Impurity absorption of SrS-Ce3+ phosphors

We investigate the impurity absorption of SrS−Ce phosphors. For this purpose, we measure the spectra of diffuse reflection of powder phosphors. It is established that the introduction of Ce simultaneously with a coactivator gives rise to a strong absorption band at 2.88 eV, and the introduction of a coactivator (NH₄F, NH₄Cl, NH₄Br, NH₄I, LiCl, NaCl or KCl), to an absorption band at about 2.36 eV. We assume that the absorption band at 2.88 eV is caused by that portion of Ce introduced that forms the center of luminescence of Ce³⁺. Tartu University, Estonian, Republic, 18, Yulikooli St., Tartu, EE2400, Estonia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 542–544, July–August, 1997.     

Evaluating the COSMO‐RS Method for Modeling Hydrogen Bonding in Solution

The ability of the Conductor‐like Screening Model for Realistic Solvation (COSMO‐RS) computational method to model hydrogen bond (HB) formation in solution is examined by comparing computational data with experimental data from literature. This is the first study of this kind where mixed solvents are also involved. Hydrogen bond formation is examined between neutral molecules, between acids and their anions, and between various anion receptor molecules and different anions in a number of aprotic solvents. HB formation equilibrium constants, the corresponding Gibbs’ free energies and, when available from the literature, enthalpies were calculated. The supermolecule (SM) approach and the contact probability (CP) approach were used. Both in the case of the SM and CP approach, good to very good correlations between the experiment and computations are found for complexes formed from neutral species, enabling quantitative predictions. When the HB acceptor is an anion, the correlations are poor and in some cases even qualitative predictions fail.     

Structural and infrared properties of zinc oxide film and nanowires

The structural and infrared properties of the highly (00.2) oriented ZnO film, randomly grown Au-catalyzed ZnO nanowires (NWs) and vertically aligned self-catalyzed ZnO NWs were compared. In the XRD analysis, (0 0 2) diffraction intensity of self-catalyzed ZnO NWs was enhanced mainly attributed to the preferential growth of NWs in [0 0 0 1] as compared to the ZnO film and the randomly grown Au-catalyzed ZnO NWs. The high UV-to-green emission ratio of self-catalyzed ZnO NWs in room temperature PL measurement indicates that they had a better crystal quality as compared to Au-catalyzed ZnO NWs and ZnO film. Infrared spectroscopy has been used to characterize these films and nanowires too. The phonon peak 407 cm⁻¹ which related to the transverse optical (TO) vibrations perpendicular to the optical axis was observed in the IR reflectivity measurements on the highly c-oriented ZnO film. The IR peaks that appeared in the 550–580 cm⁻¹ region of the spectra of the specimens could be assigned to the ZnO NWs as it was not observed in the ZnO film. These peaks were observed in the 550–580 cm⁻¹ region in both s- and p-polarized light for the randomly grown Au-catalyzed ZnO NWs. In contrast, the IR peak at 580 cm⁻¹ was clearly shown in p-polarized light but not in the s-polarized light for vertically aligned ZnO NWs. This indicated that the vibration was polarized along the vertically aligned ZnO NWs. The (00.2) orientation of the ZnO specimens could be identified by comparing the p- and s-polarized IR spectra.     

Experimental evaluation of the effect of a modified port‐location mode on the performance of a three‐zone simulated moving‐bed process for the separation of valine and isoleucine

The removal of isoleucine from valine has been a key issue in the stage of valine crystallization, which is the final step in the valine production process in industry. To address this issue, a three‐zone simulated moving‐bed (SMB) process for the separation of valine and isoleucine has been developed previously. However, the previous process, which was based on a classical port‐location mode, had some limitations in throughput and valine product concentration. In this study, a three‐zone SMB process based on a modified port‐location mode was applied to the separation of valine and isoleucine for the purpose of making a marked improvement in throughput and valine product concentration. Computer simulations and a lab‐scale process experiment showed that the modified three‐zone SMB for valine separation led to >65% higher throughput and >160% higher valine concentration compared to the previous three‐zone SMB for the same separation.     

An internal standard method for the determination of trace elements in cigarette tobacco by neutron activation analysis

An internal standard method has been applied for the determination of lanthanum, antimony, scandium, chromium, iron and cobalt in commercial cigarettes by neutron activation analysis using gold as an internal standard element. These trace elements were separated from irradiated samples by APDC (ammonium pyrrolidine dithiocarbamate)/Zeph (tetradecyl dimethyl benzyl ammonium chloride) coprecipitation, followed by direct gamma-counting of the separated precipitate using a Ge(Li) detector. Standard reference tobacco 1R1 prepared by the University of Kentucky was also analyzed by this procedure for the above 6 elements, the results of which were compared with literature values. Good results were obtained by the present method.     

Two-dimensional guided mode resonance filters fabricated in a uniform low-index material system

We demonstrate the fabrication, simulation, and experimental results of a buried, homogeneous narrowband spectral filter with a periodic, hexagonal unit cell of air pockets, encapsulated in a fused silica substrate. The leaky waveguide is formed by depositing SiO(x) on an etched fused silica grating via plasma-enhanced chemical vapor deposition. Design principles of guided mode resonance filters were utilized to achieve a resonance with 60% reflectivity at a wavelength of 1.741 μm. The device demonstrates resonance with FWHM of 6 nm.