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Síntese de nanopartículas semicondutoras de seleneto de zinco (ZnSe) aquoso e análise dos subprodutos decorrentes dessa síntese
(Universidade Federal de São Carlos, 2012-07-20) Pinto, Alexandre Henrique; Camargo, Emerson Rodrigues de; https://lattes.cnpq.br/7720754304065239; https://lattes.cnpq.br/1822508562692028
Zinc selenide (ZnSe) is a semiconductor material, which band gap is about 2.7 eV. It has many applications as blue light emission diode, data storage devices, laser diodes and waveguides optical fibers. Despite these several applications, ZnSe, generally, is synthesized in organic solvents, such as: trioctylphosphine oxide (TOPO), hexadecylamine (HDA) or octadecene (ODE). These synthetic methods are carried out at high temperatures, about 250oC. Moreover, being synthesized in organic media makes these nanoparticles unable to be dispersed in aqueous systems, and consequently, they are unable to be applied in biological media, unless some post preparative procedure is applied. In view those shortcomings, in this work, ZnSe was synthesized in aqueous media, having ZnCl2 as zinc source, NaHSe, as selenium source, which was synthesized from reduction of elemental selenium by sodium borohydride (NaBH4), and L-cisteine as capping agent. Initially, a 22 factorial design was applied. Temperature and pH were the factors studied in this factorial design, aiming to determine the influence of these factors on crystallographic coherence dominium calculated through Scherrer equation. Despite synthesis in aqueous media applies lower temperatures (90 oC), it has some disadvantages, for instance, the generation of some byproducts. Among these byproducts are: trigonal or amorphous elemental selenium and L-cistine, however, sometimes, these compounds can not be tracked through x-ray diffraction (XRD), since they are either amorphous or are below the detection limit of this technique. In this sense, Raman spectroscopy plays an important role in this work, since it is able to track these byproducts in a range of some months. Finally, a simple decantation process was carried out in order to separate these byproducts in different aliquots.
Estudo das propriedades fotoluminescentes do ZnS e ZnS: Eu obtidos pelo método solvotérmico assistido por microondas
(Universidade Federal de São Carlos, 2012-07-20) Ferrer, Mateus Meneghetti; Longo, Elson; https://lattes.cnpq.br/9848311210578810; https://lattes.cnpq.br/6355560471517685
This paper is about the synthesis, characterization and studies of nanostructures of ZnS and ZnS:Eu3+ prepared by microwave-assisted solvothermal method. The influence of the synthesis time in the microwave on the samples of ZnS was investigated in order to have the most proper sample for doping. Therefore, different concentrations of Europium (dopante) were added to the chosen sample. The characterizations of the samples was made by X-ray diffraction, Ultraviolet visible spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. The method used to the synthesis of ZnS is very efficient because it synthesizes the nanocrystals in shor time and in a low temperature. The study of the X-ray diffraction, Ultraviolet-visible spectroscopy, photoluminescence and transmission electron microscopy showed structural changes in the samples due to the low processing time and the percentage of europium added to the system. The results indicated an increase of the organization with the increase of the time of synthesis. and a disorganization when the europium is added. These structural differences were responsible for the modifications of the photoluminescence profile of the materials due to the different intermediate states. More specifically, in the synthesis of pure ZnS, the organization of the structure with the increase of the time of synthesis was responsible for a photoluminescence band with a higher contribution of the blue region. However, the disorganization due to the addition of Eu3+ resulted in a photoluminescence band with a higher contribution in the orange region.