Structure and luminescence properties of some new AgLnW(2)O(8) compounds

Three new compounds, AgLnW(2)O(8) (Ln(3+)=Eu, Gd or Tb), have been prepared by a solid-state reaction and crystallize with a scheelite-related monoclinic symmetry. Their IR spectra show absorption transitions in the region 1000-400 cm(-1) similar to KLnW(2)O(8). Broad excitation and emission bands of the tungstate group with a large Stokes shift (12573 cm(-1)) are observed in AgGdW2O8. Excitation and emission spectra of AgLnW(2)O(8) (Ln=Eu or Tb) show that energy transfer from tungstate to Eu and Tb occurs and that Eu3+ ions occupy a unique crystallographic site with C-2 site symmetry.

Luminescent properties of Ba-3(PO4)(2):Eu, Tb phosphors

Luminescence of europium (III), europium(II) and terbium(III) has been observed in Ba-3(PO4)(2):Eu, Tb phosphors which are synthesized in air atmosphere. The valence state of europium is influenced by amount of terbium. It is notable that the relative intensity of the emission spectra peaks corresponding to Eu2+ is increased if the amount of Tb3+ is increased. These phenomena can be explained by an electron transfer mechanism. We predict a new kind of two-rare-earth codoped trichromatic phosphors in Ba-3(PO4)(2) matrix.

Luminescence properties of SrB4O7: Eu, Tb phosphors

In this paper, the luminescence properties of SrB4O7: xEu, yTb phosphors were investigated. The SrB4O7: xEu, yTb phosphors were first synthesized in air atmosphere, and the emission spectra of Eu2+, Eu3+ and Tb3+ ions have been observed in phosphors. We found that the relative intensity of the emission of Eu2+ ion in the same matrix are increased when Tb3+ is incorporated in SrB4O7:Eu phosphor. So the valence state of europium is influenced by terbium. These phenomena can be explained using an electron transfer theory.

Effect of water on the electrochemical oxidation process of biliverdin in dimethylformamide

A systematic study has been made for the electrochemical oxidation reaction of biliverdin (BV) in pure dimethylformamide (DMF) and in DMF - H2O mixed solvent by in situ time resolved spectroelectrochemical and cyclic voltametric techniques. The experiments show that not only the oxidation of BV is promoted, the reaction mechanism is also changed from a ECEC to a ECCECC process by the introduction of water into DMF.

SPECTRAL CHARACTERISTICS OF ER3+-ACTIVATED AND CE3+-SENSITIZED YTTRIUM-ALUMINUM-GARNET LASER CRYSTALS

We report in this paper the spectral characteristics of Er3+ (2 at.%)-activated and Ce3+ (0.3 at.%)-sensitized yttrium aluminium garnet (YAG:Er,Ce) laser crystals grown by the Czochralski technique. The absorption and emission spectra were measured at room temperature. By using absorption spectra and Judd-Ofelt theory the experimental oscillator strengths of the Er3+ transitions in the YAG:Er,Ce crystals were calculated. The energy transfer between the Er3+ and Ce3+ ions is also discussed.

OPTICAL AND STRUCTURAL INVESTIGATION OF KMGLA(PO4)(2) PHOSPHATE DOPED WITH EUROPIUM

A new compound KMgLa(PO4)(2), isotypic with monoclinic LaPO4, is reported. Its cell parameters have been determined from X-ray powder diffraction data. Crystallization occurs in the monoclinic space group P2(1)/n (No. 14) with a = 6.839(3) Angstrom, b = 7.066(1) Angstrom, c = 6.523(3) Angstrom, beta = 103.42(4)degrees, and Z = 2. It was found that the KMgLa(PO4)(2) phase was isostructural with monoclinic LaPO4. The difference between them was that half of the La atoms in LaPO4 were couplingly substituted with the same amount of Mg and K atoms. This isomorphous substitution was confirmed by IR and Eu3+-doped excitation and emission spectra and by elemental analysis of single crystals. The spectroscopic data were compared with those of LaPO4:Eu3+. (C) 1995 Academic Press, Inc.

ENTANGLEMENT FLUCTUATION DURING PHASE-SEPARATION IN POLYMER BLENDS

For perhaps the first time, the dynamics of liquid-liquid phase separation was studied by time-resolved mechanical spectrometry in order to establish the relationship between blends' properties and the phase structures during spinodal decomposition (SD). The selected system was chlorinated polyethylene (CPE)/ethylene-vinyl acetate copolymer (EVA). It was found that in the early and intermediate stage of SD, the storage modulus (G') and the loss modulus (G'') increase with time after the initiation of the isothermal phase separation; in the later stage, G' and G'' decrease as phase separation proceeds. An entanglement fluctuation model was presented to manifest this phenomenon; it was found that the rheological behavior agrees well with the expections of the model in the early stage. For the later stage, the reduction of G' and G'' can be attributed to the increment of phase-domain size. (C) 1993 John Wiley & Sons, Inc.

LIFETIME MEASUREMENTS OF SOME TMI ODD PARITY LEVELS

Eleven new lifetimes of odd parity excited energy levels in four configurations: 4f12 5d 6s 6p, 4f12 6S2 6p, 4f13 5d 6s and 4f13 6s 7s of atomic thulium have been mesured with atomic-beam laser spectrocopy. Two pulsed dye lasers are used for stepwise excitation and the time-resolved fluorescence decay was used to determine lifetime values. The accuracy of the measurements is about 10%.

COMPARATIVE-STUDY OF KALMAN FILTERING, SYNCHRONOUS EXCITATION AND NUMERICAL DERIVATIVE TECHNIQUES IN FLUOROMETRY

The performance of Kalman filtering, synchronous excitation and numerical derivative techniques for the resolution of overlapping emission spectra in spectrofluorimetry was studied. The extent of spectrum overlap was quantitatively described by the separation degree D(s), defined as the ratio of the peak separation to the full width at half-maximum of the emission spectrum of the interferent. For the system of Rhodamine B and Rhodamine 6G with a large D(s) of about 0.4, both Kalman filtering and synchronous techniques are able to resolve the overlapping spectra well and to give satisfactory results while the derivative spectra are still overlapped with each other. Moreover, the sensitivities are greatly decreased in derivative techniques. For more closely spaced spectra emitted by the complexes of Al and Zn with 7-iodo-8-hydroxyquinoline-5-sulphonic acid (Ferron)-hexadecyltrimethylammonium bromide, the synchronous excitation technique cannot completely separate the overlapping peaks, although it increases the separation degree from 0.25 in the conventional spectra to 0.37 in the synchronous spectra. On the other hand, Kalman filtering is capable of resolving this system. When the Al/Zn intensity ratio at the central wavelength of Al was > 1, however, the accuracy and precision of the estimates for Zn concentration produced by the Kalman filter became worse. In this event, the combination of synchronous excitation and Kalman filtering can much improve the analytical results.

LIFETIMES OF RYDBERG LEVELS IN THE PERTURBED 6SNP 3P2 SERIES OF YTTERBIUM-I

Using three-step laser excitation in an atomic beam and a time-resolved spectroscopy technique, we measured both the lifetimes of the Rydberg levels of Yb I belonging to the perturbed series 6nsp 3P2 and the lifetimes of the perturbing 4f(13)5d(2)6s 3P2, 1D2 levels. An expected shortening has been observed for the lifetimes of those levels which are strongly mixed with the perturbers.

DYNAMIC SCALING OF THE STRUCTURE-FUNCTION FOR SPINODAL DECOMPOSITION IN CRITICAL AND NONCRITICAL MIXTURES OF POLY(VINYL ACETATE) POLY(METHYL METHACRYLATE)

The dynamics of phase separation in a binary polymer blend of poly(vinyl acetate) with poly(methyl methacrylate) was investigated by using a time-resolved light-scattering technique. In the later stages of spinodal decomposition, a simple dynamic scaling law was found for the scattering function S(q, t)(S(q, t) approximately I(q, t)): S(q, t)q(m)-3 S approximately (q/q(m)). The scaling function determined experimentally was in good agreement with that predicted by Furukawa, S approximately (X) approximately X2/(3 + X8) for critical concentration, and approximately in agreement with that predicted by Furukawa, S approximately (X) approximately X2/(3 + X6) for non-critical mixtures. The light-scattering invariant shows that the later stages of the spinodal decomposition were undergoing domain ripening.

INVESTIGATION OF PHASE SEPARATION BEHAVIOR IN POLY (METHYL METHACRYLATE)/POLY (STYRENE-CO-ACRYLONITRILE) MIXTURES WITH PULSED NUCLEAR MAGNETIC RESONANCE

Thermally induced phase separation in the mixture of poly (methyl methacrylate) (PMMA) with poly(styrene-co-acrylonitite (SAN) has intern studied with pulsed nuclear magnetic resonance(NMR) in single spin-lattice retaxation time T-1 of the eornpatibl. mixture two T-1 corresponding to those of PM MA-rich and SAN-rich comairis. Meanwhile, both T-1 gradually changing with annealing time provides the direct evidence that the phase separation takes place with a decomposition mechanism. Diffusion coeffieient was to lac negative, indicating an uphal diffusion characteristics, The basic parameters governing its kinetics were estimated using NMR date which were in good agreement with those evaluated from time-resolved light scattering experiments for a 60/40(PMMA/SAN) mixture annealed at 180.0 degrees C.

A potent anti-oxidant property: fluorescent recombinant alpha-phycocyanin of Spirulina

To express and product a fluorescent antioxidant holo-alpha-phycocyanin (PC) of Spirulina platensis (Sp) with His-tag (rHHPC; recombinant holo-alpha-phycocyaninof Spirulina platensis with His-tag) in 5-l bench scale. A vector harbouring two cassettes was constructed: cpcA along with cpcE-cpcF in one cassette; ho1-pcyA in the other cassette. Lyases CpcE/F of Synechocystis sp. PCC6803 (S6) could catalyse the 82 site Cys in apo-alpha-PC of Sp linking with bilin chromophores, and rHHPC was biosynthesized in Escherichia coli BL21. The constant feeding mode was adopted, and transformant reached the biomass of rHHPC up to 0.55 g l(-1) broth in 5-litre bench scale. rHHPC was purified by Ni2+ affinity column conveniently. The absorbance and the fluorescence emission spectra of rHHPC had lambda(max) at 621 and 650 nm, respectively. The IC50 values of rHHPC were 277.5 +/- 25.8 mu g ml(-1) against hydroxyl radicals and 20.8 +/- 2.2 mu g ml(-1) against peroxyl radicals. Combinational biosynthesis of rHHPC was feasible, and the constant feeding mode was adopted to produce good yields of rHHPC. Fluorescent rHHPC with several unique qualitative and quantitative features was effective on scavenging hydroxyl and peroxyl radicals. A potent antioxidant rHHPC was co-expressed, produced and characterized for nutritional and pharmacological values, which would help to develop phycobiliproteins' applications in their fluorescent and biological activities.

Interaction between phycobilisomes from Porphyridium cruentum and thylakoid membranes from Gymnodinium sp or spinach

Thylakoid membranes were isolated from Gymnodinium sp. and spinach, whereas the phycobilisomes were isolated and purified from red alga Porphyridium cruentum. The absorption spectra of the purified phycobilisomes (PBS) showed three peaks at 548, 564, and 624 nm, respectively, and the ratio of the fluorescence intensity at the lambda(680)(em) to lambda(80)(em5) that at was about 7.3. All these results demonstrated that the purified PBS remained intact. The thylakoid membranes were incubated with the purified phycobilisomes, and the thylakoid membranes, which harbored the phycobilisomes, were purified by sucrose density gradient centrifugation. Meantime, the conjugates of phycobilisome-thylakoid membranes were constructed using glutaraldehyde and further purified. Their characteristics were studied by measuring the absorption spectra and fluorescence emission spectra. The results showed that the phycobilisomes from Porphyridium cruentum can attach to the thylakoid membranes from Gymnodinium sp. and spinach without covalent cross-linking, but the excited energy transfer did not occur. The conjugate of phycobilisome-thylakoid. membranes with covalent cross-linking exhibits the excited energy transfer between the phycobilisomes and the thylakoid membranes.

Isolation of PSI from a siphonous marine green alga, Codium fragile

Three different forms of PS I complexes were isolated from a siphonous marine green alga, Codium fragile, by Triton X-100 sucrose gradient centrifugation. Zone III had a Chl a/b>20, and designated as PS I. core complex CC I because it created only CP I band in mild PAGE. Zone IV and V had absorption at 436 and 674 nm, 467 and 650 nm, and 540 nm, suggesting the presence of Chl a, Chl b, siphonaxanthin and siphonein, Chl a/b were 3.23 and 2.4, respectively. Both CP I and CP I a bands were observed when they were subjected to mild PAGE. Therefore, Zone IV and V were different forms of PS I complexes that consisted of CC I and different amount of light-harvesting complex LHC I. Zone III contained only 66 and 56 ku peptides in SDS-PAGE, while Zone IV and V had 4 different LHC I peptides of 25, 26, 26.2 and 27.5 ku in addition to 66, 56 ku peptides. Fluorescence emission spectra showed that efficient energy transfer were kept among pigments in isolated PS I complexes. Excitation energy absorbed by Chl b, siphonaxanthin and siphonein can be transferred to Chl a.