Weak Band Research Articles

Photoacoustic Detection of Weak Absorption Bands in Infrared Spectra of Calcite.

Photoacoustic spectroscopic detection of infrared absorption often produces spectra with enhanced intensities for weaker peaks, enabling the detection of features due to overtones and combinations, as well as less-abundant isotopic species. To illustrate this phenomenon, we present and discuss photoacoustic infrared spectra of calcite. We use linearization of rapid-scan spectra, as well as comparing step-scan and rapid-scan spectra, to demonstrate that saturation is not the driving force behind these enhanced intensities. Our results point to a significant knowledge gap, since a theoretical basis for the enhancement of these weak bands has not yet been developed.

A three-component copper phosphonate complex as a sensor platform for sensitive Cd2+ and Zn2+ ion detection in water via fluorescence enhancement

A three-component molecular copper phosphonate [Cu2(H4tpmm)2(Hpybim)2]·H2O (1·H2O), where H6tpmm ​= ​2,4,6-tris(phosphorylmethyl)mesitylene and Hpybim ​= ​2-(2-pyridyl)benzimidazole, showing high thermal stability up to approximately 370 ​°C has been prepared. Complex 1·H2O has a dinuclear structure symmetry-related by a crystallographic inversion center, in which the Cu(II) center suits a highly distorted square pyramidal geometry. Complex 1·H2O shows two extremely weak emission bands in both solid state and H2O suspension phase. However, as Cd2+ and Zn2+ were added into the H2O suspension of 1·H2O, the fluorescence intensity would be remarkably enhanced by 11.1 and 25.2 times, respectively, with a dramatic change in the emission band shape. The fluorescence enhancement sensing of 1·H2O toward Cd2+ and Zn2+ in H2O is highly sensitive with limit of detection (LOD) values of 1.35 and 0.89 ​μM, respectively. Such sensing performances are negligibly interfered by most perturbed metal ions but largely affected by Fe3+, Ni2+, and Co2+. EDX and XPS analyses show the occurrence of weak binding interactions between the Cd2+/Zn2+ ions and the structure of 1·H2O, resulting in fluorescence enhancement. This work demonstrates a highly water stable molecular copper phosphonate behaving as a sensor platform suitable for Cd2+ and Zn2+ ion detection in water via remarkable fluorescence enhancement, providing a new method for metal phosphonate complexes.

Visible upconversion of erbium oxide and their correlation with crystalline defects

We present the synthesis of erbium oxide (Er2O3) by chemical bath deposition technique at ~ 60 ± 2 °C for a prolonged period of 60 hr and subsequently thermally treated at ~1000 °C in an air atmosphere. The morphology of samples is analyzed by Scanning Electron Microscopy. The crystalline phase is explored by X-Ray Diffraction, identifying the cubic-bixyite phase of Er2O3 and grain size that ranges between ~7.9 nm to ~10.9 nm. The calculated bandgap energy is found of ~4.5 eV and ~3.8 eV when using the Tauc equation and the Effective mass approximation model, respectively. We consider that vacancies, interstices, grain boundaries, and stacking faults present a corpuscular behavior. In this regard, the Maxwell-Boltzmann statistics is applied as an original approach considering the crystalline native defects associated with vacancies and interstices. We discuss the photoluminescence dependence with the trap density and the surface recombination velocity in the light of the Maxwell-Boltzmann theoretical results associated with the electronic transitions related to the native intrinsic defects situated at the Vis-region. The photoluminescence spectrum shows two strong emission bands in Vis-region that correspond to 4S3/2 and 4I15/2 electronic transitions. Upconversion-emission consists of blue, green, and weak red bands originated from the 4 f→4 f intra-transitions.

Investigations on Crystalline Perfection, Raman Spectra and Optical Characteristics of Transition Metal (Ru) Co-Doped Mg:LiNbO3 Single Crystals.

Congruent lithium niobate single crystals with a Ru:Mg co-dopant have been successfully grown using the Czochralski technique from the melt containing 0.02 mol % Ru with Mg of two varied concentrations (4.0 and 6.0 mol %). The effects of Ru and Mg co-doping on the crystalline quality were determined by high-resolution X-ray diffractometry, which confirmed that the crystalline quality is good and that the dopants are statistically distributed in the crystal. The Raman scattering analysis shows no change in the lattice vibration except a slight change in the peak width and intensity due to more asymmetry in the molecular charge, which leads to enhancement of the polarizability. The optical transmission spectra indicate that both the crystals have high optical transparency in the visible region, with a shift of the absorption edge toward shorter wavelengths, as compared to un-doped LN. The weak absorption band observed below 400 nm is attributed to Ru ions. The influence of co-doping in the electronic band gap energies is calculated by the Tauc relation. The refractive index is measured by using a prism coupler at two wavelengths (532 and 1064 nm). The calculated absorption coefficients and direct and indirect band gap energies for both the samples are found to be nearly the same within experimental error. A decrease in the birefringence is observed for the Ru:Mg(6 mol %) doped sample. The observed slight reduction in refractive indices with Ru:Mg co-doping is consistent with a rise in band gap energy, which is related to the change in absorption edge to the lower wavelength. The second harmonic generation (SHG) efficiency is measured by the Kurtz and Perry powder method, and a decrease in SHG efficiency for Ru:Mg(6 mol %) is observed.

Optical Absorption of Excimer Laser‐Induced Dichlorine Monoxide in Silica Glass and Excitation of Singlet Oxygen Luminescence by Energy Transfer from Chlorine Molecules

An optical absorption (OA) band of interstitial dichlorine monoxide molecules with peak at 4.7 eV and halfwidth 0.94 eV is identified in F2 laser‐irradiated (ħω = 7.9 eV) synthetic silica glass bearing both interstitial O2 and Cl2 molecules. Alongside with intrinsic defects, this OA band can contribute to solarization of silica glasses produced from SiCl4. Although only the formation of ClClO is confirmed by its Raman signature, its structural isomer ClOCl may also contribute to this induced OA band. Thermal destruction of this band between 300 °C and 400 °C almost completely restores the preirradiation concentration of interstitial Cl2. An additional weak OA band at 3.5 eV is tentatively assigned to ClO2 molecules. The strongly forbidden 1272 nm infrared luminescence band of excited singlet O2 molecules is observed at 3–3.5 eV excitation, demonstrating an energy transfer process from photoexcited triplet Cl2 to O2. The energy transfer most likely occurs between Cl2 and O2 interstitial molecules located in neighboring nanosized interstitial voids in the structure of SiO2 glass network.

Atomic-level insights into the activation of nitrogen via hydrogen-bond interaction toward nitrogen photofixation

Summary As the activation of N2 molecules is generally regarded as the bottleneck in N2 reduction, it is of significant importance to develop promising strategies to efficiently activate N2 molecules. Herein, we discovered an innovative approach to activate N2 molecules via hydrogen-bond interaction in N2 photofixation. Porous Cu with surface modification of S atoms (3%-S/Cu) exhibited remarkable catalytic activity and stability in N2 photofixation. Further mechanistic studies revealed that surface S atoms directly participated in the catalytic process by accepting and donating H atoms. In addition, the forming S–H bond significantly promoted the activation of N2 molecules via hydrogen-bond interaction, contributing to the enhanced catalytic activity.

Bennu's global surface and two candidate sample sites characterized by spectral clustering of OSIRIS-REx multispectral images

The OSIRIS-REx spacecraft encountered the asteroid (101955) Bennu on December 3, 2018, and has since acquired extensive data from the payload of scientific instruments on board. In 2019, the OSIRIS-REx team selected primary and backup sample collection sites, called Nightingale and Osprey, respectively. On October 20, 2020, OSIRIS-REx successfully collected material from Nightingale. In this work, we apply an unsupervised machine learning classification through the K-Means algorithm to spectrophotometrically characterize the surface of Bennu, and in particular Nightingale and Osprey. We first analyze a global mosaic of Bennu, from which we find four clusters scattered across the surface, reduced to three when we normalize the images at 550 nm. The three spectral clusters are associated with boulders and show significant differences in spectral slope and UV value. We do not see evidence of latitudinal non-uniformity, which suggests that Bennu's surface is well-mixed. In our higher-resolution analysis of the primary and backup sample sites, we find three representative normalized clusters, confirming an inverse correlation between reflectance and spectral slope (the darkest areas being the reddest ones) and between b' normalized reflectance and slope. Nightingale and Osprey are redder than the global surface of Bennu by more than 1σ from average, consistent with previous findings, with Nightingale being the reddest (S′ = (−0.3 ± 1.0) × 10−3 percent per thousand angstroms). We see hints of a weak absorption band at 550 nm at the candidate sample sites and globally, which lends support to the proposed presence of magnetite on Bennu.

A far-red phosphor LaSrZnNbO6:Mn4+ for plant growth lighting

Abstract The photoluminescence characteristics of LaSrZnNbO6:Mn4+ were studied in this paper. The excitation spectrum of LaSrZnNbO6:Mn4+ can be divided into two bands. The absorption band centered at 320 nm is attributed to the charge transfer transition from O2− to Mn4+, while the absorption band centered at 366 nm is credited to the 4A2 → 4T1 transition of Mn4+. The weak absorption bands centered at 432 nm and 505 nm are due to the 4A2 → 2T2 and 4A2 → 4T2 transitions of Mn4+ ions, respectively. The emission peak appeared at 694 nm, which is matched well with the absorption wavelength of phytochromes, is caused by the 2E → 4A2 transition of Mn4+ ions. With increasing the Mn4+ ion concentration, the decay times of LaSrZnNbO6:Mn4+ are decreased from 0.2694 to 0.2448 ms. The chromaticity coordinate is (0.7199, 0.2801), which is the far-red emission. The phosphor is conducive to plant growth and has potential applications in the field of plant lighting.

Thermal and near-infrared sensor for carbon observation Fourier transform spectrometer-2 (TANSO-FTS-2) on the Greenhouse gases Observing SATellite-2 (GOSAT-2) during its first year in orbit

Abstract. The Japanese Greenhouse gases Observing SATellite-2 (GOSAT-2), in orbit since 29 October 2018, follows up the GOSAT mission, itself in orbit since 23 January 2009. GOSAT-2 monitors carbon dioxide and methane in order to increase our understanding of the global carbon cycle. It simultaneously measures carbon monoxide emitted from fossil fuel combustion and biomass burning and permits identification of the amount of combustion-related carbon. To do this, the satellite utilizes the Thermal and Near Infrared Sensor for Carbon Observation Fourier-Transform Spectrometer-2 (TANSO-FTS-2). This spectrometer detects gas absorption spectra of solar radiation reflected from the Earth's surface in the shortwave-infrared (SWIR) region as well as the emitted thermal infrared radiation (TIR) from the ground and the atmosphere. TANSO-FTS-2 can measure the oxygen A band (0.76 µm), weak and strong CO2 bands (1.6 and 2.0 µm), weak and strong CH4 bands (1.6 and 2.3 µm), a weak CO band (2.3 µm), a mid-wave TIR band (5.5–8.4 µm), and a long-wave TIR band (8.4–14.3 µm) with 0.2 cm−1 spectral sampling intervals. TANSO-FTS-2 is equipped with a solar diffuser target, a monochromatic light source, and a blackbody for spectral radiance calibration. These calibration sources permit characterization of time-dependent instrument changes in orbit. The onboard-recalibrated instrumental parameters are considered in operational level-1 processing and released as TANSO-FTS-2 level-1 version 102102 products, which were officially released on 25 May 2020. This paper provides an overview of the TANSO-FTS-2 instrument, the level-1 processing, and the first-year in-orbit performance. To validate the spectral radiance calibration during the first year of operation, the spectral radiance of the version 102102 product is compared at temporally coincident and spatially collocated points from February 2019 to March 2020 with TANSO-FTS on GOSAT for SWIR and with AIRS on Aqua and IASI on METOP-B for TIR. The spectral radiances measured by TANSO-FTS and TANSO-FTS-2 agree within 2 % of the averaged bias and 0.5 % standard deviation for SWIR bands. The agreement of brightness temperature between TANSO-FTS-2 and AIRS–IASI is better than 1 K in the range from 220 to 320 K. GOSAT-2 not only provides seamless global CO2 and CH4 observation but also observes local emissions and uptake with an additional CO channel, fully customized sampling patterns, higher signal-to-noise ratios, and wider pointing angles than GOSAT.

Synthesis, structure and photoluminescent properties of Eu:Gd2O3 nanophosphor synthesized by cw CO2 laser vaporization

Europium doped Gd2O3 sphere-like nanoparticles with dm = 9.3 ± 3.5 nm were synthesized by cw CO2 laser vaporization technique in a flowing mixture of argon and oxygen. According to XRD data, the Eu:Gd2O3 nanoparticles crystallize in the monoclinic symmetry class (C2/m space group). High-resolution luminescence spectroscopy study showed that the ultra-narrow 5D0 → 7F0 transition of Eu3+ demonstrates only two peaks corresponding to two inequivalent Cs positions of Eu3+ ion in monoclinic Gd2O3 lattice that is explained by the peculiarities of local environment of Eu3+ ion at these sites. The hypersensitive transition 5D0 → 7F2 dominates in the spectrum and is expanded to the red part of the spectrum in comparison with cubic Eu:Gd2O3 due to intense transitions terminating at higher-lying components of the crystal-field-split 7F2 state. In the luminescence spectrum, an additional weak band with the maximum at 407 nm corresponding to the electronic transitions 4f65 d1(7FJ) → 4f7(8S7/2) of Eu2+ was detected. The obtained values of chromaticity coordinates and absolute quantum yield are (0.644; 0.325) and ca. 1%, respectively. The phase transformations have been investigated using differential scanning calorimetry and thermogravimetry (50–1400 °C). After annealing in air at 700 °C, the monoclinic symmetry class of the Eu:Gd2O3 nanoparticles is preserved and the particle size increases to dm= 17.8 ± 6.1 nm. After annealing, the chromaticity coordinates (0.659; 0.334) and absolute quantum yield (ca. 4%) can be obtained using red phosphor based on monoclinic Gd2O3:Eu3+. The lifetime of the excited 5D0 state of Eu3+ in the annealed nanoparticles is longer than that in the as-synthesized nanoparticles, due to the suppression of nonradiative decay after annealing.

Complex Weblike Hydrogen Bonding in Large “Drain Pipe” Channels of Wightmanite Revealed by New X-Ray and Spectroscopic Measurements

ABSTRACT The wallpaper-type crystal structure of wightmanite, Mg5(BO3)O(OH)5·1–2H2O, has been reanalyzed in order to better understand the position and bonding of hydrogen atoms. Single-crystal structure refinement yielded the monoclinic I2/m unit cell a = 13.5165(18), b = 3.0981(3), c = 18.170(3)Å, ß = 91.441(6)°, and V = 760.65(17)Å3, Z = 4. Hydrogen atoms of OH groups pointing to the inside of the elliptical channels oriented parallel to [010] are arranged in the form of two overlying, a–c parallel planar pentagons. The two pentagons point in opposite directions. Hydrogen-bond analysis shows that the hydroxyl groups are linked by complex polyfurcated, intra-molecular hydrogen bonds forming a web-like network coating the walls of the channels. The longest distance between hydrogens (7.226 Å) is observed in the pentagonal planes of the channel. The anisotropically refined oxygen atoms of the zeolitic water show their strongest vibration parallel to the b axis and in the direction of the largest diameter of the elliptical channel and similarly form a complex inter-molecular hydrogen-bond system to the hydroxyl groups coating the channel walls. This complex bonding is expressed in the Raman spectrum by a broad band between 3100 and 3300 cm–1 that is assigned to the OH / H2O stretching mode and one strong band at 3661 cm–1 attributable to an OH-stretching mode. Infrared spectra also show a pronounced broad band between 3200 and 3700 cm–1 attributed to H2O and OH-stretching modes. The weak bands around 1600 cm–1 observed in the Raman and IR spectra are probably due to relatively weakly bound water in the channels.

Determination of Chromium Based on Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Abstract Chromium plays an irreplaceable role in the life system. The exploration of chromium is beneficial to reveal its physiological or pathological processes. In this study, a novel method was established for determination of chromium in gels by matrix-matched external standard method-laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The relative standard deviation of chromium signal intensity during ablation standard were less than 16% (n = 300), the correlation coefficient (R2) of LA-ICP-MS quantitative calibration curve was 0.9805, and the detection limit was 2.22 µg/g. The MCF-7 cells were used as an in vitro cell model, and two kinds of polyacrylamide gel electrophoresis (PAGE) method were used to separate the protein extract after chromium incubation. And then, the electrophoresis bands obtained by two electrophoresis methods were ablated respectively by LA-ICP-MS with line scan mode, and the weak chromium-containing protein bands were obtained in electrophoresis band. Finally, the LA-ICP-MS was used to measure and image the chromium in individual cell, and it was found that the cell element distribution map overlapped well with the cell contour map under the laser microscope.

Evaluation of Four Lateral Flow Assays for the Detection of Legionella Urinary Antigen.

Urinary antigen tests (UATs) are often used to diagnose Legionnaires’ disease as they are rapid and easy to perform on readily obtainable urine samples without the need for specialized skills compared to conventional methods. Recently developed automated readers for UATs may provide objective results interpretation, especially in cases of weak result bands. Using 53 defined patient urine samples, we evaluated the performance of the BinaxNOW Legionella Antigen Card (Abbott), ImmuView S. pneumoniae and Legionella (SSI Diagnostica), STANDARD F Legionella Ag FIA (SD Biosensor), and Sofia Legionella FIA (Quidel) simultaneously with their respective automated readers. Automatic and visual interpretation of result bands were also compared for the immunochromatography-based BinaxNOW and ImmuView UATs. Overall sensitivity and specificity of Legionella UATs were 53.9–61.5% and 90.0–94.9%, respectively. All four UATs successfully detected all samples from L. pneumophila serogroup 1-positive patients, but most failed to detect samples for Legionella spp., or other serogroups. Automatic results interpretation of results was found to be mostly concordant with visual results reading. In conclusion, the performance of the four UATs were similar to each other in the detection of Legionella urinary antigen with no major difference between automated or visual results reading.

Tuning of defects induced visible photoluminescence by swift heavy ion irradiation and thermal annealing in zinc oxide films

Present study reports the influence of electronic energy deposition on sol-gel grown zinc oxide thin films with different type of microstructures for tailoring the defects induced photoluminescence properties. The microstructure of the films was modified by the controlled thermal annealing and the nature of defects were tuned by swift heavy ions (SHI) irradiations at varying ion fluences of such thin films. It is observed that all the films show two emission bands in the spectral range of 350 nm–1000 nm; (i) a very weak UV-emission band and (ii) a broad visible emission band. The UV-emission band is attributed to the band to band transition while the visible emission to the deep-level defects. The maximum visible emission lies in the green emission region which enhanced with increasing annealing temperature for the samples annealed in controlled Argon gas environment in comparison of samples annealed in an oxygen environment. The intensity of the visible emission band was found to be increased with ion irradiation at low ion fluences while showing reduction at higher ion fluences along with peak broadening. The films annealed at higher annealing temperature exhibit shifting of peak maximum from green region to red region at higher fluences. The peak shifting and peak broadening at higher ion fluences could be attributed to the formation of the high density of complex defects such vacancies cluster and ionized oxygen vacancies in the lattice as tuned under the influence of electronic energy deposition through SHI irradiations. Thus, it is suggested that the intense luminescence induced by the defects could be tuned in controlled manner by selecting the proper irradiations parameters and thus it would be very interesting for the development of the optoelectronic applications.

Electric-quadrupole and magnetic-dipole contributions to the ν2+ν3 band of carbon dioxide near 3.3 µm

The recent detections of electric-quadrupole (E2) transitions in water vapor and magnetic-dipole (M1) transitions in carbon dioxide have opened a new field in molecular spectroscopy. While in their present status, the spectroscopic databases provide only electric-dipole (E1) transitions for polyatomic molecules (H2O, CO2, N2O, CH4, O3…), the possible impact of weak E2 and M1 bands to the modeling of the Earth and planetary atmospheres has to be addressed. This is especially important in the case of carbon dioxide for which E2 and M1 bands may be located in spectral windows of weak E1 absorption. In the present work, a high sensitivity absorption spectrum of CO2 is recorded by Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OFCEAS) in the 3.3 µm transparency window of carbon dioxide. The studied spectral interval corresponds to the region where M1 transitions of the ν2+ν3 band of carbon dioxide were recently identified in the spectrum of the Martian atmosphere. Here, both M1 and E2 transitions of the ν2+ν3 band are detected by OFCEAS. Using recent ab initio calculations of the E2 spectrum of 12C16O2, intensity measurements of five M1 lines and three E2 lines allow us to disentangle the M1 and E2 contributions. Indeed, E2 intensity values (on the order of a few 10–29 cm/molecule) are found in reasonable agreement with ab initio calculations while the intensity of the M1 lines (including an E2 contribution) agree very well with recent very long path measurements by Fourier Transform spectroscopy. We thus conclude that both E2 and M1 transitions should be systematically incorporated in the CO2 line list provided by spectroscopic databases.

Identification of composition and structure of functional groups of ferment lysates based on IR spectroscopy

The paper provides the analysis of IR spectra of ferment lysates, which showed that there are a number of weak bands 1050-1150 cm−1 in spectra typical for vibrations of ester bonds and frequency 1150-1300 cm−1 corresponding vibrations of CH2 groups in fats. Given the high intensity of the peaks at 2800-3000 cm−1, the high intensity of the peaks at 1600-1700 cm−1 and 1500-1550 cm−1 (typical for amino acids) can be assumed to be high in amino acids containing NH3, CH2 and CH3 groups. The study showed that hydrolysis products (ferment lysates) derived from secondary fish processing products have similar protein structure and identical peptide fragments.

Fast Hyper-Spectral Radiative Transfer Model Based on the Double Cluster Low-Streams Regression Method

Fast radiative transfer models (RTMs) are required to process a great amount of satellite-based atmospheric composition data. Specifically designed acceleration techniques can be incorporated in RTMs to simulate the reflected radiances with a fine spectral resolution, avoiding time-consuming computations on a fine resolution grid. In particular, in the cluster low-streams regression (CLSR) method, the computations on a fine resolution grid are performed by using the fast two-stream RTM, and then the spectra are corrected by using regression models between the two-stream and multi-stream RTMs. The performance enhancement due to such a scheme can be of about two orders of magnitude. In this paper, we consider a modification of the CLSR method (which is referred to as the double CLSR method), in which the single-scattering approximation is used for the computations on a fine resolution grid, while the two-stream spectra are computed by using the regression model between the two-stream RTM and the single-scattering approximation. Once the two-stream spectra are known, the CLSR method is applied the second time to restore the multi-stream spectra. Through a numerical analysis, it is shown that the double CLSR method yields an acceleration factor of about three orders of magnitude as compared to the reference multi-stream fine-resolution computations. The error of such an approach is below 0.05%. In addition, it is analysed how the CLSR method can be adopted for efficient computations for atmospheric scenarios containing aerosols. In particular, it is discussed how the precomputed data for clear sky conditions can be reused for computing the aerosol spectra in the framework of the CLSR method. The simulations are performed for the Hartley–Huggins, O2 A-, water vapour and CO2 weak absorption bands and five aerosol models from the optical properties of aerosols and clouds (OPAC) database.

Zonal Features in the Behavior of Weak Molecular Absorption Bands on Jupiter

Based on the spectral observations of Jupiter carried out over recent years, we consider the behavior of weak molecular absorption bands of methane and ammonia in a wavelength range of 600−800 nm. In the latitudinal behavior of the intensity of these bands, rather clearly expressed features, demonstrating a connection with the zonal structure of cloud belts of the planet, are traced. However, for different bands, the positions of the absorption extrema in latitude somewhat differ. The changes in the zonal spectra show the weakening in absorption observed toward the disk edge, which is most probably connected with the radiative transfer geometry in an optically active layer of the atmosphere. The importance of studying the weak absorption bands is stressed, since precisely these bands make it possible to analyze the structural features and their variations in the troposphere of Jupiter. When interpreting the observational data, it is necessary to consider at least two alternative models for forming the absorption bands. One of them should deal with an optically thick layer of ammonia clouds, where the multiple scattering on particles in this layer plays the main part in producing the molecular absorption bands. The second model should be based on the assumption of a small optical thickness of the ammonia cloud layer, according to which the absorption is mainly formed under clouds, where the scattering on a pure gaseous component is weak.

Spectrofluorimetric Determination of Hypericin in Drugs and Vegetable Raw Materials

Hypericin was isolated from Diahyperon tincture for use as a standard sample. The chromatographic purity of the hypericin was confirmed by high-performance liquid chromatography/mass spectrometry. Hypericin has the only chromatographic peak with a retention time of 23.10 min and gave a characteristic signal for the molecular ion [M – H+]– with m/z 504.05 in the mass spectrum. Electronic absorption spectra of Diahyperon tincture and the MeOH extract of Hyperici herba (Hypericum perforatum) showed characteristic hypericin bands at 550 and 590 nm and a band at 665 nm that was due to the presence of chlorophyll. It was shown that excitation of hypericin in Diahyperon tincture at λex = 470 nm gave an emission spectrum with characteristic hypericin bands at 593 and 640 nm while the emission spectrum of the MeOH extract of Hyperici herba showed the hypericin emission bands and a weak chlorophyll emission band at 670 nm. It was found that spectrophotometric and spectrofluorimetric determinations of hypericin in Diahyperon tincture and in Hyperici herba gave similar results that were consistent with the standardized values of the hypericin content in the studied samples.

Supergénne minerály z U-Cu rudného výskytu Východná-Nižný Chmelienec v Nízkych Tatrách (hronikum, Slovensko)

An association of supergene U-Cu and Y/REE minerals was found in a relic of old ore dump at the abandoned U deposit occurrence Východná-Nižný Chmelienec, the northern slopes of the Nízke Tatry Mts., Slovakia. They have partially recent origin, since exploration of the locality took place between 1965 and 1966. The studied mineral assem- blage is represented by goethite, malachite, uranophane and (meta)zeunerite, in a lesser extent baryte and rare zálesíite. Uranophane appears separately (globular aggregates, thin coatings) and it also forms the main part of the yellow to yellow-green crystalline crusts on the rock cracks. The chemical composition of the uranophane was determined by electron microprobe analyses and it is close to its ideal chemical formula Ca(UO2)2(SiO3OH)2·5H2O. The average chemical composition of the studied uranophane can be expressed by an empirical formula (Ca1.0Mg0.02K0.01Fe0.01Ba0.01)Σ1.05 (UO2)2.08(SiO3OH)1.84·5H2O. The infrared vibrational spectra of the studied uranophane show 3 (UO2)2+ at 850-760 cm-1; the 3 (SiO4)4- antisymmetric stretching vibration at 1000-900 cm-1; the 1 (SiO4)4- symmetric stretching vibration at 1150-1199 cm-1; the  H2O bending vibration at 1800-1600 cm-1 and OH stretching vibrations at 3407; 3408 and 3409 cm-1. The weak bands 2648; 2646 and 2651 cm-1 may be assigned to organic impurities. The calculated U-O bond length 1.83 Å corresponds to short U-O bonds in uranophane. The accessory admixtures of uranophane coatings are (meta)zeunerite and zálesíite. (Meta)zeunerite occasionally forms thin coatings of light green to emerald green tabular crystals (up tu 0.5 mm) on the surface of the rocks. Chemical analyses of (meta)zeunerite correspond to the empirical formula (Cu0.66K0.03Fe0.01Ca0.01)Σ0.71(UO2)2.11[(AsO4)1.96(PO4)0.01]Σ1.97·12H2O. Zálesíite occurs as crystalline aggregates, nests, formed by tiny acicular crystals, up to 100 µm in length. This is the second finding (occurrence) of this mineral in Slovakia. An average zálesíite chemical composition is (Ca0.83REE0.18U0.05Al0.03Ti0.01)Σ1.10(Cu5.81Fe0.06Zn0.02)Σ5.90[(AsO4)2.75 (SiO4)0.21(PO4)0.02(SO4)0.03]Σ3.01(OH)5.10·3H2O. Malachite, which has been also found in the association, is only a minor mineral in the studied locality. The formation of uranyl silicates (uranophane) and minerals of the mixite group (zálesíite), present at the studied locality, points to neutralization of acidic supergene fluids in the mine dumps. Possibly, this environment later (precipitation of baryte) passed to neutral or slightly basic conditions (precipitation of carbonates - malachite). The identified uranyl phosphates/arsenates (zeunerite/metazeunerite), typical of an acidic environment, are therefore rare.