InP Nanocrystals Research Articles

Highly Luminescent Water-Soluble InP/ZnS Nanocrystals Prepared via Reactive Phase Transfer and Photochemical Processing

Highly luminescent water-soluble InP/ZnS core−shell nanocrystals were prepared using a newly developed method that incorporates reactive phase transfer and photochemical processing. Poor-emitting InP nanocrystals (NCs, 2−4 nm) prepared solvothermally using toluene were transferred into alkaline aqueous solution containing thiol and zinc ions. When these NCs in aqueous solution were subsequently irradiated by ultraviolet (UV) light, they showed intense size-dependent photoluminescence (PL) from green to red due to the formation of a thick (more than 1 nm) ZnS shell on the NCs. The surface dissolution of the NCs, under conditions in which bulk InP does not dissolve due to its covalent bond nature, was observed at two steps: phase transfer and shell formation. This dissolution competed with the formation of the ZnS layer at the start of UV irradiation. Since the UV irradiation enables creation of a thick shell by optimizing the synthesizing conditions, high PL efficiency (30−68%) was obtained in water with sufficient stability. This was quantitatively explained by quantum mechanical calculations. The PL decay behavior of these water-soluble InP/ZnS NCs did not show obvious size-dependence, unlike HF-treated ones. This is attributed to the well-passivated surface states of the NCs due to their thick ZnS shell. The NCs showed a significantly higher In/P ratio than those previously reported. This indicates that In ions were preferentially located on the surface of the InP core in the NCs.

ChemInform Abstract: Facile Preparation of Highly Luminescent InP Nanocrystals by a Solvothermal Route.

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Microwave Induced In-Situ Active Ion Etching of Growing InP Nanocrystals

High quantum yield (47%) InP nanocrystals can be prepared without the need for post HF treatment by combining microwave methodologies with the presence of a fluorinated ionic liquid. Growing the InP nanocrystals in the presence of the ionic liquid 1-hexyl-3-methyl-imidazolium tetrafluoroborate (hmim BF4) allows in situ etching to be achieved. The optimization of the PL QY is achieved by balancing growth and etching rates in the reaction.

Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects

Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states rho XX. Here we introduce a DCM "figure of merit" R2(E) which is proportional to the ratio between the biexciton density of states rhoXX and the single-exciton density of states rhoX, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R2(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E0 (the energy at which R2(E) becomes >or=1) is reduced, suggesting improved DCM. However, whether the normalized E0/epsilong increases or decreases as the dot size increases depends on dot material.

Low temperature synthesis of InP nanocrystals

We present a simple method for the chemical synthesis of InP nanocrystals, which comprises several advantages: (i) the use of simple reagents, namely InCl3·4H2O and yellow P as the In and P precursors, respectively, and NaBH4 as the reducing agent in a mixed solvent of ethanol and toluene; (ii) a short reaction time (1–5 h) and low temperature (<75 °C); (iii) a high reaction yield approaching 100%. InP NCs in the zinc-blende structure have been obtained as confirmed by powder X-ray diffraction and Raman scattering measurements. Their mean size of 4 nm has been determined by transmission electron microscopy, Raman scattering and absorption spectroscopy.

Facile Preparation of Highly Luminescent InP Nanocrystals by a Solvothermal Route

Abstract Monodisperse InP nanocrystals were prepared by a facile one-pot solvothermal route via the pyrolysis reaction between indium chloride and tris(dimethylamino)phosphine at relatively low temperatures (150–180 °C). The InP nanocrystals after size-selective precipitation had a well-crystallized zinc blende structure, a narrow size distribution, and distinguishable absorption peaks. Application of HF treatment in combination with photoetching increased their emission efficiency to 58% while their emission wavelengths were tunable from green to red.

Economic Synthesis of High Quality InP Nanocrystals Using Calcium Phosphide as the Phosphorus Precursor

InP nanocrystals of low size dispersion are synthesized in 1-octadecene using indium myristate and PH3, in situ generated from the air-stable and low-cost precursor calcium phosphide. The obtained nanocrystals exhibit size-dependent emission (570–720 nm), and their fluorescence quantum yield reaches 22% after overcoating with a ZnS shell.

Benzene-thermal Route to InP and InAs Nanocrystals Using Triphenylphosphine and Triphenylarsine as Pnicogen Sources

Abstract Nanocrystalline InP and InAs were solvothermally synthesized by the reaction of newly reduced indium with triphenylphosphine (PPh3) and triphenylarsine (AsPh3) in benzene. The products were characterized by XRD, TEM, and EDX. PPh3 and AsPh3 with high safety as excellent P and As sources will provide a novelly alternative synthetic route to III–V semiconductor compouds.

A complexant-assisted hydrothermal procedure for growing well-dispersed InP nanocrystals

Well-dispersed InP nanocrystals have been synthesized via a hydrothermal reaction of In–ethylenediamine tetraacetic acid (EDTA) complex with red phosphorus and KBH 4 in aqueous solution at 160–200 °C for 26 h. The InP nanocrystals were characterized by powder X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The XRD patterns showed (1 1 1), (2 0 0), (2 2 0), (3 1 1), (2 2 2), (4 0 0) and (3 3 1) diffraction lines of the cubic InP nanocrystals. The TEM study revealed that the morphology of InP nanocrystals are of well-dispersed spherical shape. The size of InP nanocrystals can be controlled by changing the reaction temperature. The average InP nanocrystallites diameter is increased from 8.7 to 15.8 nm as the temperature increases from 160 to 200 °C. The Raman spectrum showed the transverse-optic (TO) and longitudinal-optic (LO) mode from InP nanocrystallites, and the LO and TO modes shift to lower frequencies with a decrease in the size of InP nanocrystals. The EDTA plays a key role in the nucleation and growth of InP nanocrystals, and the reaction mechanism is discussed.

Colloidal InP Nanocrystals as Efficient Emitters Covering Blue to Near-Infrared

High quality InP nanocrystals in the size range from 1 to 8 nm were synthesize at relatively low temperature (<190 °C). The low temperature was enabled by the activation of In carboxylate precursors with fatty amines. The reduced temperature enabled the elimination of the thorough degassing step usually needed in the existing schemes. By simply varying the concentration and chain length of the ligand and activation reagents, the absorption peak position was tuned continuously from 390 to 720 nm without prolonged heating. This new synthetic scheme further enabled the direct synthesis of InP/ZnS core/shell nanocrystals in a one-pot fashion. The resulting InP/ZnS core/shell nanocrystals can emit from about 450 to 750 nm, with a quantum yield as high as over 40%. The bright core/shell nanocrystals were stable in air and could be dispersed in water with hydrophilic thiols ligands. The thiol ligand replacement did not quench the emission, and the resulting water-soluble nanocrystals were stable under ambient conditions for at least 3 months.

Third-Order Nonlinear Optical Susceptibility of IndiumPhosphide Nanocrystals

InP nanocrystals synthesized by refluxing and annealing of organicsolvent are determined from XRD measurements to have an averagegranularity of 25 nm. The nonlinear optical properties of the InPnanocrystals studied by using laser Z-scan technique with 50 ps pulsesat 532 nm are found to reveal strong nonlinear optical properties andtwo-photon absorption phenomenon. Also, the nonlinear absorptioncoefficient, the nonlinear refractive index and the third-ordernonlinear optical susceptibility are determined by experiments, inwhich the nonlinear refractive index is three orders of magnitudelarger than that of bulk InP.

Surface Ligand Dynamics in Growth of Nanocrystals

Amine ligands were identified to bond on the surface of CdSe nanocrystals in a dynamic fashion under elevated temperatures in the reproducible growth domain of the specific designed growth reactions. The surface ligand dynamics was found to strongly depend on the growth temperature, the ligand concentration, and the ligand chain length. The strong chain-length dependence was originated from the interligand interactions in the ligand monolayer of a nanocrystal, provided fatty amines being weak ligands for CdSe nanocrystals. When the growth reaction was above the boiling point of an amine ligand, the surface ligand dynamics was violent, a quasi-gas-phase state, indicated by strong temperature-dependent and fast growth rates of the nanocrystals. Approximately below its boiling point, a significantly weak temperature dependence of the growth rate of the nanocrystals associated with the quasi-liquid state of the surface ligands was observed. A direct result of studying the surface ligand dynamics of this well-established nanocrystal system was the formation of high-quality CdSe nanocrystals under much reduced temperature, 150 degrees C, in comparison to the standard 250-350 degrees C temperature range. This was achieved by using fatty amines with a short hydrocarbon chain at a low ligand concentration in the solution. Preliminary results indicate that a similar temperature (160 degrees C) also worked for the growth of InP nanocrystals.

Theory of InP nanocrystals under pressure

An empirical tight-binding theory which includes the effects of lattice relaxation is employed to investigate the optoelectronic properties of InP nanocrystals under external hydrostatic pressure. For bulk InP, our model accurately describes the evolution of the lowest conduction-band edges with pressure and predicts the ${\ensuremath{\Gamma}}_{1c}\text{\ensuremath{-}}{X}_{1c}$ crossover at the same lattice contraction as measured in experiment. For small InP nanocrystals, the lattice-relaxed tight-binding model is compared with a tight-binding model which assumes a scaled bulklike arrangement for the atoms in the nanocrystal. Atomistic bond-length-scaling models predict that a direct-to-indirect band gap (the ${\ensuremath{\Gamma}}_{1c}\text{\ensuremath{-}}{X}_{1c}$ crossing) produces the redshift observed experimentally in nanocrystals at high pressure. However, the scaling models are not able to describe quantitatively the band-gap evolution with pressure. When lattice relaxation effects are included, the band-gap dependence on pressure agrees quantitatively with the experimental results. The agreement in the band-gap variation with pressure is due to the stronger mixture between ${\ensuremath{\Gamma}}_{1c}$ and ${L}_{1c}$ minima and the more localized character of hole states. Moreover, in the lattice-relaxed model, the experimental redshift results as a transition of the lowest states from bound states localized inside the dot to surfacelike states on the dot exterior, rather than as the direct-to-indirect band gap crossover.

Photoluminescence of InP nanocrystals embedded in silica gel-glasses as a function of temperature, and excitation power

InP nanocrystals embedded in silica glasses were prepared by combining the sol–gel process and the heat treatment in H2 gas. The size of InP nanocrystals was found to be from 2 to 8nm in diameter by transmission electron microscopy. A strong photoluminescence (PL) with peaks at 605, 735 and 856nm was observed from 3InP/100SiO3 nanocompositions at 77K. The temperature- and excitation power-dependent PL spectra from the nanocomposition are measured in order to confirm the origin of the PL spectra. The behaviors of the three peaks emissions suggest that 605, 735, and 856nm emissions do not have the same origin. The PL peak centered at 856nm may arise from 8nm InP nanocrystals with 5–10% size distribution instead of all the InP nanocrystals with different sizes embedded in the SiO2 gel-glasses. The 605 and 735nm emissions may arise from oxygen related defect centers in the SiO2 gel-glass matrix and at the interface between the InP crystallite core and SiO2 glass matrix. The quenching of PL from the InP nanocrystals with diameters <8nm may be quenched due to the pressure-induced Γ–X transition. The result provides an evidence for the prediction of Fu and Zunger.

Influence of the Choice of Indium Precursor and Ligand on the Synthesis of InP Nanocrystals

Well-crystallized InP nanocrystals with particle diameters ranging from 2 to 5.5nm were prepared via the reaction between tris(trimethylsilyl)phosphine and different indium precursors. The classic TOP/TOPO reaction medium was replaced by the weakly coordinating solvent diphenylether, which contained a strongly coordinating ligand at low concentrations. Different phosphine oxides, phosphines, phosphates, phosphites and phosphonates were used as ligands and their influence on the growth of InP nanocrystals was studied. The synthesis procedure allows to prepare crystalline InP quantum dots (QDs) at temperatures as low as 150°C and within short reaction times. The final size of the InP QDs is remarkably independent of the choice of ligand and indium precursor.

Amine-induced growth of an In2O3shell on colloidal InP nanocrystals

A simple and rapid method for the growth of an In2O3 shell on colloidal InP nanocrystals is described, increasing their fluorescence efficiency by one order of magnitude.

Synthesis of III-V Nanocrystals by Co-reduction Reactions

ABSTRACTThis paper describes a co-reduction colloidal method for the synthesis of In-containing III-V nanocrystals (NCs) by using pnictogen halides (such as PCl3, AsCl3, and SbCl3) as the pnictogen-sources and superhydride (LiBH(C2H5)3) as the reducing agent. The syntheses were generally carried out in octadecene in the presence of fatty acids at ∼250 °C. The as-synthesized InP NCs were monodisperse in particle size and size distribution, whereas the InAs and InSb NCs showed relatively lower quality. The growth process of NCs was studied using InP as a model system.

Pressure‐induced optoelectronic properties of InP nanocrystals: Tight‐binding approach

AbstractAn empirical tight‐binding theory is used to investigate pressure effects on the electronic and optical properties of InP nanocrystals. For bulk InP, our model predicts the Γ–X crossing of the conduction band minima at exactly the same lattice contraction as measured in the experiment. For small InP nanocrystals, the model correctly predicts the pressure dependence of the fundamental energy gap and luminescence intensity. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Ligand Adsorption/Desorption on Sterically Stabilized InP Colloidal Nanocrystals: Observation and Thermodynamic Analysis

Macroscopic characterisation: The adsorption/desorption equilibrium of trioctylphosphine oxide ligands at colloidal InP nanocrystals (see picture) is investigated with quantitative, one-dimensional 1H NMR spectroscopy. Thermodynamic analysis of the isotherm demonstrates that formation of the capping is driven by favorable adsorbate–substrate interactions and is strengthened by adsorbate–adsorbate interactions. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2267/2006/z500659_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis and electrochemical properties of InP nanocrystals

In this report, we present a new organometallic synthetic method to prepare nearly monodisperse InP nanoparticles using indium trifluoroacetate as the In precursor. Spherical particles of various sizes were prepared by modulating the growth duration. The optical and electrochemical properties were investigated and discussed with reference to band edge positions. This is the first report on the band edge position of quantum confined InP nanoparticles, which is a key parameter for development of electro-optic devices like solar cells and light-emitting diodes based on it.