Search results for "electromagnetic"

The focal plane assembly for the Athena X-ray Integral Field Unit instrument

2016

This paper summarizes a preliminary design concept for the focal plane assembly of the X-ray Integral Field Unit on the Athena spacecraft, an imaging microcalorimeter that will enable high spectral resolution imaging and point-source spectroscopy. The instrument's sensor array will be a ~ 3840-pixel transition edge sensor (TES) microcalorimeter array, with a frequency domain multiplexed SQUID readout system allowing this large-format sensor array to be operated within the thermal constraints of the instrument's cryogenic system. A second TES detector will be operated in close proximity to the sensor array to detect cosmic rays and secondary particles passing through the sensor array for off…

Radiation defects in undoped and Nd‐doped LaGaO 3 crystals

2005

Radiation induced defects have been studied in undoped and Nd-doped (6 mol% and 12 mol%) LaGaO3 crystals. Wide absorption band (2.2–2.8 eV) was observed after crystal irradiation with X-rays at 300 K. Induced defects have been annealed in air at ∼450 K. Similar absorption band was observed in transient absorption spectra after ns-pulsed electron beam excitation. The radiation defect creation efficiency is higher in undoped LaGaO3 crystal. It is shown that small concentration of Nd-doping increases the LaGaO3 crystal radiation hardness. In transient absorption spectra along with 2.7 eV band the absorption bands at 1.5 eV and 2.2 eV were observed. The decay process of transient absorption has…

<title>Large-scale first-principles calculations of Fe-doped SrTiO<formula><inf><roman>3</roman></inf></formul…

2003

The energy level positions in the optical gap and atomic geometry for the Fe4+ impurity substituting for a host Ti atom in SrTiO3 are calculated using the Unrestricted Hartree-Fock (UHF) method and supercells containing up to 320 atoms. In agreement with experiment, the high spin (S = 2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacements of six nearest O ions which is a combination of the Jahn-Teller and breathing modes. A considerable covalent bonding between the Fe ion and four nearest O ions takes place. We predict a strong dependence of optical absorption energies on the crystal compression or internal tensi…

Photoluminescence excited by ArF and KrF lasers and optical absorption of stishovite mono-crystal

2008

Two photoluminescence bands were found in a stishovite (silicon dioxide) mono-crystal sample under ArF (193 nm) and KrF (248 nm) excitation. The blue band is situated at 3.17 ± 0.02 eV in the case of ArF and at 3 ± 0.2 in the case of KrF. The UV band is at 4.55 ± 0.05 eV in the case of ArF and at 4.5 ± 0.05 eV in the case of KrF. The position of the UV emission band correlates with that excited by x rays. This position is 4.6 ± 0.05 eV with FWHM 0.8 ± 0.05 eV (Truhins et al 2003 Solid State Commun. 127 415). The blue band possesses slow decay kinetics with time constant 16 ± 2 µs and the UV band is fast on the level of 2 ± 0.5 ns, similarly for both lasers. Thermal quenching of both bands b…

<title>Nature of fundamental absorption edge of WO<formula><inf><roman>3</roman></inf></formula></title&…

1997

The fundamental absorption edge of amorphous, polycrystalline and crystalline tungsten trioxide (WO3) thin films obtained by different techniques (thermal evaporation, rf plasma sputtering, chemical gas transport) was investigated. Special attention was paid to correct measurements of absorption values of all WO3 thin films taking into account the scattered light, interference effects and reflection losses. The indirect edge at 2.70 eV was determined for crystalline WO3, but for crystal WO3:Ti the direct edge in the same place (2.72 eV) was found. For polycrystalline WO3 thin film first edge transition located at 2.76 eV had a quadratic dependence similar to the amorphous film at a higher p…

Transient Optical Absorption and Luminescence in Calcium Tungstate Crystal

2001

Ab initio calculations of the Ni K ‐edge XANES in Ni c Mg 1‐c O solid solutions

2005

An interpretation of the Ni K-edge X-ray absorption near edge structure (XANES) in pure NiO and NicMg1-cO solid solutions is given based on three types of ab initio theoretical calculations: the full-multiple-scattering (FMS) approach, the finite difference method (FDM) and the full potential linear muffin-tin orbital (FP-LMTO) method within the LSDA+U approach. The first two methods differ in the cluster potential approximation: the spherically symmetric muffin-tin potential is used in the FMS approach, whereas a non-muffin-tin numerical potential makes the core of the FDM. We found that the FMS and FDM techniques allow rather accurate description of the experimental XANES signal especiall…

Decoupling the artificial special pair to slow down the rate of singlet energy transfer

2012

Trimer 2, composed of a cofacial heterobismacrocycle, octamethyl-porphyrin zinc(II) and bisarylporphyrin zinc(II) held by an anthracenyl spacer, and a flanking acceptor, bisarylporphyrin free-base ( Ar = -3,5-(t Bu )2 C 6 H 3), has been studied by means of absorption spectroscopy, "steady state and time-resolved fluorescence" and fs transient absorption spectroscopy, and density functional theory (DFT) in order to assess the effect of decoupling the chromophores' low energy MOs on the rate of the singlet, S1, energy transfer, k ET , compared to a recently reported work on a heavily coupled trimeric system, Trimer 1, [biphenylenebis(n-nonyl)porphyrin zinc(II)]-bisarylporphyrin free-base ( A…

EXAFS study of the local structure of crystalline and nanocrystalline Y2O3using evolutionary algorithm method

2015

Temperature-dependent local structure and lattice dynamics of yttria (Y2O3) were studied by X-ray absorption spectroscopy. Novel method, which combines the reverse Monte Carlo and evolutionary algorithm techniques, was applied for the analysis of extended X-ray absorption fine structure at the Y K-edge. This approach allowed us to reconstruct 3D atomic structure models of crystalline and nanocrystalline Y2O3.

HgGa2 Se4 under high pressure: An optical absorption study

2015

High-pressure optical absorption measurements have been performed in defect chalcopyrite HgGa2Se4 to investigate the influence of pressure on the bandgap energy and its relation with the pressure-induced order–disorder processes that occur in this ordered-vacancy compound. Two different experiments have been carried out in which the sample undergoes either a partial or a total pressure-induced disorder process at 15.4 and 30.8 GPa, respectively. It has been found that the direct bandgap energies of the recovered samples at 1 GPa were around 0.15 and 0.23 eV smaller than that of the original sample, respectively, and that both recovered samples have different pressure coefficients of the dir…