Search results for "doping"
showing 10 items of 801 documents
High activity mesoporous copper doped cerium oxide catalysts for the total oxidation of polyaromatic hydrocarbon pollutants
2012
The doping of mesoporous ceria with copper significantly enhances activity for naphthalene total oxidation, the enhanced performance is controlled by the increased concentration of surface oxygen defects.
Dynamic Characterization of Upconversion in Highly Er-Doped Silica Photonic Crystal Fibers
2012
Measurements of time evolution of amplified spontaneous emission for square-wave modulated pump were made on a highly erbium-doped silica photonic crystal fiber and fitted to theoretical results calculated using different formalisms to describe the ${\rm Er}^{3+}$ -ion migration-assisted co-operative upconversion mechanism in the population densities rate equations. The determined characterization parameters are the constant homogeneous upconversion coefficient, 3.0 $\times 10^{-24}~{\rm m}^{3}/{\rm s}$ , the critical radii for upconversion and migration, 10.5 and 14A, respectively, and the rate of clustered ions, 14%. These parameters are analysed and compared to those obtained with contin…
Particle size-related limitations of persistent phosphors based on the doped Y3Al2Ga3O12 system
2021
AbstractCo-doped Ce3+, Cr3+ and Pr3+ yttrium–aluminium–gallium garnet powders of various sizes were obtained by co-precipitation method. The microstructure and morphology were investigated by XRPD, TEM and gas porosimetry. The luminescence properties were studied by excitation and emission spectra, quantum yield and decay times. Thermoluminescence measurements were performed to evaluate the activation energy, traps redistribution and frequency factor. Limitation in the energy transfer between dopant ions in the small particles, traps depth and surface defects were considered and investigated as responsible for the quenching of persistent luminescence. The phosphors annealed at 1100 °C show …
Luminescence of Eu3+-doped lanthanum titanate (La2TiO5), a system with one-dimensional energy migration
1992
Abstract The titanate and Eu 3+ luminescence of a composition La 2 TiO 5 -Eu are reported as a function of temperature. At 4.2 K the quantum efficiency is very high, because the titanate excitation energy is localized. At 300 K there is delocalization and quenching centres are easily reached, so that the quantum efficiency becomes low. This is discussed in terms of the crystal structure, as are the peculiarities of the Eu 3+ spectra.
Displacement Defect Formation in Complex Oxide Crystals under Irradiation
2000
The work is devoted to an analysis of formation processes of the radiation displacement defects (RDDs) and colour centres (CCs) in complex oxide crystals under irradiation. The calculation results on: the displacement process simulation as well as an analysis of the RDD and CC accumulation kinetics are presented. New experimental results on additional absorption spectra induced by neutron irradiation of LiNbO(3) (LNO) crystals doped with Fe and Cr and YAlO(3) (YAP) crystals doped with Nd and Er as well are presented. Dose dependencies of the additional absorption are compared and their peculiarities are discussed. The obtained results confirm that CCs causing the irradiation induced absorpt…
Characterization of LiF and CaF2 surfaces using MIES and UPS (HeI)
1998
Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combination with ab initio calculations (CRYSTALcode) were applied to study surface and bulk defects in LiF and CaF2. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF2. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W (110) and CaF2 (111) is discussed on the basis of the ab initio calculations. MIES spectra show features from Li agglomerates on the surface of electron bombarded LiF. The electronic structure of the LiF:Mg single crystal shows additional features above the valence band maximum caused b…
Electron paramagnetic resonance of doped and undoped BaFBr detected by recombination luminescence
1998
Abstract The recombination processes in the X-ray storage phosphor BaFBr:Eu2+ was investigated by measuring the microwave-induced changes in the recombination luminescence in a (high) magnetic field. Besides the resonances of the F(Br−) centre, of the VK(Br−2) centre and of the Eu2+ ground state we observed a line of a hitherto unknown hole centre. The maximum of the luminescence band in which the VK(Br−2) centre could be detected was about 400 nm. The resonance of the unknown hole centre belongs to a luminescence band peaking at about 350 nm.
Photo- and thermostimulated processes in α-Al2O3
1995
Abstract We reported on the recombination processes determined by the release of electrons from defects connected with the dosimetric 430 K thermostimulated luminescence (TSL) peak as well as with the 260 K TSL peak. These TSL peaks appear in thermochemically reduced α-Al 2 O 3 crystals containing hydrogen and emission of these TSL peaks corresponds to luminescence of the F-center. The X-ray exposure or UV excitation in the absorption band of F-centers at 6.0 eV of reduced α-Al 2 O 3 crystals doped with acceptor impurities results in the appearance of a broad anisotropic complex absorption band in the spectral region 2.5–3.5 eV and in the appearance of a predominant TSL peak at 430 K. Above…
Spectroscopy of an optical excited Ga doped SiO2 surface
2007
Abstract We present the first spectroscopical analysis of the Ga/SiO2 surface interaction in hot environment. This interaction gives rise to inclusions of Ga atoms inside the silica matrix that produce structural changes and modify the SiO2 optical characteristics. This paper discusses both the time- and the frequency-resolved spectra of the fluorescence emission following UV pulsed laser excitation of the so “doped” silica in the range 15,000–28,000 cm−1. The investigation is completed by the electron paramagnetic resonance (EPR) spectra of two high-purity synthetic silica samples of commercial origin after thermal treatment in presence and in absence of a Ga atmosphere.
Luminescence of cerium doped YAG nanopowders
2007
Abstract Cerium doped YAG nanopowders with grain size ∼ 20 nm have been synthesized by co-precipitation method. Time-resolved luminescence characteristics have been studied. The results obtained have been compared with the luminescence characteristics for well-studied YAG single crystals. In contrast to cerium doped YAG crystals, cerium doped nanocrystal does not reveal luminescence bands due to antisite defects under electron beam pulse and X-ray excitations at 80–300 K temperature range. It was detected that decay kinetic of Ce 3 + related emission in the nanocrystal can be approximated by two exponents with time constants ∼ 9 and ∼ 47 ns at 290 K. It is faster than single exponential dec…