Optical properties of doubly doped ZnO phosphors co-activated with lithium ions

Time-resolved laser-induced optical properties of didymium (a mixture of neodymium and praseodymium) doped zinc oxide phosphors have been studied using nitrogen laser as an excitation source at room as well as at liquid nitrogen temperatures. A comparison of optical properties (oscillator strength and dipole-moment) at room temperature and liquid nitrogen temperature has been done and is reported in this article. It is found that oscillator strength and dipole-moment values for doped ZnO are increasing with decreasing temperature. The increasing trend of the optical parameters obtained at liquid nitrogen temperature of the doped phosphors indicates increase in efficiency.     

Magnetic and electric studies of a new Co(II) perovskite-like material

Structural phase transitions in the perovskite-like material [(CH₄)₁₂(NH₃)₂]CoCl₄ have been observed using differential thermal scanning. The material shows an order-disorder transition at T ₁ = 396 ± 5 K with entropy, (ΔS ₁) = 12.8 J/mole/K. A "chain melting" transition with a major endothermic peak at T ₂ = 337 ± 3 K and a minor one at T ′ = 316 ± 2 K, has total entropy ΔS = 28 J/mole/K. At low temperatures, the transitions at T ₃ = 288 ± 3 K and at T ₄ = 188 ± 3 K, have entropies of ΔS ₃ = 14.4 J/mole/K and ΔS ₄ = 2.6 J/mole/K respectively. AC magnetic susceptibility in the temperature range 78-290 K, in a magnetic field of 160 A/m and at a frequency of 320 Hz is presented. The results indicate changes in symmetry at 188 K. Dielectric permittivity has been studied as a function of temperature in the range 300-430 K and frequency range (60 Hz-100 kHz), confirming the observed transitions. The dielectric permittivity reflects rotational and conformational transition for the material. The variation of the real part of the conductivity with temperature is thermally activated with different activation energies in the range of ionic hopping. The temperature dependence of the dc conductivity and that of the ions hopping rate have indicated that the concentration of mobile ions is independent of temperature. The dependence of the conductivity on frequency follows the universal power law, <artwork name="GPHT31040ei1"> in the temperature range 340 K<T<390 K. Values 0 <s ₁ <1 dominate at low frequency and correspond to translational hopping motion and values 1<s ₂<2 dominate at high frequencies and correspond to well localized hopping and/or reorientational motion. For T > 396 K, the AC conductivity was fitted to <artwork name="GPHT31040ei2"> with 0<s<1. Comparison with the corresponding Cu-containing material is discussed.     

Nodal and multiple constant sign solutions for resonant -Laplacian equations with a nonsmooth potential

In this paper we study a nonlinear Dirichlet elliptic differential equation driven by the p-Laplacian and with a nonsmooth potential (hemivariational inequality). Using a variational approach combined with suitable truncation techniques and the method of upper–lower solutions, we prove the existence of five nontrivial smooth solutions, two positive, two negative and the fifth nodal. Our hypotheses on the nonsmooth potential allow resonance at infinity with respect to the principal eigenvalue λ₁>0 of .     

A spectral radius formula for the Fourier transform on compact groups and applications to random walks

Let G be a compact group, not necessarily abelian, let ? be its unitary dual, and for f∈L¹(G), let fn?f∗?∗f denote n-fold convolution of f with itself and f? the Fourier transform of f. In this paper, we derive the following spectral radius formula

     

Uniqueness for isotropic diffusions with a linear drift

This paper proves that-valued solutions to the SDE are unique in distribution, when D^d is convex and open, D, c>0, is positive and locally Lipschitz on D and zero on D, and {xD:g(x)r} is convex for r sufficiently small. The proof (for =0) is based on the transformation X_te^ctX_t, which removes the drift, and a random time change. Although the set-up is rather specialized the result gives uniqueness for some SDEs that cannot be treated by any of the conventional techniques.Mathematics Subject Classification (2000):60J60, 60H10     

New approach to stereochemical structure determination of bis-selenium-subsituted alkenes

A new approach to determination of the stereochemical structure of bis-selenium-substituted alkenes using experimental ⁷⁷Se NMR studies and B3LYP/6-311G(d) quantum-chemical calculations is developed. Joint analysis of experimental and calculated data allows assignment of signals in the ⁷⁷Se NMR spectrum. The method was evaluated taking the model compounds (PhSe)HC=C(SePh)R (R = COOMe, CH₂NMe₂, CH₂OH, Ph) as examples.     

Online identification of the fluorescent whitening agent 4,4-bis(2-sulfostyrol)biphenyl using a sweeping technique combined with capillary electrophoresis/77 K fluorescence spectroscopy

The feasibility of combining the techniques of online concentration and CE/low-temperature fluorescence spectroscopy in the detection and identification of E,E-4,4'-bis(2-sulfostyryl)biphenyl (DSBP) in synthetic detergents at 77 K is demonstrated. The technique involves the use of sweeping-MEKC, and was used for the initial online concentration and separation, after which a cryogenic molecular fluorescence experiment was performed at 77 K. The proposed method not only permits the separation and detection of E,E-DSBP in a synthetic detergent sample, but also ensures that the online spectrum is readily distinguishable and can be unambiguously assigned at 77 K. The photoconversion and isomer separation of DSBP are also described.     

Thermal Stability and Decomposition Kinetics of the β-CD Cinnamic Aldehyde Inclusion Complex

The stability of the -CD cinnamic aldehyde inclusion complex wasinvestigated by TG and DSC. The weight loss takes place in three stages:dehydration occurs at 50–120 °C; the dissociationof -CDC₉H₈O occurs at 200–260 °C;and the decomposition of -CD begins at 280 °C. Thekinetics of the dissociation of cinnamic aldehyde from the -CD cavitywere studied by means of thermogravimetry both at constant temperatureand linear increasing temperature. The results show that the dissociationof -CDC9H8O is dominated by a one-dimensional diffusionprocess. The activation energy, E, is 160 kJmol-1. Thepre-exponential factor A is 5.8 × 1014 min-1.     

Darstellung und spektroskopische Charakterisierung von bindungsisomeren Halogenoselenocyanato-Osmaten(IV) und -Rhenaten(IV)

Preparation and Spectroscopic Characterization of Bond Isomeric Halogenoselenocyanato-Osmates(IV) and -Rhenates(IV) By oxidative ligand exchange of appropriate chloro-iodo complexes of Os^IV or Re^IV with (SeCN)₂ in CH₂Cl₂ or by heterogeneous reaction with Pb(SeCN)₂ or AgSeCN in CH₂Cl₂ the new complexes cis-[OsCl₄(NCSe)(SeCN)]^2?, tr.-[OsCl₄Br(NCSe)]^2?, tr.-[OsCl₄Br(SeCN)]^2?, [ReCl₅(NCSe)]^2?, [ReCl₅(SeCN)]^2?, tr.-[ReCl₄I(NCSe)]^2?, tr.?[ReCl₄(NCSe)(SeCN)]^2? and tr.?[ReCl₄(NCSe)₂]^2? are formed and isolated as pure compounds by ion exchange chromatography on DEAE-cellulose. The bond isomers are significantly distinguished by the frequencies of innerligand vibrations: n?_CN(Se) > n?_CN(N); n?_CSe(N) > n?_CSe(Se); δ_NCSe > δ_SeCN. The electronic spectra (10 K) of the solid salts reveal a bathochromic shift for the charge transfer bands of the Se isomers as compared with the corresponding N isomers. The intra-configurational transitions are observed for the Os^IV complexes at 600 to 2400 and for the Re^IV complexes at 500 to 1600 nm. The ⁷⁷Se nmr signals of the Os^IV bond isomers are registrated for Se binding in the region 970 to 1040 ppm, for N coordination downfield at 1540 to 1640 ppm.