Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

LUMINESCENT DECAY OF KI: Tl, KBr:Tl, AND KCl:Tl

Abstract: The luminescent decay of single crystals of KI:Tl excited in the $A$, $B$, $C$, and $D$ absorption bands has been investigated over the temperature range 10\ensuremath{\rightarrow}300\ifmmode^\circ\else\textdegree\fi{}K. A quantitative description of the decay of luminescence excited in the $A$ band is given. Four of the emission bands have decay times consistent with the Seitz model, but the decay of the 4300-\AA{} band does not agree with this model. Measurements of the luminescent decay of KBr:Tl and KCl:Tl excited in the $A$ absorption band are presented, and the results are compared with those obtained for KI:Tl. The results support the hypothesis that the 3000-\AA{} emission band in KCl:Tl at 10\ifmmode^\circ\else\textdegree\fi{}K is double.

Cubic TiO 2 as a potential light absorber in solar-energy conversion

Abstract: Materials are currently sought for use in the photo-induced decomposition of water on crystalline electrodes. Titanium dioxide is valuable in this respect. The electronic structural properties of cubic ${\mathrm{TiO}}_{2}$ polymorphs were investigated by means of first-principles methods. We demonstrate that both fluorite- and pyrite-type ${\mathrm{TiO}}_{2}$ have important optical absorptive transitions in the region of the visible light. A cubic ${\mathrm{TiO}}_{2}$ phase that can efficiently absorb the sunlight would be an important candidate material for the development of the solar cells. Also, we present results on the $\mathrm{Ti}$ $L$ edges for the two different titania forms. We predict that a qualitative spectroscopic discrimination of the cubic polymorphs can be achieved by following the $\mathrm{Ti}$ $2p\ensuremath{\rightarrow}3d$ x-ray transitions.

Electronic structure, bonding, charge distribution, and x-ray absorption spectra of the (001) surfaces of fluorapatite and hydroxyapatite from first principles

Abstract: Fluorapatite (FAP) and hydroxyapatite (HAP) are two very important bioceramic crystals. The (001) surfaces of FAP and HAP crystals are studied by ab initio density functional calculations using a supercell slab geometry. It is shown that in both crystals, the O-terminated (001) surface is more stable with calculated surface energies of 0.865 and $0.871\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2}$ for FAP and HAP, respectively. In FAP, the two surfaces are symmetric. In HAP, the orientation of the OH group along the $c$ axis reduces the symmetry such that the top and bottom surfaces are no longer symmetric. It is revealed that the atoms near the surface and subsurface are significantly relaxed especially in the case of HAP. The largest relaxations occurred via the lateral movements of the O ions at the subsurface level. The electronic structures of the surface models in the form of layer-by-layer resolved partial density of states for all the atoms show systematic variation from the surface region toward the bulk region. The calculated Mulliken effective charge on each type of atom and the bond order values between cations (Ca, P) and anions (O, F) show different charge transfers and bond strength variations from the bulk crystal values. Electron charge density calculations show that the surfaces of both FAP and HAP crystals are mostly positively charged due to the presence of Ca ions at the surface. The positively charged surfaces have implications for the absorption on apatite surfaces of water and other organic molecules in an aqueous environment which are an important part of its bioactivity. The x-ray absorption near-edge structure (XANES) spectra ($\mathrm{Ca}\text{\ensuremath{-}}K$, $\mathrm{O}\text{\ensuremath{-}}K$, $\mathrm{F}\text{\ensuremath{-}}K$, $\mathrm{P}\text{\ensuremath{-}}K$, and $\mathrm{P}\text{\ensuremath{-}}{L}_{3}$ edges) of both the surface models and the bulk crystals are calculated and compared. The calculations use a supercell approach which takes into account the electron--core-hole interaction. It is shown that the site-specific XANES spectra show significant differences between atoms near the surface and in the bulk and are very sensitive to the local atomic environment of each atom. This information will be very valuable for characterizing the apatite materials and in the interpretation of experimental data. Comparisons of several sets of experimental data with the weighted sums of the calculated spectra at different sites for the same element show very good agreement.

Forging the link between nuclear reactions and nuclear structure.

Abstract: A comprehensive description of all single-particle properties associated with the nucleus $^{40}\mathrm{Ca}$ is generated by employing a nonlocal dispersive optical potential capable of simultaneously reproducing all relevant data above and below the Fermi energy. The introduction of nonlocality in the absorptive potentials yields equivalent elastic differential cross sections as compared to local versions but changes the absorption profile as a function of angular momentum suggesting important consequences for the analysis of nuclear reactions. Below the Fermi energy, nonlocality is essential to allow for an accurate representation of particle number and the nuclear charge density. Spectral properties implied by ($e$, ${e}^{\ensuremath{'}}p$) and ($p$, $2p$) reactions are correctly incorporated, including the energy distribution of about 10% high-momentum nucleons, as experimentally determined by data from Jefferson Lab. These high-momentum nucleons provide a substantial contribution to the energy of the ground state, indicating a residual attractive contribution from higher-body interactions for $^{40}\mathrm{Ca}$ of about $0.64\text{ }\text{ }\mathrm{MeV}/\mathrm{A}$.

Detection of optical trapping of CdTe quantum dots by two-photon-induced luminescence

Abstract: Nanometer-sized CdTe quantum dots (QDs) in ${\mathrm{D}}_{2}\mathrm{O}$ can be optically trapped by a high repetition-rate picosecond Nd:YLF laser with an input power as low as $100\phantom{\rule{0.3em}{0ex}}\mathrm{mW}$. A large two-photon absorption (TPA) cross section of ${10}^{4}--{10}^{5}\phantom{\rule{0.3em}{0ex}}\mathrm{GM}$ for CdTe QDs makes it possible to detect the trapping process with TPA induced luminescence. In ${\mathrm{D}}_{2}\mathrm{O}$, the luminescence intensity of CdTe QDs was found to increase with time, whereas an intensity decrease was clearly detected in ${\mathrm{H}}_{2}\mathrm{O}$. In addition, the optically trapped CdTe QDs were fixed on a hydrophilic glass substrate. Laser trapping of QDs may provide a basic technique for quantum information and biological applications.