Luminescence in Organic Silicons Prepared from Organic Precursors in Plasma Discharges

Summary.  The photoluminescence of plasma-prepared polysilanes during the change from linear 1D Si chains to an amorphous 3D Si network was studied. The excitonic absorption band with a maximum at 353 nm in 1D Si experiences a blue shift and broadening upon introduction of branching and networking defects. With the gradual transition from 1D to 3D structure, an extensive redistribution of oscillator intensity along the absorption edge, accompanied by a decrease of the resolution of the σ-σ^* band, was observed. In the short wavelength region of the excitation spectra there is an enormous increase of excitonic emission at 328 nm. This effect is tentatively attributed to the excitation of the phenyl group or to the phenyl-silicon bond as confirmed by effusion spectra of the phenyl species. Received July 10, 2000. Accepted (revised) September 8, 2000     

Fast decomposition of biological and other materials for radiochemical activation analysis: A radiochemical study of element recoveries following alkaline-oxidative fusion

Recoveries of selected elements were studied for fast decomposition of biological and other materials using alkaline-oxidative fusion in a mixture of NaOH and Na₂O₂ at 850–900 °C. The procedure yields total mineralization of samples within 2 to 3 minutes. It is especially suitable in radiochemical activation analysis (RAA) for the determination of elements forming short-lived radionuclides. Recoveries of the elements F, Si, S, Cl, Ti, V, Mn, Ge, As, Br, Mo, Ru, In, Sb, I, Re, Os, and U determined using radiotracers were in the range 95–100%, while those for Se and Hg were significantly lower and highly variable.     

Silica coated quantum dots: a new tool for electrochemical and optical glucose detection

The application of silica coated quantum dots (QDs@SiO₂) in glucose detection in combination with glucose oxidase is reported. The high specific surface area of such particles can be exploited to immobilise a greater amount of the enzyme on a modified electrode. In addition to this electrochemical method, we report here an indirect optical technique based on the photoluminescence quenching of QDs by hydrogen peroxide produced during glucose oxidation. The results obtained with these two different detection methodologies are compared. Correspondence: Sara Cavaliere-Jaricot, Freiburg Materials Research Centre (FMF), Albert-Ludwig University Freiburg, Stefan-Meier-Strasse 21, D-79104 Freiburg, Germany     

Hyperbolic dynamics in graph-directed IFS

A cone space is a complete metric space (X,d) with a pair of functions cs,cu:X×X→R, such that there exists K>0 satisfying

     

Fluorine determination in biological and environmental samples with INAA using fast neutrons from a p(19 MeV) + Be neutron generator

Journal of Radioanalytical and Nuclear Chemistry - We present a new activation method based on the 19F(n,2n)18F reaction using fast neutrons produced by a p(19 MeV)?+?Be...     

Electrolytic behavior of SrCl2 and BaCl2 in LiCl molten salt during oxide reduction in pyroprocessing

Journal of Radioanalytical and Nuclear Chemistry - Ba and Sr elements in spent nuclear fuels are supposed to accumulate in LiCl molten salt electrolyte by forming chlorides (i.e., BaCl2, SrCl2)...     

Radiochemical separation of mostly short-lived neutron activation products

Journal of Radioanalytical and Nuclear Chemistry - It is demonstrated that radiochemical separation in neutron activation analysis (RNAA) is usually the most effective means of optimization of the...     

Optimal design of coupling waveguide structure for adiabatic optical directional full couplers weighted by sin-square and raised-cosine functions

The optimal design of coupling waveguide structure for adiabatic optical directional full couplers (AODFC) based on weighted sin-square function (SSF) and raised-cosine function (RCF) are investigated in this paper. The coupling lengths with a crosstalk smaller than −30 dB at the operating wavelength of 1.57 μm resulted in a value of 3.0 and 2.4 mm for the SSF and RCF cases, respectively. Under the same level of crosstalk, the wavelength ranges obtained by weighted SSF and RCF could be varied about 1.33-1.70 μm and 1.27-1.70 μm with coupler lengths of 6.0 and 5.5 mm, respectively. Clearly, the AODFC weighted by RCF has the superior performances of both short coupling length and broad wavelength ranges.     

Polarization of protons from the Be(d,p)Be reaction at Ed = 12.0 MeV

The polarization of protons from the ⁹Be(d,p)¹⁰Be reaction at E_d = 12.0 MeV was measured for the ground state and first excited state transitions. The results obtained are compared with the predictions of DWBA theory. It was found that better fits to the experimental data can be obtained using volume absorption in the distorting potential of the deuteron elastic channel. A comparison of the present polarization data with the vector analysing power for the same reaction and the same incident deuteron energy has also been made.     

Modification of MCM-48-, SBA-15-, MCF-, and MSU-type mesoporous silicas with transition metal oxides using the molecular designed dispersion method

Four various mesoporous silicas (MCM-48, SBA-15, MCF, and MSU) were modified by the molecular designed dispersion method using Fe(acac)3, Cr(acac)3, and Cu(acac)2 complexes. The deposition was performed at the same concentration of the metal acetylacetonate (acac) complex in a toluene solution. All as-synthesized samples were investigated by diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared photoacoustic spectroscopy, and thermogravimetric analysis. The calcined materials were studied with respect to their textural properties (Brunauer-Emmett-Teller adsorption isotherm) and chemical composition (electron microprobe analysis). It allowed elucidation of the mechanism of interaction between the acac complex and the silanol groups. For the MCM-48, SBA-15, and MCF materials, the formation of hydrogen bonding was found for the chromium- and copper-modified samples, whereas the Fe-containing materials showed the ligand exchange mechanism. The strong interaction of the MSU support and the different acetylacetonate complexes, resulting in a loss of at least one acac ligand, was observed. The mesoporous silicas modified with transition metal oxides were studied by UV-vis-DR spectroscopy. The different metal dispersions were found for the samples containing various transition metal oxides.