The effect of PbS nanoparticles on the formation of PbSe in aqueous solutions of sodium selenosulfate and lead(II)

It was established that PbS nanoparticles significantly increase the rate of formation of lead selenide during the reaction of Pb(NO₃)₂ and Na₂SeSO₃ in aqueous solutions of polymers. It was shown that the reaction product consists of PbS/PbSe nanoparticles with a “PbS core-PbSe shell” structure. A correlation was found between the forbidden band widths of the PbS nanoparticles and the PbS/PbSe nanostructures formed during the reaction. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 6, pp. 339–344, November–December, 2006.     

A reverse cation-exchange route to hollow PbSe nanospheres evolving from Se/Ag2Se core/shell colloids

A reverse cation-exchange approach for the synthesis of hollow PbSe nanospheres is successfully established. This route involves a new strategy of a stepwise, in-situ template-based evolution from spherical amorphous Se colloids to Se/Ag(2)Se core/shell colloids, then to hollow PbSe nanospheres. Se colloids are prepared as the initial product by utilizing the chelation of ethylenediamine to bulk Se. They are converted into Se/Ag(2)Se core/shell colloids through the reaction with Ag(+) in ethylene glycol. During the conversion from Ag(2)Se shell to PbSe shell, a small amount of tributylphosphine is crucial as the capping agent. The characterization results, including XRD, SEM, TEM, HRTEM, and EDX, reveal that hollow PbSe nanospheres with polycrystalline and cubic structure are prepared. The corresponding optical band gap is calculated to be 0.56 eV. This conformation is potentially beneficial to the improvement concerning the applications of PbSe nanostructures.     

单体摩尔比对PbSe纳米粒子生长的影响

本文研究了不同温度下,Se单体与Pb单体的不同摩尔比对PbSe纳米粒子晶体成核和晶体生长的影响。实验显示,摩尔比较大,Se单体比较多时,PbSe成核比较容易但是PbSe纳米粒子的生长比较慢。主要有两方面原因,一方面是因为Se单体的活度比较大,另一方面是由于PbSe纳米粒子的外壳是Pb壳的粒子结构。     

Solvothermal Synthesis and Characterization of PbSe Nanostructures with the Aid of Schiff-base Ligand

In this work, Pb(II)N,N-bis(salicylidene)-ethylenediamine; [Pb(salen)]; was applied as lead precursor to synthesis PbSe nanostructures. Besides [Pb(salen)], SeCl₄ and reducing agents like N₂H₄·H₂O have been employed for the production of PbSe nanostructures via a solvothermal route at 180 °C for 3 h in propylene glycol. The effect of preparation factors such as temperature, reaction time, and surfactant on the morphology of PbSe nanostructures was investigated. The experimental results indicated that PbSe synthesized at 150 and 210 °C was composed of agglomerated particles. On the other hand, the use of KBH₄ as reducing agent led to produce PbSe with higher particle size and agglomeration. The as-prepared PbSe nanostructures were characterized by XRD, SEM, TEM, EDS, and FT-IR.     

超声电化学制备PbSe纳米枝晶

近年来，纳米晶态半导体粒子因其具有大的表面体积比、高的活性、特殊的电学性质和独特的光学性质引起了科学界的广泛关注犤１，２犦。基于半导体纳米粒子的量子尺寸效应和表面效应，半导体纳米粒子在发光材料犤３犦、非线性光学材料犤４犦、光敏传感器材料犤５犦、光催化材料犤６犦等方面具有广阔的应用前景。如何实现对半导体纳米粒子的尺寸大小、粒度分布以及形状和表面修饰的控制，寻找更简便的合成方法以及改善制备环境等是半导体纳米粒子研究的关键。超声电化学是结合了电化学和超声辐照而建立起来的一种新方法，它显示了两者的优点犤…     

Air-stable PbSe/PbS and PbSe/PbSexS1-x core-shell nanocrystal quantum dots and their applications

The optical properties and functionality of air-stable PbSe/PbS core-shell and PbSe/PbSexS1-x core-alloyed shell nanocrystal quantum dots (NQDs) are presented. These NQDs showed chemical robustness over months and years and band-gap tunability in the near infrared spectral regime, with a reliance on the NQD size and composition. Furthermore, these NQDs exhibit high emission quantum efficiencies of up to 65% and an exciton emission band that is narrower than that of the corresponding PbSe NQDs. In addition, the emission bands showed a peculiar energy shift with respect to the relevant absorption band, changing from a Stokes shift to an anti-Stokes shift, with an increase of the NQD diameter. The described core-shell structures and the corresponding PbSe core NQDs were used as passive Q-switches in eye-safe lasers of Er:glass, where they act as saturable absorbers. The absorber saturation investigations revealed a relatively large ground-state cross-section of absorption (sigma gs = 10(-16) - 10(-15) cm2) and a behavior of a "fast" absorber with an effective lifetime of tau eff approximately 4.0 ps is proposed. This lifetime is associated with the formation of multiple excitons at the measured pumping power. The product of sigma gs and tau eff enables sufficient Q-switching performance and tunability in the near infrared spectral regime. The amplified spontaneous emission properties of PbSe NQDs were examined under continuous illumination by a diode laser at room temperature, suitable for standard device conditions. The results revealed a relatively large gain parameter (g = 2.63 - 6.67 cm-1). The conductivity properties of PbSe NQD self-assembled solids, annealed at 200 degrees C, showed an Ohmic behavior at the measured voltages (up to 30 V), which is governed by a variable-range-hopping charge transport mechanism.     

PbTe colloidal nanocrystals: synthesis, characterization, and multiple exciton generation

We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.     

Synthesis, characterization and optical band gap of NiO nanoparticles derived from anthranilic acid precursors via a thermal decomposition route

This study focuses on the preparation and characterization of single phase NiO nano particles. Four nickel anthranilic acid complexes were synthesized by the semi-solid phase reaction method as precursors for the preparation of NiO nanoparticles via a solid-state decomposition procedure at 700 °C. Thermogravimetric analysis (TGA) was applied to determine the thermal behavior of the precursors and the temperature at which the precursors decompose leaving the oxide. The crystalline structures of the products were investigated by X-ray diffraction (XRD), the morphology of particles by SEM and TEM. The particles size was determined by STM, and the average particle size was found to be 8 nm. Electronic spectra were used to clarify qualitatively the change in absorption band positions on changing the particle size of NiO. The optical band gap of the NiO nanoparticles was calculated and indicated a direct transition. The values of the optical band gap of NiO nanoparticles increase as the particle size decreases.     

Electrochemical Formation of Amorphous Selenium Films Doped by Lead Selenide Nanoparticles

The formation of amorphous Se films doped by PbSe nanoparticles during the cathodic co-deposition of Se and Pb is studied. Doping Se with PbSe makes the charge transfer more efficient both in the film bulk and at the heterojunction with electrolyte, thus making it possible to deposit Se(PbSe) films a few micrometers thick. Co-deposition of Se and Pb results from electrodeposition of adsorbed Pb atoms on surface atoms of Se at potentials more positive than the equilibrium potential of the Pb reduction (underpotential deposition). For the Se(PbSe) electrodes, spectral sensitization of photocurrent is observed up to 900 nm. As opposed to Se, which is characterized by absorption at < 600 nm, the edge of optical absorption of Se(PbSe) is displaced towards the long-wave region of the spectrum. The underpotential deposition on the Se(PbSe) surface is possible in dark, permitting their additional modification by PbSe monolayers.     

The hidden role of acetate in the PbSe nanocrystal synthesis

Monodisperse spherical, star-shaped, and octahedral PbSe nanocrystals were synthesized via a hot injection method. We show that the shape and size of the colloidal PbSe nanocrystals are determined by the concentration of acetate and that only acetate-free reaction mixtures result in spherical nanocrystals. The presence of acetate leads to efficient oriented attachment of smaller PbSe nanoparticles along the 100 crystal axis. Comparing different synthesis procedures from the recent literature with our observations, we propose that the acetate, naturally present in insufficiently dried reaction mixtures, is responsible for many of the PbSe crystal shapes reported in the literature. In addition we show that it is possible to synthesize these star-shaped nanocrystals so monodisperse that they form ordered monolayers with crystal alignment.     

Optical and Magnetic Properties of Conjugate Structures of PbSe Quantum Dots and γ‐Fe2O3 Nanoparticles

An investigation of the optical and magnetic properties of a unique hydrogen‐linked conjugate nanostructure, comprised of superparamagnetic γ‐Fe₂O₃ nanoparticles (NPs) and near‐infrared PbSe nanocrystal quantum dot (NQD) chromophores, is reported. The results show retention of the NQDs’ emission quantum efficiency and radiative lifetime, and only a small red shift of its band energy, upon conjugation to the dielectric surroundings of γ‐Fe₂O₃ NPs. The study also shows the sustainability of the superparamagnetism of the NPs after conjugation, with only a slight decrease of the ferromagnetic–superparamagnetic transition temperature with respect to that of the individual NPs. Thus, the conjugate nanostructure can be considered as a useful medical platform when PbSe NQDs act as fluorescent tags, while the γ‐Fe₂O₃ NPs are used as a vehicle driven by an external magnetic field for targeted delivery of tags or drugs.     

介电限域效应对PbSe量子点禁带宽度计算的影响研究

Considering the dielectric confinement effect on excitonics of PbSe quantum dots (QDs), a correction factor in the wave function was introduced to propose a new band gap calculation model for QDs. The modified model showed great consistency with the experimental data, especially in small size range. According to the variation of confined barrier, the band gap calculation model of PbSe QDs was analyzed in different solvents. The calculating results showed that the modified model was almost solvent-independent, which was consistent with our experimental results and related reports.     

Aspect ratio dependent air stability of PbSe nanorods and photovoltaic applications

Development of unique strategies to overcome Shockley–Queisser (SQ) limit in solar cells has gained a great deal of interest. Multiple exciton generation (MEG) process has been considered as one of the best approaches to the SQ limitation. In this respect, PbSe quantum dots (QDs) and nanorods (NRs) have been regarded as promising solar energy harvesting materials owing to their noticeable MEG yields. Although air stability has been regarded as one of the main disadvantage of PbSe QDs, no study has pointed out to the air sensitivity of PbSe NRs yet. Here, we reveal the effect of aspect ratio on air sensitivity and optical properties of PbSe NRs and discover that NRs with higher aspect ratios are more air stable, attributed to the reduced density of NR ends with air sensitive {100} facets. Furthermore, a band offset was created by utilization of tetrabutylammonium iodide and 1,2-ethanedithiol ligands in cell designs. We found that solar cells based on pristine PbSe NRs are limited by low open circuit voltages due to leakage current pathways. On the other hand, modified cells comprising light absorbing layers prepared by blending NRs and QDs and hole transporting QD layer exhibit a 10-fold improvement in solar cell efficiency.     

Aqueous-Phase Synthesis of Size-Tunable PbSe Nanocubes at Room Temperature for Optical Property Characterization

A simple aqueous-phase synthesis of PbSe nanocubes with tunable sizes has been developed by first preparing a Na₂SeSO₃ stock solution through dissolution of selenium powder in a solution of Na₂SO₃ at 90–100 °C for 30 min, and adding part of this solution to a mixture of lead acetate and acetic acid at room temperature with stirring for only 5–8 min to complete the nanocrystal growth. Adjusting the volume of acetic acid and Na₂SeSO₃ solution added enabled the size of the nanocrystals to be tuned, with average edge lengths of 13 to 121 nm attained. Changes in solution color revealed very different crystal growth rates for the 13 and 121 nm nanocubes. The PbSe cubes exhibit size-dependent absorption bands in the ultraviolet and visible-light region; the band positions show progressive redshifts with increasing particle size. Slight photocatalytic activity upon 532 nm laser irradiation of the nanocubes suggests the presence of higher energy levels in the band structure of PbSe. The synthetic conditions can be easily scaled up to obtain a large quantity of PbSe nanocubes for applications.     

Preparation and photoelectrochemical performance of PbSe/BaTiO3/TiO2 composite film

By dipping-lifting in sol–gel solution and reducing process, the TiO₂ composite film on the glass plate was first prepared. Then, the PbSe/BaTiO₃/TiO₂ composite film was fabricated by interface reaction with BaTiO₃ and PbSe on the surface of TiO₂ composite film. The characterization results show that the uniform porous TiO₂ film is made up of the anatase crystal, and the PbSe/BaTiO₃/TiO₂ composite film is constructed by doping or depositing BaTiO₃ and PbSe nanoparticles on the surface of TiO₂ film. The photoelectrochemical measurement results indicate that the PbSe/BaTiO₃/TiO₂ composite film has an interesting photoelectrochemical conversion property.     

Photoelectrochemical processes on TiO2 electrodes sensitized by lead selenide nanoparticles

The effect of spectral sensitization of photoelectrochemical processes on the surfaces of mesoporous TiO₂ modified by electrochemically deposited PbSe nanoparticles has been observed.     

Architecture of linear arrays of fluorinated co-oligomeric nanocomposite-encapsulated gold nanoparticles: a new approach to the development of gold nanoparticles possessing an extremely red-shifted absorption characteristic

Fluoroalkyl end-capped co-oligomeric nanoparticles, which were prepared by the reaction of fluoroalkanoyl peroxide with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 1-hydroxy-5-adamantylacrylate (Ad-HAc), were applied to the preparation of novel fluorinated co-oligomeric nanocomposite-encapsulated gold nanoparticles. These fluorinated gold nanocomposites were easily prepared by the reductions of gold ions with poly(methylhydrosiloxane) (PMHS) in the presence of the corresponding fluorinated nanoparticles and tri -n-octylamine (TOA) in 1,2-dichloroethane (DE) at room temperature. These fluorinated gold nanoparticles were isolated as wine-red powders and were found to exhibit good dispersibility in a variety of traditional organic solvents such as DE, methanol, and t-butyl alcohol to afford transparent wine-red solutions. The morphology and stability of these fluorinated co-oligomeic nanocomposite-encapsulated gold nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering measurements (DLS), and UV-vis spectroscopy. DLS measurements and UV-vis spectroscopy showed that these particles are nanometer-size-controlled very fine nanoparticles (185-218 nm) that exhibit a plasmon absorption band at around 530 nm. TEM images also showed that gold nanoparticles are tightly encapsulated into fluorinated co-oligomeric nanoparticle cores. Interestingly, these fluorinated co-oligomeric nanocomposites-encapsulated gold nanoparticles were found to afford linear arrays of these fluorinated nanoparticles with increases in the feed amounts of TOA. More interestingly, these fluorinated gold nanoparticles were able to afford the extremely red-shifted plasmon absorption band at around 960 nm.     

Utilizing the lability of lead selenide to produce heterostructured nanocrystals with bright, stable infrared emission

Infrared-emitting nanocrystal quantum dots (NQDs) have enormous potential as an enabling technology for applications ranging from tunable infrared lasers to biological labels. Notably, lead chalcogenide NQDs, especially PbSe NQDs, provide efficient emission over a large spectral range in the infrared, but their application has been limited by instability in emission quantum yield and peak position on exposure to ambient conditions. Conventional methods for improving NQD stability by applying a shell of a more stable, wider band gap semiconductor material are frustrated by the tendency of lead chalcogenide NQDs toward Ostwald ripening at even moderate reaction temperatures. Here, we describe a partial cation-exchange method in which we take advantage of this lability to controllably synthesize PbSe/CdSe core/shell NQDs. Critically, these NQDs are stable against fading and spectral shifting. Further, these NQDs can undergo additional shell growth to produce PbSe/CdSe/ZnS core/shell/shell NQDs that represent initial steps toward bright, biocompatible near-infrared optical labels.     

ChemInform Abstract: Revisit of Pressure‐Induced Phase Transition in PbSe: Crystal Structure,and Thermoelastic and Electrical Properties.

The pressure‐induced phase transition in PbSe is characterized by in situ high‐pressure/high‐temperature synchrotron XRD, electrical resistivity measurements, and DFT band structure calculations.     

On the Origin of the Large Stokes-Shift of the Emission of CdS Nanoparticles Embedded in a Phosphate Glass Matrix

XRD and TEM characterisation evidenced the formation of well-dispersed CdS nanoparticles inside a phosphate glass matrix. Optical absorption and time-resolved photoluminescence study were carried out on the prepared glass samples. Optical absorption revealed the fast character of the growth of CdS nanoparticles in this medium. Photoluminescence spectra showed only one large band with a maximum at almost 740 nm, which was associated to transitions between energy levels within the bandgap of the CdS nanoparticles. From the steady state and time-resolved measurements, it was suggested that the emission comes mainly from sulfur vacancies inside the nanocrystals and on its surface, which act as deep traps for the photogenerated electrons. The creation of such vacancies was attributed to the loss of sulfur during the glass preparation as evidenced from a chemical analysis using energy dispersive X-ray spectrometry. These traps may be also induced by the fast growth of CdS nanocrystals in this matrix or laser exposure during PL measurements. These CdS-doped glasses with an intense absorption in the UV–Vis region and a large emission band with long lifetime and a large Stokes-shift are adequate for luminescent solar concentrators, photocatalytic applications and solid-state lasers.