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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms of writing and decay of holographic gratings in semiconducting CdF2:Ga (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2215-2221 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We consider the mechanisms responsible for the photoinduced change in the optical properties of semiconducting CdF2 crystals with metastable Ga impurities forming DX centers. Unlike the case of compound semiconductors with DX centers (GaAlAs:Si, GaAlAs:Te, CdZnTe:Cl), this change is caused not by free electrons but by a redistribution of electrons between deep and shallow localized states. The resulting modification of the refractive index of the crystal allows writing of persistent holographic gratings at temperatures up to 200 K, high for this class of holographic materials. Holographic characteristics of CdF2:Ga crystals such as refractive index change, sensitivity, and grating decay are described. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366959
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  • 2
    Electronic Resource
    Electronic Resource
    CdF2:In: A novel material for optically written storage of information (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 31-33 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate that semiconducting CdF2 crystals doped with indium is an efficient medium for optical storage of information in static and dynamic regimes. A metastable phototransformation of 1018 cm−3 In centers from a localized deep state to a hydrogenlike shallow state leads to a change of the refractive index Δn of about 10−4 for the probe beam at the wavelength of 500 nm. The diffraction efficiency is temperature dependent due to spontaneous decay of the grating caused by thermal recovery of the In impurity from the metastable hydrogenic state to the localized ground state. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115482
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  • 3
    Electronic Resource
    Electronic Resource
    Paramagnetic susceptibility of semiconducting CdF2:In crystals: Direct evidence of the negative-U nature of the DX-like center (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1272-1274 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Paramagnetic susceptibility κpara of CdF2 crystals with bistable In centers is measured in the temperature range T=4–300 K. For crystals cooled in the dark down to liquid helium temperature, κpara is determined by the trace Mn2+ impurity. Illumination of the sample by the ultraviolet-visible light results in the appearance of the photoinduced δκpara signal due to formation of centers with the magnetic moment J=1/2. This gives a clear evidence of an absence of paramagnetism in the deep state of the bistable In center and its presence in the shallow state, i.e., proves the negative-U nature of the deep state. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118550
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of the metastable centers of the group-III atoms in IV-VI crystals (2000)
    Springer
    Semiconductors 34 (2000), S. 264-268 
    Details
    ISSN: 1063-7826
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A comparative analysis of reconstruction of the metastable impurity centers in tetrahedral (III-V and II-VI) and cubic (IV-VI) crystals is performed for the case where the charge of the center changes. The influence of the chemical structure of the crystal matrix on the nature of defect reconstruction is studied on the basis of cluster approximation. For the IV-VI:III centers, the fundamental significance of the three-center crystal bonds and the specific role of the antibonding (weakly bonding) 3a 1g state, which has the properties of both the impurity and perturbed crystal states simultaneously, are emphasized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1187968
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  • 5
    Electronic Resource
    Electronic Resource
    Donor impurities and DX centers in the ionic semiconductor CdF2 (1997)
    Springer
    Physics of the solid state 39 (1997), S. 943-947 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Group-III impurities in the wide-gap ionic crystal CdF2 are examined. After being heated in a reducing atmosphere, crystals with these impurities acquire semiconductor properties, which are determined by electrons bound in hydrogen-like orbitals near an impurity. Besides these donor states, nontransition impurities form “deep” states accompanied by strong lattice relaxation, i.e. they are strongly shifted along the configuration coordinate. These states are a complete analog of DX centers in covalent and ionic-covalent semiconductors. The difference of the behavior of nontransition impurities from that of transition and rare-earth impurities is analyzed. This difference is attributed to the character of the filling of their valence shells by electrons. A deep, multilevel analogy is drawn between the properties of deep centers in typical semiconductors with an appreciable fraction of a covalent bond component and in predominantly ionic crystal CdF2 with semiconductor properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130113
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  • 6
    Electronic Resource
    Electronic Resource
    Paramagnetic susceptibility of additively colored CdF2:In photochromic crystals (1997)
    Springer
    Physics of the solid state 39 (1997), S. 1067-1071 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The paramagnetic susceptibility K para of CdF2:In crystals with metastable indium centers has been measured in darkness after photobleaching the crystals in visible light in the temperature interval 4–300 K. For crystals cooled in darkness to liquid-helium temperature K para is wholly determined by the accompanying impurity Mn2+ with magnetic moment J=5/2. Illumination of the crystals leads to the appearance of an induced signal δ K para due to the formation of centers with J=1/2. The results of the experiments indicate the absence of paramagnetism in the deep state of the indium center and its existence in the shallow (donor) state, i.e., they confirm the two-electron (negative-U) nature of the deep indium level in CdF2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130150
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  • 7
    Electronic Resource
    Electronic Resource
    Electronic level diagram and structure of metastable centers in CdF2:Ga and CdF2:In semiconducting crystals (1997)
    Springer
    Physics of the solid state 39 (1997), S. 1906-1911 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is reported of the optical properties of wide-gap, predominantly ionic cadmium fluoride crystals in photo-and thermally stimulated transformations of metastable indium and gallium centers. An analysis of these properties leads one to a conclusion of gallium having two metastable states (two types of deep centers). The deep-center binding energies and the barriers separating the shallow (hydrogenic) and deep centers have been determined for both impurities. Configuration-coordinate diagrams are developed, and microscopic models for the deep centers are proposed. It is concluded that these centers are identical with the metastable DX centers in typical semiconducting crystals. Thus cadmium fluoride is the most ionic among the crystals where DX centers have thus far been found. The potential of using such crystals for optical information recording is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130197
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  • 8
    Electronic Resource
    Electronic Resource
    Thermo-and photostimulated depolarization in self-compensated CdF2:Ga and CdF2:In crystals (1999)
    Springer
    Physics of the solid state 41 (1999), S. 1444-1449 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is reported of the conductivity of CdF2 semiconductor crystals doped by indium and gallium donor impurities and residing in a semi-isolated state. The latter results from self-compensation of the impurities, in the course of which one half of them creates two-electron DX centers, and the second is ionized. Photo-and thermostimulated depolarization of these crystals has been studied. It was shown that the observed polarization/depolarization phenomena have a nonlocal nature and are due to the charges present in these crystals changing their positions. These changes may be formally considered as charge displacement to macroscopic distances considerably in excess of the interatomic ones. The mechanisms responsible for these phenomena are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1131028
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