Morphology-dependent photoluminescence property of red-emitting LnOCl:Eu (Ln=La and Gd)

Three different synthetic methods, the liquid phase process in HCl solution, the solvothermal reaction, and the surfactant-assisted solvothermal reaction, were explored to selectively control the particle shape and to enhance the luminescence intensity of the PbFCl-type red-emitting oxychloride phosphors LnOCl:Eu (Ln=La and Gd). The solvothermal pressure facilitated the low-temperature crystallization of the rod-shape particles for both Ln=La and Gd. It is noted that LaOCl:Eu nanorods show highly porous particle surface and quite low photoemission intensity. In contrast, the solvothermal synthesis could highly enhance the red-emission of GdOCl:Eu with no porous surface so as to be comparable to that of commercial Y₂O₃:Eu phosphor. An addition of surfactant material during solvothermal reaction yielded a rhomboidal-shape phosphor particles with no porous surface for both Ln=La and Gd. Interestingly, the elimination of surface porosity by using a surfactant significantly increased the emission intensity of LaOCl:Eu. It is proposed that the application of solvothermal technique for the synthesis of the PbFCl-type oxychloride phosphors is very effective to selectively control the particle shape and consequently to enhance the photoemission intensity if we use an appropriate surfactant material.     

Synthesis and luminescence properties of U-shaped polycyclic molecules containing syn-facial functionalized quinoxaline rings

[reaction: see text] Rigid U-shaped molecules containing syn-facially situated quinoxaline rings have been synthesized in three steps, by a combination of the Diels-Alder reaction, the ruthenium-catalyzed oxidation, and the Zn(OAc)(2)-catalyzed condensation of the resulting bis-alpha-diketones with benzene-1,2-diamines. The unsymmetric bis-quinoxalines, with electronically different substituents, and the quinoxaline ring-attached alpha-diketones were also prepared. Their luminescence properties were examined and described.     

K3PO4 promoted dipolar [3+3] cyclization: Direct synthesis of pyrazino[2,1-a]isoquinoline derivatives

A K₃PO₄ promoted dipolar [3+3] cyclization of dihydroisoquinoline imines and arylacyl bromides has been developed. This process realized the direct synthesis of pyrazino[2,1-a]isoquinoline derivatives in 44–69% yields. A head to tail dimerization was proposed as key step for this procedure.     

Forming the graded-refractive-index antireflection layers on light-emitting diodes to enhance the light extraction

Distributed antireflection (AR) layers with different composition ratios of ITO and SiO(2) formed on an ITO electrode of GaN-based LEDs provide substantial enhancement in light-extraction efficiency. By using the coradio frequency magnetron sputtering deposition, four 50 nm thick AR layers with graduated refractive indices were fabricated. The effect of the AR layers on enhancing the efficiency of the LED device was analyzed by electroluminescence (EL) and I-V measurements. As a result, the EL intensity of the LED device grown on the patterned sapphire substrate with AR layers was increased by up to 13% compared to the conventional patterned sapphire substrate-applied LED device without AR layers at a drive current of 20 mA. The AR layers on top of the LED device gradually changed the refractive indices between ITO (n=2.1) and air (n=1.0), which minimized the total internal reflection of generated light. And no degradation in the electrical characteristic of the LEDs was observed according to the I-V measurements.     

Imaginary quadratic fields with noncyclic ideal class groups

Let g be an odd positive integer and X be a positive real number. We shall show that for any ∊ > 0, the number of imaginary quadratic fields with discriminant ≥ − X and ideal class group having a subgroup isomorphic to ℤ/g ℤ× ℤ/g ℤ is ≫ X^1/g−∊. 2000 Mathematics Subject Classification Primary—11R11, 11R29 This work was supported by KRF-R08-2003-000-10243-0 and partially by KRF-2002-003-C00001.     

Synthesis,structure and DNA-binding studies of tetranuclear copper(II) complexes bridged by asymmetrical<Emphasis Type="Italic"> N</Emphasis>,<Emphasis Type="Italic">N′</Emphasis>-bis(substituted)oxamides

Two tetranuclear copper(II) complexes bridged by asymmetrical N,N′-bis(substituted)oxamides have been synthesized and characterized as [Cu₄(dmapob)₂(Me₂bpy)₂](pic)₂·6H₂O (1) and [Cu₄(oxbe)₂(dabt)₂](pic)₂ (2), where H₃dmapob and H₃oxbe denote N-benzoato-N′-[3-(dimethylamino)propyl]oxamido and N-benzoato-N′-(2-aminoethyl)oxamide, respectively; and Me₂bpy, dabt, and pic represent 4,4′-dimethyl-2,2′-bipyridine 2,2′-diamino-4,4′-bithiazole, and 2,4,6-trinitrophenol, respectively. Complex 1 was characterized by elemental analyses, IR and electronic spectra, and single-crystal X-ray diffraction. Its structure consists of two asymmetrical binuclear copper(II) units linked by carboxyl bridges into a circular tetranuclear copper(II) complex with an embedded center of inversion. The copper(II) centers are in square-planar and distorted square-pyramidal environments. Hydrogen bonds and aromatic stacking interactions link the tetranuclear copper(II) fragments into a 3D supramolecular structure. The interactions of complexes 1 and 2 with herring sperm DNA (HS-DNA) were investigated by electronic and fluorescence spectra and viscosity measurements. Both complexes bind to HS-DNA via the intercalative mode, and complex 2 displays a significant binding propensity to HS-DNA.     

Real Quadratic Fields with Class Number Divisible by 5 or 7

We shall show that the number of real quadratic fields whose absolute discriminant is ≤ x and whose class number is divisible by 5 or 7 is improving the existing best known bound for g = 5 and for g = 7 of Yu (J Number Theory 97:35–44, 2002).This work was supported by KRF-R08-2003-000-10243-0 and partially by KRF-2005-070-C00004.     

A nano-porous TiO2 thin film coating method for dye sensitized solar cells (DSSCs) using electrostatic spraying with dye solution

The dye coloring process on a nano-porous TiO₂ thin film for DSSCs was studied using an electrostatic spraying (ESS) method. In this study, dye coating experiments were performed using homemade ESS equipment. The coating patterns on the TiO₂ thin film are changed by adjusting the applied voltages of the ESS system. The geometry of the coating patterns is observed by a charge-coupled device (CCD) camera. The TiO₂ thin film is fabricated by controlling the electric field which allows a uniform color distribution to be obtained with a high dyeing capacity. The colored TiO₂ thin films are compared with those obtained using a conventional immersed dye solution by means of an UV–vis spectrometer. The performance of this novel coloring process was confirmed by measuring I–V curve characteristics.     

On the Hénon equation with a Neumann boundary condition: Asymptotic profile of ground states

Consider the Hénon equation with the homogeneous Neumann boundary condition

$?\mathrm{\Delta }u+u=|x{|}^{\alpha }{u}^p,u>0\text{in}\mathrm{\Omega },\frac{?u}{?\nu }=0\text{ on }?\mathrm{\Omega },$

where $\mathrm{\Omega }?B(0,1)?{\mathbb{R}}^N,N\ge 2$ and $?\mathrm{\Omega }\cap ?B(0,1)\ne ?$. We are concerned on the asymptotic behavior of ground state solutions as the parameter $\alpha \to \infty$. As $\alpha \to \infty$, the non-autonomous term $|x{|}^{\alpha }$ is getting singular near $|x|=1$. The singular behavior of $|x{|}^{\alpha }$ for large $\alpha >0$ forces the solution to blow up. Depending subtly on the $(N?1)?$dimensional measure $|?\mathrm{\Omega }\cap ?B(0,1){|}_{N?1}$ and the nonlinear growth rate p, there are many different types of limiting profiles. To catch the asymptotic profiles, we take different types of renormalization depending on p and $|?\mathrm{\Omega }\cap ?B(0,1){|}_{N?1}$. In particular, the critical exponent $2_{?}=\frac{2(N?1)}{N?2}$ for the Sobolev trace embedding plays a crucial role in the renormalization process. This is quite contrasted with the case of Dirichlet problems, where there is only one type of limiting profile for any $p\in (1,2^{?}?1)$ and a smooth domain Ω.     

Elliptic curves of rank 1 satisfying the 3-part of the Birch and Swinnerton–Dyer conjecture

Let E be an elliptic curve over Q of conductor N and K be an imaginary quadratic field, where all prime divisors of N split. If the analytic rank of E over K is equal to 1, then the Gross and Zagier formula for the value of the derivative of the L-function of E over K, when combined with the Birch and Swinnerton–Dyer conjecture, gives a conjectural formula for the order of the Shafarevich–Tate group of E over K. In this paper, we show that there are infinitely many elliptic curves E such that for a positive proportion of imaginary quadratic fields K, the 3-part of the conjectural formula is true.