Optical Spectral Data Research Articles

Research on the Optical and EPR Spectral Data and the Local Structure for the Tetragonal Nb4+Center in Glasses

Research on the Optical and EPR Spectral Data and the Local Structure for the Tetragonal Nb4+Center in Glasses

Theoretical studies of the local structure of Cu2 + center in aluminium lead borate glasses by their EPR and optical spectra

The local structure of the Cu2+ center in aluminium lead borate glasses was theoretically studied based on the optical spectral data and high-order perturbation formulas of the electron paramagnetic resonance (EPR) parameters (g factors g||, g⊥ and the hyperfine structure constants A||, A⊥) for a 3d9 ion in a tetragonally elongated octahedron. In the calculations, the ligand orbital and spin–orbit coupling of the impurity Cu2+ are taken into account; the required crystal-field parameters are estimated from the superposition model. Based on the calculations, the defect model of the Cu2+ center was confirmed and the defect structure (i.e., the ligand O2− octahedron around Cu2+ is determined to suffer about 19.2% relative elongation along the C4 axis due to the Jahn–Teller effect) was acquired, and a negative sign for A|| and positive sign of A⊥ for the Cu2+ center were suggested in the discussion.

Effect of annealing on the structural and optical properties of laser ablated nanostructured barium tungstate thin films

High quality BaWO4 thin films are successfully deposited on quartz substrate for a duration of 30min using pulsed laser ablation technique and using a laser radiation of wavelength 355nm and the effect of thermal annealing on the structural and optical properties is studied by using techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, micro-Raman, FTIR and UV–visible spectroscopy. All the films show monoclinic crystalline structure with (202) plane as the preferred orientation of crystal growth. From the XRD analysis it is found that the optimum annealing temperature for better crystallization of the BaWO4 film is 700°C and there is no phase change observed with annealing temperature. The presence of the characteristic bands for the BaWO4 in the Raman spectra of the films suggests the formation of BaWO4 crystalline phase in all the films. SEM and AFM analyses show that as the annealing temperature increases the connectivity between individual grains increases and shows an ordered packing. The geometrical optimization and energy calculation of the title compound were done using the Gaussian 09 software package and the calculations were carried out using the CAM-B3LYP functional combined with standard Lanl2Dz basis set. The thickness of the films was calculated using lateral SEM images and also from optical transmission spectral data using PUMA software.

Red-Shift Index Concept in Solvent Effects of Chromophore-Substituted Metallophthalocyanines: A Look at the Empirical Relationship of the Macroscopic Properties of the Solute–Solvent Interactions

Solvent effects on the UV/vis spectra of metallopthalocyanines (MPcs) have been interpreted using the red-shift index concept (R s I). The concept connects empirically, direct, experimental, easily accessible optical spectral data, which are explained by considering the differential behavior of the solute–solvent interactions at the ground state and excited state using the spectral values of MPcs along with the derived concept, called the associated solvation energy (ASE). R s I is formulated from three fundamental parameters, which are: ground state electronic absorption spectrum, polarization red-shift and a scaling factor of MPc (N dye) in the respective solvents. The R s I is a reflection of the index value of the chromophore substituent of MPc in the solvent; thus, the concept can be used as a solvatochromic parameter to study a wide range of supramolecular and heterocyclic compounds that can be modified at their periphery or ‘handles’. Particularly, in this study, the concept has been used to rank MPc candidates by using the statistical mean performance of the solvatochromic parameters, which are red shift index, polarizability efficiency and ASE. We hereby review the solvent effects on the UV/vis spectra of substituted and unsubstituted MPcs.

Calculations of the optical and EPR spectral data for Cr3+ ion in Y3Ga5O12 crystal from the complete diagonalisation method

The complete diagonalisation (of energy matrix) method is applied in this paper to calculate together the optical and electron paramagnetic resonance (EPR) spectral data for Cr3+ ion at the trigonal Ga3+ site of Y3Ga5O12 crystal. The method is founded on the two-spin-orbit-parameter model where in addition to the contributions from the spin-orbit parameter of central dn ion (i.e., one-spin-orbit-parameter model) in the traditional crystal field theory, those from the spin-orbit parameter of ligand ion via covalence effect is also considered. The calculated results propose that by using only four adjustable parameters, the 12 observed spectral data (nine optical band positions and three EPR parameters g//, g⊥ and D) in Y3Ga5O12: Cr3+ are reasonably explained. The impurity-induced local lattice distortion of Cr3+ in Y3Ga5O12 crystal is also estimated through the calculations. The results are discussed.

The effect of donor content on the efficiency of P3HT:PCBM bilayers: optical and photocurrent spectral data analyses.

State-of-the-art organic solar cells mostly rely on bulk-heterojunction architectures, where the photoactive layer is cast from a solution containing both the electron donor and acceptor components and subsequently annealed. An alternative route for device preparation is the sequential deposition of the two components using "orthogonal" solvents. The morphology of sequentially deposited bilayers has been extensively studied, but the interplay between optical and electrical properties and its influence on device efficiency is still unclear. Here we present a study of poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) bilayers with variable P3HT content, including also a standard bulk-heterojunction device for comparison. Measured optical absorption, external quantum efficieny (EQE), and internal quantum efficiency (IQE) data are analysed and interpreted with the aid of numerical models. In agreement with other studies, our results suggest substantial intermixing between the PCBM and P3HT component, regardless of the P3HT content. In the bulk heterojunction and the bilayer devices with an active layer thickness of 100 nm or less, our best fits to both the optical and optoelectronic data highlight a concentration inversion, with an accumulation of PCBM on the anode side. Through the numerical analysis of device performance at short-circuit, we also find that exciton diffusion toward the P3HT:PCBM interface and geminate recombination can be the main IQE loss factors. Additional losses, attributed to bimolecular electron-hole recombination, are also observed upon increasing the P3HT content.

Unified calculation of optical and EPR spectral data for Cr3+-doped KAl(MoO4)2 crystal

This paper reports an unified calculation of optical and EPR spectral data for Cr3+ ion at the trigonal Al3+ site of KAl(MoO4)2 crystal from the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model. In this model, differing from that in the conventional crystal-field theory, not only the contributions from the spin–orbit parameter of central dn ion, but also those from the spin–orbit parameter of ligand ion via covalence effect are taken into account. The calculation shows that by using only three adjustable parameters, the observed twelve optical and EPR spectral data (nine optical band positions and three EPR parameters g||, g⊥ and D) are reasonably explained in a unified way with this method. The results are discussed.

Two new triterpenoid saponins obtained by microbial hydrolysis with Alternaria alternata AS 3.6872

Compound 1, a triterpenoid saponin from Ardisia gigantifolia Stapf showing potential anti-tumour activity, was hydrolysed into two deglycosyl derivatives (2 and 3) by Alternaria alternata AS 3.6872. Both these derivatives are new compounds. Their structures were elucidated on the basis of 1D, 2D NMR, HR-ESI-MS and optical rotation spectral data. Compounds 1–3 were evaluated for their cytotoxicity against human hepatocellular carcinoma and normal liver cells by Cell Counting Kit 8 colorimetric assay.

Investigations on spectral features of tungsten ions in sodium lead alumino borate glass system

Na2O–PbO–Al2O3–B2O3 (NPAB) glasses mixed with different concentrations of WO3 (ranging from 0 to 2.5mol%) are synthesized by conventional melt quenching method. The samples are characterized by X-ray diffraction (XRD), optical absorption, Electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) spectroscopic techniques. Glass formation is confirmed by X-ray diffraction spectra. The optical absorption spectra of these glasses exhibited a predominant broad band peak at about 850–870nm is identified due to dxy–dx2−y2 transition of W5+ ions. From the optical absorption spectral data, optical band gap (Eopt) and Urbach energy (ΔE) are evaluated. From EPR spectra the strength of the signal is increased and hyperfine splitting is resolved with increasing concentration of WO3 in the glass matrix. The FT-IR spectral studies have pointed out the existence of conventional BO3, BO4, B–O–B, PbO4, WO4 and WO6 structural units of these glasses. Various physical properties and optical basicity are also evaluated with respect to the concentration of WO3 ions.

Unified calculations of optical and EPR data for Cu3+ ion in Al2O3 crystal

The optical band positions and EPR parameters ( g factors g ∥ , g ⊥ and zero-field splitting D ) for Cu 3+ ion in Al 2 O 3 crystal are calculated by using the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model. In the model, both the contribution to the spectral data from the spin-orbit parameter of central 3d n ion and that of ligand ion are contained. The calculated results show reasonable agreement with the experimental values. The defect structure of Cu 3+ impurity center is estimated from the calculations. • Unified calculation for the optical and EPR spectral data of Cu 3+ in Al 2 O 3 is made. • The complete diagonalization (of energy matrix) method is used in the calculation. • The diagonalization method is based on the two-spin–orbit-parameter model. • The defect structural data is obtained from the calculation.

Structural, spectroscopic and magnetic characterization of undoped, Ni2+ doped ZnO nanopowders

Structural, magnetic and optical properties of undoped and Ni2+ doped ZnO nanopowders have been prepared by sonochemical assistance. Powder XRD studies confirm the hexagonal structure of both undoped and Ni2+ doped of ZnO nanopowders and its average crystallite sizes are evaluated. Optical absorption and Electron Paramagnetic Resonance spectral data confirmed the site symmetry for Ni2+ ions as octahedral. Photoluminescence spectra exhibited the emission bands in ultraviolet and blue regions at an excitation wavelength of 328nm. FT-IR spectra showed the characteristic vibrational bands of Zn–O. Vibrating sample magnetometer was used for the magnetic property investigations and indicates room temperature ferromagnetism which is intrinsic in nature and attributed to oxygen and/or Zn deficiencies.

SIGNATURES OF CLOUD, TEMPERATURE, AND GRAVITY FROM SPECTRA OF THE CLOSEST BROWN DWARFS

We present medium resolution optical and NIR spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman 16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the first detection of Li I absorption in a T dwarf. Combined with the lack of surface gravity features, the Li I detection constrains the system age to 0.1 - 3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243, and 1.254 {\mu}m in both components. Compared to the strength of KI line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 {\mu}m and 1.25 {\mu}m regions than Luhman 16A. Converting flux units to a brightness temperature we interpret this to mean that the secondary is ~ 50 K warmer than the primary in regions dominated by condensate grain scattering. One plausible explanation for this difference is that Luhman 16B has thinner clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter regions. We also detect comparably strong FeH in the 0.9896 {\mu}m Wing-Ford band for both components. Traditionally, a signpost of changing atmosphere conditions from late-type L to early T dwarfs, the persistence and similarity of FeH at 0.9896 {\mu}m in both Luhman 16A and Luhman 16B is an indication of homogenous atmosphere conditions. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within 1{\sigma} with resultant Teffs of 1310+/-30 K and 1280+/-75 K for Luhman 16AB respectively.

Optical, electrochemical and thermal properties of Co2+-doped CdS nanoparticles using polyvinylpyrrolidone

Co2+ (1–5 and 10 %)-doped cadmium sulfide nanoparticles were synthesized by the chemical precipitation method using polyvinyl pyrrolidone (PVP) as a surfactant. The X-ray diffraction results showed that Co ions were successfully incorporated into the CdS lattice and the transmission electron microscopy results revealed that the synthesized particles were aligned as rod-like structures. The absorption spectra of all the prepared samples (undoped and doped) were significantly blue shifted (472–504 nm) from the bulk CdS (512 nm). However, the absorption spectra of the doped samples were red shifted (408–504 nm) with respect to the doping concentrations (1–5 and 10 %). Furthermore, a dramatic blue shift absorption is observed at 472 nm for PVP-capped CdS:Co2+ (4 %) nanoparticles. In the photoluminescence study, two emission peaks were dominated in the green region at 529 and 545 nm corresponding the CdS:Co2+ nanoparticles. By correlating optical and EPR spectral data, the site symmetry of Co2+ ion in the host lattice was determined as both octahedral and tetrahedral. The presence of functional groups in the synthesized nanoparticles was identified by Fourier transform infrared spectroscopy. The thermal stability of the Co ions in CdS nanoparticles was studied by TG–DTA. In addition, an electrochemical property of the undoped and doped samples was studied by cyclic voltammetry for electrode applications.

Spectroscopic studies of chromium doped alkali earth lead zinc phosphate glasses

X-Ray diffraction, energy dispersive X-ray, Fourier transform infrared, Raman spectroscopy, differential scanning calorimetry, UV–Visible spectroscopy and electron paramagnetic resonance spectroscopic studies have been carried out on alkali earth lead zinc phosphate glasses doped with 0.1 % chromium ions. The energy dispersive X-ray spectra reveal fundamental compositional information of the glasses. Infrared spectra indicate that phosphate network is depolymerized with progressive substitution of alkali earth content and inform the characteristic vibrations of PO4 3− units. Raman spectra suggest that these glasses are consisting of metaphosphate [Q2] units along with some bands related to pyrophosphate [Q1] and orthophosphate [Q0] units. The crystal-field parameter and inter-electronic repulsion parameters have been evaluated from optical absorption spectral data. Electron spin resonance spectra of Cr3+ systems indicate that g ∥ > g ⊥ and Cr3+ ions are located at sites with lower symmetry. It is obtained that the glass transition temperatures fall in region of 377–360 °C. Increase in density of the glass system brings changes in structure of the glasses on replacement of alkali earth content.

Synthesis and spectral investigations of Cu(II) ion-doped NaCaAlPO4 F3 phosphor.

Cu(II) ion-doped NaCaAlPO(4)F(3) phosphor has been synthesized using a solid state reaction method. The prepared sample is characterized by powder X-ray diffraction, scanning electron microscope, optical absorption, electron paramagnetic resonance photoluminescence and Fourier transform infrared spectroscopy techniques. The crystallite size evaluated from x-ray diffraction data is in nanometers. Scanning electron microscopy micrographs showed the presence of several irregular shaped particles. From optical absorption and electron paramagnetic resonance spectral data the doped Cu(II) ions are ascribed to distorted octahedral site symmetry. The synthesized phosphor exhibits emission bands in ultraviolet, blue and green regions under the excitation wavelength of 335 nm. The CIE chromaticity coordinates (x = 0.159, y = 0.204) also calculated for the prepared sample from the emission spectrum. The Fourier transform infrared spectroscopy spectrum revealed the characteristic vibrational bands of the prepared phosphor material.

Unified calculations of the optical band positions and EPR g factors for NaCrS2 crystal

Six optical band positions and EPR g factors g, g⊥ for the trigonal Cr3+ octahedral clusters in NaCrS2 crystal are calculated together through the complete diagonalization (of energy matrix) method based on the two-spin–orbit-parameter model, where besides the contribution due to the spin–orbit parameter of central dn ion in the conventional crystal-field theory, the contribution due to the spin–orbit parameter of ligand ion via the covalence effect is also considered. In the calculations, the crystal-field parameters Bkl are obtained from the superposition model with the structural data of Cr3+ octahedral clusters in NaCrS2 crystal measured exactly by the X-ray diffraction method. The calculated optical and EPR spectral data are in a reasonable agreement with the observed values. So, the reliability of the superposition model in the studies of crystal-field parameters for dn ions in crystals is confirmed, and the complete diagonalization (of energy matrix) method based on the two-spin–orbit-model is effective in the unified calculations of optical and EPR spectral data for dn ions in crystals.

UV–vis spectroscopic studies of gamma irradiated lead sodium borosilicate glasses

Sodium borosilicate glasses containing lead with composition xPbO–15Na2O–(70 − x) B2O3–15SiO2 where x=5, 10, 15, 20 and 25 (mol%) were prepared using the melt quenching technique. UV–vis spectroscopy has been employed to study the optical properties of these glasses before and after gamma irradiation in the dose range 0.1–60kGy. From the optical absorption spectral data, the optical band gap and Urbach energies are evaluated. The results assert that the optical band gap energy values depend sensitively on added lead oxide content. Influence of modifier lead oxide on the optical behavior of these glasses is also reported.

Unified calculations of optical and EPR spectral data for two tetragonal Cu2+ centers in Cu2+-doped ZnO nanocrystals

Three optical band positions and four spin-Hamiltonian (or EPR) parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) of two tetragonal Cu2+ centers in Cu2+-doped ZnO nanocrystals synthesized at room temperature by mild and simple solution method are calculated from the complete diagonalization (or energy matrix) method based on the cluster approach (where the covalence effect due to the admixture between the orbitals of dn ion and ligands is considered). The calculations rest on the defect models suggested in the previous paper that both Cu2+ centers are Cu2+ on the interstitial octahedral sites in ZnO nanocrystals and the tetragonal elongations of octahedra are due to the static Jahn–Teller effect. The calculated results are in reasonable agreement with the experimental values. The defect models of both Cu2+ centers are therefore confirmed and their defect structures (i.e., the tetragonal elongations R//−R⊥) are acquired. The results are discussed.

Cycloartane Triterpenes from Beesia calthaefolia (Maxim.)

Three new cycloartane triterpenoids (1–3) and two known compounds (4, 5) were isolated from the whole plant of Beesia calthaefolia. Their structures were elucidated by 1D and 2D NMR, HRESIMS and optical rotation spectral data. All isolates were investigated for their inhibitory effects on the classical pathway of the complement system. Among them, compound 4 showed stronger inhibitory activity (IC50 136.7μM) than positive control (Rosmarinic acid, IC50 181.8μM) while compounds 2 and 3 were moderately active with IC50 value of 206μM and 200.9μM. Chemical compound studied in this article: Rosmarinic acid (PubChem CID: 5281792).

EPR, optical and physical properties of chromium ions in CdO–SrO–B2O3–SiO2 (CdSBSi) glasses

Chromium ions doped 10CdO–(20−x) SrO–50B2O3–20SiO2 (x=0.5, 1.0, 1.5, 2.0, 2.5mol%) (CdSBSi) glasses have been studied by using Electron Paramagnetic Resonance (EPR) and optical absorption techniques at room temperature. Powder XRD pattern of all the samples confirms amorphous nature of the glass. The low field spectral line of the EPR spectrum of chromium ions in CdSBSi glass is attributed to isolated Cr3+ ions and the high field spectral line is assigned for exchange of coupled pairs Cr3+ ions in all these glasses. The optical absorption spectra of Cr3+ ions in these glasses shows single broad band characteristic of Cr3+ ions in near octahedral symmetry. From this optical absorption spectral data the crystal field parameter (Dq) is evaluated from ultraviolet absorption edges, the optical band gap and Urbach energies are evaluated. The results assert that the optical band gap energy values are depended quite sensitively on added chromium content. The FT-IR spectral investigations of chromium ion doped glasses exhibits characteristic vibrations of BO3 units. Several physical parameters are also evaluated for these glasses with respect to the composition.