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  • 1
    Electronic Resource
    Electronic Resource
    Reverse saturable absorption in C60-doped porous glasses studied by single- and double-pulse pump–probe experiments (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5929-5937 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the nonlinear absorption of C60-doped porous sol-gel glasses by single- and double-pulse pump–probe experiments. We find that the reverse saturable absorption (RSA) of these samples can be explained in the frame of a five level system as it is commonly used for C60 solutions. We observe a strong saturation of the RSA at high fluences, especially if the molecules are prepared in the triplet state. In a double-pulse pump–probe experiment we measure the triplet quantum yield for C60 solutions (0.8) and doped glasses (0.25) and the singlet and triplet absorption cross sections. In the first excited singlet state (S1) lifetimes of 1 ns and 65 ps are determined in solutions and glasses, respectively. We find that the dynamics of both depopulation processes, direct S1–S0 relaxation, and intersystem crossing is faster in glasses than in the case where C60 is in solution in a liquid aromatic solvent. We tentatively explain these findings by the absence of a stabilizing solvent and a perturbation of the molecular energy levels due to interaction with the solid glass matrix. We finally determine the lifetime of the triplet states in our glass samples to 2 μs. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479888
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  • 2
    Electronic Resource
    Electronic Resource
    Optical limiting properties and dynamics of induced absorption in C60-doped solid xerogel matrices (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 8599-8604 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present measurements of induced absorption and its dynamics in C60-doped solid xerogel matrices. The measurements are performed in a pump-test geometry using picosecond pulses generated from a frequency doubled mode locked Nd:YAG laser at 532 nm. We observe an induced absorption leading to optical limiting. We find outstanding optical limiting qualities for single shot excitation but some degradation above a certain threshold intensity for repetitive pulses. Below this degradation threshold, the material is stable and its limiting dynamics is studied. A decrease of the initial laser-induced absorption with a time constant of 150 ps is observed, down to a very long-lived constant level. We attribute this dynamics of induced absorption to a transition from excited singlet to triplet electronic states in the C60 molecule. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476290
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  • 3
    Electronic Resource
    Electronic Resource
    Methane activation over La2xY2-2xO3 (0 ⩽x ⩽ 1) catalysts (1991)
    Springer
    Catalysis letters 10 (1991), S. 111-120 
    Details
    ISSN: 1572-879X
    Keywords: Methane activation ; perovskite ; bixbyite ; La-Y compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of the structure on the catalytic methane activation coupling activity has been shown for La2x Y2−2x O3 (0 ⩽x ⩽ 1) compounds. A perovskite structure leads to total oxidation (CO, CO2) whereas a bixbyite structure results in C2 hydrocarbon formation. This change in selectivity is interpreted in terms of the difference in oxygen environment of lanthanum in the two stuctures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764742
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  • 4
    Electronic Resource
    Electronic Resource
    Structural evolution of a formamide modified sol—Spectroscopic study (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 183-187 
    Details
    ISSN: 1573-4846
    Keywords: gelation mechanism ; structural evolution ; formamide ; FTIR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We investigated the influence of formamide on the acid-catalyzed sol-gel process at 40°C, by Fourier transformed infrared spectroscopy. Two silica sols were studied: one containing formamide and one without. Following the time evolution of both the Si−O(H) stretching vibration at around 950 cm−1 and the Si−O(−Si) vibration between 1080 and 1200 cm−1, we were able to describe the structural evolution of each sol. We thus observed, in the case of the formamide containing sol, a peculiar two-step structural evolution which eventually resulted in a highly interconnected gel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436838
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  • 5
    Electronic Resource
    Electronic Resource
    Nanocomposites Fe2O3/SiO2-preparation by sol-gel method and physical properties (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 615-618 
    Details
    ISSN: 1573-4846
    Keywords: sol-gel ; magnetic nanocomposite ; iron oxide ; Mössbauer spectroscopy ; Kerr effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Magnetic nanocomposites γ-Fe2O3/silica were prepared by a one-step sol-gel method. The sol was prepared by TEOS (tetraethyl orthosilicate) acid hydrolysis in the presence of an iron salt soluble in methanol. After gelation and drying, the transparent samples were characterized after treatment at different temperatures. The particle size, observed by HR TEM, was in the range of 2–10 nm and depended on Fe-concentration and heating temperature. Magnetic measurements showed either a ferromagnetic or a superparamagnetic behaviour and could be explained by the particle size. The dependence of the magnetic behaviour on the particle size was also studied by Mössbauer spectroscopy. The samples in which the Fe2O3 particle size was approximately 10 nm showed magnetic splitting (sextet) at room temperature, while smaller particles (2–3 nm) showed this splitting only at the temperature of liquid helium. The optomagnetic properties of the samples were also measured (Kerr effect).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436910
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  • 6
    Electronic Resource
    Electronic Resource
    Temperature behaviour of optical properties of Si -implanted SiO (2000)
    Springer
    The European physical journal 8 (2000), S. 395-398 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 78.55.Hx Other solid inorganic materials - 61.46.+w Clusters, nanoparticles, and nanocrystalline materials - 78.45.+h Stimulated emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Silicon nanocrystals were prepared by Si+-ion implantation and subsequent annealing of SiO2 films thermally grown on a c-Si wafer. Different implantation energies (20-150 keV) and doses - cm -2 ) were used in order to achieve flat implantation profiles (through the thickness of about 100 nm) with a peak concentration of Si atoms of 5, 7, 10 and 15 atomic%. The presence of Si nanocrystals was verified by transmission electron microscopy. The samples exhibit strong visible/IR photoluminescence (PL) with decay time of the order of tens of μs at room temperature. The changes of PL in the range 70-300 K can be well explained by the exciton singlet-triplet splitting model. We show that all PL characteristics (efficiency, dynamics, temperature dependence, excitation spectra) of our Si+-implanted SiO2 films bear close resemblance to those of a light-emitting porous Si and therefore we suppose similar PL origin in both materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050049
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