Search results for "Mines"
showing 10 items of 2609 documents
Optical Properties of Natural and Synthetic Minerals
2015
The results of investigation of optical absorption and photoluminescence (PL) of topaz, beryl and yttrium aluminium garnet crystals doped with different concentrations of transition ions exposed to fast neutron irradiation and electron irradiation are presented. We suppose that irradiation leads to the formation of two types of complex centers: "Me2+-F+ (or F) centre" and complex centers, which consist of a cation vacancy and an impurity (iron, manganese and chromium) ion. Exchange interaction between radiation defects and impurity ions during neutron or electron irradiation gives rise to appearance of additional absorption and luminescence band broadening in investigated crystals.
Optical Properties of Irradiated Yttrium Aluminum Garnet
2012
The results of investigation of the photoluminescence (PL) and optical absorption of crystals Y3Al5O12(YAG) doped with different concentrations of manganese ions exposed to fast neutron irradiation and electron irradiation are presented. Photoluminescence spectra of YAG before neutron irradiation at T=80 K contain fine lines in orange region of spectrum, ascribed to Mn2+ ions in octahedral position. After irradiation band broadening is observed in the luminescence spectra of garnet crystals. Electron irradiation produced broad band with a complex structure related to Mn4+ ions. Exchange interaction between radiation defect and impurity ions during neutron irradiation and electron irradiatio…
Influence of radiation defects on tritium release parameters from Li2O
1998
Abstract The study of the influence of radiation defects on tritium release behavior from polycrystalline Li2O was performed by simultaneous measurements of the luminescence emission and tritium release. It was found that the radiation defects in Li2O introduced by electron irradiation cause the retention of tritium. It is thought that the tritium recovery is affected by the formation of a Li–T bond, which is tolerant of high temperatures. The retardation of tritium decreases with increasing absorbed dose in the dose range from 50 to 140 MGy. The aggregation of radiation defects at high irradiation doses is considered to be responsible for the decrease of the interaction of tritium with rad…
The study of time-resolved absorption and luminescence in PbWO4 crystals
2000
Abstract The transient absorption and luminescence under pulsed electron beam excitation were studied for undoped and La3+ doped PbWO4 crystals. The absorption band at ∼1.0 eV is suggested to be due to self-trapped electrons and the absorption band at 3.5 eV may be due to self-trapped holes. The formation of luminescence centers via electron–hole recombination is affected by La3+ in doped crystals. The large fraction of electrons and holes undergoes thermostimulated recombination within geminate pairs and the spatial separation of geminate pairs components is important in recombination process. The intrinsic (blue) luminescence arises in this recombination. The mechanism of La3+ influence o…
Irradiation Effects in Optical Fibers
2010
Intrinsic and extrinsic optical fiber-based sensors are promising devices to be used in very different and complex environments, by their very nature: capabilities to work under electromagnetic fields; possibility to carry multiplexed signals (time, wavelength multiplexing); small size and low mass; ability to handle multi-parameter measurements in distributed configuration; possibility to monitor sites far away from the controller. In the case of the optical fibers, the possibility to be incorporated into various types of sensors and actuators, free of additional hazards (i.e. fire, explosion), made them promising candidates to operate in adverse conditions as those required by space appli…
Dependence of the emission properties of the germanium lone pair center on Ge doping of silica
2011
We present an experimental investigation regarding the changes induced by the Ge doping level on the emission profile of the germanium lone pair center (GLPC) in Ge doped silica. The investigated samples have been produced by the sol-gel method and by plasma-activated chemical vapor deposition and have doping levels up to 20% by weight. The recorded photoluminescence spectra show that the GLPC emission profile is the same when the Ge content is lower than ∼ 1% by weight, whereas it changes for higher doping levels. We have also performed Raman scattering measurements that show the decrease of the D1 Raman band at 490 cm( - 1) when the Ge content is higher than 1% by weight. The data suggest…
Facile Synthesis of Fluorescent Polymer Nanoparticles by Covalent Modification-Nanoprecipitation of Amine-Reactive Ester Polymers
2015
Emission wavelength control in fluorescent nanoparticles (NPs) is crucial for their applications. In the case of inorganic quantum dots or dye-impregnated silica NPs, such a control is readily achieved by changing the size of the particles or choosing appropriate fluorescent dyes, respectively. A similar modular approach for controlling the emission wavelength of fluo-rescent polymer NPs, however, is difficult. This article reports on fluorescent polymer NPs, the synthesis of which provides a platform for a modular approach towards the preparation of fluorescent NPs of desired emission wavelength. Atom-transfer radical polymerization (ATRP) is employed to synthesize reactive ester polymers,…
Study of aromatic nucleophilic substitution with amines on nitrothiophenes in RTILs: are the different effects on the behavior of para-like and orto-…
2006
The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers) with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three roomtemperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm2im][BF4], where bmim ) 1-butyl-3- methylimidazolium and bm2im ) 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration sim…
Determination of basic strenght of aliphatic amines through ion pair formation in some ionic liquid solutions
2010
To have an evaluation of the basic strength of aliphatic amines in ionic liquid solution, the stability constants relevant to the formation of amine/p-nitrophenol ion pairs were determined in different ionic liquids at 298 K. In particular, aliphatic (pyrrolidinium) and aromatic (imidazolium) ionic liquids were used. Imidazolium ions, bmim(+) and bm(2)im(+), having different hydrogen bond donor abilities were taken into account. Anions were chosen ([BF(4)(-)], [PF(6)(-)], and [NTf(2)(-)]; where NTf(2) = bis(trifluoromethansulfonyl)imide) showing different shape, size, and coordination ability. Several primary, secondary (cyclic or not), and tertiary amines were used to study the effect of a…
Ligand-Centred Fluorescence and Electronic Relaxation Cascade at Vibrational Time Scales in Transition-Metal Complexes
2015
Using femtosecond-resolved photoluminescence up-conversion, we report the observation of the fluorescence of the high-lying ligand-centered (LC) electronic state upon 266 nm excitation of an iridium complex, Ir(ppy)(3), with a lifetime of 70 +/- 10 fs. It is accompanied by a simultaneous emission of all lower-lying electronic states, except the lowest triplet metal-to-ligand charge-transfer ((MLCT)-M-3) state that shows a rise on the same time scale. Thus, we observe the departure, the intermediate steps, and the arrival of the relaxation cascade spanning similar to 1.6 eV from the (LC)-L-1 state to the lowest 3MLCT state, which then yields the long-lived luminescence of the molecule. This …