Tin oxide (SnO2) is an n-type wide band gap (3.6 eV) semiconductor which has been used for various applications as catalytic support materials, transparent electrodes, in solar cells and solid-state gas sensors [1]. During the last two years, novel gas nanosensors have been proposed using the luminescent properties of metallic oxides (ZnO, SnO2) where luminescence intensity is modified according to the nature and concentration of adsorbed gases [2]. On the other hand, the optical fiber sensor is based on the evanescent-wave absorption which has potential to monitor a leakage over wide area. In this case, the material absorbs the wavelengths carried by the fiber and modifies the absorption as a function of gas concentration to be detected [3]. In this work, SnO2 nanoparticles (NPs) were deposited on optical fibers and glass substrates. A morphological and chemical analysis were performed on the obtained samples.SnO2 nanoparticles were prepared using 3.0 g of SnCl4·2H2O dissolved in 25 ml of anhydrous ethanol. 4 ml glacial acetic acid was added as chelating agent. The solution became clear and homogeneous after stirring during 20 min. The cleaned glass substrate and optical fibers (10 µm of diameter) were independently dipped into SnCl4 solution. After that, they were removed from the solution (pull rate of 200 mm/min). Another reduced optical fiber (120 µm of diameter) were also fabricated using the flamebrushing technique [4] upon which a drop of SnCl4 solution was deposited. All samples were dried at 250 °C for 20 min. Figure 1a) shows a SEM image of spherical SnO2 fine particles deposited on glass substrate having diameters of 20-30 nm. The typical photoluminescence (PL) spectrum of SnO2 NPs is presented in the inset the figure 1a). The visible emission (550 nm) is generally suggested that come from defects such as oxygen vacancies and tin interstitial or dangling bonds [5]. Figure 1b) shows the XPS survey spectrum of SnO2 NPs, which revels the presence of carbon, sodium, chlorine, oxygen and tin. The peaks of C 1s and Na (KLL) are attributed mainly to contamination during storage of samples. The peaks of Sn 3d, 4d, 3p, 4p and 4s from SnO2 also are observed. Two XPS peaks located at 486.15 and 494.55 eV are related to Sn 3d5/2 and Sn 3d3/2 spin orbit peaks of SnO2, confirming the formation of SnO2 NPs. However, traces of SnCl2 (487.39 eV) and metallic Sn (484.90 eV) were also found on the surface of the sample. This could be due to an incomplete oxidation of tin precursor salt during thermal annealing. On the other hand, the surface morphology of reduced optical fiber exhibits a cluster morphology with varying cluster sizes and random distribution across the surface (Fig. 2a). The average cluster size is 200 nm, which was estimated from inset Fig. 2a). In addition, the clusters might be formed by SnO2 NPs (20-30 nm). Fig 2b) shows a SEM image of the optic fiber (120 µm) surface morphology after the deposition of the SnO2 NPs using the drop-casting method. The surface was uniformly covered after thermal anneal...
The alkaline earth stannates (ASnO3) have been recently investigated for their potential applications, such as components in lithium ion batteries and high-temperature humidity sensors [1]. Rare earth element doped semiconductors materials and perovskites, such SrSnO3, are of interest for visible and infrared light emitting diodes applications [2]. Among the rare earth elements, samarium (Sm 3+ ) is an element which is often employed as dopant for making orange-emitting phosphors [3]. In this work, we present the synthesis of SrSnO3:Sm 3+ nanoparticles using a co-precipitation method and investigated their structural properties and photoluminescent characteristics.In a typical co-precipitation synthesis [4], 55 mL of a 0.02M solution of SnCl4•5H2O and 55 mL of a 0.055M solution of Sr(NO3)3•5H2O were prepared in deionized water. 60 mL of hydrogen peroxide was added independently in both solutions. While keeping the SrNO3 solution under constant stirring, 11 ml of ammonium hydroxide were added to this solution. After 30 min, the SrNO3 solution was slowly mixed with SnCl4 solution, acquiring a cloudy yellow appearance. For Sm-doped samples, Sm(NO3)3•6H2O was added in the following molar concentrations (1, 2 and 4 %). Finally, the samples were washed and centrifuged several times alternating between water and ethanol. Obtained precipitates were dried in an oven at 80 °C for 2 h. Samples were sintered at two different temperatures (800 and 1300 °C) during 4 h.Figure 1a-c) shows FE-SEM images of SrSnO3 spherical nanoparticles annealed at different temperatures. The average particle size is about 20, 65, and 500 nm for samples without annealing, annealed at 800, and 1300 °C, respectively. The SrSnO3 sample annealed at 1300 °C present elongated shapes compared to the other two samples. Sm-doped samples did not show significant changes in the morphology, shape and size respect to the un-doped sample (Fig. 1d). The corresponding Sr, Sn and O maps present a homogenous distribution of these elements (Fig. 2). Structural properties were studied by Raman spectroscopy. Fig. 3 presents the Raman spectra of Sm (4%)-doped SnSnO3 nanoparticles annealed at different temperatures. For sample without annealing, Raman peaks can be observed at 147 and 179 cm -1 assigned to Ag vibrational mode which is related to the Sn-O-Sn and O-Sn-O bonds, respectively. Other band located at 571 cm -1 is associated to surface defects in SnO2 nanocrystals, while the peaks at 701 and 1071 cm -1 are related to presence of SrCO3 [4]. At increased annealing temperature, intense Raman peaks at ll4 (B2g mode), 223 (Ag mode) and 257 cm -1 (Ag mode) are observed, which have been associated with orthorhombic phase of SrSnO3 [5]. On the other hand, the peaks related to SrCO3 decrease due to the annealing temperature. The PL properties of the samples were measured at room temperature, under excitation of a He-Cd laser (λ = 325 nm). Figure 4 shows PL spectra of Sm-doped SrSnO3 annealed at 1300 °C, the spectra reveal a gradual increase in the intensity of transi...
Over past decade, thin films have been important component in device fabrication of many technological applications such optical transmitters, gas sensors, conducting films, solar cells [1]. In recent years, a new category of thin films technology is based on luminescent materials which are mainly used in applications as white light emitting diodes (LED) and field emission displays (FED). Recently, luminescent thin films have been proposed to efficiency enhancement of solar cells [2]. Zinc oxide (ZnO) is currently one of the key functional materials in advanced optoelectronic and photonic applications, including photovoltaics, due to its high transparency across the solar spectrum, excellent electrical properties, and the possibility to synthesize a rich variety of nanostructures [3].In this study, the ZnO thin films were synthetized using a typical chemical bath process. Before the chemical bath, a ZnO layer was deposited on glass substrates by sol-gel method using dip-coating technique. The sol solution was prepared by mixing zinc acetate dihydrate (Zn(CH3COO)2·2H2O), diethylamine (DEA), and adequate volume of deionized water, the mixture was added to 25 ml ethyl alcohol. The cleaned glass was dipped in the sol-gel by a controlled withdrawal speed of 200 mm/min. The dip-coating process was repeated 1 and 3 times to get seed ZnO layers (ZnO-1C and ZnO-3C, respectively). The seed ZnO layers were then placed in the heated (80 ºC) aqueous solution containing 0.025M zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and hexamethylenetetramine (HMT) for 30 min.The morphological information about the ZnO thin films, prior and after coating with the chemical bath process, was obtained by SEM. Fig. 1a) shows the surface imagen of ZnO seed layer deposited by solgel method. It can be observed the formation of nanoparticles which are spherical in shape with a diameter around 30-50 nm. Figure 1b) and 1c) present the nanorods growth using seed ZnO layers with 1 and 3 cycles of deposit, respectively. Comparing the two figures, it can be seen that nanorods diameter slightly increases from 80 to 120 nm as the seed layer growth cycle is increased. However, for ZnO-3C thin film, it is evident that the nanorods grew disorderly which could be explained due to an inhomogeneous deposit of ZnO seed layer on the surface of glass substrate. In order to analyze the structural properties of obtained ZnO thin films, they were characterized by Raman spectroscopy. Both Raman spectra shown four fundamental bands located at 98, 380, 436, and 580 cm -1 , which correspond to the E2(low), A1(TO), E2(high), and E1(LO) vibrational modes of ZnO in hexagonal phase (Fig. 2a)). The Raman bands around 200 and 330 cm -1 are associated to the second order 2E2(low) and multi-phonon E2(high)-E2(low) modes, respectively. As can be observed, there is a decrease in the intensity of all the Raman bands for ZnO-3C film respect to the ZnO-1C film. This indicated that the film had a low degree of crystallinity, possibly due to the formation of structural defects induced by...
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