White Light Absorption Research Articles

Site‐selective fluorescence and spectroscopic properties of Yb‐doped lanthanum titanate glasses

AbstractYtterbium‐doped lanthanum titanate glasses were prepared by levitation melting for the detailed characterization of the spectroscopic properties in the rare‐earth titanate glass host. Low‐temperature fluorescence spectroscopy reveals distinct site‐selectivity in both static and lifetime fluorescence measurements suggesting an absence of clustering as well as significant variation of local ytterbium environments. Typical site‐selectivity behavior of a shrinking Stark manifold with lower excitation energy is observed. At 77 K, both the mean emission frequency and the fluorescence lifetime initially increase as the excitation energy decreases from about 11100 to 10750 and then slightly decrease at lower excitation energy. Temperature‐dependent lifetime measurements between 77 and 420 K show a decreasing lifetime with increasing temperature and are well described by a two‐level thermal activation model. The temperature‐dependent fluorescence spectroscopy coupled with a room temperature white light absorption measurement allow the determination of the Stark energy levels of in lanthanum titanate glass as well as the calculation of the laser cross‐sections.

Comparative Study of Antibacterial Activity between Selected International and Indian Essential Oils against Selected Pathogenic Bacteria

In recent years, the rapid growth in Antimicrobial resistance (AMR) has become a global concern. Essential oils derived from plants that include bioactive components with proven antioxidative and antibacterial activities could be a potential solution to arrest this problem. In this study, antibacterial activities of DoTERRA essential oils such as Onguard, Clove, Teatree, Lavender and Eucalyptus were evaluated with Indian essential oils against clinical pathogenic bacteria. The GC-MS study revealed that cineole, terpinene, eucalyptol, and eugenol were the most prevalent bioactive components in these essential oils. The purity of the essential oils was confirmed with zeta potential and white light absorption spectrophotometer and shows that the Zeta potential of all the essential oils ranges from -51.4 to 0 mV. Using agar well diffusion and Micro broth dilution procedures, the antimicrobial activity of essential oils of clove, lavender, tea tree, eucalyptus, and On-Guard (combined) was assessed against several multi-drug-resistant bacteria. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of essential oils in aqueous and micellar solutions were determined by Micro broth dilution techniques. The most effective antibacterial essential oils were clove, tea tree, and On guard (a blended essential oil with a predominance of Limonene and Eugenol). The current research could result in development of formulas that contain micelle or colloid suspensions of whole essential oils such as clove, On-Guard, or Tea-Tree oil to aid in antimicrobial treatment.

White light induced photo-thermal switching in a graphene-flake-mixed ZnO nanoparticle random laser

We experimentally demonstrate lasing mode switching within a graphene-flake-mixed ZnO nanoparticle film, in which the lasing suppression is observed when white light is illuminated on the film. The similar changes are also observed by changing the temperature of the same sample (about 30 °C increase form room temperature), while no lasing suppression is observed in a ZnO nanoparticle film without graphene flakes. In addition, we also observe that a thin glass substrate coated by a graphene-flake-mixed ZnO nanoparticle film shows a bend toward the film-coated side with increasing the white light intensity, due to the negative thermal expansion of graphene flakes. From these results, we consider that, beside the temperature dependent ZnO emission property, the photo-thermal response of graphene flakes is the dominant key for our observed lasing mode changes, in which the local structural change in a graphene-flake-mixed ZnO nanoparticle film would be induced by the white light absorption of graphene flakes. This study suggests the possibility to provide a method to remotely and non-invasively control and tune the lasing modes by external white light illumination.

Synthesis, chemical characterization and nonlinear optical properties of thallium(III) phthalocyanine halide complexes

The synthesis, chemical characterization and nonlinear optical properties of a family of soluble thallium(III) phthalocyanine(Pc) halide complexes are reported. Tl(t-Bu4Pc)X (X = Cl, Br, or I) were made from 4-t-butylphthalonitrile via oxidation of a dithallium(I) phthalocyanine complex and were characterized by elemental analysis, spectroscopy (UV-vis, 1H NMR and X-ray fluorescence) and MALDI-TOF mass spectrometry. Transient white light absorption measurements of the iodo complex in toluene showed a broad band (440 – 610 nm) excited state absorption with a multiexponential decay dominated by species with lifetimes of ~4.8 ± 1 ps and > 20 ns. The ratio of the long lived excited state absorption coefficient to that of the ground state is ~100 at 500 nm. Nonlinear transmission and Z-scan experiments (532 nm, f5 optics) confirmed the above and also showed that the real part of the nonlinear refractive index is negative.

Individual identification of free hole and electron dynamics in CuIn1−xGaxSe2 thin films by simultaneous monitoring of two optical transitions

The photocarrier dynamics of CuIn1−xGaxSe2 (CIGS) thin films were studied using white-light transient absorption (TA) measurements, as an understanding of this behavior is essential for improving the performance of solar cells composed of CIGS thin films. A characteristic double-peak structure due to the splitting of the valance bands in the CIGS was observed in the TA spectra under near-band-gap resonant excitation. From a comparison of the TA decay dynamics monitored at these two peaks, it was found that the slow-decay components of the electron and hole relaxation are on the nanosecond timescale. This finding is clear evidence of the long lifetimes of free photocarriers in polycrystalline CIGS thin films.

Diagnostics of low-pressure discharges containing InBr studied for lighting applications

The utilization of InBr in low-pressure rare-gas plasmas for lighting applications may serve as an efficient alternative to hazardous mercury, which is used in common fluorescent lamps as a radiator. In order to perform systematic investigations of these discharges, diagnostic methods are required to gain insight into the relevant plasma parameters. This goal can be achieved by using white light absorption and optical emission spectroscopy supported by an extended corona model of the indium atom and a simulation of the relative intensity of the InBr emission. The set of diagnostic methods is exemplarily applied to measurements on an inductively coupled argon discharge at 100 W power with varying InBr content. The plasma parameters are derived and the processes determining their changes with varying InBr density are identified. Increasing the InBr density results in a decrease in Te but an increase in ne, which can be explained by considering the ionization and power balance. The relevant population processes for the rovibrational states of InBr are inelastic collisions with heavy particles with an increasing importance of electron impact excitation at a higher InBr density. The radiated power is maximal at a cold spot temperature between 210 and 220 °C as reabsorption occurs at a high InBr density.

Size dependence of two-photon absorption in semiconductor quantum dots

Quantum confinement plays an important role in the optical properties of semiconductor quantum dots (QDs). In this work, we combine experiment and modeling to systematically investigate the size dependence of the degenerate two-photon absorption (TPA) of below-band-gap radiation in CdSe QDs. The TPA coefficient β at 800 nm of CdSe QDs of varying radii was measured using femtosecond white-light transient absorption spectroscopy by probing the pump-induced bleaching at the first exciton transition energy. β was also calculated using a model based on the multiband effective-mass approximation. Satisfactory agreement between experiment and theory was obtained. Our findings show the evolution of the TPA in the QDs from that of atom-like to bulk-like with increasing the radius R. The TPA coefficient (or the volume normalized TPA cross-section) increases with radius approximately linearly in the strong confinement regime due to the rapid increase of the joint density of states for the two-photon allowed transitions, and saturates for R > 5 nm (the exciton Bohr radius), approaching that of bulk CdSe.

Noninvasive, real-time measurements of plasma parameters via optical emission spectroscopy

Plasma process control applications require acquisition of diagnostic data at a rate faster than the characteristic timescale of perturbations to the plasma. Diagnostics based on optical emission spectroscopy of intense emission lines permit rapid noninvasive measurements with low-resolution (∼1 nm), fiber-coupled spectrographs, which are included on many plasma process tools for semiconductor processing. Here the authors report on rapid analysis of Ar emissions with such a system to obtain electron temperatures, electron densities, and metastable densities in argon and argon/mixed-gas (Ar/N2, Ar/O2, Ar/H2) inductively coupled plasmas. Accuracy of the results (compared to measurements made by Langmuir probe and white-light absorption spectroscopy) are typically better than ±15% with a time resolution of 0.1 s, which is more than sufficient to capture the transient behavior of many processes, limited only by the time response of the spectrograph used.

Note: Implementation of a cold spot setup for controlled variation of vapor pressures and its application to an InBr containing discharge lamp

In order to allow for a systematic investigation of the plasma properties of discharges containing indium halides, which are proposed as an efficient alternative for mercury based low pressure discharge lamps, a controlled variation of the indium halide density is mandatory. This can be achieved by applying a newly designed setup in which a well-defined cold spot location is implemented and the cold spot temperature can be adjusted between 50 and 350 °C without influencing the gas temperature. The performance of the setup has been proved by comparing the calculated evaporated InBr density (using the vapor pressure curve) with the one measured via white light absorption spectroscopy.

Correction factors for saturation effects in white light and laser absorption spectroscopy for application to low pressure plasmas

In white light absorption spectroscopy, the broadening of the absorption signal due to the apparatus profile of the spectrometer may lead to an underestimation of the determined density as one measures an apparent optical depth. This is in particular true for high optical depth where saturation effects of the transmitted intensity occur. Provided that the line profile of the absorption line is known, the apparent optical depth effect can be accounted for by introducing a correction factor. The impact of the saturation and the approach of considering the effect are demonstrated for argon and indium lines in low pressure plasmas where correction factors of one order of magnitude or even higher are reached very easily. For the indium line, the hyperfine splitting has been taken into account. In laser absorption, the line profile is resolved. However, the weak but rather broad background emission of the laser diode can cause a saturation signal at the photo diode resulting also in an underestimation of the density obtained from the analysis. It is shown that this can be taken into account by fitting the theoretical line profile to the measured absorption signal which yields also a correction factor. The method is introduced and demonstrated at the example of the cesium resonance line including the hyperfine splitting. Typical correction factors around two are obtained for the cesium ground state density at conditions of a low pressure negative hydrogen ion source in which cesium is evaporated to enhance the negative ion production.

Correction for specimen movement and rotation errors for in-vivo Optical Projection Tomography.

The application of optical projection tomography to in-vivo experiments is limited by specimen movement during the acquisition. We present a set of mathematical correction methods applied to the acquired data stacks to correct for movement in both directions of the image plane. These methods have been applied to correct experimental data taken from in-vivo optical projection tomography experiments in Caenorhabditis elegans. Successful reconstructions for both fluorescence and white light (absorption) measurements are shown. Since no difference between movement of the animal and movement of the rotation axis is made, this approach at the same time removes artifacts due to mechanical drifts and errors in the assumed center of rotation.

Measurement of metastable and resonance level densities in rare-gas plasmas by optical emission spectroscopy

Excitation and ionization of atoms out of the 4 energy levels of the excited np5(n + 1)s configuration of rare gases play an important role in many low temperature rare-gas plasmas. We compare two optical methods for measuring the number densities of atoms in these excited levels in an inductively coupled plasma under a variety of operating conditions (600 W, 1–25 mTorr). The first method is a standard white light absorption technique, whereas the second method exploits changes in the effective branching fractions of np5(n + 1)p → np5(n + 1)s emissions brought about by radiation trapping of atoms in np5(n + 1)s levels. The branching fraction method was found to produce results that agree well with the direct white light absorption method for both argon and neon plasmas using little more than a low-resolution spectrum of the plasma glow.

Photons and evolution: Quantum mechanical processes modulate sexual differentiation

This paper will show that the fractional difference in the human gender ratio (GR) between the GR(at death) for those born in solar cycle peak years (maxima) and the GR(at death) in those born in solar cycle non-peak years (minima), e.g., 0.023, divided by Pi, yields a reasonable approximation of the quantum mechanical constant, alpha, or the fine structure constant (FSC) approximately 0.007297... or approximately 1/137. This finding is based on a sample of approximately 50 million cases using common, readily available demographic data, e.g., state of birth, birth date, death date, and gender. Physicists Nair, Geim et al. had found precisely the same fractional difference, 0.023, in the absorption of white light (sunlight) by a single-atom thick layer of graphene, a carbon skeleton resembling chicken wire fencing. This absorption fraction, when divided by Pi, yielded the FSC and was the first time this constant could "so directly be assessed practically by the naked eye". As the GR is a reflection of sexual differentiation, this paper reveals that a quantum mechanical process, as manifested by the FSC, is playing a role in the primordial process of replication, a necessary requirement of life. Successful replication is the primary engine driving evolution, which at a biochemical level, is a quantum mechanical process dependent upon photonic energy from the Sun. We propose that a quantum-mechanical, photon-driven chemical evolution preceded natural selection in biology and the mechanisms of mitosis and meiosis are manifestations of this chemical evolution in ancient seas over 3 billion years ago. Evolutionary processes became extant first in self-replicating molecules forced to adapt to high energy photons, mostly likely in the ultraviolet spectrum. These events led to evolution by natural selection as complex mixing of genetic material within species creating the variety needed to match changing environments reflecting the same process initiated at the dawn of life. Both evolutionary mechanisms coexist and are interactive. The periodic energy of solar maxima is likely modulating the human genome from maternal integument to an embryo in utero with non-local mechanisms intrinsic to quantum mechanics.

Determination of the Rb atomic number density in dense rubidium vapors by absorption measurements of Rb 2 triplet bands

A simple and accurate way of determining atom number densities in dense rubidium vapors is presented. The method relies on the experimental finding that the reduced absorption coefficients of the Rb triplet satellite bands between 740 nm and 750 nm and the triplet diffuse band between 600 nm and 610 nm are not temperature dependent in the range between 600 K and 800 K. Therefore, the absolute values of the reduced absorption coefficients of these molecular bands can provide accurate information about atomic number density of the vapor. The rubidium absorption spectrum was measured by spatially resolved white-light absorption in overheated rubidium vapor generated in a heat pipe oven. The absolute values for the reduced absorption coefficients of the triplet bands were determined at lower vapor densities, by using an accurate expression for the reduced absorption coefficient in the quasistatic wing of the Rb D1 line, and measured triplet satellite bands to the resonance wing optical depth ratio. These triplet satellite band data were used to calibrate in absolute scale the reduced absorption coefficients of the triplet diffuse band at higher temperatures. The obtained values for the reduced absorption coefficient of these Rb molecular features can be used for accurate determination of rubidium atomic number densities in the range from about 5 × 10 16 cm − 3 to 1 × 10 18 cm − 3 .

Absorption spectroscopy of the rubidium dimer in an overheated vapor: An accurate check of molecular structure and dynamics

Experimental studies of the absorption spectrum of the ${\mathrm{Rb}}_{2}$ dimer are performed in the $600--1100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ wavelength range for temperatures between 615 and $745\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The reduced absorption coefficient is measured by spatially resolved white light absorption in overheated rubidium vapor with a radial temperature gradient, which enables simultaneous measurements at different temperatures. Semiclassical and quantum spectral simulations are obtained by taking into account all possible transitions involving the potential curves stemming from the 5 $^{2}S+5$ $^{2}S$ and 5 $^{2}S+5$ $^{2}P$ asymptotes. The most accurate experimental potential curves are used where available, and newly calculated potential curves and transition dipole moments otherwise. The overall consistency of the theoretical model with the experimental interpretation is obtained only if the radial dependence of both the calculated transition dipole moments and the spin-orbit coupling is taken into account. This highlights the low-resolution absorption spectroscopy as a valuable tool for checking the accuracy of molecular electronic structure calculations.

Spin-exchange optical pumping ofHe3with Rb-K mixtures and pure K

We have studied the efficiency of spin-exchange optical pumping SEOP in cells that contain either pure rubidium, mixtures of rubidium and potassium, or pure potassium. Optical pumping was performed with spectrally narrowed diode array lasers operating at either the wavelength of the Rb 5s1/2-5p1/2 transition 795 nm or the K 4s1/2-4p1/2 transition 770 nm. Calculations of the expected efficiency are shown for practical conditions and compared to measurements. We have measured the vapor density ratio in Rb-K mixture cells using absorption of white light. Our focus is on the conditions that are relevant for neutron spin filters, but the results are relevant to all applications of SEOP. We find that both Rb-K and pure K cells yield improvements in the spin-exchange efficiency, and each approach has its own advantages. Overall, the best results for high polarizing rate with high polarization were obtained with mixture cells with K-Rb vapor density ratios between 2 and 6.

Nucleation of calcium carbonate in presence of citric acid, DTPA, EDTA and pyromellitic acid

The influence of four calcium complexing additives, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), and their concentration on the induction time of calcium carbonate nucleation has been studied. The experiments were performed by rapidly mixing a sodium carbonate solution and a calcium chloride solution of various concentrations. The induction time was obtained by recording the white light absorption of the solution. Chemical speciation was used to estimate the initial thermodynamic driving force of each experiment. The induction time was found to increase with additive concentration. The effect varies from one additive to another. CIT causes the greatest increase in induction time and PMA the least. Using classical nucleation theory the experimental data were evaluated in terms of the interfacial energy. In pure water a value of 37.8 mJ m −2 was obtained, showing good agreement with other works. CIT, DTPA and EDTA caused a notable increase of the interfacial energy at a concentration of 0.5 mmol l −1. PMA does not appear to have any effect at all on the interfacial energy. Different mechanisms for the influence of the additives on the measured induction time and on the estimated interfacial energy are discussed.

Highly efficient p–i–n type organic photovoltaic devices

We present results on p–i–n-type photovoltaic devices based on donor–acceptor organic small molecule blends and doped wide-gap charge transport layers. The doped transport layers are formed using a high vacuum co-evaporation deposition technique (i.e. co-sublimation of matrix and dopant). Solar cell devices have been fabricated based on a blend of zinc-phthalocyanine as donor (D) and fullerene (C 60) as electron acceptor (A) with doped charge transport layers. Optionally, a layer of neat layer of a perylene dye, perlenetetracarboxylic-bis-benzimidazole, is added to extend the absorption spectrum of the active layer system. The energy conversion efficiency of these cells under 1 sun, standard AM1.5 illumination (100 mW/cm 2) is up to 1.9%. This represents an almost twofold improvement as compared to previously reported cells with similar active layer system in a conventional architecture. In this report, I– V characteristics, power conversion efficiencies, the dependence of short circuit current on incident white light intensity and absorption spectra of the active layer system are discussed.

Profiles of 14C fixation through spinach leaves in relation to light absorption and photosynthetic capacity

ABSTRACTThe profile of photosynthetic rate with depth through a leaf depends on the profiles of light absorption and photosynthetic capacity. Using a combination of several techniques, a comprehensive description of spinach leaves has been obtained. Profiles of CO2 fixation were obtained by exposing leaves to 14CO2 for 10 s under blue or green light before freeze clamping and paradermal sectioning. Profiles of light absorption were measured on adjacent parts of the leaf by quantifying chlorophyll fluorescence images of the transversely cut face obtained when blue or green light was applied to the adaxial or abaxial surface. The profile of CO2 fixation was modelled using the measured profiles of light absorption and photosynthetic capacity. There was remarkably good agreement between the observed and modelled CO2 fixation profiles for the eight combinations of colour, orientation and irradiance tested. Gas exchange of an intact leaf was also measured concurrently with conventional chlorophyll fluorescence under blue or green light. These data were consistent with the multi‐layer leaf model with the exception of blue light applied to the abaxial surface, where chlorophyll fluorescence appeared to come from layers deeper than expected. Photosynthetic capacity matched the profile of green but not white light absorption through the leaf.

Depth Profiling of Light-Induced Defects in Hydrogenated Amorphous Silicon by Transient Photocurrent Spectroscopy

AbstractThe sensitivity of transient photocurrent measurements to the spatial location of native and metastable electronic defects in hydrogenated amorphous silicon films is demonstrated. The technique utilises red and green laser excitation to generate excess carriers in the bulk and at the surfaces of the film, respectively. In annealed films the defect density is found to be higher in the surface regions. Following white light soaking, the metastable defect density at the surface at which the light is incident is greater than that in the bulk, which in turn is greater than that at the exit surface. This is attributed to the white light absorption profile within the film. Green light soaking creates metastable defects at the incident surface, with the bulk of the film largely unaffected.