Growth and luminescence properties of micro- and nanoneedles in sintered CdSe

Sintering CdSe powder under argon flow at temperatures in the range 800-900 degreesC produces the formation of needles on the sample surface. Bundles of parallel needles of a diameter of about 50 nm give rise to a domain-like appearance in the sample. In addition, rods and needles with a wide range of dimensions up to several microns appear distributed in the surface. The influence of ball milling of the starting powder on the formation of the needles is investigated. Cathodoluminescence in the scanning electron microscope has been used to characterize the sintered samples

Study of structure and luminescence of CdSe Nanocrystals obtained by ball milling

The effect of mechanical milling on the structure and luminescent properties of CdSe powder has been investigated by means of cathodoluminescence (CL) in the scanning electron microscope, transmission electron microscopy (TEM) and x-ray diffraction. The starting powders were ball milled for times between 5 and 20h. TEM of the milled samples reveals the presence of nanocrystals with a wide range of sizes including nanocrystals of 10 nm and smaller. The CL spectra of the untreated samples show the characteristic band edge emission centered at 1.8 eV. In the milled samples a band centered at about 2.5 eV is observed which appears to be associated to the presence of nanocrystals. The evolution of defect structure with milling time has been monitored by recording infrared cathodoluminescence spectra. A partial phase transformation from wurtzite to zinc blende structure also has been observed

Photocatalytic activity of electric-arc furnace flue dusts

Two electric-arc furnace flue dusts, a waste generated during the steel production process, were characterized and their photocatalytic activity was assessed. Chemical composition by X-ray fluorescence (XRF) analysis identified that both dusts were principally formed by iron, zinc and chromium oxides. Structural characterization carried out by X-ray diffraction patterns (XRD), and micro-Raman measurements demonstrated that ZnFe_2O_4 (zinc ferrite), FeCr_2O_4 (chromite) and ZnO (zincite) are present in both waste dusts as majority phases. Scanning electron microscopy (SEM) images showed that both dusts are formed by nanoparticles with a globular and octahedral morphology characteristic of the type of flue dusts formation and the obtained phases. Cathodoluminescence (CL) spectra show the characteristics bands of spinel structure (ZnFe_2O_4) and Fe^(3+) emission. X-ray photoelectron spectroscopy (XPS) measurements indicate that Fe ions could be present in 2+ and 3+ oxidation state in the spinel structure, while zinc and chromium ions are in 2+ and 3+, respectively. In addition, the photocatalytic experiments demonstrated that the analyzed samples could be useful as photocatalyzed showing a degradation percentage above 75 %

Characterization, luminescence and optical resonant modes of Eu-Li Co-Doped ZnO Nano- and microstructures

ZnO nano- and microstructures co-doped with Eu and Li with different nominal concentrations of Li were grown using a solid vapor method. Different morphologies were obtained depending on the initial Li content in the precursors, varying from hexagonal rods which grow on the pellet when no Li is added to ribbons to sword-like structures growing onto the alumina boat as the Li amount increases. The changes in the energy of the crystallographic planes leading to variations in the growth directions were responsible for these morphological differences, as Electron Backscattered Diffraction analysis shows. The crystalline quality of the structures was investigated by X-ray diffraction and Raman spectroscopy, showing that all the structures grow in the ZnO wurtzite phase. The luminescence properties were also studied by means of both Cathodoluminescence (CL) and Photoluminescence (PL). Although the typical ZnO luminescence bands centered at 3.2 and 2.4 eV could be observed in all cases, variations in their relative intensity and small shifts in the peak position were found in the different samples. Furthermore, emissions related to intrashell transitions of Eu3+ ion were clearly visible. The good characteristics of the luminescent emissions and the high refraction index open the door to the fabrication of optical resonant cavities that allow the integration in optoelectronic devices. To study the optical cavity behavior of the grown structures, mu-PL investigations were performed. We demonstrated that the structures not only act as waveguides but also that Fabry-Perot optical resonant modes are established inside. Quality factors around 1000 in the UV region were obtained, which indicates the possibility of using these structures in photonics applications

Optical properties of 2D micro- and nanostructures of ZnO:K

ZnO nano- and microstructures doped with K were grown by the Vapor-Solid method. Wires and needles are the main morphology observed, although some structures in the form of ribbons and triangular plates were also obtained. Besides these, ball-shaped structures which grow around a central wire were also detected. Raman and cathodoluminescence investigations suggest that variations in morphology, crystalline quality and luminescence emissions are related to the different lattice positions that K occupies depending on its concentration in the structures. When the amount is low, K ions mainly incorporate as interstitials (K_(i)), whereas K occupies substitutional positions of Zn (K_(Zn)) when the amount of K is increased. Electron Backscattered Diffraction shows that ribbons and triangular plates are oriented in the (0001) direction, which indicates that the growth of this type of morphologies is related to distortions introduced by the K-i since this position favors the growth in the (0001) plane. In the case of the ball-shaped structures, the compositional analysis and Raman spectra show that they consist of K_(2)SO_(4). Finally, the capability of the elongated structures to act as waveguides and optical resonators was investigated. Due to the size of the K ion, practically double that of the Zn, and the different positions it can adopt within the ZnO lattice (K_(i)or K_(Zn)), high distortions are introduced that compromise the resonators performance. Despite this, quality factor (Q) and fineness (F) show acceptable values (80 and 10 at 544 nm, respectively), although smaller than those reported for doping with smaller size alkali, such as Li

Dysprosium removal from water using active carbons obtained from spent coffee ground

This paper describes the physicochemical study of the adsorption of dysprosium (Dy^(3+)) in aqueous solution onto two types of activated carbons synthesized from spent coffee ground. Potassium hydroxide (KOH)-activated carbon is a microporous material with a specific Brunauer-Emmett-Teller (BET) surface area of 2330 m^2.g^-1 and pores with a diameter of 3.2 nm. Carbon activated with water vapor and N_2 is a solid mesoporous, with pores of 5.7 nm in diameter and a specific surface of 982 m^2.g^-1. A significant dependence of the adsorption capacity on the solution pH was found, but it does not significantly depend on the dysprosium concentration nor on the temperature. A maximum adsorption capacity of 31.26 mg.g^-1 and 33.52 mg.g^-1 for the chemically and physically activated carbons, respectively, were found. In both cases, the results obtained from adsorption isotherms and kinetic study were better a fit to the Langmuir model and pseudo-second-order kinetics. In addition, thermodynamic results indicate that dysprosium adsorption onto both activated carbons is an exothermic, spontaneous, and favorable process

Morphology, Luminescence, and Optical Properties of Tb‐ and Li‐Codoped ZnO Elongated Nano‐ and Microstructures

A variety of morphologies of ZnO elongated nano- and microstructures doped with Li and Tb are obtained by a vapor–solid method. The amount of Tb incorporated depends on the morphology which is controlled by the amount of Li in the initial mixture and the growth conditions. X-ray diffraction and Raman experiments show the good crystalline quality of the samples. A small quantity of Tb3+ ions seems to be present in the structures, as both cathodoluminescence and photoluminescence suggest. The intensity of the ZnO and Tb3+ intrashell emission bands is strongly influenced by the amount of Li due to the different positions that it can occupy in the ZnO lattice. This fact leads to variations in the defect structure that change the concentration of native defects and the rare earth surroundings. The elongated structures also show waveguiding behavior and Fabry–Perot optical resonant modes with good quality factor

From spent alkaline batteries to Zn_xMn_3__xO_4 by_xO4 by a hydrometallurgical route: synthesis and characterization

A series of Zn/Mn binary oxides with different molar ratios (1.4-11) were synthesized via co-precipitation from a solution obtained through the acidic (HCl) leaching of a black mass originating from the mechanical recycling of spent alkaline and Zn-C batteries. The oxides obtained were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Magnetic properties of the samples were also investigated. The Raman spectroscopy results showed all the binary metallic oxides belong to the ZnxMn3-xO4 (0.25 = 1.75) type. All showed a spinel crystalline structure. The saturation magnetization decreases with the Zn_xMn_3_xO_4 (0.25 # x $ 1.75) type. All showed a spinel crystalline structure. The saturation magnetization decreases with the Zn/Mn molar ratio; a maximum of 13.19 emu g__1 was found for the molar ratio of 11 at the Curie temperature (25.5 K). XPS showed that all the synthesized compounds contained Mn_2_+, Mn_3_+ and Mn4+. Mn_2_+ was the most prominent at a molar ratio of 11, Mn_3_+ was most common at a molar ratio of 2, and Mn_4_+ at 1.4

Growth and characterisation of ZnO micro/nanostructures doped with cerium for photocatalytic degradation applications

ZnO:Ce structures have been obtained by a vapour-solid method. Different dopant concentrations have been used, and the incorporation of cerium in the crystalline structure of zinc oxide has been verified by means of Energy Dispersive Spectroscopy and Raman investigations. The morphology of the structures varies depending on the initial content of Ce in the samples, changing from long and thin rods and wires to "bottle-like" and truncated hexagonal pyramids as the Ce content increases. Cathodoluminescent properties have also been studied, the near band edge and deep level emissions change depending on both Ce content and morphology of the structures. Photocatalysis investigations show that an increase above 5 wt % of cerium oxide in the material causes a slight decrease in the efficiency of these structures in the degradation of the contaminant

Growth of Zr/ZrO_(2) core-shell structures by fast thermal oxidation

This research has been conducted to characterize and validate resistive heating as a synthesis method for zirconium oxides (ZrO_(2)). A wire of Zr has been oxidized to form a core-shell structure, in which the core is a metal wire, and the shell is an oxide layer that is around 10 mu m thick. The characterization of the samples has been performed by means of several techniques based on Scanning Electron Microscopy (SEM). The topography images show that thermal gradient appears to have little influence on morphology, unlike time, which plays an important role. The chemical composition was analyzed by X-ray spectroscopy (EDX) and X-ray diffraction (XRD), and Raman spectroscopy has been used to assess crystallinity and crystal structure. The oxide layer is mainly formed by monoclinic ZrO_(2), alongside other, less significant, phases. Photoluminescence (PL) and cathodoluminescence (CL) measurements have allowed us to study the distribution of defects along the shell and to confirm the degree of uniformity. The oxygen vacancies, either as isolated defects or forming complexes with impurities, play a determinant role in the luminescent processes. Color centers, mainly electron centers such as F, F-A and F-AA, give rise to several visible emissions extending from blue to green, with main components at around 2 eV, 2.4-2.5 eV and 2.7 eV. The differences between PL and CL in relation to distinct recombination paths are also discussed