Search results for " paramagnetic resonance"
showing 10 items of 567 documents
Formation of optically active oxygen deficient centers in Ge-doped SiO2 by γ- and β-ray irradiation
2010
Abstract We report an experimental study on the comparison between the γ- or β-ray induced Ge related point defects in Ge-doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol–gel technique have been irradiated with γ-ray or with β-ray. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E’Ge, GLPC (Germanium lone pair center) and H(II) point defects. No relevant differences between the concentrations of γ- or β-ray induced Ge(1) and E’Ge point defects have been observed and, in addition, it ha…
Optical, Structural and Paramagnetic Properties of Eu-Doped Ternary Sulfides ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y)
2015
Eu-doped ternary sulfides of general formula ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y) are presented as a novel interesting material family which may find usage as X-ray phosphors or solid state white light emitting diode (LED) lighting. Samples were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, time-resolved photoluminescence spectroscopy, electron paramagnetic resonance, and X-ray excited fluorescence. Corresponding characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra, and decay k…
Luminescence-detected EPR of oxygen-fluorine vacancy complexes in CaF2
2009
In several CaF2 single crystals grown by the Bridgman method and doped with CaO or in addition with SrF2 or NaF a luminescence band between 470 nm and 600 nm could be excited at 212 nm, its peak wavelength depending on the doping. With photo-luminescence (PL) detected EPR five spin triplet centres were identified. Their axial fine structure constants D varied from 87 mT to 690 mT whereby the most intense spectra had the smallest D value. Theoretical calculations of the fine structure tensors and superhyperfine interactions show that the most intense and probable triplet centre consists of a pair of an OF– on a F– site next to a nearest neighbour F– vacancy which, compared to the well-known …
Optically detected magnetic resonance investigation of oxygen luminescence centres in BaF2
2002
The structure of two oxygen-related luminescence centres in oxygen-doped BaF2 was investigated by means of photoluminescence (PL) and photoluminescence-detected electron paramagnetic resonance (PL-EPR). One of the oxygen-related luminescences peaking at 2.83 eV is associated with 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 can be described as an oxygen on a fluorine lattice site with a next-nearest fluorine vacancy along the 110 direction. The luminescence at 2.25 eV is also associated with a triplet state. Its PL-EPR spectrum is probably due to oxygen–vacancy complexes with a nearest …
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…