Synthesis and electroluminescent properties of a novel terbium complex

A new carboxylic acid ligand (o-amino-4-hexadecane benzoic acid, AHBA) and a corresponding terbium complex (Tb(AHB)(3)) were synthesized and characterized. A multilayer electroluminescent device with poly(N-vinylcarbazole) (PVK), 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) and the terbium complex as emissive layer was fabricated: glass substrate/ITO/PPV/PVK:-To(AHB)(3):PBD/Alq(3)/Al. The photoluminescence (PL) and electroluminescence (EL) spectra were discussed. This EL cell exhibited characteristic emission of terbium ions with a maximum luminance of 35 cd/m(2) at 20 V. (C) 2000 Elsevier Science S.A. All rights reserved.

High PL quantum efficiency of poly(phenylene vinylene) systems through exciton confinement

Photoluminescence (PL) quantum efficiency is a key issue in designing successful light-emitting polymer systems. Exciton relaxation is strongly affected by exciton quenching at nonradiative trapping centers and the formation of excimers. These factors reduce the PL quantum yield of light-emitting polymers. In this work, we have systematically investigated the effects of exciton confinement on the PL quantum yield of an oligomer, polymer, and alternating block copolymer (ABC) PPV system. Time-resolved and temperature-dependent luminescence studies have been performed. The ABC design effectively confine photoexcitations within the chromophores, preventing exciton migration and excimer formation. An unusually high (PL) quantum yield (above 90%) in the solid state is reported for the alternating block copolymer PPV, as compared to that of similar to 30% of the polymer and oligomer model compounds. (C) 2000 Elsevier Science S.A. All rights reserved.

Infrared spectra and VUV excitation properties of BaLnB(9)O(16): Re (Ln = La, Gd; Re = Eu, Tb)

The infrared spectra of BaLnB(9)O(16):Re, along with the VUV excitation spectra, have been measured. The spectra were tentatively interpreted in terms of the data on absorptions of the borate groups and band structure. It was observed that there are absorption due to BO3 and BO4 groups, indicating that there are BO3 and BO4 groups in BaLnB(9)O(16). It is found that absorption of the borate groups is located in the range from 120 to 170 mn. This result reveals that there is an energy transfer from host to the rare earth ions. It also observed that the energy of charge transfer band, the host absorption, the total crystal field splitting of d-levels of Tb3+ increase with the decrease in the Ln(3+) radius. (C) 2001 Elsevier Science B.V. All rights reserved.

Surface photovoltage spectra and photoelectrochemical properties of semiconductor-sensitized nanostructured TiO2 electrodes

Three kinds of TiO2 nanostructured thin films and their CdS-sensitized films, consisting of different sizes of TiO2 nanoparticles prepared with different methods, have been investigated. The surface photovoltage spectra (SPS) measurements indicate that the density of surface states on TiO2 is likely dependent upon the details of prepared methods. TiO2 particles prepared from basic sol have more surface states than that prepared from acidic sol. When the TiO2 thin films prepared using the TiO2 sols were sensitized by CdS particles, the SPS responses relative to the surface states on TiO2 from 350 to 800 nm were decreased. The photoelectrochemical properties of nanostructured TiO2 electrodes suggest that the fewer the surface states and the smaller the particle sizes of TiO2, the larger the photocurrent response. For CdS sensitized TiO2 thin film electrode, it is shown that the semiconductor sensitization is an efficient way to decrease the influence of surface states on the charge separation, and can improve the intensity of photocurrent response. (C) 2001 Elsevier Science B.V. All rights reserved.

Study of energy transfer between rare earth ions in CaS host by photoluminescence spectra

When CaS:Sm3+, Eu2+ is excited at 476.5 nm (Ar+), the emission spectra taken at room temperature and at 77 K are different, indicating that there are two competitive energy transfer processes-Sm3+ --> Eu2+ and Eu2+ --> Sm3+ with phonon participation. So, the luminescence intensity of Sm3+ increases first, and then decreases as the concentration of Eu2+ is increasing. (C) 2001 Elsevier Science Ltd. All rights reserved.

Synchronous fluorescence spectra of myoglobin

The synchronous fluorescence spectra of myoglobin were studies for the first time. The fluorescence peals observed in the spectra were assigned, When the wavelength interval (Delta lambda) is 80 nm, the main peak at 335 nm is originated from the tryptophan residues in the myoglobin molecule. When Delta lambda is 20 nn, the peak at 308 nm is mainly due to the tyrosine residues in the myoglobin molecule and in a small part due to the tryptophan residues. Two peaks at 322 and 596 nm were observed in the spectrum of myoglobin for Delta lambda = 40 nm. The peak at 322 nm is due to both tyrosine and tryptophan residues. The peak at 596 nm is attributed to the heme group in the myoglobin molecule.

The site symmetry of Eu3+ in ZnS : Eu nanoparticle

Nanosized ZnS doped with different concentrations of Eu3+ were prepared and analyzed by x-ray diffraction technique. The experimental results show that ZnS belongs to the cubic structure. From the photoluminescence (PL) emission spectra, it can be seen that the ratio of the emission intensity of Eu3+ 616 nm to that at 590 nm increases as the increasing of Eu3+. This phenomenon reveals that the site symmetry of Eu3+ reduces as the increasing of Eu3+.

Fluorescence spectra of hemorrhagin III from the snake venom of Agkistrodon acutus

Hemorrhagin III (AaH III) was separated and purified from the crude snake venom of Agkistrodon acutus, and its molecule weight was determined accurately to be 23; 284.4 +/- 0.1 by LDI1700-MALDI-TOF-MS. Emission spectra of AaH III showed that Trp residues were located by a great degree in the hydrophobic area. Addition of SDS and guanidine-HCl led to change of the molecular conformation of AaH III, and caused the fluorescence quenching of Trp residues. The red-shifted emission band of AaH III after adding guanidine-HCl showed that Trp residues exposed in polar solvents. The effects of pH, EDTA and metal ions on the fluorescence spectra of AaH III were also investigated.

Preparation and spectra study of TiO2 gel doped with fluorescein

TiO2 gel doped with fluorescein was prepared by a sol-gel method, and the fluorescence of fluorescein and its effect on formation of the: gel were investigated with absorption, fluorescence, IR spectroscopies and TG-DTA analysis. The results indicated that FL incorporated into TiO2 gel had exhibited big changes compared to that in ethanol solution both in the absorption and the emission spectra, and the formation of TiO2 gel was influenced greatly by FL.

X-ray photoelectron spectroscopy and mass spectra study of alpha-amino acid

X-ray photoelectron spectroscopy and mass spectrometry have been used to study the ten alpha-Amino Acids. The chemical shiftss of N-1s electron binding energy have been explained by means of the difference in the hydrocarbon group of amino acids. The influence of the hydrocarbon group on NH2 has been disscussed using the XPS and MS results.

Vibrational spectra and structure of zinc phthalocyanine

Semi-empirical molecular orbital calculations using PM3 Hamiltonian were employed to determine qualitative assignments of the vibrational spectrum of zinc phthalocyanine (ZnPc). The assignments are from the potential energy distribution calculations in the normal coordinate analysis and optimized geometry in the PM3 calculations. The structure of the ZnPc molecule is also deduced. (C) 1999 Elsevier Science B.V. All rights reserved.

Synchronous fluorescence spectra of hemoglobin: A study of aggregation states in aqueous solutions

The synchronous fluorescence spectra of hemoglobin solutions are reported for the first rime. The main fluorescence peaks observed in the spectra are assigned. The effect of the concentration of hemoglobin solution on the spectra is studied. Characteristic fluorescence peaks due to the dimer and tetramer of hemoglobin molecules are recognized. (C) 1998 Academic Press.

Structures and vibrational spectra of C-2 and LaC2+ clusters

C-2 and LaC2+ were studied using Hartree-Fock(HF), B3LYP (Becke 3-paremeter-Lee-Yang-Parr) density functional method, second-order Moller-Plesset perturbation (MP2) and coupled cluster singles and doubles with non-iterative triples(CCSD(T)) methods. The basis set employed was LANL1DZ. Geometries, vibrational frequencies and other quantities were reported. The results showed that for C-2, all the methods performed well for low spin state (singlet), while only HF and B3LYP remained so for high spin state (triplet). For LaC2+, four isomers were presented and fully optimized. The results suggested that linear isomers with C-infinity v and D-infinity h symmetries were predicted to be saddle points on the energy surface for all the methods, while for isomers with C-2 upsilon and C-s symmetries, they were local minima except C-2 upsilon at B3LYP level, and were isoenergetic at HF, MP2 and CCSD(T) levels, near isoenergetic at B3LYP level. From the differences between HOMO and LUMO, it is also known that the isomers with C-2 upsilon and C-s symmetries offer the largest values and therefore correspond to the most stable structure. For La-C bond lengths, B3LYP gives the shortest, the order is B3LYP

Structure, Stability and Vibrational Spectra of LaC_5~n(n=-1,0,+1) Clusters

用密度泛含方法研究了ＬａＣ５ｎ（ｎ＝－１，０，＋１）分子簇的结构和稳定性及振动光谱，对这个六原子体系提出了三种可能构型，点群结构为Ｃ２ｖ对称性．第一个构型为Ｌａ接在弯曲的Ｃ５链上，第二个是Ｌａ通过二个键与Ｃ５环相连第三个是Ｌａ通过一个键与Ｃ５环相连；结果表明，第一个构型即当Ｌａ接在弯曲的Ｃ５链上时能量最低．振动光谱分析指出，当ｎ＝－１时，第二个构型为局域极小值；当ｎ＝＋１时，第一个和第二个构型为局域极小值；对ｎ＝０，局域极小值没有找到.

Mossbauer spectra of Fe-57 in a thick film of YBa2(Cu0.97Fe0.03)(3)O7-x irradiated by a large dose of gamma-rays

Mossbauer spectra of Fe-57 in a thick film YBa2(Cu0.97Fe0.03)(3)O7-x irradiated by a large dose of gamma-rays from Co-60 have been measured. The variation of the relative intensities of some subspectra of Fe-57 in the. Mossbauer spectra of the thick film YBa2(Cu0.97Fe0.03)(3)O7-x after irradiation can be observed. This variation indicates that the change of the coordination environment around some Fe atoms in the lattice occurs due to irradiation. The relative intensity of subspectrum D1(Fe) at the Cu(1) site decreases and that of subspectrum D4(Fe) at the Cu(1) site increases. This may be because of the possible oxygen atom hopping between the coordination environments of D1(Fe) and D4(Fe) in the lattice caused by irradiation. The effect of irradiation on the coordination environment around the Fe atom at the Cu(2) site is not appreciable. (C) 1997 Elsevier Science B.V.