| 1. |
- Arapan, Sergiu, et al.
(författare)
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Exciton levels and optical absorption in coupled double quantum well structures
- 2005
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 112:1-4, s. 216-219
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Tidskriftsartikel (refereegranskat)abstract
- We study exciton states in a coupled double quantum well (CDQW) semiconductor structure. Exciton levels and binding energies of direct and indirect excitons are calculated for a symmetric CDQW system with an applied electric field. The exciton states are obtained by solving the exciton effective-mass equation in the momentum space using the modified Gaussian quadrature method. Within this approach we perform realistic calculations of the exciton states by taking into account the coupling between different subband pairs and calculate optical-absorption coefficients. The calculated values of the exciton binding energy are in a good agreement with the experiment and the calculated absorption spectra qualitatively agree with the measured photoluminescence excitation spectra.
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| 2. |
- Auzel, Francois, et al.
(författare)
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Homogeneous line width of rare-earth-doped glasses for levels in a Stark level ladder : A new simple rule
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 122:1-2, s. 453-455
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Tidskriftsartikel (refereegranskat)abstract
- Concentrating on higher Stark states in multiplet ladders of lanthanide-doped glasses, we show that at 10 K, the homogeneous widths along Stark ladders vary quasi-linearly with the energy position in the ladder.Assuming that the mechanisms creating the homogeneous widths are first-order processes, either direct processes or two-phonon nonradiative transitions, the observed behavior is simply explained by the fact that energy separations between Stark levels for usual glasses are less, i.e., not far from kT(D), the Debye energy. This in turn provides quasi-equal phonon transition probabilities between individual Stark states. A simple theoretical relationship is derived and compared with experiments.
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| 3. |
- Auzel, Francois, et al.
(författare)
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Photon trapping in ruby and lanthanide-doped materials: Recollections and revival
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 125:1-2, s. 25-30
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Tidskriftsartikel (refereegranskat)abstract
- After some recollections of phonon and photon trapping in ruby, a critical review of this effect of renewed interest in trivalent lanthanide-doped materials is presented showing that the two independent derivations taking their roots in the work of Milne for gases and of Birks for organic scintillators are practically described by an analogous phenomenological equation when re-absorption is weak. The problem of obtaining "extrinsic" quantum efficiency larger than one is briefly discussed.
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| 4. |
- Fitting, H.-J., et al.
(författare)
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Multimodal electronic-vibronic spectra of luminescence in ion-implanted silica layers
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 122-123, s. 743-746
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Tidskriftsartikel (refereegranskat)abstract
- Thermally oxidized SiO2 layers of 100 and 500 nm thickness have been implanted by oxygen and sulfur ions with a dose of 3×1016 and 5×1016 ions/cm2, respectively, leading to an atomic dopant fraction of about 4 at.% at the half depth of the SiO2 layers. The cathodoluminescence spectra of oxygen and sulfur implanted SiO2 layers show besides characteristic bands a sharp and intensive multimodal structure beginning in the green region at 500 nm over the yellow-red region extending to the near IR measured up to 820 nm. The energy step differences of the sublevels amount on average 120 meV and indicate vibration associated electronic states, probably of O2-interstitial molecules, as we could demonstrate by a respective configuration coordinate model.
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| 5. |
- Hultell (Andersson), Magnus, 1978-, et al.
(författare)
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Nonradiative relaxation processes in molecular crystals
- 2008
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 128:12, s. 2019-2026
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Tidskriftsartikel (refereegranskat)abstract
- Internal conversion is the dominant relaxation channel from higher lying excited states in molecular crystals and involves the transfer of energy from the electronic system to the lattice. In this work, we present results from simulations of the nonradiative relaxation process with an emphasis on both intra- and interband transitions. We find the internal conversion process to be strongly nonadiabatic and the associated relaxation time in the case of large energy excitations to be limited by the transitions made between states of different bands.
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| 6. |
- Kayanuma, K, et al.
(författare)
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Transient photoluminescence spectroscopy of spin injection dynamics in double quantum wells of diluted magnetic semiconductors
- 2006
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 119, s. 418-422
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Tidskriftsartikel (refereegranskat)abstract
- Dynamics of spin injection has been studied in double quantum wells (DQWs) composed of diluted magnetic and non-magnetic semiconductors. Picosecond-transient photoluminescence (PL) of excitons in the DQWs has been measured in magnetic field. In the Cd1-xMnxTe-based DQWs, the PL intensity of the magnetic well (MW) excitons decays faster with decreasing barrier width from 12 to 2 nm. This provides the evidence for carrier tunneling from the MW to the non-magnetic well (NW) through the barrier layer. The degree of circular polarization in the transient PL of the NW exciton in magnetic field shows marked evidence for spin injection and rapid spin relaxation in the DQW system. In the Zn1-yMnySe-based DQWs, the degree of circle polarization in the NW exciton PL at 3T shows a rise with a time constant of 400 ps, while the PL of the MW exciton decays within 50 ps. The observed result is interpreted by the individual spin injection for electrons and holes from the MW to the NW. The results of the transient PL of excitons in the DQWs are compared with the transient absorptions of excitons studied by the pump-and-probe spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.
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| 7. |
- Lindgren, L.J, et al.
(författare)
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Blue light-emitting diodes based on novel polyfluorene copolymers
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 122-123:1-2, s. 610-613
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Tidskriftsartikel (refereegranskat)abstract
- This study presents the synthesis and characterisation of a series of fluorene-based conjugated copolymers, together with the preparation and characterisation of the corresponding light-emitting devices. The polymers consist of alkoxyphenyl-substituted fluorene units together with different amounts of a hole-transporting triphenylamine-substituted fluorene unit: 0%, 10%, 25% and 50%. All polymers (P0, P1, P2, and P3) show high photoluminescence efficiency (ηPL) and light emission (both PL and EL) in the blue spectral region. Electrochemical studies show improved hole injection as the ratio of the triphenylamine-substituted segment is increased. The electroluminescence quantum efficiencies (EQEs) of the devices increase six times going from P0 to P1. Compared with P1, polymers P2 and P3 show lower efficiencies in devices. These findings indicate the presence of an optimal polymer composition, where balance between the charge-carrier mobilities has been reached. © 2006 Elsevier B.V. All rights reserved.
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| 8. |
- Lindgren, Mikael, et al.
(författare)
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Electronic states and phosphorescence of dendron functionalized platinum(II) acetylides
- 2007
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313 .- 1872-7883. ; 124:2, s. 302-310
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties of bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine) platinum(II) with 2,2-bis(methylo])propionic acid (bis-MPA) dendritic substituents were studied. The fluorescence emission decay upon excitation in the UV (typically 350-380 nm) was rapid, in the order of I ns or shorter. In oxygen-saturated tetrahydrofuran solvent, the phosphorescence decay time was in the order of 200 ns. Bright phosphorescence at 530 nm was found for dendrimers under certain conditions. The associated phosphorescence decay time considerably increased to above 100-200 mu s at higher concentrations (30-100 mu M), and in oxygen-evacuated samples. Thus, it was clarified that the strongest triplet quenching was caused by oxygen dissolved in the sample, since it was possible to reversibly go between the bright and quenched phosphorescent state by freeze-thaw pumping cycles. The bright phosphorescence formed spontaneously for the cases with the larger dendritic substituents is implying a chromophore protecting effect. From time-dependent density functional calculations, the electronic structure of a few low-lying singlet and triplet states are discussed. A new mechanism for efficient triplet state formation and phosphorescence of Pt-ethynyls is proposed. Here, a fast relaxation via internal conversion takes the excited population of the dominant pi -> pi*, excitation into a lower singlet state of ligand-to-metal charge transfer character of pi sigma* type. This allows an efficient inter system crossing to the triplet state manifold.
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| 9. |
- Linnros, Jan, 1953-, et al.
(författare)
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Silicon-based photonics
- 2006
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Ingår i: Journal of Luminescence. - : ELSEVIER SCIENCE BV. - 0022-2313 .- 1872-7883. ; 121:2, s. V-V
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Mirzov, Oleg, et al.
(författare)
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Fluorescence blinking in MEH-PPV single molecules at low temperature
- 2005
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 112:1-4, s. 353-356
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence intensity transients of single molecules of the conjugated polymer poly[2-methoxy,5-(2-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) were studied at 15 K. Fluorescence blinking behavior was observed despite the expected low-temperature suppression of energy migration in such disordered molecular systems. Presence of the fluorescence blinking effect at 15K indicates that the single molecules possess a collapsed conformation with characteristic size of not more than several nanometers, which corresponds to only a few exciton hops over a polymer chain. (c) 2004 Elsevier B.V. All rights reserved.
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