Luminescence of Cr ions associated with surpassing the green-emissive defect centers in β-Ga2O3

Photoluminescence of undoped and Cr³⁺-doped β-Ga₂O₃ was investigated. The transparent, undoped β-Ga₂O₃ film was successfully prepared by thermal conversion from GaOOH. The film exhibited predominant green luminescence in response to ultraviolet light excitation at 250 nm. This luminescence behavior, which was proposed to result from the oxygen defect centers, was used in examining excitation and emission mechanisms for Cr³⁺ ions doped in β-Ga₂O₃. It was found that red luminescence of Cr³⁺ surpasses green luminescence of the host lattice, as evidenced by the dependence of the spectral structure on the Cr³⁺ concentration. The excitation of Cr³⁺ was then suggested to be caused by the energy transfer from Ga³⁺O₆ octahedra present in the monoclinic β-Ga₂O₃ lattice.     

Quantification of ultrasonic intensity based on the decomposition reaction of porphyrin

A simple method is proposed for quantification of the effective ultrasonic intensity in the reaction vessel based on the decomposition reaction of 5,10,15,20-tetrakis(4-sulfotophenyl) porphyrin (H₂TPPS⁴⁻). The change of concentration of porphyrin in solution irradiated by the ultrasound wave depends on the irradiation time and the output power of ultrasound generator. The decomposition ratio of porphyrin is defined as the ratio of the concentration of porphyrin after ultrasonic irradiation to that before ultrasonic irradiation. A linear relationship between the decomposition ratio of porphyrin and the concentration Fe³⁺ in the Fricke solution under sonication was obtained. The decomposition ratio was related to the absorption dose in radiation chemistry.     

Performance characteristics of narrow linewidth fiber laser pumped mid-IR difference frequency mixing light source for methane detection.

A high-power, narrow-linewidth Yb fiber laser with a fiber Bragg grating (FBG) pumped difference frequency generation (DFG) in a periodically poled lithium niobate (PPLN) crystal was investigated in detail. A mid-IR power of approximately 2.3 microW at 3.3 micrometers with a slope efficiency of 0.85 mW/W2 was achieved. A Doppler-broadened absorption spectrum of CH4 at 3038.497 cm-1 (3.2911 micrometers) was obtained with a 0.1-m long-gas cell at a pressure of 133 Pa. The linewidth of the DFG source was evaluated to be less than 96 MHz from the observed spectral linewidth. Real-time monitoring of CH4 (approximately 1.78 ppm) in ambient air in a multipass cell which has an optical path length of 10 m was also demonstrated.     

Stoichiometry and conformation of the azacrown moiety in sodium complexes of azacrown ethers. A Raman/IR spectroscopic study. Part I: Complexes of 4,13-Diaza-18-crown-6

Three sodium complexes (bromide, iodide and thiocyanate) of 4,13-diaza-18-crown-6 were studied using Raman and IR spectroscopy and normal coordinate calculations to probe the stoichiometry of the complexes and the variation in the conformation of azacrown moiety on complex formation. complex formation is accompanied by characteristic shifts of the bands, especially of those in the 800–900 cm^–1 region. Complexes of both 11 and 21 stoichiometry were observed. Normal coordinate calculations showed the reduction of symmetry of azacrown moiety toC _i , in contrast to theC _2h symmetry known for the parent azacrown and potassium thiocyanate complex.     

Binary and ternary complexes involving manganese(II), 2,2’-bipyridine and halide or thiocyanate ions inN,N-dimethylformamide

Ternary complexation involving the manganese(II) ion, 2,2’-bipyridine (bipy), and halide (chloride, bromide) or pseudohalide (thiocyanate) ions has been studied by precise titration calorimetry inN,N -dimethylformamide (DMF) at 298K. All the titration curves are explained well in terms of formation of mononuclear complexes of the type [MnX_m(bipy)_n](^2-m) + (X = CI, Br or SCN), and the formation of [MnCl(bipy)]⁺, [MnCl₂(bipy)], [MnCl(bipy)₂]⁺ and [MnCl₂(bipy)₂] has been established in the chloride system, [MnBr(bipy)]⁺, [MnBr₂(bipy)], [MnBr(bipy)₂]⁺ in the bromide system, and [Mn(NCS)(bipy)]⁺, [Mn(NCS)₂(bipy)], [Mn(NCS)₃(bipy)]^-, [Mn(NCS)(bipy)₂]⁺, and [Mn(NCS)₂(bipy)₂] in the thiocyanate system. The data were analyzed on the basis of the thermodynamic parameters for the binary Mn^lIbipy and Mn^II-X (X = Cl, Br and SCN) systems, the latter being determined in previous work. The formation constants, reaction enthalpies, and entropies of the ternary complexes were extracted. The thermodynamic parameters thus obtained are discussed in comparison with those of the corresponding systems of other transition metal(II) ions.     

Hydrothermal routes to prepare nanocrystalline mesoporous SnO2 having high thermal stability

We report simple hydrothermal routes to prepare thermally stable SnO2 particles having high specific surface areas and mesoporosity. The preparation method includes a new combination of synthetic processes: hydrolysis of tin(IV) chloride at 95 degrees C in the absence of alkaline solutions (aqueous NH3 or NaOH), formation of nanocrystalline SnO2, and subsequent hydrothermal treatments at temperatures between 100 and 200 degrees C. After annealing treatments of the hydrothermally treated SnO2 particles at 400 or 500 degrees C, their crystallite sizes remained smaller than 7.7 nm and their specific surface areas were still higher than 110 m2/g, indicative of the high thermal stability against particle growth and sintering. Furthermore, mesoporosity evolved with a relatively narrow pore size distribution typically in the range of 3.0-4.3 nm. The effects of the hydrothermal treatment were explained by uniformization of the particle size that was beneficial to the suppression of particle growth.     

Quantitative evaluation of d-pi interaction in copper(I) complexes and control of copper(I)-dioxygen reactivity

Crystal structures of the copper(I) complexes 1(X), 2, and 3 of a series of tridentate ligands L1(X), L2, and L3, respectively (L1(X): p-substituted derivatives of N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine; X=H, Me, OMe, Cl, NO(2); L2: N,N-bis[2-(2-pyridyl)ethyl]-2-methyl-2-phenylethylamine; L3: N,N-bis[2-(2-pyridyl)ethyl]-2,2-diphenylethylamine) were solved to demonstrate that all the copper(I) complexes involve an eta(2) copper-arene interaction with the phenyl ring of the ligand sidearm. The Cu(I) ion in each complex has a distorted tetrahedral geometry consisting of the three nitrogen atoms (one tertiary amine nitrogen atom and two pyridine nitrogen atoms) and C(1)-C(2) of the phenyl ring of ligand sidearm, whereby the Cu-C distances of the copper-arene interaction significantly depend on the para substituents. The existence of the copper-arene interaction in a nonpolar organic solvent (CH(2)Cl(2)) was demonstrated by the observation of an intense MLCT band around 290 nm, and the magnitude of the interaction was evaluated by detailed analysis of the (1)H and (13)C NMR spectra and the redox potentials E(1/2) of the copper ion, as well as by means of the ligand-exchange reaction between the phenyl ring and CH(3)CN as an external ligand. The thermodynamic parameters DeltaH(o) and DeltaS(o) for the ligand-exchange reaction with CH(3)CN afforded a quantitative measure for the energy difference of the copper-arene interaction in the series of copper(I) complexes. Density functional studies indicated that the copper(I)-arene interaction mainly consists of the interaction between the d(z(2) ) orbital of Cu(I) and a pi orbital of the phenyl ring. The copper(I) complexes 1(X) reacted with O(2) at -80 degrees C in CH(2)Cl(2) to give the corresponding (micro-eta(2):eta(2)-peroxo)dicopper(II) complexes 4, the formation rates k(obs) of which were significantly retarded by stronger d-pi interaction, while complexes 2 and 3, which exhibit the strongest d-pi interaction showed significantly lower reactivity toward O(2) under the same experimental conditions. Thus, the d-pi interaction has been demonstrated for the first time to affect the copper(I)-dioxygen reactivity, and represents a new aspect of ligand effects in copper(I)-dioxygen chemistry.     

Spatially resolved gas phase composition measurements in supersonic flows using tunable diode laser absorption spectroscopy

We used a tunable diode laser absorption spectrometer to follow the condensation of D(2)O in a supersonic Laval nozzle. We measured both the concentration of the condensible vapor and the spectroscopic temperature as a function of position and compared the results to those inferred from static pressure measurements. Upstream and in the early stages of condensation, the quantitative agreement between the different experimental techniques is good. Far downstream, the spectroscopic results predict a lower gas phase concentration, a higher condensate mass fraction, and a higher temperature than the pressure measurements. The difference between the two measurement techniques is consistent with a slight compression of the boundary layers along the nozzle walls during condensation.     

Dissolved states of ionene polymers in water-acetone and their relation to the ionic partial molar adiabatic compressibility and volume

Solution properties of water-soluble synthetic polymer, 3,3-ionene and 6,6-ionene chloride and bromide disolved in water-acetone mixtures up to acetone content 50 wt% were investigated. Their partial molar volumes V ₂ ^o and partial molar adiabatic compressibilities K _s ^o were determined. Ionic additivity of V ₂ ^o with respect to the cation of backbone polymer chain and the counter-anion was confirmed quantitatively. The ionic additivity of V ₂ ^o is discussed along with the K _s ^o in their relation to the counterion binding of ionene polymers. Effects of ionic sites on the ionene are strong but they don't break the solvation layer.     

Aerobic ruthenium-catalyzed oxidative cyanation of tertiary amines with sodium cyanide

RuCl3-catalyzed oxidative cyanation of tertiary amines with sodium cyanide under molecular oxygen (1 atm) at 60 degrees C gives the corresponding alpha-aminonitriles, which are versatile synthetic intermediates of various compounds such as amino acids and unsymmetrical 1,2-diamines, in excellent yields. This reaction is clean and should be an environmentally benign and useful process.