Inorganic Colloidal Nanocrystals Research Articles

Recent Progress in Synthesis of Nanostructures through Ion Exchange Route and their Applications

AbstractThe inorganic colloidal nanocrystals (ICNCs) have received a great deal of interest because of their tunable electronic and optical properties with coarse and finely controlled compositions, morphologies and thus, hybrid nanostructures have a wide range of applications in supercapacitor, luminescent solar concentrators (LSCs) and photothermal therapy (PPT). The ion exchange (IEx) process includes great diffusion rates of parent nanoparticles (NPs) ions from their crystal structure and their complete dissociation in specific solvents. The bond dissociation energies (BDEs) of different transition metal atoms with specific p‐block elements have been reviewed to analyze their effect on the IEx process. The alloy and doped and inorganic perovskite ICNCs have been synthesized via different IEx methodologies, showing varied photoluminescence quantum yields (PLQYs), nano‐dimensional morphology, composition, reaction time and temperature, and their performance for a specific application have been tabulated. The perovskite nanocrystals (NCs) are responsible for fast IEx dynamics that drop to homogenization in their composition, leading to NCs emitting in a narrow spectral region acting as an intermediate between those of the model NPs. The nanoscale metal‐organic particles (NMOPs) have opened plausible opportunities for their application in nanomedicine having highly enriched functionalities, well‐designed shapes/sizes, adjustable compositions, and intrinsic biodegradability. The potential to develop well‐designed heterostructures and for the growth of large‐area monocrystalline CsPbBr3 thin films provide a strong base for fundamental investigations of the intrinsic properties of perovskite‐based devices. The Cs3Sb2I9 is an active emitter layer that directs us toward low‐dimensional lead‐free A3B2X9 perovskite optoelectronic materials.

Constraints in post-synthesis ligand exchange for hybrid organic (MEH-PPV)–inorganic (CdSe) nanocomposites

For an optimum charge/energy transfer performance of hybrid organic–inorganic colloidal nanocrystals for applications such as photonic devices and solar cells, the determining factors are the distance between the nanocrystal and polymer which greatly depends upon nanocrystal size/nanocrystal ligands. Short chain ligands are preferred to ensure a close contact between the donor and acceptor as a result of the tunnelling probability of the charges and the insulating nature of long alkyl chain molecules. Short distances increase the probability for tunnelling to occur as compared to long distances induced by long alkyl chains of bulky ligands which inhibit tunnelling altogether. The ligands on the as-synthesized nanocrystals can be exchanged for various other ligands to achieve desirable charge/energy transfer properties depending on the bond strength of the ligand on the nanocrystal compared to the replacement ligand. In this work, the constraints involved in post-synthesis ligand exchange process have been evaluated, and these factors have been tuned via wet chemistry to tailor the hybrid material properties via appropriate selection of the nanocrystal capping ligands. It has been found that both oleic acid and oleylamine (OLA)-capped cadmium selenide (CdSe) quantum dots (QDs) as compared with trioctylphosphine oxide (TOPO)-passivated CdSe QDs are of high quality, and they provide better steric stability against coagulation, homogeneity, and photostability to their respective polymer:CdSe nanocomposites. CdSe QDs particularly with OLA capping have relatively smaller surface energies, and thus, lesser quenching capabilities show dominance of photoinduced Forster energy transfer between donors (polymer) and acceptors (CdSe nanocrystals) as compared to charge transfer mechanism as observed in polymer:CdSe (TOPO) composites. It is conjectured that size quantization effects, stereochemical compatibility of ligands (TOPO, oleic acid, and oleyl amine), and polymer MEH-PPV stability greatly influence the photophysics and photochemistry of hybrid polymer–semiconductor nanocomposites.

Innovative nanocrystal-based technologies for ceramic devices with novel electronic functions

There has been a great progress in the synthesis of a variety of inorganic colloidal nanocrystals (NCs) with highly controlled size and shape in the last decade. This achievement has promoted comprehensive researches on the fabrication and engineering of NC devices with novel structure and function with the aim of utilizing them in a wide area of applications, including electronics and optoelectronics, by using various NC assembling and patterning methods. However, colloidal NCs having been extensively investigated so far are mostly metals, semiconductors and magnetic materials, and only limited investigations on oxide NCs from a point of view of NC ceramic engineering have been done. Here, innovative nanocrystal-based technologies necessary for the fabrication of NC ceramic devices with novel and gigantic electronic functions, limiting the materials to perovskite oxides, and a new perspective on the future ceramic technology are discussed.

Inorganic Colloidal Solution-Based Approach to Nanocrystal Synthesis of (Bi,Sb)2Te3

There is an interest in higher-ZT thermoelectric materials for high-watt-density cooling of electronics. Reducing thermal conductivity through increased phonon scattering in nanomaterials has been shown to be effective and is being investigated by many groups. Solution-based synthesis is a method for making thermoelectric nanomaterials that can provide particle sizes <20 nm and can be scaled to production quantities of materials. We are exploring an approach that proceeds through formation of an “ink” that contains inorganic colloidal nanocrystals of thermoelectric materials. This approach has the advantage that, by adjustments within the basic synthesis process, the size, shape, and composition of the nanocrystals can be tightly controlled to study changes in the transport properties. Currently we are making materials from inks that contain Bi2Te3 nanocrystals with Sb2Te3 ligands, suspended in a solvent. Powders formed by curing the inks are made into solid pellets by hot pressing, and the pellets are used for characterization and transport property measurements. The best result from our thermoelectric property measurements is ZT = 0.9 with power factor of 27 μW/cm K2, which to our knowledge is the best value for solution-based synthesis.

Sodium Doping Controlled Synthesis of Monodisperse Lanthanide Oxysulfide Ultrathin Nanoplates Guided by Density Functional Calculations

Doping of nanocrystals is an intriguing field, since the intentional introduction of impurities has long been regarded as a major way of tailoring the properties of materials. Furthermore, it was recently found that the use of dopants in the synthesis of inorganic colloidal nanocrystals can not only introduce novel properties but also influence shape and size evolution during nanocrystal nucleation and growth. For example, Liu and co-workers showed that NaYF4-based nanocrystals can be precisely tuned in size, phase, and upconversion emission through Gd doping. Wang and co-workers reported that lanthanide doping of alkaline earth metal fluoride nanocrystals can lead to a significant increase in monodispersity. On the other hand, the special 4f electron configurations of lanthanides endow their compounds with promising functionalities, such as luminescence, catalytic activity, and permanent magnetism. This has therefore stimulated recent efforts to synthesize colloidal lanthanide-based nanocrystals (Ln-based NCs) with tunable morphologies and unique material properties. For example, both the small size and excellent luminescence properties make Ln-based NCs a potential new type of fluorescent probes. Specifically, lanthanide oxysulfides (Ln2O2S; Ln=La, Gd, Y) can serve as one of the most effective hosts for fluorescence applications, and research on Ln2O2S NCs is therefore highly intriguing. [4] However, the synthesis of monodisperse Ln2O2S NCs remains a challenge, since the theory of hard and soft acids and bases (HSAB) predicts a lack of affinity between the hard Lewis acid Ln and the soft Lewis base S . Previously, Gao and coworkers presented pioneering work in the synthesis of monodisperse lanthanide oxysulfide nanocrystals, yet due to the difficulty in preparing the corresponding single-source precursors, this method was limited to only a few lanthanides (i.e., Sm, Eu, Gd). On the basis of both experimental characterization and DFT calculations, we now demonstrate that introduction of monovalent Na ions as dopants in trivalent Ln host lattices can significantly facilitate the formation of Ln2O2S NCs in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE) mixed solvent by creating oxygen vacancies in the host lattice during sulfurization reactions. In a typical synthesis, monodisperse and single-crystalline Na-doped La2O2S nanoplates were formed with a diameter of (22.3 2.0) nm (Figure 1a and b). High-resolution transmission electron microscopy (HRTEM) revealed that the morphology of the as-synthesized nanoplates was mainly hexagons with six {100} facets as their side planes (Figure 1b). When the dispersion of nanoplates in cyclohexane was highly

Emerging methods for fabricating functional structures by patterning and assembling engineered nanocrystals

Inorganic nanocrystals and nanoparticles have aroused increasing attention in the last years due to their original optoelectronic, thermodynamic, mechanical and catalytic properties, which are extremely attractive for fundamental understanding as well as for their huge potential in applications. The ability to strongly exploit the original potential of such nano-objects and access their properties relies on the ability to bridge the gap between the nanoscopic and mesoscopic scale. Indeed, to integrate nanoparticles in structures, materials and finally devices, their incorporation in processable systems, and their organization in morphologically controlled assembly and/or ordered arrays is crucial. The fabrication of 2/3 D patterned micro- and nanostructure is a promising strategy for integrating the nanoparticles in macroscopic entities in order to properly exploit their unprecedented functionality for biomedical, electronic, catalytic materials and devices. In this paper, different and complementary strategies able to engineer inorganic colloidal nanocrystals due to their organization in original functional materials and structures will be described.

Synthesis and perspectives of complex crystalline nano‐structures

AbstractResearch on inorganic colloidal nanocrystals has moved from the synthesis of simple structures, such as spherical nanoparticles, to more elaborate particles with shapes such as rods, stars, discs, and branched nanocrystals, and recently to nanoparticles that are composed out of sections of different materials. Nanocrystal heterostructures represent a convenient approach to the development of nanoscale building blocks, as they merge sections with different functionality in the same particle, without the need of inorganic cross‐linkers. The present article gives an overview of synthesis strategies to complex nanocrystals and will highlight their structural properties, as well as discuss some envisaged applications. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)