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  • 1995-1999  (9)
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  • 1
    Digitale Medien
    Digitale Medien
    Improved energy transfer in electrophosphorescent devices (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 442-444 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: External quantum efficiencies of up to (5.6±0.1)% at low brightness and (2.2±0.1)% at 100 cd/m2 are obtained from a red electrophosphorescent device containing the luminescent dye 2,3,7,8, 12,13,17,18-octaethyl-21H23H-phorpine platinum(II) (PtOEP) doped in a 4,4′-N,N′-dicarbazolebiphenyl (CBP) host. Due to weak overlap between excitonic states in PtOEP and CBP, efficiency losses due to nonradiative recombination are low. However, energy transfer between the species is also poor. In compensation, a thin layer of 2,9-dimethyl-4,7 diphenyl-1,10-phenanthroline is used as a barrier to exciton diffusion in CBP, improving the energy transfer to PtOEP. This technique may be applied to improve the efficiency of other electrophosphorescent devices. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.123055
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  • 2
    Digitale Medien
    Digitale Medien
    Low pressure organic vapor phase deposition of small molecular weight organic light emitting device structures (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3033-3035 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new technique for the deposition of amorphous organic thin films, low pressure organic vapor phase deposition (LP-OVPD), was used to fabricate organic light emitting devices (OLEDs) consisting of a film of aluminum tris-(8 hydroxyquinoline) (Alq3) grown on the surface of a film of N′-diphenyl-N,N′-bis(3-methylphenyl)1-1′biphenyl-4-4′diamine. The resulting heterojunction OLED was found to have a performance similar to conventional, small molecular weight OLEDs grown using thermal evaporation in vacuum. The LP-OVPD grown device has an external quantum efficiency of 0.40±0.05% and a turn-on voltage of approximately 6 V. The rapid throughput demonstrated with LP-OVPD has the potential to facilitate low cost mass production of conventional small molecule based OLEDs, and its use of low vacuum in a horizontal reactor lends itself to roll-to-roll deposition of organic films for many photonic device applications. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.120281
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  • 3
    Digitale Medien
    Digitale Medien
    Very high-efficiency green organic light-emitting devices based on electrophosphorescence (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 4-6 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We describe the performance of an organic light-emitting device employing the green electrophosphorescent material, fac tris(2-phenylpyridine) iridium [Ir(ppy)3] doped into a 4,4′-N,N′-dicarbazole-biphenyl host. These devices exhibit peak external quantum and power efficiencies of 8.0% (28 cd/A) and 31 lm/W, respectively. At 100 cd/m2, the external quantum and power efficiencies are 7.5% (26 cd/A) and 19 lm/W at an operating voltage of 4.3 V. This performance can be explained by efficient transfer of both singlet and triplet excited states in the host to Ir(ppy)3, leading to a high internal efficiency. In addition, the short phosphorescent decay time of Ir(ppy)3 (〈1 μs) reduces saturation of the phosphor at high drive currents, yielding a peak luminance of 100 000 cd/m2. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124258
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  • 4
    Digitale Medien
    Digitale Medien
    Interfacial diffusion controlled reactions with time varying absorbing domains (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8404-8412 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A theoretical study for diffusional crossing of a tracer through a membrane, where the size of the adsorbing domain (receptor) is time dependent, is presented. A periodic array of absorbing and reflecting domains at the membrane surface was assumed. This model is described by a time-dependent diffusion equation with mixed boundary conditions, where the boundaries are themselves varying with time. Both analytical and numerical methods were employed in order to calculate the total flux of a tracer across the membrane as a function of the oscillation frequency (ω) and amplitude (ε) of the receptor site. The results show an increase in the absorption rate with frequency, reaching a plateau at very high values of ω. The space and time behavior of the diffusing tracer concentration was analyzed, evidencing dephasing effects at high ω which are common to many nonlinear systems where the dynamic response becomes time independent in the high frequency limit. This approach could be useful in studying the anomalous effect of an oscillating electric field on the membrane permeability. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.472695
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  • 5
    Digitale Medien
    Digitale Medien
    Study of lasing action based on Förster energy transfer in optically pumped organic semiconductor thin films (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 4096-4108 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We present a study of optically pumped waveguide and microcavity lasers based on vacuum-deposited thin films of small molecular weight organic semiconductors. Lasing action in waveguide lasers is characterized by high output peak power (50 W), high differential quantum efficiency (70%), low lasing threshold (1 μJ/cm2), and long operational lifetime (〉106 laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, 300 μJ/cm2 lasing threshold, and lifetimes of 〉106 pump laser pulses (operating at 6 times the threshold power). We demonstrate wavelength variability from 460 to 700 nm by changing the composition of the organic films. The confinement of excitations on the dopant molecules leads to quantum dot-like behavior such as high temperature stability of the lasing threshold, output power, and emission wavelength in the temperature range from 0 to 140 °C. The linewidth of laser emission from microcavity structures is found to be 0.2±0.1 Å and is transform limited by 40 ps long relaxation oscillations. We present a theoretical estimate for the linewidth of organic semiconductor laser emission which is found to be at least an order of magnitude smaller than for inorganic laser diodes. The prospects for realizing electrically pumped organic semiconductor lasers are considered. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368624
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  • 6
    Digitale Medien
    Digitale Medien
    Highly efficient phosphorescent emission from organic electroluminescent devices (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 395 (1998), S. 151-154 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] The efficiency of electroluminescent organic light-emitting devices, can be improved by the introduction of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/25954
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  • 7
    Digitale Medien
    Digitale Medien
    Critical experiments in the search for fermion condensation (1997)
    Springer
    JETP letters 65 (1997), S. 863-869 
    Details
    ISSN: 1090-6487
    Schlagwort(e): 05.30.Fk
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The specific features of fermion condensation — a phase transition associated with the rearrangement of the one-particle degrees of freedom in strongly correlated Fermi systems — by which this phenomenon can be detected experimentally are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.567438
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  • 8
    Digitale Medien
    Digitale Medien
    Multiply connected Fermi sphere and fermion condensation (1998)
    Springer
    Journal of experimental and theoretical physics 87 (1998), S. 1129-1135 
    Details
    ISSN: 1090-6509
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We examine the structure of the ground state of a homogeneous Fermi liquid beyond the instability point of the Fermi-like quasiparticle momentum distribution in the effective-functional method with a strong repulsive effective interaction. A numerical study of the initial stage of rearrangement of the ground state, based on a simple effective functional, showed that there exists a temperature T 0, above which the behavior of the system is the same as in the theory of fermion condensation, and for T〈T 0 the scenario of rearrangement of the ground state is different. At low temperatures an intermediate structure arises, with a multiply connected quasiparticle momentum distribution. The transition of this structure with growth of the coupling constant to a state with a fermion condensate is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.558604
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  • 9
    Digitale Medien
    Digitale Medien
    Performance of platinum-based spherical mercury microelectrodes in cyclic voltammetry and stripping analysis (1995)
    Weinheim : Wiley-Blackwell
    Electroanalysis 7 (1995), S. 980-986 
    Details
    ISSN: 1040-0397
    Schlagwort(e): Microelectrodes ; Stripping analysis ; Mercury ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The performance of spherically shaped mercury microelectrodes, formed by electroreduction of mercury onto an inlaid platinum microdisk of radius r, characterized by different deposit heights, h, have been investigated for cyclic (CV) and anodic stripping (ASV) voltammetry. Electrodes with h/r ratio in the range 0.1-2 have been tested in solutions containing Pb2+ and Cd2+ in NaCl and NaClO4 + HClO4 as supporting electrolytes. For cyclic vodtammetry the results obtained indicated that the width at half height (w1/2), the peak current (ip) and the charge of the anodic stripping peak (Qs) depend on the h/r parameter. Particular attention has been devoted to the relation between the charge of the cathodic process and the anodic charge of the stripping peaks. It has been found that the experimental charge values involved in the cathodic and anodic scan agree within 3%, irrespective of the mercury thickness, indicating a complete stripping of the metals deposited in the mercury. For ASV the Pt-Cd intermetallic compounds have been found to influence the stripping peak of cadmium for electrodes with h/r ≤ 1 and for concentrations of Cd2+ lower than 10-6 M. By exploiting the known properties of the mercury microelectrodes in stripping analysis, an absolute method, based on the charge associated with the stripping peak, has been applied for determining the labile fraction of the above cations in a pore-water sample of the Venice lagoon.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/elan.1140071013
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