Raman Profiles Research Articles

In-situ preparation of titania/graphene nanocomposite via a facile sol–gel strategy: A promising anodic material for Li-ion batteries

In the current work, a simple and scalable route has been adapted to synthesize TiO2@Gr nanocomposites using in-situ sol–gel method. A systematic study of anatase TiO2 and TiO2@Gr nanocomposite based electrodes has been carried out to investigate their structural and morphological properties using XRD, Raman profile, FESEM and TEM. The results confirmed the insertion of TiO2 nanoparticles in graphene sheets. Further, the electrochemical performance of the as-prepared electrodes has been investigated using galvanostatic charge/discharge profile. Benefiting from the unique heterostructure, as-prepared TiO2@Gr composite showed high discharge capacity (~203 mAhg−1 at 0.2C) and stability with columbic efficiency ~97.3% as compare to anatase TiO2 (~125 mAhg−1 at 0.2C), which makes it a potential anodic materials for Li ion batteries (LIBs).

Doping and plasmonic Raman enhancement in hybrid single walled carbon nanotubes films with embedded gold nanoparticles

Novel optical hybrid materials can be produced with carbon nanotubes and metallic nanoparticles. Such hybrids may allow coupling between plasmons in metals and excitons in nanotubes. We develop novel hybrid materials in the form of thin films using vacuum filtration, where gold nanoparticles are embedded into the entire volume of the nanotube film, not only on the top of the film. After producing semiconducting and metallic hybrids, we investigate their electronic properties. Free charge carriers in metallic nanoparticles extend into nanotubes, resulting in the doping effect. The doping effect manifests in changes the phonon energy and lifetime, scaling with gold nanoparticle concentration. We implement statistical Raman analysis and determine 20 meV p-doping. The statistical data were cross-correlated with parameters of the 2D and G modes, which helped to clearly disentangle doping and strain. Further, we studied optical properties of the films. The gold nanoparticles enhance the CNTs Raman scattering efficiency. The enhancement is wavelength dependent, as confirmed by resonance Raman spectroscopy on radial breathing modes. The enhancement factors vary from 2 to 3.5 times, with maximum at 1.7 eV. The shapes of enhanced resonance Raman profiles were interpreted with the fifth-order perturbation theory incorporating plasmonic effect.

Multi-walled vanadium oxide nanotubes modified 3D microporous bioderived carbon as novel electrodes for hybrid capacitive deionization

Herein, a promising rationally-designed, high surface area multi-walled vanadium oxide nanotubes (VOx NTs) with a large interlayer spacing (6.5 Å) has been demonstrated as a cathodic dopant for efficient hybrid capacitive deionization (c-HCDI). The VOx NTs enhanced the surface charge of the 3D microporous graphene-like carbon, derived from natural palm tree (CNPT), as verified by Raman profiles and potential of zero charge measurements. The CDI batch-fashion testing has been performed using large surface area electrodes (6 × 7 cm2) and 135 ml of saline NaCl electrolyte. Interestingly, the used c-HCDI showed high salt adsorption capacity (SAC) of 25.0 mg/g for 6 mM NaCl at 1.6 V compared to the symmetric capacitive deionization configuration (s-CDI) that is only sustaining 16.0 mg/g. Besides, the cell demonstrates efficient stable SAC regardless of the initial feed concentration (1.6–25 mM) of NaCl. The charge efficiency of the c-HCDI markedly raised by around 25% over s-CDI for 5 mM NaCl, indicating the improved permselective manner of sodium ion diffusion/intercalation at the VOx NTs/CNPT cathode. Most importantly, the c-HCDI demonstrates a superior salt adsorption retention of 94.7% after 50 successive charge/discharge cycles compared to s-CDI that showed a decline of 7% after only 15 cycles. The Improved surface charge and wettability together with the pseudocapacitive storage manner of the cathode composite illustrate the synergism obtained via the hybrid configuration..

Raman and Fluorescence Profiles Modifications of Muscular and Adipose Tissues Exposed to Low Energy X-ray Beams.

This work aims to investigate changes induced by low-energy radiation in adipose and muscular tissues employing autofluorescence and Raman spectroscopic techniques. X-ray beams expositions with 25 and 35 kV at 0.11, 1.1, and 2.1 Gy radiation dose levels were applied. Changes in Raman line intensities at specific bands assigned to collagen, proteins, and lipids were observed. Autofluorescent analysis exhibit variations in the collagen and nicotinamide adenine dinucleotide emission (NADH), resulting from the structural modifications, variations on the reduced/oxidized fluorophores equilibrium followed by radiation exposure. Results show that Raman and fluorescence spectroscopy are suitable techniques to evaluate radiation effects on biomolecules even at low radiation doses and energies.

Catalytically Active Site Identification of Molybdenum Disulfide as Gas Cathode in a Nonaqueous Li-CO2 Battery.

Li-CO2 batteries have recently attracted attention as promising candidates for next-generation energy storage devices due to their extremely high theoretical energy density. The real application of Li-CO2 cells involves addressing several drawbacks, including high charging potential, poor coulombic efficiency, and low rechargeability. Molybdenum disulfide supported on carbon nanotubes (MoS2/CNT) with various ratios functioned as a cathode catalyst for Li-CO2 batteries. The optimal MoS2/CNT composite achieved a maximum discharge capacity of 8551 mAh g-1 with a coulombic efficiency of 96.7%. This hybrid also obtained an initial charging plateau of 3.87 V at a current density of 100 mA g-1 with a cutoff capacity of 500 mAh g-1. It provided ideal electrochemical stability of 142 cycles at the current densities of 100 mA g-1, which was comparable with that of some precious metal catalysts. This optimized MoS2/CNT was also cycled at 200 and 400 mA g-1 for 112 and 55 times, respectively. Density functional theory calculations demonstrated that the sulfided Mo-edge (s-Mo-edge) on MoS2 materials showed appropriate adsorption strengths of Li, CO2, and Li2CO3. Moreover, joint results of Raman profiles and extended X-ray absorption fine structure spectra elucidated that the catalytic efficiencies of MoS2/CNT hybrids were proportional to the quantities of exposed s-Mo-edge active sites.

Synthesis and investigation of the structural properties of vanadium pentaoxide nano thread at low temperature

Vanadium Oxides nanomaterial has shown a great potential in numerous application due to its high light absorption phenomena in the visible range. Among all the possible phases of vanadium oxides, herein we report a simple and facile hydrothermal route for the synthesis of vanadium pentaoxide (V2O5) synthesis at low temperatures. Thread like nanostructures of V2O5 were developed by calcination of vanadyl glycolate (VO(CH2O)2) which was synthesized by hydrothermal route using ammonium vanadate as precursor in the presence of hydrochloric acid (HCL) at low temperature 180 °C. Our develop process of synthesis is free from any templates and reduction agents. Further, the morphology, chemical and structural properties was characterized using Field Emission-Scanning Electron Microscopy, X-ray diffraction, Raman profile and FTIR spectroscopy. The FESEM studies confirms the formation of vanadium pentaoxide in thread shape with thickness in the range of 80 ± 20 nm and length in 4–5 µm. Also, X-Ray diffraction and Raman profile reveals the formation of the orthohombic phase of V2O5.The above synthesized nanostructure materials can be further used in enhancing li-ion batteries efficiency and various thermal and optoelectronic applications.

Analysis and Electrochemical Capacitance of Single Walled Carbon Nanotubes (10, 4) Synthesized Via Chemical Vapour Deposition Method

Single walled carbon nanotubes are receiving considerable attention in the nanotechnology industry, especially in electronics, as efficient energy storing materials. However, obtaining these materials of desired chirality via chemical vapour deposition method has posed a persistent challenge for over twenty years. In the current report, single walled nanotubes (10, 4) were successfully grown via pyrolysis of C6H14/N2 feedstock on Fe2O3/Al2O3 catalyst. Field emission scanning electron microscopy and high resolution transmission electron microscopy images showed bundled network of single walled carbon nanotubes and resulting analysis of the Raman profile for the sample showed consistency with the results established via Extended Tight Binding model. This was a suggestion that if this method is fully optimized, it may help alleviate the stated global challenge. Specific capacitance (F/g) of 242, 174 and 50, was recorded for the sample in the neutral, acidic and alkaline electrolytes, respectively, also suggesting promising potentials as electrodes for Pseudocapacitor and electrochemical double layer capacitor.

Titania coated Zinc Oxide nanorods: A study of structural and optical properties for photocatalytic applications

In the present work, we investigated the structural and optical properties of Titania (TiO2) coated Zinc Oxide (ZnO) nanorods array developed using the low-cost technique. Initially, highly oriented ZnO nanorods were grown over FTO substrate using chemical bath deposition technique. Simultaneously, TiO2 nanoparticles were synthesized using low-temperature hydrothermal techniques and were spin-coated over the ZnO/FTO substrate. Further, the TiO2/ZnO/FTO heterostructure properties were characterized using UV–Vis spectroscopy, Field Effect Scanning Electron Microscopy (FESEM) and Raman spectroscopy. The FESEM result shows the formation of highly ordered hexagonal-shaped ZnO nanorods coated with spherical shaped Titanium Dioxide Nanoparticles of radius ∼ 80 nm−100 nm. The transmission spectra observed from UV–Vis spectroscopy reveals the wideband semiconductor properties using the tauc plots. Further, the Raman profile confirms the synthesis of TiO2 nanoparticles (anatase phase) and ZnO nanorods. Therefore, the obtained results prove Titania-coated-ZnO nanorods heterostructure a promising and suitable material for photocatalytic and photo-electrochemical applications.

Preparation and characterization of solid-state neopentyl glycol / expanded graphite micro composite for thermal energy storage applications

Phase Change Materials (PCM) are used in the thermal energy storage system (TESS) for their heat absorption capacity at a constant temperature. Among the various phase change materials (PCM), neopentyl glycol (NPG) with its structural properties undergo solid-state crystal transformations (∼41 °C) which absorb and release substantial latent heat (131 kJ/kg). The major advantage of such PCM in TESS is that this PCM can be used without concern about the liquid leakage and massive volumetric expansion during phase transitions. In the current work, the micro composite of NPG and expanded graphite (EG) were successfully synthesized and characterized using the one-step technique. NPG is saturated into the expanded graphite with different weight ratios in order to increase the thermal performance of PCM for thermal energy storage (TES) application. NPG was uniformly mixed with the matrix of the expanded graphite (EG). Further, the morphological and structural characterization was carried out to analyze the formation of micro composite (NPG/EG). The Field effect-scanning electron microscopy (FESEM), Fourier Transformation Infrared Spectroscopy, Raman profile and DSC results revealed the formation of shape stabilized NPG/EG micro composites. Also, the thermal conductivity of the micro composite showed the enhancement of up to 10 times as compared to the pure NPG. This micro composite can be well suitable for thermal energy storage.

Anisotropic optical phonons in MOCVD grown Si-doped GaN/Sapphire epilayers

Micro-Raman spectroscopy is employed to study the anisotropic optical phonons of Si-doped GaN/Sapphire epifilms grown by metal organic chemical vapor deposition method. In an undoped 3.6 μm thick sample – our polarized Raman measurements in the backscattering geometry revealed major first order modes of GaN and sapphire. Careful analyses of the second-order Raman spectra using critical-point-phonons from a rigid-ion-model fitted inelastic X-ray spectroscopy data with appropriate selection rules helped us attain expedient data for the lattice dynamics of GaN. In Si-doped films, a modified phonon confinement model is used for simulating Raman line shapes of E2high phonons to monitor crystalline quality. While the optical phonons in lightly doped samples are coupled to electron plasma– at higher carrier concentration the over-damped A1(LO) mode vanished in the background. For each sample we assessed the transport parameters by simulating Raman profiles of A1(LO) line shape with contributions from plasmon-LO-phonon and Lorentzian shaped Eg sapphire mode. A realistic Green’s function theory is adopted to study the vibrational modes of Si donors and Mg acceptors in GaN by including force constant changes estimated from lattice relaxations using first-principles bond-orbital model. Theoretical results of impurity-activated modes compared favorably well with the existing Raman scattering data.

Alterations of Raman profiles of nasopharyngeal carcinoma cells after treated with chemodrugs detected by laser tweezer Raman spectroscopy.

e15513 Background: To explore the metabolic alterations of nasopharyngeal carcinoma (NPC) cells after treated with chemodrugs, the Raman profiles were characterized with laser tweezer Raman spectroscopy. Methods: Two NPC cell lines (CNE2 and C666-1) were treated with gemcitabine, cisplatin, and paclitaxel, respectively. The high-quality Raman spectra of cells without or with treatments were recorded at the single-cell level with label-free laser tweezers Raman spectroscopy (LTRS) and analyzed for the differences of alterations of Raman profiles. Results: Tentative assignments of Raman peaks indicated that the cellular specific biomolecular changes associated with drug treatment, including changes in protein structure (e.g. 1655 cm−1), changes in DNA content and structure (e.g. 830 cm−1), destruction of DNA base pairs (e.g. 785 cm−1), and reduction in lipids (e.g. 970 cm−1). Besides, both principal components analysis (PCA) combined with linear discriminant analysis (LDA) and the classification and regression trees (CRT) algorithms were employed to further analyze and classify the spectral data between control group and treated group, with the best discriminant accuracy of 96.7% and 90.0% for CNE2 and C666-1 group treated with paclitaxel, respectively. Conclusions: This exploratory work demonstrated that LTRS technology combined with multivariate statistical analysis has promising potential to be a novel analytical strategy at the single-cell level for the evaluation of NPC-related chemotherapeutic drugs.

Raman and SEM‐EDS insights into technological aspects of Medieval and Renaissance ceramics from Southern Italy

AbstractAn analytical investigation performed on Southern Italy pottery highlighted the usefulness of Raman spectroscopy to give answers to archaeological questions. It can provide important information concerning the production technology and raw materials constituting the glassy coatings. Raman spectroscopy was supported by Scanning Electron Microscopy coupled with Energy Dispersive X‐ray Spectroscopy (SEM‐EDS) for observations and elemental analysis. The studied samples, ranging from the 13th century lead‐tin‐glazed protomajolica to the 15th –16th enamelled pottery, come from the Castles of Montella and Ariano Irpino (Campania), from the castles of Scicli and Modica and from surveys carried out in Buscemi and Caltagirone (Sicily). Glassy matrices, opacifying agents, colour‐related raw materials and body‐coating interface crystalline phases were investigated. Though the coatings resulted all typically lead‐rich glass types, lumps showing a different Raman profile suggested that at least in one case, the batch was adultered with recycled glass waste. Furthermore, samples coming from Montella, belonging to the three main classes of ceramics defined by archaeological hypothesis, could be grouped according to their cassiterite content. The crystallization of lead–potassium feldspars at the coating‐body interface in a group of samples was ascertained. With regard to the origin of colours, the spectra of blue coatings highlighted phases that can be traced back to the use of Co‐based and Co–As‐based raw materials, while turquoise decorations were found to contain malayaite.

Study on the chemodrug-induced effect in nasopharyngeal carcinoma cells using laser tweezer Raman spectroscopy.

To explore the effect in nasopharyngeal carcinoma (NPC) cells after treatment with chemodrugs, Raman profiles were characterized by laser tweezer Raman spectroscopy. Two NPC cell lines (CNE2 and C666-1) were treated with gemcitabine, cisplatin, and paclitaxel, respectively. The high-quality Raman spectra of cells without or with treatments were recorded at the single-cell level with label-free laser tweezers Raman spectroscopy (LTRS) and analyzed for the differences of alterations of Raman profiles. Tentative assignments of Raman peaks indicated that the cellular specific biomolecular changes associated with drug treatment include changes in protein structure (e.g. 1655 cm-1), changes in DNA/RNA content and structure (e.g. 830 cm-1), destruction of DNA/RNA base pairs (e.g. 785 cm-1), and reduction in lipids (e.g. 970 cm-1). Besides, both principal components analysis (PCA) combined with linear discriminant analysis (LDA) and the classification and regression trees (CRT) algorithms were employed to further analyze and classify the spectral data between control group and treated group, with the best discriminant accuracy of 96.7% and 90.0% for CNE2 and C666-1 group treated with paclitaxel, respectively. This exploratory work demonstrated that LTRS technology combined with multivariate statistical analysis has promising potential to be a novel analytical strategy at the single-cell level for the evaluation of NPC-related chemotherapeutic drugs.

Raman profile alterations of irradiated human nasopharyngeal cancer cells detected with laser tweezer Raman spectroscopy.

Radiotherapy has been widely used for nasopharyngeal carcinoma (NPC) treatment, which causes DNA damage and alterations of macromolecules of cancer cells. However, the Raman profile alterations of irradiated NPC cells remain unclear. In the present study, we used laser tweezers Raman spectroscopy (LTRS) to monitor internal structural changes and chemical modifications in NPC cells after exposure at a clinical dose (2.3 Gy) to X-ray irradiation (IR) at a single-cell level. Two types of NPC cell lines, CNE2 (EBV-negative cell line) and C666-1 (EBV-positive cell line), were used. The Raman spectra of cells before and after radiation treatment were recorded by LTRS. The analysis of spectral differences indicated that the IR caused Raman profile alterations of intracellular proteins, DNA base and lipids. Moreover, by using the multivariate statistical analysis including principal component analysis (PCA) and linear discriminant analysis (LDA) algorithm, an accuracy of 90.0% for classification between CNE2 cells before and after IR could be achieved, which was 10% better than that of C666-1 cells. The results demonstrated that CNE2 cells were more sensitive to IR in comparison to C666-1 cells, providing useful information for creating a treatment strategy in clinical practice. This exploratory study suggested that LTRS combined with multivariate statistical analysis would be a novel and effective tool for evaluating the radiotherapeutic effect on tumor cells, and for detection of the corresponding alterations at the molecular level.

87 Analyzing metabolomic profile of bovine IVF and somatic cell nuclear transfer embryos through Raman spectroscopy

While knowledge of early embryo development and viability has continually increased, there is still a need for noninvasive methods to identify embryos with the highest chances of development to term when transferred. The most widely used technique, morphological assessment, is highly subjective and limited by personnel experience. Spent media from invitro culture could be used as a valuable noninvasive marker for embryo quality assessment. Raman spectroscopy has proven to be a powerful tool for identifying the molecular characteristics of spent culture media by measuring vibration of chemical bonds, allowing for metabolomic profiling of varying stages and quality of embryos. It is well documented that embryos produced through somatic cell nuclear transfer (SCNT) result in lower pregnancy rates and higher incidences of pregnancy loss when compared with embryos produced through IVF (Heyman et al. 2002 Biol. Reprod. 66, 1-13). This study was designed to examine differences in spent media between bovine embryos produced by IVF and SCNT. The SCNT embryos with a metabolomic profile more similar to IVF embryos may have a higher developmental competence. Bovine cumulus-oocyte complexes (COCs) were retrieved from abattoir-derived ovaries and matured for 21h in maturation medium. After IVM, COCs were either used for IVF or SCNT and cultured in 50μL droplets of synthetic oviductal fluid medium + fetal bovine serum in groups of 45 from Day 0-5. On Day 5, embryos that had reached morula stage were placed in individual droplets of 13μL of synthetic oviductal fluid + bovine serum albumin until Day 7. All embryos were cultured at 38.5°C and 5% CO2. On Day 7 embryos were assessed for developmental stage and quality and 10μL of medium from individual culture drops was collected for Raman spectroscopy. Samples were loaded on an MgF2 optical window, dried, and analysed using a 785nm near-infrared laser in the spectral range of 600 to 1800cm−1. Raw Raman data were first pre-processed by baseline correction (asymmetric least-squares smoothing) and normalization. Principal component analysis and partial least squares were then applied to reduce data dimensions. The score of the most significant principal components from principal component analysis and the optimum number of scores from partial least squares were used for linear discriminant analysis. Spent media samples from 4 SCNT embryos, 3 IVF embryos, and 3 empty media samples were analysed, with 50 spectra obtained from each sample. Preliminary data showed grouping of medium containing embryos developed to blastocyst from medium containing embryos arrested at morula or empty medium. We also saw grouping of medium containing SCNT embryos from medium containing IVF embryos within both the morula and blastocyst stage from empty medium. This shows evidence of metabolomic differences between embryos of different developmental potential and embryos produced by IVF and SCNT. Further investigation of the Raman profile of these groups can display specific differences in chemical components and help to identify candidate genes causing differing metabolism of these groups.

Thickness and tensile stress determination of black silicon layers by spectral reflectance and Raman scattering

Abstract In this work black silicon (b-Si) samples were prepared by anodic (electrochemical) etching of p-type silicon substrate in solution of hydrofluoric acid (HF). We studied influence of anodic etching conditions (etching time, electrical potential and current) on the spectral reflectance and Raman scattering spectra. Optical properties of b-Si structures were experimentally studied by UV-VIS (AvaSpec-2048) and Raman (Thermo DXR Raman) spectrometers. B-Si layer thickness of formed substrate were determined by using SCOUT software. Effective medium approximation theory (Looyenga) was used in construction of the reflectance model. Influence of the deformation of crystal lattice introduced during the substrate etching was studied by Raman scattering method. Teoretical model of the 1st order Raman scattering profile was constructed by using pseudo-Voigt function and the profile parameters were extracted. The values of biaxial tensile stress were estimated by using optimized Raman profile parameters.

Cancer signaling by plasmonic quantum probes

Although the use of gold quantum dots for non-cellular sensing is growing rapidly, the use of quantum gold dots are still limited because of comparatively large overall size (biocompatible layer), overlapped Raman readout of lower concentrated metabolites inside the cells and dispersion of QDs inside the cancer cells. This is due to the labelling of QDs which results in specific binding and non-uniform distribution of QDs inside the cells. Besides this, QDs are toxic in nature due to the presence of chemical residues from the wet synthesis, hampering its rendition to clinical application. To increase biocompatibility and surge the cellular uptake, gold probes are usually layered with bio-films (PEG). However, layering impedes the interaction of metabolites and gold QDs and damp the surface plasmonic resonance, resulting in low Raman signal. The addition of biofilm increases the overall hydrodynamic size of gold QDs, limiting the dispersion and internalization of plasmonic QDs inside the cell as well as the nucleus. Therefore, the unique properties that arise from the quantum size of the plasmonic probe are lost. To retain the quantum size of QDs, there is a need to use a physical method of synthesis and use gold QDs layering free. In this research manuscript, we introduce the quantum sized layering free Plasmonic Quantum Probes (PQPs), a potential tool for cancer sensing which provides the opportunity to attain the sensing of surface oncoprotein, intracellular oncoprotein and nuclear metabolites simultaneously. In this work, we introduce the concept of Plasmonic Quantum Probes (PQPs) for intercellular sensing. To the best of our knowledge, it is the first time the probe close to the size of cellular metabolites was synthesized. By using physical synthesis (multiphoton laser ionization), biocompatible PQPs were synthesized without the chemical adulteration and eliminated the need of biocompatible layering. Since the PQPs are non-toxic in nature, no layering is required, enabling the study of true quantum effect in plasmonic cellular signaling. The naked PQPs demonstrated self-cellular uptake with even dispersion and non-specific attachment to all the cell components. As a result, the Raman spectra revealed rich information of multiple cell components, including surface (e.g., EGFR), intracellular (e.g., HPV E6/HPV E7) and nuclear metabolites (e.g., DNA/RNA), simultaneously in one single Raman profile. Due to the difference in the number of probes inside the cells, the signal strength of cancerous cell is significantly higher than that of fibroblast cells, implying that the differentiation of cancerous cells is possible through the analysis of the intensity of Raman readout. The probe size is found to be inversely related to the signal strength of the plasmonic readout. The PQP provides a holistic picture of cell states and may open up new possibilities for accurate diagnosis of cancer.

Measuring the effects of heat treatment on SiC/SiC ceramic matrix composites using Raman spectroscopy

AbstractThe evolution of residual stresses found within a silicon carbide/silicon carbide (SiC/SiC) ceramic matrix composite through thermal treatments was investigated using Raman microspectroscopy. Constituent stress states were measured before, during, and after exposures ranging from 900 to 1300°C for varying times between 1 and 60 minutes. Silicon carbide particles in the as‐received condition exhibited average hydrostatic tensile stresses of approximately 300 MPa when measured at room temperature before and after heat treatment. The room temperature Raman profile of the silicon matrix was altered in both shape and location with heat treatment cycles due to increasing activation of boron within the silicon lattice as heat treatment temperatures increased. By accounting for boron activation in the silicon–boron system, little to no permanent change of any constituent stresses were observed, and the silicon matrix subsequently exhibited a complimentary average hydrostatic compressive stress of approximately 300 MPa at room temperature, measured before and after heat treatment. This result builds upon previous literature and offers increased insight into boron activation phenomena measured through Raman spectroscopy methods.

NIR luminescence and energy transfer kinetics in Nd3+/Yb3+ co-doped sodium aluminium bismuth fluoro-borosilicate glasses

Here, we demonstrate the results pertaining to energy transfer kinetics in Nd3+/Yb3+ ions combinedly doped in oxy-fluoride based sodium aluminum bismuth fluoro-borosilicate glasses. The thermal stability for the parent NABFBS glass is evaluated from TG-DTA measurement, and Raman & FT-IR spectral profiles were investigated to realize the influence of phonon energy of host NABFBS glass and OH− content on luminescence features of Nd3+ and Yb3+ ions. Upon pumping at 808 nm, Nd3+ glasses displayed intense NIR emission for 1 mol% concentration at 903, 1068 and 1348 nm labeled to corresponding transitions 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2. Effect of multiphonon-, cross-relaxation and OH− group on Nd3+ emission causing luminescence quenching above 1.0 mol % Nd3+ is interpreted. The sensitizing effect of Nd3+ emission on Yb3+ luminescence is investigated by co-doping Nd3+ ion (optimized to 1 mol%) with different Yb3+ ion concentrations. The probability of energy-transfer (ET) between these ions has been substantiated by the considerable spectral overlap of Yb3+ absorption and Nd3+ emission, luminescence features, emission decay rates and energy level diagram. On co-doping Yb3+ to Nd3+, the emission intensity of Yb3+is enhanced along with simultaneous decrement in Nd3+ emission owing to transfer of Nd3+ excitation energy. This process is further supported by the shortening of Nd3+ life-times in co-doped glasses compared with individually Nd3+ doped glasses. The probability of transfer of energy in Nd3+ and Yb3+ combinedly doped system is estimated along the same lines of Dexter's theory and Inokuti-Hirayama (I-H) fitting model for dipole-dipole coupling. The results reveal that, the energy-transfer mechanism from Nd3+(4F3/2)→Yb3+(4F5/2) is a non-radiative type governed by electric dipole-dipole interaction with phonon assistance. The energy transfer parameters, donor-acceptor coupling constant (CDA), energy-transfer efficiency (η) and probability of energy transfer (P) for co-doped glasses are computed from lifetime curves. In addition, back energy transfer Nd3+←Yb3+ is also investigated.

Stellar-wind accretion and Raman-scattered O vi features in the symbiotic star AG Draconis

We present high resolution spectroscopy of the yellow symbiotic star AG Draconis with ESPaDOnS at the {\it Canada-France-Hawaii Telescope}. Our analysis is focused on the profiles of Raman scattered \ion{O}{VI} features centered at 6825 \AA\ and 7082 \AA, which are formed through Raman scattering of \ion{O}{VI}$\lambda\lambda$1032 and 1038 with atomic hydrogen. These features are found to exhibit double component profiles with conspicuously enhanced red parts. Assuming that the \ion{O}{vi} emission region constitutes a part of the accretion flow around the white dwarf, Monte Carlo simulations for \ion{O}{VI} line radiative transfer are performed to find that the overall profiles are well fit with the accretion flow azimuthally asymmetric with more matter on the entering side than on the opposite side. As the mass loss rate of the giant component is increased, we find that the flux ratio $F(6825)/F(7082)$ of Raman 6825 and 7082 features decreases and that our observational data are consistent with a mass loss rate $\dot M\sim 2 \times 10^{-7} {\rm\ M_{\odot}\ yr^{-1}}$. We also find that additional bipolar components moving away with a speed $\sim 70{\rm\ km\ s^{-1}}$ provide considerably improved fit to the red wing parts of Raman features. The possibility that the two Raman profiles differ is briefly discussed in relation to the local variation of the \ion{O}{VI} doublet flux ratio.