Clear Red Shift Research Articles

Catalytic Activation of Mg-Doped GaN by Hydrogen Desorption Using Different Metal Thin Layers

The annealing of Mg-doped GaN with Pt and Mo layers has been found to effectively improve the hole concentration of such material by more than 2 times as high as those in the same material without metal. Compared with the Ni and Mo catalysts, Pt showed good activation effect for hydrogen desorption and ohmic contact to the Ni/Au electrode. Despite the weak hydrogen desorption, Mo did not diffuse into the GaN epilayer in the annealing process, thus suppressing the carrier compensation phenomenon with respect to Ni and Pt depositions, which resulted in the high activation of Mg acceptors. For the GaN activated with the Ni, Pt, and Mo layers, the blue emission became dominant, followed by a clear peak redshift and the degradation of photoluminescence signal when compared with that of GaN without metal.

Complex formation of trivalent americium with salicylic acid at very low concentrations

For the first time, the complexation of americium(III) with salicylic acid was studied at trace metal concentrations using a 2.0 m Long Path Flow Cell for UV–vis spectroscopy. The detection limit of Am(III) in aqueous solution at pH 3.0 was found to be 5 × 10−9 M. Two Am(III)-salicylate complexes were formed at pH 5.0 in 0.1 M NaClO4, indicated by a clear red shift of the absorption maximum. The absorption spectra obtained from spectrophotometric titration were analyzed by means of factor analysis and complex stabilities were calculated to be log β110 = 2.56 ± 0.08 and log β120 = 3.93 ± 0.19.

Enhanced photocatalytic activity of indium and nitrogen co-doped TiO 2–Pd nanocomposites for hydrogen generation

Indium and nitrogen co-doped TiO 2, indium- or nitrogen-doped TiO 2 and undoped TiO 2 were synthesized by polyol method and studied their photocatalytic activity for hydrogen generation from water. Crystalline nanoparticles of predominantly anatase phase of TiO 2 were obtained by this method. A clear red shift of the absorption edge and stronger absorption in the visible region was observed for indium and nitrogen co-doped TiO 2 compared to the other samples. The presence of bonded nitrogen in the N-doped samples was evidenced from their N 1s X-ray photoelectron spectra. Photocatalytic activity for hydrogen generation using sunlight type radiation showed enhanced activity for the doped samples compared to pristine TiO 2. The photocatalytic activity of different samples decreased in the following order: N and In co-doped TiO 2 > In-doped TiO 2 > N-doped TiO 2 > undoped TiO 2. The enhanced photocatalytic activity of the In and N co-doped TiO 2 for hydrogen generation is attributed to the enhanced light absorption resulting from the narrowing of the band gap caused by the contribution of 5s5p orbitals of In to the conduction band and 2p orbitals of N to the valence band of TiO 2. A pronounced enhancement of photocatalytic activity was observed for all catalysts when Pd metal was present as co-catalyst due to the efficient separation of photogenerated charge carriers in this nanocomposite system.

Luminescent gold–poly(thiophene) nanoaggregates prepared by one-step oxidative polymerization

We report the facile synthesis, formation mechanism, and photoluminescent (PL) properties of gold–poly(thiophene) (Au–PTh) nanoaggregates. They were prepared by one-step oxidative polymerization, in which Au3+ ion was utilized as an oxidizing agent for the polymerization of thiophene. Transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) analyses demonstrated that the ‘raspberry-like’ Au–PTh nanoaggregates consist of individual Au NPs covered by PTh and stabilized by Tween 80. For Au–PTh nanoaggregates, a clear red shift in the SP peak was observed in the UV absorption spectra as compared with pristine Au nanoparticles (NPs). This red shift of the SP band is a consequence of the location of π-conjugated PTh on the surface of Au NPs, resulted from a strong binding between sulfur atoms of PTh and the Au NPs (sulfur–gold interaction). The strong interaction between the gold and sulfur atoms of PTh in the Au–PTh nanoaggregates was observed by X-ray photoelectron spectroscopy (XPS) analysis. The SP effect contributes to the PL intensity enhancement of the Au–PTh nanoaggregates and was confirmed by confocal laser scanning microscopy (CLSM).

Spectra of ZnO nanoparticles under low photon energy excitation

Time-integrated photoluminescence (PL) spectra between 1.2 and 2.25 eV of ZnO nanoparticles were observed at ambient temperatures when they were excited by a picosecond (ps) laser pulse at a low photon energy of 2.33 eV/532 nm, to show clear red shift when the excitation intensity increased. Gaussian analysis shows that the red shift is due to increase of the relative magnitudes of the Gaussian combination in the low energy region. Temporal evolution of the dominant emissions exhibited a similar double-exponential decay process, in which the respective two distinct decay durations of 189 ps at the corresponding amplitude of 82% and 2081 ps at 18% were identified. Speculation based on the surface-state emission due to the large surface-to-volume ratio of nanoscale materials is used to explain the phenomena.

Sensitivity of Crescent-Shaped Metal Nanoparticles to Attachment of Dielectric Colloids

The response of the plasmonic resonances of crescent-shaped nanoparticles to the attachment of a dielectric colloidal particle was investigated. The colloid serves as a model analyte which is easy to handle and allows for benchmarking of the sensing capabilities of plasmonic resonators. A clear red shift of the resonances is observed in agreement with the prediction from numerical simulations. From the response for different colloid positions, we obtain information on the nanoscale near field distribution. A field localization to length scales of 20 nm is proven directly. All resonators under study show a comparable response which is important for possible sensing application. We estimate that a further increase of the sensitivity by a factor of 8 would allow for label-free single biomolecule detection.

Synthesis and optical properties of novel red phosphors YNbTiO 6:Eu 3+ with highly enhanced brightness by Li + doping

Highly luminescent euxenite phased YNbTiO 6:Eu 3+ and Li +-doped YNbTiO 6:Eu 3+ red phosphors have been prepared through a facile sol–gel combustion process and investigated for the first time. The introduction of Li + ions into YNbTiO 6:Eu 3+ is able to result in significant changes of the crystallinity and particle size, and bring a clear red-shift of absorption edge. A dominant red emission peak at 611 nm due to the 5D 0 → 7F 2 transition of Eu 3+ was observed from photoluminescence spectra of the YNbTiO 6:Eu 3+ and Li +-doped YNbTiO 6:Eu 3+ phosphors. In particular, the emission intensity of the optimal Li +-doped YNbTiO 6:Eu 3+ was examined to be close to 400% of commercial Y 2O 3:Eu 3+ phosphor. The mechanism of the enhanced emission by Li + doping was discussed.

The synthesis of novel core-substituted naphthalene diimides via Suzuki cross-coupling and their properties

This paper reports the efficient core-substitution of halogenated naphthalene diimides utilizing the Suzuki cross-coupling reaction to install various aryl substituents at the 2,6 positions. The UV-visible spectra of these compounds show a clear absorbance red shift and an enhanced fluorescence output, making them potential candidates for solar-cell dyes and electroactive elements for supramolecular materials.

Biomimetic photocatalyst system derived from the natural prototype in leaves for efficient visible-light-driven catalysis

A green leaf can be viewed as a solar collector and an energy converter crammed with photosynthetic cells, and could be termed a “natural photocatalyst system (natural-PCS)”. Here, we put forward a general biomimetic strategy of copying Mother Nature—an artificial photocatalyst system (artificial-PCS) produced by replacing the natural one in green leaves. The artificial N-doped ZnO photocatalyst system, as a typical prototype, is generated through a two step infiltration process by copying the elaborate architecture of green leaves from macro-, micro- to nanoscales and the N contained in original leaves is self-doped into the resulting samples. The absorbance intensities within the visible light range of artificial N-ZnO PCS derived from different leaves increase by 84%–131%, and the band gap absorption edges exhibit clear red shifts compared with the bulk counterparts, demonstrating the highly efficient light-harvesting capacity in the UV-visible light region. Moreover, the artificial N-ZnO PCS possesses superior photocatalytic activity especially in the visible light region proved by EPR study and by degradation of methylene blue under solar energy irradiation. Thus, the artificial biomimetic analogues realize the structure inheritance and function imitation of the natural-PCS. This work may establish a methodology for learning from nature and for utilization of solar energy with man-made analogues.

Macrocyclic bis(amidonaphthol)s for anion sensing: tunable selectivity by ring size in proton transfer process

The investigation on anion sensing properties for a series of macrocyclic bis(amidonaphthol)s 3a– 3c reveals the significant effects of macrocyclic ring size. Among them, macrocycle 3c with the largest ring size shows F − ion selectivity by causing clear red shift (24 nm) in fluorescence emission after complexation with F −, which results in significant color change of fluorescence from blue to green. This excellent selectivity toward F − ion might be attributed to the fitness between the acidity of –OH group and the basicity of F − ion. Further exploration indicates that the acidity of –OH group can be tuned by ring size to give it the capability to discriminate the subtle difference in the affinity of F −, CH 3COO −, and H 2PO 4 − to –OH proton.

Morphology conversion and highly enhanced green emission of ZnO phosphors by annealing of ZnS in KCl flux

Abstract KCl flux has been used to enhance the green emission of the ZnO phosphors prepared by direct annealing of ZnS powders in air. Compared with the ZnO powders obtained without using KCl flux, the morphology of as-prepared powders was changed from spherical clusters to “hexagonal prisms”. In addition, the intensity of the green emission was enhanced ∼5 times, as well as a clear red-shift (∼30 nm) in excitation band with a new excitation level located at 380 nm was found. The significant enhancement of the green emission observed from the ZnO phosphors prepared with KCl flux is ascribed to the morphology conversion and the shift in the maximum excitation wavelength induced by the incorporation of Cl − ions into ZnO lattice.

Surface-Enhanced Raman Spectroscopic Studies of Coactivator-Associated Arginine Methyltransferase 1

We report, for the first time, the surface-enhanced Raman spectra of an important enzyme, coactivator-associated arginine methyltransferase 1 (CARM1), involved in various biological activities such as tumor suppressor function and stem cell differentiation. We have employed surface-enhanced Raman scattering (SERS) to obtain insight into the structural details of CARM1 by adsorbing it to silver (Ag) nanoparticles. The enzyme retains its activity even after its adsorption onto Ag nanoparticles. We observe strong SERS modes arising from amide vibrations and aromatic ring amino acids. The SERS spectra revealed amide I bands at 1637 cm(-1) and 1666 cm(-1), which arise as a result of the alpha helix of the protein and the polypeptide backbone vibration of a random coil, respectively. In order to confirm the amide vibrations, we have performed SERS on deuterated CARM1, which exhibits a clear red shift in amide band positions. The SERS spectra may provide useful information, which could be harnessed to study the functional interactions of CARM1 with small molecule modulators.

Shape and size dependence of the surface plasmon resonance of gold nanoparticles studied by Photoacoustic technique

We report on the optical absorption properties of as prepared gold naoparticles of different shapes and sizes measured by photoacoustic (PA) method. The gold nanoparticles of two different shapes (dots, rods) have been prepared using the seed mediated growth method. The shape and the size of these different nanoparticles were determined by STM measurements. PA spectra show the splitting of the surface plasmon resonance (SPR) into two modes (transverse and longitudinal) in case of gold nanorods. The increase in the aspect ratio of the nanorods leads to clear redshifts of the longitudinal SPR. These shifts were used to determine the dielectric constant of the surrounding medium and its variation with the aspect ratios.

Effect of nitrogen doping on bonding state of ZnO thin films

Nitrogen (N) is the most promising p-type dopant for zinc oxide (ZnO) with wurtzite structure. The substitution of N atoms for partial replacement of O atoms in wurtzite structure is predicted to cause the slight change in bonding state. We have synthesized ZnO and N-doped ZnO thin films by utilizing a pulsed laser deposition method. Compared with the ultraviolet-visible spectrum of the ZnO thin film, since the absorption edge of the N-doped ZnO thin film denoted a clear redshift, the band gap shrank for the incorporation of N atoms. The band-gap shrinkage of the N-doped ZnO thin film was considered to be due to the existence of Zn–N bond having smaller ionicity than Zn–O bond. Additionally, from the results of Fourier transform infrared measurements, the absorption peaks of the ZnO and N-doped ZnO thin films emerged at 415 and 408±2cm−1, respectively, and were attributed to transverse optical phonon of E1 mode. The reduction in phonon frequency of approximately 7cm−1 can be induced by the complex factors consisting of not only the decrease in reduced mass and interionic distance but also the increase in covalency.

Effect of ZnSe partial capping on the ripening dynamics of CdSe quantum dots

The ripening dynamics of CdSe quantum dots (QDs) partially capped with ZnSe layer are investigated. Atomic force microscopy (AFM) images show that the ripening of QDs is dramatically accelerated by depositing a ZnSe partial capping layer. The driving force of ripening enhancement is attributed to the increasing strain energy with capping thickness. For a ZnSe partial capping layer of below 3 ML, photoluminescence exhibits a clear redshift with increasing ZnSe monolayers. It is attributed to the size of the CdSe QD increases with ZnSe partial capping, in a manner that is consistent with the results of the AFM study.

Preparation of N-doped TiO2 photocatalyst by atmospheric pressure plasma process for VOCs decomposition under UV and visible light sources

The nitrogen doped (N-doped) titanium dioxide (TiO2) photocatalyst was prepared by the atmospheric-pressure plasma-enhanced nanoparticles synthesis (APPENS) process operated under normal temperature, i.e. the dielectric barrier discharge plasma process. The N2 carrier gas is dissociated in the AC powered nonthermal plasma environment and subsequently doped into the TiO2 photocatalyst that was capable of being induced by visible light sources. The APPENS process for producing N-doped TiO2 showed a higher film deposition rate in the range of 60–94 nm/min while consuming less power (<100 W) as compared to other plasma processes reported in literatures. And the photocatalytic activity of the N-doped TiO2 photocatalyst was higher than the commercial ST01 and P25 photocatalysts in terms of toluene removals in a continuous flow reactor. The XPS measurement data indicated that the active N doping states exhibited N 1s binding energies were centered at 400 and 402 eV instead of the TiN binding at 396 eV commonly observed in the literature. The light absorption in the visible light range for N-doped TiO2 was also confirmed by a clear red shift of the UV-visible spectra.

Emission Properties of InGaAsSbN Quantum Well Laser Diodes in 2 µm Wavelength Region Grown on InP Substrates

InGaAsSbN quantum well laser diodes operating in the 2 µm wavelength region were grown by molecular beam epitaxy (MBE) on InP substrates and their emission properties were studied. Two types of laser diodes with different Sb composition were compared. It was found that an increase in the Sb composition induces a marked redshift of the peak wavelength and a reduction of the spectral line width of the electroluminescence (EL) spectrum. A blueshift of the EL peak energy and a reduction of the EL spectral line width as well as a marked enhancement of the EL intensity were obtained by postgrowth rapid thermal annealing. The Sb composition dependence of the lasing characteristics was also studied. A clear redshift of the lasing wavelength was observed by increasing Sb composition.

Depth dependence of optical property beyond the critical thickness of an InGaN film

We study the depth-dependent variation of optical property beyond the critical thickness in an InGaN thin film. In the sample, both free-carrier and localized-state recombination activities are observed. The emission peak corresponding to the localized states in photoluminescence (PL) measurement becomes more prominent with increasing sample depth, implying stronger clustering in the deeper layers. Although the PL spectral peak variation is weak, that of cathodoluminescence (CL), corresponding to the activities of the localized states, shows a clear red shift trend with depth. The red shift trend is attributed to the stronger clustering behavior and possibly stronger quantum-confined Stark effect in the nano-clusters, which is due to the residual strain beyond the critical thickness, in a deeper layer.

Density functional theory study of the origin of IR and Raman band shifts in H‐bond complexes of triethylamine with water

AbstractThe present article discusses the results of density functional calculations obtained using B3LYP functional and the standard 6‐31G* basis sets for mono‐, di‐, and triethylamines (MEA, DEA, and TEA, respectively) and their H‐bonded complexes with water molecules. In particular, the origin of the observed experimentally clear red shift for methylene νCH mode due to the nanosecond laser T‐jump in TEA/H2O system is validated theoretically by explicit consideration of related infrared (IR) and Raman peaks appeared at the CH absorbance region. All theoretical calculations were performed with full geometry optimizations without imposing any constraints, and followed by direct harmonic frequency calculations. The effects of nonspecific and specific solvations were accounted for using simple Onsager model and explicit water molecules. It was shown that the former continuum model does not strongly perturb the observed spectral changes in the CH region because of shallow potential energy surface for the interacting subsystems. Both the structural changes in geometry and electron redistribution as a result of H‐bonding were found to be main factors to explain the observed experimental spectral changes in IR and Raman spectra. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Controlling the conformation of arylamides: computational studies of intramolecular hydrogen bonds between amides and ethers or thioethers.

The role of an ortho-alkylthioether group in controlling the conformation around the ring-N bonds of meta-connected arylamide oligomers is studied. Density functional theory (DFT) geometries of model compounds, including acetanilide, an ether acetanilide, and a thioether acetanilide, and their corresponding diamides, show that for either monoamide or diamide the alkyl side chain of the thioether should be perpendicular to the aryl plane, whereas for the ether monoamide, the alkyl side chain is in the aryl plane. DFT ring-N torsional potentials and constrained geometries of the model compounds demonstrate that carbonyl-S repulsion leads to a high torsional barrier and that intramolecular N-H...S and C-H...O hydrogen bonds and ring-amide conjugation lead to N-H having a preferred orientation in the benzene plane pointing towards S. The N-H bond lengthens and the ortho-ring C-H bond shortens in a regular pattern in the approach to the preferred orientation. Calculated IR frequencies for the N-H stretch show a clear red shift between model compounds without and with the thioether side chain.