Spectroscopic properties of Er(3+)/Yb(3+) co-doped Bi(2)O(3)-B(2)O(3)-GeO(2) glasses

Er(3+)/Yb(3+) co-doped 60Bi(2)O(3)-(40 - x)B(2)O(3)-xGeO(2) (BBG; x=0, 5, 10, 15 mol%) glasses that are suitable for fiber lasers, amplifiers have been fabricated and characterized. The absorption spectra, emission spectra, and lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition were measured and calculated. With the substitution of GeO(2) for B(2)O(3), both Delta lambda(eff) and sigma(e) decrease from 75 to 71 nm and 9.88 to 8.12 x 10(-21) cm(2), respectively. The measured lifetime of the (4)I(13/2) level and quantum efficiency of Er(3+):(4)I(13/2) --> (4)I(15/2) transition increase from 1.18 to 1.5 ms and 36.2% to 43.2%, respectively. The emission spectra of Er(3+):(4)I(13/2) --> (4)I(15/2) transition was also analyzed using a peak-fit routine, and an equivalent four-level system was proposed to estimate the stark splitting for the (4)I(15/2) and (4)I(13/2) levels of Er(3+) in the BBG glasses. The results indicate that the (4)I(13/2) --> (4)I(15/2) emission of Er(3+) can be exhibit a considerable broadening due to a significant enhance the peak A, and D emission.     

Spectroscopic properties and thermal stability of Er3+ -doped TeO2-B2O3-Nb2O5-ZnO glass for potential WDM amplifier

A series of novel 70TeO2-(15-x)B2O3-xNb2O5-15ZnO-1wt.% Er2O3 (TBN x=0, 3, 6, 9, 12 and 15 mol%) tellurite glasses were prepared. The thermal stability, absorption spectra, emission spectra, and the lifetime of the (4)I(13/2) level of Er(3+) ions were measured and investigated. Three Judd-Ofelt intensity parameters Omega(t) (t=2, 4 and 6) (Omega(2)=(5.42-6.76)x10(-20)cm(2); Omega(4)=(1.37-1.73)x10(-20)cm(2); Omega(6)=(0.70-0.94)x10(-20)cm(2)) of Er(3+) ions were calculated by Judd-Ofelt theory. It is found that the Omega(6) first increases with the increase of Nb2O5 content from 0 to 6 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section (sigma(e)(peak)=(0.77-0.91)x10(-20)cm(2)) of Er(3+): (4)I(13/2)-->(4)I(15/2) transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=65-73 nm) of the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions were measured. The results indicate that these new TBN glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Quenching of I(2P1/2) by NO2, N2O4, and N2O

Quenching of excited iodine atoms (I(5p5, 2P1/2)) by nitrogen oxides are processes of relevance to discharge-driven oxygen iodine lasers. Rate constants at ambient and elevated temperatures (293-380 K) for quenching of I(2P1/2) atoms by NO2, N2O4, and N2O have been measured using time-resolved I(2P1/2) --> I(2P3/2) 1315 nm emission. The excited atoms were generated by pulsed laser photodissociation of CF3I at 248 nm. The rate constants for I(2P1/2) quenching by NO2 and N2O were found to be independent of temperature over the range examined with average values of (2.9 +/- 0.3) x 10(-15) and (1.4 +/- 0.1) x 10(-15) cm3 s(-1), respectively. The rate constant for quenching of I(2P1/2) by N2O4 was found to be (3.5 +/- 0.5) x 10(-13) cm3 s(-1) at ambient temperature.     

Inter- and intraconfigurational transitions of Nd3+ in hexafluoroelpasolite lattices

Excitation of the 4f3 ion Nd3+ in hexafluoroelpasolite lattices by synchrotron radiation of wavelength approximately 185 nm leads to fast 4f(2)5d --> 4f3 emission below 52,630 cm(-1) and slower 4f3 --> 4f3 emission from the luminescent states (4)F(3/2) gamma8u (11 524 cm(-1)) and 2G2(9/2) gamma8u (approximately 47,500 cm(-1)). The near-infrared emission is well-resolved, and a clear interpretation of the 4I(9/2) crystal field levels and of the one-phonon vibronic sideband is given. The excitation spectrum of the 2G2(9/2) emission enables clarification of the structure of the 4f(2)5d configuration (which extends from approximately 52,000 to 128,000 cm(-1)). Detailed energy level and intensity calculations have been performed, which provide simulations of the d-f emission and the f-d excitation spectra in good agreement with experiment. It is interesting that although the 4f3 2G2(9/2) gamma8u --> 4f3 4I(J) transitions are very weak in intensity compared with transitions terminating upon higher multiplet terms, most of the 4f(2)5d (3H) 4I(9/2) gamma8g --> 4f3 emission intensity resides in the transitions to 4I(J).     

Electronic excited states of [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm= bis(dimethylphosphine)methane)

We present studies of the resonance Raman and electronic luminescence spectra of the [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm = bis(dimethylphosphine)methane) complex, including excitation into an intense band at 256 nm and into a weaker absorption system centered about approximately 300 nm. The resonance Raman spectra confirm the assignment of the 256 nm absorption band to a (1)(dsigma --> psigma) transition, a metal-metal-localized transition, in that nu(Au-Au) and overtones of it are strongly enhanced. A resonance Raman intensity analysis of the spectra associated with the 256 nm absorption band gives the ground-state and excited-state nu(Au-Au) stretching frequencies to be 79 and 165 cm(-1), respectively, and the excited-state Au-Au distance is calculated to decrease by about 0.1 A from the ground-state value of 3.05 A. The approximately 300 nm absorption displays a different enhancement pattern, in that resonance-enhanced Raman bands are observed at 103 and 183 cm(-1) in addition to nu(Au-Au) at 79 cm(-1) The compound exhibits intense, long-lived luminescence (in room-temperature CH(3)CN, for example, tau = 0.70 micros, phi(emission) = 0.037) with a maximum at 550-600 nm that is not very medium-sensitive. We conclude, in agreement with an earlier proposal of Mason (Inorg. Chem. 1989, 28, 4366-4369), that the lowest-energy, luminescent excited state is not (3)(dsigma --> psigma) but instead derives from (3)(d(x2-y2,xy --> psigma) excitations. We compare the Au(I)-Au(I) interaction shown in the various transitions of the [Au(2)(dmpm)(3)](ClO(4))(2) tribridged compound with previous results for solvent or counterion exciplexes of [Au(2)(dcpm)(2)](2+) salts (J. Am. Chem. Soc. 1999, 121, 4799-4803; Angew. Chem. 1999, 38, 2783-2785; Chem. Eur. J. 2001, 7, 4656-4664) and for planar, mononuclear Au(I) triphosphine complexes. It is proposed that the luminescent state in all of these cases is very similar in electronic nature.     

Simultaneous determination of Cl(-), Br(-), I(-) and F(-) with flow-injection/ion-selective electrode systems

Flow-through ion-selective electrodes were constructed from compressed pellets (8-10 mm thick, 13 mm diameter, 10 tons/cm(2) pressure) of Ag(2)S/AgX (X = Cl(-), Br(-) or I(-)) drilled longitudinally (1.5 mm diameter hole) to be suitable for use in flow-injection analysis. A column of AgCl (5.5 cm long, 2-3 mm i.d.) was included in the Cl(-)-electrode manifold to remove interferences from 10(-4)M Br(-) and 3 x 10(-5)M I(-) and S(2-). A column of amalgamated lead (2-3 cm long, 2-3 mm i.d.) was used in the Br(-) electrode manifold to remove interference from 2 x 10(-5)M I(-), 3 x 10(-5)M S(2-) and 7 x 10(-4)M Cl(-). These columns and the addition of ascorbic acid were not required when I(-) was determined with the iodide electrode. The carrier stream was 0.1M sodium perchlorate (pH 4) at a flow-rate of 0.5 ml/min. The sample pH could be 4-7. Simultaneous determination of Cl(-) and I(-), Cl(-), I(-) and Br(-) and Cl(-), I(-), Br(-) and F(-) ions was possible with combinations of the corresponding electrodes and columns in series and/or parallel in specially designed manifolds. Calibration plots were linear, with almost theoretical slopes, down to 10(-6)M I(-), 5 x 10(-6)M Br(-), 10(-4)M Cl(-) and 5 x 10(-6)M F(-), with precision better than 1%. Sampling rates for single-ion determinations were 72, 102, 90 and 80 per hr for the one-, two-, three- and four-electrode systems respectively. Determinations of these ions in water samples by the recommended procedure and by established batch methods showed no significant difference at the 95% confidence limits in a paired comparison t-test.     

Ultraviolet photochemistry of trichlorovinylsilane and allyltrichlorosilane: vinyl radical (HCCH2) and allyl radical (H2CCHCH2) production in 193 nm photolysis

The absolute gas phase ultraviolet absorption spectra of trichlorovinylsilane and allyltrichlorosilane have been measured from 191 to 220 nm. Over this region the absorption spectra of both species are broad and relatively featureless, and their cross sections increase with decreasing wavelength. The electronic transitions of trichlorovinylsilane were calculated by ab initio quantum chemical methods and the observed absorption bands assigned to the A(1)A'<-- X[combining tilde](1)A' transition. The maximum absorption cross section in the region, at 191 nm, is sigma = (8.50 +/- 0.06) x 10(-18) cm(2) for trichlorovinylsilane and sigma = (2.10 +/- 0.02) x 10(-17) cm(2) for allyltrichlorosilane. The vinyl radical and the allyl radical are formed promptly from the 193 nm photolysis of their respective trichlorosilane precursors. By comparison of the transient visible absorption and the 1315 nm I atom absorption from 266 nm photolysis of vinyl iodide and allyl iodide, the absorption cross sections at 404 nm of vinyl radical ((2.9 +/- 0.4) x 10(-19) cm(2)) and allyl radical ((3.6 +/- 0.8) x 10(-19) cm(2)) were derived. These cross sections are in significant disagreement with literature values derived from kinetic modeling of allyl or vinyl radical self-reactions. Using these cross sections, the vinyl radical yield from trichlorovinylsilane was determined to be phi = (0.9 +/- 0.2) per 193 nm photon absorbed, and the allyl radical yield from allyltrichlorosilane phi = (0.7 +/- 0.2) per 193 nm photon absorbed.     

ESR Studies of A(1u) and A(2u) Oxoiron(IV) Porphyrin pi-Cation Radical Complexes. Spin Coupling between Ferryl Iron and A(1u)/A(2u) Orbitals

This study shows the ESR spectra of oxoiron(IV) porphyrin pi-cation radicals of 1-8 in dichloromethane-methanol (5:1) mixture. We reported in a previous paper that oxoiron(IV) porphyrin pi-cation radicals of 1-4 are in an a(1u) radical state while those of 5-8 are in an a(2u) radical. The ESR spectra (g( perpendicular)(eff) approximately 3.1 and g( parallel)(eff) approximately 2.0) for the a(1u) radical complexes, 1-4, appear quite different from those reported previously for the oxoiron(IV) porphyrin pi-cation radical of 5 (g(y) = 4.5, g(x) = 3.6, and g(z) = 1.99). The unique ESR spectra of the a(1u) radical complexes rather resemble those of compound I from Micrococcus lysodeikticus catalase (CAT) and ascorbate peroxidase (ASP). This is the first examples to mimic the ESR spectra of compound I in the enzymes. From spectral analysis based on a spin Hamiltonian containing an exchange interaction, the ESR spectra of 1-4 can be explained as a moderate ferromagnetic state (J/D approximately 0.3) between ferryl S = 1 and the porphyrin pi-cation radical S' = (1)/(2). The magnitudes of zero-field splitting (D) for ferryl iron and isotropic J value, estimated from the temperature-dependence of the half-saturation power of the ESR signals, are approximately 28 and approximately +8 cm(-1), respectively. A change in the electronegativity of the beta-pyrrole substituent hardly changes the ESR spectral feature while that of the meso-substituent slightly does owing to the change in the E/D value. On the basis of the present ESR results, we propose the a(1u) radical state for compound I of CAT and ASP.     

Electronic spectra and crystal field analysis of energy levels of Ho3+ in HoF6(3-)

The electronic absorption spectra of single crystals of Cs(2)NaHoF(6) have been recorded in the spectral region between 4700 and 42000 cm(-1) at temperatures down to 10 K. The structure in the (5)I(8) → (5)I(J) (J = 7-4), (5)F(J) (J = 5-1), (5)S(2), (5)G(J) (J = 4-6), (3)K(J) (J = 7, 8) transitions has been analyzed and assigned. The emission spectra (5)S(2) → (5)I(J) (J = 6-8) and (5)G(4) → (5)I(J) (J = 5-7), (5)F(5) have also been recorded at 10 K for crystals of Cs(2)NaHoF(6) and partly also for samples of Cs(2)NaHoF(6):Yb(3+). The spectra comprise magnetic dipole zero phonon lines and electric dipole allowed one-phonon vibronic sidebands. From the detailed interpretation of the emission and absorption spectra, aided by a clear understanding of the vibrational behavior of the HoF(6)(3-) moiety and by magnetic dipole intensity calculations, a data set of 59 energy levels spanning 17 multiplet terms was derived. Crystal field calculations were then performed using a 4f(10) basis, as well as including the configuration interaction with a p-electron configuration. The latter calculation, which employed 14 parameters, gave better agreement with experiment and the mean deviation was 13.5 cm(-1). A comparison with the energy level fittings for Cs(2)NaHoCl(6) has been included. The crystal field parameters for the fluoro- and chloro-systems followed empirically predicted ratios.     

Infrared spectroscopic ellipsometry of n-alkylthiol (C5-C18) self-assembled monolayers on gold

The infrared spectroscopic ellipsometry (IRSE) of n-alkylthiol (CH3(CH2)xSH, x = 4, 6, 7, 8, 10, 13, 15, and 17, self-assembled monolayers (SAMs), with 5-18 carbon atoms (C5-C18), grown on gold-coated Si(100) substrates) was investigated at room temperature. The C-H stretching vibrations could be resolved even for pentathiol, the shortest chain studied. The symmetric and asymmetric stretching vibrations of the CH2 groups are located at about 2850 and 2920 cm(-1), and those of CH3 are at about 2877 and 2962 cm(-1), respectively; they show a slight shift with the number of CH2 units. In addition, Fermi resonance of the symmetric CH3 stretching vibration at 2940 cm(-1) appears with decreasing chain length due to weak coupling with the asymmetric CH2 stretching vibration. The "odd-even effect" of the n-alkylthiol SAMs with varying CH2 units could be distinguished by the two interactive IRSE parameters. The relative ellipsometric spectra for the four longest chains could be reproduced quite well by using a Lorentz multioscillator model with a three-phase optical model (air/SAMs/gold). On the basis of the theoretical calculations, the vibrational strength of these oscillators is very weak, its magnitude being 10(-4)-10(-5). The full width at half-maximum (fwhm) of the peaks varies from 7 to 33 cm(-1). Moreover, the intensity of the C-H vibrations increases with the number of methylene units, due to strong lateral interactions and ordering effects occurring for longer chains.     

Experimental and theoretical investigations of the reactions NH(X 3Sigma-) + D(2S)-->ND(X 3Sigma-) + H(2S) and NH(X 3Sigma-) + D(2S)-->N(4S) + HD(X 1Sigmag+)

The rate coefficient of the reaction NH(X (3)Sigma(-))+D((2)S)-->(k(1) )products (1) is determined in a quasistatic laser-flash photolysis, laser-induced fluorescence system at low pressures. The NH(X) radicals are produced by quenching of NH(a (1)Delta) (obtained in the photolysis of HN(3)) with Xe and the D atoms are generated in a D(2)/He microwave discharge. The NH(X) concentration profile is measured in the presence of a large excess of D atoms. The room-temperature rate coefficient is determined to be k(1)=(3.9+/-1.5) x 10(13) cm(3) mol(-1) s(-1). The rate coefficient k(1) is the sum of the two rate coefficients, k(1a) and k(1b), which correspond to the reactions NH(X (3)Sigma(-))+D((2)S)-->(k(1a) )ND(X (3)Sigma(-))+H((2)S) (1a) and NH(X (3)Sigma(-))+D((2)S)-->(k(1b) )N((4)S)+HD(X (1)Sigma(g) (+)) (1b), respectively. The first reaction proceeds via the (2)A(") ground state of NH(2) whereas the second one proceeds in the (4)A(") state. A global potential energy surface is constructed for the (2)A(") state using the internally contracted multireference configuration interaction method and the augmented correlation consistent polarized valence quadrupte zeta atomic basis. This potential energy surface is used in classical trajectory calculations to determine k(1a). Similar trajectory calculations are performed for reaction (1b) employing a previously calculated potential for the (4)A(") state. The calculated room-temperature rate coefficient is k(1)=4.1 x 10(13) cm(3) mol(-1) s(-1) with k(1a)=4.0 x 10(13) cm(3) mol(-1) s(-1) and k(1b)=9.1 x 10(11) cm(3) mol(-1) s(-1). The theoretically determined k(1) shows a very weak positive temperature dependence in the range 250< or =TK< or =1000. Despite the deep potential well, the exchange reaction on the (2)A(") ground-state potential energy surface is not statistical.     

Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds

The photophysical properties of singlet and triplet metal-to-ligand charge transfer (MLCT) states of [Cu(I)(diimine)(2)](+), where diimine is 2,9-dimethyl-1,10-phenanthroline (dmphen), 2,9-dibutyl-1,10-phenanthroline (dbphen), or 6,6'-dimethyl-2,2'-bipyridine (dmbpy), were studied. On 400 nm laser excitation of [Cu(dmphen)(2)](+) in CH(2)Cl(2) solution, prompt (1)MLCT fluorescence with a quantum yield of (2.8 +/- 0.8) x 10(-5) was observed using a picosecond time-correlated single photon counting technique. The quantum yield was dependent on the excitation wavelength, suggesting that relaxation of the Franck-Condon state to the lowest (1)MLCT competes with rapid intersystem crossing (ISC). The fluorescence lifetime of the copper(I) compound was 13-16 ps, unexpectedly long despite a large spin-orbit coupling constant of 3d electrons in copper (829 cm(-1) ). Quantum chemical calculations using a density functional theory revealed that the structure of the lowest (1)MLCT in [Cu(dmphen)(2)](+) (1(1)B(1)) was flattened due to the Jahn-Teller effect in 3d(9) electronic configuration, and the dihedral angle between the two phenanthroline planes (dha) was about 75 degrees with the dha around 90 degrees in the ground state. Intramolecular reorganization energy for the radiative transition of 1(1)B(1) was calculated as 2.1 x 10(3) cm(-1), which is responsible for the large Stokes shift of the fluorescence observed (5.4 x 10(3) cm(-1)). To understand the sluggishness of the intersystem crossing (ISC) of (1)MLCT of the copper(I) compounds, the strength of the spin-orbit interaction between the lowest (1)MLCT (1(1)B(1)) and all (3)MLCT states was calculated. The ISC channels induced by strong spin-orbit interactions (ca. 300 cm(-1)) between the metal-centered HOMO and HOMO - 1 were shown to be energetically unfavorable in the copper(I) compounds because the flattening distortion caused large splitting (6.9 x 10(3) cm(-1)) between these orbitals. The possible ISC is therefore induced by weak spin-orbit interactions (ca. 30 cm(-1)) between ligand-centered molecular orbitals. Further quantum mechanical study on the spin-orbit interaction between the lowest (3)MLCT (1(3)A) and all (1)MLCT states indicated that the phosphorescence borrows intensity from 2(1)B(1). The radiative rate of the phosphorescence was also structure-sensitive. The flattening distortion reduced the transition dipole moment of 2(1)B(1) --> the ground state, and decreased the extent of mixing between 1(3)A and 2(1)B(1), thereby considerably reducing the phosphorescence radiative rate at the MLCT geometry compared to that at the ground state geometry. The theoretical calculation satisfactorily reproduced the radiative rate of ca. 10(3) s(-1) and accounted for the structure-sensitive phosphorescence intensities of copper(I) bis(diimine) compounds recently demonstrated by Felder et al. (Felder, D.; Nierengarten, J. F.; Barigelletti, F.; Ventura, B.; Armaroli, N. J. Am. Chem. Soc. 2001, 123, 6291).     

Metal-metal interactions in dinuclear d(8) metal cyanide complexes supported by phosphine ligands. Spectroscopic properties and ab initio calculations of [M(2)(mu-diphosphine)(2)(CN)(4)] and trans-[M(phosphine)(2)(CN)(2)] (M = Pt,Ni)

Structural, spectroscopic properties on the dinuclear [M(2)(dcpm)(2)(CN)(4)] (M = Pt, 1a; Ni, 2a, dcpm = bis(dicyclohexylphosphino)methane) and [M(2)(dmpm)(2)(CN)(4)] (M = Pt, 1b; Ni, 2b, dmpm = bis(dimethylphosphino)methane) and the mononuclear trans-[M(PCy(3))(2)(CN)(2)] (M = Pt, 3; Ni, 4, PCy(3) = tricyclohexylphosphine) and theoretical investigations on the corresponding model compounds are described. X-ray structural analyses reveal Pt.Pt and Ni.Ni distances of 3.0565(4)/3.189(1) A and 2.957(1)/3.209(8) A for 1a/1b and 2a/2b, respectively. The UV-vis absorption bands at 337 nm (epsilon 2.41 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1a and 328 nm (epsilon 2.43 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1b in CH(2)Cl(2) are assigned to (1)(5d(sigma) --> 6p(sigma)) electronic transitions originating from Pt(II)-Pt(II) interactions. Resonance Raman spectroscopy of 1a, in which all the Raman intensity appears in the Pt-Pt stretch fundamental (93 cm(-)(1)) and overtone bands, verifies this metal-metal interaction. Complexes 1a and 1b exhibit photoluminescence in the solid state and solution. For the dinuclear nickel(II) complexes 2a and 2b, neither spectroscopic data nor theoretical calculation suggests the presence of Ni(II)-Ni(II) interactions. The intense absorption bands at lambda > 320 nm in the UV-vis spectra of 2a and 2b are tentatively assigned to d --> d transitions.     

Ca3Pt(4+x)Ge(13-y) and Yb3Pt4Ge13: new derivatives of the Pr3Rh4Sn13 structure type

The new phases Ca(3)Pt(4+x)Ge(13-y) (x = 0.1; y = 0.4; space group I2(1)3; a = 18.0578(1) ?; R(I) = 0.063; R(P) = 0.083) and Yb(3)Pt(4)Ge(13) (space group P4(2)cm; a = 12.7479(1) ?; c = 9.0009(1) ?; R(I) = 0.061, R(P) = 0.117) are obtained by high-pressure, high-temperature synthesis and crystallize in new distortion variants of the Pr(3)Rh(4)Sn(13) type. Yb(3)Pt(4)Ge(13) features Yb in a temperature-independent non-magnetic 4f(14) (Yb(2+)) configuration validated by X-ray absorption spectra and resonant inelastic X-ray scattering data. Ca(3)Pt(4+x)Ge(13-y) is diamagnetic (χ(0) = -5.05 × 10(-6) emu mol(-1)). The Sommerfeld coefficient γ = 4.4 mJ mol(-1) K(-2) for Ca(3)Pt(4+x)Ge(13-y), indicates metallic properties with a low density of states at the Fermi level in good agreement with electronic structure calculation (N(E(F)) = 3.3 eV(-1)/f.u.)); the Debye temperature (θ(D)) is 398 K.     

Li(+) ion conductivity in rock salt-structured nickel-doped Li(3)NbO(4)

Two mechanisms of doping Li(3)NbO(4), which has an ordered, rock salt superstructure, have been established. In the "stoichiometric mechanism", the overall cation-to-anion ratio is maintained at 1:1 by means of the substitution 3Li(+) + Nb(5+) --> 4Ni(2+). In the "vacancy mechanism", Li(+) ion vacancies are created by means of the substitution 2Li(+) --> Ni(2+). Solid solution ranges have been determined for both mechanisms and a partial phase diagram constructed for the stoichiometric join. On the vacancy join, the substitution mechanism has been confirmed by powder neutron diffraction; associated with lithium vacancy creation, a dramatic increase in Li(+) ion conductivity occurs with increasing Ni content, reaching a value of 5 x 10(-4) Omega(-1) cm(-1) at 300 degrees C for composition x= 0.1 in the formula Li(3-2x)Ni(x)NbO(4). This is the first example of high Li(+) ion conductivity in complex oxides with rock salt-related structures.     

Determination of riboflavin by enhancing the chemiluminescence intensity of peroxomonosulfate-cobalt(II) system

A weak chemiluminescent (CL) emission was observed in the decomposition of peroxomonosulfate (HSO5-), which would be accelerated in the presence of trace amounts of cobalt (II). The mechanism was due to the production of singlet oxygen (1O2). Interestedly, riboflavin can enhance the CL and the CL intensity was strongly dependent on riboflavin concentration. Based on this phenomenon, a flow injection analysis (FIA) CL method was established for the determination of riboflavin. Additionally, the possible CL mechanism is proposed based on the kinetic curve of the CL reaction, CL spectra, UV-vis spectra and fluorescent spectra. The CL intensity was correlated linearly with concentration of riboflavin over the range of 1.0x10(-4) to 1.0x10(-8) g mL-1; the detection limit was 9.0x10(-9) g mL-1(S/N=3); the relative standard deviation was 1.4% for 9x10(-7) g mL-1 riboflavin (n=11). Furthermore, this method was applied to the determination of riboflavin in real tablets and injections successfully.     

Luminescence Properties of Platinum(II) Dithiooxamide Compounds

Tight contact ion pairs of general formula {Pt(H(2)-R(2)-dto)(2)(2+),(X(-))(2)} have been prepared, and their absorption spectra and luminescence properties (at room temperature in dichloromethane fluid solution and at 77 K in butyronitrile rigid matrix) have been studied (dto = dithiooxamide; R = methyl, X = Cl (1); R = butyl, X = Cl (2); R = benzyl, X = Cl (3); R = cyclohexyl, X = Cl (4); R = cyclohexyl, X = Br (5); R = cyclohexyl, X = I (6)). The absorption spectra of all the compounds are dominated by moderately strong Pt(dpi)/S(p) to dithiooxamide (pi) charge transfer (Pt/S --> dto CT) bands in the visible region (epsilon in the 10(4)-10(5) M(-)(1) cm(-)(1) range). Absorption features are also present at higher energies, due to pi-pi transitions centered in the dto ligands (ligand centered, LC). All the compounds exhibit a unstructured luminescence band in fluid solution at room temperature, with the maximum centered in the 700-730 nm range. The luminescence bands are blue-shifted about 4000 cm(-)(1) on passing to the rigid matrix at 77 K. Luminescence lifetimes are on the 10(-)(8)-10(-)(7) s time scale at room temperature and 1 order of magnitude longer at 77 K. Luminescence is assigned to triplet Pt/S --> dto CT excited states in all cases. Compounds 3-6 also exhibit a second higher-energy luminescence band at room temperature, centered at about 610 nm, attributed to a LC excited state. Charge transfer interactions between halides and dto ligands destabilize dto-centered orbitals, affecting the energy of Pt/S --> dto CT transitions and states. The X counterions and X --> dto CT levels are proposed to play a role in promoting excited state conversion between LC and Pt/S --> dto CT levels. The R substituents on the nitrogen atoms of the dto ligands influence the absorption and photophysical properties of the compounds, by affecting proximity of the ion pairs. The possibility to functionalize the R substituents may open the way to interface these luminescent compounds with desired substrates and to construct supramolecular assemblies.     

Structure and white luminescence of Eu-activated (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66 materials

The optical properties of Eu-activated (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66 materials have been determined after the structural reinvestigation of the hypothetical Ba 13Al 22Si 10O 66 material on the basis of the Gebert's model. The white fluorescence and phosphorescence of the (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66:Eu series result from the existence of two broad emission bands associated with (8)H-4f(6)5d(1)-->(8)S-4f(7) transitions peaking at 534 and 438 nm, the intensities of which may be tuned at room temperature via the control of the europium concentration and the substitution of Sr for Ba. This suggests the possibility to adjust the emission of the material to white LED requisites.     

Collisional deactivation of Ba 5d7p (3)D1 by noble gases

Collisional deactivation of the 5d7p (3)D1 state of Ba by noble gases is studied by time- and wavelength-resolved fluorescence techniques. A pulsed, frequency-doubled dye laser at 273.9 nm excites the 5d7p (3)D1 level from the ground state, and fluorescence at 364.1 and 366.6 nm from the 5d7p (3)D1 --> 6s5d (3)D1 and 5d7p (3)D1 --> 6s5d (3)D2 transitions, respectively, is monitored in real time to obtain the deactivation rate constants. At 835 K these rate constants are as follows: He, (1.69 +/- 0.08) x 10(-9) cm(3) s(-1); Ne, (3.93 +/- 0.14) x 10(-10) cm(3) s(-1); Ar, (4.53 +/- 0.15) x 10(-10) cm(3) s(-1); Kr, (4.64 +/- 0.13) x 10(-10) cm(3) s(-1); Xe, (5.59 +/- 0.22) x 10(-10) cm(3) s(-1). From time-resolved 5d7p (3)D1 emission in the absence of noble gas and from the intercepts of the quenching plots, the lifetime of this state is determined to be 100 +/- 1 ns. Using time- and wavelength-resolved Ba emission with a low background pressure of noble gas, radiative lifetimes of several near-resonant states are determined from the exponential rise of the fluorescence signals. These results are as follows: 5d6d (3)D3, 28 +/- 3 ns; 5d7p (3)P1, 46 +/- 2 ns; 5d6d (3)G3, 21.5 +/- 0.8 ns; 5d7p (3)F3, 48 +/- 1 ns. Integrated fluorescence signals are used to infer the relative rate constants for population transfer from the 5d7p (3)D1 state to eleven near-resonant fine structure states.     

Uptake of NH(3) and NH(3) + HOBr reaction on ice surfaces at 190 K

The uptake of NH3 and the heterogeneous reaction of NH3 + HOBr --> products on ice surfaces at 190 K have been investigated in a flow reactor coupled with a differentially pumped quadrupole mass spectrometer. The uptake coefficient gammat for NH3 was determined to be (3.8 +/- 1.4) x 10(-4) on ice films at 189.8 K, for a partial pressure of NH3 in the range of 7.0 x 10(-7) to 3.8 x 10(-6) torr. The amount of NH3 uptake on the ice film was determined to be >2.9 x 10(15) molecules/cm(2), based on the total ice surface area at 189.2 K. The heterogeneous reaction of NH3 + HOBr on ice surfaces has been studied at 190 K. The reaction probability gammat was determined to be (5.3 +/- 2.2) x 10(-4) and was found to vary insignificantly as HOBr surface coverage changes from 2.1 x 10(13) to 2.1 x 10(14) molecules/cm(2). A reaction pathway is proposed on the basis of experimental observations.