Melt Flow Type and Physical Model of Semisolid Rheo-Casting Process by Cooling Sloping Plate

In this paper, a physical model of semisolid rheo-casting process by cooling sloping plate is established, and the features and parameters of this process are analyzed. The calculation results show that there exists lamellar flow and turbulent flow on the sloping plate surface commonly. The critical transfer distance from lamellar flow to turbulent flow decreases with the increment of the initial flow velocity gradually. The critical transfer distance decreases with the increment of the sloping angle slowly. The effect of the sloping angle on the critical transfer distance is relatively not obvious.

Neutron Rietveld Analysis for Optimized CaMgSi2O6:Eu2+ and its Luminescent Properties

We optimized synthesis conditions of blue-emitting CaMgSi2O6:Eu2+ (CMS:Eu2+) with conventional solid-state reaction and successfully determined structure parameters by Rietveld refinement method with neutron powder diffraction data. The final weighted R-factor Rwp was 6.42% and the goodness-of-fit indicator S (= Rwp/Re) was 1.34. The refined lattice parameters of CMS:Eu2+ were a = 9.7472(3) Å, b = 8.9394(2) Å, and c = 5.2484(1) Å. The β angle was 105.87(1)°. The concentration quenching process was observed, and the critical quenching concentration of Eu2+ in CMS:Eu2+ was about 0.01 mol and critical transfer distance was calculated as 12 Å. With the help of the Rietveld refinement and Dexter theory, the critical transfer distance was also calculated as 27 Å. In addition, the dominant multipolar interaction of CMS:Eu2+ was investigated from the relationship between the emission intensity per activator concentration and activator concentration. The dipole–dipole interaction was a dominant energy transfer mechanism of electric multipolar character of CMS:Eu2+.

1,4-Bis (β-Pyridyl-2-Vinyl) Benzene (P2VB) and 2,5-Distyryl-pyrazine (DSP) as Blue Laser Dyes

Solutions of P2VB and DSP in dimethyl-sulphoxide (DMSO) of concentration ca. 10–3 M/l act as laser dyes on pumping with nitrogen laser. P2VB and DSP are lasing in the ranges 390–440 nm (λmax = 416 nm) and 435–465 nm (λmax = 447 nm) respectively. An equimolar mixture of P2VB and DSP behaves as an energy transfer dye laser (ETDL) and is lasing in the range 429–455 nm (λmax = 438 nm). Such ETDL system obeys a long range coulombic energy transfer mechanism with a critical transfer distance R0 = 7.5 nm.The fluorescence quantum yields of both dyes have been measured, and in DMSO φf = 0.46 and 0.35 for P2VB and DSP respectively.Both dyes show a remarkable photostability upon nitrogen laser excitation. This has been attributed to the role of the 337 nm light in inducing a back photo-chemical reaction of the initially formed photoproducts consisting mainly of photo-oligomers and cis-photoisomers.

Interactions between Rhodamine B and wool. Analysis of luminescence quenching and energy transfer

A reflectance technique is described for quantitatively analysing the luminescence behaviour of wool in the presence of a dye, rhodamine B. The bound dye exhibits delayed fluorescence which is sensitized by one of the two naturally occurring phosphorescent groups in wool. At low dye concentrations the phosphorescence of wool is quenched mainly by simple optical screening and radiative transfer of energy from the donor phosphorescent group to the dye, but radiationless dipole-dipole T → S transfer becomes the predominant quenching process at high dye concentrations. This process is characterized by a critical transfer distance ro of 5�0-5�3 nm. The fluorescence of wool is quenched only slightly by rhodamine B. The results indicate that optical screening and radiative energy transfer are the most important factors in the fluorescence quenching, and that radiationless dipole-dipole S → S transfer has a negligible effect on the fluorescence.

Die Zeitabhängigkeit der Emissionsanisotropie, gemessen an 9-Methylanthracen in Azetylzellulosefolie / The Time Dependent Emission Anisotropy of 9-methylanthracene

The time dependence of the emission anisotropy r(t) after linearly polarised impulse excitation gives information about the intermolecular energy transfer. According to the usual theory of the energy transfer between donors and acceptors - neglecting remigration - ln r/r0 should depend linearly on √t/τ. The measurements on 9-methylanthracene in foiles of acetylcellulose are in agreement with this prediction if one takes a second thermally conditioned depolarisation com­ ponent into consideration. From the slope of the experimental plot a critical transfer distance of 24.2 Å is obtained.