The synthesis and study of so-called "nanoparticles", particles with diameters in the range of 1-20 nm, has become a major interdisciplinary area of research over the past 10 years. Semiconductor nanoparticles promise to play a major role in several new technologies. The intense interest in this area derives from their unique chemical and electronic properties, which gives rise to their potential use in the fields of nonlinear optics, luminescence, electronics, catalysis, solar energy conversion, and optoelectronics, as well as other areas. The small dimensions of these particles result in different physical properties from those observed in the corresponding macrocrystalline, "bulk", material. As particle sizes become smaller, the ratio of surface atoms to those in the interior increase, leading to the surface properties playing an important role in the properties of the material. Semiconductor nanoparticles also exhibit a change in their electronic properties relative to that of the bulk material; as the size of the solid becomes smaller, the band gap becomes larger. This allows chemists and material scientists the unique opportunity to change the electronic and chemical properties of a material simply by controlling its particle size. Research has already led to the fabrication of a number of devices. This review aims to highlight recent advances in the synthesis of compound semiconductor nanoparticle materials and their potential use in areas such as catalysis and electronic device fabrication.

Energy transfer from semiconductor nanocrystal monolayers to metal surfaces revealed by time-resolved photoluminescence spectroscopy

Efficient carrier multiplication in InP nanoparticles is reported; ultrafast transient absorption measurements at the band edge were used to determine the number of excitons per photoexcited nanoparticle for a range of both excitation fluences and photon energies. At photon energies greater than 2.1Ϯ 0.2 times the band gap, an average of more than 1 exciton per photoexcited nanoparticle was found even in the limit of vanishing fluence. The average number of excitons generated by an absorbed photon was measured to be 1.18Ϯ 0.03 for excitation photons with energies 2.6 times the band gap.

CdSe quantum dots with polymerisable ligands have been incorporated into polystyrene beads, via a suspension polymerisation reaction, as a first step towards the optical encoding of solid supports for application in solid phase organic chemistry.Approaches to synthetic organic chemistry have developed rapidly over recent years with the increased demand for high speed synthesis and screening techniques. Combinatorial techniques, such as 'split and mix' and high-throughput parallel synthesis, are now used routinely. We are concerned in particular with approaches that involve the on-support synthesis and in situ screening of large numbers of diverse molecules prepared using split-and-mix techniques. Whilst there has been much success in synthesising libraries of this type, a major problem with this approach is being able to identify exactly which molecule is attached to a particular bead. To this end, a number of innovative deconvolution approaches have been developed to encode individual beads. These include: chemical encoding with molecular tags; 1 organic fluorophores; 2 fluorescent colloids; 3 Raman fingerprints; 4 and radio frequency transponders. 5 More recently, Nie et al. 6 have utilised fluorescent inorganic semiconductor quantum dots.This last approach is most attractive since quantum dots offer significant advantages over conventional fluorescent dyes since they are brighter, more photostable materials with narrow emission bands that can be excited by any wavelength greater than the energy of their lowest transition. 7 These properties also allow optical barcoding 6 of polymer supports by combining different colour quantum dots with different intensity levels. However, the approach described to generate the quantum dot encoded materials simply involved embedding the quantum dots into the outer layers of 1-2 mm resin beads then sealing with a final silica layer. Whilst encoded materials of this type appear to be ideal for the optical encoding of biomolecules 6 the method of quantum dots immobilisation is non-covalent in nature and thus materials generated in this manner would not be suitable for widespread application in solid phase organic synthesis. We thus elected to establish the feasibility of incorporating quantum dots covalently into the polymer matrices of supports of the type used routinely in the solid phase synthesis of combinatorial libraries.A recent publication by Emrick et al. 8 described an elegant approach to incorporate quantum dots covalently into spin and solution cast polymer films by pre-coating quantum dots with polymerisable ligand 2. We were intrigued to investigate whether such an approach could be extended to incorporate quantum dots into polymer beads utilising well established suspension polymerisation techniques. We believed that if successful, this new procedure would enable the facile production of many of the bead-types that are available commercially for combinatorial chemistry applications but with the added benefit of quantum dot encoding.Quantum dots were synthesised f...

Methods for the preparation of II-VI, III-V, and II-V as well as other compound semiconductor nanoparticles using main group single-molecular precursors have been developed. The work involves the design and synthesis of compounds containing all the elements required within the desired nanoparticulate material. Precursors are tailored to give reproducible, clean decomposition at moderate temperatures, leading to high quality, defect free, mono-dispersed nanoparticles. In this article we cover key aspects of precursor and nanoparticle synthesis. One of the more successful and reproducible series of single-source precursors used, and the one on which we have concentrated our research efforts, is the bis(dialkyldithio-/diseleno-carbamato)cadmium(II)/zinc(II) compounds, M(E(2)CNR(2))(2) (M = Zn or Cd, E = S or Se, and R = alkyl) for the preparation of chalcogenide nanoparticulate materials. Preliminary mechanistic studies suggest that the precursor to nanoparticle deposition route is strongly influenced by the alkyl substituent groups present, and may well determine the phase and quality of the final metal chalcogenide nanoparticles produced. Herein we discuss the synthesis of semiconductor nanoparticles using such single-molecular precursors.

Polystyrene microbeads doped with highly luminescent CdS quantum dots (QDs) have been prepared. Polystyrene particles with diameters ranging from 100 nm to 500 mm were prepared by a suspension polymerization method and with different loadings of QDs. The resulting organic-inorganic microspheres have been characterized by FTIR, elemental analysis and SEM. Confocal microscopy and photoluminescence studies proved that the CdS nanoparticles were evenly distributed throughout the polystyrene spheres. The QDcontaining composites have similar optical properties to isolated CdS QDs. The thermal decomposition of the hybrid materials occurred at higher temperature than for the parent organic materials

In this paper, we report on the growth and characterization of quantum dot-quantum well nanostructures with photoluminescence (PL) that is tunable over the visible range. The material exhibits a PL efficiency as high as approximately 60% and is prepared by reacting ZnS nanocrystals in turn with precursors for CdSe and ZnS in an attempt to form a simple "ZnS/CdSe/ZnS quantum-well structure". Through the use of synchrotron radiation-based photoelectron spectroscopy in conjunction with detailed overall compositional analysis and correlation with the size of the final composite nanostructure, the internal structure of the composite nanocrystals is shown to consist of a graded alloy core whose composition gradually changes from ZnS at the very center to CdSe at the onset of a CdSe layer. The outer shell is ZnS with a sharp interface, probably reflecting the relative thermodynamic stabilities of the parent binary phases. These contrasting aspects of the internal structure are discussed in terms of the various reactivities and are shown to be crucial for understanding the optical properties of such complex heterostructured nanomaterials.

During the past few years there has been a significant progress in adapting the properties of non-Cd quantum dots (QDs) for lighting applications. It includes synthesis of novel materials, improvement of quantum efficiency and thermal stability, and most importantly, manufacturability on a scale large enough to meet the needs of the lighting industry. In this paper, we review the characteristics of three most mature non-Cd QD material systems, InP, CuInS2 and doped ZnS/ZnSe, from the perspective of lighting applications. Of these three systems, the InP-based QDs with core/shell structure are now available with quantum efficiency (QE) comparable to the best performing CdSe QDs, and in quantities large enough to meet the lighting needs. The CuInS2 QDs have also emerged as another non-toxic alternative to CdSe QDs but they need significant development to be comparable to InP and CdSe QDs.