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61.
62.
The stilbene-3 doped lead-tin-fluorophosphate glasses were successfully prepared and the luminescence spectra obtained from VUV-UV synchrotron radiation were investigated. The emission peaked about 440 nm from the undoped glass is observed at low temperature but quenches at room temperature. The doped glass exhibits strong characteristic emission of stilbenen-3 with 467 and 436 nm Gaussian bands under ultraviolet 250-330 nm excitation (characteristic excitation of stilbene-3) but weak emission under vacuum ultraviolet 190 nm excitation (host excitation). It is suggested that the energy transfer from host to the stilbene-3 dye can occur but the efficiency is still fairly low. 相似文献
63.
We studied viscoelastic properties and scaling behavior of multilamellar vesicles (MLVs) confined between two parallel plates
as a function of the shear rate and sample thickness (gap size between parallel plates). The rheological properties are classified
into two regimes; the shear-thinning regime at high shear rates and the shear-thickening regime at low shear rates. In the
former, the MLV radius results from the mechanical balance between the effective surface tension σeff and viscous stress force. The MLV radius is independent of the gap size. σeff estimated by van der Linden model is 2.1 ±0.15 ×10-4 Nm-1 corresponding to the same value obtained by SANS measurement. Power law exponents for the steady state viscosity and yield
stress against pre-shear rate (
,
) well agree with prediction based on the layering of membranes. Therefore, viscoelastic properties in this regime could be
modeled by assuming that the dynamics of MLVs are driven by layering of MLV polydomains, which could be accompanied by the
viscous dissipation, i.e., the stress relaxation on the MLV, induced by continuous sequence of yields of MLVs. The flow curve is empirically explained
by the assumption of a relaxation time for the MLV shape. In the latter, however, scaling laws observed in the shear-thinning
regime break down. The MLV radius increases when the gap size is reduced below the threshold value and MLV is no longer formed
at very small gap sizes. Different dynamics from the shear-thinning regime seem to dominate the viscoelasticity. 相似文献
64.
We report on the rheology of a lyotropic lamellar surfactant solution (SDS/dodecane/pentanol/ water), and identify a discontinuous
transition between two shear thinning regimes which correspond to the low-stress lamellar phase and the more viscous shear-induced
multilamellar vesicle, or “onion” phase. We study in detail the flow curve, stress as a function of shear rate, during the
transition region, and present evidence that the region consists of a shear-banded phase where the material has macroscopically
separated into bands of lamellae and onions stacked in the vorticity direction. We infer very slow and irregular transformations
from lamellae to onions as the stress is increased through the two-phase region, and identify distinct events consistent with
the nucleation of small fractions of onions that coexist with sheared lamellae. 相似文献
65.
Sommer JU 《The European physical journal. E, Soft matter》2006,19(4):413-422
The equilibrium state of polymer single crystals is considered by explicitly taking into account the amorphous fraction formed
by loops and tails of the chains using a statistical model introduced by Muthukumar (Philos. Trans. R. Soc. London, Ser. A
361, 539 (2003)). We show that under realistic conditions below the equilibrium melting temperature, tight loops and close re-entries
are favored, and that the amorphous fraction can be mapped into an excess surface free energy. The model is extended to many-chain
crystals where it is shown that the lamellar thickness increases with the number of chains in the crystal and extended-chain
conformations are thermodynamically favored if the number of chains in the crystal is sufficiently large. The number of chains
necessary to form an extended-chain crystal in thermodynamic equilibrium scales with the square of the degree of polymerization
of the chains. We discuss the temperature behavior of the equilibrium crystal thickness in the under-cooled state. 相似文献
66.
Reactive magnetron co-sputtering of two confocal SiO2 and Er2O3 cathodes in argon-hydrogen plasma was used to deposit Er-doped Si-rich SiO2 layers. The effects of the deposition conditions (such as RF power applied on each cathode and total plasma pressure) and annealing treatment (temperature and duration) on structural, compositional and photoluminescence (PL) properties of the layers were examined. It was found that a significant enhancement of both Er3+ PL intensity and emission lifetime up to 9 ms have been reached through monitoring of the conditions of both deposition process and annealing treatment. The effective absorption cross section and the fraction of Er ions coupled to Si clusters were analyzed. It was shown an increase of the fraction of Er3+ ions coupled to Si up to 11%. 相似文献
67.
Transmission spectra (400–1500 nm) of thermally evaporated amorphous [(As2Se3)90Ge10]95M5 thin films have been analyzed to study the effect of impurities (M = Cd and Pb) on their optical properties. The refractive
index increases with addition of metal impurities. The dispersion of refractive index has been studied using Wemple–DiDomenico
single oscillator model. The optical gap has been estimated using Tauc’s extrapolation and was found to decrease with the
addition of metal impurities from 1.46 to 1.36 eV (Cd) and 1.41 eV (Pb) with an uncertainty of ±0.01 eV. The change in optical
properties with metal impurities has been explained on the basis of density, polarizability and bond energy of the system. 相似文献
68.
X. Liu S. Ye Y. Qiao G. Dong B. Zhu D. Chen G. Lakshminarayana J. Qiu 《Applied physics. B, Lasers and optics》2009,96(1):51-55
In the present paper, we investigate the near-infrared (NIR) luminescence of Tb3+–Yb3+ codoped lanthanum borogermanate (LBG) glasses under visible and ultraviolet light excitation. The results indicate that NIR
quantum cutting occurs through cooperative energy transfer from Tb3+ to Yb3+ ions when only 4f
8 levels of Tb3+ ions are excited in the wavelength region of 300–490 nm. The highest quantum efficiency under the excitation 5
D
4 level of Tb3+ at 484 nm is 146%. Ultraviolet excitation that populates the charge transfer band (CTB) of Yb3+ near 270 nm does not result in quantum cutting as the fast nonradiative decay from CTB to 2
F
5/2 level dominates. These materials are expected to be used as a converting layer for silicon solar cells to enhance their efficiency
by splitting each high-energy photon into two NIR photons. 相似文献
69.
ZnO–CuO core–shell nanorods and CuO-nanoparticle–ZnO-nanorod integrated structures were synthesized for the first time by
a two-stage solution process. Scanning electron microscopy and high-resolution transmission electron microscopy show that
the diameter and the length of the nanorods are around 60 and 800 nm, respectively. The morphologies of outer CuO could be
varied from nanoparticles to nanoshells by adjusting the solvent and dipping processes of copper (II) nitrate solution. The
CuO nanoparticles are single-crystalline or highly textured structures with size of around 30 nm. The CuO shell with thickness
of around 10 nm is constructed of nanocrystals with sizes in the range of 3–10 nm embedded in an amorphous matrix. Room-temperature
cathodoluminescence measurements of the CuO–ZnO nanocomposites exhibit relatively sharp ultraviolet emissions at 380 nm as
well as broad green and yellow emissions at 500 and 585 nm. The p-CuO/n-ZnO one-dimensional nanocomposites are promising for
optoelectronic nanodevice applications. 相似文献
70.
F. Lahoz P. Haro-Gonzalez F. Rivera-López S. González-Pérez I. R. Martín N. E. Capuj C. N. Afonso J. Gonzalo J. Fernández R. Balda 《Applied Physics A: Materials Science & Processing》2008,93(3):621-625
Thin films of Er3+-doped lead–niobium germanate have been produced by pulsed laser deposition from Er3+-doped 25PbO2–25Nb2O5–50GeO2 (mol%) transparent glasses with an Er content in the range 0.5–3 wt%. The room-temperature infrared to visible upconversion
properties of these thin films have been investigated under 800-nm laser excitation. An energy transfer upconversion mechanism
has been identified to be responsible for the population of the 4S3/2:2H11/2 excited level, from which an intense green emission occurs. A rate equation analysis supports the proposed mechanism. 相似文献