High-efficiency erbium ion luminescence in silicon nanocrystal systems

The photoluminescence spectra and kinetics of both erbium-doped and undoped multilayer structures of quasi-ordered silicon nanocrystals in a silicon dioxide matrix were studied. It was shown that the optical excitation energy of silicon nanocrystals 2–3 nm in size can be practically completely transferred to Er³⁺ ions in the oxide surrounding the nanocrystals, with its subsequent radiation at 1.5 μm. Possible reasons for the high excitation efficiency of the Er³⁺ ions are discussed, and the conclusion is drawn that the F?rster mechanism is dominant in the energy transfer processes occurring in these structures. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 105–109. Original Russian Text Copyright ? 2004 by Kashkarov, Kamenev, Lisachenko, Shalygina, Timoshenko, Schmidt, Heitmann, Zacharias.     

Laser spectroscopy of desorbing molecules

In this article the application of tunable dye lasers to desorption phenomena is illuminated. These lasers provide radiation continuously tunable from 105 nm in the vacuum ultraviolet to about 10 m in the mid-IR. By employing either laser induced fluorescence (LIF) or resonance enhanced multiphoton ionization (REMPI) spectroscopy almost all diatomic and many polyatomic molecules can be probed with the sensitivity required to detect desorbing molecules under UHV conditions. The spectral resolution of the lasers is sufficiently high that rotational state selectivity is achieved. Recent developments permit in addition the velocity distributions of molecules to be determined with internal quantum state resolution. Therefore very detailed information about the molecular dynamics has been obtained. In most experiments so far reactive recombinations off surfaces have been investigated. In this paper special emphasis will be given to the recombination of hydrogen on copper and palladium surfaces. For these systems very detailed data about the internal state populations at various surface temperatures have been obtained. The rotational cooling previously observed in molecular beam scattering has also been established for desorption. Strong vibrational excitation has been observed, which in the case of desorption from copper may be associated with the recombination dynamics, whereas for desorption of D₂ from Pd(100) a molecular precursor state might be responsible. By measuring the velocity distribution in each quantum state, the complete energetics of the desorbing molecules has been determined. Some first experiments on laser induced desorption with state selective detection of the desorbing molecules will also be discussed. Finally, making use of the polarization analysis of the signal, alignment effects in the desorption can be observed, permitting observation of molecular dynamics with a magnifying glass.Heisenberg fellow of the Deutsche Forschungsgemeinschaft     

A comparison of the thermal behaviour of α-AIF3 and aluminium fluoride hydrates

The thermal decompositions of-AlF₃ · 3H₂O, AlF₃ · 3.5H₂O, AlF₃ · 1.5H₂O,-AlF₃ and hydroxyfluorides of aluminium were investigated. The literature data were complemented with X-ray results. The first stages of decomposition are described. The AlF₃ hydrates and hydroxyfluorides were used as model systems in order to interpret the thermal behaviour of -AlF₃ in more detail.

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Zusammenfassung Die thermische Zersetzung von-AlF₃ · 3H₂O, AlF₃ · 3,5H₂O, AlF₃ · 1,5H₂O,-AlF₃ und Hydroxyfluoriden des Aluminiums wurden untersucht und die in der Literatur beschriebenen Ergebnisse durch Röntgenuntersuchungen ergänzt. Die ersten Phasen der Zersetzung werden beschrieben. Die AlF₃-Hydrate und Hydroxyfluoride des Aluminiums können als Modellsystem genutzt werden, um das thermische Verhalten von -AlF₃ detailliert zu beschreiben.

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-AlF₃ · ₂, AlF₃ · 3,5₂, AlF₃ · 1,5₂,-AlF₃ . . . - lF₃.

     

Near threshold channel selective photodissociation of NO2

The dynamics of the photodissociation of NO₂ into NO(X ²Π_Ω″, ν″=0,J″)+O(³ P _0,1,2) is investigated near the thermodynamic threshold. Cooling the internal degrees of freedom by a supersonic beam expansion provides a nearly complete quantum state selection prior to the predissociation. Measurements of the wavelength dependent dissociation yield into specific product quantum states are reported. At certain wavelengths Λ″ doublet resolved rotational population distributions of the fragments are obtained. Up to an excess energy ofE _exc=121 cm^?1 about 42% of this energy is partitioned into the rotation of the NO molecules, and correspondingly 58% into the translational degree of freedom. The role of electronic and total parity is discussed.     

Stereospecific reactions of copper(II) complexes of serine and threonine with formaldehyde

Summary Condensations of Cu(L-ser)₂ and Cu(L-thr)₂ (where L-ser=L-serinato anion and L-thr=L-threoninato anion) with formaldehyde at pH 4.5 yield two new optically active products:bis[L-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) andbis[L-(N-hydroxymethyl-5-methyloxazolidine-4-carboxylato)]copper(II) dihydrate (2), respectively. Cu(D-ser)₂ and Cu(D-thr)₂ also undergo similar reactions. The new products are different from the products obtained from Cu(DL-ser)₂ and Cu(DL-thr)₂, and a mechanism has been suggested to explain the stereospecificity of these conversions. Condensation of Cu(L-ser)₂ with formaldehyde and ammonia at pH 4.5 yields the new product, [3N,7N-(1,3,5,7-tetraazabicyclo-[3.3.1]nonyl)di(hydroxymethyl)-acetato]copper(II), (3). The compexes have been characterized by analytical and by i.r. electronic and c.d. spectral data. Complexes (1) and (2) undergo a reversible Cu^II/Cu^I redox process in aqueous media at –0.18 Vversus s.c.e.; complex (3) exhibits irreversible Cu^II/Cu^I reduction at –0.49 V confirming the presence of a rigid pentamethylenediaza-bridged ligand system.     

Laser excited fluorescence of CH in a low pressure flame

Production of CH(X²Π) in a low pressure H/O/C₂H₂ flame has been observed by laser excited fluorescence in the 0, 0 band of the A² Δ ← X²Π system at 431 nm. Laser excitation spectra have been recorded of the P, Q, and R branches with a bandwidth of 0.03 nm and of the head of the Q branch with a bandwidth of 0.0009 nm. Values of the spin—orbit and spin—rotation coupling constants in the A²Δ state have been obtained.