Search results for "absorption."

Unraveling exciton dynamics in amorphous silicon dioxide: Interpretation of the optical features from 8 to 11 eV.

2011

Physical review / B 83, 174201 (2011). doi:10.1103/PhysRevB.83.174201

Theory of bound polarons in oxide compounds

2001

We present a multilateral theoretical study of bound polarons in oxide compounds MgO and \alpha-Al_2O_3 (corundum). A continuum theory at arbitrary electron-phonon coupling is used for calculation of the energies of thermal dissociation, photoionization (optically induced release of an electron (hole) from the ground self-consistent state), as well as optical absorption to the non-relaxed excited states. Unlike the case of free strong-coupling polarons, where the ratio \kappa of the photoionization energy to the thermal dissociation energy was shown to be always equal to 3, here this ratio depends on the Froehlich coupling constant \alpha and the screened Coulomb interaction strength \beta.…

Comment on "Total Cross Section for Photon Absorption by Two Protons inHe3"

1995

Impact of crystal quality, geometry and surface finish for 3D impact position measurements in gamma ray detection systems

2007

We have studied several ways of optimizing the 3D impact position measurements for gamma ray imaging detectors based on continuous monolithic large sized and thick scintillation crystals. The readout of such detectors is performed with position sensitive photo multipliers and with a depth of interaction (DOI) enhanced charge division readout. We have studied the effect of the crystal truncation angle, the reflective covering and the absorption and scattering mean free paths of the crystal. In particular, we have simulated and measured the impact on the energy resolution and the 3D spatial resolution. The results show that by optimization of the accessible crystal parameters we can enhance t…

Impact of the scattering coefficient of scintillation crystals (LYSO and LSO) on depth of interaction resolution

2008

Intrinsic parameters in scintillation crystals play a crucial role in the measured spatial and energy resolutions. In many cases the measurement of these intrinsic parameters is difficult to be carried out or even there are parameters that need a specific setup to be measured directly, e.g. the intrinsic light yield and the absorption and scattering coefficients. These uncertainties in the parametrization of the characteristics of the scintillation crystals make it quite difficult to evaluate the quality and characteristics of the scintillation crystals and their impact on the resolutions. Results of measurements of depth of interaction and its resolutions for three different scintillation …

XAFS study of interchain and intrachain order inSe1−xTexglasses: Nearest neighbors

1998

XAFS measurements (LURE and NSLS) of ${\mathrm{Se}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ glasses have been carried out on both the Se and Te $K$ edges at low and room temperatures. Using a multishell best-fit analysis procedure, we have reconstructed the Se and Te local environment: first-shell intrachain nearest neighbors $(\mathrm{Se}\ensuremath{-}{\mathrm{Se}}_{1}, \mathrm{Se}\ensuremath{-}{\mathrm{Te}}_{1}, \mathrm{Te}\ensuremath{-}{\mathrm{Se}}_{1},$ and $\mathrm{Te}\ensuremath{-}{\mathrm{Te}}_{1}).$ We conclude that the intrachain chemical order (preferential of Se-Te pairs) increases with Te content in the glasses. On the other hand, we suggest a random distribution of Se and Te atom…

Local structure aroundEr3+inSiO2−HfO2glassy waveguides using EXAFS

2007

${\mathrm{Er}}^{3+}$-doped $\mathrm{Si}{\mathrm{O}}_{2}\text{\ensuremath{-}}\mathrm{Hf}{\mathrm{O}}_{2}$ glassy waveguides with $\mathrm{Hf}{\mathrm{O}}_{2}$ concentrations ranging from $10\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}50\phantom{\rule{0.3em}{0ex}}\mathrm{mol}\phantom{\rule{0.2em}{0ex}}%$ were prepared using the sol-gel route and deposited on $v\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ substrates using the dip-coating technique. The local environment around ${\mathrm{Er}}^{3+}$ ions was determined from Er ${L}_{3}$-edge extended x-ray-absorption fine-structure (EXAFS) measurements. The first coordination shell around ${\mathrm{Er}}^{3+}$ ions is comp…

Optical absorption band at5.8eVassociated with theEγ′centers in amorphous silicon dioxide: Optical absorption and EPR measurements

2008

Line shape modifications induced by thermal treatment in the optical absorption and electron paramagnetic resonance (EPR) signals associated with the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center are experimentally investigated in various types of $\ensuremath{\gamma}$-irradiated amorphous silicon dioxide $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$. The $g$ values of the EPR main resonance line of the ${E}_{\ensuremath{\gamma}}^{\ensuremath{'}}$ center show a shift correlated with the peak energy variation of the absorption band at about $5.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ associated with this defect. These spectroscopic changes are proposed to originate from structu…

Line strengths of the ν2 + ν3 and ν3 − ν2 bands of methane (12CH4)

1992

Abstract The individual linestrengths of two related bands of 12 CH 4 , ν 2 + ν 3 near 4545 cm −1 and ν 3 − ν 2 near 1484 cm −1 , were measured with accuracies of 3% and 5%, respectively. In the analysis, an eight-term expansion of the dipole moment through second order was required to fit the strengths of transitions up to J ′ = 10 in ν 2 + ν 3 and J ′ = 12 in ν 3 − ν 2 and to explain the considerable perturbations observed. Application of this model reduced the rms deviations from 68% (zero-order) to 6.3% with the 248 selected lines of ν 2 + ν 2 and from 37% to 5.8% with 186 lines of ν 3 − ν 2 . The integrated bandstrengths for the two bands, respectively, are 1.84(5) and 0.0085(4) cm −2 …

Solvation of triplet Rydberg states of molecular hydrogen in superfluid helium

2004

We report ab initio interaction potentials, transition dipole moments, and radiative lifetimes for the four lowest triplet states of ${\mathrm{H}}_{2}:$ $b$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+},$ $c$ ${}^{3}{\ensuremath{\Pi}}_{u},$ $a$ ${}^{3}{\ensuremath{\Sigma}}_{g}^{+},$ and $e$ ${}^{3}{\ensuremath{\Sigma}}_{u}^{+},$ and their response to the perturbation due to approaching ground state He atom. Hybrid density functional\char21{}quantum Monte Carlo calculations employing the ab initio interaction potentials are then used for calculating the liquid structure around the molecular excimers in bulk superfluid ${}^{4}\mathrm{He}.$ Calculations demonstrate a wide variety of possible solvation …