A. S. B. Sombra

Optical temperature sensing using upconversion fluorescence emission in Er3+/Yb3+-codoped chalcogenide glass

Optical temperature sensing using upconversion fluorescence emission in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glass excited at 1.06 μm is reported. Temperature measurements in the region of 20–225 °C with a resolution of approximately 0.5 °C using excitation powers of a few tens of milliwatts were obtained. The temperature sensing mechanism is independent of variations in the excitation intensity, possible fluctuations of transmission, and utilizes a simple signal detection and processing system. The results also revealed that the glass host material plays an important role in the performance of the sensing system.

Upconversion fluorescence spectroscopy of Er3+/Yb3+-doped heavy metal Bi2O3–Na2O–Nb2O5–GeO2 glass

Upconversion fluorescence emission of Er3+/Yb3+-doped Bi2O3–Na2O–Nb2O5–GeO2 heavy metal glass samples excited at 1.06 μm is experimentally investigated. The results reveal the existence of intense emission bands centered around 520, 545, and 655 nm. The germano-niobate based host glass presents high transparency in the region of 400–2700 nm, the capability of incorporating high dopant concentrations, high melting temperature, and large resistance to atmospheric moisture. The observed intensity of the green fluorescence emission, suggested that the niobium based host glass material plays an important role in the efficiency of the upconversion process. Emission lines centered at 425, 483, 503, 608, and 628 nm were also observed.

Structural properties of hydroxyapatite obtained by mechanosynthesis

In this paper mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) using five different experimental procedures in a pure dry process. The milled HA were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For four different procedures, HA was obtained after a couple of hours of milling (in average 60 hours of milling, depending in the reaction procedure). This milling process, used to produce HA, presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with crystallite size in the range of 22 nm to 39 nm.

Thermally induced threefold upconversion emission enhancement in nonresonant excited Er3+/Yb3+-codoped chalcogenide glass

Thermally induced threefold infrared-to-visible upconversion emission enhancement in Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glasses excited at 1.064 μm is reported. The times three upconversion efficiency enhancement was achieved by heating the sample in the temperature range of 23–155 °C, and is assigned to the temperature-dependent multiphonon-assisted anti-Stokes sideband excitation process of the ytterbium sensitizer. A theoretical analysis based upon rate equations considering the sensitizer absorption cross section as a function of the phonon occupation number in the host material exhibited very good agreement with experimental data.

Optical thermometry through infrared excited upconversion fluorescence emission in Er/sup 3+/- and Er/sup 3+/-Yb/sup 3+/-doped chalcogenide glasses

Optical thermometry based upon infrared excited upconversion fluorescence emission in Er/sup 3+/- and Er/sup 3+/-Yb/sup 3+/- doped Ga/sub 2/S/sub 3/-La/sub 2/O/sub 3/ chalcogenide glasses excited at 1.54 and 1.06 /spl mu/m, respectively, is presented. Temperature sensing in the region of 20/spl deg/C-220/spl deg/C with 0.3/spl deg/C accuracy using excitation powers readily obtainable from commercially available semiconductor lasers was achieved. The temperature sensing approach is independent of fluctuations in excitation intensity and transmission and requires a simple and low-cost signal detection and processing system. The results also indicate that the glassy host material plays a major role in the performance of the sensing system.

Impedance and modulus studies of magnetic ceramic oxide Ba2Co2Fe12O22 (Co2Y) doped with Bi2O3

Polycrystalline samples of a layered magnetic ceramic oxide, Ba2Co2Fe12O22 (Co2Y), doped with Bi2O3 were prepared by the solid state reaction method. The dielectric impedance properties were studied over the range of frequency between 1 Hz–1MHz and in the temperature range of 313–493 K, using the modulus formalism. The impedance plot showed a first semicircle at high frequency which was assigned to the grain intrinsic effect and a second semicircle, at lower frequencies, which corresponds to grain boundary polarization (conduction phenomenon). A complex modulus spectrum was used to understand the mechanism of the electrical transport process, which indicates that a non-exponential type of conductivity relaxation characterizes this material. The values of the activation energy of the compound (calculated both from dc conductivity and the modulus spectrum) are very similar, suggesting that the relaxation process may be attributed to the same type of charge carriers. The dielectric measurements were studied ...

Soliton switching in three-core nonlinear directional fiber couplers

We present an analytical investigation of the propagation and the switching of fundamental solitons in a three-core nonlinear fiber coupler with a variational method using the Lagrangian density formulation. The analytical solutions were obtained directly from the coupled nonlinear Schrodinger equations. The transmission characteristics of first order solitons obtained by the analytical procedure agree well with the results from numerical analysis. Three different geometries for the nonlinear three-core directional coupler were studied. Taking into account the length of the coupler and the critical power a comparative study between these geometries was done.

Raman and infrared spectra of KNbO3 in niobate glass-ceramics

Potassium niobophosphate glasses and glass-ceramics of the family [xNb2O5.(50-x) P2O5.50K2O]:yFe2O3 were studied by x-ray powder diffraction, infrared and Raman scattering spectroscopy. For the potassium-phosphate samples [50P2O5-50K2O] the iron oxide presents a network former behaviour, for 2 mol% of Fe2O3 doping. The precipitation of crystalline K4Nb6O17 and ferroelectric KNbO3 crystals was confirmed by x-ray powder diffraction in the samples with x = 40 and 50 mol% respectively. The infrared and Raman scattering spectroscopy results suggest that the increase of the ratio Nb2O5/P2O5 leads the niobium to sites of octahedral symmetry and consequently to the formation of ferroelectric KNbO3, as seen by x-ray diffraction analysis.

Polyanionic collagen membranes for guided tissue regeneration: Effect of progressive glutaraldehyde cross-linking on biocompatibility and degradation.

The ultimate goal of periodontal therapy is to control periodontal tissue inflammation and to produce predictable regeneration of that part of the periodontium which has been lost as a result of periodontal disease. In guided tissue regeneration membranes function as mechanical barriers, excluding the epithelium and gingival corium from the root surface and allowing regeneration by periodontal ligament cells. This report aims to study the effect of glutaraldehyde (GA) cross-linking on mineralized polyanionic collagen (PAC) membranes by conducting a histological evaluation of the tissue response (biocompatibility) and by assessing the biodegradation of subcutaneous membrane implants in rats. We studied six different samples: a PAC, a PAC mineralized by alternate soaking processes for either 25 or 75 cycles (PAC 25 and PAC 75, respectively) and these films cross-linked by GA. Inflammatory infiltrate, cytokine dosage, fibrosis capsule thickness, metalloproteinase immunohistochemistry and membrane biodegradation after 1, 7, 15 and 30 days were measured. The inflammatory response was found to be more intense in membranes without cross-linking, while the fibrosis capsules became thicker in cross-linked membranes after 30 days. The membranes without cross-linking suffered intense biodegradation, while the membranes with cross-linking remained intact after 30 days. The cross-linking with GA reduced the inflammatory response and prevented degradation of the membranes over the entire course of the observation period. These membranes are thus an attractive option when the production of new bone depends on the prolonged presence of a mechanical barrier.

Dielectric permittivity and loss of CaCu3Ti4O12 (CCTO) substrates for microwave devices and antennas

The solid state procedure was used to produce bulk ceramics of CCTO (CaCu3Ti4O12). The samples of the CCTO ceramic were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. The infrared and Raman scattering spectroscopy confirm the formation of the CCTO phase as seen by X-ray diffraction analysis. For one experimental procedure one uses an organic binder in the process of shaping the samples. In the second procedure the samples were prepared without the presence of the organic phase. For the second situation, we had higher dielectric constant (ɛr=7370) with high loss (D=0.2) at 1 KHz. For the first procedure one has the lower dielectric constant (ɛr=1530) and lower loss (D=0.11) at 1 KHz. Simple rectangular antenna prototypes were also designed on substrate samples (C1, C2, P1 and P2). For the antennas (with P2, C1 and C2 as substrates), the bandwidth (BW) is 90 MHz (around 3%). The antenna with P1 substrate presented a surprisingly high BW of 270 MHz that corresponds to a 10% bandwidth. In the microwave range one observes that higher values of the ɛr in the range of 3 GHz antennas is also presented by the P1 sample (ɛr=41.6), and the lowest one was presented by P2 (ɛr=33.7). Sample P1 also presents the highest value for the loss (Q−1) which is around 0.1 compared to the other samples which is around 0.03. Therefore, these measurements confirm the potential use for small high dielectric planar antennas. These materials are also attractive for capacitor applications and certainly for microelectronics, and microwave devices (e.g., cell mobile phones), where the miniaturization of the devices is crucial.