Investigation of emission properties of Tm3＋：Y2O3 transparent ceramic

A transparent and emitting ceramic of Y 2 O 3 doped with 6% Tm 3+ ions is fabricated by vacuum sintering with ZrO 2 . Absorption, photoluminescence (PL), and PL excitation (PLE) spectra are investigated in a spectral range of 200 to 2 100 nm at various temperatures between 296 and 12 K. Intense emission band appears at 450 to 465 nm in the visible range. Near-infrared emission bands are observed at 1 200 to 1 300 nm and 1 400 to 1 550 nm, with intense peaks at 1 270, 1 450, and 1 523 nm. The luminescence mechanisms and potential applications of the emissions are discussed with the help of Judd-Ofelt theory and PLE spectra.     

Polarization mechanism of LiNbO3 crystal due to thermoelectric power and current-induced electric fields during growth via micro-pulling-down method

The mechanism of polarization due to thermoelectric power and current-induced electric fields during the growth of LiNbO₃ crystals was studied using a micro-pulling-down method. With no applied electric current, a +c single-domain crystal was grown regardless of the domain orientation of the seed crystal. This +c domain growth was consistent with the direction of the electric field caused by the thermoelectric power in the liquid, despite an opposing electric field in the solid due to the opposite sign of the Seebeck coefficient. Thus, it was the electric field in the liquid that determined the domain structure of the growing crystal. On the other hand, when a current was applied from the melt to the crystal, a −c domain crystal was grown. The electric current required for this domain inversion to occur became larger as the temperature gradient in the solid phase decreased. This shows that the electric field in the solid phase became large enough to induce domain inversion from +c to −c through a combination of the thermoelectric power in the solid phase and current-induced electric field.     

On Theories Having Three Countable Models

A theory T is called almost ??₀-categorical if for any pure types p₁(x₁),…,p_n(x_n) there are only finitely many pure types which extend p₁(x₁) ∪…∪p_n(x_n). It is shown that if T is an almost ??₀-categorical theory with I(??₀,T) = 3, then a dense linear ordering is interpretable in T.     

Inversion and internal rotation in methyl-d-amine: Microwave spectrum

The microwave spectrum of CH₂DNH₂ has been observed in the 8–74 GHz region. The spectrum shows that this molecule takes essentially two distinguishable conformers, trans and gauche forms, although a small amount of coupling between them can be detected. For each line of the trans form a small inversion splitting has been found. It is 93.97 MHz at K = 0 and a periodic function of K. The mean frequencies of the inversion pairs of lines are well explained as the frequencies of a rigid rotor. The gauche spectrum is extremely complicated; each rotational line splits into four because of inversion and gauche-gauche tunneling interactions. The analysis was carried out based on the theory developed in the preceding paper. Tunneling energy parameters of internal-rotation, ?_gg and ?_tg, and inversion, δ_gg and δ_tg, were determined as ?_gg = 3476.6 MHz, ?_tg = 3233.1 MHz, δ_gg = 2790.6 MHz and δ_tg = 3052.7 MHz. Energy difference between trans and gauche conformers ΔE_tg was estimated to be 7.060 cm^?1 from these values of parameters and also on the basis of the observed anomaly in the Q branch series of trans form which is due to an accidental degeneracy between the K = 1 level of trans and K = 2 level of gauche. The effects on the internal-rotation of other internal motions have also been discussed.     

Reversible catenation of coordination rings with Pd(II) and/or Pt(II) metal centers: Chirality induction through catenation

A Pd(II)-linked coordination ring is reversibly transformed into its catenanted dimer at room temperature through the efficient organic stacking of the component rings. An analogous Pt(II)-linked ring is also catenated only at high temperature (100 °C), but not at room temperature because of the kinetic inertness of Pt(II)-ligand interaction. Interestingly, the combination of the Pd(II)- and the Pt(II)-linked coordination rings selectively gives a Pd(II)/Pt(II) cross-catenane, because the kinetically inert Pt(II) ring can be catenated only via the dissociation of the kinetically labile Pd(II) ring. Planer conformation of the monomer rings is twisted upon catenation, inducing helical chirality in the catenated structure. Thus, induced circular dichroism (ICD) is observed in the catenation when chiral-1,2-cyclohexandiamine is attached as a chiral auxiliary on the metal centers. The ICD decreases with increasing temperature due to less effective chiral aromatic stacking at higher temperature. The Pd(II) ring shows higher ICD than the Pt(II) ring, probably due to the more flexible conformation of the Pd(II) ring that can adopt chiral orientation easily. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3478–3485, 2003     

Fragmentation of tertiary cyclopropanol compounds catalyzed by vanadyl acetylacetonate

Tertiary cyclopropanol compounds react with a catalytic amount of vanadyl acetylacetonate in the presence of oxygen affording β-hydroxyketones and β-diketones. For 3-substituted-bicyclo[4.1.0]alkanols, peroxides are obtained, as are the β-hydroxyketones. Conversely, 2-ethoxycarbonylcyclopropyl silyl ethers produce ethyl γ-oxocarboxylate derivatives given the same reaction conditions.     

Measurement of the absolute oscillator strengths of gadolinium using an atomic vapor produced by electron beam heating

The absolute values of the oscillator strength ƒ were measured for the six spectral lines of Gd by means of laser absorption spectroscopy with the atomic vapor produced by electron beam heating. The ƒ values obtained for the transition are 0–17381 cm⁻¹, 215–17750 cm⁻¹, 533–17795 cm⁻¹, 999–18070 cm⁻¹, 999–17931 cm⁻¹, 1719–18070 cm⁻¹ were obtained to be 0.0036, 0.012, 0.014, 0.019, 0.0075 and 0.039, respectively. The error of ƒ values was 24% due to uncertainty of metastable states' density.