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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 1219-1223 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Luminescence characteristics in Er3+-ion activated, Yb3+-ion sensitized infrared upconversion materials have been investigated, especially for their energy back transfer processes from Er3+ to Yb3+ ions. Decay characteristics of Er3+ ion green emission have been examined in various fluoride crystals and fluoride glasses for the purpose of elucidating the energy transfer processes involved in the upconversion phenomena. It has been shown that decay characteristics of the green emission are sensitive to the host materials as well as Yb3+ concentration. The decay characteristics have been analyzed with a model taking into account configurations of Yb3+ ions around an Er3+ ion. It has been shown that the analyses present useful methods for characterizing energy transfer processes in materials containing higher amount of Yb3+ ions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4160-4164 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Energy transfer processes from Yb3+ to Tm3+ ions have been investigated in various fluoride microcrystals to examine the application limit of a simple rate equation model and to obtain methods for characterizing the host materials as to energy transfer. It has been shown that the energy transfer coefficients from donor Yb3+ to acceptor Tm3+ ions differ by nearly one order of magnitude even for fluoride lattices that have similar luminescence characteristics. The energy transfer coefficients increase monotonically with Yb3+ concentration at low Yb3+ concentrations, while they take nearly constant values at high Yb3+ concentrations. The present experimental results were compared with computer simulation results as well as related analyses. It is shown that the apparently complicated behaviors are consistently explained by a microscopic model. As an example of the application of the present results, the optimization of the infrared emission of Tm3+ ions is shown. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 797-801 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical absorption and related characteristics in undoped, semi-insulating GaAs crystals have been investigated, especially at the bleaching and thermal recovery stages. It has been shown that a broad absorption band at a longer wavelength grows as bleaching proceeds, in a reciprocal relation with the near-infrared absorption band. It has been found that the bleached near-infrared absorption shows rather abrupt recovery at a temperature around 130 K and that the recovery profile, i.e., the temperature derivative of the recovering absorption, is dependent upon the crystal composition and thermal prehistory. Hence, the present method, recovery characteristics of the bleached absorption method, may have applicability for elucidating defect properties as well as crystal characterization. Simultaneous measurements of extrinsic photoconductivity combined with related experimental results have lead to a conclusion that the extrinsic photoconductivity in the enhanced state is related to the metastable state of the deep lying defects. These experimental results are discussed systematically on the basis of the defect transition to and recovery from the metastable state.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5325-5329 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extrinsic photoconductive characteristics of undoped, semi-insulating GaAs have been investigated, especially the characteristic enhancement effect at low temperatures. It has been shown that two quasistable photoconductive states exist, in which photoconductivity differs by orders of magnitude and that the two states are partly interchangeable by irradiating with an appropriate wavelength light. Spectra and temperature dependencies were investigated to elucidate the enhancement mechanism. Discussions are made on the basis of metastable states in As-rich defects.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 1391-1393 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extrinsic photoconductivity spatial and spectral distribution characteristics in undoped, semi-insulating GaAs crystal wafers have been investigated and the results are compared with those for optical absorption. The photoconductivity spatial distribution in a single wafer has been shown generally in reverse relation with that for optical absorption.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4703-4709 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Frequency upconversion characteristics in Er3+- or Tm3+-ion-activated and Yb3+-ion- sensitized luminescent materials have been investigated. The principal goal was to obtain high-brightness, blue and green light sources under 980 nm emitting laser diode light excitation. Processes leading to the efficient upconversion have been investigated both by experimental and analytical methods. It has been shown that upconversion efficiencies are principally determined with Yb3+ ion excited state lifetime, which is highly influenced by device optical confinement as well as material characteristics. The effect of the optical confinement has been analyzed quantitatively on the basis of a rate equation model. Criteria for realizing efficient infrared upconversion devices have been presented. A strong tendency toward temperature quenching has been observed especially in blue emitting materials. This temperature dependence has been shown to be principally due to increase of nonradiative decay in the Yb3+ ion excited state.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2223-2225 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Intense infrared emission peaking at a wavelength of 1.35 μm has been observed in Ge-doped ZnSe crystals at low temperatures. The emission was particularly strong in the crystals doped with Ge in Se atmosphere and was then rapidly quenched. The emission was accompanied by a characteristic additive absorption band centered around a wavelength of 500 nm, which showed a partial but distinct metastable change upon light irradiation. The excitation spectrum and the preparation conditions of the infrared emission corresponded to those of electron spin resonance signals, owing to isolated, trivalent Ge ions in ZnSe. The nature and the possible applications of the emission are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 802-804 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Efficient frequency upconversion from 980 nm infrared light to 480 nm wavelength blue emission has been observed in Tm3+-activated, Yb3+-sensitized fluoride glass. Similar upconversion to green emission has been obtained with higher efficiency in Er3+-containing luminescent materials. The conversion efficiencies have been markedly improved when the luminescent material small in size is contained in a reflective cavity. The improvement effect is pronounced when transparent luminescent material is adopted. Processes leading to the generation of visible emission have been examined and criteria for optimizing the upconversion efficiency are presented.
    Type of Medium: Electronic Resource
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