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  • Chemistry  (2)
  • 64.70 Dv  (1)
  • 78.50Ge  (1)
  • 1990-1994  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 91 (1993), S. 429-436 
    ISSN: 1434-6036
    Keywords: 71.70Ej ; 78.50Ge ; 78.55Et
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Optical spectra of thed 4 configuration have been studied with II–VI compounds. Failure of static crystal-field description led various authors to introduce static or dynamic Jahn-Teller models for the Cr2+ ground and excited states. With ZnS, the main optical transition5 E(D)↔5 T 2(D) now appears as a doublet at 5218 and 5212 cm−1 coinciding for emission and absorption spectra. This no-phonon structure indicates a splitting of the gound-and excited-state multiplets under combined Jahn-Teller and spin-orbit interactions. In the cubic host ZnSe and in the hexagonal compounds CdS and CdSe, the optical properties exhibit the same general behaviour but with a decreasing shaping of the structural details. In addition to the NIR measurements, middle-infrared spectra have been recorded by Fourier spectroscopy in the transmission mode. For the first time a broad band could be detected for ZnS and interpreted as the $$^5 \hat E\left( {T_2 } \right) \leftarrow ^5 \hat B\left( {T_2 } \right)$$ absorption between the sheets of the respective adiabatic potential surfaces inD 2d symmetry. Its maximum near 1300 cm−1 indicates $$\bar v_{JT} \approx 430cm^{ - 1} $$ cm−1 following the common interpretation of this transition.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 64.70 Dv ; 71.30+h
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Femtosecond-laser-induced changes of the optical reflectivity and the reflected second harmonic are measured over a wide range of times and laser fluences. Changes of the linear and nonlinear optical properties suggestive of a transition to a metallic state have been observed. For relatively low fluences these changes take tens of picoseconds to develop. For higher fluences the transition takes place in just a few hundred femtoseconds. Our data suggest that, depending on the laser excitation conditions, two distinctly different types of phase transformations are observed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Advanced Materials for Optics and Electronics 3 (1994), S. 253-260 
    ISSN: 1057-9257
    Keywords: Seeded chemical vapour transport ; Titanium doping ; Electron spin resonance ; Paramagnetic impurities ; Static Jahn-Teller effect ; Dynamic Jahn-Teller effect ; Photoiuminescence ; Excitation spectra ; Photo-ionization of impurities ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Znse:Ti crystals were grown by seeded chemical vapour transport (SCVT) in a hydrogen atmosphere. In situ doping with titanium was carried out from an additional TiSe source in the quartz ampoule at 1460 K. The Good homogeneity of the Ti distribution and the presence of only a few defects have been demonstrated by etch pit and X-ray topography studies. For the frist time, Ti3+ (3d1) centres in a II-VI semiconductor compund are detected. The concentration of localized centres of Ti2+ and Ti3+ in high-resistivity material determined by EPR is about 5 × 1016 cm-3. Fe3+, Ni2+ and traces of Mn2+ are additionally observed. Below 77K an anisotropic EPR spectrum of Ti3+ (d1) is recorded, indicating both a dynamic and a static Jahn-Teller effect of the 2E(D) ground state. At lower temperatures clear evidence of the static Jahn-Teller effect is observed. The frist emission and excitation spectra of Ti impurities in II-VI compounds are presented. An emission near 3400 cm-1 is assigned to the 3T2(F) → 3A2(F) transition of Ti2+ (d2). Its excitation structures coincide with the known absorption bands to 3T1(P) and 3T1(F). A further structured luminescence band at 4700 cm-1 is related to 2T2 → 2E(D) transition of Ti3+ (d1). Ti ions form a deep donor level Ti2+/Ti3+ situated approximately 14,100 cm-1 above the valence band. This photo-ionization threshold is derived from the excitation measurements in accordance with previous photoconductivity experiments.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 583 (1990), S. 195-204 
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Spectroscopic Investigations on Substituent Effects in SilylmethylsilanesThe silanes Me3-n(Me3SiCH2)nSiH (n = 1-3), (RMe2SiCH2)3SiH (R = n-Bu, n-Pr, Et, PhCH2, Ph) and Me3ElCH2SiMe2H (El = Ge, Sn) were prepared. The frequencies of the Si—H stretching vibration, the 29Si—1H coupling constants and the 29Si n.m.r. chemical shifts were measured. The ṽ(SiH) and J(29Si—1H) values in the silanes Me3-n(Me3SiCH2)nSiH depend on the number of trimethylsilymethyl groups. There is hardly an influence of the substituents R on these values in the silanes (RMe2SiCH2)3SiH. The frequencies of the Si—H stretching vibrations in the silanes Me3ElCH2SiMe2H (El = Si, Ge, Sn) show the order Si=Ge 〉 Sn. The 29Si n.m.r. chemical shifts of the Si(H) signals are approximately equal in the silanes Me3-n(Me3SiCH2)nSiH and (RMe2SiCH2)3SiH.
    Notes: Die Silane Me3-n(Me3SiCH2)nSiH (n = 1-3), (RMe2SiCH2)3SiH (R = n-Bu, n-Pr, Et, PhCH2, Ph) und Me3ElCH2SiMe2H (El = Ge, Sn) wurden dargestellt. Die Bandenlagen der Si—H-Valenzschwingungen, die 29Si—1H-Kopplungskonstanten und die 29Si-NMR-chemischen Verschiebungen wurden gemessen. Die ṽ(SiH)- und J(29Si—1H)-Werte der Silane Me3-n(Me3SiCH2)nSiH sind von der Anzahl der Trimethylsilylmethylgruppen abhängig. Die Substituenten R haben auf diese Werte in den Silanen (RMe2SiCH2)3SiH kaum einen Einfluß. Für die Frequenzen der Si—H-Valenzschwingungen in den Silanen Me3ElCH2SiMe2H (El = Si, Ge, Sn) ergibt sich die Abstufung Si=Ge 〉 Sn. Die 29Si-NMR-chemischen Verschiebungen des Si(H)-Signals der Silane Me3-n(Me3SiCH2)nSiH und (RMe2SiCH2)3 SiH sind annähernd gleich.
    Additional Material: 5 Tab.
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