Surface modification and crystallization of the BaO-B2O3-SiO2 glassy system using CO2 laser irradiation

The surface modification and crystallization process of BaO-B2O3-SiO2 glass compositions when exposed to CO2 laser irradiation was evaluated as a function of the laser power, irradiation time and surface condition. The glass surface was modified by the application of laser power exceeding 0.40 W and an irradiation time of more than 300 s. Micro-Raman and X-ray diffraction measurements revealed at high laser power the formation of beta-BaB2O4 (beta-BBO) crystalline phase. The crystallization of the irradiated region was enhanced when beta-BBO micrometer sized particles were dispersed on the surface of the glass sample. The intensity of the second harmonic generation observed in the crystallized region was found to depend mainly on the condition of the glassy surface prior to glass irradiation. (C) 2007 Elsevier B.V. All rights reserved.

Laser microstructuring for fabricating superhydrophobic polymeric surfaces

In this paper we show the fabrication of hydrophobic polymeric surfaces through laser microstructuring. By using 70-ps pulses from a Q-switched and mode-locked Nd:YAG laser at 532 nm, we were able to produce grooves with different width and separation, resulting in square-shaped pillar patterns. We investigate the dependence of the morphology on the surface static contact angle for water, showing that it is in agreement with the Cassie-Baxter model. We demonstrate the fabrication of a superhydrophobic polymeric surface, presenting a water contact angle of 157 degrees. The surface structuring method presented here seems to be an interesting option to control the wetting properties of polymeric surfaces. (C) 2010 Elsevier B.V. All rights reserved.

Effect of Eu(2)O(3) doping on Ta(2)O(5) crystal growth by the laser-heated pedestal technique

High energy band gap hosts doped with lanthanide ions are suitable for optical devices applications To study the potential of Ta(2)O(5) as a host compound pure and Eu(2)O(3)-doped Ta(2)O(5) crystal fibers were grown by the laser-heated pedestal growth technique in diameters ranging from 250 to 2600 pm and in lengths of up to 50 mm The axial temperature gradient at the solid/liquid interface of pure Ta(2)O(5) fibers revealed a critical diameter of 2200 gm above which the fiber cracks X-ray diffraction measurements of the pure Ta(2)O(5) single crystals showed a monoclinic symmetry and a growth direction of [1 (1) over bar 0] An analysis of the pulling rate as a function of the fiber diameter for Eu(2)O(3)-doped Ta(2)O(5) fibers indicated a well defined region in which constitutional supercooling is absent Photoluminescence measurements of pure Ta(2)O(5) crystals using excitation above the band gap (3 8 eV) were dominated by a broad unstructured green band that peaked at 500 nm Three Eu(3+)-related optical centers were identified in the doped samples with nominal concentrations exceeding 1 mol% Two of these centers were consistent with the ion in the monoclinic phase with different oxygen coordinations The third one was visible in the presence of the triclinic phase (C) 2010 Elsevier B V All rights reserved

Micro Far-Infrared Reflectivity of CaNb(2)O(6) Single Crystal Fibers Grown by the Laser-Heated Pedestal Growth Technique

CaNb(2)O(6) single crystal fibers were grown by the laser-heated pedestal growth technique, directly from the starting reagents. Optically transparent fibers were obtained in the form of rods with elliptical cross-section, free from cracks, impurities, and secondary phases, with an average diameter of 0.4 mm and about 20 mm of length. The fibers grew within the orthorhombic Pbcn columbite structure, with the growth axis nearly parallel to the crystallographic a-direction. The parameters b and c were parallel to the shorter and larger ellipsis axes. A special setup using a microscope was developed to obtain the far-infrared reflectivity spectra of these micrometer-sized fibers, allowing the identification and assignment of 34 of the 38 polar phonons foreseen for the material. From these phonons, the intrinsic dielectric constant ( = 18.2) and quality factor ( of 185 THz) could be estimated, showing the potential of the material for applications in microwave circuitry. These results, along with previous polarized Raman data (Cryst. Growth Des. 2010, 10, 1569), allow us to present a comprehensive set of optical phonon modes and to discuss the potential use of designed CaNb(2)O(6) microcrystals in compact optical devices.

Structural Characterization of Rare-Earth Doped Yttrium Aluminoborate Laser Glasses Using Solid State NMR

The structure of laser glasses in the system (B(2)O(3))(0.6){(Al(2)O(3))(0.4-x)(Y(2)O(3))(x)} (0.1 <= x <= 0.25) has been investigated by means of (11)B, (27)Al, and (89)Y solid state NMR as well as Y-3d core-level X-ray photoelectron spectroscopy, (11)B magic-angle spinning (MAS) NMR spectra reveal that the majority of the boron atoms are three-coordinated, and a slight increase of four-coordinated boron content with increasing x can be noticed. (27)Al MAS NMR spectra show that the alumina species are present in the coordination states four, five and six. All of them are in intimate contact with both the three- and the four-coordinate boron species and vice versa, as indicated by (11)B/(27)Al rotational echo double resonance (REDOR) data. These results are consistent with the formation of a homogeneous, nonsegregated glass structure. For the first time, (89)Y solid state NMR has been used to probe the local environment of Y(3+) ions in a glass-forming system. The intrinsic sensitivity problem associated with (89)Y NMR has been overcome by combining the benefits of paramagnetic doping with those of signal accumulation via Carr-Purcell spin echo trains. Both the (89)Y chemical shifts and the Y-3d core level binding energies are found to be rather sensitive to the yttrium bonding state and reveal that the bonding properties of the yttrium atoms in these glasses are similar to those found in the model compounds YBO(3) and YAl(3)(BO(3))(4), Based on charge balance considerations as well as (11)B NMR line shape analyses, the dominant borate species are concluded to be meta- and pyroborate anions.

Solid state NMR as a new approach for the structural characterization of rare-earth doped lead lanthanum zirconate titanate laser ceramics

To facilitate the design of laser host materials with optimized emission properties, detailed structural information at the atomic level is essential, regarding the local bonding environment of the active ions (distribution over distinct lattice sites) and their extent of local clustering as well as their population distribution over separate micro- or nanophases. The present study explores the potential of solid state NMR spectroscopy to provide such understanding for rare-earth doped lead lanthanum zirconate titanate (PLZT) ceramics. As the NMR signals of the paramagnetic dopant species cannot be observed directly, two complementary approaches are utilized: (1) direct observation of diamagnetic mimics using Sc-45 NMR and (2) study of the paramagnetic interaction of the constituent host lattice nuclei with the rare-earth dopant, using Pb-207 NMR lineshape analysis. Sc-45 MAS NMR spectra of scandium-doped PLZT samples unambiguously reveal scandium to be six-coordinated, suggesting that this rare-earth ion substitutes in the B site. Static Pb-207 spin echo NMR spectra of a series of Tm-doped PLZT samples reveal a clear influence of paramagnetic rare-earth dopant concentration on the NMR lineshape. In the latter case high-fidelity spectra can be obtained by spin echo mapping under systematic incrementation of the excitation frequency, benefiting from the signal-to-noise enhancement afforded by spin echo train Fourier transforms. Consistent with XRD data, the Pb-207 NMR lineshape analysis suggests that statistical incorporation into the PLZT lattice occurs at dopant levels of up to 1 wt.% Tm3+, while at higher levels the solubility limit is reached. (C) 2008 Elsevier Masson SAS. All rights reserved.

Time-resolved study electronic and thermal contributions to the nonlinear refractive index of Nd3+: SBN laser crystals

The propagation of an optical beam through dielectric media induces changes in the refractive index, An, which causes self-focusing or self-defocusing. In the particular case of ion-doped solids, there are thermal and non-thermal lens effects, where the latter is due to the polarizability difference, Delta alpha, between the excited and ground states, the so-called population lens (PL) effect. PL is a pure electronic contribution to the nonlinearity, while the thermal lens (TL) effect is caused by the conversion of part of the absorbed energy into heat. In time-resolved measurements such as Z-scan and TL transient experiments, it is not easy to separate these two contributions to nonlinear refractive index because they usually have similar response times. In this work, we performed time-resolved measurements using both Z-scan and mode mismatched TL in order to discriminate thermal and electronic contributions to the laser-induced refractive index change of the Nd3+-doped Strontium Barium Niobate (SrxBa1-xNb2O6) laser crystal. Combining numerical simulations with experimental results we could successfully distinguish between the two contributions to An. (C) 2007 Elsevier B.V. All rights reserved.

N3-Dye-Induced Visible Laser Anatase-to-Rutile Phase Transition on Mesoporous TiO(2) Films

Titanium dioxide has been extensively used in photocatalysis and dye-sensitized solar cells, where control of the anatase-to-rutile phase transformation may allow the realization of more efficient devices exploiting the synergic effects at anatase/rutile interfaces. Thus, a systematic study showing the proof of concept of a dye-induced morphological transition and an anatase-to-rutile transition based on visible laser (532 nm) and nano/micro patterning of mesoporous anatase (Degussa P25 TiO(2)) films is described for the first time using a confocal Raman microscope. At low laser intensities, only the bleaching of the adsorbed N3 dye was observed. However, high enough temperatures to promote melting/densification processes and create a deep hole at the focus and an extensive phase transformation in the surrounding material were achieved using Is laser pulses of 25-41 mW/cm(2), in resonance with the MLCT band. The dye was shown to play a key role, being responsible for the absorption and efficient conversion of the laser light into heat. As a matter of fact, the dye is photothermally decomposed to amorphous carbon or to gaseous species (CO(x), NO(x), and H(2)O) under a N(2) or O(2) atmosphere, respectively.

Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy)(2)((4,4 `-PO(3)H(2))(2)bpy)](2+) in TiO(2) Nanoparticle Films in Aqueous Environments

Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru-(bpy)(2)(4,4`-(PO(3)H(2))(2)bpy)](2+) surface-bound to TiO(2) (TiO(2)-Ru(II)). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, - were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO(2)(e(-))-Ru(3+) -> TiO(2)-Ru(2+). The appearance of pH-dependent decreases in the efficiency of formation of TiO(2)-Ru(3+) and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond-microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.

Amazonian Vegetable Oils and Fats: Fast Typification and Quality Control via Triacylglycerol (TAG) Profiles from Dry Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) Mass Spectrometry Fingerprinting

Amazonian oils and fats display unique triacylglycerol (TAG) profiles and, because of their economic importance as renewable raw materials and use by the cosmetic and food industries, are often subject to adulteration and forgery. Representative samples of these oils (andiroba, Brazil nut, buriti, and passion fruit) and fats (cupuacu, murumuru, and ucuba) were characterized without pre-separation or derivatization via dry (solvent-free) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Characteristic profiles of TAG were obtained for each oil and tat. Dry MALDI-TOF MS provides typification and direct and detailed information, via TAG profiles, of their variable combinations of fatty acids. A database from spectra could be developed and may be used for their fast and reliable typification, application screening, and quality control.