Search results for "Paramagnetic"
showing 10 items of 600 documents
Gallium doped SiO2: Towards a new luminescent material
2007
We show how the interaction between Ga atoms and silica samples in a hot environment gives rise to permanent inclusions of Ga inside the silica matrix which, in turn, produce typical luminescence features. The Ga doped silica is analyzed via laser induced fluorescence, photoluminescence and electron paramagnetic resonance spectroscopies. The results evidence the presence of modifications induced by the Ga inclusions inside the silica matrix and some preliminary hypothesis on their nature are advanced. Possible applications of such Ga doped silica are also mentioned.
Optically detected magnetic resonance investigation of a luminescent oxygen–vacancy complex in Mn-doped LiBaF3
2006
The structure of an oxygen-related luminescence centre in manganese-doped LiBaF 3 was investigated by means of photoluminescence (PL) and PL-detected electron paramagnetic resonance. At 20 K an oxygen-related complex shows two luminescence bands peaking at about 430 and 475 nm, when excited at 220 nm. These bands can be attributed to an excited triplet state (S = 1) of an oxygen-vacancy complex with the z axis of the fine structure tensor parallel to the (110) direction. This complex is believed to be next to a Mn 2+ impurity on a Ba 2+ site and can be described as an oxygen on a fluorine lattice site with a nearest fluorine vacancy along the (110) direction.
Photoluminescent and paramagnetic centers in gamma irradiated porous silica
2005
Abstract The photoluminescence and electron spin resonance properties of gamma irradiated (up to 500 kGy) porous silica are reported. By exciting at 5.6 eV a photoluminescence contribution can be detected before irradiation, peaked at about 4.1 eV. Gamma irradiation causes the generation of the E′ centers (about 1 × 1014 defects cm−3) of paramagnetic hole centers and modifies the photoluminescence properties of the sample: the emission amplitude decreases and three contributions can be singled out at about 3.3, 3.8 and 4.4 eV.
Gamma ray induced 11.8 mT ESR doublet in natural silica
1998
Abstract We report electron spin resonance (ESR) measurements in natural and synthetic vitreous SiO2 samples irradiated by γ rays. An 11.8 mT doublet, asymmetrically centered on the resonance line of the E′ center, was detected only in natural samples. The intensity of this doublet as a function of γ exposure tends to saturate for doses as low as 0.2 Mrad and is not related to the growth kinetics of the E′ centers. Photoluminescence (PL) measurements on the same samples have shown that two emissions at 3.15 and 4.26 eV bleach with the same kinetics as does the 11.8 mT doublet on increasing the γ ray dose. We tentatively suggest the presence of a conversion mechanism, activated by γ irradiat…
Thermal stability of gamma-irradiation-induced oxygen-deficient centers in silica
2006
The effects of isochronal thermal treatments on three {gamma}-irradiation-induced point defects, named the E{sup '}, ODC(II), and H(I) centers, are investigated in various types of commercial silica (a-SiO{sub 2}). ODC(II) is investigated by means of photoluminescence spectroscopy, and the H(I) and E{sup '} centers by electron paramagnetic resonance. The annealing processes of the ODC(II) and H(I) center are shown to be independent of each other, and no conversion mechanisms are evidenced. In contrast, a strong similarity is observed between the annealing curves of the ODC(II) and E{sup '} centers. We tentatively ascribe the annealing processes to reactions of the defects with radiolyticall…
Defect formation in photochromic Ca2SnO4: Al3+
2021
Abstract Photoluminescence, photochromism and defect formation were analysed in Ca2SnO4 doped with 0–20% Al3+. Bright cyan luminescence attributed to Sn2+ was detected in all samples. Introduction of Al3+ in Ca2SnO4 led to an enhancement of Sn2+ emission by up to 70% in comparison with an undoped sample. After exposure to UV irradiation, two absorbance bands centered at 520 nm and 710 nm and three paramagnetic defects were observed in Al3+-doped Ca2SnO4 samples. The paramagnetic centers were identified as a hole type and two different Sn3+ centers. Electron paramagnetic resonance (EPR) data suggested that one of the Sn3+ centers is located in a close proximity of Al3+. Analysis of the stabi…
Alpha and deuteron irradiation effects on silica nanoparticles
2014
We present an experimental investigation focused on the effects of alpha and deuteron irradiation on different silica nanoparticles. The study has been devoted also to characterize the induced point defects and the eventual structural modifications to evaluate the effects of the different irradiation source in comparison with the bulk materials. After irradiation up to about 10^16 ions cm^-2, we performed electron paramagnetic resonance (EPR), photoluminescence (PL), infrared (IR) absorption, Raman, and atomic force microscopy (AFM) measurements. We found that the two types of irradiation qualitatively induce comparable effects. Furthermore, irradiation generates the socalled twofold coordi…
Optical properties of phosphorous-related point defects in silica fiber preforms
2009
Physical review / B 80, 205208 (2009). doi:10.1103/PhysRevB.80.205208
Twofold coordinated Ge defects induced by gamma-ray irradiation in Ge-doped SiO2
2008
We report an experimental study by photoluminescence, optical absorption and Electron Paramagnetic Resonance measurements on the effects of exposure of Ge-doped amorphous SiO2 to gamma ray radiation at room temperature. We have evidenced that irradiation at doses of the order of 1 MGy is able to generate Ge-related defects, recognizable from their optical properties as twofold coordinated Ge centers. Until now, such centers, responsible for photosensitivity of Ge-doped SiO2, have been induced only in synthesis procedures of materials. The found result evidences a role played by gamma radiation in generating photosensitive defects and could furnish a novel basis for photosensitive pattern wr…
Post UV irradiation annealing of E’ centers in silica controlled by H2 diffusion
2004
Abstract We investigate the isothermal annealing of E′ centers generated by UV photons (266 nm) of a pulsed Nd:YAG laser in two natural silica types differing for their OH content. Electron spin resonance and absorption spectra recorded at room temperature at different delays from the laser exposure evidenced a partial reduction of E′ centers, more pronounced in the wet silica. These post irradiation kinetics complete within 10 5 s, regardless the silica type, and they are consistent with a diffusion limited reaction between the E′ centers and the molecular hydrogen H 2 . Analysis of our data is done by theoretical fits using the Waite's equation and compared with the H 2 diffusion paramete…