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Showing papers on "Photoluminescence published in 1996"


Journal ArticleDOI
TL;DR: In this article, the authors explore the interrelationships between the green 510 nm emission, the free-carrier concentration, and the paramagnetic oxygen vacancy density in commercial ZnO phosphors by combining photoluminescence, optical absorption, and electron paramagnetic resonance spectroscopies.
Abstract: We explore the interrelationships between the green 510 nm emission, the free‐carrier concentration, and the paramagnetic oxygen‐vacancy density in commercial ZnO phosphors by combining photoluminescence, optical‐absorption, and electron‐paramagnetic‐resonance spectroscopies. We find that the green emission intensity is strongly influenced by free‐carrier depletion at the particle surface, particularly for small particles and/or low doping. Our data suggest that the singly ionized oxygen vacancy is responsible for the green emission in ZnO; this emission results from the recombination of a photogenerated hole with the singly ionized charge state of this defect.

3,487 citations


Journal ArticleDOI
TL;DR: By combining electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopy, a strong correlation is observed between the green 510 nm emission, the free-carrier concentration, and the density of singly ionized oxygen vacancies in commercial ZnO phosphor powders as mentioned in this paper.
Abstract: By combining electron paramagnetic resonance (EPR), optical absorption, and photoluminescence (PL) spectroscopy, a strong correlation is observed between the green 510 nm emission, the free‐carrier concentration, and the density of singly ionized oxygen vacancies in commercial ZnO phosphor powders. From these results, we demonstrate that free‐carrier depletion at the particle surface, and its effect on the ionization state of the oxygen vacancy, can strongly impact the green emission intensity. The relevance of these observations with respect to low‐voltage field emission displays is discussed.

1,888 citations


Journal ArticleDOI
TL;DR: A simple model is described to explain the recombination in these devices, and how the absorption, charge separation, and transport properties of the composites can be controlled by changing the size, material, and surface ligands of the nanocrystals.
Abstract: We study the processes of charge separation and transport in composite materials formed by mixing cadmium selenide or cadmium sulfide nanocrystals with the conjugated polymer poly(2-methoxy,5-(2\ensuremath{'}-ethyl)-hexyloxy-$p$-phenylenevinylene) (MEH-PPV). When the surface of the nanocrystals is treated so as to remove the surface ligand, we find that the polymer photoluminescence is quenched, consistent with rapid charge separation at the polymer/nanocrystal interface. Transmission electron microscopy of these quantum-dot/conjugated-polymer composites shows clear evidence for phase segregation with length scales in the range 10-200 nm, providing a large area of interface for charge separation to occur. Thin-film photovoltaic devices using the composite materials show quantum efficiencies that are significantly improved over those for pure polymer devices, consistent with improved charge separation. At high concentrations of nanocrystals, where both the nanocrystal and polymer components provide continuous pathways to the electrodes, we find quantum efficiencies of up to 12%. We describe a simple model to explain the recombination in these devices, and show how the absorption, charge separation, and transport properties of the composites can be controlled by changing the size, material, and surface ligands of the nanocrystals.

1,517 citations


Journal ArticleDOI
TL;DR: The observed shortening of the luminescence decay time in CdSe nanoncrystals in a magnetic field is in excellent agreement with the theory, giving further support to the validity of the model.
Abstract: We present a theoretical analysis of the band-edge exciton structure in nanometer-size crystallites of direct semiconductors with a cubic lattice structure or a hexagonal lattice structure which can be described within the framework of a quasicubic model. The lowest energy exciton, eightfold degenerate in spherically symmetric dots, is split into five levels by the crystal shape asymmetry, the intrinsic crystal field (in hexagonal lattice structures), and the electron-hole exchange interaction. Transition oscillator strengths and the size dependence of the splittings have been calculated. Two of the five states, including the ground state, are optically passive (dark excitons). The oscillator strengths of the other three levels (bright excitons) depend strongly on crystal size, shape, and energy band parameters. The relative ordering of the energy levels is also heavily influenced by these parameters. The distance between the first optically active state and the optically forbidden ground exciton state increases with decreasing size, leading to an increase of the Stokes shift in the luminescence. Our results are in good agreement with the size dependence of Stokes shifts obtained in fluorescence line narrowing and photoluminescence experiments in CdSe nanocrystals. Mixing of the dark and bright excitons in an external magnetic field allows the direct optical recombination of the dark exciton ground state. The observed shortening of the luminescence decay time in CdSe nanoncrystals in a magnetic field is also in excellent agreement with the theory, giving further support to the validity of our model. \textcopyright{} 1996 The American Physical Society.

1,180 citations


Journal ArticleDOI
TL;DR: Electronic energy transfer between close packed quantum dots using cw and time resolved photoluminescence is demonstrated and is consistent with long-range resonance transfer of electronic excitations from the more electronically confined states of the small dots to the higher excitedStates of the large dots.
Abstract: We demonstrate electronic energy transfer between close packed quantum dots using cw and time resolved photoluminescence. Optically clear and thin, close packed quantum dot solids were prepared from mixtures of small and large CdSe quantum dots (38.5 and 62 \AA{}, $\ensuremath{\sigma}l4.5%$). Quenching of the luminescence (lifetime) of the small dots accompanied by enhancement of the luminescence (lifetime) of the large dots is consistent with long-range resonance transfer of electronic excitations from the more electronically confined states of the small dots to the higher excited states of the large dots.

862 citations


Journal ArticleDOI
TL;DR: A photoluminescence study of excitons localized by interface fluctuations in a narrow GaAs/AlGaAs quantum well that provides a valuable system for the optical study of quantum dots by reducing the area down to the optical near-field regime.
Abstract: We report a photoluminescence study of excitons localized by interface fluctuations in a narrow GaAs/AlGaAs quantum well. This type of structure provides a valuable system for the optical study of quantum dots. By reducing the area of the sample studied down to the optical near-field regime, only a few dots are probed. With resonant excitation we measure the excited-state spectra of single quantum dots. Many of the spectral lines are linearly polarized with a fine structure splitting of 20--50 \ensuremath{\mu}eV. These optical properties are consistent with the characteristic asymmetry of the interface fluctuations.

804 citations



Journal ArticleDOI
TL;DR: In this paper, it was shown spectroscopically that electronic energy transfer in close-packed CdSe quantum-dot (QD) solids arises from dipole-dipole interdot interactions between proximal dots.
Abstract: We show spectroscopically that electronic energy transfer in close-packed CdSe quantum-dot (QD) solids arises from dipole-dipole interdot interactions between proximal dots. We use cw and time-resolved photoluminescence to study electronic energy transfer in optically thin and clear, close-packed QD solids prepared from CdSe QD samples tunable from 17 to 150 \AA{} in diameter (\ensuremath{\sigma}4.5%). High-resolution scanning electron microscopy and small-angle x-ray scattering are used to build a well-defined structural model for the QD solids. In mixed QD solids of small and large dots, we measure quenching of the luminescence (lifetime) of the small dots accompanied by enhancement of the luminescence (lifetime) of the large dots consistent with electronic energy transfer from the small to the large dots. In QD solids of single size dots, a redshifted and modified emission line shape is consistent with electronic energy transfer within the sample inhomogeneous distribution. We use F\"orster theory for long-range resonance transfer through dipole-dipole interdot interactions to explain electronic energy transfer in these close-packed QD solids. \textcopyright{} 1996 The American Physical Society.

723 citations


Journal ArticleDOI
TL;DR: In this paper, the authors collected and spectrally resolved photoluminescence from single CdSe nanocrystallite quantum dots and confirmed the atomiclike nature of the emitting state in CdSE nanocrystites.
Abstract: We collect and spectrally resolve photoluminescence from single CdSe nanocrystallite quantum dots. The elimination of spectral inhomogeneities reveals resolution limited spectral linewidths ( $l120\ensuremath{\mu}\mathrm{eV}$ at 10 K) more than 50 times narrower than expected from ensemble measurements. Light driven spectral diffusion is observed as a form of power broadening. These studies confirm the atomiclike nature of the emitting state in CdSe nanocrystallites.

691 citations


Journal ArticleDOI
TL;DR: In this paper, quantum-confined InP nanocrystals from 20 to 50 A in diameter have been synthesized via the reaction of InCl3 and P(Si(CH3)3 )3 in trioctylphosphine oxide (TOPO) at elevated temperatures.
Abstract: Quantum-confined InP nanocrystals from 20 to 50 A in diameter have been synthesized via the reaction of InCl3 and P(Si(CH3)3)3 in trioctylphosphine oxide (TOPO) at elevated temperatures. The nanocrystals are highly crystalline, monodisperse, and soluble in various organic solvents. Improved size distributions have been obtained by size-selectively reprecipitating the nanocrystals. The UV/vis absorption spectra of the particles show the characteristic blue shift of the band gap of up to 1 eV due to quantum confinement, a moderately well-resolved first excitonic excited state, and, in some cases, the resolution of a higher excited state. Structurally, the nanocrystals are characterized with powder X-ray diffraction and transmission electron microscopy. Raman spectroscopy reveals TO and LO modes near the characteristic bulk InP positions as well a surface mode resulting from finite size. The Raman line widths, line positions, and relative intensities are all size-dependent . X-ray photoelectron spectroscopy ...

485 citations


Journal ArticleDOI
TL;DR: InAs nanocrystal quantum dots have been prepared via colloidal chemical synthesis using the reaction of InCl3 and As[Si(CH3)3]3.
Abstract: InAs nanocrystal quantum dots have been prepared via colloidal chemical synthesis using the reaction of InCl3 and As[Si(CH3)3]3. Sizes ranging from 25 to 60 A in diameter are produced and isolated with size distributions of ±10%–15% in diameter. The nanocrystals are crystalline and generally spherical with surfaces passivated by trioctylphosphine giving them solubility in common organic solvents. The dots have been structurally characterized by transmission electron microscopy (TEM) and powder x‐ray diffraction (XRD) and the optical absorption and emission have been examined. Quantum confinement effects are evident with absorption onsets well to the blue of the bulk band gap and size dependent absorption and emission features. The emission is dominated by band edge luminescence. These quantum dots are particularly interesting as they provide an opportunity to make important comparisons with comparably sized InAs quantum dots synthesized by molecular beam epitaxy techniques.

Journal ArticleDOI
TL;DR: In this article, a thin-film quantum dot composites incorporating bare and overcoated CdSe nanocrystals in a ZnSe matrix were synthesized by electrospray organometallic chemical vapor deposition (ES-OMCVD).
Abstract: Electronic and chemical passivation of CdSe nanocrystals (quantum dots) has been achieved with a thin ZnSe overlayer grown in solution from trioctylphosphine selenide and diethylzinc. Layered particles with a [ZnSe/CdSe] ratio ranging from 0 to ∼5.0 were prepared and characterized by optical absorption spectroscopy, photoluminescence, high-resolution transmission electron microscopy, Auger electron spectroscopy, and X-ray scattering. The overgrown particles were crystalline and displayed band-edge absorption and emission characteristic of the initial CdSe nuclei. Thin-film quantum dot composites incorporating bare and overcoated CdSe nanocrystals in a ZnSe matrix were synthesized by electrospray organometallic chemical vapor deposition (ES-OMCVD). The photoluminescence spectra of the composites with bare CdSe dots were dominated by broad deep-level emission and the photoluminescence yield deteriorated with increasing deposition temperature. In contrast, the composites incorporating the overcoated dots sho...

Journal ArticleDOI
05 Jul 1996-Science
TL;DR: The homogeneous linewidths in the photoluminescence excitation spectrum of a single, naturally formed gallium arsenide (GaAs) quantum dot have been measured with high spatial and spectral resolution and provide a new perspective on the dephasing dynamics of the exciton in a quantum-confined, solid-state system.
Abstract: The homogeneous linewidths in the photoluminescence excitation spectrum of a single, naturally formed gallium arsenide (GaAs) quantum dot have been measured with high spatial and spectral resolution. The energies and linewidths of the homogeneous spectrum provide a new perspective on the dephasing dynamics of the exciton in a quantum-confined, solid-state system. The origins of the linewidths are discussed in terms of the dynamics of the exciton in zero dimensions, in particular, in terms of lifetime broadening through the emission or absorption of phonons and photons.

Journal ArticleDOI
TL;DR: In this article, the activation kinetics of acceptors were investigated for heteroepitaxial layers of GaN, doped with Mg. After growth, the samples were exposed to isochronal rapid thermal anneals in the temperature range from 500 to 775°C.
Abstract: The activation kinetics of acceptors was investigated for heteroepitaxial layers of GaN, doped with Mg. After growth, the samples were exposed to isochronal rapid thermal anneals in the temperature range from 500 to 775 °C. The samples were studied by variable temperature Hall effect measurements and photoluminescence (PL) spectroscopy in the as‐grown condition and after each temperature step. The thermal treatment reduced the resistivity by six orders of magnitude and the p‐type conductivity was found to be dominated by an acceptor with an activation energy of ∼170 meV. This acceptor is attributed to Mg atoms substituting for Ga in the GaN lattice and the activation process is consistent with dissociation of electrically inactive Mg–H complexes. It is shown that the appearance of a blue emission band in the PL spectrum of Mg‐doped GaN does not directly correlate with the increase in p‐type conductivity.

Journal ArticleDOI
01 Nov 1996
TL;DR: In this article, a series of oxidize-stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4 nm has been prepared in aqueous solution using 2-mercaptoethanol and 1-thioglycerol as stabilizers.
Abstract: In order to expand the range of high-quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize-stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4 nm has been prepared in aqueous solution using 2-mercaptoethanol and 1-thioglycerol as stabilizers. It has been investigated by means of UV-vis absorption and photoluminescence spectroscopy, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x-ray analysis (EDX).

Journal ArticleDOI
TL;DR: In this article, the authors identify two sources of room temperature visible luminescence from SiO2 films containing ion beam synthesized Si nanocrystals, which are attributed to defects in the SiO 2 matrix.
Abstract: Two sources of room temperature visible luminescence are identified from SiO2 films containing ion beam synthesized Si nanocrystals. From a comparison of luminescence spectra and photoluminescence decay lifetime measurements between Xe + -implanted SiO2 films and SiO2 films containing Si nanocrystals, a luminescence feature attributable to defects in the SiO2 matrix is unambiguously identified. Hydrogen passivation of the films selectively quenches the matrix defect luminescence, after which luminescence attributable to Si nanocrystals is evident, with a lifetime on the order of milliseconds. The peak energy of the remaining luminescence attributable to Si nanocrystals ``redshifts'' as a function of different processing parameters that might lead to increased nanocrystal size and the intensity is directly correlated to the formation of Si nanocrystals. Upon further annealing hydrogen-passivated samples at low temperatures (< 500 °C), the intensity of nanocrystal luminescence increases by more than a factor of 10.

Journal ArticleDOI
TL;DR: In this article, the formation of self-assembling CdSe quantum dots during molecular beam epitaxial growth on ZnSe and ZnMnSe was reported.
Abstract: We report the formation of self‐assembling CdSe quantum dots during molecular beam epitaxial growth on ZnSe and ZnMnSe. Atomic force microscopy measurements on specimens with uncapped dots show relatively narrow dot size distributions, with typical dot diameters of 40±5 nm, and with a diameter‐to‐height ratio consistently very close to 4:1. Uncapped CdSe dots are unstable with time: their density was observed to drop by an order of magnitude in 10 days, with clear evidence of ripening observed for some dots. Photoluminescence from capped dots indicates exciton localization much stronger than in ZnCdSe/ZnSe quantum wells, due to the additional lateral confinement.

Journal ArticleDOI
TL;DR: In this article, steady-state and transient optical characterization of phenylenevinylene polymers and extract a picture of the photoexcitations and dynamics which may apply more generally to non-degenerate ground-state conjugated polymers.

Journal ArticleDOI
TL;DR: The luminescence mechanism in a-C:H is described as a modification of the band tail luminescent in hydrogenated amorphous Si and paramagnetic defects are confirmed as the nonradiative recombination centers.
Abstract: The luminescence mechanism in a-C:H is described as a modification of the band tail luminescence in hydrogenated amorphous Si The tail states of a-C:H are formed from clusters of ${\mathit{sp}}^{2}$ sites and luminescence occurs by recombination within each cluster The paramagnetic defects are confirmed as the nonradiative recombination centers The weaker temperature dependence of the luminescence efficiency of a-C:H than a-Si:H is attributed to its wider tails which inhibit carrier hopping The luminescence efficiency is also quenched by narrow optical gaps, because carriers can tunnel to defects more easily in the ${\mathit{sp}}^{2}$-rich, narrow-gap a-C:H Defect quenching is less strong, however, because of the shorter Bohr radius of localized states in a-C:H \textcopyright{} 1996 The American Physical Society

Journal ArticleDOI
TL;DR: The green luminescence of polycrystalline ZnO is investigated by diffuse reflection, steady state and time-resolved photoluminescence as well as photoconductivity and is assigned to a donor-acceptor-type transition.

Journal ArticleDOI
TL;DR: High quality InP quantum dots with diameters ranging from 25 to 45 A, have been prepared; these quantum dots (QDs) show high quantum yields for band-edge photoluminescence (lowest energy HOMO•LUMO transition) as discussed by the authors.
Abstract: High quality InP quantum dots with diameters ranging from 25 to 45 A, have been prepared; these quantum dots (QDs) show high quantum yields for band‐edge photoluminescence (lowest energy HOMO‐LUMO transition). The wavelength of the blue‐shifted band‐edge emission ranges from about 575 to 730 nm depending on QD size. The quantum yield for photoluminescence is 30% at 300 K and 60% at 10 K; the multiexponential decay of this emission exhibits lifetimes ranging from 5 to 50 ns. Deep red‐shifted emission due to trapping of carriers in defect states on the QD surface which exhibits lifetimes above 500 ns, has been eliminated by treating the QDs with a dilute solution of HF or NH4F.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional growth mode (step flow) of GaN quantum dots on AlxGa1−xN (x=0-0.2) surfaces that is energetically commenced under the conventional growth conditions was intentionally modified into a three-dimensional mode by using a "surfactant" to inhibit the GaN film from wetting the AlGaN surface.
Abstract: Nanoscale GaN quantum dots were fabricated on AlxGa1−xN layer surfaces via metalorganic chemical vapor deposition. In order to achieve a self‐assembling dot structure, a two‐dimensional growth mode (step flow) of GaN films on AlxGa1−xN (x=0–0.2) surfaces that is energetically commenced under the conventional growth conditions was intentionally modified into a three‐dimensional mode by using a ‘‘surfactant.’’ The surfactant is believed to inhibit the GaN film from wetting the AlGaN surface due to the change in surface free energy. The resulting morphological structures of GaN dots were found to be sensitive to the doping rate of tetraethyl silane used as a surfactant, the Al content (x) of the AlxGa1−xN layer, and the growth temperature. A very intense photoluminescence emission was observed from the GaN dots embedded in the AlGaN layers.

Journal ArticleDOI
TL;DR: In this paper, large energy shifts in the luminescence emission from strained InGaAs quantum dots are observed as a result of postgrowth annealing and also when raising the upper cladding layer growth temperatures.
Abstract: Large energy shifts in the luminescence emission from strained InGaAs quantum dots are observed as a result of postgrowth annealing and also when raising the upper cladding layer growth temperatures. These blueshifts occur concurrently with narrowing (from 61 to 24 meV) of the full width at half‐maxima for the emission from the quantum dot ensemble. These energy shifts can be explained by interdiffusion or intermixing of the interfaces rather than strain effects due to variations in capping layer thickness. Temperature behavior of the luminescence in annealed and nonannealed samples indicates a change in the shape and depth of the quantum dot confining potential. Quenching of the wetting layer luminescence after interdiffusion is also observed.


Journal ArticleDOI
TL;DR: In this article, two novel lumophores based on aluminum and zinc metallo-8-hydroxyquinolates have been prepared as electroluminescent materials, and their absorbance, photoluminescence, and electrolUMinescence properties compared with unsubstituted versions of these same complexes.
Abstract: Two novel lumophores based on aluminum and zinc metallo-8-hydroxyquinolates have been prepared as electroluminescent materials, and their absorbance, photoluminescence, and electroluminescence properties compared with unsubstituted versions of these same complexes. 8-Hydroxy-5-piperidinylquinolinesulfonamide (1) was synthesized in order to add an electron-withdrawing substituent at the 5-position in 8-hydroxyquinoline, increasing the solubility of the corresponding metal quinolate complexes in nonpolar solvents, and producing a blue-shift in the emission wavelength maximum, relative to complexes formed from the unsubstituted compound. The aluminum complex (Al(QS)3) and the zinc complex (Zn(QS)2) of 1 were compared with the aluminum and zinc complexes of unsubstituted 8-hydroxyquinoline (AlQ3 and ZnQ2), both as solutions and as pure thin films, or as poly(N-vinylcarbazole) (PVK) thin films doped with the metal quinolates. Ultraviolet photoelectron spectroscopy data are presented to assist in estimating the...

Journal ArticleDOI
TL;DR: It is shown that nonradiative energy back transfer from the excited Er $4f$ shell causes luminescence quenching below 200 K, and the decrease of emission intensity above 100 K is caused by an unidentified second back-transfer process.
Abstract: Recombination processes in rare-earth metals in semiconductors are a special case due to the localized nature of $f$ electrons. Our work explores in detail the radiative and nonradiative mechanisms of energy transfer for erbium in silicon by investigating the temperature dependence of the intensity and the decay time of the photoluminescence of Er-related centers in Si. We show that nonradiative energy back transfer from the excited Er $4f$ shell causes luminescence quenching below 200 K. We study electroluminescence decay by applying different bias conditions during the decay. In a two-beam experiment the photoluminescence decay is monitored for different background-excitation laser powers. Changes in the decay time are strong evidence of the impurity Auger effect as an efficient luminescence-quenching mechanism for Er in Si. A fast initial luminescence decay component at high pumping powers is related to quenching by excess carriers. The power dependence, the decay-time components, and the two-beam experiment are simulated by a set of rate equations which involve the formation of excitons, a decrease of the pumping efficiency by exciton Auger recombination, and a decrease of radiative efficiency by the impurity Auger effect with free electrons. As a nonradiative deexcitation path competing with spontaneous emission, the impurity Auger effect decreases the excited-state lifetime of Er in Si, and dominates the thermal quenching of luminescence in the temperature range from 4 to 100 K. We find that the decrease of emission intensity above 100 K is caused by an unidentified second back-transfer process.

Journal ArticleDOI
TL;DR: Si ions were implanted into thermally grown SiO2 films on crystalline Si at an energy of 120 keV and with a dose of 1016 cm−2 under an ultraviolet excitation of ∼50 eV, the implanted films exhibit blue luminescence with a peak of ∼27 eV at room temperature as mentioned in this paper.
Abstract: Si ions were implanted into thermally grown SiO2 films on crystalline Si at an energy of 120 keV and with a dose of 1016 cm−2 Under an ultraviolet excitation of ∼50 eV, the implanted films exhibit blue luminescence with a peak of ∼27 eV at room temperature The blue emission is caused by oxygen vacancies in the films

Journal ArticleDOI
TL;DR: In this paper, the temperature effect on exciton localization in self-organized InAs quantum dots was investigated and the energy for excitons in reference quantum well and quantum dot was found to be 2 and 7 meV, respectively.
Abstract: We investigated the temperature effect on exciton localization in self‐organized InAs quantum dots Quenching energy for excitons in reference quantum well and quantum dots was found to be 2 and 7 meV, respectively Thermoactivation energy of electron‐hole emission through a GaAs barrier in the quantum dots was measured as 46 meV We observed an unusual decrease of photoluminescence peak full width at half maximum with temperature, suggesting suppression of nonpredominant size quantum dot emissions due to carrier tunneling between nearby dots

Journal ArticleDOI
TL;DR: By increasing the photoexcitation intensity, excited-state interband transitions up to n=5 can be observed in photoluminescence, allowing the Fermi level to be raised by more than 200 meV due to the combined large intersublevel spacing and the low density of states.
Abstract: We present radiative lifetime measurements of excited states in semiconductor self-assembled quantum dots. By increasing the photoexcitation intensity, excited-state interband transitions up to n=5 can be observed in photoluminescence. The dynamics of the interband transitions and the intersublevel relaxation in these zero-dimensional energy levels lead to state filling of the lower-energy states, allowing the Fermi level to be raised by more than 200 meV due to the combined large intersublevel spacing and the low density of states. The decay time of each energy level obtained under various excitation conditions is used to evaluate the intersublevel thermalization time. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: In this article, the absorption, photoexcitation and internal and external luminescence efficiencies for Alq3 films grown by vacuum deposition have been measured accurately for the first time, and the internal quantum efficiency was found to be (32 ± 2)% independent of film thickness from 100 A to 1.35 μm.