Search results for "silica"
showing 10 items of 1092 documents
Multiband light emission and nanoscale chemical analyses of carbonized fumed silica
2018
Fumed silica with a specific area of 295 m2/g was carbonized by successive phenyltrimethoxysilane treatments followed by annealing in inert atmosphere up to 650 °C. Emission, excitation, kinetics, and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopies. The local chemistry was also studied by infrared transmission spectroscopy. Strong ultraviolet and visible photoluminescence was observed in the samples after the chemical treatments/modifications and thermal annealing. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups, while near ultraviolet and visible em…
Insight into the defect-molecule interaction through the molecular-like photoluminescence of SiO2 nanoparticles
2016
Luminescence properties due to surface defects in SiO2 are the main keystone with particles that have nanoscale dimensions, thus motivating their investigation for many emission related applications in the last few decades. A critical issue is the role played by the atmosphere that, by quenching mechanisms, weakens both the efficiency and stability of the defects. A deep knowledge of these factors is mandatory in order to properly limit any detrimental effects and, ultimately, to offer new advantageous possibilities for their exploitation. Up to now, quenching effects have been interpreted as general defect conversion processes due to the difficulty in disentangling the emission kinetics by…
Local structure of gadolinium in oxyfluoride glass matrices containing SrF2 and BaF2 crystallites
2016
Abstract Gd3 + doped aluminosilicate oxyfluoride glasses and glass-ceramics containing SrF2 and BaF2 crystallites have been studied by differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopy techniques. A pronounced EPR fine structure emerges after the heat treatment of the glass matrix. EPR spectra simulations indicate the formation of cubic, tetragonal and trigonal Gd3 + centres in the studied compositions.
Near-IR- and UV-femtosecond laser waveguide inscription in silica glasses
2019
The influence of laser parameters on silica based waveguide inscription is investigated by using femtosecond laser pulses at 1030 nm (near-IR) and at 343 nm (UV). Negative phase contrast microscopy technique is used to measure the refractive index contrast for different photo-inscribed waveguides and shows the effects of both laser wavelength and scanning speed. In particular, UV photons have a higher efficiency in the waveguide production process as also confirmed by the lower optical losses at 1550 nm in these waveguides. These measurements are combined with micro-Raman and photoluminescence techniques, highlighting that laser exposure induces both structural modification of the silica an…
Luminescence and energy transfer in Dy3+/Eu3+ co-doped aluminosilicate oxyfluoride glasses and glass-ceramics
2018
Abstract A series of oxyfluoride glasses with the composition SiO2–CaF2–Al2O3–CaO, doped with Dy2O3 (0.5–1 mol%) and Eu2O3 (0–4 mol%), have been prepared using the melt quenching method. The glass-ceramics have been obtained by heating the as-made glasses at 680 °C and 750 °C for 1 h. The glasses and the glass-ceramics were investigated using photoluminescence techniques in the near-UV and visible ranges, and differential thermal analysis (DTA) and x-ray diffraction (XRD) measurements were performed. The samples doped with 0.5 mol% Dy3+ were observed to have the highest luminescence intensity under 453 nm excitation compared to the samples doped with 1 mol% Dy3+ and the co-doped samples. Th…
Luminescence of localized states in oxidized and fluorinated silica glass
2019
This work was supported by the Latvian Science Council Grant No lzp-2018/1-0289.
Entrapping of O2 Molecules in Nanostructured Silica Probed by Photoluminescence
2013
We studied the emission of the O2 molecules embedded in fumed silica (amorphous silicon dioxide) nanoparticles differing for diameters and specific surface. By using a 1064 nm laser as a source we recorded both the O2 emission and the Raman signal of silica. Our experimental data show that the O2 emission/Raman signal (at 800cm-1) ratio decreases with increasing the specific surface both for the as received and the loaded samples. By performing a thermal treatment (600 °C for 2h) we modified the structure and the water content of the smallest nanoparticles without observing any significant change in the O2 emission/Raman signal ratio. Our data are explained by a shell model showing that the…
Visible-ultraviolet vibronic emission of silica nanoparticles
2014
We report the study of the visible-ultraviolet emission properties and the structural features of silica nanoparticles prepared through a laboratory sol-gel technique. Atomic force microscopy, Raman and Infrared investigations highlighted the 10 nm size, purity and porosity of the obtained nanoparticles. By using time resolved photoluminescence techniques in air and in a vacuum we were able to single out two contributions in the visible emission: the first, stable in both atmospheres, is a typical fast blue band centered around 2.8 eV; the second, only observed in a vacuum around the 3.0-3.5 eV range, is a vibrational progression with two phonon modes at 1370 cm(-1) and 360 cm(-1). By fully…
Photoluminescence of Point Defects in Silicon Dioxide by Femtosecond Laser Exposure
2021
The nature of the radiation-induced point defects in amorphous silica is investigated through online photoluminescence (PL) under high intensity ultrashort laser pulses. Using 1030 nm femtosecond laser pulses with a repetition rate of 1 kHz, it is possible to study the induced color centers through their PL signatures monitored during the laser exposure. Their generation is driven by the nonlinear absorption of the light related to the high pulse peak powers provided by femtosecond laser, allowing to probe the optical properties of the laser exposed region. The experiment is conducted as a function of the laser pulse power in samples with different OH contents. The results highlight the dif…
Generation and excitation of point defects in silica by synchrotron radiation above the absorption edge
2010
We report photoluminescence measurements carried out on amorphous SiO{sub 2} upon excitation by synchrotron light. Exposure of the as-grown material to above-edge light at low temperature induces the formation of nonbridging oxygen hole centers (NBOHC), localized in a thin layer below the surface limited by the penetration depth (tens of nm) of impinging light. After concluding the exposure to 11 eV light, stable defects are revealed by observing their characteristic 1.9 eV photoemission band excited at 4. 8eV. The local concentration of induced defects, supposedly formed by nonradiative decay of excitons, is very high (close to approx10{sup 21} cm{sup -3}) and independent of the previous h…