196,327 research outputs found
Dy3+-doped nano-glass ceramics comprising NaAlSiO4 and NaY9Si6O26 nanocrystals for white light generation
No full textThe radiative emission properties of the Dy3+ ions in oxyfluoride glasses and glass ceramics have been investigated for the generation of white light. The X-ray diffraction pattern of the glass ceramics reveals the presence of NaAlSiO4 nanocrystals along with secondary phase of NaY9Si6O26 in the glass matrix after a suitable thermal treatment of the pristine glasses. Intense white light emission has been observed when the samples are excited with 350 nm light. Yellow to blue emission intensity ratios and chromaticity color coordinates have been determined from the visible luminescence spectra. All color coordinates are found to lie in the white region of the chromaticity color diagram proposing the suitability of the present studied materials for color display devices. © 2012 Elsevier B.V
Graphitic carbon in a nanostructured titanium oxycarbide thin film to improve implant osseointegration
No full textA nanostructured coating layer on titanium implants, able to improve their integration into bones and to protect against the harsh conditions of body fluids, was obtained by Ion Plating Plasma Assisted, a method suitable for industrial applications. A titanium carbide target was attached under vacuum to a magnetron sputtering source powered with a direct current in the 500-1100 W range, and a 100 W radio frequency was applied to the sample holder. The samples produced at 900 W gave the best biological response in terms of overexpression of some genes of proteins involved in bone turnover. We report the characterization of a reference and of an implant sample, both obtained at 900 W. Different micro/nanoscopic techniques evidenced the morphology of the substrates, and X-ray Photoelectron Spectroscopy was used to disclose the surface composition. The layer is a 500 nm thick hard nanostructure, composed of 60% graphitic carbon clustered with 15% TiC and 25% Ti oxides. © 2014 Elsevier B.V. All rights reserved
High refractive index gold nanoparticle doped Bi2O3-B2O3 glasses for THz frequencies
No full textDirect incorporation of gold nanoparticles from suspensions in 30%Bi2O3:70%B2O3 glass was achieved. This method has advantage over traditional methods where a gold salt is added to the precursor mixture and gold nanoparticles are obtained with subsequent heat treatment, eventually inducing crystallization with associated scattering of light and hence resulting in reduced optical quality of material. X-ray diffraction and differential thermal analysis were carried out in order to confirm the amorphous nature of the material and thermal properties of the prepared glasses, respectively. The size of the gold nanoparticles in the prepared glass matrix was measured using scanning electron microscopy. Optical characterization of prepared glass samples in ultraviolet–visible and terahertz regions was performed using ellipsometry, UV-VIS spectrophotometry and THz-time-domain spectroscopy. Comparison was made between glasses with and without gold nanoparticles and the effect of gold nanoparticle concentration on their optical behaviour is studied. These glasses are found to have high refractive index in the THz region making them suitable for photonic applications. © 2017 Elsevier B.V
Structural and Optical Investigation of Rare Earth Doped Oxyfluoride Glasses
No full textUV-Vis and FTIR analyses have been performed on an aluminosilcate base glass doped with two different rare earths (Dy3+ and Eu3+) with varying concentrations. The glasses were prepared by conventional melt quenching technique. While the absorption intensity of the observed bands was found to increase with increase of RE concentration, the RE doping did not cause any new structural unit and the FTIR spectra practically remained unchanged. © 2013 Copyright The Indian Ceramic Society
Influence of lead and cadmium fluoride variation on white light emission characteristics in oxyfluoride glasses and glass-ceramics
No full textThe radiative properties of Dy-doped glasses and glass-ceramic phosphors with varying lead and cadmium fluoride content are investigated in the present study for white light emitting applications. The precipitation of cubic lead fluoride phase of 10-18 nm crystallites was determined with the help of x-ray diffraction studies and the nanocrystalline nature was confirmed with scanning electron microscopy studies. The small size of the nanocrystallites enables the fabrication of transparent glass-ceramics which is verified by UV-vis spectroscopic study. The photoluminescence and lifetime measurements indicate towards progressive changes in the Dy3+ ion surroundings and propose enhanced energy transfers taking place post-heat treatments. Finally, CIE chromaticity coordinates are found to lie in the white region proposing the suitability of the present studied materials for color display devices. ©2014 Elsevier B.V. All rights reserved
On the influence of lead and cadmium fluoride content on thermal, optical and structural properties of oxyfluoride glass
No full textThis study reveals the effect of PbF2 and CdF2 addition on the aluminosilicate oxyfluoride glass network over a wide compositional range. The structure of glasses in SiO2-Al 2O3-PbF2 and SiO2-Al 2O3-PbF2-CdF2 system matrices was studied by using DTA, XRD, UV-VIS, density, Raman and FTIR spectroscopy. The observed shifts of absorption edge due to band gap variations with heavy metal fluoride (HMF) addition are compared with theoretical model of optical basicity and physical parameters derived from density. The variation in Tg, and stability factor are supported by Raman and FTIR results which show formation of NBOs and other super structural units with addition of HMF in the aluminosilicate network. © 2014 Published by Elsevier B.V
Comparison of Tm-sensitized Ho:YAG and Ho:YLF crystals for a laser-pumped 2 mu m CW oscillator
No full textWe report on a comparison of YAG and YLF crystals for Tm,Ho based CW laser systems operating at 2 mu m. As pump source we have used both a Ti:Al2O3 laser and an array of diode lasers in order to quantitatively assess the relevance of the pump beam spatial features on the 2 mu m laser performance. The results are compared with the predictions of a computer simulation using a rate equation model
Luminescence study of mixed valence Eu-doped nanocrystalline glass-ceramics
No full textEu-doped nanocrystalline NaAlSiO4/NaY9Si 6O26 glass-ceramics have been prepared by controlled crystallization of melt quenched bulk glasses. XRD, SEM and FTIR spectroscopy techniques were employed to characterize the crystallization process and the structural properties of the precursor glass and corresponding glass-ceramics. The formation of divalent europium (Eu2+) from Eu3+ ions during high temperature synthesis under ambient atmosphere was analyzed by photoluminescence spectroscopy and is discussed using the optical basicity model. The observed luminescence properties of Eu: NaY9Si 6O26 are compared with that of Eu: β-PbF2 nanocrystals and their marked differences are discussed. © 2013 Elsevier B.V. All rights reserved
A multi-technique approach for the characterization of Roman mural paintings
No full textIn the frame of an ongoing archeological study on the Sabina area, a countryside close to Rome, white and red samples of roman wall paintings have been investigated by combining X-ray diffraction and different spectroscopic methodologies, namely laser induced breakdown spectroscopy, μ-Raman and Fourier transform infrared attenuated total reflectance spectroscopy. The used multi-technique approach has allowed the unambiguous identification of the red pigment as red ochre and has provided insight on the provenance of both the pigment and the material used for the realization of the wall paintings. The experimental results have confirmed some assumptions on the use of local materials in roman rural architecture. © 2013 Elsevier B.V. All rights reserved
Experimental determination of the light-trapping-induced absorption enhancement factor in DSSC photoanodes
No full textFor dye-sensitized solar cells (DSSC), the fundamental process that determines the maximum short-circuit current is the absorption of light. In such devices, this is produced by the concurrent phenomena of light absorption by dye molecules and light trapping in the mesoporous, titania photoanode structure. The decoupling of these two phenomena is important for device characterization and the design of novel photoelectrode geometries with increased optical performance. In this paper, this task is addressed by introducing a spectral absorption enhancement factor as a parameter to quantify the light trapping effect. The experimental value of this parameter was obtained by comparing the experimentally determined fraction of absorbed light by a dye-sensitized photoanode with the light absorbed by the dye without the mesoporous titania structure. In order to gain more insight from this result, the fraction of light absorbed in the photoanode (on the basis of the dye loading capacity of the titania nanospheres) was also calculated by an optical model for the two extreme cases of the absence of light trapping and maximum light trapping. Accordingly, the photocurrent was calculated under the assumption of solar irradiation, which defined two useful boundaries. Using the experimentally derived values of the spectral absorption enhancement factor in the photoanode optical model, the DSSC short-circuit current can be calculated with good agreement with the value measured in practical devices based on the same photoanode structures. Therefore, our approach provides a realistic description of a practical device and can be exploited as an useful tool to assess the optical functionality of novel photoanode structures
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