Europium doped silver tungstates α-Ag2-3xEuxWO4 (x = 0, 0.0025, 0.005, 0.0075 and 0.01 mol) were synthesized by the coprecipitation method at 90 °C for 30 minutes. These crystals were structurally characterized by means of X-ray diffraction (XRD), Rietveld refinement, and micro-Raman (MR) and Fourier transformed infrared (FT-IR) spectroscopies. Field emission scanning electron microscopy (FE-SEM) images were employed to observe the shape of the crystals. The optical properties were investigated by ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) measurements. The XRD pattern indicated structural organization at a long range for all undoped and Eu-doped samples, while MR and FT-IR revealed that the presence of the Eu(3+) ions favors the structural organization at a short range. The Rietveld refinement showed that all the crystals are monophasic with an orthorhombic structure and the Pn2[combining macron]n space group. The refined lattice parameters and atomic positions were employed to model the WO6 and AgOn (n = 2, 4, 6 and 7) polyhedra in the unit cell. FE-SEM analysis revealed nanorod-like microcrystals with growth of metallic silver on the surface. Further, the UV-vis absorption spectra indicated the existence of intermediary energy levels within the band gap. PL spectra showed a broad band related to the [WO6] group and characteristic narrow peaks due to the f-f transitions of Eu(3+) as a result of efficient energy transfer from the matrix. Also, the emission line shape transitions from (5)D0 to (7)FJ (J = 0-4) levels of the Eu(3+) were noticed. Among the samples, the most intense photoluminescence results were observed for the α-Ag2-3xEuxWO4 (x = 0.0075) sample. Lifetime decays support that the Eu(3+) ions occupy at least two crystallographic sites. CIE coordinates confirmed the colors of the emission spectra which classify this material as a potential phosphor in the visible range.

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Over the last two decades, oxide nanostructures have been continuously evaluated and used in many technological applications. The advancement of the controlled synthesis approach to design desired morphology is a fundamental key to the discipline of material science and nanotechnology. These nanostructures can be prepared via different physical and chemical methods; however, a green and ecofriendly synthesis approach is a promising way to produce these nanostructures with desired properties with less risk of hazardous chemicals. In this regard, ZnO and TiO2 nanostructures are prominent candidates for various applications. Moreover, they are more efficient, non-toxic, and cost-effective. This review mainly focuses on the recent state-of-the-art advancements in the green synthesis approach for ZnO and TiO2 nanostructures and their applications. The first section summarizes the green synthesis approach to synthesize ZnO and TiO2 nanostructures via different routes such as solvothermal, hydrothermal, co-precipitation, and sol-gel using biological systems that are based on the principles of green chemistry. The second section demonstrates the application of ZnO and TiO2 nanostructures. The review also discusses the problems and future perspectives of green synthesis methods and the related issues posed and overlooked by the scientific community on the green approach to nanostructure oxides.

A B S T R A C TRegular sized nanostructures of indium oxide (In 2 O 3 ) were homogeneously grown using a facile route, i.e. a microwave-hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of Er 3+ doping plays an important role in controlling the formation of cubic (bcc) and rhombohedral (rh) In 2 O 3 phases. The samples presented broad photoluminescent emission bands in the green-orange region, which were attributed to the recombination of electrons at oxygen vacancies. The photocatalytic activities of pure bcc-In 2 O 3 and a bcc-rh-In 2 O 3 mixture towards the UVA degradation of methylene blue (MB) were also evaluated. The results showed that Er +3 doped In 2 O 3 exhibited the highest photocatalytic activity with a photonic efficiency three times higher than the pure oxide. The improved performance was attributed to the higher surface area, the greater concentration of electron traps due the presence of the dopant and the possible formation of heterojunctions between the cubic and rhombohedral phases.

Agricultural use and management systems in tropical soils of the Brazilian Cerrado may directly influence its chemical properties, in the conventional cultivation systems with pastures or grains, as well as in areas with a crop-livestock-forest integration system. Thus, the objective was to evaluate the chemical attributes of the soil under different use and management systems. The research was carried out at Boa Vereda Farm, in the state of Goiás, Brazil. The experimental design was completely randomized with a 5 x 3 factorial arrangement divided into five production systems: (1) among the rows of Eucalyptus (CLFI), (2) within the rows of Eucalyptus (CLFI), (3) in conventional agricultural monoculture, (4) pasture, and (5) -natural Cerrado (control treatment). Samples were collected in three soil depths (0-0.5; 0.5-0.1 and 0.1-0.2 m), with four replicates each. Among the chemical properties of the soil studied, the organic matter, calcium, magnesium and potassium contents, base saturation, and cation exchange capacity, are higher in the soil with natural Cerrado. The area of agricultural monoculture showed the highest levels of phosphorus and copper, but has the lower levels of organic matter in the soil. The chemical properties of the soil were similar in the CLFI system, regardless of the evaluation point (within or among rows). The chemical properties of the soil evaluated were similar between the pasture cultivated in CLFI and the conventional system. Therefore, the land use and management system do not directly influence the chemical properties of the soils evaluated.

Recebido em 12/6/03; aceito em 27/5/04; publicado na web em 27/8/04 PHOTOLUMINESCENCE AND CO 2 ABSORPTION ON LANTHANUM DOPED CaTiO 3 NANOPARTICLES. Ca 1-x La x TiO 3 powders were prepared by the polymeric precursor method. X-ray diffraction (XRD), FT-Raman spectroscopy, transmission electron microscopy (TEM), and N 2 and CO 2 adsorption were used for the microstructural and surface characterization of the powders. Room temperature photoluminescence (PL) was observed in Ca 1-x La x TiO 3 amorphous particles. The PL intensity of these powders was found to be dependent on the lanthanum molar concentration.Keywords: CaTiO 3 ; lanthanum; photoluminescence; CO 2 adsorption. INTRODUÇÃOA estrutura da matéria condensada é ditada pelo arranjo eletrônico e este, por sua vez, dita as propriedades do sistema nas suas interações com campos externos, elétricos, magnéticos ou com a própria luz. O conhecimento destas propriedades tem permitido a construção de dispositivos eletrônicos e optoeletrônicos variados, de diodos e transistores a lasers, de diodos emissores de luz a sensores de gases.O desenvolvimento de materiais semicondutores com propriedades ópticas ativas, tais como fotoluminescência (FL), eletroluminescência (EL) e propriedades ópticas não-lineares, pode levar ao desenvolvimento de novos dispositivos que apresentem melhor desempenho. Semicondutores amorfos podem substituir semicondutores monocristalinos em uma série de aplicações, em particular quando o fator custo é importante ou nos casos em que a dimensão do dispositivo é fator limitante. Semicondutores de banda larga (3,0-4,0 eV) do tipo ATiO 3 , para A= Ca, Sr, Ba, Pb apresentam forte FL na região do visível, quando este composto está no estado amorfo. Estudos mais detalhados destes materiais, processados quimicamente pelo método dos precursores poliméricos, mostram que existe uma relação íntima entre FL e seu estado amorfo. Nestes casos não se trata de uma simples transição eletrôni-ca, pois o comprimento de onda de emissão depende do comprimento de onda de excitação, sendo esta dependência linear [1][2][3] . Titanato de cálcioO titanato de cálcio CaTiO 3 é um material de estrutura peroviskita do tipo ABO 3 com o cátion B sendo o Ti e o cátion A sendo o Ca. Esta cerâmica não apresenta anisotropia e sua estrutura é cúbica acima da temperatura de 1580 K, tetragonal entre 1380 e 1500 K e ortorrômbica abaixo de 1380 K 4,5 . Porém Coates e McMillan 6 mostraram que a estrutura peroviskita cúbica poderia ser obtida à temperatura ambiente, quando o CaTiO 3 é dopado com impurezas aceptoras.O titanato de cálcio é usado como um elemento de resistor com sensibilidade térmica, devido a seu coeficiente de temperatura negativo, além de ser um material refratário com alta resistência à corrosão com soluções cáusticas 7 .Houve significantes avanços na síntese química de cerâmicas avançadas usando técnicas tais como sol-gel, coprecipitação, síntese hidrotérmica e método dos precursores poliméricos . Estes compostos apresentam importantes propriedades estruturais, elétricas e ó...

Manganese (Mn) is important to increase forage crop yields. However, there is little information regarding the adequate Mn-fertilizer rates for Brachiaria humidicula species. The objective of this research was to evaluate the effect of manganese on growth, nutrition and yield of Brachiaria humidicula. The study was carried out in a green house in a randomized block design with five rates of manganese (0, 15, 30, 60 and 120 mg dm -3 ) and four replicates. Were evaluated plant height, leaf area, relative chlorophyll index, dry matter production, manganese accumulation and content, besides absorption efficiencies and transport and use of manganese (Mn). Brachiaria humidicula showed high tolerance to this nutrient, because the application of only 120 mg dm -3 to the soil was phytotoxic, showing symptoms such as brown spots and leaf tip curling. Manganese applied at a dose of 120 mg dm -3 reduced aerial part biomass yield by 25% and promoted lower efficiency of use of this nutrient by the forage by 49%. However, even with the initial content of manganese in the soil considered sufficient to meet nutritional demands to achieving high yields, the application of 60 mg dm -3 of manganese to the soil is recommended.

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