Search results for "SILICA"
showing 10 items of 1092 documents
Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time…
2008
The article describes an experimental method that allows to estimate the inhomogeneous and homogeneous linewidths of the photoluminescence band of a point defect in an amorphous solid. We performed low temperature time-resolved luminescence measurements on two defects chosen as model systems for our analysis: extrinsic Oxygen Deficient Centers (ODC(II)) in amorphous silica and F+ 3 centers in crystalline Lithium Fluoride. Measurements evidence that only defects embedded in the amorphous matrix feature a dependence of the radiative decay lifetime on the emission energy and a time dependence of the first moment of the emission band. A theoretical model is developed to link these properties to…
Inhomogeneous width of oxygen-deficient centers induced by electron irradiation of silica
2009
We report a study of the luminescence activity of oxygen-deficient centers stabilized in as-grown synthetic silica, as compared with the same defects induced by $\ensuremath{\beta}$ irradiation at increasing doses, ranging from $1.2\ifmmode\times\else\texttimes\fi{}{10}^{3}$ to $5\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{kGy}$. We experimentally observe a progressive broadening of the luminescence band with increasing total electron dose released on samples. By analyzing our data within a theoretical model capable of separating homogeneous and inhomogeneous contribution to the total luminescence linewidth, we observe that the increasing of the width is entirely ascribable to t…
Photoluminescence and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles
2013
An experimental study by Raman and Photoluminescence (PL) spectroscopies on the emission and diffusion properties of O2 molecules in amorphous SiO2 nanoparticles of commercial origin with diameters from 14 to 40 nm is reported. Stationary and time resolved PL measurements have been carried out to characterize the Near Infrared (NIR) emission at 1272 nm of O2. Emission features similar to those of bulk silica systems with a sharp PL band and excitation channels in the NIR, at 1070 nm, and in the visible, at 765 and 690 nm are found, with peculiarities arising from embedding O2 in nanostructures. The study of the NIR PL lifetime as a function of temperature down to 10 K enabled to reveal the …
Optical properties of phosphorous-related point defects in silica fiber preforms
2009
Physical review / B 80, 205208 (2009). doi:10.1103/PhysRevB.80.205208
Luminescence and absorption spectroscopy of Sn-related impurity centers in silica
2006
We report an experimental study on the absorption and luminescence spectra of oxygen deficient point defects in Sn-doped silica. The absorption band at 4.9 eV (B2β band) and the two related photoluminescence bands at ∼4.2 eV (singlet-singlet emission, S1 → S0) and at ∼3.2 eV (triplet-singlet emission, T1 → S0), linked by a thermally activated T1 → S1 inter-system crossing process (ISC), are studied as a function of temperature from 300 to 20 K. This approach allows us to investigate the dynamics properties of the matrix in the surroundings of the point defects and the effects of local disorder on the two relaxation processes from S1: the radiative channel to S0 and the ISC process to T1. We…
Luminescence activity of surface and interior Ge-oxygen deficient centers in silica
2005
We report a comparative study on the optical activity of surface and interior Ge–oxygen deficient centers in pressed porous and sol–gel Ge-doped silica, respectively. The experimental approach is based on the temperature dependence of the two photoluminescence bands at 4.2 (singlet–singlet emission, S1! S0) and 3.1 eV (triplet–singlet emission, T1! S0), excited within the absorption band at about 5 eV. Our data show that the phonon assisted intersystem crossing process, linking the two excited electronic states, more effective for surface than for interior centers in the temperature range 5–300 K. For both centers, a distribution of the activation energies of the process is found. Based on th…
Generation of oxygen deficient point defects in silica by γ and β irradiation
2007
We report an experimental study of the effects of y and β irradiation on the generation of a point defect known as ODC(II) in various types of commercial silica (a-SiO 2 ). The ODC(II) has been detected by means of photoluminescence (PL) spectroscopy measuring the PL band centered at 4.4 eV and excited at 5.0 eV associated to this defect. Our experiments show that ODC(II) are induced in all the investigated materials after irradiation at doses higher than 5 x 10 2 kGy. A good agreement is observed between the efficiencies of generation of ODC(II) under y and β irradiation, enabling a comprehensive study up to the dose of 5 x 10 6 kGy. Two different growth rates, one in the low and one in th…
Laser wavelength effects on the refractive index change of waveguides written by femtosecond pulses in silica glasses
2018
We investigate the influence of two fs-laser wavelengths (343 and 800 nm) on the induced refractive index change (Δn) of waveguides written in silica materials. Results show that Δn is higher for waveguides photo-inscribed with UV photons.
Effects induced by UV laser radiation on the blue luminescence of silica nanoparticles
2013
The effects induced on the blue luminescence centered around 2.8 eV, characteristic of silica nanoparticles, were investigated by monitoring its intensity during and after exposure to the third and the fourth harmonic of a Nd:YAG pulsed laser. The luminescence trend is found to be dependent on the UV photon energy: 3.50 eV photons induce a partial bleaching followed by a recovery in the post-irradiation stage; 4.66 eV photons cause a total bleaching permanent after the irradiation. These results are interpreted as the conversion of luminescent defects towards stable and metastable configurations.
ORMOSIL thin films: Tuning mechanical properties via a nanochemistry approach
2006
The mechanical properties (hardness and elastic modulus) of organically modified silicate thin films can be finely tuned by varying the degree of alkylation and thus the fraction of six- and four-membered siloxane rings in the organosilica matrix. This opens the way to large tunability of parameters that are of crucial practical importance for films that are finding increasing application in numerous fields ranging from microelectronics to chemical sensing.