Absorption spectra of solid rare earth complexes obtained from the inner filter effect on luminescence

The inner filter effect is observed in luminescence whenever a second substance is present that has absorptions which overlap the luminescence. This results in a diminution of the luminescence at those wavelengths and is generally observed in solution. In the present communication we show that this effect can be observed when a solid rare earth complex is physically mixed with a solid luminescent organic matrix with which it does not interact. The resulting luminescence is reduced in emission intensity at those wavelengths corresponding to the absorptions of the rare earth ion. This is illustrated with a mixture of Na₃[Ho(ODA)₃] ·2NaClO₄·6H₂O and pyrene at 77 K, and it is shown that the absorption spectrum of the holmium complex can be extracted from the luminescence spectrum of pyrene. This absorption spectrum is in good agreement with that obtained by conventional spectroscopy with a single crystal.     

Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes

The ²⁹Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.     

Stepwise-Graded Si3N4–SiC Ceramics with Improved Wear Properties

The processing of stepwise graded Si₃N₄/SiC ceramics by pressureless co-sintering is described. Here, SiC (high elastic modulus, high thermal expansion coefficient) forms the substrate and Si₃N₄ (low elastic modulus, low thermal expansion coefficient) forms the top contact surface, with a stepwise gradient in composition existing between the two over a depth of ∼1.7 mm. The resulting Si₃N₄ contact surface is fine-grained and dense, and it contains only 2 vol% yttrium aluminum garnet (YAG) additive. This graded ceramic shows resistance to cone-crack formation under Hertzian indentation, which is attributed to a combined effect of the elastic-modulus gradient and the compressive thermal-expansion-mismatch residual stress present at the contact surface. The presence of the residual stress is corroborated and quantified using Vickers indentation tests. The graded ceramic also possesses wear properties that are significantly improved compared with dense, monolithic Si₃N₄ containing 2 vol% YAG additive. The improved wear resistance is attributed solely to the large compressive stress present at the contact surface. A modification of the simple wear model by Lawn and co-workers is used to rationalize the wear results. Results from this work clearly show that the introduction of surface compressive residual stresses can significantly improve the wear resistance of polycrystalline ceramics, which may have important implications for the design of contact-damage-resistant ceramics.     

Multifactorial assessment of bulimia nervosa.

Investigated a multifactorial approach to the assessment of bulimia nervosa by means of hierarchical factor analysis. 245 bulimia nervosa patients and 68 patients with either anorexia nervosa or eating disorders not otherwise specified were administered a self-report battery that was organized into 21 dimensions relevant to eating disorder patients. When dimensions from this battery were subjected to hierarchical factor analysis, support for bulimia nervosa as a unique diagnostic category was obtained. However, the emergence of 3 secondary factors and 6 primary factors suggests that bulimia nervosa can also be described more complexly. The emergence of a multifactorial model of bulimia nervosa that incorporates several existing unidimensional models suggests the potential for both divergent and complicated clinical presentation in bulimia nervosa patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Obtaining Characteristic 4f–4f Luminescence from Rare Earth Organic Chelates

We report a study of a series of heavy rare earth tris‐8‐hydroxyquinolines (REQ₃s), using UV‐visible absorption spectroscopy, infrared absorption spectroscopy, and photoluminescence (PL) measurements. We show that the heavy REQ₃s are all chemically similar to each other and to aluminium tris‐8‐hydroxyquinoline, at least in terms of the ligand behavior. Characteristic rare earth 4f–4f luminescence is only observed for ErQ₃ and YbQ₃ due to the relatively low energy of the ligand triplet state. We show that a triplet transfer mechanism cannot be responsible for the observed Yb 4f–4f luminescence observed in YbQ₃. Instead, an internal chemiluminescent process is shown to be energetically favorable. The thin film PL spectra of all the heavy REQ₃s are dominated by triplet emission, except for that of ErQ₃, for which transfer to the Er³⁺ ion represents an efficient alternative. The PL spectra of powder samples, which would be expected to consist of approximately equal amounts of both isomers, are dominated by singlet emission. This is in contrast to the results from the thin films, and suggests that the isomer which predominates in the thin films has a much higher intersystem crossing rate than the other isomer.     

A reliable and manufacturable method to induce a stress of >1 GPa on a P-channel MOSFET in high volume manufacturing

This letter discusses a reliable and manufacturable integration technique to induce greater than 1 GPa of stress into a p-channel MOSFET, which will be required to increase the drive current beyond 1 mA//spl mu/m at the sub-90-nm process generation. Uniaxial compressive stress is introduced into the p-channel by both a selective deposition of SiGe in the source/drain and an engineered 2.5-GPa compressively stressed nitride. The highest to date compressively stressed SiN film is obtained by heavy ion bombardment during the deposition of the film.     

Synthesis and applications of heterobifunctional poly(ethylene oxide) oligomers

Poly(ethylene oxide) (PEO) oligomers are employed extensively in pharmaceutical and biomedical arenas mainly due to their excellent physical and biological properties, including solubility in water and organic solvents, lack of toxicity, and absence of immunogenicity. PEO can be chemically modified and reacted with, or adsorbed onto, other molecules and surfaces. Sophisticated applications for PEO have increased the demand for PEO oligomers with tailored functionalities, and heterobifunctional PEOs are often needed. This review discusses the synthesis and applications of heterobifunctional PEO oligomers possessing amine, carboxylate, thiol, and maleimide functional groups.