Showing papers on "Quantum dot published in 1996"
TL;DR: In this article, the authors focus on the properties of quantum dots and their ability to join the dots into complex assemblies creates many opportunities for scientific discovery, such as the ability of joining the dots to complex assemblies.
Abstract: Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.
10,737 citations
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
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
TL;DR: Coulomb oscillations in vertical quantum dots containing a tunable number of electrons starting from zero are measured, as predicted by Hund’s rule, to favor the filling of parallel spins.
Abstract: We study atomiclike properties of artificial atoms by measuring Coulomb oscillations in vertical quantum dots containing a tunable number of electrons starting from zero. At zero magnetic field the energy needed to add electrons to a dot reveals a shell structure for a two-dimensional harmonic potential. As a function of magnetic field the current peaks shift in pairs, due to the filling of electrons into spin-degenerate single-particle states. When the magnetic field is sufficiently small, however, the pairing is modified, as predicted by Hund’s rule, to favor the filling of parallel spins. [S00319007(96)01418-4]
1,090 citations
TL;DR: In this article, a planar array of nanometer-diameter metal clusters that are covalently linked to each other by rigid, double-ended organic molecules have been self-assembled.
Abstract: Close-packed planar arrays of nanometer-diameter metal clusters that are covalently linked to each other by rigid, double-ended organic molecules have been self-assembled. Gold nanocrystals, each encapsulated by a monolayer of alkyl thiol molecules, were cast froma colloidal solution onto a flat substrate to form a close-packed cluster monolayer. Organic interconnects (aryl dithiols or aryl di-isonitriles) displaced the alkyl thiol molecules and covalently linked adjacent clusters in the monolayer to form a two-dimensional superlattice of metal quantum dots coupled by uniform tunnel junctions. Electrical conductance through such a superlattice of 3.7-nanometer-diameter gold clusters, deposited on a SiO2 substrate in the gap between two gold contacts and linked by an aryl di-isonitrile [1,4-di(4-isocyanophenylethynyl)-2-ethylbenzene], exhibited nonlinear Coulomb charging behavior.
1,081 citations
TL;DR: The growth of multilayer arrays of coherently strained islands self-organizes into a more regular three-dimensional arrangement, providing a possible route to obtain the size uniformity needed for electronic applications of quantum dot arrays.
Abstract: We investigate the growth of multilayer arrays of coherently strained islands, which may serve as ``quantum dots'' in electronic devices. A simple model reproduces the observed vertical correlation between islands in successive layers. However, the arrangement of islands is not simply repeated from layer to layer. Instead, the island size and spacing grow progressively more uniform. In effect, the structure ``self-organizes'' into a more regular three-dimensional arrangement, providing a possible route to obtain the size uniformity needed for electronic applications of quantum dot arrays.
1,040 citations
TL;DR: In this article, the number of electrons in these "artificial atoms" and the energy required to add successive electrons were investigated. But the authors were restricted to experiments in a regime that is inaccessible to experiments on real atoms.
Abstract: Progress in semiconductor technology has enabled the fabrication of structures so small that they can contain just one mobile electron. By varying controllably the number of electrons in these 'artificial atoms' and measuring the energy required to add successive electrons, one can conduct atomic physics experiments in a regime that is inaccessible to experiments on real atoms.
957 citations
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
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
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
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.
TL;DR: Thermoelectric and other transport measurements were made, indicating that an increase in Z over bulk values is possible through quantum confinement effects in the Si/Si 1- x Ge x quantum-well structures.
Abstract: The Si/Si1-xGex quantum well system is attractive for high temperature thermoelectric applications and for demonstration of proof-of-principle for enhanced thermoelectric figure of merit Z, since the interfaces and carrier densities can be well controlled in this system. We report theoretical calculations for Z in this system, based on which Si/Si1-xGex quantum-well structures were grown by molecular-beam epitaxy. Thermoelectric and other transport measurements were made, indicating that an increase in Z over bulk values is possible through quantum confinement effects in the Si/Si1-xGex quantum-well structures.
TL;DR: In this paper, the authors used photoluminescence excitation and fluorescence line narrowing spectroscopies to examine structure observed in the band-edge absorption feature of CdSe quantum dots.
Abstract: We use photoluminescence excitation and fluorescence line narrowing spectroscopies to examine structure observed in the band-edge absorption feature of CdSe quantum dots. We study eight samples ranging from \ensuremath{\sim}15 to \ensuremath{\sim}50 \AA{} in radius to probe the size dependence of this structure. We compare our results with recent theories, which predict band-edge exciton splittings in CdSe dots due to their internal crystal structure, nonspherical shape, and the exchange interaction between the electron and hole. We find reasonable agreement between our data and theory, supporting the observation of exciton fine structure. \textcopyright{} 1996 The American Physical Society.
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 ...
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.
TL;DR: In this paper, a laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs parts, was found to decrease the radiative lifetime and to result in low energy shifts of the corresponding peaks in luminescence and absorption spectra.
Abstract: Alternate short-period GaAs-InAs deposition following InAs pyramid formation on a GaAs (100) surface leads to the creation of vertically split pyramids. This splitting is driven by the energetics of the Stranski-Krastanow growth mode. The strain energy is reduced due to the successive transfer of InAs from the buried part of the pyramid to the uncovered part. The resulting arrangement represents a laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs parts. Results of optical studies demonstrate the expected electronic coupling in vertical direction. Coupling is found to decrease the radiative lifetime and to result in low-energy shifts of the corresponding peaks in luminescence and absorption spectra. Vertically coupled quantum dots exhibit injection lasing at very low current densities. \textcopyright{} 1996 The American Physical Society.
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...
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.
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).
TL;DR: A plane-wave semiempirical pseudopotential method with nonlocal potentials and spin-orbit coupling is used to calculate the electronic structure of surface-passivated wurtzite CdSe quantum dots with up to 1000 atoms, finding the correct form of Coulomb interaction energy with size-dependent dielectric constant is found to be essential.
Abstract: A plane-wave semiempirical pseudopotential method with nonlocal potentials and spin-orbit coupling is used to calculate the electronic structure of surface-passivated wurtzite CdSe quantum dots with up to 1000 atoms. The calculated optical absorption spectrum reproduces the features of the experimental results and the exciton energies agree to within \ensuremath{\sim}0.1 eV over a range of dot sizes. The correct form of Coulomb interaction energy with size-dependent dielectric constant is found to be essential for such good agreement. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this article, the authors presented electrical measurements of single Au and CdSe nanocrystals, which were fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind nanocrystal in tunneling contact between two closely spaced metallic leads.
Abstract: We present electrical measurements of single Au and CdSe nanocrystals. The devices are fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind nanocrystals in tunneling contact between two closely spaced metallic leads. The current–voltage characteristics of these devices exhibit a Coulomb staircase with a charging energy of ∼50 meV. This technique is readily adapted to the study of a host of nanocrystals made by solution chemistry.
TL;DR: In this paper, the authors confirm the strength of confinement effects and discuss the underlying considerations in the operation of the memory that are related to the reduced volume, strength of the barrier, and random distribution of the trapped charge in nano-crystals.
Abstract: Use of nano‐crystals of silicon in close proximity (1.5–4.5 nm) of a transistor channel lead to structures with pronounced memory where effects due to discrete number of electrons, confinement‐induced subbands in inversion layers and discrete energy states in quantum dots, random charge distribution in quantum dots, and transmission through a strong barrier are very important. Experimental results show plateaus in threshold voltage at low temperatures, spaced nearly equally apart, and indicative of single electron effects. Varying the oxide thickness shows strong influence on speed and charge retention. We confirm the strength of confinement effects and discuss the underlying considerations in the operation of the memory that are related to the reduced volume, strength of the barrier, and random distribution of the trapped charge in nano‐crystals.
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.
TL;DR: In this paper, the electronic properties of self-assembled InAs/GaAs quantum dots are investigated theoretically and the microscopic distribution of the strain, valence-band mixing, and shape of the conduction band of InAs with strain are fully taken into account.
Abstract: The electronic properties of the self-assembled InAs/GaAs quantum dots are investigated theoretically. In our calculation the microscopic distribution of the strain, valence-band mixing, and the shape of the conduction band of InAs with strain are fully taken into account. New states are brought to light and their status in the framework of established approximate models of the electronic structure is critically examined.
TL;DR: In this paper, gain measurements and calculations for InAs/GaAs quantum dot injection lasers are presented and the modal gain and estimation of the confinement factor by transmission electron microscopy yield an exceptionally large material gain of 6.8(± 1)×104 cm−1 at 80 A cm−2.
Abstract: We present gain measurements and calculations for InAs/GaAs quantum dot injection lasers. Measurements of the modal gain and estimation of the confinement factor by transmission electron microscopy yield an exceptionally large material gain of 6.8(±1)×104 cm−1 at 80 A cm−2. Calculations including realistic quantum dot energy levels, dot size fluctuation, nonthermal coupling of carriers in different dots, and band filling effects corroborate this result. A large maximum differential gain of 2×10−12 cm2 at 20 A cm−2 is found. The width of the gain spectrum is determined by participation of excited quantum dot states. We record a low transparency current density of 20 A cm−2. All experiments are carried out at liquid nitrogen temperature.
TL;DR: In this paper, the current vs voltage curves of a mesoscopic device consisting of two electrodes and a molecular wire were studied at the Hartree-Fock level with electron repulsion.
Abstract: We have studied the current vs voltage curves (I–V characteristics) of a mesoscopic device consisting of two electrodes and a molecular wire. The wire Hamiltonian includes both electronic tunneling and Coulomb repulsion within a Hubbard model that is treated at the Hartree–Fock level. The inclusion of electron repulsion is an extension of our previous work that only considered the case of noninteracting electrons. We have found several important features in the calculated characteristics of the wire. These include (1) a staircaselike structure that strongly resembles that associated with Coulomb blockade in heterostructures and quantum dots, but that in the case of the wire is associated with the discrete nature of the molecular resonances; (2) regions of negative differential resistance associated with increased localization of the molecular resonances. Our theoretical model includes a consistent treatment of the conduction in the linear and nonlinear regimes which remains valid even when the device is o...
TL;DR: In this article, semi-empirical tight-binding and ab initio local density calculations demonstrating the meta-stability of self-trapped excitons at the surface of silicon nanocrystallites are presented.
Abstract: We present semiempirical tight-binding and ab initio local density calculations demonstrating the (meta)stability of self-trapped excitons at the surface of silicon nanocrystallites. These are obtained for dimer bonds passivated, for instance, by hydrogen atoms or by silicon oxide. Light emission from these trapped excitons is predicted in the infrared or in the near visible. We are thus led to the interpretation that part of the luminescence is due to such surface states while optical absorption is characteristic of quantum confinement effects. These conclusions should extend to other semiconductor crystallites.
TL;DR: In this article, a theoretical analysis of the gain and threshold current of a semiconductor quantum dot (QD) laser is given which takes account of the line broadening caused by fluctuations in quantum dot sizes.
Abstract: Theoretical analysis of the gain and threshold current of a semiconductor quantum dot (QD) laser is given which takes account of the line broadening caused by fluctuations in quantum dot sizes. The following processes are taken into consideration together with the main process of radiative recombination of carriers in QDs: band-to-band radiative recombination of carriers in the waveguide region, carrier capture into QDs and thermally excited escape from QDs, photoexcitation of carriers from QDs to continuous-spectrum states. For an arbitrary QD size distribution, expressions for the threshold current density as a function of the root mean square of relative QD size fluctuations, total losses in the waveguide region, surface density of QDs and thickness of the waveguide region have been obtained in an explicit form. The minimum threshold current density and optimum parameters of the structure (surface density of QDs and thickness of the waveguide region) are calculated as universal functions of the main dimensionless parameter of the theory developed. This parameter is the ratio of the stimulated transition rate in QDs at the lasing threshold to the spontaneous transition rate in the waveguide region at the transparency threshold. Theoretical estimations presented in the paper confirm the possibility of a significant reduction of the threshold currents of QD lasers as compared with the conventional quantum well lasers.
TL;DR: The effective mass approximation is used to study the dependence of energy levels of lens-shaped SAD on size, depth of confining potential, and the magnetic field and relate the electron and hole energy levels to the magneto-optical properties of the SAD.
Abstract: The electronic structure of lens-shaped self-assembled quantum dots is studied as a function of the dot size, the confining potential, and the magnetic field. The parabolic confining potential and its corresponding energy spectrum are shown to be an excellent approximation. The magnetoexciton spectrum is calculated and compared with recent experiments. \textcopyright{} 1996 The American Physical Society.
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.