Producing nanocrystals

Confocal micro-luminescent has been developed to analyze the optical changes produced by exciting the sample with an argon laser. The emission of the Er I11/2 -> and I13/2 -> I15/2 transitions are reported and shown structural differences after the femtosecond irradiation. The lifetimes of the levels involved in these transitions are measured inside and outside the damaged area. These measurements are compared with the bulk glass ceramic sample to estimate the optimal condition to produce nanocrystals in a localized area. 

Nanocrystals of BaTiO, are obtained by the thermal decomposition of MOeVD reagents (alkoxides such as BaTifOiCCjHis) [OCH(CH,),],) in diphenyl ether containing oleic acid, followed by the oxidation of the product with HjOi. Thermal decomposition of uranyl acetylacetonate in a mixture solution of oleic acid, oieylamine, and octadecene at 423 K gives uranium oxkle nanocrystals. Treatment of metal acetylacetonates under solvothermal conditions produces nanocrystals of metal oxides such as GajOj, ZnO and cubic lujOs. Nearly monodisperse InjOj nanocrystals have been obtained starting with indium acetate, oieylamine and oleic acid. TiOj nanocrystals can be prepared... 

Some imperfections arise from dislocations at the interface of microcrystalline domains along the microfibril length. These imperfections were exploited to advantage by treatment of the sample with acid to produce nanocrystals called whiskers, having the same diameter as the starting mierofibrils but of much shorter lengfli. 

Intelligent processing techniques described in the next sections are currently used to produce nanocrystals, also called rod-like nanowhiskers, of polysaccharides that can act as reinforcing fillers in bionanocomposites as well as carriers for therapeutic compounds. The chemical nature of these nanocrystals, along with their rigid, uniform, hierarchical structure, is the reason for their excellent reinforcing properties. 

One of the important factors that determine the quality of a sjmthetic procedure is the monodispersity of the nanocrystals obtained. It is desirable to have nanoparticles of nearly the same size, in order to be able to relate the size and the property under study. Hence, narrower the size distribution, more attractive is the S3mthetic procedure. The best S3mthetic schemes today produce nanocrystals with diameter distribution of aroimd 5%. The other important issues are the choice of the capping agent and control over the shape. 

Biswas and Rao [250] have prepared metallic Re03 nanocrystals of different sizes by the solvothermal decomposition of the rhenium(VII)oxide-dioxane complex, (Re207-(C4H802)a ), in toluene (see Fig.2.10). The diameter of the nanocrystals could be varied in the range of 8.5-32.5 nm by varying the decomposition conditions. The reaction of metal acetylacet-onates under solvothermal conditions produces nanocrystals of metal oxides... 

Ingert, D. and Pileni, M.P. (2001) Limitations in producing nanocrystals using reverse micelles as nanoreactors. Advanced Functional Materials, 11,136-9. 

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