Sidney José Lima Ribeiro

Bacterial cellulose from glucanacetobacter xylinus: Preparation, properties and applications

Sao Paulo State University Institute of Chemistry Dept. of General and Inorganic Chemistry, R. Prof. Francisco Degni, s/n, Araraquara, SP

Sol-Gel Erbium-Doped Silica-Hafnia Planar and Channel Waveguides

Erbium activated SiO2-HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-gel method. The films were deposited on v-SiO2 and silica-on-silicon substrates using dip-coating technique. The waveguides show high densification degree, effective intermingling of the two film components, and uniform surface morphology. The waveguide deposited on silica-on-silicon substrates shows one single propagation mode at 1.5μm, with a confinement coefficient of 0.81 and an attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuous-wave excitation at 980 nm or 514.5 nm. The shape of the emission band corresponding to the 4I13/2→4I15/2 transition is found to be almost independent both on erbium content and excitation wavelength, with a FWHM between 44 and 48 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1-6.6 ms, depending on the erbium concentration. Infrared to visible upconversion luminescence upon continuous-wave excitation at 980 nm was observed for all the samples. Channel waveguide in rib configuration was obtained by etching the active film in order to have a well confined mode at 1.5 μm.

Erbium-activated silica-titania planar waveguides prepared by rf-sputtering

Erbium-activated silica-titania planar waveguides were prepared by rf-sputtering technique. The films were deposited both on v-SiO2 and silica-on-silica substrates obtained by plasma-enhanced chemical vapor deposition. The refractive index, the thickness and the total attenuation coefficient of the waveguides were measured by prism coupling technique. Scanning electron microscopy was used to analyze the morphology of both substrates and waveguiding film. Energy Dispersive Spectroscopy was performed in order to obtain a compositional analysis. Roughness measurements were carried out by means of a stylus profilometer. After thermal annealing at 600 degrees C for 6 hours the waveguides exhibited several well confined TE and TM propagating modes at 633 nm and one mode at 1550 nm. The attenuation coefficient at 1550 nm was 0.9 and 0.7 dB/cm for the films deposited on silica-on-silicon waveguide Raman spectroscopy. Waveguide luminescence spectroscopy was used to study the 4I13/2 yields 4I15/2 transition of Er3+ ion. The emission at 1530 nm was observed at room temperature upon continuous wave excitation at 514.2 nm. A lifetime of 3.7 ms for the metastable 4I13/2 level was measured.

UV and Temperature-Sensing Based on NaGdF4:Yb3+:Er3+@SiO2–Eu(tta)3

A multifunctional nanosystem was synthesized to be used as a dual sensor of UV light and temperature. NaGdF4:Yb3+:Er3+ upconverting nanoparticles (UCNPs) were synthesized and coated with a silica shell to which a europium(III) complex was incorporated. The synthesis of NaGdF4 UCNPs was performed via thermal decomposition of lanthanide ion fluoride precursors in the presence of oleic acid. To achieve sufficient water dispersibility, the surface of the hydrophobic oleate-capped UCNPs in the hexagonal phase was modified by a silica coating through a modified Stöber process through a reverse microemulsion method. An Eu(tta)3 (tta: thenoyltrifluoroacetonate) complex was prepared in situ at the silica shell. A dual-mode nanothermometer was obtained from a near infrared to visible upconversion fluorescence signal of Er3+ ions together with UV-excited downshifting emission from the Eu3+ complex. Measurements were recorded near the physiological temperature range (293–323 K), revealing excellent linearity (R2 > 0.99) and relatively high thermal sensitivities (≥1.5%·K–1). The Eu(tta)3 complex present in the silica shell was tested as the UV sensor because of the Eu3+ luminescence dependence on UV-light exposure time.

Optical properties and energy-transfer frequency upconversion of Yb3+-sensitized Ho3+- and Tb3+-doped lead-cadmium-germanate glass and glass ceramic

In this report we investigate the optical properties and energy-transfer upconversion luminescence of Ho3+- and Tb3+/Yb3+-codoped PbGeO3-PbF2-CdF2 glass-ceramic under infrared excitation. In Ho3+/Yb3+-codoped sample, green (545 nm), red(652 nm), and near-infrared(754 nm) upconversion luminescence corresponding to the 4S2(5F4) → 5I8, 5F5 → 5I8, and 4S2(5F4) → 5I7, respectively, was readly observed. Blue (490 nm) signals assigned to the 5F2,3 → 5I8 transition was also detected. In the Tb3+/Yb3+ system, bright UV-visible emission around 384, 415, 438, 473-490, 545, 587, and 623 nm, identified as due to the 5D3(5G6) → 7FJ(J=6,5,4) and 5D4→7FJ(J=6,5,4,3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicate that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.

Erbium-activate HfO 2 -based waveguides for photonics

70SiO2 - 30 HfO2 planar waveguides, activated by Er3+ concentration ranging from 0.3 to 1 mol%, were prepared by sol-gel route, using dip-coating deposition on silica glass substrates. The waveguides showed high densification degree, effective intermingling of the two components of the film, and uniform surface morphology. Propagation losses of about 1 dB/cm were measured at 632.8 nm. When pumped with 987 nm or 514.5 nm continuous-wave laser light, the waveguides showed the 4I13/2 → 4I15/2 emission band with a bandwidth of 48 nm. The spectral features were found independent both on erbium content and excitation wavelength. The 4I13/2 level decay curves presented a single exponential profile, with a lifetime between 2.9 - 5.0 ms, depending on the erbium concentration.

Infrared-to-visible frequency upconversion in transparent glass ceramics containing trivalent-rare-earth-doped nanocrystals

In this work we report on visible upconversion emission in Er3+- and Ho3+-doped PbGeO3-PbF2-CdF2-based transparent glass ceramics under 980 nm infrared excitation. In erbium-doped vitroceramic samples, blue(410 nm), green(530, and 550 nm) and red(660 nm) emission signals were generated, which were identified as due to the 2H9/2, 2H11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground-state, respectively. Intense red(650 nm) upconversion emission corresponding to the 5F5-5I8 transition and very small blue(490 nm) and green(540 nm) signals assigned to the 5F2,3-5I8 and 4S2,5F4-5I8 transitions, respectively, were observed in the holmium-doped samples. The 540 nm is the dominant upconversion signal in Ho3+-doped vitroceramics under 850 nm excitation. The dependence of the upconversion processes upon pump power and doping concentration are also investigated, and the main routes for the upconversion excitation processes are also identified. The comparison of the upconversion process in transparent glass ceramics and the precursor glass was also examined and the results revealed that the former present higher upconversion efficiencies.

Red, green, and blue upconversion luminescence in ytterbium-sensitized praseodymium-doped lead-cadmium-germanate glass

Blue, green, red, and near-infrared upconversion luminescence in the wavelength region of 480 - 740 nm in Pr3+/Yb -codoped lead-cadmium-germanate glas under 980 nm diode laser excitation, is presented. Upconversion emission paks around 485, 530, 610, 645, and 725 nm which were ascribed to the 3P0 - 3HJ (J=4, 5, and 6), and 3P - 3FJ (J=2, and 3,4), transitions, respectively, were observed. The population of the praseodymium upper 3P0 emitting level was accomplished through a combination of ground-state absorption of Yb3+ ions at the 2F7/2, energy-transfer Yb3+(2F5/2) - Pr3+(3H4), and excited-state absorption of Pr3+ ions provoking the 1G4 - 3P0 transition. The dependence of the upconversion luminescence upon the Yb3+-concentration and diode laser power, is also examined, in order to subsidize the proposed upconversion excitation mechanism.

Optical limiting behavior of tungstate fluorophosphate glasses

Nonlinear absorption measurements were performed on fluorophosphate glasses with hgih concentration of tungsten oxide. Large two-photon absorption coefficients, α2, were determined at 660 nm using nanosecond laser pulses. It was observed that α2 increases for increasing tungsten oxide concentrations and therefore the optical limiting performance of this new glass composition can be controlled.

Rare-earth-doped HfO2 nanoparticles embedded in SiO2-HfO2 planar waveguides: preparation and optical, structural, and spectroscopic characterization

In this work we present result on the preparation of planar waveguides based on HfO2 and HfO2-SiO