Lanthanide sensitization in II-VI semiconductor materials: a case study with terbium(III) and europium(III) in zinc sulfide nanoparticles

This work explores the sensitization of luminescent lanthanide Tb(3+) and Eu(3+) cations by the electronic structure of zinc sulfide (ZnS) semiconductor nanoparticles. Excitation spectra collected while monitoring the lanthanide emission bands reveal that the ZnS nanoparticles act as an antenna for the sensitization of Tb(3+) and Eu(3+). The mechanism of lanthanide ion luminescence sensitization is rationalized in terms of an energy and charge transfer between trap sites and is based on a semiempirical model, proposed by Dorenbos and co-workers (Dorenbos, P. J. Phys.: Condens. Matter 2003, 15, 8417-8434; J. Lumin. 2004, 108, 301-305; J. Lumin. 2005, 111, 89-104. Dorenbos, P.; van der Kolk, E. Appl. Phys. Lett. 2006, 89, 061122-1-061122-3; Opt. Mater. 2008, 30, 1052-1057. Dorenbos, P. J. Alloys Compd. 2009, 488, 568-573; references 1-6.) to describe the energy level scheme. This model implies that the mechanisms of luminescence sensitization of Tb(3+) and Eu(3+) in ZnS nanoparticles are different; namely, Tb(3+) acts as a hole trap, whereas Eu(3+) acts as an electron trap. Further testing of this model is made by extending the studies from ZnS nanoparticles to other II-VI semiconductor materials; namely, CdSe, CdS, and ZnSe.     

Synthesis of cationic quantum dots via a two-step ligand exchange process

A new class of quaternary ammonium derivatives has been used to synthesize cationic CdSe/ZnS quantum dots with exceptional stability in water as well as in biological media.     

Fluorescent nanoparticles based on a microporous organic polymer network: fabrication and efficient energy transfer to surface-bound dyes

Well-defined nanoparticles composed of a tetraphenylmethane-based microporous polymer network with an average particle diameter of 30-60 nm were fabricated by a miniemulsion polymerization technique. Strong green emission was observed and efficient excitation energy transfer from nanoparticles to surface-bound dye molecules was explored.     

Unique role of ionic liquid [bmin][BF4] during curcumin-surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (～2-fold decrease) association with cationic surfactant solution.     

Mechanistic pathway for controlled extraction of guest molecule bound to herring sperm DNA using α-cyclodextrin

trans-2-[4-(Dimethylamino)styryl]benzothiazole (DMASBT) is known to have dual emitting states where the locally excited (LE) state is responsible for fluorescence in less polar environment and in polar milieu fluorescence is from the twisted intramolecular charge transfer (TICT) state. This compound also undergoes minor groove binding to herring sperm DNA (hsDNA) evidenced by the absorption spectra before and after the binding process and an effect on DMASBT fluorescence by an anionic quencher. The binding occurs efficiently in a 1:1 manner, i.e. one guest molecule binds to one site on the hsDNA. Instead of following the DNA twist, the aromatic part seems to project outward. Thus, the bound molecule can be successfully extracted out from the DNA in a controlled way by the hydrophobic cavity of α-cyclodextrin (α-CD). The extraction starts even with a low concentration of α-CD and increases as the concentration is increased. Absorption, steady-state and time resolved fluorescence spectroscopic methods have been employed to explore the mechanistic pathway of binding of DMASBT to hsDNA. The mechanistic approach toward controlled extraction of the guest molecules from hsDNA by α-CD is reported and is expected to serve a significant purpose in treatment of drug overdose.     

Stencils with isotropic discretization error for differential operators

We derive stencils, i.e., difference schemes, for differential operators for which the discretization error becomes isotropic in the lowest order. We treat the Laplacian, Bilaplacian (= biharmonic operator), and the gradient of the Laplacian both in two and three dimensions. For three dimensions ??(h²) results are given while for two dimensions both ??(h²) and ??(h⁴) results are presented. The results are also available in electronic form as a Mathematica file. It is shown that the extra computational cost of an isotropic stencil usually is less than 20%. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2006     

Evidence of Dynamical Fluctuation of Target Residues in Relativistic Nuclear Interaction at 14.5 AGeV

An analysis of data of target fragments of ²⁸Si-AgBr (at 14.5 AGeV) reveals the existence of emission asymmetry in the azimuthal plane, which is found to depend on the number of target fragments. The comparison with the data of ³²S-AgBr (at 200 AGeV) and ¹⁶O-AgBr (at 60 AGeV) interactions indicates that emission asymmetry depends on the projectile mass and energy.     

Carbon-13 resonance assignments of some friedelanes and taraxasteranes

Carbon-13 signal assignments of taraxasteryl acetate, taraxasteryl palmitate, taraxasterol and epi-friedelinyl acetate are reported. Some signal assignments of the friedelanones, reported recently by others, are inconsistent and require revision.