Cadmium bis(phenyldithiocarbamate) [Cd(PTC)2] is prepared and structurally characterized. The compound crystallizes in the monoclinic space group P21/n. A one-dimensional polymeric structure is adopted in the solid state, having bridging PTC ligands and 6-coordinate pseudo-octahedral Cd atoms. The compound is soluble in DMSO, THF, and DMF and insoluble in EtOH, MeOH, CHCl3, CH2Cl2, and toluene. {CdSe[n-octylamine]0.53} quantum belts and Cd(PTC)2 react to deposit epitaxial CdS shells on the nanocrystals. With an excess of Cd(PTC)2, the resulting thick shells contain spiny CdS nodules grown in the Stranski–Krastanov mode. Stoichiometric control affords smooth, monolayer CdS shells. A base-catalyzed reaction pathway is elucidated for the conversion of Cd(PTC)2 to CdS, which includes phenylisothiocyanate and aniline as intermediates, and 1,3-diphenylthiourea as a final product.

The solution–liquid–solid (SLS) and related solution-based methods for the synthesis of semiconductor nanowires and nanorods are reviewed. Since its discovery in 1995, the SLS mechanism and its close variants have provided a nearly general strategy for the growth of pseudo-one-dimensional nanocrystals. The various metallic-catalyst nanoparticles employed are summarized, as are the syntheses of III–V, II–VI, IV–VI, group IV, ternary, and other nanorods and nanowires. The formation of axial heterojunctions, core/shell nanowires, and doping are also described. The related supercritical-fluid–liquid–solid (SFLS), electrically controlled SLS, flow-based SLS, and solution–solid–solid (SSS) methods are discussed, and the crystallographic characteristics of the wires and rods grown by these methods are summarized. The presentation of optical and electronic properties emphasizes electronic structures, absorption cross sections, polarization anisotropies, and charge-carrier dynamics, including photoluminescence intermittency (blinking) and photoluminescence modulation by charges and electric fields. Finally, developing applications for the pseudo-one-dimensional nanostructures in field-effect transistors, lithium-ion batteries, photocathodes, photovoltaics, and photodetection are discussed.

A simple and potentially general means of eliminating the planar defects and phase alternations that typically accompany the growth of semiconductor nanowires by catalyzed methods is reported. Nearly phase-pure, defect-free wurtzite II–VI semiconductor quantum wires are grown from solid rather than liquid catalyst nanoparticles. The solid-catalyst nanoparticles are morphologically stable during growth, which minimizes the spontaneous fluctuations in nucleation barriers between zinc blende and wurtzite phases that are responsible for the defect formation and phase alternations. Growth of single-phase (in our cases the wurtzite phase) nanowires is thus favored.

We report ensemble extinction and photoluminesence spectra for colloidal CdTe quantum wires (QWs) with nearly phase-pure, defect-free wurtzite (WZ) structure, having spectral line widths comparable to the best ensemble or single quantum-dot values, to the single polytypic (having WZ and zinc blende (ZB) alternations) QW values, and to those of two-dimensional quantum belts or platelets. The electronic structures determined from the multifeatured extinction spectra are in excellent agreement with the theoretical results of WZ QWs having the same crystallographic orientation. Optical properties of polytypic QWs of like diameter and diameter distribution are provided for comparison, which exhibit smaller bandgaps and broader spectral line widths. The nonperiodic WZ–ZB alternations are found to generate non-negligible shifts of the bandgap to intermediate energies between the quantum-confined WZ and ZB energies. The alternations and variations in the domain sizes result in inhomogeneous spectral line width broadening that may be more significant than that arising from the 12–13% diameter distributions within the QW ensembles.Keywords: crystal structure; extinction spectroscopy; homogeneous and inhomogeneous broadening; photoluminesence; polytypism; quantum wire; wurtzite; zinc blende

Semiconductor nanocrystals having an extended length dimension and capable of efficiently transporting energy and charge would have useful applications in solar-energy conversion and other emerging technologies. Pseudocylindrical semiconductor nanowires and quantum wires are available that could potentially serve in this role. Sadly, however, their defective surfaces contain significant populations of surface trap sites that preclude efficient transport. The very large surface area of long wires is at least part of the problem. As electrons, holes, and excitons migrate along a nanowire or quantum wire, they are exposed to an extensive surface and to potentially large numbers of trap sites.A solution to this dilemma might be found by identifying “long” semiconductor nanocrystals of other morphologies that are better passivated. In this Account, we discuss a newly emerging family of flat semiconductor nanocrystals that have surprising characteristics. These thin, flat nanocrystals have up to micrometer-scale (orthogonal) lateral dimensions and thus very large surface areas. Even so, their typical photoluminescence efficiencies of 30% are astonishingly high and are 2 orders of magnitude higher than those typical of semiconductor quantum wires. The very sharp emission spectra of the pseudo-two-dimensional nanocrystals reflect a remarkable uniformity in their discrete thicknesses. Evidence that excitons are effectively delocalized and hence transported over the full dimensions of these nanocrystals has been obtained. The excellent optical properties of the flat semiconductor nanocrystals confirm that they are exceptionally well passivated.This Account summarizes the two synthetic methods that have been developed for the preparation of pseudo-two-dimensional semiconductor nanocrystals. A discussion of their structural features accounts for their discrete, uniform thicknesses and details the crystal-lattice expansions and contractions they exhibit. An analysis of their optical properties justifies the sharp photoluminescence spectra and high photoluminescence efficiencies. Finally, a bilayer mesophase template pathway is elucidated for the formation of the nanocrystals, explaining their flat morphologies. Magic-size nanocluster intermediates are found to be potent nanocrystal nucleants, allowing the synthesis temperatures to be decreased to as low as room temperature. The potential of these flat semiconductor nanocrystals in the form of nanoribbons or nanosheets for long-range energy and charge transport appears to be high.

Reaction of n-octylamine-passivated {CdSe[n-octylamine]0.53±0.06} quantum belts with anhydrous metal carboxylates M(oleate)2 (M = Cd, Zn) results in a rapid exchange of the L-type amine passivation for Z-type M(oleate)2 passivation. The cadmium-carboxylate derivative is determined to have the composition {CdSe[Cd(oleate)2]0.19±0.02}. The morphologies and crystal structures of the quantum belts are largely unaffected by the exchange processes. Addition of n-octylamine or oleylamine to the M(oleate)2-passivated quantum belts removes M(oleate)2 and restores the L-type amine passivation. Analogous, reversible surface exchanges are also demonstrated for CdS quantum platelets. The absorption and emission spectra of the quantum belts and platelets are reversibly shifted to lower energy by M(oleate)2 passivation vs amine passivation. The largest shift of 140 meV is observed for the Cd(oleate)2-passivated CdSe quantum belts. These shifts are attributed entirely to changes in the strain states in the Zn(oleate)2-passivated nanocrystals, whereas changes in strain states and confinement dimensions contribute roughly equally to the shifts in the Cd(oleate)2-passivated nanocrystals. Addition of Cd(oleate)2, which electronically couples to the nanocrystal lattices, increases the effective thickness of the belts and platelets by approximately a half of a monolayer, thus increasing the confinement dimension.

Five new, discretely sized, magic-size II–VI nanoclusters are synthesized in primary-amine bilayer templates and are isolated as the derivatives [(CdS)34(n-butylamine)18], [(ZnS)34(n-butylamine)34], [(ZnSe)13(n-butylamine)13], [(CdTe)13(n-propylamine)13], and [(ZnTe)13(n-butylamine)13]. The nanoclusters are characterized by elemental analysis, UV–visible absorption spectroscopy, laser-desorption-ionization mass spectrometry, and transmission electron microscopy. Four of the nanocluster precursors are converted to wurtzitic CdS, ZnS, and ZnSe quantum platelets and CdTe quantum belts, respectively, under mild conditions.

CuInS2 nanocrystals are prepared by ion exchange with template Cu2–xS nanoplatelets and InX3 [X = chloride, iodide, acetate (OAc), or acetylacetonate (acac)]. The morphologies of the resultant nanocrystals depend on the InX3 precursor and the reaction temperature. Exchange with InCl3 at 150 °C produces CuInS2 nanoplatelets having central holes and thickness variations, whereas the exchange at 200 °C produces intact CuInS2 nanoplatelets in which the initial morphology is preserved. Exchange with InI3 at 150 °C produces CuInS2 nanoplatelets in which the central hollowing is more extreme, whereas exchange with In(OAc)3 or In(acac)3 at 150 °C produces intact CuInS2 nanoplatelets. The results establish that the ion exchange occurs through the thin nanoplatelet edge facets. The hollowing and hole formation are due to a nanoscale Kirkendall Effect operating in the reaction-limited regime for displacement of X– at the edges, to allow insertion of In3+ into the template nanoplatelets.Keywords: cation exchange; copper(I) indium disulfide; copper(I) sulfide; hollow; nanoplatelets; nanoscale Kirkendall Effect;

The growth of silver nanowires via polyol synthesis is studied by employing AgCl nanocubes of varying size as the heterogeneous nucleants. The final mean silver nanowire diameter is found to be independent of the size of the heterogeneous nucleant, showing that the diameter is not significantly influenced by the nucleation event. Kinetic studies determine that nanowire diameter, length, and aspect ratio grow in parallel to one another and with the extent of the Ag+ reduction reaction, demonstrating that growth is limited by the reduction rate. The results are interpreted to support nanowire growth by a surface-catalyzed reduction process occurring on all nanowire surfaces and to exclude nanoparticle aggregation or Ostwald ripening as a primary components of the growth mechanism.

The aggregative growth and oriented attachment of nanocrystals and nanoparticles are reviewed, and they are contrasted to classical LaMer nucleation and growth, and to Ostwald ripening. Kinetic and mechanistic models are presented, and experiments directly observing aggregative growth and oriented attachment are summarized. Aggregative growth is described as a nonclassical nucleation and growth process. The concept of a nucleation function is introduced, and approximated with a Gaussian form. The height (Γmax) and width (Δtn) of the nucleation function are systematically varied by conditions that influence the colloidal stability of the small, primary nanocrystals participating in aggregative growth. The nucleation parameters Γmax and Δtn correlate with the final nanocrystal mean size and size distribution, affording a potential means of achieving nucleation control in nanocrystal synthesis.Keywords: aggregation; coalescence; growth; kinetics; mechanism; nanocrystal; nucleation;

Thin (1 nm) PbS quantum platelets are prepared from lead acetate and thiourea in n-octylamine solvent at and near room temperature. Mechanistic studies establish that the quantum platelets are formed within lamellar amine-bilayer mesophase templates. UV–visible extinction spectra contain discrete features assigned to the n = 1 and n = 2 quantum-well transitions in the quantum platelets. The observed shifting of the spectral features to lower energies during growth of the quantum platelets is ascribed to increasing multi-quantum-well coupling between adjacent quantum platelets in the template stacks. Re-examination of a previously published higher-temperature synthesis of PbS nanosheets provides strong evidence for an analogous oleate-bilayer templated pathway. The lamellar mesophases investigated here undergo elastic expansion in the high-vacuum environment of the TEM, which appears to be a general phenomenon. Thus, lamellar spacings measured by TEM are larger than the actual spacings at ambient pressure.

Reaction of Cd(OAc)2·2H2O and selenourea in primary-amine/secondary-amine cosolvent mixtures affords crystalline CdSe quantum platelets at room temperature. Their crystallinity is established by X-ray diffraction analysis (XRD), high-resolution transmission electron microscopy (TEM), and their sharp extinction and photoluminescence spectra. Reaction monitoring establishes the magic-size nanocluster (CdSe)34 to be a key intermediate in the growth process, which converts to CdSe quantum platelets by first-order kinetics with no induction period. The results are interpreted to indicate that the critical crystal-nucleus size for CdSe under these conditions is in the range of (CdSe)34 to (CdSe)68. The nanocluster is obtained in isolated form as [(CdSe)34(n-octylamine)16(di-n-pentylamine)2], which is proposed to function as crystal nuclei that may be stored in a bottle.

A breakthrough in semiconductor nanowire synthesis that allows fine control over axial heterostructuring was recently advanced by Hollingsworth and co-workers.1 The report also reveals fascinating mechanistic aspects of catalyzed nanowire growth.Catalyzed wire or whisker growth was discovered by Wagner and Ellis in 1964.2 They found that gold droplets on a silicon substrate catalyze silicon wire growth under chemical-vapor-deposition conditions. Gaseous precursors react at the gold-droplet surfaces, depositing silicon into solution within the gold droplets. The droplets become supersaturated, inducing precipitation of crystalline silicon upon the substrate. As precipitation occurs only at the droplet–silicon interfaces, the silicon crystallites acquire pseudo-cylindrical wire morphologies as they grow upward from the substrate. The gold-catalyst droplets rise elevator-like from the substrate, riding upon the tips of the growing wires. Wagner and Ellis2 named this method ‘vapor-liquid-solid’ or ‘VLS’ growth after the three participating phases: the vaporous precursors, liquid catalyst droplets and solid silicon wires.The VLS synthesis was subsequently adapted to a wide range of wire compositions, and to nanometer-scale wire diameters.3 A solution-based analog of VLS growth was also developed, in which precursors are delivered to the catalyst droplets in an organic-solvent phase, and nanowires grow in a solvent dispersion. By analogy, this method was named ‘solution-liquid-solid’ or ‘SLS’ growth.4, 5Certain advantages accrue to the SLS method, principally that it is conducted in a cocktail of surface ligands, which control growth, passivate electronic surface traps and provide nanowire dispersibility. However, a major drawback to SLS growth is that it is typically a batch process that does not readily support heterostructure formation. Many nanowire applications require heterojunctions, and therefore nanowire heterostructuring in which the composition is varied in segments along the axial dimension. In contrast, VLS growth supports axial heterostructuring by its easy variation of the gaseous precursors delivered.Hollingsworth and co-workers1 have combined the advantages of the SLS and VLS approaches in a new flow-SLS method. Here heterostructured (CdSe-ZnSe) nanowires are grown in a microfluidic reactor, in which the precursor flow can be abruptly varied in an alternating manner between solutions A and B (Figure 1), resulting in nanowires having to date as many as eight alternating axial segments.Moreover, the flow-SLS method slows the growth kinetics sufficiently to provide important new mechanistic insights. The results establish that nanowire growth occurs both by direct precursor impingement on the catalyst droplet, and by impingement on the nanowire sidewall with precursor diffusion along the wire to the catalyst droplet at the tip. In the latter case, nanowires elongate more rapidly as they lengthen and thus their sidewall area increases.Further work on the flow-SLS method is required to achieve finer diameter control, to establish the sharpness of the heterojunctions formed, and to determine the electrical and optical properties of the heterostructured nanowires so produced.

Four [(CdSe)13(RNH2)13] derivatives (R = n-propyl, n-pentyl, n-octyl, and oleyl) are prepared by reaction of Cd(OAc)2·2H2O and selenourea in the corresponding primary-amine solvent. Nanoclusters grow in spontaneously formed amine-bilayer templates and are characterized by elemental analysis, IR spectroscopy, UV–vis spectroscopy, TEM, and low-angle XRD. Derivative [(CdSe)13(n-propylamine)13] is isolated as a yellowish-white solid (MP 98 °C) on the gram scale. These compounds are the first derivatives of magic-size CdSe nanoclusters to be isolated in purity.

Various additives are employed in the polyol synthesis of silver nanowires (Ag NWs), which are typically halide salts such as NaCl. A variety of mechanistic roles have been suggested for these additives. We now show that the early addition of NaCl in the polyol synthesis of Ag NWs from AgNO3 in ethylene glycol results in the rapid formation of AgCl nanocubes, which induce the heterogeneous nucleation of metallic Ag upon their surfaces. Ag NWs subsequently grow from these nucleation sites. The conclusions are supported by studies using ex situ generated AgCl nanocubes.Keywords: nanowire; nucleation; polyol; silver

Colloidal CdTe quantum wires are reported having ensemble photoluminescence efficiencies as high as 25% under low excitation-power densities. High photoluminescence efficiencies are achieved by formation of a monolayer CdS shell on the CdTe quantum wires. Like other semiconductor nanowires, the CdTe quantum wires may contain frequent wurtzite–zinc-blende structural alternations along their lengths. The present results demonstrate that the optical properties, emission-peak shape and photoluminescence efficiencies, are independent of the presence or absence of such structural alternations.

Di-n-octylphosphine oxide (DOPO) and di-n-octylphosphinic acid (DOPA), as two of impurities found in commercial tri-n-octylphosphine oxide (TOPO), generate significant differences in the outcomes of CdSe-nanocrystal (NC) syntheses. Using n-tetradecylphosphonic acid (TDPA) as the primary acid additive, quantum dots (QDs) are grown with DOPO added, whereas quantum rods (QRs) are grown in the presence of DOPA. While using oleic acid (OA) as the primary acid additive, QDs are generated and the QDs produced with DOPA exhibit larger sizes and size distributions than those produced with DOPO. 31P NMR analyses of the reaction mixtures reveal that the majority of the DOPO has been converted into DOPA and di-n-octylphosphine (DOP) with DOP being removed via evacuation over the course of Cd-precursor preparation. The origin of the puzzling differences in the shape control of CdSe NCs in the presence of DOPO and DOPA is elucidated to be the small quantity of DOPO present, which liberates DOP during NC synthesis. In the presence of DOP, regardless of DOPA, the precursor-conversion kinetics and thus the nucleation kinetics are dramatically accelerated, generating a large number of nuclei by consuming a significant amount of CdSe nutrients, favoring QD growth. Similarly, QD growth is favored by the fast nucleation kinetics in the presence of OA, and the broader size distributions of QDs with DOPA are due to a second nucleation event initiated by the more stable Cd-di-n-octylphosphinate component. In contrast, a slow nucleation event results in the growth of QRs in the case of using DOPA and TDPA, where no DOPO or DOP is present. The results, thus, demonstrate the important role of precursor-conversion kinetics in the control of NC morphologies.

Here, we elucidate a double-lamellar-template pathway for the formation of CdSe quantum belts. The lamellar templates form initially by dissolution of the CdX2 precursors in the n-octylamine solvent. Exposure of the precursor templates to selenourea at room temperature ultimately affords (CdSe)13 nanoclusters entrained within the double-lamellar templates. Upon heating, the nanoclusters are transformed to CdSe quantum belts having widths, lengths, and thicknesses that are predetermined by the dimensions within the templates. This template synthesis is responsible for the excellent optical properties exhibited by the quantum belts. We propose that the templated-growth pathway is responsible for the formation of the various flat, colloidal nanocrystals recently discovered, including nanoribbons, nanoplatelets, nanosheets, and nanodisks.

The kinetics and mechanism of Bi-nanocrystal growth from the precursor Bi[N(SiMe3)2]3 are determined at various Na[N(SiMe3)2] additive concentrations. The results establish that aggregative nucleation and growth processes dominate Bi-nanocrystal formation. The time dependence of the aggregative nucleation rate−the nucleation function−is determined over the range of Na[N(SiMe3)2] concentrations studied. The time width of aggregative nucleation (Δtn) is shown to remain reasonably narrow, and to correlate with the final Bi-nanocrystal size distribution. The maximum aggregative nucleation rate (Γmax) is shown to vary systematically with Na[N(SiMe3)2] concentration, producing a systematic variation in the final nanocrystal mean size. The Na[N(SiMe3)2] additive functions as both a nucleation-control agent and an Ostwald-ripening agent.

We report the growth of cadmium-selenide (CdSe) quantum-wire (QW) films on a variety of substrates by the solution–liquid–solid (SLS) method. Our SLS syntheses employ size-controlled, near-monodisperse bismuth (Bi) nanoparticles (NPs) as the catalysts for QW growth, which offers several advantages over Bi NPs thermally generated from thin Bi films, including mean QW diameter control, narrow diameter distributions, small diameters in the quantum-confinement regime, and control of the QW density on the substrates. The Bi NPs are deposited on the substrates via drop casting of a Bi-NP solution and subsequently annealed in a reducing atmosphere, a key step to ensure firm attachment of the Bi NPs onto the substrates and maintenance of their catalytic activity for the QW-film growth. The QW growth density is proportional to the Bi-NP coating density, which is determined by the concentration of the Bi-NP deposition solution. Lower concentrations are used for small Bi NPs to reduce their high tendency for agglomeration and to achieve control over mean QW diameter and to produce narrow diameter distributions. Spectroscopic evidence of quantum confinement is provided. Related films of InP, InAs, and PbSe QWs are also described.Keywords: bismuth; film; quantum wire; semiconductor; solution−liquid−solid growth; substrate

CdSe quantum belts (QBs) having lengths of 0.5−1.5 μm and thicknesses of 1.5−2.0 nm exhibit high photoluminescence (PL) efficiencies of ∼30%. Epifluorescence studies establish the PL spectra to be uniform along single QBs, and nearly the same from QB to QB. Photogenerated excitons are shown to be effectively delocalized over the entire QBs by position-selective excitation. Decoration of the QBs with gold nanoparticles indicates a low density of surface-trap sites, located primarily on the thin belt edges. The high PL efficiencies and effective exciton delocalization are attributed to the minimization of defective {11̅00} edge surface area or edge-top/bottom (face) line junctions in QBs relative to quantum wires having roughly isotropic cross sections, for which very low PL quantum efficiencies have been reported. The results suggest that trap sites can be minimized in pseudo-one-dimensional nanocrystals, such that the facile transport of energy and charge along their long axes becomes possible.

A mechanistic study of Ag-nanoparticle growth by reaction of [(PPh3)2Ag(O2CC13H27)] and AIBN is reported. The half-life for precursor disappearance at 130.0 ± 0.1 °C under the reaction conditions is determined to be 3.65 ± 0.42 min, which defines the time scale for classical (LaMer) nucleation and growth to be within the first 15 min (4 half-lives). The nanoparticle-growth kinetics are separately determined by TEM monitoring and UV−visible spectroscopy. Fits to the kinetic data establish that the active-growth regime extends to 58 min, and that Ostwald ripening ensues shortly thereafter. Evidence for an aggregative nucleation and growth process is obtained. The quantitative data indicate that classical nucleation and growth, aggregative nucleation and growth, and Ostwald ripening occur in consecutive time regimes with little overlap, and that nanoparticle growth is dominated by the aggregative regime. Aggregative growth should be considered a potential contributing mechanism in all nanoparticle-forming reactions.

The thermal coarsening (180 °C) of decanethiolate-capped Au nanocrystals is studied at various tetraoctylammonium bromide concentrations. The coarsening kinetics are determined by measuring nanocrystal size distributions (CSDs) as a function of time. The results are shown to be consistent with aggregative nucleation and growth. For each kinetic trial, the time dependence of the aggregative nucleation rate is extracted from the early time CSDs and fitted by a Gaussian profile. The height of the profile is the maximum nucleation rate, Γmax, and the 2σ width is the time window for nucleation, Δtn. These nucleation parameters are shown to control the final mean size and size distribution of the coarsened nanocrystals. The coarsening kinetics are influenced by tetraoctylammonium bromide concentration because the nanocrystals are partially electrostatically stabilized.

Tri-n-octylphosphine oxide (TOPO) is a commonly used solvent for nanocrystal synthesis. Commercial TOPO samples contain varying amounts of phosphorus-containing impurities, some of which significantly influence nanocrystal growth. Consequently, nanocrystal syntheses often give irreproducible results with different batches of TOPO solvent. In this study, we identify TOPO impurities by 31P NMR, and correlate their presence with the outcomes of CdSe nanocrystal syntheses. We subsequently add the active impurity species, one by one, to purified TOPO to confirm their influence on nanocrystal syntheses. In this manner, di-n-octylphosphine oxide (DOPO) is shown to assist CdSe quantum-dot growth; di-n-octylphosphinic acid (DOPA) and mono-n-octylphosphinic acid (MOPA) are shown to assist CdSe quantum-rod growth, and DOPA is shown to assist CdSe quantum-wire growth. (The TOPO impurity n-octylphosphonic acid, OPA, has been previously shown to assist quantum-rod growth.) The beneficial impurities are prepared on multigram scales and can be added to recrystallized TOPO to provide reproducible synthetic results.

Near-monodisperse Bi dots in the diameter range of 3−115 nm are synthesized by a simple, solution-based one-step approach by varying the amounts of Bi[N(SiMe3)2]3, Na[N(SiMe3)2], and a polymer surfactant, poly(1-hexadecene)0.67-co-(1-vinylpyrrolidinone)0.33, employed. The reaction conditions are further modified to produce Bi nanorods and nanoplates. Alternatively, near-monodisperse Bi dots in the diameter range of 30−45 nm are synthesized by a secondary-addition technique. With a slight modification of this technique, nanoribbons are obtained. The roles of polymer and Na[N(SiMe3)2] in the size and shape control of these Bi nanoparticles are discussed.

Colloidal InAs quantum wires having diameters in the range of 5−57 nm and narrow diameter distributions are grown from Bi nanoparticles by the solution−liquid−solid (SLS) mechanism. The diameter dependence of the effective band gaps (ΔEgs) in the wires is determined from photoluminescence spectra and compared to the experimental results for InAs quantum dots and rods and to the predictions of various theoretical models. The ΔEg values for InAs quantum dots and wires are found to scale linearly with inverse diameter (d−1), whereas the simplest confinement models predict that ΔEg should scale with inverse-square diameter (d−2). The difference in the observed and predicted scaling dimension is attributed to conduction-band nonparabolicity induced by strong valence-band−conduction-band coupling in the narrow-gap InAs semiconductor.Keywords: effective band gap; InAs quantum wire; nonparabolicity; photoluminescence; quantum confinement; solution−liquid−solid; valence-band−conduction-band coupling