Temperature effect on emission spectra and fluorescence lifetime of the ~4I_(13/2) state of Er~(3+)-doped Gd_2SiO_5 crystal

By measuring the emission spectra and the fluorescence lifetime of the 4 I 13 /2 state of Er 3+ ions in Gd 2 SiO 5 crystal at different temperatures,the effects of temperature on the spectra and the lifetime of the 4 I 13 /2 state are investigated. When the temperature increases,the emission line width for the 4 I 13 /2 → 4 I 15 /2 transition is broadened,and the main emission lines at 1 596,1 609,and 1 644 nm shifte toward shorter wavelengths. The measured lifetime of the 4 I 13 /2 state decreases from 13.2 to 8.4 ms with temperature increase from 13 to 300 K,which is mainly due to the temperature dependence of multiphonon relaxation between the 4 I 13 /2 and 4 I 15 /2 states and the changing population distribution among the Stark levels within the 4 I 13 /2 state. The experimental results imply that low temperature condition is better for the ～1.6-μm laser output.     

Activation of olefins with low-valent gallium compounds under ambient conditions

The reactions of Ar'GaGaAr' (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) with alkenes revealed the addition of two olefins per Ar'GaGaAr' under ambient conditions for ethylene, propene, 1-hexene and styrene but no reactions with more hindered or cyclic olefins.     

Experimental demonstration of wakefield acceleration in a tunable dielectric loaded accelerating structure

We report on a collinear wakefield experiment using the first tunable dielectric loaded accelerating structure. By introducing an extra layer of nonlinear ferroelectric, which has a dielectric constant sensitive to temperature and dc bias, the frequency of a dielectric loaded accelerating structure can be tuned. During the experiment, the energy of a witness bunch at a fixed delay with respect to the drive beam was measured while the temperature of the structure was scanned over a 50?°C range. The energy change corresponded to a change of more than half of the nominal structure wavelength.     

Reactions of heavier main‐group compounds with hydrogen,ammonia, ethylene and related small molecules

The first reaction between hydrogen and a main‐group compound under ambient conditions was reported in 2005. This unexpected result has been followed by numerous others which show that such reactivity is widespread in unsaturated and multiple bonded main‐group species. These may react spontaneously not only with hydrogen, but also with ethylene, ammonia and related molecules. This account focuses on results from the author's laboratory but also on parallel work by other groups. The link between HOMO‐LUMO separations, symmetry considerations and reactivity of the main‐group species is emphasized as is their similarity in reactivity to transition‐metal organometallic compounds. DOI 10.1002/tcr.201100016     

Two-coordinate, quasi-two-coordinate, and distorted three coordinate, T-shaped chromium(II) amido complexes: unusual effects of coordination geometry on the lowering of ground state magnetic moments

The synthesis and characterization of the mononuclear chromium(II) terphenyl substituted primary amido-complexes Cr{N(H)Ar(Pr(i)(6))}(2) (Ar(Pr(i)(6)) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2) (1), Cr{N(H)Ar(Pr(i)(4))}(2) (Ar(Pr(i)(4)) = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2) (2), Cr{N(H)Ar(Me(6))}(2) (Ar(Me(6)) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2) (4), and the Lewis base adduct Cr{N(H)Ar(Me(6))}(2)(THF) (3) are described. Reaction of the terphenyl primary amido lithium derivatives Li{N(H)Ar(Pr(i)(6))} and Li{N(H)Ar(Pr(i)(4))} with CrCl(2)(THF)(2) in a 2:1 ratio afforded complexes 1 and 2, which are extremely rare examples of two coordinate chromium and the first stable chromium amides to have linear coordinated high-spin Cr(2+). The reaction of the less crowded terphenyl primary amido lithium salt Li{N(H)Ar(Me(6))} with CrCl(2)(THF)(2) gave the tetrahydrofuran (THF) complex 3, which has a distorted T-shaped metal coordination. Desolvation of 3 at about 70 °C gave 4 which has a formally two-coordinate chromous ion with a very strongly bent core geometry (N-Cr-N= 121.49(13)°) with secondary Cr--C(aryl ring) interactions of 2.338(4) ? to the ligand. Magnetometry studies showed that the two linear chromium species 1 and 2 have ambient temperature magnetic moments of about 4.20 μ(B) and 4.33 μ(B) which are lower than the spin-only value of 4.90 μ(B) typically observed for six coordinate Cr(2+). The bent complex 4 has a similar room temperature magnetic moment of about 4.36 μ(B). These studies suggest that the two-coordinate chromium complexes have significant spin-orbit coupling effects which lead to moments lower than the spin only value of 4.90 μ(B) because λ (the spin orbit coupling parameter) is positive. The three-coordinated complex 3 had a magnetic moment of 3.79 μ(B).     

Synthesis, structural characterization, and spectroscopy of the cadmium-cadmium bonded molecular species Ar'CdCdAr' (Ar' = C6H3-2,6-(C6H3-2,6-Pri2)2)

The synthesis and first structural characterization of a cadmium-cadmium bonded molecular compound Ar'CdCdAr' (Ar' = C6H3-2,6-(C6H3-2,6-Pri2)2) are reported. The existence of the Cd-Cd bond was established by 113Cd NMR spectroscopy and X-ray diffraction (Cd-Cd = 2.6257(5) A). Like its group 12 analogue Ar'ZnZnAr', DFT calculations showed that Ar'CdCdAr' had significant p-character in the Cd-Cd sigma-bonding HOMO.     

Solid-state 119Sn NMR and Mössbauer spectroscopy of "distannynes": evidence for large structural differences in the crystalline phase

The "distannynes" Ar'SnSnAr' (Ar' = C6H3-2,6(C6H3-2,6-Pr(i)2)2) and ArSnSnAr (Ar = C6H3-2,6(C6H2-2,4,6-Pr(i)3)2) were examined by solid-state (119)Sn NMR and M?ssbauer spectroscopy. The two compounds display substantially different spectroscopic parameters, while differing only in the absence (Ar'SnSnAr') or presence (ArSnSnAr) of a para-Pr(i) group in the flanking aryl rings of their terphenyl substituents. The spectroscopic differences can be interpreted in terms of a more trans-bent geometry and a longer Sn-Sn bond for ArSnSnAr in comparison to the wider Sn-Sn-C angle (125.24(7) degrees ) and shorter Sn-Sn bond length (2.6675(4)A) determined from the crystal structure of Ar'SnSnAr'. The differences are consistent with previously published calculations by Nagase and Takagi for ArSnSnAr.     

Synthesis and structural characterisation of lower rim halogenated pyrogallol[4]arenes: bi-layers and hexameric nano-capsules

Two lower rim halogenated pyrogallol[4]arenes have been synthesised and structurally characterised as either bi-layer or hexameric nano-capsule motifs depending upon chain length and functionalisation.     

Lawvere theories enriched over a general base

We generalise the correspondence between Lawvere theories and finitary monads on in two ways. First, we allow our theories to be enriched in a category V that is locally finitely presentable as a symmetric monoidal closed category: symmetry is convenient but not necessary. And second, we allow the arities of our theories to be finitely presentable objects of a locally finitely presentable V-category A. We call the resulting notion that of a Lawvere A-theory. We extend the correspondence for ordinary Lawvere theories to one between Lawvere A-theories and finitary V-monads on A. We illustrate this with examples leading up to that of the Lawvere -theory for cartesian closed categories, i.e., the -enriched theory on the category for which the models are all small cartesian closed categories. We also briefly investigate change-of-base.