Effects of citric acid additive on photoluminescence properties of YAG:Ce nanoparticles synthesized by glycothermal reaction

We synthesize Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce³⁺) nanoparticles in the presence of citric acid by glycothermal method. Fourier transform infrared absorption spectroscopy measurement indicates that the intensity of the peak corresponding to carboxyl groups coordinating to the nanoparticles increases with increasing amount of citric acid. At the same time, the primary particle diameter decreases from 10.2 to 4.0 nm. In addition, the internal quantum efficiency of the photoluminescence (PL) due to the 4f-5d transition of Ce³⁺ increases from 22.0% to 40.1% with increasing amount of citric acid. Two kinds of PL decay lifetimes, 16-26 and 72-112 ns, are detected for YAG:Ce³⁺ nanoparticles, whereas the micron sized YAG:Ce³⁺ bulk shows the lifetime of 57 ns. We discuss these phenomena from the aspects of the coordination of citric acid and the incorporation of Ce³⁺ ions into the nanoparticles.     

Two-dimensional measurements of flow velocity in a microscopic region using two rotating gratings

A two-dimensional vector velocimeter is proposed on the basis of the time-varying spatial filtering method using a rotating disc with two transmission gratings. The filtering characteristics of the spatial filter used in the velocimeter are studied theoretically. This velocimeter was applied to measure the velocity vector of flowing water in a small glass pipe. The experimental results show the usefulness of the present velocimeter for measurements of the flow velocity in a microscopic region.     

Selective enhancement of scopadulcic acid B production in the cultured tissues of Scoparia dulcis by methyl jasmonate

The effects of methyl jasmonate (MeJA) on isoprenoid production were evaluated in cultured tissues of Scoparia dulcis. It was found that MeJA suppressed the accumulation of chlorophylls, carotenoids, phytol and beta-sitosterol in the tissues. MeJA, however, remarkably enhanced the production of scopadulcic acid B (SDB), with 10 microM being optimal observed concentration for stimulation of SDB production. The maximum concentration of SDB was observed 6 d after MeJA treatment.     

Effects of dissolved gas species on ultrasonic degradation of (4-chloro-2-methylphenoxy) acetic acid (MCPA) in aqueous solution

Sonochemical degradation of MCPA ((4-chloro-2-methylphenoxy) acetic acid) in dilute aqueous solutions was studied using ultrasound with a frequency of 500 kHz. The effect of gas atmosphere on MCPA degradation was investigated in nitrogen (N(2)), air (O(2)/N(2)), oxygen (O(2)), argon (Ar) and Ar/O(2) (60/40% v/v) atmospheres. For sonochemical degradation of MCPA in N(2), air (O(2)/N(2)), O(2) and Ar atmospheres, the rate enhancement of MCPA decomposition by sonolysis was found to be more effective in an O(2)-enriched atmosphere compared to Ar atmosphere. It was considered that a higher amount of oxidants was formed in a higher O(2) partial pressure, which accelerated MCPA decomposition in a radical reaction system. On the other hand, both dechlorination and total organic carbon (TOC) removal rates were higher in Ar atmosphere, compared to those in O(2)/N(2) atmosphere. It was found that, MCPA was most effectively decomposed by sonication in Ar/O(2) (60/40% v/v) atmosphere, with higher rates of decomposition, dechlorination and TOC removal.     

Desulfurization reactions on Ni2P(001) and alpha-Mo2C(001) surfaces: complex role of P and C sites

X-ray photoelectron spectroscopy and first-principles density-functional calculations were used to study the interaction of thiophene, H(2)S, and S(2) with Ni(2)P(001), alpha-Mo(2)C(001), and polycrystalline MoC. In general, the reactivity of the surfaces increases following the sequence MoC < Ni(2)P(001) < alpha-Mo(2)C(001). At 300 K, thiophene does not adsorb on MoC. In contrast, Ni(2)P(001) and alpha-Mo(2)C(001) can dissociate the molecule easily. The key to establish a catalytic cycle for desulfurization is in the removal of the decomposition products of thiophene (C(x)H(y) fragments and S) from these surfaces. Our experimental and theoretical studies indicate that the rate-determining step in a hydrodesulfurization (HDS) process is the transformation of adsorbed sulfur into gaseous H(2)S. Ni(2)P is a better catalyst for HDS than Mo(2)C or MoC. The P sites in the phosphide play a complex and important role. First, the formation of Ni-P bonds produces a weak "ligand effect" (minor stabilization of the Ni 3d levels and a small Ni --> P charge transfer) that allows a high activity for the dissociation of thiophene and molecular hydrogen. Second, the number of active Ni sites present in the surface decreases due to an "ensemble effect" of P, which prevents the system from deactivation induced by high coverages of strongly bound S. Third, the P sites are not simple spectators and provide moderate bonding to the products of the decomposition of thiophene and the H adatoms necessary for hydrogenation.     

A facile method for oxytelluration of olefins

Treatment of olefins with phenyltellurium(I) or (IV) species [(PhTe)₂, PhTeCN, PhTeBr₃] in alcohol at room to reflux temperature for 1–24 h produces the corresponding (2-alkoxyalkyl)phenyltellurium dihalides in good yields, the reaction being trans-stereoselective and highly regioselective.     

Tuning characteristic of flashlamp-pumped dye laser with oxygen

The effect of oxygen in the flashlamp-pumped tunable Rhodamine 6G dye laser is experimentally studied. It becomes clear that the laser tuning range is shifted by adding oxygen in the dye solution.     

First-order probability density function of the laser speckle phase

An expression for the first-order probability density function of the laser speckle phase is analytically derived under the assumption that the speckle field obeys a non-circular, complex Gaussian, random process with a certain correlation between the real and imaginary parts of its complex amplitude. The probability density function of the speckle phase is actually evaluated for various cases and shown three-dimensionally as a function of the standard deviation of random object phase variations. The effect of random object phase variations on the probability density function is also investigated in detail.     

Effect of aberrations on off-axis gaussian beams

The effect of aberrations of an optical system on gaussian beams is analyzed. If an incident position of the beams of the optical system does not coincide with the center of its pupil, the beams suffer from aberrations differently in accordance with the various incident positions. The Strehl definition of the beams is studied as a function of the incident position of the beams and the kind of abberations present in the optical system.     

Partially coherent Fresnel diffraction by a slit aperture. II. Axial intensity distributions

The general formula derived in a previous paper is applied to obtain the intensity distribution along the axis normal to a slit aperture in the Fresnel diffraction field when the spatial mutual coherence function of the illumination over the aperture takes three different forms of correlation. It is shown that the axial intensity distribution of Fresnel diffraction by the slit aperture is effectively influenced by the coherence condition across the diffracting aperture.