorption spectrum of oxidized cytochrome c oxidase, whereas the least effective wavelength, 728 nm, did not. The results are consistent with our hypothesis that the mechanism of photobiomodulation involves the up-regulation of cytochrome c oxidase, leading to increased energy metabolism in neurons functionally inactivated by toxins.

Relative Contributions of Hemoglobin and Myoglobin to Near-Infrared Spectroscopic Images of Cardiac Tissue

Near-infrared (NIR) spectroscopic imaging is emerging as a unique tool for intra-operative assessment of myocardial oxygenation, but quantitative interpretation of the images is not straightforward. One confounding factor specific to muscle tissue (both skeletal and cardiac) is that the visible/NIR absorbance spectrum of myoglobin (Mb), an intracellular O(2) storage protein, is virtually identical to that of hemoglobin (Hb). As a consequence, the relative contributions of Mb and Hb to the NIR spectra measured in vivo for blood perfused muscle tissue cannot be determined from the measured spectra alone. To estimate the relative contributions of Mb and Hb to NIR spectra and spectroscopic images, isolated pig hearts were perfused first with a Hb-free blood substitute (Krebs-Henseleit buffer; KHB) and then with a 50/50 KHB/blood mixture, with spectroscopic images acquired at each step. Tissue Mb levels were estimated directly from the measurements during KHB perfusion, and total (Mb+Hb) levels were estimated from the images acquired during 50/50 blood/KHB perfusion. Myoglobin accounted for 63 +/- 11% of the total heme content during perfusion with the 50/50 mixture (implying that Mb would contribute 46% of the combined (Mb+Hb) NIR profile during whole blood perfusion), confirming that Mb contributes substantially to near-infrared absorbance spectra of blood perfused cardiac tissue.

Automated high-resolution frequency-stabilized cavity ring-down absorption spectrometer

We describe a frequency-stabilized cavity ring-down absorption spectrometer with automated scanning capabilities. The system utilizes the comb of ring-down cavity resonances as frequency markers for spectral scans. The comb is actively stabilized with respect to a frequency-stabilized reference laser, and the continuous wave, single-mode probe laser frequency is in turn actively stabilized with respect to resonances of the ring-down cavity frequency comb. Ring-down spectra are obtained by locking the external-cavity diode laser probe to sequential cavity resonances (separated by the ring-down cavity free spectral range), and the ring-down cavity frequency comb is translated by controlled amounts using acousto-optic frequency shifting methods for fine frequency steps less than the free-spectral range. A computer-controlled method for automating frequency tuning and probe laser locking to the cavity resonances is described, and high-resolution near-infrared (vicinity of 10712cm−1) absorption spectra of water vapor are presented. A frequency resolution of ≈1MHz and minimum measurable line intensity of 10−27cm2cm−1molecule−1 are demonstrated.

Tuning Near-Infrared Optical Properties of Aromatic Model Compounds by Substituents

In this study, the effects of substituents on the near-infrared (NIR) absorption spectra of model compounds were examined theoretically and experimentally, including benzene (B), fluorobenzene (FB), 1,4-difluorobenzene (DFB), and 1,4-bis(trifluoromethyl) benzene (6FB). It was found that a stronger electron-withdrawing substituent resulted in a smaller C–H bond length and thus a blue-shifted overtone position. Thus, the order of B > FB > DFB > 6FB was found for the positions of C–H fundamentals and overtones. The variations of optical windows were primarily influenced by the C–H molar density as well as by the shifting of the absorption band by the substituent. A pseudo compound (PC) with the same C–H number density as the 6FB but with the same band position as B was used to address the effect of a polarized substituent on the optical window. It was found that 6FB could have the optical window at the lower wavelength regions of the S-band (1480–1530 nm) and C-band (1530–1570 nm) but that of the PC at the higher wavelength regions of the C-band and L-band (1570–1610 nm). The present study provides another approach for designing new organic polymers for optical waveguides besides the current approach of reducing the C–H number density.

Kinetics of Catalytic Isomerization of Quadricyclane to Norbornadiene Using Near Infrared Absorption Spectroscopy: Conversion Rate and Diffusion Motion in Heterogeneous Reaction

By use of Fourier transform near-infrared (NIR) absorption spectroscopy and the aid of a kinetic model, we have investigated the conversion of quadricyclane to norbornadiene catalyzed by anhydrous CuSO4 and SnCl2 in chloroform. The reaction mixture is not agitated so as to avoid the effect of sample heterogeneity. The NIR absorption spectra are acquired, at a position ∼2 mm above the catalyst surface, at 30-s intervals during 4 h. The concentrations of quadricyclane and norbornadiene are determined with the analysis of partial least squares. The isomerization of quadricyclane, as numerically solved from the model, is expected to describe its behavior more accurately in the catalytic system than that obtained previously. In addition to the isomerization rate, the kinetic model takes into account the contribution of diffusion. The diffusion coefficients of quadricyclane can be determined to be 3.8 × 10-5 cm2 s-1 in chloroform and 1.14 × 10-5 and 2.85 × 10-6 cm2 s-1 inside the CuSO4 and SnCl2 stacks, respectively. Diffusion is slowed inside the solid stacks, and thus the molecular mechanism cannot be suitable for this system. Given the diffusion coefficients, the pseudo-first-order depletion rate constants are evaluated to be (3.7 ± 0.1) × 10-3 and (3.8 ± 0.1) × 10-3 s-1 for CuSO4 and SnCl2, respectively. The corresponding second-order rate constants are determined to be (1.3 ± 0.2) × 10-5 and (2.0 ± 0.1) × 10-6 s-1 A-1 by considering the density and the size of the catalyst particles; A denotes the total catalyst surface area per unit effective volume of solvent. The rate constant with the CuSO4 catalyst is consistent with others obtained in a continuously stirred mixture. In the surface-mediated reaction, the catalytic isomerization is subject to one-site coordination (1:1 complex) between the reactant and the catalyst. Nevertheless, a two-site coordinated reaction cannot be excluded unless the interstitial size dependence of the depletion rate is known.

Band analysis of temperature-dependent near-infrared spectra of oleic acid in the pure liquid state by the analytic geometric approach.

The applicability of the band-stripping and complementary matching method has been demonstrated by the analysis of temperature-dependent near-infrared (NIR) absorption spectra in the 7500-6500 cm(-1) region of oleic acid (cis-9-octadecenoic acid) in the pure liquid state. This method is based on first derivative-second derivative pair (D1-D2) plots and a new concept called the complementary band, cBDi, created by subtracting all the rest of the bands, exclusive of the ith estimated band, eBDi, from an experimental spectrum. The degree of coincidence of both band shapes provides a suitable measure for the quality of fit for each individual component band. It has been confirmed from the present analysis of the NIR spectra of oleic acid measured over a temperature range of 16-79 degrees C that the change of the peak intensity of the component band at around 6915 cm(-1) due to the first overtone of an O-H stretching vibration of the monomer has two transition points around 35 and 55 degrees C. Moreover, the present study has provided new insight into the analysis of temperature-dependent spectral variations of oleic acid. Among the three temperature ranges, 16-35 degrees C, 35-55 degrees C, and 55-79 degrees C, in the first range the band near 6915 cm(-1) shows a slight increase and in the second range it has a linear intensity change with a slope of 0.002 a.u./degree C. In the third range, a rapid increase of the peak intensity is observed. This band exists even at 15 degrees C (just below the melting point) and shows a shift from 6910 to 6915 cm(-1) and a band narrowing from 85 to 80 cm(-1) (full width at half-height) over a temperature range of 16 to 79 degrees C. Furthermore, it has been found that there are two broad bands at around 6835 and 6778.

Langmuir–Blodgett Films of Single-Wall Carbon Nanotubes: Layer-by-layer Deposition and In-plane Orientation of Tubes

The Langmuir–Blodgett technique has been applied to build optically homogeneous thin films of chemically solubilized single-wall carbon nanotubes (s-SWNTs) which possess good surface spreading properties at the air/water interface. Deposition can be performed in a layer-by-layer fashion up to 100 or more layers either by horizontal lifting or vertical dipping, allowing to readily control the film thickness. Their visible to near-infrared absorption spectra showing the characteristic features of semiconducting and metallic SWNTs prove the intactness of their one-dimensional electronic states during the preparation process. Polarized absorption spectroscopy and atomic force microscope (AFM) observation demonstrate that the tubes are oriented in the direction of the trough barrier (horizontal lifting) or in the dipping direction (vertical dipping). These are attributed to compression-induced or flow-induced orientation, respectively, the latter found to be much stronger than the former. The realization of homogeneous thin films of SWNTs with a controllable thickness and tube orientation should be an important basis for the future development of their scientific understanding and technological applications.

Growth and vibrational spectra of doped KMgF 3 single crystal

The different ions doped KMgF 3 single crystals are prepared by the vertical Bridgman method. The near-infrared absorption spectra for different parts of all as-growth crystals indicate that there is the best transparency in middle part. The correlation between the vibronic frequencies of Eu 2+ and the site displacement of Cu + co-doped ions is firstly studied, which indicates that Cu + ions replace the site of the Mg 2+ ions. The co-doped Eu 2+ counteracts the charge misfit causing by the replacement of Mg 2+ with Cu +. The overlapping of the emission spectra of the Eu 2+ and the excitation spectra of the Cu + results in the energy transfer from Eu 2+ to Cu +.

Predicting the cold hardiness of willow stems using visible and near-infrared spectra and sugar concentrations

Closely related, fast-growing clones of willows from northern/continental and southern/maritime origins were assessed for their levels of cold hardiness. Assessments were made during active growth and, subsequently, during cold hardening at mean temperatures of 3°C (the COLD regime) and 8°C (the MILD regime). The onset of hardening was triggered simultaneously in all clones by administering a drastic day length reduction on the first day. The northern/continental clones showed consistently higher rates of hardening than the southern/maritime ones. This was particularly true under the COLD regime, suggesting that their hardening was less sensitive to low temperatures. The stems' visible and near-infrared absorption spectra, and concentrations of ten major soluble sugars, were also determined. Multivariate analysis revealed that spectral data could predict up to 96% of the variation in cold hardiness, when the analysis was restricted to the MILD regime and the data corrected for irrelevant systematic information. Possible direct links between spectral changes and chemical changes are discussed. Multivariate analysis also revealed that sugar concentrations could be used to predict up to 73% of the variation in cold hardiness. Different sugars displayed different patterns of variation during hardening. Concentrations of mannose and myo-inositol both decreased, whereas concentrations of galactose, sucrose, maltose, raffinose and stachyose all increased, but at different times. Dry matter increased markedly during hardening, so expressing the concentrations of sugars relative to dry matter does not provide an accurate measure of the amounts present.

Optical absorption of Co2+-doped silica gel-derived glasses

Abstract Monolithic samples of silica and Co-doped silica gels were obtained by the sol–gel method and heat-treated at temperatures from 40 to 1000 °C. The colors of Co-doped silica samples depended on heat-treatment temperature. Ultraviolet, visible and near-infrared (NIR) absorption spectra of the samples heated at different temperatures were recorded and compared with those of undoped silica samples. Results showed that 0.4 wt.% Co-doped silica samples heated at temperatures ranging 750–1000 °C exhibited broad absorption band in the range of 1200–1600 nm, and the intensity of the absorption band increased with heat-treatment temperatures. Co-doped silica glass is potential to be used as a kind of laser passive Q-switching material in NIR range.

Calculation of Near-Infrared Intersubband Absorption Spectra in GaN/AlN Quantum Wells

Intersubband transitions in GaN multiple quantum wells (MQW) are expected to be applicable to 1-Tb/s all-optical switches. The near-infrared (1.33–2.15 µm) intersubband absorption spectra of GaN/AlN MQW samples have been theoretically investigated. The measured spectra have been well explained by a model in which zero-voltage drop across one quantum well period and 0.5- to 0.75-nm-thick interface graded layers were assumed. The effective electric field in the well was estimated to be greater than 5 MV/cm. For thick wells, absorption spectra are sensitive to the electric field, and hence to the strain, barrier thickness, and doping level. In thin wells, the effect of the electric field is negligible, but the quality of the interface affects the spectra. The calculation model has been applied to the design of coupled quantum wells (CQW), where faster optical response is expected. Higher-order intersubband absorption at wavelengths of less than 1 µm is also expected to be enhanced in CQWs.

Electronic and photophysical properties of C60Cl24

This work examines, by using quantum-chemical calculations, the electronic and optical properties of three highly symmetrical isomers of the C60Cl24 halogenofullerene. The ground state properties of these derivatives are calculated using the semi-empirical Hartree–Fock AM1 approach and discussed in terms of symmetry, charge distribution and electronic conjugation on the fullerene cage. Starting from the optimized geometry, the optical absorption spectrum of each molecule is calculated at the semi-empirical Hartree–Fock INDO/S level, using a large configuration interaction scheme. The results are compared to a visible and near-infrared absorption spectrum of C60Cl24, recorded in solid matrices, at low temperature. From the comparison, it is concluded that a D2h C60Cl24 isomer is responsible for the spectrum observed. The spectrum is analyzed in terms of electronic singlet transitions.