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  • 1
    Electronic Resource
    Electronic Resource
    Method for the determination of photostimulable defect center concentrations, production rates, and effective formation energies (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4658-4661 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new method is proposed to determine radiation-induced defect center concentrations in solids which exhibit photostimulable luminescence. The technique relies on the determination of the number of photons released by spontaneous and photostimulated luminescence. A comparison with the x-ray-absorbed energy yields the effective formation energy of spontaneous luminescence photons and photostimulable centers. The method is applied representatively to BaFBr:Eu2+, which is utilized commercially as photostimulable x-ray storage phosphor in image plates for x-ray, γ-ray, electron, and neutron radiography. It is shown that in the utilized material on average 8 photostimulable F(Br−) centers (color centers based on bromine vacancies) and about 5 spontaneously emitted photons are generated by the absorption of 1 keV x-ray energy. Taking recent investigations into account which show that the x-ray generation of spontaneous luminescence and photostimulated luminescence centers is accompanied by the creation of approximately 36 nonphotostimulable defect centers, an average formation energy of about 20 eV per defect center can be calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355917
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  • 2
    Electronic Resource
    Electronic Resource
    Photostimulation mechanisms of x-ray-irradiated RbBr:Tl (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4418-4424 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physical mechanism of photostimulated luminescence (PSL) of RbBr:Tl, resulting from x-ray irradiation, has been investigated. Spectroscopic methods have been utilized to identify the bromine F center as the occupied electron trap. By means of absorption studies the charge state of the dopant Tl was found to be monovalent. The spectral emission showed the characteristic Jahn–Teller splitting of the 3P1 state of the Tl+ and its known temperature dependence. PSL lifetime and efficiency experiments have been conducted in the temperature regime from liquid helium to 500 K to understand the charge transport from the F center to the activator and have been compared with corresponding data obtained from direct optical excitation into the A band of the Tl+. The observed temperature dependencies of both lifetimes could be explained by the properties of the s2 ion Tl+. As a resulting model for the PSL process a tunneling from the relaxed excited state of the F center to an excited state of the Tl2+ ion following photostimulation is suggested. The temporal, thermal, and spectral behavior of the subsequent radiative fraction of the deexcitation process is solely determined by the properties of the Tl+ ion in the RbBr matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343936
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  • 3
    Electronic Resource
    Electronic Resource
    Dielectric hysteresis behavior in form I poly(vinylidene fluoride) (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4514-4517 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric hysteresis behavior of polymer ferroelectrics has until now been described by an energy approach in which the redistribution of the crystal dipole orientation under an applied field is determined by the probability for the molecular dipoles to rotate about the long chain axes from one energetically stable position to the other. We propose an alternative approach in which the orientation of the dipole is determined by the equilibrium between the field-induced torque and the elastic restoring torque generated by the excursion of the dipoles from their initial stable positions. Measurements of hysteresis loops performed on both uniaxially and biaxially oriented films of form I poly(vinylidene fluoride) reveal that all the important features of the loops can be accounted for by our model. An added advantage of our model is that it allows for description of switching experiment where inertial effects become important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339834
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  • 4
    Electronic Resource
    Electronic Resource
    Tris(dibenzoylmethane)(monophenanthroline)europium(III) based red emitting organic light emitting diodes (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5357-5362 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The concept of a blue light emitting diode containing a hole blocking layer (HBL) is generalized to efficiently excite dye molecules introduced in the form of an emission layer on the hole transporting side. The concept allows the excitation of an emitting molecule even if the molecule does not act primarily as a recombination center. On the basis of this concept pure red emitting organic light emitting diodes were produced utilizing tris(dibenzoylmethane)(monophenanthroline)europium(III) [Eu(dbm)3phen] as the emitting layer in an Al/LiF/Aluminum tris(8-hydroxyquinoline) (Alq3)/HBL/Eu(dbm)3phen/N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD)/copper-phthalo- cyanine (CuPc)/indium tin oxide structure. Additionally, the luminance output of such a device was improved by partially adding a hole transport material to the emitting layer in order to increase the penetration of holes into the emission region. A maximum luminance output of 200 cd/m2 at 15 V was achieved without optimizing the layer thickness. Furthermore, the effect of saturation of the Eu3+ emission is studied and discussed. The basic device architecture presented here is expected to work with other transport and emitting materials also. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410319
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  • 5
    Electronic Resource
    Electronic Resource
    Trap engineering in organic hole transport materials (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5559-5563 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chemical impurities with known highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energies were incorporated in organic hole transport materials. The effect of these dopants on quantity and depth of trap levels, transport properties, and luminescence of organic light emitting devices was examined. This was achieved by investigating current–voltage characteristics, luminance–voltage characteristics, and utilizing the method of thermally stimulated current for trap level detection. It was found that 4,4′,4″-tris-[N-(1-naphthyl)-N-(phenylamino)]triphenylamine (1-NaphDATA) doped into N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD) generates a trap level whose activation energy corresponds to the HOMO energy difference between dopant and matrix molecules. Therefore, the detected electronic states can be assigned to hole traps. The influence of those traps on the charge transport will be reported. For doping α-NPD into 1-NaphDATA no new trap levels could be detected. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1362371
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  • 6
    Electronic Resource
    Electronic Resource
    Luminescence properties of nanocrystalline Y2O3:Eu3+ in different host materials (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 1679-1686 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study, the optical properties of nanocrystalline europium doped yttria, Y2O3:Eu3+ were investigated in dependence on different caging hosts such as porous MCM-41, porous silica, and porous alumina with pore sizes ranging between 2.7 to 80 nm. These results were compared to nanopowders measured in air and aqueous solution whose particle sizes were 5 nm and 8 nm, respectively. All these results were compared to a commercial lamp phosphor powder with a grain size of about 5 μm. The structural properties of the samples were determined by x-ray diffraction and transmission electron microscopy. Investigated optical properties are the photoluminescence emission spectra, the excitation spectra, the lifetimes, and the quantum efficiencies. A heavy dependence of the charge transfer process on the surrounding will be reported and discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1333033
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  • 7
    Electronic Resource
    Electronic Resource
    Mechanisms of injection enhancement in organic light-emitting diodes through an Al/LiF electrode (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 420-424 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanisms of enhanced electron injection into the electron transport layer of Alq3 [tris(8-hydroxyquinoline)-aluminum] via LiF interlayers are studied by means of I–V characteristics, secondary ion mass spectroscopy (SIMS), and Kelvin probe measurements. Devices for single carrier injection were prepared using aluminum electrodes, Alq3 electron transport layers, and thin intermediate layers of LiF. It was found that devices deposited in the order Alq3-LiF-aluminum have a much higher electron injection capability than structures deposited in the order aluminum-LiF-Alq3. SIMS depth profile analysis reveals that the evaporation of Al on LiF leads to a spatial separation of Li and F probably induced by a chemical reaction of Al with LiF. Simple thermodynamic calculations support the energetic feasibility of such a reaction. Titanium cathodes in the same layer sequence also exhibit electron injection enhancement, probably due to their similar chemical reactivity. However, electron injection from Ag electrodes is not significantly improved by the introduction of a LiF interlayer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1331651
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  • 8
    Electronic Resource
    Electronic Resource
    Radiographic imaging with image plates: The influence of the readout intensity on the image quality (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5887-5895 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The image quality of radiographic images from image plate detectors is limited by two factors: first, the quality of the image plate itself and, second, the scanning procedure of the individual scanning device. In this study the impact of the latter on the image quality is investigated. A method to calculate the spatial resolution in the form of the line-spread function and the photostimulated luminescence intensity for various scanning laser beam intensities is presented. Theoretical results are compared to experimental ones obtained from a commercially available image plate. It is shown experimentally that the spatial resolution is reduced with increasing laser intensity of the readout beam, that the detected information shifts spatially and that the response of the photostimulated luminescence does not vary linearly with the intensity of the laser light. The results are explained by light scattering in the phosphor layer of the image plate and information bleaching during the readout procedure. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364375
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  • 9
    Electronic Resource
    Electronic Resource
    Optoacoustic generation and electrical detection of subnanosecond acoustic pulses (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 119-121 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optoacoustic generation and electrical detection of acoustic pulses of about 0.5-ns duration in quartz and in several polymer materials is demonstrated. The ultrasonic pulses are generated by thermoelastic effects and/or ablation due to absorption of 70-ps laser-light pulses in an opaque coupling layer deposited on one of the sample surfaces. Detection of the acoustic pulses is possible by using electrically charged, piezoelectric, or biased samples which yield electrode signals upon transit of the pulses. The acoustic pulses have also have been used to measure ultrasonic velocity and attenuation in various materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335712
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  • 10
    Electronic Resource
    Electronic Resource
    Physical model of photostimulated luminescence of x-ray irradiated BaFBr:Eu2+ (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1405-1412 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A dynamical model of the temporal dependence of photostimulated luminescence of the storage phosphor BaFBr:Eu2+ as a result of preceeding x-ray irradiation is presented. The model is based on a monomolecular recombination mechanism. The commonly used bimolecular mechanism leads to contradictions with experimental observations. The monomolecular recombination is explained by the existence of a photostimulable luminescence complex with a recombination center and an electron trap in close proximity. Charge transfer after optical excitation occurs through tunneling. The simulation of the transient charge carrier dynamics is performed through rate equations. Good agreement wih experimentally determined temporal responses for different x-ray doses applied and stimulating light intensities is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341838
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