Transition metal nanocrystals, synthesis

The synthesis of transition metal nanocrystals can be divided basically into two major groups salt reduction and decomposition method. Examples of these methods are described below. 

In this chapter, we describe the design and important properties of supra-molecularly organized dye molecules in the channels of hexagonal nanocrystals. We focus on zeolite L as a host. The principles, however, hold for other materials as well. As an example, we mention ZSM-12 for which some preliminary results have been reported [55], We have developed different methods for preparing well-defined dye-zeolite materials, working for cationic dyes, neutral dyes, and combinations of them [3, 22, 25, 52], The formula and trivial names of some dyes that so far have been inserted in zeolite L are reported in Section II.C. The properties of natural and commercially available zeolites can be influenced dramatically by impurities formed by transition metals, chloride, aluminiumoxide, and others. This fact is not always sufficiently taken care of. In this chapter, we only report results on chemically pure zeolites, the synthesis of which is described in [53]. 

Biomimetic Synthesis of Nanoparticles Carbonyl Complexes of the Transition Metals Metallic Materials Deposition Metal-organic Precursors Polynuclear Organometallic Cluster Complexes Porous Inorganic Materials Self-assembled Inorganic Architectures Semiconductor Nanocrystal Quantum Dots Sol-Gel Encapsulation of Metal and Semiconductor Nanocrystals. 

N. L. Wu, S. Y. Wang, and I. A. Rusakova. Inhibition of crystallite growth in the sol-gel synthesis of nanocrystalline metal oxides. Science, 285 1375-1377, 1999 A. Vioux. Nonhydrolytic sol-gel routes to oxides. Chem. Mater., 9 2292-2299, 1997 J. Rockenberger, E. C. Scher, and A. P. Alivisatos. A new nonhydrolytic single-precursor approach to surfactant-capped nanocrystals of transition metal oxides. J. Am. Chem. Soc., 121 11595-11596, 1999... 

The other interesting challenge from a synthetic viewpoint is the synthesis of doped QDs, particularly to study their magneto-optical properties. Doping transition metal ions in bulk as well as nanoscale semi-conductors has been an important area of study for the past couple of decades. Recent studies have further shown that for several applications, dopant associated emission from semiconductor nanocrystals may be more advantageous than the usual band-edge emission. Extensive attempts have been made to dope intentional impurities in various semiconductor nanocrystals, including those in ZnSe, ... 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

G., Djerdj, 1., Antonietti, M., and Niederberger, M. (2008) Generalized nonaqueous sol-gel synthesis of different transition-metal niobate nanocrystals and analysis of the growth mechanism. Chem. Asian J., 3 (4), 746-752. 

Chen J, Wu X-J, Yin L, Li B, Hong X, Fan Z, Chen B, Xue C, Zhang H (2015) One-pot synthesis of CdS nanocrystals hybridized with single-layer transition-metal dichalcogenide nanosheets for efficient photocatalytic hydrogen evolution. Angew Chem Int Ed 54 1210-1214... 

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