Synthesis and luminescence properties of a novel Eu-doped γ-LiAlO2 phosphor

A novel phosphor, Eu³⁺-doped γ-LiAlO₂, was successfully prepared by a facile sol-gel process. The synthesis, characterization and luminescence properties of the phosphor were detailed investigated. Based on powder X-ray diffraction and scanning electron microscopy results, pure phase tetragonal LiAlO₂ was obtained by sol-gel process at 800 °C and the sphere-like particles have the diameter of 1 μm and suffer from little aggregation. Luminescence test indicated that the γ-LiAlO₂:Eu³⁺ phosphor exhibited an intense characteristic luminescence of Eu³⁺ ions, and the luminescence intensity of samples enhanced with the Eu/Li molar ratio increasing from 0.005 to 0.1.     

Synthesis and luminescent properties of novel Ba2−xEuxZr2−yHfySi3O12 phosphor

A series of Eu²⁺ activated luminescent materials according to the composition of Ba_2−xEu_xZr_2−yHf_ySi₃O₁₂ were synthesized using a high temperature solid-state reaction method starting from metal oxides and carbonates. Single phase powders were obtained using two annealing steps and boric acid as a flux. Firstly, starting materials were sintered at 1450 °C for 5 h under CO atmosphere and subsequently annealed at 1200 °C for 5 h under N₂/H₂ (95%/5%) gas flow. All samples were characterized by powder X-ray diffraction (XRD) analysis, thermal quenching (TQ), fluorescence lifetime measurements and photoluminescence (PL) techniques. Moreover, emission colour points, luminous efficacies and quantum efficiencies (QE) were calculated and discussed as a function of Eu²⁺ concentration and Zr/Hf ratio of the host lattice.     

Raman spectroscopy and imaging of graphene

Graphene has many unique properties that make it an ideal material for fundamental studies as well as for potential applications. Here we review recent results on the Raman spectroscopy and imaging of graphene. We show that Raman spectroscopy and imaging can be used as a quick and unambiguous method to determine the number of graphene layers. The strong Raman signal of single layer graphene compared to graphite is explained by an interference enhancement model. We have also studied the effect of substrates, the top layer deposition, the annealing process, as well as folding (stacking order) on the physical and electronic properties of graphene. Finally, Raman spectroscopy of epitaxial graphene grown on a SiC substrate is presented and strong compressive strain on epitaxial graphene is observed. The results presented here are highly relevant to the application of graphene in nano-electronic devices and help in developing a better understanding of the physical and electronic properties of graphene. This article is published with open access at Springerlink.com     

Polar and longitudinal magneto-optical spectroscopy of bismuth substituted yttrium iron garnet films grown by pulsed laser deposition

Ferrimagnetic bismuth substituted yttrium iron garnet Bi_xY_3 − xFe₅O₁₂ (BiYIG) films with x = 1 and 2 pulsed laser deposited onto (111) Gd₃Ga₅O₁₂ (GGG) substrates were studied using magneto-optical (MO) Kerr spectroscopy in the photon energy range of 1.8-5 eV at both polar and longitudinal magnetizations. The interference at lower photon energies provided the refined film thicknesses ranging between 70 and 200 nm. The films were grown under compressive strain and displayed saturation magnetizations (μ₀M_s) lower than that of their bulk counterparts due to the presence of nanograins forming BiYIG layers and/or magnetically dead interface layers. The trends in the MO spectra agree with those deduced from the published permittivity tensor data for BiYIG using a transfer matrix model applied to a film (BiYIG)-substrate (GGG) system. Due to the reduced μ₀M_s the predicted amplitudes are typically higher. The agreement was improved using effective medium approach or by incorporating into the model MO passive interface layers. The information on MO activity at longitudinal magnetization in the garnet layers below 100 nm presents interest for MO imaging and magnetophotonic devices. The results suggest that the MO Kerr spectroscopy combined with MO Kerr magnetometry may represent a valuable, cheap and nondestructive tool for the characterization of magnetic garnet films less than 200 nm thick.     

Study of strontium- and magnesium-doped lanthanum gallate solid electrolyte surface by X-ray photoelectron spectroscopy

The chemical states of the surface of the oxygen ion conducting solid electrolyte La_0.9Sr_0.1Ga_0.85Mg_0.15O_3−δ (LSGM 1015) as prepared by solid-state synthesis was analyzed by X-ray photoelectron spectroscopy. It was found that adventitious carbon did not interact with any of the constituent elements of LSGM 1015. Ga and La were found to exist in trivalent states. But, due to ionic bombardment presence of Mg could not be detected in the electrolyte surface.     

Investigation of the excitonic luminescence band of CdTe solar cells by photoluminescence and photoluminescence excitation spectroscopy

The excitonic luminescence band of polycrystalline cadmium telluride layers has been investigated by Photoluminescence (PL) and Photoluminescence excitation spectroscopy (PLE). CdTe was deposited by means of close space sublimation and the samples were activated by different chlorine containing compounds, i.e. cadmium chloride, hydrochloric acid, and sodium chloride as well as by simple air activation or received no post deposition treatment. In the PL spectra, four different peaks within the excitonic luminescence band were resolved. These include the free-exciton peak and two transitions of excitons bound to defects. Furthermore, free excitons and band to band transitions were detected by means of PLE. The PL and PLE spectra are discussed with respect to the post deposition treatments.     

Vacuum-UV excitation and visible luminescence of nano-scale and micro-scale NaLnF4:Pr3+ (Ln = Y,Lu)

The UV–Vis luminescence of NaLnF₄:Pr³⁺ (Ln = Y, Lu) materials can be efficiently excited by vacuum UV radiation (VUV) such as the 172 nm emission of mercury-free Xe-discharge lamps. In this work, the optical properties of the cubic α-phase and the hexagonal β-phase of NaLnF₄:Pr³⁺ (Ln = Y, Lu) powders are compared regarding particle sizes in the nano- and micrometer regime. Upon VUV excitation, the emission spectra of both crystal phases are found to be dominated by intraconfigurational [Xe]4f²–[Xe]4f² transitions, which is explained by the chemical properties of the ternary fluorides. Furthermore it is observed that the emission and excitation spectra of nano- and micro-scale powders are very similar, but that the luminescence intensity is affected by the average particle size.     

Study of a new resin-based composites containing hydroxyapatite filler using Raman and infrared spectroscopy

The degree of conversion of polymeric matrix in hydroxyapatite-containing dental fillings by Raman and infrared spectroscopy has been determined. Resin-based dental composites are one of the most popular filling materials used in dentistry. These light-cured materials are characterized by the value of the degree of conversion, which depends on curing time and influences the quality of obtained dental filling. Distribution of the filler into polymeric matrix, which has a significant impact on the properties of the final product, has been determined by Raman mapping. The applied procedure also has allowed to present the changes of the degree of conversion on the examined surfaces. The results of the study demonstrate the versatility of the Raman spectroscopy as the analytical spectroscopic technique for determining chemical properties of dental fillings and providing insight into their organization at the microstructural level. The obtained degree of conversion values have been compared with data for the commercially available dental fillings characterized by other authors.     

Raman and optical spectroscopy characteristics of Se-doped Bi12SiO20 crystals

Crystals of BSO doped with Se in two different concentrations (BSO:Se(I) and BSO:Se(II)) were grown by the Czochralski method. It is established that doping with Se is accompanied with preferential absorption of Fe from the melt. According to the in-depth chemical analysis, it is assumed that the doping Se ions enter the tetrahedral positions by means of the substitution of 3Si⁴⁺ by (Se⁶⁺ + 2Fe³⁺) ions. The measured absorption spectrum of the low-concentration Se-doped crystal (BSO:Se(I)) confirms such a conclusion as the absorption coefficient is increased in a broad spectral interval (1.4-3.1 eV) - an effect typical for all Fe-doped Bi₁₂SiO₂₀ crystals. The polarized Raman spectra of BSO:SeI show that the doping-induced lattice distortions are small. The IR spectrum of the BSO:SeI crystal yields indications for local lowering of the symmetry of the Fe-occupied tetrahedral positions. Doping with Se at high concentration (BSO:Se(II)) leads to occasional second phase inclusions and to a downshift of practically all modes in the Raman spectrum by 2-5.5 cm⁻¹. It is concluded that the doping with Se at high concentrations follows the same mechanism as that at low concentrations but the introduced lattice distortions are more significant, and lead to an enlargement of the unit cell while preserving the overall cubic symmetry.     

Characterization of original and expanded leaf-roots of tobacco by terahertz spectroscopy and X-ray microanalysis

Expanded leaf-roots of tobacco are used as fillers into cigarette products to reduce cost and contents of tar and nicotine and improve quality. To study the difference between expanded and original leaf-roots of tobacco, terahertz (THz) time-domain spectroscopy was used to detect the absorption spectra in the frequency range from 0.2 to 1.5 THz. Significant difference in terahertz absorption was observed in original and expanded leaf-roots. To understand the origin, scanning electron microscope was employed for microanalysis, revealing the difference in element compositions and surface appearances between original and expended leaf-roots. Non-polar and low-polar components of leaf-roots were largely lost after dissolving into liquid CO₂ during expansion, accounting for the difference in THz absorption spectroscopy.     

Structure determination of chitosan-stabilized Pt and Pd based bimetallic nanoparticles by X-ray photoelectron spectroscopy and transmission electron microscopy

Chitosan (CTS)-stabilized bimetallic nanoparticles were prepared at room temperature (rt.) in aqueous solution. Palladium (Pd) and platinum (Pt) were selected as the first metals while iron (Fe) and nickel (Ni) functioned as the second metals. In order to obtain the noble metal core-transition metal shell structures, bimetallic nanoparticles were prepared in a two-step process: the preparation of mono noble metallic (Pd or Pt) nanoparticles and the deposition of transition metals (Fe or Ni) on the surface of the monometallic nanoparticles. The structures of the nanoparticles were studied using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The XPS results show that Pd and Pt exist mainly in zero valences. The presence of Fe and Ni in the bimetallic nanoparticles affects the binding energy of Pd and Pt. Moreover, the studies of O 1s spectra indicate the presence of Fe or Ni shells. The analyses of TEM micrographs give the particle size and size distributions while the high-resolution TEM (HRTEM) micrographs show the existence of noble metal core lattices. The results confirm the formation of noble metal core-transition metal shell structures.     

Formation of Mn-oxide clusters in Mn-implanted SiO2 probed by soft X-ray emission and absorption spectroscopy

Mn⁺-implanted a-SiO₂-samples were studied with the help of soft X-ray emission and absorption spectroscopy (Si L_2,3 3d3s → 2p_3/2,1/2 and Mn L_2,3 3d4s → 2p_3/2,1/2 emission transitions) using synchrotron excitation. The samples were obtained using a pulsed ion source (ion beam current density ∼2-7 mA/cm², E_impl. = 30 keV, ion fluence ∼2 × 10¹⁷ cm⁻², pulse duration 400 μs) without thermal annealing. It was established that Mn-ion provides a formal valence state 2+, so arranging in implanted a-SiO₂ the low-sized MnO antiferromagnetic clusters probably of crystalline type. The data obtained well coincides with the electronic spin resonance results reported earlier.     

Evaluation of interfacial shear stress between multi-walled carbon nanotubes and epoxy based on strain distribution measurement using Raman spectroscopy

This study investigated the stress recovery of aligned multi-walled carbon nanotubes (MWCNTs) embedded in epoxy using Raman spectroscopy, and evaluated interfacial shear stress between MWCNTs and epoxy using shear-lag analysis. To this end, ultralong aligned MWCNTs (3.8 mm long) were embedded in epoxy to obtain Raman spectra at multiple points along the MWCNTs. Downshift of the G′-band due to tensile strain was measured from the nanotube end to the center, and the strain distribution of embedded MWCNTs was evaluated successfully. Interfacial shear stress was then estimated by minimizing the error between the shear-lag analysis and measured strain distribution. The maximum interfacial shear stress between the embedded MWCNTs and epoxy was 10.3–24.1 MPa at the failure strain of aligned MWCNT-reinforced epoxy composites (0.46% strain). Furthermore, the interfacial shear stress between an individual MWCNT and epoxy was investigated.     

GABRIELA: A new detector array for -ray and conversion electron spectroscopy of transfermium elements

With the aid of the Geant4 Monte Carlo simulation package a new detection system has been designed for the focal plane of the recoil separator VASSILISSA situated at the Flerov Laboratory of Nuclear Reactions, JINR, Dubna. GABRIELA (Gamma Alpha Beta Recoil Investigations with the ELectromagnetic Analyser VASSILISSA) has been optimised to detect the arrival of reaction products and their subsequent radioactive decays involving the emission of - and β-particles, fission fragments, γ- and X-rays and conversion electrons. The new detector system is described and the results of the first commissioning experiments are presented.     

Glow discharge optical emission spectroscopy for accurate and well resolved analysis of coatings and thin films

In the last years, glow discharge optical emission spectrometry (GDOES) gained more and more acceptance in the analysis of functional coatings. GDOES thereby represents an interesting alternative to common depth profiling techniques like AES and SIMS, based on its unique combination of high erosion rates and erosion depths, sensitivity, analysis of nonconductive layers and easy quantification even for light elements such as C, N, O and H. Starting with the fundamentals of GDOES, a short overview on new developments in instrument design for accurate and well resolved thin film analyses is presented.The article focuses on the analytical capabilities of glow discharge optical emission spectrometry in the analysis of metallic coatings and thin films. Results illustrating the high depth resolution, confirmation of stoichiometry, the detection of light elements in coatings as well as contamination on the surface or interfaces will be demonstrated by measurements of: a multilayer system Cr/Ti on silicon, interface contamination on silicon during deposition of aluminum, Al₂O₃-nanoparticle containing conversion coatings on zinc for corrosion resistance, Ti₃SiC₂ MAX-phase coatings by pulsed laser deposition and hydrogen detection in a V/Fe multilayer system. The selected examples illustrate that GDOES can be successfully adopted as an analytical tool in the development of new materials and coatings. A discussion of the results as well as of the limitations of GDOES is presented.     

Thermal imidization optimization of polyimide thin films using Fourier transform infrared spectroscopy and electrical measurements

The influence of the imidization temperature on the molecular structure and on the thermal and electrical properties of polyimide thin films is investigated. The effects of the imidization temperature on the formation of the imide rings are studied by Fourier transform infrared (FTIR) spectroscopy through the changes of the extent of imidization. However, the determination of the optimal imidization temperature shows a poor accuracy through this technique. Therefore, the quantification of several electrical properties used as probes of the imidization reaction advancement (particularly high field electrical measurements) allows obtaining a highest accuracy of the optimal imidization temperature. An optimum temperature is found at 400 °C while desimidization is observed at 450 °C. This is in good agreement with FTIR results.