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  • 1990-1994  (27)
  • 1
    Electronic Resource
    Electronic Resource
    1.54 μm wavelength emission of highly Er-doped CaF2 layers grown by molecular-beam epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 270-273 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CaF2:Er layers have been grown by molecular-beam epitaxy on (100)-oriented CaF2 substrates; the Er concentration ranges from 1% to 50% (mole fraction). The 1.54 μm emission observed under excitation around 800 nm was studied by photoluminescence. Up to 35% Er concentration the integrated emission increases monotonously, quenching appearing for higher doping levels. Photoluminescence results are discussed within the framework of previous studies of Er3+ emission in the near-infrared range (830–860 nm) in order to gain insight into the Er centers involved in the 1.54 μm emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357140
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of growth temperature and doping concentration on the distribution of the emitting centers in CaF2:Er molecular beam epitaxial layers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2749-2752 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular beam epitaxy of Er-doped CaF2 layers on (100)oriented CaF2 substrates was performed using CaF2 and ErF3 evaporation cells. The effect of growth temperature and Er concentration on the distribution of the different emission centers observed in these epitaxial Er-doped layers was investigated. Photoluminescence analyses were performed in the 830–860 nm wavelength range in which the 4S3/2→4I13/2 transitions of the Er3+ ions take place. The evolution of the relative emission intensity between single and aggregate Er3+ centers as a function of growth temperature shows that the emission from isolated Er3+ ions is favored in a growth temperature range of 500–520 °C. Emission lines from complex Er3+ centers are found to rise relative to those of isolated sites as Er concentration increases. Finally, no quenching of the integrated luminescence intensity occurs in the concentration range investigated, 0.05–6 mol % (0.1–16 wt%).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356211
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  • 3
    Electronic Resource
    Electronic Resource
    Aging study of nickel-copper-manganite negative temperature coefficient thermistors by thermopower measurements (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4705-4709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ceramic nickel-copper-manganite based negative temperature coefficient thermistors are unstable under thermal constraint, which increases the resistivity of these devices. This unstability can be reduced by the addition of a small amount of barium. These ceramics have a spinel structure, and the conduction takes place by a hopping process involving [Mn3+]/[Mn4+] octahedral ions. This study by the use of thermopower measurements points out that the resistivity change under thermal constraint is principally due to the disproportionation of [Mn3+]/[Mn4+] ions in the octahedral sites. Furthermore, it seems that some nickel ions migrate from octahedral to tetrahedral sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352076
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of Nd3+ concentration on the emission spectra of CaF2:Nd layers grown by molecular-beam epitaxy (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4485-4489 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd3+-doped CaF2 monocrystalline films have been grown by molecular-beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high-energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+-F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular-beam epitaxy technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349082
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature dependence of the fundamental absorption edge of mercury cadmium telluride (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6454-6460 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the temperature dependence of the fundamental absorption edge of a series of Hg1−xCdxTe alloys (with composition x ranging from 0.5 to 1). Analyzing our data in the light of the three-dimensional theory of direct-allowed excitons, we find precise values for the fundamental Γ8-Γ6 interband transition energy in a temperature range extending from 0 to 300 K. All experimental results, including previous data for HgTe and mercury-rich Hg1−xCdxTe alloys, are well accounted for using a simple empirical formula: Eg (eV)=−0.303(1−x)+1.606x−0.132x(1−x)+[6.3(1−x) −3.25x −5.92x(1−x)]10−4T2/[11(1−x)+78.7x+T]. This expression, which is valid for all compositions 0≤x≤1 and temperatures 0≤T≤500 K, predicts an alloy composition such that the band-gap energy is temperature independent: We find x=0.505. Finally, it can be used for technological application purpose (far-infrared detection as well as optical-fiber communications performed at realistic values of the temperature) and gives accurate values for the temperature and composition dependence of the effective mass in the semiconducting range of alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345119
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  • 6
    Electronic Resource
    Electronic Resource
    Nd3+ incorporation in CaF2 layers grown by molecular beam epitaxy (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 152-154 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular beam epitaxy of Nd3+-doped CaF2 monocrystalline layers on CaF2 substrates is demonstrated. Nd concentration is controlled by the temperature of an evaporation cell containing NdF3. Photoluminescence spectra of the samples show emissions from Nd3+ centers in tetragonal symmetry sites as a consequence of the charge compensation mechanism provided by interstitial F− ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106003
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  • 7
    Electronic Resource
    Electronic Resource
    Structural properties of nickel manganite Ni x Mn3−x O4 with 0.5 ⩽x ⩽ 1 (1990)
    Springer
    Journal of materials science 25 (1990), S. 4410-4414 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Single-phase nickel manganite spinels, Ni x Mn3−x O4, with 0.5 ⩽x ⩽ 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni2+ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni2+ ions (forx〉0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni2+ in A sites =P = − 82.1x 2+192.4x−81.5 and thus the general formula for cation distribution is $${\text{Mn}}_{{\text{1 - }}y}^{{\text{2 + }}} {\text{Ni}}_y^{{\text{2 + }}} [{\text{Ni}}_{x{\text{ - }}y}^{{\text{2 + }}} {\text{Mn}}_{{\text{2 - 2(}}x - y)}^{{\text{3 + }}} {\text{Mn}}_{x{\text{ - }}y}^{{\text{4 + }}} ]{\text{O}}_{\text{4}}^{{\text{2 - }}} $$ withy=xP/100 This relationship explains the electrical properties of semiconducting nickel manganite ceramics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581101
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of chemical composition on sintering of bismuth-titanium-doped zinc oxide (1992)
    Springer
    Journal of materials science 27 (1992), S. 2397-2405 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Liquid-phase sintering (LPS) of ceramics issued from powders of bismuth-titanium-doped zinc oxide, made of spherical grains constituted of small crystallites, were studied by dilatometry. A correlation can be established between the shape of the shrinkage curves and the microstructure of the ceramics. During sintering the spherical grains are destroyed as soon as the liquid phase appears and the rearrangement proceeds directly between crystallites. Systematic studies were carried out on bismuth-titanium-doped ZnO. For small Bi contents, the beginning of a solid-phase sintering process occurs. For 1 at % Bi in the binary system Bi-doped ZnO, rapid shrinkage leads to a well-densified ceramic with a grain size of 70 μm on average. The influence of the amount of titanium iny% Ti-1% Bi-doped ZnO is discussed. Whatever the amount of Ti, LPS is observed. The shrinkage curves depend greatly on the amount of Ti: only a Ti content ofy=0.6 % leads to an increase in grain size (100 μm on average).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01105049
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  • 9
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    Nd3+incorporation in CaF2layers grown by molecular beam epitaxy (1991)
    American Institute of Physics
    Details
    Publication Date: 1991-07-08
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Influence of chemical composition on sintering of bismuth-titanium-doped zinc oxide (1992)
    Springer
    Details
    Publication Date: 1992-01-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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