Maria José V. Bell

Frequency upconversion in Er3+ doped PbO–GeO2 glasses containing metallic nanoparticles

The authors report the infrared-to-visible frequency upconversion (UPC) process in Er3+ doped PbO–GeO2 glasses containing silver nanoparticles (NPs) with an average diameter of 2.2nm. The absorption spectra of the samples present a band centered at 470nm due to the surface plasmons associated with the NPs. The intensity of the band grows with increasing NP concentration. The experiments were performed by exciting the samples with a 980nm diode laser and observing the UPC emissions in the red-green region. The enhanced UPC intensity is attributed to the local field effect in the proximity of the NPs.

Ultra-structural mapping of sugarcane bagasse after oxalic acid fiber expansion (OAFEX) and ethanol production by Candida shehatae and Saccharomyces cerevisiae

BackgroundDiminishing supplies of fossil fuels and oil spills are rousing to explore the alternative sources of energy that can be produced from non-food/feed-based substrates. Due to its abundance, sugarcane bagasse (SB) could be a model substrate for the second-generation biofuel cellulosic ethanol. However, the efficient bioconversion of SB remains a challenge for the commercial production of cellulosic ethanol. We hypothesized that oxalic-acid-mediated thermochemical pretreatment (OAFEX) would overcome the native recalcitrance of SB by enhancing the cellulase amenability toward the embedded cellulosic microfibrils.ResultsOAFEX treatment revealed the solubilization of hemicellulose releasing sugars (12.56 g/l xylose and 1.85 g/l glucose), leaving cellulignin in an accessible form for enzymatic hydrolysis. The highest hydrolytic efficiency (66.51%) of cellulignin was achieved by enzymatic hydrolysis (Celluclast 1.5 L and Novozym 188). The ultrastructure characterization of SB using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform–near infrared spectroscopy (FT-NIR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed structural differences before and after OAFEX treatment with enzymatic hydrolysis. Furthermore, fermentation mediated by C. shehatae UFMG HM52.2 and S. cerevisiae 174 showed fuel ethanol production from detoxified acid (3.2 g/l, yield 0.353 g/g; 0.52 g/l, yield, 0.246 g/g) and enzymatic hydrolysates (4.83 g/l, yield, 0.28 g/g; 6.6 g/l, yield 0.46 g/g).ConclusionsOAFEX treatment revealed marked hemicellulose degradation, improving the cellulases’ ability to access the cellulignin and release fermentable sugars from the pretreated substrate. The ultrastructure of SB after OAFEX and enzymatic hydrolysis of cellulignin established thorough insights at the molecular level.

Quantification of Extra-virgin Olive Oil Adulteration with Soybean Oil: a Comparative Study of NIR, MIR, and Raman Spectroscopy Associated with Chemometric Approaches

In this work, blends of olive and soybean oils were analyzed by near-infrared spectroscopy (NIR), mid-infrared (MIR), and Raman techniques to evaluate adulterations in olive oils. A representative group of different commercial brands of soybean oil and extra-virgin olive oil were analyzed by gas chromatography with flame ionization detector in order to explore the chemical similarity and composition of the fatty acid (FA) profile. Two stock solutions were prepared, one produced from a mixture of soybean oils and the other from the mixture of olive oils. From these stock solutions, 60 samples were prepared, simulating adulteration levels of extra-virgin olive oil with soybean oil between 0 and 100xa0%. It was possible to fit a model able to predict fraud within the interval investigated by partial least squares regression approach, with precision and accuracy values for root mean squared error of prediction of 1.76 (NIR), 4.89 (MIR), and 1.57 (Raman) and coefficient of determination R2 greater than 0.98 for the three techniques. The methodologies demonstrated to be very useful for the quantification of extra-virgin olive oil adulteration with soybean oil, presenting short analysis time, low cost, and absence of sample preparation procedures as main advantages.

Thermo-optical properties of silver and gold nanofluids

This work focuses on the study of thermal diffusivity and physical properties of nanofluids with very low concentrations of silver or gold nanoparticles. Thermal measurements were performed by means of thermal lens spectroscopy in the dual beam configuration. Improvements of 20 and 16xa0% in the thermal diffusivity were observed for silver and gold nanofluids, respectively, in comparison with pure water. The estimation of the size distribution of the metallic nanoparticles was obtained through the fitting of the extinction spectra via Mie theory and images of field emission gun scanning electron microscopy.

Thermal and Optical Properties of

In this work, we study the thermal and optical properties of ion-doped phosphates glasses using the thermal lens (TL) technique. Three samples were characterized: Nd³⁺-doped Q-98; Nd³⁺-doped Q-100; and Yb³⁺-doped QX. We report multiwavelength TL measurements for a more accuracy determination of the fluorescence quantum efficiency and temperature coefficient of the optical path length change (<i>ds</i>/<i>dT</i>). In Nd-doped glasses, it was carried out using four discrete excitation wavelengths (between 514 and 872 nm) chosen to match with the ion absorption lines. In Yb-doped glass, the spectrum of heat generated along the Yb³⁺ transition (² <i>F</i> _5/2rarr² <i>F</i> _7/2) was obtained. In addition, parameters as thermal diffusivity and conductivity, thermal loading, etc were achieved. The advantages to obtain fluorescence quantum efficiency using the TL technique, mainly in Yb³⁺ doped materials, which are normally overestimated due to radiation trapping effect, are presented. The accuracy knowledge of these parameters is very important for design of high-power solid-state lasers, since these properties are directly related to the heat generation.

{\hbox {Yb}}^{3+}

Spectroscopic properties of ytterbium-doped tellurite glasses with different compositions are reported. Results of linear refractive index, absorption and emission spectra, and fluorescence lifetimes are presented. The studied samples present high refractive index (~2.0) and large transmission window (380-6000nm). Absorption and emission cross-sections are calculated as well as the minimum pump laser intensity. The results are compared with the values of other laser materials, in order to investigate applications as laser media in the infrared region.

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In this work we report a room temperature green upconversion in Er-doped fluoroindogallate glasses, pumped at 833 nm. The rise time and stationary intensity of the 4S3/2+2H11/2→4I15/2u2002Er3+ transition as a function of laser intensity were monitored. Some possible pumping mechanisms are discussed in detail, and it is concluded that the main pumping route may be described in terms of the looping mechanism. It is also shown that cross relaxation among neighboring pairs of Er3+ ions is near the threshold value to achieve the photon avalanche region.

{\hbox {Nd}}^{3+}

Abstract The search for rare-earth-doped glasses exhibiting large linear and nonlinear optical properties is motivated by their applications in lasers, optical amplifiers, color displays, and ultrafast devices. In particular, germanate and tellurite glasses are good candidates for these applications due to their wide transmission window (400–5000xa0nm), high refractive index (~2.0), large chemical durability, and low phonon energy (800xa0cm−1). These glasses have also proven to be adequate hosts for rare-earth ions and for the nucleation of metallic nanoparticles (NPs). In this chapter, we review our contribution to the field of rare-earth doped glasses, by reporting the nonlinear optical properties of germanate oxide glasses containing silver/gold/silicon NPs, their enhanced luminescence properties due to the nucleation of metallic NPs, the laser action in Nd3+ doped TeO2-ZnO glasses, and the Er3+ doped PbO-GeO2-Ga2O3 waveguide amplifiers written with a femtosecond laser. Throughout the examples discussed, we have used the melt-quenching technique for the preparation of the glasses and an adequate heat treatment for the nucleation of metallic NPs. Investigation of the presence of the NPs and determination of their size and shape were achieved through electron microscopy. Finally, our research on rare-earth doped germanate and tellurite glasses is put into the broader context, and very recent reports on the literature, by other research groups, are examined and discussed.

-Doped Phosphate Glasses Determined by Thermal Lens Technique

Electronic and thermal lineshape were determined by thermal lens and Z-scan spectroscopy in QX/Yb3+-doped phosphate glass. Several optical and photothermal properties were obtained. It was done a comparison between the magnitudes of these contributions.