Novel red phosphors for solid state lighting; the system BixLn1−xVO4; Eu/Sm (Ln=Y, Gd)

Solid solutions of vanadates of formula Bi_xLn_1−xVO₄ (Ln=Y, Gd) doped with Eu³⁺ or Sm³⁺ ions have been synthesized by solid-state reactions. Intense red/orange-red luminescence is obtained in these samples on excitation in the broad charge-transfer band in the near UV. The excitation in the Eu³⁺ levels leads to much less intense red emission. These materials could find applications as red phosphors for solid-state white lighting devices utilizing GaN-based excitation in the near UV.     

Intermarriage of Halide Perovskites and Metal-Organic Framework Crystals

This Review examines how the intermarriage of perovskite and metal-organic framework crystals brings new paradigms for material design and functionality. The strategic combination of halide perovskites and metal–organic frameworks (MOFs) has generated a new family of porous composite materials that will enable new applications, including optoelectronic, catalysis, sensing, and data encryption. This Review surveys the current progress of this exciting new area. Fundamental aspects, including perovskite nucleation and growth, heterojunction electron–hole transfer, electronic structure, and luminescence within confined spaces, are highlighted, with suggestions of approaches by which guest confinement within MOFs can be synthetically designed. We further address the underlying principles and discuss the new insights and tools for the manipulation of these composite materials for the development of synthetic microporous semiconducting composites, as well as new strategies for host–guest interfacial engineering.     

Review of technetium chemistry research conducted at the University of Nevada Las Vegas

The chemistry of technetium is being explored at the University of Nevada Las Vegas. Our goal is to investigate both the applied and fundamental aspects of technetium chemistry, with a special emphasis on synthesis, separations, and materials science. The synthetic chemistry focuses on metal–metal multiple bonding, oxides and halides. Synthesis and characterizations of (n-Bu₄N)₂Tc₂X₈, Tc₂(O₂CCH3)₄X₂ (X = Cl, Br), TcO₂, Bi₂Tc₂O₇, Bi₃TcO₈, TcBr₃ and TcBr₄ have been performed. The applied chemistry is related to the behavior of Tc in the UREX process. Separation of U/Tc has been conducted using anion exchange resin and metallic Tc waste form synthesized and characterized.     

Anhydrous deuterium β-alumina: Powder neutron diffraction studies at 4.2, 298, 573, and 720 K

The structure of anhydrous stoichiometric deuterium β-alumina, Dal₁₁O₁₇, has been determined at 4.2, 298, 573, and 720 K by profile refinement of powder neutron diffraction data. At each temperature the deuterium is found to lie in well-defined threefold sites close to the spacer oxygen, O(5). There is no evidence for delocalization of the deuterium away from O(5) and such a hydroxyl linkage is in accord with the low protonic conductivity observed in related materials. The effect of this unusual mirror-plane arrangement on the remainder of the structure and the variation with temperature of the lattice constants, bond lengths, and angles are discussed.     

Travelling Modes in Wave-Heated Plasma Sources

This paper describes a theoretical and experimental study of surface- and helicon-wave-heated plasma sources in which standing waves are set up in the cavity between the closed end plate to a plasma vessel and a wave launcher while travelling waves propagate from the opposite side of the launcher into a region which is long compared with the attenuation distance of the waves. We model the situation as a lossy transmission line of finite length coupled at the launcher to a lossy transmission line of infinite extent. RF power applied to the launcher divides in the ratio of the input impedances of the two transmission lines. For a conducting end plate, the power delivered to the travelling waves is a maximum when the cavity length is an odd number of 1/4 wavelengths long for which its input impedance is a maximum. Similarly, for an insulated end plate, the power delivered to the travelling waves is a maximum for a cavity with a length equal to an integer number of half wavelengths for which its input impedance is again a maximum.      

Diverse structures and dimensionalities in hybrid frameworks of strontium and lanthanum with isomeric dihydroxybenzoates

Investigations of Sr and La derivatives of 2,3-, 2,4-, 3,5-, and 2,6-dihydroxybenzoic acids have revealed that it is possible to obtain chain and layered structures of these materials. [Sr2(2,3-DHB)4(H2O)4].3H2O, I, and [Sr(2,4-DHB)2(H2O)4].H2O, II, are both one-dimensional coordination polymers based on dimers; both the carboxylate and phenolic oxygens bond to the metal in I and only the carboxylate oxygens bond to the metal in II. [Sr(3,5-DHB)2(H2O)2].4H2O, III, has a one-dimensional chain structure with large channels and involves extended Sr-O-Sr connectivity. [Sr(CH3CO2)(2,4-DHB)(H2O)3].H2O, IV, also has a chain structure with extended Sr-O-Sr connectivity, but the chain structure is formed by bridging acetate units, unlike in III where the Dihydroxybenzoate (DHB) is the bridging unit. [Sr(2,6-DHB)2(H2O)2].0.5H2O, V, is a two-dimensional coordination polymer where both carboxylate and phenolic oxygens coordinate to the metal. A lanthanum compound with the composition [La(CH3CO2)2(2,4-DHB)H2O].0.18H2O, VI, with a one-dimensional chain structure with extended La-O-La connectivity, has been prepared. Besides these chain and layered structures, zero-dimensional dimers of rare-earth DHBs with the general formula [La(CH3CO2)2(DHB)(H2O)2], with 3,5- (VII), 2,6- (VIII), and 2,3-dihydroxybenzoic acids (IX) have been synthesized. The diverse structures of the strontium and lanthanum DHBs are described. The study demonstrates that it is possible to obtain interesting structures of metal DHBs with different dimensionalities. The structures appear to be controlled largely by geometrical rather than electronic factors.     

Synthesis of open-framework zinc phosphates from organophosphorus amides

The use of hexamethylphosphoramide as a single source of amine and phosphorus has made it possible to synthesize new three-dimensional zinc phosphate frameworks under solvothermal conditions.     

A high-field C-NMR study of the aqueous copolymerisation of acrylonitrile and vinyl acetate. Microstructural observations

A detailed examination has been undertaken of the high field ¹³C-NMR spectrum of various acrylonitrile/vinyl acetate copolymers prepared by radical initiation in a heterogeneous aqueous batch reaction (taken to low conversion). It has been possible to establish the triad, tetrad and pentad sequences for copolymers employing sequence patterns and peak fractions as an aid to peak assignments. These results indicate that the copolymer cotacticity is virtually independent of the comonomer feed ratio.